I wrote down how to transfer samples for STM measurements with not limited LT-STM (Omicron), along with how to cool down Temp. There is no description of Sputtering, Annealing, Evaporation, or LEED at this page. If interesting in them, you can look at other page in my site.
PS: there are various errors inevitably, so plz correct them.
Sample Transfer Methods
1. Vent N2 gas in LL-C
(1) Close GV5, V8, V10, V13.
(2) Close V12, V3 (before and after TMP3).
(3) Close V1, V2, when TMP1 is running.
(4) Close V11, V9. Turn off RP2.
(5) Flow into N2 gas from LV1, atmospheric pressure.
(6) Open V13, flow N2 gas in LL-C, atmospheric pressure.
(7) Close LV1, Close the valve of N2 gas cylinder.
2. Insert Samples to the LL-C
(1) Turn off BA.
(2) Close QV4. Stop TMP1.
(3) Leak N2 *1
(4) Sample exchange
(5) Exhasut start. Open the QV4 slightly. TMP1 start.
(6) When TMP1 becomes normal operation, QV4 is fully open. Wait 1~2min and open BA. *2
*1 The pressure from the gas cylinder is rougly kgf/cm2. The crew fasterning the Fast-entry door should be completely loosened so that LL does not be higher than atomspheric pressure. LV4 is easy to leal, so tighten it a little tigher after the leak is completed.
*2 To prevent direct dagassing fron the BA gauge, rotate the transfer holder horizaontally 180. It’s bteer to turn it around. The bolt for cleavage prevents is for turning, but it can be turned by lifting the transfer rod a few centimeters.
Open the lid, insert the sample holder into the LL-C, close the lid.
3. Draw the Vacuum in LL-C
(1) RP2 on. Open V9 and V11.
(2) Reading TC2 became 1×10-3 Torr (7V). If the voltage of TC2 becomes 7.4V or more, close V13 open V3.
(3) If the voltage of TC2 becomes 7.4V or more, V12 open (TMP3 draws the Load Lock).
(4) Reading TC2 becomes worse again, but if the voltage of TC2 recovers to 7.4V or more, V2 open V1 open.
(5) Turn on the BA gauge after about 10 min. It takes about an hour to draw 1×10-7 Torr.
4. Transfer sample from Load Lock to STM Chamber
(1) Confirm the vacuum in Load lock is about 1×10-7 Torr.
(2) Make sure the LEED manipulator is in a position not to be disturbed.
(3) Attach an extension tube of PVC to the transfer rod in the STM Chamber.
(4) GV5 open
(5) Transfer the sampole from Load Lock to STM chamber. The maximum reding of UHV2 is 2.1V.
(6) GV5 close
3. Transfer Samplers from Load-Lock Chamber to Preparation Chamber
(1) degass LL to BA below 2×10-7 Torr.
(2) Install PVC pipe on horizontal transfer rod. Adjust the position with the micrometer (Horizontal 13.5mm)
(3) If the sample has been rotated 180, reture to the original direction.
(4) Open GV5
(5) Use vertical transfer rod to lift the transfer holder.
(6) Close the horizontal transfer rod and fix the female screw at its tip to the male screw of the transfer holder.
(7) Pull out the conveying holder.
(8) Lower the vertical transfer rod and close GV5.
4. Transfer Samples from Prep Chamber to STM Chamber
(1) Prep dagass to UHV2 with 2×10-10 Torr.
(2) Remove the PVC pipe from the horizontal transfer rod. Adjust position (4.5mm long, 17.5-18.55 mm wide). Adjust the direction so that 240-270 is directly above.
(3) Rotate the Wobble carrosel with a Wobble Stick and bring the free space forward. *2
(4) Open GV3.
(5) Move the horizontal transfer rod and insert the transfer holder into the transfer holder fixing bracket of the Ana. The horizontal position of the transfer rod should be adjusted between 17.5mm and 18.5mm.
(6) Pull out the sample plate from the transfer holder with Wobble Stick and insert it into the free space of the carousel.
(7) Return the conveying holder to the Prep Chamber. Close GV3.
1* One nut on the rotating shaft of Wobble Stick’s scissors has been removed, making it easier to remove the screws on the rotating shaft. As much as possible, do not let the side of the nut come off rise.
2* The plate spring of the carousel is weak. When the carousel is turned vigorously, the inserted sample plate and tip holder “protrude”. Turn as slowly as possible.
3* Attention! to carry tip. if the bottom of the tip hanging on the tip holder interfers with the bottom of the transfer holder fixing bracket, the tip will come off. So, when the transfer holder reaches the fixing bracket, proceed 1-2 mm and lightly turn the transfer rod (as seen from the Main side) in the half-hour meter direction repeatedly. This operation raises teh carrier holder slightly, and the tip, which wa being dragged, is pulled to a safe position by magnetic force.you don’t have to worry about this when you bring your tip from Main to Prep.
5. Transfer Samples from STM Chamber to Prep Chamber
Reverse the above operation. *1
*1 Precautions! insert the sample plate into the conveying holder. Four “screws” are proturding form the rotation shaft of the Wobble Stick’s scissors. When this screw is pulled, the clamp opens. the sample had been held fell off.
6. Transfer Sample from Prep Chamber to LL Chamber
Reverse the above operation.
7. How to turn off the pump before measuing STM
(1) Cut BA, UHV2.
(2) [Prep sealing] close GV1 (before TMP2) and GV2 (before TGP).
(3) [TMP1, TMP2, TMP3 sealing] close QV3 (after TMP1), QV4 (after TMP3), and V7 (TMP2).
(4) TMP1, TMP2, TMP3 stop.
(5) V5, V6 close. RP3 stop. V11, V9 close. RP2 stop.
(6) Turn off the TMP2 controller after the TMP is completely stopped. *1
(7) Remove the bellows leading to QV3 and QV4. *2
(8) Unplug the power line of the TMP1, TMP3 and the fan. Remove the power line of TMP2. Unplug the fan of TMP2.
*1 Touch down the knob on the back of the controller.
*2 A plastic lid or aluminum foil should be attached to the tip of the KF flange and bellows to prevent dust from sticking to the flange.
8. Degass after STM measurement
(1) Connect bellows to QV3 and QV4.
(2) Connect the TMP1, TMP2, TMP3 power line to the fan power line.
(3) RP2 start. V9, V11 open. PR3 start. V6 open. V5 open.
(4) TMP1, TMP2, TMP3 start. *1
(5) When TMP1 becomes normal operatio, open QV3. Open QV4 when TMP3 is running noramlly. When TMP2 i in normal operaiton open V7.
(6) Wait a or 2 min and add BA.
(7) After a while *2, open GV1. Add UHV2.
(8) 10-9 Torr in the first half , open GV2.
*1 If the degass side of the TMP3 is kept at atmospheric pressure for a few days, the vacuum inside the TMP3 becomes worse, and the rotation speed of the TMP3 stops increasing by about 50% after the power is turned on. If you open QV4 for a moment and dagass it. the number of revolutions starts to rise again. if you do nohing, the interlock will work after about 10 min.
*2 if the stop period is less than 1 day, wait about 30 min to open GV1. If the shutdown period is more than a weak, wait a few hours before opening GV1. If you’re not in a hurry. you can open it the next day.
Mounting of Sample to STM Chamber
(1) Make sure the STM hanging lever is in the fixed position.
(2) Illuminate STM with LED light. Reduce the zoom ratio of the CCD camera and adjust the focus.
(3) Open the outer cylindrical rotating door (N2 Temp). The tip of the Wobbles Stick is turned vertically and hooked to the screw on the rotating door. *1, *2
(4) Open the inner rotating door (N2 or He Temp). Hanging the tip of the Wobble Stick into a decent groove and turning it.
(5) Pull out the sample from the Wobble carosel with a Wobble Stick and insert it into the STM. *3 *4 *5
(6) Close the two rotating doors and wait for the sample temp ro decrease. *6
*1 It seems that there is a ratte on the rail of the rotating door, sometimes it is difficult to move. Using Wobble Stick to gently press the entire cylinder makes it easier to work with the rails.
*2 If there is a Temp change, the rotating door may not open due to biting. Push the Wobble Stick on thge left side of the cylinder and it will (sometimes) move.
*3 The position to be inseted into the STM is very diffcult to see. Tilt the Wobble Stick and straighten the sample plate while tapping yhe handle with your finger. The large pewport adjusts the Wobble Stick left and right, the small viewport adjusts the up and down, and gently plugs in while grasping the positio nof the STM with the eye of the mind. (BTW, the new flange has already been completed after adjusting the direction of the viewport).
*4 If you thought that the sample plate was caught on the STM plate spring, turn the Wobble Stick clockwise and counterclockwise and do not press, check that there is a response in both directions.
*5 Push while applying a slight torque clockwise or counterclockwise, or pull back a little and then push again, it often goes smoothly.
*6 By sample exchange, it is OK to warm up to about 81K at the time of N2 temp and drop to about 78 K. when measured at He temp, it warms up to 30K. Diving below 4.3 K is probably fine, but it’s better to wait longer for the stability of the measurement.
Cryostat
The cryostat is a double structure of the inner and outer containers. The inner and outer vessels, and the outer vessels and the outer walls are insulated in an UHV.
It contains either LN2 or LHe. And when you put in LN2, it’s going to go up to 78K. It can be cooled down to 4.3 K and 0.35 K when the L3He and L4He is added. The thermometer is attached to the stage where the sample plate is located, and the sample should be cooled to this temp. It is not clear how cold the tip. *1
LN2 is placed in the outer container to prevent radiant heat from the room temp from reaching the inner container. *2 LN2 will be empty in ~2d. As long as the outer container is cooled to LN2 temp, the inner container will last for 3d and at least 1 week.
*1 One way to determine how cold a tip is to build a tip with superconductor like Nb and measure the size of the gap observed in the tunnel spectrum.
*2 By Stefan Boltzmann’s Law, the radiant heat is proportional to the fourth power of the absolute temp. There is a big difference between roome temp and LN2 temp.
1. Liquid N2
Introduction of LN2 (Outer)
(1) Cover Anal and Prep viewport. If LN2 is directly exposed to them, there is a risk of cracking.
(2) Remove the rubber valve LN2-In and GN2-Out.
(3) LN2-In is released from LN2-In. It is finished when liquid spouts from GN2-Out.
(4) Attach the rubber valve to LN2-In, and then attach the rubber valve of GN2-Out. In reverse of order, LN2 is ejected from LN2-In.
Introduction of LN2 (Inner)
(1) Cover the Anal and Prep viewport.
(2) Remove the SUS pipe of LHe-In, rubber valve of GHe-Out tee.
(3) Pour LN2 from SUS pipe of LHe-In. When LN2 spouts from the ea od GHe-OUt, it’s over.
(4) Attach rubber valve to SUS pipe of LHe-In, tee of GHe-Out.
Measure Residual LN2
Insert a thin SUS pipe (~3mm in diameter).*1 When the liquid pops out from the top, the surface of the liquid is usually at that height. If inside, use LHe-In. If outside, use LN2-Probe.
*1 It is often used after removing the membrane of the dipstick (described follows).
(1) If the outer LN2 is reduced, pour the LN2 that is expelled from the inside into the outside as it is. If not, it is returned to the LN2 container, so the pressure of the container is removed and the atomspheric pressure is set.
(2) Connect the GHe-Out tee to the pressure tube from the N2 gas cylinder. The gas pressure is about 0.5 KGF/cm2. There is no valve that can be operated by hand during the removal process.
(3) Install SUS pipe to LHe-Probe. Do not let the pipe reach the liquid surface.
(4) Remove the lid of the LN2-Probe and insert the tube (outlet) of the SUS pipe for explusion for a few cm.
(5) Lower the SUS pipe for discharging LN2 comes out. The tip of the pipe is lowered to ~ 1cm from the bottom. It is not attached to the bottom for better conductance.
(6) When LN2 does not come out, pressurize with N2 gas. Remove the clip of the pressurized tube.
(7) When LN2 does not come out again, attach a clip to the pressurizing tube to stop pressurizing, and lower that the SUS pipe to the bottom.
(8) Pressure again with N2 gas.
(9) When LN2 does not come out, complete the removal.
2. Liquid Helium
In the field of low temp, the process of transferring LHe from a container to a cryostat is called “transfer”. Even if you are impatient or slow down you will waste LHe.
LHe is more expensive than LN2*1. Use cheap LN2 to precool it well before filling it with LHe.
It is useless to flow LHe while the inner container is warm, as it only uses the latent heat of He to cool it. In addition to the latent heat of vaporization, the heat capacity of the He gas is used to cool the LHe until it begins to accumulate. The needle valve of the transfer tube should be slightly opened and the pressure agent applied to the He container should be lower.
When the liquid begins to flow, in this case the LHe passeds through the transfer tube, in order to minimize the heat inflow, transfer is carried out as quickly as possible. The pressure applied to the He container is approximately 0.1 bar *2.
Do not empty the He supply container (leave about 10L and return it). When empty , the temp of the container increases and it must be precooled before another supply.
*1 He gas is mainly extracted from natural gas in the US. Since Japan does not produce such natural gas, it imports mostly from abroad. There is a possibility that prices will rise in the future, so use it with care.
*2 The current pressure balloon will increase to the size of a pumpkin.
Helium transfer procedure
(1) Piping. Attach a metal bellows to the GHe-Out and wrap it in a towel to prevent frost.
(2) Put the He supply container on the lift. Do not let the He supply vessel tilt when lifting the lift. Keep it straight. The lifting height of the lift is only a few centimeters higher than that handle of the He supply vessel that the steel mezznine floor. Finally fasten firmly with a belt.
(3) Open the needle valve of the transfer tube and lower the diameter conversion part to 20cm form the bottom. Insert the clip into the He supply container for ~20cm, so that the transfer tube does not slip.
(4) precool the transfer tube. Slowly lower the supply side. When the tube is close to the surface of the liquid, He gas is released from the tube. Then stop lowering the transfer tube.
(5) After waiting for a while, the gas will cool and become white.
(6) Insert teh device side of the transfer tube. In the first transfer, insert it to the bottom. In the case of splicing, the device is inserted about 70cm so that it does not touch the surface of LHe remaining in the device.
(7) Lower the supply vessel side of the transfer tube. When the pressure gauge approaches 1 meter, open the green valve to reduce the pressure. Stop lowering the transfer tube when the tip of the transfer tube reaches a height of ~ 5cm from the bottom of the supply vessel *1.
(8) Keep the pressure gauge at ~0.5 scale *2, sometimes push the balloon. If it takes longer than usual, you may want to open the needl valve a little, as there may not be much gas flowing.
(9) When the value of the liquid level gauge starts to increase, open the needle valve fully *3 *4. Push and boost the ballon from time to time to maintain one scale of the pressure gauge.
(10) Stop pushing the balloon whrn the value of the liquid level gauge exceeds 280mm. Flod up to 300mm with remaining pressure.
(11) Close the needle valve when the value of the liquid gauge becomes 300mm.
(12) Pull out the device side of the transfer tube *4 and immediately close the lid.
(13) Open the green valve of the He supply vessel and reduce pressure until atmospheric pressure is reached.
(14) Pull out the supply vessel side of the transfer tube and close the lid. The transfer tube should be placed in the designated storage area.
(15) lower the lift while loosening the belt and lower the helium supply vessel.
(16) When measuring STM, remove the bellows of GHe-Out and replace it with a thin rubber tube.
*1 The reason why it is not lowered to the bottom is to improve the conductance and not to empty the helium supply vessel.
*2 The reason why the pressure is changed is to cool the transfer tube (and the device for the first transfer) using the heat capacity of helium gas.
*3 The LHe evaporates even while passing through the transfer tube.
*4 If the tip of the transfer tube breaks the liquid surface at the supply vessel side, gas instead of liquid will appear. Flow, evaporation intensifies. Be careful if the gas meter suddenly becomes loud.
*5 If it has no direction, the air colum vibration occurs and the helium evaporates rapidly.
Measure Remaining Helium Supply Vessel
(1) For the liquid level (cm) to volum (L) conversion table for the helium supply vessel (MESSER 100L), see table 1.
(2) Open the lid of the helium supply container and insert the tip of the dipstick *1. And when you do this, you dip it into a dipstick. Cover the area around the inlet with a towel to prevent fas leakage. If you don’t do this, the evaporated cold helium will hit your hand and you will feel cold.
(3) Lower the dipstick at a slow space of ~ 1cm/SEC. The membrane vibrates when it comes close to the liquid surface*2.
(4) When it reaches the bottom, lower the two marks *3 to the height of the insertion opening.
(5) Hold down the mark on the bottom side with the liquid surface, the vibration of the membrane changes discontinous. The distance between the two marks is equal to the height of the liquid surface.
*1 A tool with a rubber film atached to a thin SUS pipe.
*2 Thermoacoustic effect called “taconis vibration”. Helium evaporates coz it carries heat.
Log before and after He Transfer
(1) Before He transfer
ai=remaining He supply vessel (L)
bi=remaining He in the device (mm)
ci=gas meter value (m3)
write to the log.
(2) After the He transfer
af=remaining He supply vessel (L)
bf=remaining He in the device (mm)
cf=value of gas meter (m3)
write to the log
(3) Convert to L by the following equation.
(ai-af)=amount of He extracted from the supply vessel (L)
(bf-bi)/54=LHe in the device.
(cf-ci)/0.7=evaporated LHe(L)
Confirm that the amount of extruded, the amount of entered, and the amount of evaporated are consistent.
Problems and Solutions
P1: Refill LN2 induce equipment lead to gauge 过压保护。
P2: we can modify setpoint to see fluctuation value of real time sugnal.
P3: Bias 2-3 V. Noisy disapperance?
P4: Not sharp tip: handset to coarse tip
S4: flash tip 1nA
P4: feedback loop = ~2, small: tip; large: iamge quality is low.
P5: artifacts or noise
P6: tip couple pize leading to pesudo singal
S6: scanning velocity
QING SHI 