stm:measurement_procedure
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| stm:measurement_procedure [2011/03/21 23:35] – galli | stm:measurement_procedure [2013/07/10 09:58] (current) – galli | ||
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| ===== Coarse and fine approach procedure with STM in lower position: ===== | ===== Coarse and fine approach procedure with STM in lower position: ===== | ||
| - | - Position and focus USB camera such that you can see clearly sample and tip (start software " " on Labview/ | + | - Position and focus USB camera such that you can see clearly sample and tip holdres |
| - Femto preamp: check back side of RHK, switch to BNC. Start Labview VI: STM Conductance. Set correct gain. | - Femto preamp: check back side of RHK, switch to BNC. Start Labview VI: STM Conductance. Set correct gain. | ||
| - RHK premp: check back side of RHK, switch towards D9. | - RHK premp: check back side of RHK, switch towards D9. | ||
| - Prepare RHK controller: XYZ offsets in the middle (5.0). Set initially: time constant ~0.2, gain ~0.3. Set appropriate bias and current set points. | - Prepare RHK controller: XYZ offsets in the middle (5.0). Set initially: time constant ~0.2, gain ~0.3. Set appropriate bias and current set points. | ||
| - | - In RHK software, set Waveform " | + | - In RHK software, set Waveform " |
| - Use gain as Z-piezo motor speed control. When the tip and sample gap is very large, set gain ≥ 0.5. Observe if the Z motor moves fast enough. Keep the motor approaching " | - Use gain as Z-piezo motor speed control. When the tip and sample gap is very large, set gain ≥ 0.5. Observe if the Z motor moves fast enough. Keep the motor approaching " | ||
| - When the gap gets small enough (less than 1 mm), slow down the Z motor by decreasing the gain. Decrease the gain till it's very hard to see the motor moving. Now the motor has to move very slowly, or the tip can crash. This is the **fine approach**. | - When the gap gets small enough (less than 1 mm), slow down the Z motor by decreasing the gain. Decrease the gain till it's very hard to see the motor moving. Now the motor has to move very slowly, or the tip can crash. This is the **fine approach**. | ||
| - When the fine approach is finished successfully (software will pop-up a window), set gain~0 and time constant~2 before releasing the tip via the software. | - When the fine approach is finished successfully (software will pop-up a window), set gain~0 and time constant~2 before releasing the tip via the software. | ||
| - | - It is not advisable to scan when the STM is in the pin. Retract therefore 3 x 100 steps (Waveform " | + | - It is not advisable to scan when the STM is in the pin. Retract therefore 3 x 100 steps (Waveform " |
| ===== Approach at ~40K, with tip and samples " | ===== Approach at ~40K, with tip and samples " | ||
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| - Perform a careful **fine approach** when the 3He temperature is still at 2K, and remain in tunneling down to 300mK (to avoid approaching at 300mK, as it gives some heat load). | - Perform a careful **fine approach** when the 3He temperature is still at 2K, and remain in tunneling down to 300mK (to avoid approaching at 300mK, as it gives some heat load). | ||
| - After ~ 45 minutes the 3He temperature will drop to 300mK and the STM will follow (T-STM~20 KΩ) | - After ~ 45 minutes the 3He temperature will drop to 300mK and the STM will follow (T-STM~20 KΩ) | ||
| + | - Normally there is no need to re-approach, | ||
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stm/measurement_procedure.1300750505.txt.gz · Last modified: 2011/03/21 23:35 by galli