A Brief User`s Manual of The Scanning Tunneling Microscope
Contents
1. 16 image Press OK and finally choose the location and the name of the files For example if the 10 to 14 buffers are chosen the first serial number is 1 and the file name is test the resulting files will be test 1 test 2 test 3 test 4 and test 5 To retract the tip set the Steps Per Millisecond in the InchWorm Control Panel to a negative value typically 400 and press Run Watch the STM module through the glass on the vacuum chamber A distance of 5mm between the tip and the sample is enough After that press Stop Turn off the BACK CENTER and FRONT switches on the green panel Fig 3 2 b Turn off the LINE and ON OFF switches on the light grey panel Fig 3 2 c Turn off the power under the computer desk Fig 3 2 d 17 Venting the vacuum chamber 1 Close the gate valve turning clockwise Fig 2 1 f 2 Turn off the ion pump controlled by the upper dark grey panel Fig 2 5 a by pressing the yellow HV ENABLE button again Figure 4 1 Venting the chamber with the help of nitrogen 3 Bring the nitrogen can Fig 2 6 a and wrap the plastic tube together with the right angle valve Fig 2 1 d using a plastic bag Turn on the flow of nitrogen See Fig 4 1 4 Slowly open the right angle valve using the torque Fig 2 3 b After about 10 minutes fully open it 5 After about 20 minutes close the ri2. the stage using the clamp To demount the sample and the tip follow the reverse steps Acetone helps to remove the silver paste Be careful to watch where the metal piece lands Preparing vacuum C Figure 2 1 Schematic of the UHV STM system composed of the a vacuum chamber b Al slab c pneumatically elevated legs d roughing valve e ion pump f gate valve g STM module h STM vacuum flange and i STM module holder 1 Wear a pair of gloves 2 Change the gasket on the flange h in Fig 2 1 3 Gently lift the STM module g in Fig 2 1 and move it inside the vacuum chamber h in Fig 2 1 May need somebody else to secure the position of the STM module using a few screws Mechanical Pump 7 JP Valve operated au Valve operat using the torque 4 Figure 2 3 a The roughing valve on the vacuum chamber b the torque and c the O ring 4 Put all the screws on the flange h in Fig 2 1 and tighten them in a diagonal order 5 Connect the hose of the mechanical turbo pumps on the pump rack Fig 2 2 to the valve on the vacuum chamber d in Fig 2 1 using an O ring Fig 2 3 c between them Tighten the connection using a clamp Fig 2 3 a 6 Get rid of the gloves 7 Start the mechanical pump by turning on the switch on the outlet fixed on the pump rack 8 Open the valve Fig 2 3 a using the torque Fig 2 3 b Figure 2 4 a The vacuum gaug
3. A Brief User s Manual of The Scanning Tunneling Microscope Prepared by Min Wu based on some materials from Paul Morrow thesis Text was commented by David Hunt July 30 2008 Preparing the tip and the sample motor a housing motor wiring ring bm fg shaft Figure 1 2 a The box containing the tips b the tip mount without a tip c fixing the tip mount into the mount holder and d mounting the sample Pick up a new tip in the box Fig 1 2 a with a pair of tweezers Fix the tip into the tip mount Fig 1 2 b using silver paste Heat up the silver paste under the heat lamp for about one hour Fix the tip mount into the mount holder with the help of a small metal piece Fig 1 2 c The metal piece should be on the flat side of the tip mount There are two ways of mounting the sample One way is to glue the sample on the sample holder using silver paste Before doing this you have to glue a conductive wire on the surface of the sample using silver paste After heating the silver paste under the heat lamp fix the sample holder on the stage using a screw Finally connect the clamp leads to the circuit and the wire from the sample The other way is designed for those samples which cannot be heated up Put the sample into the slot on the sample holder and tighten the screws Fig 1 2 d Since the sample holder is in contact with the surface of the sample all you have to do is to fix the sample holder on
4. V high voltage of the inchworm may be conducted by the metal table and hurt people While the tip is approaching open the STM Control Panel Fig 3 3 b by choosing Hardware gt STM Control Panel in the menu Set the Tip Velocity typically 5nm s Tip Bias typically 0 5V for good conducting surface and 1 5V for oxide surface and Tunneling Current Set typically 0 5nA Then press the button Write to input these values into the system STM will be operating in constant current mode unless the button Constant Height Mode is pressed When the tip finishes approaching the Position value on the InchWorm Control Panel will stop changing Press the button Read on the STM Control Panel to refresh the parameters The Tunneling Current value should be close to the Tunneling Current Set value 12 Figure 3 4 The Square Centered On window 15 Choose STM gt Set Scan gt Square Centered On in the menu In the opened window Fig 3 4 set the x and y coordinates of the Center in the unit of nm the size of each Side of the square in the unit of nm typically a few hundred the X Size and the Y Size number of pixels in the image typically 128 256 and so on and finally the Gate Time related to the scan speed typically Smsec for a general scan Press OK to finish the setting 13 Figur
5. e 3 5 The STM Buffer Scan window 16 Choose STM gt Buffer Scan in the menu Fig 3 5 to start scanning and save the image into the buffer of the computer memory After the previous step most of the parameter should be ready You can also choose an area from an existing image See 20 Switch from normal to retrace if you need to generate two separate images corresponding to the two directions in which the tip scans Choose the Starting Corner between one of the four corners depending on the position of the tip right now Press OK 17 18 14 Figure 3 6 Choosing places to score the images Then you will have to choose the places buffers where you want to store your images Fig 3 6 To do this click on one of the empty lines in the Image Sorter window opened by choosing View gt Image Sorter in the menu and press OK There will be two images if it is in the retrace mode and they will be the results of the scanning in two opposite directions Be careful not to choose previously assigned buffer locations for the images to be scanned as the program will error and all data that has not been saved will be lost The scanning begins The tip will first move to the Starting Corner in a speed controlled by the Tip Velocity in the STM Control Panel and you will see the Tip X and Tip Y values in the STM Control Panel changin
6. e and b the black panel controlling the turbo pump 9 When the vacuum level reaches about 100 mTorr read from the gauge shown in Fig 2 4 a open the turbo pump by pressing the start button on the black panel Fig 2 4 b on the pump rack Fig 2 4 b 10 When the NORMAL OPERATION light on the black panel Fig 2 4 b is on leave the turbo pump on overnight s Rate of Rise DIGITEL 500 lon Pump System Controller yrr P a i AKIN ELMER Baas art f GAUGE gt 2 4 ar p BAYARD ALPERT SDR _ 0 m SP 3 aR On Tust _ a a ae dia 3 EXT RANGE WULTIPLIER PC wr 7 Een ye a BOGS BO DIGITAL GAUGE CONTROL IK TY SUEL NAT IOR PNTE Figure 2 5 a The ion pump panel b the ion vacuum gauge panel and c the sublimation pump panel 11 At the same time turn on the ion vacuum gauge using the lower dark grey panel Fig 2 5 b Turn the knob on the left from OFF to UHV choose between gauges 1 2 using the 1 and 2 button on the right and finally press the I T button to turn on the gauge 12 At the same time use the sublimation pump controlled by the light grey panel Fig 2 5 c to help the main pumps Switch from OFF to ON and turn the knob clockwise until it reaches about 40A on the meter Watch the reading on the ion gauge It may rise at the beginning and then start to decrease and finally stabilize Turn off t
7. e piezoelectric actuators of the inchworm 6 Turn the Z OFFSET knob on the blue panel Fig 3 2 a counter clockwise to the limit 7 Sometimes keeping the system on for a few hours before the measurement helps to improve the quality of the STM imaging Figure 3 3 Interface of the STM software 8 In the computer software open the InchWorm Control Panel Fig 3 3 a by choosing Hardware gt InchWorm Control Panel in the menu 9 Set the Steps Per Millisecond to a positive value typically 400 for retracting tips or 200 for approaching tips set the Current Threshold typically between InA and 3nA and start approaching the tip towards the sample by pressing the 10 11 12 13 14 11 button Run The approaching will automatically stop when the tunneling current reaches the current threshold However it 1s good to pay closer attention to the inchworm behavior as the tip approaches in case there is a bad connection and it does not stop automatically If the button Step is pressed the tip will move by only one step Turn the Z OFFSET knob on the blue panel Fig 3 2 a clockwise until the Z AMPL Reading on the top reaches 0 From this moment on do not touch anything on the isolation table The distance between the tip and the sample maybe disturbed by this Besides if the system is not operating in the vacuum chamber i e on the table the 500
8. g 15 19 20 21 22 23 Figure 3 7 The image window When they stop changing double click on the place you have chosen in the Image Sorter to see the image Fig 3 7 The software has some problems so the image does not automatically refresh while scanning Press Auto I or Auto X Y on the bottom to help refreshing The 2 button zooms out the image by twice while the 2 button zooms in the image by twice You can also right click on the image drag the cursor to the upper right to select an area and right click again to magnify the area The auto I button adjusts the intensity of the image to achieve best contrast The auto XY button adjusts the zooming of the image to fit the window size Choose Experiment gt Point selector in the menu to open the Point selector window Left click on any points on the image and the three coordinates of that point will be displayed in the Point selector window Change the center position and scan size to get other images Adjusting the parameters such as gate time tip bias and tunneling current will also help to improve the quality of the images To save the buffer images into files choose Experiment gt Save gt Multiple Buffers In the opened window choose the starting and ending numbers of the buffers you want to save Press OK and then enter the serial number of the first 24 25 26 Di
9. ght angle valve and turn off the nitrogen Remove the plastic bag 6 Remove the screws on the flange Fig 2 1 h and take the STM module out of the chamber Slowly put it down on the STM module holder Fig 2 1 4 7 Wrap the open flange with a piece of aluminum foil
10. he sublimation pump before the reading start to increase again 13 Next morning when the reading on the ion gauge reaches 10 Torr start the ion pump controlled by the upper dark grey panel Fig 2 5 a by pressing the red POWER button and then the yellow HV ENABLE button Switch the reading between voltage current and pressure different from the chamber pressure and usually one order of magnitude higher by pressing the VOLTS CURR and PRESS buttons 14 Close the valve d in Fig 2 3 a on the vacuum chamber using the torque Fig 2 3 b 15 Monitor the reading on the ion gauge to make sure it is decreasing If not open the valve again and wait for another hour S D Figure 2 6 a The nitrogen and b the turbo pump showing the venting valve 16 Bring the nitrogen Fig 2 6 a and connect the plastic tube to the venting valve shown in Fig 2 6 b on the turbo pump Slightly open the flow of nitrogen 17 Stop the turbo pump by pressing the stop button on the black panel Fig 2 4 b on the pump rack Open the venting valve shown in Fig 2 6 b on the turbo pump 18 When the vacuum level reaches about 100 mTorr stop the mechanical pump by turning off the switch on the outlet fixed on the pump rack 19 Disconnect the hose of the mechanical turbo pumps on the pump rack from the 20 21 22 valve on the vacuum chamber d in Fig 2 1 Again use the sublimation pum
11. p to help the main pump Turn off the ion gauge by pressing the I T button on the lower dark grey panel Fig 2 5 b Because of the heating effect the high vacuum chamber requires a few hours to reach equilibrium necessary for STM after the ion gauge is turned off Monitor the change of the vacuum level by the pressure reading on the upper dark grey panel Fig 2 5 a usually one order of magnitude higher than the vacuum level in the chamber After a few hours when the pressure reading on the upper dark grey panel Fig 2 5 a reaches 10 Torr the actual vacuum level should be 10 Torr Start the STM measurement with the ion pump on STM Imaging l Figure 3 1 Logging in the Linux system Start the computer on the left of the screen Choose Linux system Login with username Paul and password 123456 Enter the command startx to start the graphic interface Fig 3 1 lL Ea MODEL 205A20R High Voltage Power Supply Figure 3 2 Three panels controlling the STM module 10 2 Double click on Paul s Home at the upper left of the desktop Enter the folder Apps copy and execute the program DataAcq 3 Turn on the power under the computer desk Fig 3 2 d 4 Turn on the LINE and ON OFF switches on the light grey panel Fig 3 2 c 5 Turn on the BACK CENTER and FRONT switches on the green panel Fig 3 2 b They control the thre
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