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--- stm:blog_uhv_stm [2011/03/23 17:23] – galli
+++ stm:blog_uhv_stm [2015/09/16 14:39] (current) – galli
@@ Line 21: / Line 21: @@
 In Approach Control, Main: use always "Tip Retract" method, with TTL-Feedback control, Tip back in motion ON.
   - APPROACH: Waveform: Parabola, Asymmetry: 0%
-  - RETRACT: Waveform: Sawtooth, Asymmetry: 100%
+  - RETRACT: Waveform: Sawtooth, Asymmetry: 100%\\
+After the tip has been retracted sufficiently far using above method, there is a way to move the slider faster down (to make tip/sample exchange for example):\\
+  * invert Z piezo polarity by inverting the switch on the back side of the RHK controller
+  * Choose: Waveform: Parabola\\
+  * Click "Retract" a number of times until the slider moved back sufficiently.
 Federica
@@ Line 151: / Line 161: @@
 Very nice flat terraces on Au<111> single crystal from Surface Preparation Lab, without any in-situ treatment (RT, High Vacuum):\\
-{{stm:16082010_topo0001.jpg?200}}\\
+{{stm:16082010_topo0001.jpg?200}}{{stm:16082010_topo0002.jpg?200}}{{stm:16082010_topo0003.jpg?200}}\\
+And atomic resolution on Au<111> single crystal from Surface Preparation Lab, without any in-situ treatment (RT, High Vacuum):\\
+{{stm:06082010_topo0016.jpg?200}}{{stm:06082010_topo0018.jpg?200}}
@@ Line 160: / Line 174: @@
 Federica\\
-**12 January 2011 - **\\
+**12 January 2011 - 24 March 2011**\\
-Operators: Federica, Marius Trowuborst
+Operators: Federica, Marius Trowuborst\\
+Cool down cryogenically speaking was successful. The 1K pot could run continuously several weeks, therefore the contamination was successfully removed from the liquid helium. The system was operated regularly at 300mK. No magnetic field was used.\\
+Issues that lead to warming up:\\
+  - Problem with wobble stick (gripping mouth was mounted on a too bent rod so there was too much friction).
+  - A low-ohmic short between the bias-signal and the bias-shield (later found, in the SSMC connector down at the STM, insert side).
+  - No energy resolution for Nb-gaps and smaller. Probably related to previous point (to be able to continue the experiments the bias-shield was interrupted just before it entered the cryostat, maybe introducing too much bias noise).
+  - Problem with Au surface preparation (later we found it was related to accidental sample swap between <110> and <111>.)
+Federica, Marius Trouwborst
+**20 April 2011 - 18 August 2011**\\
+  * Repaired the wobble-stick (Chris Pen)
+  * Repaired the short (Marius, Federica). The short was inside one of the 2 SSMC connectors at the end of the refrigerator, in the macor-piece. Note that the macor-piece broke during the repair, so we isolated and fixed the SSMC inside glass-fiber sleeves.
+  * Did a number of experiments at RT primarily to be sort out the Au <110> surface treatment for the missing-row reconstruction. Raphael Mueller, bachelor student from Germany, sorted out the procedure successfully.\\
+Really nice STM images at room temperature in HV (~2x10-8 mbar) of Au<111> surface (herring-bone reconstruction) (V_b~100mV, I_t~4nA):\\
+{{stm:2011_04_29_topo0013.png?200}}{{stm:2011_05_02_topo0004.png?200}}\\
+{{stm:2011_05_04_topo0005.png?200}}{{stm:2011_05_04_topo0006.png?200}}\\
+Really nice STM images at room temperature in HV (~2×10-8 mbar) of Au<110> surface (missing-row reconstruction) (V_b~100mV, I_t~4nA):\\
+Initially, after the 1st cycle of 2 x sputter/anneal the surface is still a bit dirty (note absorbates/particles pinned by the step-edges)\\
+{{stm:2011_05_04_topo0001.png?200}}{{stm:2011_05_06_topo0005.png?200}}{{stm:2011_05_06_topo0007.png?200}}\\
+But after more sputter/anneal cycles the surface becomes clearly more clean and the atomic chains become more clear:\\
+{{stm:2011_05_10_topo0007.png?200}}{{stm:2011_05_10_topo0009.png?200}}\\
+{{stm:2011_05_13_topo0005.png?200}}{{stm:2011_05_13_topo0006new.png?200}}\\
+{{stm:2011_05_16_topo0011.png?200}}{{stm:2011_05_16_topo0012.png?200}}\\
+Cooled down STM. Cryogenic run starts. Operators: Federica Galli, Marius Trouwborst (postdoc) and Raphael Mueller (bachelor student).\\
+Coarse approach is troublesome: probably due to again wear of Ti slider, the motor gets stuck at certain reproduceable positions. We use the function generator to drive the motor at increasingly higher frequencies and amplitudes to jump over the scratches. In combination with very short tips, the cryogenic run can continue.\\
+Missing row reconstruction on Au<110> was imaged successfully and several times at low T. The external XYZ control programs implemented by Marius Trouwborst worked very well, apart that for some reasons the pilot experiments of chain pulling did not work.\\
+{{stm:2011_06_16_topo0019.png?200}}{{stm:2011_06_23_topo0015.png?200}}\\
+{{stm:2011_07_04_topo0004.png?200}}{{stm:2011_07_04_topo0010.png?200}}\\
+{{stm:2011_07_20_topo0023.png?200}}{{stm:2011_07_20_topo0038.png?200}}\\
+{{stm:2011_07_25_topo0018.png?200}}{{stm:2011_07_26_topo0007.png?200}}\\
+**2012 - 2013**\\
+System was mostly warm for maintenance and several "radical" changes to 1) increase system reliability and 2) enable in situ evaporation on cold sample in STM.\\
+  * Original Oxford lead-screw was replaced with a new high quality electrochemically polished lead-screw from Dutch company XXX which makes screws for ASML machines
+  * Original bellow-rotary drive on top of cryostat, to actuate lead-screw rotation, was replaced with UHV Deigns (UK company) "MagiDrives" rotary drives (magnetic drives). Mention type / model of drive !
+  * A complete new manipulation system based on 3 concentrical Magi Drives was developed by C. Pen (FMD) and F. Galli to be able to rotate the STM insert in the desired position when down in tip/sample change position. This to achieve 2 things: a) position the STM in perfect alignment with the wobble stick to facilitate tip/sample exchange and b) to be able to rotate the STM insert towards the evaporator (K-cell).
+  * replaced old twisted stainless steel rods of the insert with new ones
+  * installed a new Si3N4 triangular slider (machined and polished by Ceratec) in the STM. This caused 2 consecutive problems during cool-down possible because: different thermal expansion coefficient between Ti-body and silicon nitride slider, geometrical mis-match of the slider (it was delivered too big), not very good surface finish. We then decided to go back to a new (undamaged) Ti/TiNC slider, having trust in the fact that with the new manipulator tip and sample changes would be less distructive for the coating.
+  * Replaced all springs in the STM with CuBe springs instead of phosphor bronze.
+  * Installed a "hot plug" K-cell in the main chamber
+  * Installed Cu-powder RF filters from Cryolinks in the cold right above the STM for bias and tunneling current lines.
+  * Installed π-filters at room-temperature outside vacuum, on all electrical lines entering the system.
+All pumps and o-rings maintenance.\\
+In July 2013, cool-down to 300mK was sucessfull. No measurement was performed, only test cool-down. STM was kept closed.
+**September 2013 - December 2013**\\
+Cryogenic run. Operators: F.Galli, Christian Wagner (Juelich), Sumit Tewari (Leiden, JvR), Sasha Vrbica (Leiden, JvR).\\
+SUMIT SUMMERIZE FALL 2013 CRYOGENIC RUN WITH SOME TXT AND NICE PICS!\\
+At the end of the cool-down a first attempt was made to evaporate gold atoms on the cold sample in the STM in the "inclined K-cell geometry" (using a bottom tilted flange) with a K-cell. The attempt failed probably due to the faulty geometry (1K-shield of STM was shadowing the sample!).\\
+So the decision was taken to warm up over the Xmas break to exclusively change the K-cell position (needed venting of main chamber).
+**January 2014 - December 2014**\\
+Changed the evaporator position from bottom tilted to horizontal (slight grazing angle evaporation geometry).\\
+Cryogenic run (February 2014). Operators: F.Galli, Christian Wagner (Juelich), Sumit Tewari (Leiden, JvR), Sasha Vrbica (Leiden, JvR).\\
+SUMIT AND SASHA SUMMERIZE 2014 CRYOGENIC RUN WITH SOME TXT AND NICE PICS!\\
+**January 2015 - June 2015**\\
+System warmed up for maintenance and to fix a few shorts which developed over time.
+System develops a leak in the OVC (1st bottom flange) during 1st cool-down in April because of heavy corrosion at the flanges. Repaired.
+Several improvements in the electrical diagram, see attached PDF (Sumit!)
+**July 2015 - Mid-August 2015**\\
+Cool-down. Coarse approach works well with external drive (HV amplifier and Sumit's labview program). Several noise issues improved by previous repairs and improvements. Succesfull drag of atoms with PtIr tips but run interrupted by problem with lead-screw mechanism.
+Repaired by Sumit and Chris.
+**September 2015 - **\\