Differences

This shows you the differences between two versions of the page.

--- stm:measurement_procedure [2011/03/21 23:27] – galli
+++ stm:measurement_procedure [2013/07/10 09:58] (current) – galli
@@ Line 5: / Line 5: @@
 ===== 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/T-control computer)
+  - Position and focus USB camera such that you can see clearly sample and tip holdres (start software "MicroCaputre" on Labview/T-control computer)
-  - Femto preamp: check back sidde 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.
   - 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 "Parabola" and "Approach steps = 1".
+  - In RHK software, set Waveform "Parabola" or "Sawtooth" and "Approach steps = 1". Click "Approach" button.
   - 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 "fast" until the sample gets close enough that the tip-sample gap can't be seen anymore (either via the camera or by eye looking into the view port).
   - 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.
-  - It is not advisable to scan when the STM is in the pin. Retract therefore 3 x 100 steps (Waveform "Sawtooth" and "Adjust steps = 100", press +) and send the STM up with the "lift".
+  - It is not advisable to scan when the STM is in the pin. Retract therefore 3 x 100 steps (Waveform "Sawtooth" and "Adjust steps = 100", press -) and send the STM up with the "lift".
 ===== Approach at ~40K, with tip and samples "hot" =====
@@ Line 35: / Line 35: @@
   - At 2K, perform again a **fine approach**. Remain in tunneling if possible.
   - **Slowly** rise the sorb-pump temperature to 35K.
-  - Retract 1 x 100 and adjust if necessary the 1K-pot flow to achieve 2K on the 1K-pot.
+  - **Retract 1 x 100** and adjust if necessary the 1K-pot flow to achieve 2K on the 1K-pot. Do not adjust the 1K-pot needle valve in tunneling, as it can crash the tip!
   - As the sorb pump is heated to 35K, the signal (in and out of tunneling) will be noisy.
@@ Line 41: / Line 41: @@
   - After 1 hour or 1 hour and 15 minutes, stop condensing by switching off the sorb heater: T sorb can be set to zero.
-  - Perform a careful **fine approach** and remain in tunneling down to 300mK (to avoid approaching at 300mK, as it gives some heat load).
+  - Initially the temperature will stay at ~ 2K for a while before starting to drop very rapidly to base temperature.
+  - 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)
+  - Normally there is no need to re-approach, as there's very little drift from 2K.