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1.
2. csse seen eene tenente nnns 25 2 4 3 XE Cable Connections esses E teens etes enne nentes 25 2 4 4 Connection to Power 1 seen eee eene eene nnn 31 24 5 Installation GheckUD ea o edit 31 Chapter 3 Cantilever Selection ne Cura tru 33 3 1 CHARACTERISTICS OF THE 2 o ton 33 2 2 CANTILEVER SELECTION 35 Chapter 4 37 4 1 TURNON THE XE 1O00 37 4 2 KEP SOFTWARE 37 4 3 Z STAGE AND FOCUS STAGE CONTROL 38 XE 100 User s Manual 4 4 CANTILEVER PREPARATION ex a ope eret kane T wn Ed 39 235 LASER BEAM ALIGNMENT 40 AzG SAMPLE pe e ortas o pA 44 4 7 MEASUREMENT PROCEDURE om 44 4 8 SCAN PARAMETER DEEINITIONS eO a Ed e eee ode EEG 48 Chapter 5 Ser up S
3. 1 Figure 1 2 Scanning Probe Microcope 2 AS CAG 4 Figure 1 4 Dovetail Lock Head Mount leeren eene eene enne nennen 4 Figure 1 5 Z scanner Assembly e vaisseau tt tabes D FOUE ord Figure 1 7 X Y scanner 50um x 50um left 100um x 100 right 6 a N 7 Figure 1 9 Optical Microscope Frame 7 Figure 1 10 XE 100 Control 8 Figure 1 11 Diagram of conventional AFM s scanning 10 Figure 1 12 Nonlinearity and Hysteresis a and Cross Coupling b Observed in Piezoelectric Tube Scanrliers oco m sd 12 Figure 1 13 Z scanner separated from X Y 13 Figure 1 14 Background Flatness Images from a conventional AFM a and XE SOROS AFM 14 Figure 1 15 Laser beam path related to the cantilever s movement 15 Figure 1 16 Captured optical microscope image 16 Figure 1 27 Dovetail Lock Head sicnt inor ena Esame
4. T2 SEM image of ULTRASHARP silicon cantilever the NSC15 series 74 Silicon chip of the NSC15 series has 1 rectangular cantilever 74 Non contact AFM setup and voltage mode selection 75 tese bas une uc 78 Resonant frequency shift b Amplitude vs Z feedback 79 80 Resonant frequency setup in 81 XE 100 User s Manual Blank Page gt xii Chapter 1 Introduction to XE 100 Chapter 1 Introduction to XE 100 1 1 Primary Components of XE 100 system The XE 100 SPM System consists of four primary components the XE 100 SPM stage the XE 100 Control Electronics a computer amp monitor and a video monitor Video Monitor 100 SPM Stage Computer amp Monitor XE 100 Control Electronics Figure 1 1 The XE 100 SPM System The XE 100 SPM stage is where actual measurements are made and the XE 100 Control Electronics controls the movement of the XE 100 SPM stage according to the commands from the computer The Video Monitor which displays the image from the optical microscope that is mounted on the XE 100 SPM stage is used to locate the exact spot that is to be measured on the sample surface It is also used to view the cantilever that will be used to make the
5. Table Air Compressor Included or Active Vibration Isolation System Standard Sample 3 um x 3 um Grating Height 130nm e Cantilevers Silicon Cantilevers for Contact AFM 10ea Silicon Cantilevers for Non contact AFM 10ea e Multi Tab 220 V Ground Type Tweezers for wafer for sample and cantilever lea e Sample disk pucks 20ea 2 4 Hardware Installation 2 4 1 Installation of an Air Table or an Active Vibration Isolation System B Air Table Installation The function of an Air Table is to suspend the XE 100 on a floating platform so that it can be free from surrounding vibrations the equipment is placed on a marble 21 XE 100 User s Manual table that floats on air At the bottom of each of the four corners of the Air Table you will find a leg and a wheel To level the Air Table the height of each of the four legs can be adjusted as follows suspend the legs by rotating the lower bolt in the frame of the wheel Figure 2 1 counterclockwise and making sure that the Air Table is fixed properly adjust the legs using the levels on top of the table Figure 2 1 Below Air Table Once the Air Table is properly leveled connect the air compressor to the compressed air line There are three levers as shown in Figure 2 2 a on the Air Table Adjust these three levers as shown in Figure 2 2 b so that the Air Table s top plate is suspended in air a few millimeters high To be sure no
6. ec feste 30 Figure 2 13 Diagram of cable connections for the XE system ol FOWE 3 t Cantilever eD 33 Figure 3 2 SEM image of silicon 34 Figure 4 1 User Interface cox RUE 38 Figure 4 2 Z stage Control 39 Pidure 4 3 45Z Snap tip exchange qc cnp octo d acdsee cans 40 Figure 4 4 Edge of the probe arm beore left and after right the cantilever chip plate RI 40 Figure 4 5 Laser beam alignment on the Cantilever 4 Figure 4 6 Laser beam alignment display in 43 Figure 4 7 Motor Control nemen 45 Figure 4 8 Scan Control 46 Figure 4 9 Servo gain at the proper level top Servo too high resulting in oscillations of the Z scanner 47 Figure 5 1 Select Scanner 50 Figure 5 2 XY Servoscan is ON cn de i od Figure 5 3 Scanner s observable od Figure 5 4 X
7. Cantilever General v 0 Figure 9 3 Conversion to 9 3 Resonant Frequency setup As explained in section 1 DFM uses non contact mode feedback but as opposed to non contact mode the driving frequency should be selected at the left part of the peak in the graph The other conditions are the same as the non contact mode 80 Chapter 9 Dynamic Force Microscopy Frequency Set Report Start Freq 288300 Hz Selected Freq 299790 Hz Set Point 0 285 Control Drive 5 25 E Zoom Phase Figure 9 4 Resonant frequency setup in DFM 9 4 Cantilever Selection Since DFM uses the same method as non contact AFM which is to vibrate the cantilever when measuring the sample surface the same type of cantilevers are used in DFM as in non contact mode unless the user prefers a different type of cantilever for a specific purpose Please refer to Chapter 8 section 4 for information on cantilever selection for DFM 9 5 Measurement Procedure The method of measurement of DFM is the same as that of non contact mode The absolute value of the set point also means the distance between the probe tip and the sample surface just as in non contact mode but the value is much smaller As explained in Chapter 8 section 1 the vibrating probe tip moves as if it is pecking the sample surface using the same feedback circuit Determining the set point plays a very important role in obtain
8. Selecting the appropriate probe is a critical aspect of using AFM Choosing a probe means determining the combination of a tip which interacts with sample surface atoms and a cantilever which deflects depending on the interatomic forces and quantifies the deflection Generally the upper surface of a cantilever is coated with a metal such as gold Au or aluminum Al This coating which enhances the surfaces reflectivity has a thickness of about 10000 There are several types of cantilevers that vary in material shape softness represented by the spring constant intrinsic frequency and Q factor The type of cantilever selected is primarily determined by the measurement mode As mentioned in Chapter 3 a soft cantilever is used for contact mode AFM Typically such cantilevers are made of silicon and have a spring constant less than 1 3 N m With such a low spring constant the contact mode cantilever is 57 XE 100 User s Manual sensitive to extremely small forces and it will bend more significantly than a cantilever with a higher spring constant when exposed to an equal force This allows the AFM to depict even extremely tiny structures Figure 6 3 shows the SEM image of a cantilever commonly used for contact mode the CSC12 series To improve the laser beam reflectivity the upper surface of the cantilever the opposite side of the tip is coated with aluminum Figure 6 3 SEM image of the shorter cantilev
9. oe ratto e Sdn 16 Figure 1 18 EZ Snap Probe Tip 17 Figure 1 19 Data Acquisition 18 Figure 1 20 Image Processing 18 Figure 2 1 Below Air Table te ena Ursa adeo eodein 22 Figure 2 2 a Compressed air lever b Air Table suspended in air 20 Figure 2 3 Active Vibration Isolation System 24 Figure 2 4 Rear panelo AVIS seusia cum te stabit 24 Figure 2 5 Front panel t AVIS ua tee qe 29 Figure 2 6 Basic arrangement of 100 29 Figure 2 7 Cables needed to be checked prior to installation 26 Figure 2 8 Connection between 100 SPM main body and the head and X Y T TL DOT E 2 XE 100 User s Manual Figure 2 9 Rear panel of the XE 100 SPM 28 Figure 2 10 Cable connections of the 100 Control Electronics 29 Figure 2 11 Rear panel of the Video monitor 30 EIgure 2 12
10. 48 Open loop 50 Optical fiber 30 optical microscope 7 orthogonality 13 84 piezoelectric 10 piezoelectric tube scanner 3 power supply 31 PSPD 3 41 Q Q factor 57 Quad cell PSPD 62 R reflection angle 40 Refresh 73 Repeat 48 resonance 69 resonant frequency 68 response rate 11 Rotation 48 Scan OFF 48 Control 46 Scan Direction 65 Scanner Mode 49 Scanning Probe Microscope 8 Scanning Tunneling Microscope 9 SEM 8 Set point 48 set point value 73 Silicon cantilever 34 Silicon Nitride cantilever 34 Slope 48 software calibration 11 spring constant 58 standard sample 11 steering mirror 15 TEM 8 Tip Bias 48 tube scanner 11 tunneling current 9 Two way 48 V van der Waals Force 67 vertical resolution 9 54 Video Monitor 29 X Y 48 XE 100 Head 2 XEI 17 Index XEP 17 37 XEP Part selection 50 X Y scanner range 50 XY Servoscan 50 X Y scanner 5 XY Stage 6 XY Voltage mode 49 Z Z scanner 2 4 Z scanner Range 53 Z Servo 48 Z Servo Gain 48 Z stage 38 Z stage pad 44 Z Voltage mode 49 Zoom Out 73 85 XE 100 User s Manual Blank Page gt 86 Customer s Document Feedback Form In an effort to ensure that the content of this manual is updated and accurate PSIA welcomes any and all customer feedback If during the course of using this manual you come upon any errors inaccuracies or procedura
11. PORE RATING OARE T II 2 1 General operating Safety ede eive dette eli eee teta ii ze Laser Salely GAUlIOFS odit repo n ec I be debet ES iii Chapter 1 Introduction to XE 100 1 1 1 PRIMARY COMPONENTS OF XE 100 SYSTEM 1 IIT SFM SAJO Dod Mau dna cactus 2 18152 COMDULC Oe MONON 8 Video 8 1 2 PRINCIPLES OF XE 100 S MEASUREMENTS 2220 2002 400 0000000000000000004000000320 8 1 2 1 Scanning Probe 5 8 ATOIDIC MICTOSCODONS doi t A 9 142532 KESSVSICIN s advantage 13 Chapter 2 Installation iii aa 19 Pe ENVIRONMENT M MH 19 2 2 PRESNSTADEATION S eL di 20 2 3 COMPONENT hts toan 20 2 4 HARDWARE INSTALLATION eene ts ose 21 2 4 1 Installation of an Air Table or an Active Vibration Isolation System 21 2 4 2 Computer Installation
12. bring the cantilever closer to the surface by clicking the Z stage pad button 4 f the sample surface is well focused then lower the Z stage until the shape of the cantilever starts to show faintly while watching the video monitor CAUTION 45 XE 100 User s Manual When lowering the cantilever do so very slowly to avoid a potential collision with the sample 5 Click the Approach button Approach All possible software selections will be restricted until the completion of a system controlled tip approach except for the Stop button Sep It might take long time to complete the Approach process because the 2 stage moves only a few microns per step Therefore to minimize the time required to complete tip s approach the cantilever must first be brought very close to the sample surface In order to decrease the approach time become familiar with process 2 4 and practise using the optical microscope to bring the probe very close to the sample surface 6 After an Auto Approach is completed several parameters in the Scan Control window should be adjusted Scan Control Repeat Twa X OY slope 0 000 Scan OFF Scan Sizes O Y 10 000 Offset t 0 0000 em 0 0000 Rotation sera 0 00 deg ScanHate 2 Servo Gain 1 00 Hz 1 000 set Tip Bias 0 030 Drive 15 0 4 NCM ASetup normal
13. CAUTION To replace a cantilever it is desirable to raise the Scanner Head to a suitable height so as to allow proper clearnce for your fingers to avoid contact with the sample surface Figure 4 3 EZ snap tip exchange 2 There are two holes in a cantilever chip a round hole and an elongated slot When you precisely overlay the two ruby nodules located on the end of the probe arm with these holes the cantilever chip will be attached into place by a magnet and the position of the cantilever will be firmly fixed in one position see Figure 4 4 Ruby nodules Elongated slot Round hole Magnets Steel ball Cantilever Figure 4 4 Edge of the probe arm beore left and after right the cantilever chip plate is attached to it 4 5 Laser beam alignment The AFM obtains an image by monitoring the deflection of a cantilever Since this deflection is too tiny to be measured the actual measurement is made indirectly by utilizing a laser beam The laser beam is reflected off the backside of the cantilever and onto a PSPD position sensitive photo detector When the cantilever deflects the reflection angle of the laser beam will change resulting in a change of the location where the laser beam enters the PSPD This change is in general much greater than the deflection of the cantilever usually smaller than a radius of an atom which makes 40 Chapter 4 Setup Procedure the position detection much easier There are two
14. Off icon in the Tool bar 49 XE 100 User s Manual 2 Open the Part selection window by clicking the Select Parts icon 4 then select HIGH or LOW AEP Part selection Head made AT Voltage made Voltage mode Z Scanner Range 1 000000 Cantilever General v a Figure 5 1 Select Scanner mode 5 2 1 High voltage mode In the High voltage mode two measurement types Closed Loop and Open Loop are possible depending on the status of the XY Servoscan Closed loop refers to when XY Servoscan is and Open loop is when XY Servoscan is OFF In general piezoelectric materials display nonlinear behavior in response to an applied voltage Therefore the scanner which is made of a piezoelectric material displays nonlinearity and hysteresis Refer to Chapter 1 When the scanner s range of motion increases nonlinearity and hysteresis can be calibrated by means of hardware corrections In this case a detector is used to linearize the scanner s motion throughout the user determined X Y scanner range It should be decided whether or not to use this detector in the XY Servoscan Setup When in the High voltage mode the XY Servoscan is recommended to be ON 50 Chapter 5 Set up Scanner Mode XY Setup GUN OFF Hold feedback Integral gain Integral ratio 05 Y feedback Integral gain Inte
15. SPM components for easy connection and operation please arrange them as shown in Figure 2 6 Figure 2 7 shows the cables to be checked before the initial installation Video Monitor 100 SPM Stage Computer amp Monitor XE 100 Control Electronics Figure 2 6 Basic arrangement of XE 100 25 XE 100 User s Manual W gt F Figure 2 7 Cables needed to be checked prior to installation BNC cable with A V jack converter USB cable Optical fiber Power cable Motor cable Analog cable B XE 100 SPM Main Body As shown in Figure 2 8 there are two connectors on the side of the XE SPM main body Connect the upper connector to the Z scanner head using the Z scanner cable 26pin Connect the lower connector to the X Y scanner using the X Y scanner cable 20pin 26 Chapter 2 Installation 26 pin Head cable AE Head T M 20 pin M Scanner cable i AY Scanner Figure 2 8 Connection between XE 100 SPM main body and the XE head and X Y scanner 27 XE 100 User s Manual e BNC for Video Monitor Motor 40 Analog 50 Illuminator Figure 2 9 Rear panel of the XE 100 SPM Base B XE 100 Control Electronics As shown in Figure 2 9 and 10 connect the Analog connector C on the rear panel of the XE 100 Control Electronics to the 50pin connector C on the back of the main body using the Analog cable 50 Connec
16. and panning the axis lining the sample and the CCD camera is always fixed and therefore the high quality optical view is preserved The XE 100 s standard 10X objective lens yields about 500 times magnification and the optional 20X objective lens yields about 1000 times magnification on the 10 inch video monitor Figure 1 9 Optical Microscope Frame 1 1 2 XE 100 Control Electronics The Control Electronics plays an important role in mediating between the XE SPM stage and the computer In order to maintain fast effective communication between the computer and the XE 100 Control Electronics a USB interface is used The DSP contained in the XE XE 100 User s Manual 100 Control Electronics is the TMS320C6701 running at 167MHz 1 000MFLOPS e e eee eH hM d LL 3 4 hh nummum XE MX Figure 1 10 XE 100 Control Electronics 1 1 3 Computer amp Monitor The computer is connected to the XE 100 Control Electronics via USB cable The computer is equipped with a PentiumIV CPU Processor 256MB DDR RAM a 40GB HDD It uses a Windows XP operating system The 17 inch LCD monitor gas 12801024 pixels with 32 bit color This monitor is digitally connected to the computer via DVI Digital Video Interface port 1 1 4 Video Monitor The Video Monitor a 10 4 LCD displ
17. between the sample and the probe tip Even though the interatomic repulsive force in this case is merely 1 10 nN the spring constant of the cantilever is also sufficiently small less than 1 N m thus allowing the cantilever to react very sensitively to very minute forces The AFM is able to detect even the slightest amount of a cantilever s deflection as it moves across a sample surface Therefore when the cantilever scans a convex area i 5 of a sample it will deflect upward and when it scans a concave area it will deflect downward This probe deflection will be used as a feedback loop input that is sent to an actuator z piezo In order to produce an image of the surface topography the z piezo will maintain the same cantilever deflection by keeping a constant distance between the probe and the sample 56 Chapter 6 AFM in Contact Mode 6 2 Contact mode setup To use contact mode AFM select the appropriate Head mode as follows 1 Turn off the laser by clicking the Laser On Off button in the Tool bar 2 Once the laser is off set the Head mode to C AFM after clicking the Select Parts button 3 on the laser by clicking the Laser On Off button AEP Part selection Head made oe 1 Ar Voltage made HIGH 2 Voltage mode Z Scanner Range 1 000000 Cantilever General Figure 6 2 Contact mode AFM setup 6 3 Cantilever Selection
18. change due to the distance change becomes greater and greater Therefore contact AFM measures surface topography by utilizing the system s sensitive response to the Repulsive Coulomb Interactions that exist between the ion cores when the distance between the probe tip and the sample surface atoms is very small However as shown in Figure 8 1 when the distance between the probe tip and the sample atoms is relatively large the attractive force becomes dominant lon cores become electric dipoles due to the valence electrons in the other atoms and the force induced by the dipole dipole interaction is the van der Waals Force Non contact AFM NC AFM measures surface topography by utilizing this attractive atomic force in the relatively larger distance between the tip and a sample surface 67 XE 100 User s Manual Contact Mode sample AFM image Non contact Mode sample AFM image Figure 8 1 Concept diagram of Contact mode and Non Contact mode Figure 8 1 compares the movement of the probe tip relative to the sample surface for images being acquired between in contact AFM and in non contact AFM Contact AFM uses the physical contact between the probe tip and the sample surface whereas non contact AFM does not require this contact with the sample In Non Contact mode the force between the tip and the sample is very weak so that there is no unexpected change in the sample during the measurement Therefore Non Contact AFM i
19. current method AC detection makes more sensitive responds to the force gradient as opposed to the force itself Thus it is also applied in such techniques as MFM Magnetic Force Microscopy and DFM Dynamic Force Microscopy A bimorph is used to mechanically vibrate the cantilever When the bimorph s drive frequency reaches the vicinity of the cantilever s natural intrinsic vibration frequency fo resonance will take place and the vibration that is transferred to the cantilever becomes very large This intrinsic frequency can be detected by measuring and recording the amplitude of the cantilever vibration while scanning the drive frequency of the voltage being applied to the bimorph Figure 9 2 displays the relationship between the cantilever s amplitude and the vibration frequency From this output we can determine the cantilever s intrinsic frequency amplitude frequency Figure 8 2 Resonant frequency On the other hand the spring constant affects the resonant frequency fo of the cantilever and the relation between the spring constant in free space and the resonant 69 XE 100 User s Manual frequency fo is as in Equation 2 NU 2 As in Equation 1 since becomes smaller than due to the attractive force fes too becomes smaller than f as shown in Figure 8 3 a If you vibrate the cantilever at the frequency f a little larger than fo where a steep slope is observed in the graph
20. easy Figure 4 8 Scan Control Window 7 Input the one dimensional value for the sample in the Scan Size text box 46 Chapter 4 Setup Procedure SIZE A 10 000 m 8 Choose a Scan Rate in the range of 0 5 10 2 The Hz unit in the Scan Rate scroll box represents the frequency or how many times per second the scanner moves in the fast scan direction 5 can Hate 1 00 Hz 9 As shown in Figure 4 9 adjust the 7 Servo Gain in order to stabilize the line trace Increase or decrease the gain value as necessary until the Trace Line is repeatable and there are no oscillations present in the oscilloscope display 10 Once the trace line is stabilized set the scan direction to X or Y and then click Image Now the measurement will begin SC _________ iT rr 2 upira fi 1 Figure 4 9 Servo gain at the proper level top Servo gain too high resulting in oscillations of the Z scanner bottom 47 XE 100 User s Manual 4 8 Scan parameter Definitions below 48 The definition of the parameters in the Scan Control window is explained Repeat After selecting Image The same area will be imaged repeatedly Two way Successive images will be acquired by alternating the slo
21. major steps in aligning the laser beam on the top of the cantilever At first adjust the laser beam so that it strikes the backside of the cantilever This procedure is facilitated by bringing the cantilever relatively close to the sample so that it is easy to find the laser spot when it reflects off of the sample surface 1 As shown in Figure 4 5 using the two laser aligning screws which are located on the upper part of the XE 100 head move the laser beam vertically and horizontally on the video monitor 2 Move the laser beam from the outside area of the cantilever chip to the outer edge of the chip from the lower part of the monitor to the upper part accordingly Once the laser beam reaches the cantilever chip you will be able to see the reflected laser light at the chip s edge 3 After the laser beam touches the edge of the cantilever chip adjust the laser beam by moving horizontally on the video monitor to focus it on the cantilever 4 Asshownin Figure 4 5 bring the laser beam to the tip of the cantilever CVV spot moves to the upper side COA spot moves to the lower side RRR T TTTTTT LiL IT TT iT spot moves to the left COW spot moves to the right d Figure 4 5 Laser beam alignment on the cantilever Secondly place the reflected laser beam on the center of the PSPD as follows 41 XE 100 User s Manual 42 Adjust the steering mirror loc
22. protective earth ground contact WARNING Before the power is turned on the power selections for the individual components need to be inspected The voltage selector switch is located on the rear panel of the XE 100 Control Electronics and it can be set to the following voltages 100 V 120 V 230 V or 240 V WARNING Do not open the XE 100 Control Electronics or the AFM head Doing so may result serious electrical shock as high voltages and electrostatic sensitive componenst are used in the XE 100 Control Electronics and the AFM head CAUTION Check regularly to ensure that the XE 100 s cables are free from damage and that all connections are secure If any damaged cables or faulty connections are found contact your local PSIA service representative Never try to operate the equipment under these conditions Safety Precautions of XE 100 system CAUTION All parts in the XE 100 system should be handled with extreme care If not handled properly these parts can be easily damaged as they are made of fragile electromagnetical equipment CAUTION An EMI filter must be installed to meet operating safety ElectroMagnetic Compatibility compliance CAUTION The AFM head should always be handled with care When removed from the XE system the AFM head needs to be carefully placed on a flat surface This will protect the scanner the cantilever and the laser beam adjustment knobs Never al
23. representing free space frequency vs amplitude the amplitude change at 1 becomes very large even with a small change of intrinsic frequency caused by atomic attractions Therefore the amplitude change measured in f reflects the distance change Ad between the probe tip and the surface atoms If the change in the intrinsic frequency resulting from the interaction between the surface atoms and the probe or the amplitude change AA at a given frequency 1 can be measured the non contact mode feedback loop will then compensate for the distance change between the tip and the sample surface as shown in Figure 8 3 b By maintaining constant cantilever s amplitude Ao and distance do non contact mode can measure the topography of the sample surface by using the feedback mechanism to control the Z scanner movement following the measurement of the force gradient represented in Equation 1 fett fo amplitude h frequency 70 Chapter 9 Dynamic Force Microscopy tip sample z feedback distance do AQ amplitude Figure 8 3 a Resonant frequency shift b Amplitude vs Z feedback 8 2 Non contact mode setup The non contact mode setup can be done easily by selecting NC AFM as the Head mode similar to the setup for contact mode explained in Section 2 of Chapter 6 1 Turn off the laser switch by clicking the Laser On Off button in the Tool bar 2 Once the laser is Off set the Head mode to NC
24. resonates and amplifies greatly This is called the intrinsic frequency fo 77 XE 100 User s Manual amplitude f frequency Figure 9 1 Resonant frequency DFM uses the non contact mode feedback circuit with keeping the vibrating frequency fi a little bit lower than the resonant frequency while oscillating in free space Then as the tip is lowered the real spring constant reduces due to the attractive van der Waals force which becomes larger as the tip comes closer to the sample surface as shown in Figure 9 2 a Therefore the resonant frequency changes to effective frequency fe in non contact regime and the amplitude at the frequency f increases by A A Since the amplitude increases by AA the non contact mode feedback circuit decreases the distance between the tip and the sample surface by Ad indicated in the graph of vibration amplitude vs tip sample distance and z feedback as shown in Figure 9 2 b This part was explained in detail in Chapter 8 so please refer to Chapter 8 section 1 Therefore the vibrating cantilever which is oscillating above the sample approaches the sample almost in contact or in collision with the surface This method keeping intermittent contact between the sample surface and the vibrating cantilever is called Dynamic force microscopy DFM Similar to the initial approach of making contact with the sample while scanning larger amplitude reduces the distance between the tip and sample and s
25. to measure topographic data by collecting a laser beam signal on a PSPD Position Sensitive Photo Detector after it is reflected from the back side of a cantilever To align the laser beam conventional SPMs use additional positioning equipment the operation which is often difficult and cumbersome However Laser alignment becomes very easy and convenient with the XE 100 Manageable control knobs on the XE 100 head can be adjusted manually with the help of the control software and the video monitor display making location and movement of the laser beam easy and accurate 4 Whenever it is necessary to remove the XE 100 head from the main frame it is very easy to do so This procedure can be accomplished by unlocking the dovetail thumb locks and sliding the XE 100 head off the dovetail rail after having disconnected the cable from between the head and the main frame Remounting the head is as easy as removing it CAUTION Before disconnecting the cable the Laser switch on the XE 100 head must first be turned off WARNING Do not disassemble the XE 100 head on your own PSIA will not be responsible for any personal physical damage or degraded performance that may result from unauthorized disassembly XE 100 User s Manual Figure 1 3 XE 100 Head Z Scanner Laser Position Indicator Laser Switch Laser Aligning screws Steering mirror adjusting screws Figure 1 4 Dovetail Lock Head Mount B XE 100Z scann
26. AFM by clicking the Select Parts button 4 3 Turn on the laser by clicking the Laser On Off button 71 XE 100 User s Manual AEP Part selection Head made AT Voltage mode HIGH made HIGH T Z Scanner Range 1 000000 E MM Cantilever I sns 06 Figure 8 4 Non contact mode setup 8 3 Resonant Frequency setup Once the Head mode is selected as NC AFM turn on the laser by clicking the Laser On Off button When all selections are completed click the OK button system will then automatically find the resonant frequency Besides the method of turning the laser on and off you can find the resonant frequency for non contact mode by using the NCM frequency button Frequency Set Report Start Freg 288300 Hz Selected Freq 300560 Hz Set Point 41 243 Control Drive g Phase Figure 8 5 Resonant Frequency setup in Non Contact Mode 72 Chapter 9 Dynamic Force Microscopy When the NCM Frequency Setup window opens you can manually select the resonant frequency as follows 1 If the Refresh button or Zoom Out button is clicked one unit on the X axis represents 5 kHz as shown above 2 Select the resonant frequency as follows At first press the Refresh button and then the graph of frequency vs amplitude will appear Press the Refresh button whil
27. Environment B Temperature and Humidity Hecommended Temperature OG 2390 Recommended Humidity 30 96 80 96 Not condensing The XE 100 should be installed in a clean dry atmosphere with proper ventilation Vibration The XE 100 is extremely sensitive to external vibrations Thus it is important to isolate all possible vibrations from the equipment s surroundings It is recommended that an Air Table or Active Vibration Isolation System be installed to remove external vibrations Floor Vibration vertical floor vibration less than 1x10 m sec for 0 50 Hz B Acoustic and Electromagnetic Noise The XE 100 should be installed where outside noise and light can be minimized To eliminate noise and light interference it is advisable to operate the XE 100 with the Acoustic Enclosure closed B Electrical Requirements The XE 100 requires an AC power supply 19 XE 100 User s Manual Power Supply 100 120 V or 230 240V 60 Hz 300 W Since the XE 100 SPM is highly sensitive equipment it is ideal to use it with a UPS Uninterruptible Power Supply installed to provide a stable power supply The resistance in the ground system should be less than 100 ohms to optimize operation 2 2 Pre Installation The XE series SPM Scanning Probe Microscope is a precision instrument that can measure up to sub nanometer scale features Consequently it is very susceptible to surrounding noise and vibrations and the following precaution
28. High Accuracy Small Sample SPM User s Manual Version 1 0 Copyright 2002 PSIA Corporation All rights reserved Notice This manual is copyrighted by PSIA Corp with all rights reserved This manual may not be reproduced in any form or translated into any other language in whole or in part without written permission from PSIA Corp PSIA is not responsible for any mistakes or damages that may occur either accidentally or willfully as a result of using this manual PSIA is not responsible for typographical errors This manual may be changed without prior notice and it will be examined and revised regularly PSI A Advanced Scanning Probe Microscopes We welcome any user feedback that may result in future improvements to the quality of this manual If you have any suggestions please contact PSIA PSIA Corp Induspia 5F SangDaewon Dong 517 13 Sungnam Korea 462 120 Tel 82 31 734 2900 www psia co kr PSIA Inc 47339 Warm Springs Blvd Fremont CA 94539 www advancedspm com Preface The Scanning Probe Microscope SPM is not only at the top of the list of equipment pioneering the nano scale world it is also the most fundamental technology Succeeding the first generation optical microscope and the second generation electron microscope the SPM has every right to be known as a third generation microscope since it enables us to look into the nano scale world At the same time it has many advantag
29. Y Servoscanils OFF iit eo ni Figure 6 1 Relation between the force and the distance between atoms 96 Figure 6 2 Contact mode AFM D7 Figure 6 3 SEM image of the shorter cantilevers A B C from a chip of the CSC12 feto Figure 6 4 Silicon of the CSC12 series has 6 rectangular cantilevers 59 Figure 6 5 Contact AFM setup and voltage mode selection 60 Figure Guadscell PSP D sided o Met reu 62 Figure LEN SIQNAl 63 Figure 7 3 C nversion to LEM ioi oio re 65 Figure 7 4 od 66 Figure 8 1 Concept diagram of Contact mode and Non Contact mode 68 Figure 8 2 Resonant fr guenocy esee enter enne den ex Rab e UTR cesta 69 Figure 8 3 a Resonant frequency shift Amplitude vs Z feedback 71 Figure 8 4 Non contact mode AFM setup 12 Figure 8 5 Figure 8 6 Figure 8 7 Figure 8 8 Figure 9 1 Figure 9 2 Figure 9 3 Figure 9 4 Figure Contents Resonant Frequency setup in Non Contact Mode
30. ated on the front side of the XE 100 head so that the path of the reflected laser beam will reach the PSPD as shown in Figure 4 6 Generally the A B value will be more than 2V when the alignment is optimized the value indicates the total intensity of the laser beam detected by the PSPD When the cantilever surface is not coated with metal the A B value is closer to 1V because of the difference in surface reflectivity This will be the case with the cantilevers that are provided with the XE 1 00 for Contact mode operation To position the laser beam on the center of the PSPD adjust the knobs located on the front of the scanner head see Figure 4 5 so that the A B value is smaller than 0 5V the value indicates the difference in the laser intensity detected in the upper half and the lower half of the PSPD cell During imaging this value is related to the deflection of the cantilever When the above alignment condition is met there will be an increase in the intensity of the small red circle on the PSPD display see Figure 4 6 Jouueos 7 X Y scanner Chapter 4 Setup Procedure FSPD Sig Scanner head custom Figure 4 6 Laser beam alignment display in XEP Even if the value is within the acceptable range if the A B value is too small then it may be difficult for the laser beam t
31. ays the image obtained by the Optical microscope and the CCD camera specifically the position of the cantilever in relationship to the region of interest on the sample surface that is to be measured 1 2 Principles of XE 100 s measurements 1 2 1 Scanning Probe Microscope The Scanning Probe Microscope SPM proved false the prevailing concept that an atom is too small to be observed with even the best microscope It now has every right to be called the third generation microscope with optical and electron microscopes named as the first and second generation microscope Whereas the maximum magnifying power of an optical microscope is several thousands and that of a scanning electron microscope SEM is tens of thousands an SPM has the magnifying power of tens of millions enough to observe individual atoms Even though a transmission electron microscope TEM has the lateral resolution high enough to image at the atomic level its vertical resolution is much weaker at observing individual atoms On the Chapter 1 Introduction to XE 100 other hand the vertical resolution of SPM is even better than its horizontal resolution making it possible to measure on the scale of fractions of the diameter of an atom 0 01nm The SPM with its exceptional resolution not only makes it possible to understand the various nanoscale worlds which heretofore were not completely revealed but also to bring the unbelievable into reality providing such capabil
32. canner iio parue due Erant ceu mus urat 49 5 1 100 SCANNER CONFIGURATION 49 5 2 SELECT SCANNER MODE iterare edo d ea Do 49 AHON volage plan VERIS 50 5 2 2 LOW voltage TIJOOGO t c Sos E 52 SCanner 53 Chapter 6 AFM in Contact Mode 55 6 1 PRINCIPLE OF CONTACT MODE 20 020200000 0 000000002 020000002000000 55 622 OONTACT MODE SETUB e Ses aa eto vut 57 CANTILEVER SELECTION ee 57 Dd SCANNER EUR More arde eb 59 MEASUREMENT PROCEDURE er ee 4 60 Chapter 7 Lateral Force Microscopy 61 7 1 PRINCIPLE OF LATERAL FORCE MICROSCOPY LEM 61 7 2 GONVERSION reri 64 TROU GANTLCEVER SFLECTION do 65 24 MEASUREMENT PROC DU E 0 ue hae ea o t 65 Chapter 8 AFM in Non Contact nnmnnn 67 8 1 PRINCIPLE OF NON CONTACT MODE AFM eese Ren eene nnne n
33. configuration for most AFMs This scanning AFM is typically used to measure a wide variety of samples which have relatively small roughness The force between the atoms at the sample s surface and those at the cantilever s tip can be detected by monitoring how much the cantilever deflects This deflection of the cantilever can be quantified by the measurement of a laser beam that is reflected off the backside of the cantilever and onto the Position Sensitive Photo Detector PSPD The tube shaped scanner located under the sample moves a sample in the horizontal direction X Y and in the vertical direction 2 repetitively scans the sample line by line while the PSPD signal is used to establish a feedback loop which controls the vertical movement of the scanner as the cantilever moves across the sample surface XE 100 User s Manual Feedback E miror pu sample cantilever it adi X y Z piezo tube scanner X Y Scan Control Figure 1 11 Diagram of conventional AFM s scanning The AFM can easily take a measurement of a conductor a non conductor and even some liquids without delicate sample preparation unlike SEM or TEM Also it is a powerful tool that can measure extremely small structures which other instruments have difficulties investigating Despite its many advantages the AFM does have some drawbacks as well Since
34. e adjusting the drive 9e 25 0 1 to make the strongest peak fall within the first three units of the y axis After adjusting the height of the peak press the Zoom In button until the x axis unit is 1kHz div 3 After positioning the mouse pointer on the slope just to the right hand side of the strongest peak as shown in Figure 8 5 click there with the left mouse button and a sign will appear The location of the sign corresponds to the selected frequency f at which the cantilever will vibrate in non contact mode After positioning the mouse pointer on the red horizontal line move this red line up and down while holding the left mouse button this will allow you to change the set point value In general make the set point just higher than half of the peak height and press the OK button once to enter the selection The value of the drive amplitude and set point can also be changed in the Scan Control window 8 4 Cantilever selection The non contact mode cantilever has a relatively large frequency since the non contact mode use the vibrating cantilever method which enables to measure the force gradient by the amplitude and phase change due to the interaction between the probe and a sample surface Figure 8 6 shown below is a SEM image of a typical non contact mode cantilever the NSC15 series The upper surface of the cantilever the opposite side of the tip is coated with aluminum Al to enhance the laser beam
35. e optical microscope is located on the same axis as the laser beam that is reflected at the prism as shown in Figure 1 13 15 XE 100 User s Manual BRPRE RL LET ET TG Figure 1 16 Captured optical microscope image Figure 1 16 shows the cantilever with the laser beam focused on it as it is displayed on the video monitor Since the CCD camera is aligned directly with the cantilever with nothing blocking its view it is very convenient to focus on or to observe the sample while moving the camera up and down This view also provides superb quality for an optical microscope The superiority of the XE system s design and its intention to accommodate the convenience of the user appears in many different aspects in addition to the optical microscope The AFM head which includes the Z scanner is easily inserted by sliding it along a dovetail rail and locking it into place with a convenient turn of two thumb locks There are no additional knobs or springs to adjust as is common with other designs The replacement of the tip is just as easy and no special tools are required for this procedure Figure 1 18 shows the easy operation of replacing a tip by hand Figure 1 17 Dovetail Lock Head Chapter 1 Introduction to XE 100 Figure 1 18 EZ Snap Probe Tip Exchange The XE system not only achieved a structural design change that yielded e
36. ed PSPD MIRROR TIP CANTILEVER Figure 1 15 Laser beam path related to the cantilever s movement The cantilever and the PSPD move together with the Z scanner while the laser beam a steering mirror and a fixed mirror in front of the PSPD are fixed relative to the scanner frame The laser beam positioned at one side of the scanner is aimed at a prism that is situated above the cantilever The prism reflects the laser beam downward and onto the back surface of the cantilever The laser beam will always hit the same spot on the cantilever s surface since the Z scanner only moves vertically Therefore once the laser beam is aligned there is no need to realign the laser beam even after the Z scanner has been moved up and down to change samples The steering mirror located at the front of the Z scanner assembly adjusts the reflection angle of the laser beam that is reflected off the cantilever s surface The steering mirror reflects the laser beam to a fixed mirror which in turn reflects the beam at once to the PSPD Another clever feature of this alignment design is that as a result of placing the second fixed mirror next to the PSPD it allows changing of the Z scanner position without having to readjust the position of the PSPD Therefore only the deflection of the cantilever will be detected independent of the Z scanner movement Since there is nothing obstructing the view above the cantilever in the structure Figure 1 15 th
37. efore being installed the AVIS should be in Lock mode in order to protect the TS 150 from outside impacts that may occur during shipping or storage When the AVIS is initially installed or after the lock condition has been selected prior to system transport or long term storage the lock mode will be automatically released once power is supplied to the AVIS Be sure to securely place the four corners of the TS 150 on a solid flat surface before turning on the power supply When the power switch is on and after the inside motor stops turning the upper table will be floating and the Isolation Disable sign will be displayed At this time if you push the button labeled E on the front panel the active vibration isolation will begin and the red LED will turn on 24 Chapter 2 Installation POWER o Figure 2 5 Front panel of AVIS ARS Seientifie Instruments If the AVIS is to be kept in storage again or transported you may scroll the screen while the power is still on until the message to lock push appears Pushing the button will initialize the motor which slowly lowers the isolation stage until it finally halts You may turn off the power when the System locked message appears The AVIS will remain locked until the power supply is turned on again 2 4 2 Computer Installation Please refer to the manual supplied by the computer manufacturer 2 4 3 XE Cable Connections Before connecting the XE 100
38. ement in other directions This cross talk and non linearity see Figure 1 12 caused by the scanner s three axes being non orthogonal to another has a more pronounced effect in the case of measuring larger areas or flat samples This intrinsic problem can be eliminated completely however by physical separation of the Z scanner from the X Y scanner The breakthrough that eliminated these cumbersome problems came when the XE series Cross talk Elimination SPMs introduced a new concept of separating the Z scanner from the X Y scanner The XE scan system is designed so that the X Y scanner scans a sample in two dimensional space while the Z scanner moves the tip only in the z direction Figure 1 13 shows a diagram of the XE system in which the Z scanner separated from the X Y scanner The symmetrical flexure scanner used in the XE series SPM moves only in the X Y plane and has superb orthogonality This scanner s design also makes it possible to place much larger samples on the sample stage than could normally be accommodated by a piezoelectric tube type scanner Furthermore since the flexure scanner only moves in the X Y direction it can be scanned at much higher rates 10 50 Hz than would be possible with a standard AFM 13 XE 100 User s Manual Because the stacked piezoelectric actuator used for the Z scanner has a very fast response speed at least 10 kHz it is able to respond to topographic changes on the sample surface more than 10 time
39. er The Z scanner which is mounted on the XE 100 head makes it possible for the tip to maintain constant feedback conditions force or distance as it is moved over a sample surface maximum measurement range of sample surface s height is determined by the Z scanner range The XE 100 s Z scanner can move up to 12 On the other hand the minimum obtainable vertical resolution is determined by the control unit and the electric voltage that is applied to the Z scanner Chapter 1 Introduction to XE 100 WARNING Never disassemble the Z scanner on your own PSIA will not be responsible for any personal physical damage or degraded performance that may result from unauthorized disassembly Figure 1 5 Z scanner Assembly B XE 100 X Y scanner The XE 100 s X Y scanner is a Body Guided Flexure scanner The X Y scanner is fabricated from a solid aluminum block The desired area is cut out from inside the aluminum block and the lines indicated in Figure 1 6 are then fabricated with a special technique called Wire Electric Discharge Machining this results in a flexure hinge structure An X Y scanner with a flexure hinge structure has the advantage of highly orthogonal two dimensional movement with minimal out of plane motion Due to the Parallel Kinematics design the X Y scanner has low inertia and axis independent performance The closed loop please refer to Chapter 5 scanning is accomplished by means of an optical
40. ers A B C from a chip of the CSC12 series Figure 6 4 shows the detailed standardized gauge of the CSC12 series chip Altogether this chip contains six cantilevers three to a side all with different spring constants Among these the three cantilevers on one side become non functional during the process of affixing them to the cantilever chip Thus only the three on the other side are usable e g in Figure 6 4 the unmounted cantilevers are purchased separately you may choose either set of cantilevers A B C or D E F 58 Figure 6 4 Silicon chip of the CSC12 series has 6 rectangular cantilevers 3 4 mm 0 4 a ee e e e o o c c Chapter 6 AFM in Contact Mode 8 i gt Table 6 1 gives the dimensions and characteristics of the six cantilevers in the CSC12 series Table 6 1 Specifications of CSC12 Series Cantilevers Cantilever Cantilever Cantilever Type Length 5 um w t3 4M min typical max 110 90 130 300 350 EN ROS O NEM gt 250 35 35 35 35 35 35 6 4 Scanner Setup Wiath Cantilever Resonant Thickness um Frequency kHz 0 7 0 7 0 7 0 7 0 7 0 7 1 0 1 0 1 0 1 0 1 0 1 0 1 3 1 3 1 3 1 3 1 3 1 3 min typical max 65 95 50 9 5 7 0 14 105 155 75 14 10 20 150 230 105 19 14 28 Force Constant N m min t
41. es over manual microscopes which passively look at the samples The SPM is like a miniature robot fabricating specific structures by manipulating atoms on the sample surface and using a probe tip to take measurements of those structures The SPM originated with the invention of the Scanning Tunneling microscope STM The STM uses a tunneling current between a probe tip and a sample in a vacuum state to measure surface topography As a result it is limited in that it can only measure a sample which is a conductor or a semiconductor Once the Atomic Force Microscope AFM was developed however a whole new range of measurement capabilities became possible Now it is not only possible to measure non conductors in air but also to measure the physical chemical mechanical electrical and magnetic properties of a sample s surface and even measure live cells in solution The SPM is indeed the key to entering the world of nano technology that has yet to flourish and it is essential equipment for various research in the basic sciences physics chemistry and biology and in applied industry mechanical and electrical engineering The importance of the SPM stands only to grow greater and greater in the future Blank Page gt Safety Precautions of XE 100 system Safety Precautions of System This preview section describes the procedures related to the general operating safety of the XE 100 in detail This section should be thorough
42. eux Scan Cam Y 5000 fs wt 0001 m 000 Y vene PT T 1902 Sei 00000 Drew ris Wom h ER Massoum entry size M24 Er Si 2502 mi 2 Sage 0803 aes zx 5 77777 nope em pie Edi Work Window Help Cee HN fife gt Imaging mode Data sovita Topogiapls rize ume 5440 Sean fimansioe 612612 Comment Contacthole Dae 12442 03433 0 2573 2002021 Hadum 0 173 Axum 206 Agua 2589 0 Sce 7 2 1 68 35 ass 42 38 661122 qarz 7 e gt WWiGasWXxEWXE Image Work For Help praes F1 Figure 1 20 Image Processing Program 18 Chapter 2 Installation Chapter 2 Installation The installation procedure and environmental specifications for the XE 100 play a significant role in the safe operation of XE 100 Since the durability safety and overall performance of the XE 100 depend on the environment and proper installation please pay close attention to the following installation environment and procedures that are recommended in this chapter 2 1
43. ever in the horizontal direction in LFM The lateral deflection of the cantilever is a result of the force applied to the cantilever when it moves horizontally across the sample surface and the magnitude of this deflection is determined by the frictional coefficient the topography of the sample surface the direction of the cantilever movement and the cantilever s lateral spring constant Lateral Force Microscopy is very useful for studying a sample whose surface consists of inhomogeneous compounds is also used to enhance contrast at the edge of an abruptly changing slope of a sample surface or at a boundary between different compounds Since the LFM measures the cantilever movement in the horizontal direction as well as the vertical one to quantitatively indicate the surface friction between the probe tip and the sample it uses a PSPD position sensitive photo detector that consists of four domains quad cell as shown in Figure 7 1 61 XE 100 User s Manual Figure 7 1 Quad cell PSPD Generally in AFM to measure the topography of a sample surface the A B signal is used This signal is related to the difference between the upper cells the lower cells B D of the PSPD Topographic information A C B D The LFM signal which is related to the change in the surface friction on a sample surface measures the deflection of the cantilever in the horizontal direction and can be represented as the difference in t
44. ge and the vertical resolution Before adjusting 53 XE 100 User s Manual the scanner range consider at first the overall height variation of the sample surface Of course this height difference must not be greater than the Z scanner s maximum available range For example if a sample has a height difference it cannot measured in the Low voltage mode since the Z scanner s maximum range will be only 1 7um Secondly the smallest height difference on the sample surface should be greater than the vertical resolution For example it is not possible to distinguish atomic scale steps with height differences of 10 in the High voltage mode which has a vertical resolution of 1 86 Therefore it should be changed to Low voltage mode Also changing the Z scanner Range from 1 0 to 0 5 will produce even better vertical resolution If the Z scanner Range is set to 0 5 the height of 10 would be indicated by eight 0 1251 scaled pixels When the Z scanner Range is set at 1 0 however 1 step would be indicated by only four 0 250 scaled pixels 54 Chapter 6 AFM in Contact Mode Chapter 6 AFM in Contact Mode 6 1 Principle of Contact Mode AFM The AFM Atomic Force Microscope is an instrument that is used to study the surface structure of a sample by measuring the force between atoms At the lower end of the Z scanner there is a cantilever of very ti
45. gral ratio 08 L Figure 5 2 XY Servoscan is XE 100 scanners both X Y scanner and Z scanner have a maximum range of movement X Y scanner s maximum movable range is 50um 2 scanner s maximum movable range is 12um In the High voltage mode the applied voltage allows the scanner to reach this maximum limit Figure 5 3 depicts the maximum XY range as a solid gray shaded square The area outside of this square cannot be observed For example if the scanner s maximum range is 50 um it is not possible to scan both areas A and C even though they have the same scan size 15 Area A is impossible to scan because its offset the black point extends its range over the maximum range of the scanner Area C however is possible to scan Also although B and D have the same size and the same offset it is impossible to scan area B which extends over the maximum range due to its different angle of rotation Whenever the user enters an excessive range like A and B the scan range will be changed automatically to an observable area that falls within the scanners maximum allowable range a b Figure 5 3 Scanner s observable area 51 XE 100 User s Manual 5 2 2 Low voltage mode Aside from the High voltage mode which enables investigation of a wide range of surface structures from several micrometers to the maximum range the scanner can move the Low voltage mode can investigate tiny scales and very fine struct
46. he cantilever so that it is very close to the sample place the mouse pointer at the lower part of the Z stage pad button and click the left mouse button The speed of the Z stage movement is controlled by the location of the pointer on the Z stage pad button when the left mouse button is clicked When Focus follow is chosen as in the diagram below the Focus stage will move simultaneously with the Z stage 44 Chapter 4 Setup Procedure WARNING If the Z stage is lowered too fast the cantilever may crash into the sample surface Such a forceful interaction may break the probe tip damage or destroy the sample and or seriously damage the Z scanner xj Z Focus Focus Follow um F um E LII ELE B Figure 4 7 Motor Control Window 3 After lowering the probe tip to a few millimeters above the sample surface using the Z stage pad button de select the Focus Follow fccusFelow And then focus on the surface of the sample by pressing the appropriate area of the Focus stage pad considering its speed The speed will be adjusted based upon the distance between the pointer and the mid line indicated on the Focus stage pad like Z stage pad The top half of the pad will adjust the focus upward while the lower half will adjust it downward CAUTION If the cantilever is too far from the sample surface it may be very difficult to adjust the focus In this case
47. he signals recorded in the right cells A B and the left cells C D Frictional information A B C D 62 Chapter 7 Lateral Force Microscopy BS iva Scan Direction Figure 7 2 AFM and LFM signal Figure 7 2 a shows a surface structure with a centrally located step with low smooth areas on either side The flat part on the left contains a domain with a relatively high frictional coefficient Profile b indicates the cantilever s deflection as it encounters topographic features as well as different frictional coefficients as it scans from left to right Profile c is an AFM image of the surface topography and structure it is represented by the change in the vertical deflection of the cantilever which does not include the horizontal deflection Profile d and Profile e show the LFM signal which indicates the horizontal deflection of the cantilever When scanning left to right the surface structure of a sudden peak will instantaneously twist the cantilever to the right This results in a lateral force signal with a convex shape as seen in Figure 7 2 d 3 The opposite occurs when the probe encounters a sudden downward step as depicted at location 4 The region between D and 2 indicates an area on the sample surface 63 XE 100 User s Manual where there is a material with a higher surface frictional coefficient compared to the surrounding area There are no distinguishable surface features that will allow the user t
48. ial alignment problem sources Also check to ensure that the cantilever chip is properly mounted at the end of the scanner arm and is being firmly held in place with the backside of the cantilever facing upwards 43 XE 100 User s Manual 4 6 Sample Preparation The sample loading procedure for using the magnetic sample holder is as follows 1 Raise the Head and the Focus stage high enough to have no difficulty in loading the sample onto the magnetic sample holder on the X Y scanner CAUTION If the Head and the Focus stage are not rasied high enough the sample or the cantilever may be damaged 2 Fixthe sample on a sample disk using glues or double faced tapes You can complete the preparation for measurement by placing the sample disk on the magnetic holder of the X Y scanner 4 7 Measurement Procedure Before the tips approaching to the sample surface you should set up the scanner mode XY and Z voltage mode to High or Low Please refer to chapter 5 about how to set up the scanner mode Since the High voltage mode is used often here we make an assumption that the X Y Z scanner is set to use High voltage mode Once you are ready to proceed images may be obtained following the procedure below 1 When all of the preliminary steps including the laser alignment and the sample preparation are completed open the motor control window by clicking the Motor Control Bar button LIS 2 n order to position t
49. igh or Low for the XY Voltage mode and or the Z Voltage mode AEP Part selection Head mode Ar Voltage made He Voltage mode HIGH Z Scanner Range 1 000000 T Cantilever General Advanced Figure 8 8 Non contact AFM setup and voltage mode selection 8 6 Measurement Procedure The measurement procedure hereafter is the same as in Chapter 4 Please refer to Chapter 4 75 XE 100 User s Manual Blank Page gt 76 Chapter 9 Dynamic Force Microscopy Chapter 9 Dynamic Force Microscopy DFM 9 1 Principle of Dynamic Force Microscopy Dynamic Force Microscopy DFM is very similar to Non contact mode AFM in many ways such as the applied force and the measurement principle Before you read this chapter please read carefully Chapter 8 Non contact Mode measurement DFM is a hybrid of the two most fundamental measurement methods represented by contact mode and non contact mode In LFM the cantilever vibrates in free space in the vicinity of the resonant frequency like in non contact mode At the same time since the vibrating cantilever gets very close to the sample surface it taps the surface repeatedly and the tip contacts the sample surface as in contact mode If you measure the amplitude of vibration of the cantilever used in DFM while changing the frequency as shown in Figure 9 1 there appears a special frequency where the amplitude
50. ing the best image The measurement method hereafter is the same as in Chapter 4 Please refer t to Chapter 4 81 XE 100 User s Manual Blank Page gt 82 value 42 A B value 42 AC Track 65 Acoustic Enclosure 19 Active vibration Isolation System 23 Air Table 21 amplitude change 70 Approach 46 Atomic Force Microscope 9 Auto Flat 65 bimorph 69 BNC socket 23 cantilever 33 cantilever vibration 68 CCD camera 16 chip 33 Closed loop 50 Contact Mode 55 Control Electronics 7 28 cross coupling 10 Index Index dovetail rail 3 drive amplitude 73 drive frequency 69 E effective spring constant 69 electrostatic repulsion 55 excessive range 51 external vibration 19 EZ snap 40 flexure hinge 5 Floor Vibration 19 Focus Follow 39 45 Focus stage 38 Focus stage pad 45 force gradient 69 frictional coefficient 61 H Head mode 57 High voltage mode 50 hysteresis 10 83 XE 100 User s Manual illuminator 30 Input Configuration 65 interatomic force 56 intrinsic frequency 69 intrinsic spring constant 69 K Kinematic Mount 3 L Laser beam alignment 40 lateral deflection 61 Lateral Force Microscopy 61 lateral force mode 64 lateral resolution 8 52 Low voltage mode 52 LPF 65 M Magnetic Force Microscopy 69 maximum movable range 51 N Non contact Mode 67 non linearity 10 objective lens 7 Offset X Y
51. itialized 4 2 XEP Software The XE 100 is operated by the XEP software When you click the XEP icon Y in CAPSIA the program will start 37 XE 100 User s Manual XE Data Acquisition Program PSIA XE 100 NC AFM XY HIGH Z HIGH CANTILEVER General File View Mode Setup Tools Help meee ENENKEKEKEFNENENEKN NEWEEKEETKEIFKZEEENKNIE 200nm v Two X OY Scan Size X 10 000 um Gi Difset X Y 0 0000 pm 0 0000 pm Rotation ____ v ZSemo 0 00 deg Scan Rate Z Servo Gain 500Hz 1 000 Set Point Tip Bias 0028 _ 0 000v Drive m Bias 1605 000 V normal Maxinum entry size 1024 PSPD Sig 2 Scanner 2 Focus 2 v Focus Follow ses J head custom a Flum 4 P Log History h Result 7 Ready MANUAL Figure 4 1 XEP User Interface As shown above the individual windows are separated and may be arranged according to the user s preferences For example the location and the size of the windows may be changed for the user s convenience Please refer to the software manual for more detailed information 4 3 Z stage and Focus stage control When you open the Z stage control window you will find two control pads for the Z
52. ities as allowing a user to change the position of individual atoms or to write letters by transforming the surface of a material at the atomic level 1 2 2 Atomic Force Microscope Among SPMs the first to be invented was the Scanning Tunneling Microscope STM The STM measures the tunneling current between a sharp conducting tip and a conducting sample The STM can image the sample s topography and also measure the electrical properties of the sample by the tunneling current between them The STM technique however has a major disadvantage in that it cannot measure non conducting material This problem has been solved by the invention of the Atomic Force Microscope AFM which may be used to measure almost any sample regardless of its electrical properties As a result the AFM has greatly extended the SPM s applicability to all branches of scientific research Instead of a conducting needle the AFM uses a micro machined cantilever with a sharp tip to measure a sample s surface Please refer to Chapter 3 for a more detailed discussion of the cantilever Depending on the distance between the atoms at the tip of the cantilever and those at the sample s surface there exists either an attractive or repulsive force interaction that may be utilized to measure the sample surface Please refer to Chapter 6 and Chapter 8 for a detailed explanation of sensing types of forces and the different modes of AFM measurement Figure 1 11 displays the basic
53. ixels data points it is necessary to scan at a rate of about one line per second Thus it takes approximately 4 minutes to acquire an image For most cases the second and third problems listed above can be minimized by software calibration This is a reasonably simple and inexpensive procedure that involves imaging a standard sample usually a grid structure with a known pitch in order to create a calibration file that will be used to control the scanner s movements when unknown samples are imaged Correction using software however still depends heavily on the scan speed and scan direction and such a correction becomes accurate only when the center of the scan range used to measure an unknown sample coincides exactly with the center of the scanning range that was used to image the standard sample and to create the calibration file 11 XE 100 User s Manual Piezo Extension Applied bias V Extension of Y axis Extension of X axis Figure 1 12 Nonlinearity and Hysteresis a and Cross Coupling b Observed in Piezoelectric Tube Scanners Chapter 1 Introduction to XE 100 1 2 3 XE system s advantages X Y scanner Figure 1 13 Z scanner separated from X Y scanner Since the conventional tube type scanner cannot move in one direction independently from other directions movement in direction will always simultaneously affect the scanner s mov
54. ixels you can get a lateral resolution of 3 91 per data point Therefore when you want to measure fine structure it is desirable to reduce the scan size 52 Chapter 5 Set up Scanner Mode Also the scanner s ability to make elaborate motion is another factor that influences the lateral resolution The scanner expands or shrinks in proportion to an applied voltage Hence you can manage the scanner s motion more precisely by dividing the applied voltage into smaller units in the DAC digital to analog converter This is effectively done by operating in Low voltage mode The XE 100 system uses a 16 bit DAC for controlling scan movement in X and in Y A 12 bit DAC is used for determining offset and scale so that the scanner s motion and position can be controlled to a maximum of 2 bits When an applied voltage that can make the scanner move 50um is controlled using a simple 16 bit DAC the lateral resolution is 50 um 2 7 6 As mentioned above the High voltage mode will parse the allowable 16 bits over the scanner s maximum range On the other hand in Low voltage mode the scanner s maximum motion is limited and the 16 bit DAC is then applied to a much smaller range thus offering higher lateral resolution This principle can be carried over to the macro scale for easier interpretation For example in measuring a distance of 10cm a 50cm ruler would make an adequate measurement To measure a 1cm distance however a 5cm ruler
55. l inconsistencies or if you have other content suggestions please take the time to forward your comments to us for consideration in future manual revisions Please check that you think this comment is critical or moderate or minor Comments Customer Information Name Date Company Institution System model Address E mail Fax Phone Country You may fax this form or e mail to PSIA Homepage www advancedspm com E mail info advancedspm com Address Induspia 5F Sang Daewon Dong 517 13 Sungnam Korea 462 120 Fax 82 31 734 2995 82 31 734 2900 Customer s Document Feedback Form In an effort to ensure that the content of this manual is updated and accurate PSIA welcomes any and all customer feedback If during the course of using this manual you come upon any errors inaccuracies or procedural inconsistencies or if you have other content suggestions please take the time to forward your comments to us for consideration in future manual revisions Please check that you think this comment is critical or moderate or minor Comments Customer Information Name Date Company Institution System model Address E mail Fax Phone Country You may fax this form or e mail to PSIA Homepage www advancedspm com E mail info advancedspm com Address Induspia 5F Sang Daewon Dong 517 13 Sungnam Korea 462 120 Fax 82 31 734 2995 82 31 734 2900
56. low anything to impact the AFM head When separated from the main frame it is safe to keep the head in its storage box CAUTION Before the AFM head is mounted or unmounted from the Z stage the ON OFF switch for the laser beam must be turned off Otherwise the laser diode in the AFM head may be damaged CAUTION When the AFM head is mounted or unmounted from the Z stage ensure that the AFM head does not sustain any damage and that it is properly grounded The AFM head is extremely sensitive to electrostatic discharge CAUTION To meet the EMC guidlines the Acoustice Enclosure should be closed while making measurements with the XE 100 2 2 Laser Safety Cautions The laser diode used in the XE 100 has a maximum output power of 5 mW and a wavelength of 650 nm WARNING Any deviations from the procedure described in this manual may result in hazardous laser exposure XE 100 User s Manual Figure 1 Laser Warning Lables Figure 1 shown above is two laser warning labels found on the AFM head These warning labels must be strictly followed Also Figure 2 shows the position of these two laser warning labels that attached to the AFM head Figure 2 Location of warnings posted on the AFM head Contents Contents Safety Pr cautions of Syslelm ui e recte e Ra a iu suu i 12 DEFINITION OF GAFETY SYNIBOLS 5 OE a oou I
57. ly understood before operating the XE 100 for your safety CAUTION If a user operates the XE 100 in a manner not specified in this User s Manual serious damage to the instrument may result 1 Definition of safety symbols Table shown below explains the meaning of the safety symbols WARNING CAUTION NOTE Table Safety terms and their meanings Symbols Meaning WARNING Alerts Users to potential danger Consequences countermeasures are described users fail to follow the procedures described in this manual serious injury or instrument damage may occur Such damage will NOT be covered by warranty CAUTION Calls attention to possible damage to the system that may result if users do not follow the procedures described in this manual NOTE Draws attention to a general procedure that is to be followed XE 100 User s Manual Please understand these safety terms thoroughly and follow the associated instructions It is important to read all safety terms very carefully WARNINGs CAUTIONs and NOTEs include information that when followed ensure the operating safety of XE 100 2 Operating Safety 2 1 General operating safety The following are most of the WARNINGs CAUTIONs and NOTEs necessary to operate the XE 100 safely WARNING The XE 100 should be grounded before its components are connected to electric power The main power plug needs to be connected to a three prong outlet which includes a
58. maller amplitude increases the distance depending on the surface roughness to determine the surface topology 78 Chapter 9 Dynamic Force Microscopy fo amplitude 4 f frequency tip sample z feedback distance do amplitude of vibration Figure 9 2 Resonant frequency shift b Amplitude vs Z feedback For certain samples DFM yields better measurements than contact mode or non contact mode AFM Dynamic force microscopy DFM has an advantage over contact mode in the sense that it will damage the sample less since there is no drag force to pull the sample sideways frictional or lateral force Moreover it is more effective than non contact mode when you measure a sample with relatively rough surface and a large height difference over a large area The importance and the application of DFM become more significant than before as it overcomes the limit of both contact mode and non contact 79 XE 100 User s Manual mode while maintaining the merits of both modes 9 2 Conversion to DFM In dynamic force microscopy the Head mode will be set to NC AFM just as in non contact mode However be sure to set the resonant frequency manually lower than the intrinsic frequency fo because DFM uses a different measurement principle than NC AFM AEP Part selection _ Head made Ar Voltage made 2 Voltage mode Z Scanner Range 1 000000
59. measurement XE 100 User s Manual 1 1 1 XE 100 SPM Stage The XE 100 SPM is much easier to operate than a conventional SPM and measurements are made faster and more accurately Figure 1 2 shows overall structure of the XE 100 SPM stage with the acoustic enclosure open The following explains the individual components in detail CCD Camera Figure 1 2 XE Scanning Probe Microcope B XE 100 Head The XE 100 head is the component which actually interacts with the sample and takes measurements A unique characteristic of the XE 100 compared to that of conventional SPM is that the Z scanner which controls vertical movement of the SPM tip is completely separated from the X Y scanner which moves in horizontal direction on the sample This structural change provides the user with several operational advantages 1 The Z scanner being separate from the X Y scanner is designed to have a Chapter 1 Introduction to XE 100 higher resonant frequency than conventional piezoelectric tube scanners This enables the tip to precisely follow the topography of a sample surface at faster rate and increases the speed of the measurement and protects the tip resulting in the ability to acquire clear images for an extended period of time 2 Since the tip wears out eventually it is necessary to replace it after some amount of usage The XE 100 has a Kinematic Mount that makes tip exchanges routine and easy 3 Most SPMs detect probe s movement
60. ng the Laser On Off button in the Tool bar 2 Once the laser is off set the Head mode to C AFM by clicking the Select Parts button 3 Turn on the laser by clicking the Laser on off button 64 Chapter 7 Lateral Force Microscopy AEP Part selection Head made 7 AT Voltage made 2 Voltage mode Z Scanner Range 1 000000 4 Cantilever di Figure 7 3 Conversion to LFM 7 3 Cantilever Selection The Lateral Force Microscope LFM measures the horizontal deflection of cantilever under the same conditions as the contact AFM Therefore LFM uses the same type of cantilever as is used for contact AFM Please refer to Chapter 6 section 3 Cantilever selection in contact mode 7 4 Measurement Procedure You can obtain an LFM image and a topography image simultaneously when a you measure in contact mode If you press the Input Config button the Input Configuration window will appear as shown in Figure 7 4 below You can take an LFM image if you selected Lateral Force option in this Input Configuration box When the selected input signal the Lateral Force does not appear press the Setup button which will open the Select Input window There you can choose Lateral Force Also LPF Data processing AC Track and Auto Flat and Scan Directions forward and or backward should be selected considering sample s topographic situation How
61. nne nin 67 8 2 MODE SETUP ssccccccceseccccccecceccccececccusseccceuceceseusececeusaesceceaaeeeeceeaees 71 8 3 RESONANT 72 S A CANTILEVER SELECTION ott atl es Dee M ote pi enu 73 S OVOCANNER otto ost EE es a A E 75 S 6 MEASUREMENT PROGEDURE 75 Chapter 9 Dynamic Force Microscopy 2 2 1 77 9 1 PRINCIPLE OF DYNAMIC FORCE 5 020 0 0 0 0 0000000000000002000000 77 9 2 CONVERSION TO 80 9 3 RESONANT FREQUENCY SETUP 202 2 00000000000002 00005 800000 ss rris ss arse sese aua 80 vi Contents 9 4 CANTILEVER pe Ee oo ae ne o en Lotes 81 9 5 MEASUREMENT PROCEDURE Eee br pea a iS 81 M 83 vil XE 100 User s Manual Blank Page gt viii Figure Contents Figure contents Figure 1 Laser Warning Figure 2 Location of warnings posted on the AFM head Figure 1 1 The 100 SPM System
62. nstead of a single piezoelectric tube scanner used in most other SPM The X Y scanner moves the sample in horizontal direction for the range you want to image Simultaneously the Z scanner moves the cantilever in vertical direction to trace the morphology of the sample These independent movements of the X Y direction and the Z direction are combined to make a three dimensional image As a result the sample s topography can be investigated very precisely The XE 100 can be used over a broad range of scan sizes High Voltage mode is used to investigate large areas while the Low Voltage mode is commonly used to acquire high resolution scans of small scan areas down to atomic scales This chapter offers detailed description about how to set up these two modes as well as their functions 5 2 Select Scanner Mode When selecting between High and Low Voltage mode it is important to consider several factors including the surface s roughness structure fluctuation and the size of the scan area The proper mode selection will allow you to acquire the best image Although the High Voltage mode is most commonly used the Low Voltage mode should be used in cases where you want to investigate a very small area a very smooth surface or possibly atomic level structure You can change both modes by following this procedure you should select High or Low in the XY Voltage mode and or the Z Voltage mode 1 Turn off the laser by clicking the laser On
63. ntilever manufactured this way Figure 3 2 SEM image of silicon cantilever The cantilever is the part sensing the surface properties for example the topographic distribution the physical solidity electrical properties magnetic properties chemical properties etc by detecting the degree of deflection due to the interaction with the sample surface and is very important component determining the sample resolution When viewed from the top the structures of cantilevers are divided into two groups those with a rectangular shape and those with a triangular shape Each design has a different force constant depending on the width depth thickness and the composition of the material Among them the Silicon Nitride cantilever is stronger that the Silicon cantilever but it has some disadvantages 1 When the thickness is more than 1m contortion may occur 2 curvature of the end of the tip is large on the order of tens of nanometers low aspect ratio Compared to the Silicon Nitride cantilever the Silicon cantilever has a curvature of the tip of less than 10nm and is more commonly used Moreover in non contact mode which has a high resonant frequency and the cantilever with the high force constant the rectangular shaped cantilever with a bigger Q factor is used more than the V shape The cantilever provided with the XE 100 as a default is a Silicon rectangular shaped cantilever for use in both contac
64. ny dimensions 100 um long 10 um wide and 1 um thick which is manufactured by means of micro machining techniques At the free end of the cantilever there is a very sharp cone shaped or pyramid shaped tip As the distance between the atoms at this tip and the atoms on the surface of the sample becomes shorter these two sets of atoms will interact with each other As shown in Figure 6 1 when the distance between the tip and the surface atoms becomes very short the interaction force is repulsive due to electrostatic repulsion and when the distance gets relatively longer the interatomic force becomes attractive due to the long range van der Waals forces 55 XE 100 User s Manual Energy 4 repulsive interaction Distance tip sample separation attractive interaction Figure 6 1 Relation between the force and the distance between atoms This interatomic force between atoms can bend or deflect the cantilever and the amount of the deflection will cause a change in the reflection angle of the laser beam that is bounced off the upper surface of the cantilever This change in laser path will in turn be detected by the PSPD Position Sensitive Photo Detector thus enabling the computer to generate a map of the surface topography In contact mode AFM the probe makes soft contact with the sample surface and the study of the sample s topography is then conducted by utilizing the repulsive force that is exerted vertically
65. o approach the center of the PSPD It should be done first to get a proper value before adjusting the A B If the A B value is too small and not adjusted to 2V 1V for uncoated cantilevers then the laser beam path depicted in Figure 4 6 is not optimized In order to maximize the A B signal try to adjust each of the mirror positioning knobs on the front of the scanner head one at once Adjust one of the knobs until a peak in the A B value is observed and then follow the same process with the other knob Try fine tuning these knobs individually until the A B value increases to the appropriate range If this procedure does not work other trouble shooting steps may be required Using an object which shows a laser beam very brightly like a piece of paper check to make sure that the laser beam being reflected from the cantilever strikes the fixed mirror located in the rear of the Head after it passes through the hole in the center of the probe arm If you cannot locate the laser beam properly with maximum turns of the mirror adjusting knobs it may be that either the cantilever is not properly placed or the cantilever arm is broken If the cantilever is broken you can easily see this on the video monitor In this case you should exchange the broken cantilever for a new one Even if the cantilever is not broken it is still a good idea to try another cantilever before proceeding to troubleshoot other potent
66. o differentiate this region utilizing the topography signal Even though the topographical information is the same between D 2 there will be a conspicuous difference noticeable in the LFM signal When the cantilever scans this area from left to right an increase in relative friction will cause it to tilt to the right thus producing an increase in the LFM signal Figure 7 2 e shows the LFM signal when the scan direction is reversed If the cantilever scans direction as indicated by the arrow there will be no change in the LFM signal at region 3 and 4 which are related to the topographic features of the sample surface However when the scan direction is reversed the cantilever will now tilt to the left in the area where the frictional coefficient between D and is larger yielding a decrease in the LFM signal in this area Considering the simple comparison described above the LFM result contains the surface frictional information as well as the surface topographical information Hence when you analyze the result of the LFM measurement it is necessary to distinguish the information due to difference in the frictional coefficient from the information due to the change in the sample surface topography by taking the AFM image into account 7 2 Conversion to LFM As mentioned above since lateral force mode is an extension of contact mode the Head mode will be set to Contact mode 1 Turn off the laser switch by clicki
67. ontact mode detects the bending of a cantilever the non contact mode vibrates a cantilever at a high resonant frequency and measures the force gradient by the amplitude and phase change due to the interaction between the probe and the sample which yields the topography of the sample When an AFM is operating in the atmosphere or if the probe tip is situated on a moist or contaminated layer it may often stick to the layer due to the surface tension of the tip This happens more frequently if the spring constant of the cantilever is smaller Because of the small spring constant it is difficult to bring it back to the original position Therefore we need a cantilever with a spring constant which can overcome the surface tension The sharper the tip the more stable operation can be expected because the surface area of the tip and the surface tension are reduced 35 XE 100 User s Manual Blank Page gt 36 Chapter 4 Setup Procedure Chapter 4 Setup Procedure 4 1 Turn on the XE 100 To properly initialize the XE 100 turn on the system and start the program in the following order 1 Turn on the Control Electronics 2 Turn on the computer 3 Turn on the video monitor the illuminator and the computer monitor CAUTION First turn on the Electronics then turn on the computer Since the electronics are connected to the computer at the USB port the computer can only recognize the electronics after they have been in
68. ou can check to ensure that system initialization completes without any error messages If there is a problem check whether the power supply is on and make sure all the components are arranged correctly as shown in Figure 2 13 Electronics Computer Analog Motor USB C e 8 SS USB Cable XE Main Body 10 4 CCD Monitor Illuminator e 2 S Wii Figure 2 13 Diagram of cable connections for the XE system 31 XE 100 User s Manual Blank Page gt 32 Chapter 3 Cantilever Selection Chapter 3 Cantilever Selection 3 1 Characteristics of the cantilever In general the term cantilever includes the silicon chip a cantilever hanging from the chip and a tip hanging from the end of the cantilever Figure 3 1 below shows the overall view and the names of the parts of the cantilever used in the SPM in safekeeping Cantilever Chip in scanning Figure 3 1 Cantilever chip The chip the cantilever and the tip are made from Silicon Si or Silicon Nitride Si3N4 and are manufactured using macro machining techniques Because a cantilever has very small dimensions 10jm width 100 m length and several gm thickness it is very difficult to handle in the process of attaching to the SPM To make it easier to use the SPM uses a relatively large chip of size several 33 XE 100 User s Manual millimeters Figure 3 2 is the SEM image of a ca
69. reflectivity 73 XE 100 User s Manual Figure 8 6 SEM image of ULTRASHARP silicon cantilever the NSC15 series Figure 8 7 shows the standard dimensions of the NSC15 series chip The thickness of the chip is 0 4 mm and a rectangular shaped cantilever is at the end of the chip Table 8 1 lists the specifications for this cantilever The non contact mode cantilever has a thickness of about and the spring constant is very large 40N m relative to that of a contact mode cantilever 3 4 mm 0 4mm __ 16mm _ Figure 8 7 Silicon chip of the NSC15 series has 1 rectangular cantilever Table 8 1 Specifications of of NSC15 series 74 Chapter 9 Dynamic Force Microscopy Cantilever Cantilever Cantilever Cantilever Resonant Force Constant Type Length Width Thickness Frequency kHz N m 5 um min typical max min typical max min typical max A 125 35 35 40 45 265 325 400 20 40 75 8 5 Scanner setup Before measuring a sample surface you first need to select either the High voltage mode or the Low voltage mode depending on the roughness of the sample and the size of the measurement area In general the High voltage mode is selected but to measure fine features on samples with a low surface s roughness the Low voltage mode is used Changing the voltage mode was already introduced in Chapter 5 Click the Select part button to open the part selection box as below and choose H
70. s faster than is possible with a conventional tube type scanner Having the X Y scanner separated from the Z scanner in the uniquely designed XE system not only increases the data collecting speed by at least 10 times compared to a conventional tube type scanner but also isolates the vertical and horizontal scan axes completely eliminating cross coupling resulting in a very accurate measurement Moreover this independent scanning system improves the error due to the inherent non linearity of the scanner itself Figure 1 14 compares the background image of a conventional tube scanner compared to that of the new XE scan system New scan system of Conventional AFM c 2 2p o Distance sa b New scan system of XE Figure 1 14 Background Flatness Images from a conventional AFM and XE series AFM b Figure 1 15 shows a diagram that explains the cantilever movement detection mechanism used in the XE series SPMs This laser beam PSPD configuration which permits the acquisition of stable images at high measurement speeds is distinguishing mark of the XE series and satisfies the following two important imaging conditions First the PSPD should be able to measure only the deflection of the cantilever without interference from the Z scanner 14 Chapter 1 Introduction to XE 100 Second to improve the response rate in the Z direction the weight of the 2 scanner must be minimiz
71. s need to be followed very carefully in order to obtain stable operation and the best measurement results The optimal location to install the XE 100 is a room with no vibrations such as a basement or the lower floor of a building where the inside and outside vibrations have the least effect If the XE 100 must be installed in a location where there is considerable air flow or electrical noise caused by electromagnetic fluctuations you may isolate the noise by using an Acoustic Enclosure To protect the system from electric shock the power supply electric outlet extension cord and plugs must be grounded 2 3 Component List 20 XE 100 SPM Main Body XE 100 Control Electronics XE Manuals XE Software Installation CD XE Scanner X Y scanner Single module parallel kinematics flexure scanner 50 um 100 Z scanner Guided flexure scanner 12 um Illuminator Input power AC 90 130 180 260 V Auto select 50 60 Hz 12V 100 W Halogen Lamp Chapter 2 Installation e Cables from Control Electronics Motor cable 40 2 m Analog cable 50pin 2 m XE Base to scanner X Y scanner cable 20pin 25 cm Z scanner cable 26pin 25 cm Optical fiber cable 3m USB standard cable 2m cable with A V jack converter 2m e Video Monitor 10 4inch LCD e Acoustic Enclosure Computer Pentium IV DDR RAM 256MB 40GB HDD Window XP Operating System 7inch LCD Monitor DVI Type e
72. s very useful when a biological sample or other very soft sample is being measured the tip will also have an extended lifetime because it is not abraded during the scanning process On the other hand the force between the tip and the sample in the non contact regime is very low and it is not possible to measure the deflection of the cantilever directly So Non Contact AFM detects the changes in the phase or the vibration amplitude of the cantilever that are induced by the attractive force between the probe tip and the sample while the cantilever is mechanically oscillated near its resonant frequency A cantilever used in Non Contact AFM typically has a resonant frequency between 100 kHz and 400 kHz with vibration amplitude of a few nanometers Because of the attractive force between the probe tip and the surface atoms the cantilever vibration at its 68 Chapter 9 Dynamic Force Microscopy resonant frequency near the sample surface experiences a shift in spring constant from its intrinsic spring constant This is called the effective spring constant and the following equation holds kg 1 When the attractive force is applied ks becomes smaller than ko since the force gradient F is positive Accordingly the stronger the interaction between the surface and the tip in other words the closer the tip is brought to the surface the smaller the effective spring constant becomes This alternating
73. sensor in the flexure scanner There are two X Y scanners that may be used with the XE 100 50 um x 50 um or 100 um x 100 um depending on the desired maximum measurement range see Figure 1 7 XE 100 User s Manual WARNING Never disassemble the X Y scanner on your own PSIA will not be responsible for any personal physical damage or reduced performance resulting from unauthorized disassembly Flexure Hinge Figure 1 6 X Y scanner Figure 1 7 X Y scanner 50um 50um left 100 x 100um right B XE 100 XY Stage The X Y scanner is affixed to the XY Stage By adjusting manual micrometer screws the X Y stage can be used to horizontally position the sample The X Y stage has a maximum range of 25mm in both X and Y with a resolution or minimum unit of movement of 10 Chapter 1 Introduction to XE 100 Figure 1 8 XY Stage B XE 100 Optical Microscope The optical microscope is used to focus the laser beam onto the cantilever and to locate the cantilever to interesting region on the sample surface that is to be measured Since the optical microscope is located parallel with the Z scanner it is possible to have a direct on axis view of the cantilever in conjunction with the sample area that is to be scanned All of the components of the optical microscope the objective lens the tube lens and the CCD camera are rigidly fixed on a single body Since the entire assembly moves together for focusing
74. stage and Focus stage If you press the upper lower part of the button using the left mouse button the stage will move up or down accordingly Extra care must be exercised by the operator when the stage is close to the sample since the further from the center the stage button is pressed the faster the Z scanner will move toward the sample stage 38 Chapter 4 Setup Procedure x Z Stage Focus Focus Follow Approach Figure 4 2 Z stage Control Window WARNING When the Z scanner s arm and the sample are very close a rapid movement of the Z scanner may cause the scanner s arm to collide with the sample This may result in severe damage to the probe tip the sample and or the scanner itself If Focus Follow is selected the Focus stage movement will be synchronized with that of the Z stage It is recommended to have this option activated for most routine system operations 4 4 Cantilever Preparation The XE 100 is provided with cantilevers for both contact and non contact modes of operation It is important to choose the appropriate cantilever depending on the mode of operation It is very simple to install and replace a cantilever for the XE 100 system and no extra tools are necessary The following is the procedure for changing cantilevers 1 As shown below hold the sides of the cantilever chip with your thumb and index finger and bring it close to the probe arm 39 XE 100 User s Manual
75. t mode and non contact mode In addition the upper surface of the cantilever the opposite side of the tip is 34 Chapter 3 Cantilever Selection coated very thinly with a metal such as gold Au or aluminum Al to enhance the high reflectivity However for EFM Electrostatic Force Microscopy or MFM Magnetic Force Microscopy when the whole cantilever and tip is coated to measure the electric or magnetic properties there is no extra coating on the cantilever to enhance the high reflectivity 3 2 Cantilever Selection There are several types of cantilevers varying in material shape softness represented by the spring constant intrinsic frequency and Q factor The choice of a cantilever from among these is primarily determined by the type of the measurement mode In the contact mode a soft cantilever which has a small spring constant of about 0 01 N m 3N m to respond sensitively to the tiny force between atoms is usually chosen The probe tip used in the contact mode has a thickness of about to achieve a small spring constant This is because a cantilever with a small spring constant makes a relatively large deflection to a small force and can thus provide a very fine image of the surface structure On the other hand in non contact mode a cantilever has a greater thickness compared to contact mode It has a spring constant of 40N m which is very stiff and a relatively large resonant frequency While c
76. t the Motor output D on the rear panel of the XE 100 Control Electronics to the 40pin connector on the back of the main body using the 40 Motor cable Connect the USB connector E on the rear panel of the XE 100 Control Electronics to the USB port of the computer using the standard USB cable 28 Chapter 2 Installation Fan BNC Output Cable connectors XE 150 only Figure 2 10 Cable connections of the XE 100 Control Electronics B Video Monitor Connect the video input of the Video Monitor shown in Figure 2 11 to the BNC port A shown in Figure 2 9 using the BNC cable which has an A V jack converter at one end 29 XE 100 User s Manual BNC Output Figure 2 11 Rear panel of the Video monitor B As shown in Figure 2 12 connect the illuminator to the illuminator connector referred to as in Figure 2 9 using the Optical fiber Optical fiber Figure 2 12 Illuminator 30 Chapter 2 Installation 2 4 4 Connection to Power supply Connect the XE 100 Control Electronics the illuminator the computer and the video monitor to the grounded power supply Make sure all the switches are turned off to prevent any damage to the equipment 2 4 5 Installation Checkup After the installation is complete turn the power supply on If you click the XEP icon d on the main window screen or in the folder C PSIA Bin the program will start and y
77. t to tilt the marble plate use the level 22 Chapter 2 Installation Figure 2 2 a Compressed air lever b Air Table suspended in air B Active Vibration Isolation System An Active vibration Isolation System AVIS uses an electromagnetic transducer to isolate any vibrations generated by the building as well as system The AVIS TS 150 available with the XE system consumes in general under 10W and in extreme cases a maximum of 40W Either AC 110V or 230V can be used for the power supply but it should always be connected to an electric outlet with a separate ground The AVIS can block the vibrations in the frequency range of 0 7Hz 1kHz but vibrations above 1kHz will penetrate the AVIS Figure 2 3 shows the general view of the TS 150 an object of up to 150kg can be placed on the table top Figure 2 4 shows the power supply connection located on the TS 150 s rear panel On the left hand side of the rear panel there are two fuses 1 6 230 On the right hand side a socket gives a multiplexed output showing the signals from all six accelerometers that are used to isolate vibrations and an oscilloscope may be used to display changes due to the AVIS 23 XE 100 User s Manual lt Figure 2 3 Active Vibration Isolation System 100 120V 200 240V 47 63Hz SOVA MODEL TS 150 RS 23 RS DIAGNOSTIC SNe 84 E e S EID 2x1 6A 250V SLOW gt Fuses Figure 2 4 Rear panel of AVIS B
78. the tip has to mechanically follow a sample surface the measurement speed of an AFM is much slower than that of an optical microscope or an electron microscope In general the scanners used in AFMs are piezoelectric ceramic tubes Figure 1 11 Due to the non linearity and hysteresis of piezoelectric materials this may result in measurement errors as seen in Figure 1 12 a b The geometrical and structural restraints imposed by the tube type scanner results in cross coupling of the individual scan axes Thus independent movement in the x y and z directions is impossible Since the tip has a finite size it is very difficult and sometimes impossible to measure a narrow deep indentation or a steep slope Often even though such a measurement may be possible the convolution effect due to the shape of the tip and the sample profile may result in measurement errors Chapter 1 Introduction to XE 100 The most inconvenient aspect of using the AFM is its slow speed As mentioned above since the image is obtained by the tip s mechanically following a sample surface it is much slower than other microscopes that use electrons or light The main factors slowing the speed of the AFM are the Z scanner s response rate and the response rate of the circuit which detects changes in the cantilever s resonant frequency The resonant frequency of the typical tube scanner is several hundred Hz order to accurately measure a sample area with 256x256 p
79. to set them is recommended to consult the software manual for XEP 65 XE 100 User s Manual Select Input Available Remove all Available Inputs Topography Eror Signal 2 Detector O 2 Scanner Amplitude O STM Current 4 Lateral Force Magnetic Force Phase Input configurati ET selected Input Unit LFF JE Processing Scan Direction 4 Topography um 000 ACTrack O AutoFlet 0 Error Signal v 000 O ACTrack O AutoFlat O Z Detector 000 ACTrack O AutoFlat O vf Lateral Force v 000 O ACTrack O AutoFlat We Figure 7 4 Setup for LFM mode The procedure to measure in the Lateral Force mode is the same as that in contact mode The measurement method hereafter can be consulted by Chapter 4 66 Chapter 9 Dynamic Force Microscopy Chapter 8 AFM in Non Contact Mode 8 1 Principle of Non contact Mode There are two major forces the static electric repulsive force and attractive force existing between atoms a short distance apart The static electric repulsive forces Fion between ion cores and the static electric attractive forces between valence electrons and ion cores When the distance between the atoms at the end of the probe tip and the atoms on the sample surface becomes much shorter the repulsive forces between them become dominant and the force
80. ure with high resolution In the Low voltage mode however the resolving power increases but the maximum allowable scan range decreases For the XE 100 the maximum range of the XY and the Z scanner in the Low voltage mode is reduced to approximately 1 10th and 1 7th respectively of that in the High voltage mode In the Low voltage mode the nonlinearity and hysteresis is less than in the High voltage mode because the X Y scanner s moving distance is much smaller Furthermore in this case the accuracy of the detector itself is inferior to the scanner Therefore the detector does not have to be used That is it is recommended to select XY Servoscan OFF when operating in the Low voltage mode AY ServoScan Setup Hald M Feedback Integral qain Integral ratio ps f 1 feedback Integral qain Integral ratio 05 P D Figure 5 4 XY Servoscan is OFF The lateral resolution of an image acquired by AFM is calculated by dividing the scan size by the pixel size If you measure a 10 um square image with 256 1256 pixels the lateral resolution is 10 um 256 39 1 nm This means the size of data point in the 10 uim square image is 39 1 nm Even though you can increase an image s pixel count to get higher lateral resolution it will take a much longer time to acquire an image Another solution to get higher resolution data is to decrease the scan size If you measure 100 nm image with 25601256 p
81. w scan direction X Y The fast scan direction can be chosen to be either the X or Y axis Slope The slope of the tip sample interaction can be adjusted by software Scan OFF The X Y scanner is stopped while the Z scanner continues to operate and maintain feedback conditions Offset X Y Specifies the center of the scan area in a relative coordinate system with 0 0 being the center of the X Y scanner Rotation Allows the direction of scanning to be changed within the range of 45 45 2 Servo Select 2 scanner feedback on off Z Servo Gain Controls the sensitivity of the Z scanner feedback loop If this value is too high the Z scanner will oscillate producing noise in the image or line scan If it is too small then the AFM probe will not track the sample surface properly Set point Contact mode specifies the force that will be applied by the end of the tip to the sample surface when the system is in feedback In Non Contact mode the absolute value of the set point refers to the distance between the tip and the sample surface representing the cantilever amplitude change that is due to attractive forces between the AFM probe and the sample surface Tip Bias Controls the voltage applied to the tip when EFM or C AFM modes are used Chapter 5 Set up Scanner Mode Chapter 5 Set up Scanner Mode 5 1 XE 100 Scanner Configuration The XE 100 scanner is separated into an X Y scanner and a Z scanner i
82. would be more sensible The XE 100 s X Y scanner ratio of high voltage to low voltage is set to 1 10th Therefore the XY scanner s lateral resolution can be improved by a factor of 10 5 um 2 0 76 resolution in Low voltage mode Thus Low voltage mode can provide more detailed and better control than the High Voltage Mode 5 2 3 Z scanner Range The resolution of the Z scanner can be adjusted by limiting the Z scanner s motion range in addition to selecting between the High and Low voltage mode The number entered in the text box labeled Z scanner Range can be regarded as a proportionality factor related to the Z scanner s maximum movable range in the user selected mode High or Low voltage Basically if the Z scanner Range is 1 0 then the Z scanner can move through a 124m range in the High voltage mode and a 1 7 range in the Low voltage mode However if the Z scanner Range is 0 5 then the Z scanner s maximum movable range would be reduced and 0 85um in the High and Low voltage mode respectively This adjustment that effectively reduces the Z scanner s maximum range results in an increase in vertical resolution The vertical resolution which is 1 8 in the High voltage mode and 0 25 in the Low voltage mode will be improved to 0 9 and 0 125A respectively when the Z scanner range is set to 0 5 To use the Z scanner Range feature effectively two points should be considered the z scanner s available maximum ran
83. xemplary SPM efficiency but it also brought lots of improvements to the electronic controller and to the supporting software The electronic controller has a fast and powerful DSP Digital Signal Processor 14 DACs Digital to Analog Converters and 5 ADCs Analog to Digital Converters The XE Control Electronics are designed to enable the scanner the core unit of the AFM to provide efficient accurate and fast control and to facilitate the acquisition of a stable image even beyond a scan speed of 10Hz In addition the controller contains input output terminals that provide a simple means for users to design advanced experiments that extend far beyond and are much more complicated than obtaining basic images Furthermore the up to date computer is equipped with the most recent high power Pentium chip and Windows XP operating system A 17 LCD monitor displays crystal clear images using a DVI Digital Video Interface All necessary software including XEP the Data Acquisition program and XEI the Image Processing program is installed on the computer Figure 1 19 shows the XEP program s clean and easy to use interface complete with safety functions and various measurement capabilities that are required to perform advanced applications Figure 1 20 shows the XEI program that is used to convert acquired data into an image and to perform various analyses that meet the user s requirements 17 XE 100 User s Manual Skye one
84. ypical max 0 25 0 45 0 15 0 01 0 01 0 02 0 95 1 75 0 60 0 05 0 03 0 08 2 5 5 0 169 0 1 0 08 0 20 Depending on the roughness of the sample or the measurement range it is necessary to select either the High voltage mode or the Low voltage mode In general High voltage mode is selected see Figure 6 5 but when measuring small areas or when imaging samples with a low degree of roughness switching to the Low voltage mode may produce a higher resolution image 99 XE 100 User s Manual AEP Part selection Head made T Voltage made Voltage mode Z Scanner Range 1 000000 E Figure 6 5 Contact AFM setup and voltage mode selection To change the voltage mode as is the case with a change to contact mode click the button High or Low in the XY voltage mode and or the 7 voltage mode to open the Part selection box as shown above and choose 6 5 Measurement Procedure The measurement procedure hereafter is the same as in Chapter 4 Please refer to Chapter 4 60 Chapter 7 Lateral Force Microscopy Chapter 7 Lateral Force Microscopy LFM 7 1 Principle of Lateral Force Microscopy LFM The principle of Lateral Force Microscopy LFM is very similar to that of Contact mode AFM Whereas in contact mode we measure the deflection of the cantilever in the vertical direction to gather sample surface information we measure the deflection of the cantil

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