Omicron LT UHV STM Do’s and Don’ts

General (Instrument) Eye protection should be worn when near to a viewport, even if using protective covers. Never touch any UHV surfaces with bare hands. Always use clean polythene gloves and degreased tools. Don’t touch table when it’s floating on air legs. Always be aware of which panel you’re dealing with (STM vs. Prep Chamber). Avoid burst valve on STM chamber. Remember that sample transfers have greatest potential for disaster. Never forget to update contents of carousel Never turn on ion pumps or gauges when pressure is >1x10 mbar Never stand on compressed air lines or let them get loose. -6

General Instrument continued Do not vent the chambers with ion pumps, ion gauges or STM on. Never flash the TSP with a clean sample in the chamber. Turn the TSP off on the control panel after it turns off in the chamber. Never turn off the sample heather without turning the dials on the panel all the way to zero. Never put large forces on the position handle on top of the STM. Never use the tunneling position, where STM is hanging freely, when moving the STM, operating the wobblestick, or during bakeout. Do not forget to take the cap off of the Helium cylinder before it’s returned to the Airgas company.

General (Nuts & Bolts) Do not use tools made from Ni-alloys when handling silicon samples. Steel and stainless steel contain sufficient amounts of nickel to contaminate the sample. Omicron recommends using molybdenum or ceramic tools. Never use a stainless steel sample plate at high temperatures, such as during degassing, in order to avoid nickel contamination in the UHV system. Use a tantalum sample plate. Use only the originally supplied molybdenum wrench for tightening the molybdenum nuts. The sample holders are delicate – use care when changing sample

General (Matrix) Do not press buttons while the matrix loads. Avoid excessive button-pressing after matrix has loaded. Be sure to load the experiment, change the Raster setting to Single Point, and choose the correct temperature settings after loading matrix. When a line scan is unresponsive, close it out and open another by duplicating the topology screen. Use the coarse movement remote box to move the scanner close to the sample, but use the auto-approach option in matrix when approaching.

Wobblestick The wobblestick can be moved to and fro, up and down and sideways, but should never be rotated. Avoid damage to bellows as to prevent vacuum leaks: – Do not scratch the wobblestick bellows at parts of the cryostat, carousel or chamber. – Do not bend the wobblestick too heavily to avoid deformations to the sleeve. If movements prove difficult try gently wobbling the wobblestick. – Always use small angle wobblestick movements. Never use wobblestick without fully retracting tip, or there is a danger of snapping off the scan tube. Never use wobble stick if STM stage isn’t locked in cold position. During a transfer, do not move the wobblestick up and down, as it will damage the sample holder clips. Always be sure that the wobblestick is secure after use, by wobbling it back and forth. Stay away from wobblestick when not in use.

Bakeout Maximum bakeout temperature: 150°C. Bring the LT STM to its bakeout position before starting a bakeout procedure or the suspension springs may extend and cause major problems to the eddy current damping system. Never bake in the cool-down position or the STM stage may stick to the chamber. Never leave a sample plate in the STM during a bakeout, because the clips could be damaged. Never use the Si diode for bakeout temperature control (considering the weak thermal coupling between SPM head and system during bakeout).

Bakeout continued In order to avoid charge build up during bakeout due to the pyroelectric effect fit all FT12/19 feedthroughs with their short circuit plugs. Remove all non-bakeable parts from the system (including the LHe cryostat fast coupling port and LHe probe) and check the table for loose plastic. Shield all viewports with aluminium foil. Never bake with the magnets on the sputter gun or the transfer arm in the load lock. Figure 28 (from manual) FT 12 connectors

Cool Down The sample stage must stay locked in the cool-down position with the STM firmly against the cryostat to ensure maximum thermal contact for cool-down process. The scanner should not be operated at temperatures above 50°C, because it may lead to a depolarization. Do not let N 2 vents get blocked or clogged with ice. Never leave liquid Helium cylinder with all vents shut (apart from transfer itself). Do not bend the LHe probe. The thin superconducting wire and stainless steel support tube are very fragile. Never scan > 200 nm when at 4 K. Never scan > 300 nm when at 77 K. The vacuum must be in the lower mbar regime to avoid residual gas particles adsorbing upon the cold sample surface. The surface sticking probability is close to 1 for temperatures of 10 K and below.

LHe Fill Procedure 1. Always fill any cryogen with the quiet room door(s) open for ventilation 2. Always wear safety glasses and cryogen appropriate gloves 3. Double check the extender on the long end of the transfer rod is tightened (it loosens after every fill) 4. Check pressure inside 60 L or 100 L liquid helium storage dewar with pressure gauge connected to the vent valve. Release any pressure that is above 0.5 psi. 5. Close all vent valves and open the top valve. Open the inlet of the inner cryostat of the LT-STM. Put LT in bakeout position. 6. Slowly insert the transfer rod in the storage dewar and in the inner cryostat, keeping the bellows horizontal at all times. 7. Monitor pressure of storage dewar with the pressure gauge during the fill. It can fill on its own at 0.5 psi. If additional “pushing” is needed, do not push higher than 1 psi. Only use helium gas to push, all other gases will freeze! 8. Once fill is complete, remove the helium gas line and open the vent valve to release pressure. Remove transfer rod from storage dewar and inner cryostat of LT-STM. 9. Close all valves and open the road safety valve. Added 4/6/16

Setup The allowed tip length is limited. The tip must not stick out more than 2 mm above the tip holder tube. During loading of sample and tip holder, make sure the scanner is fully retracted and at its lowest position, and lock stage. When transferring a sample, do not use up or down movements with the wobblestick, and check that the sample plate is rigidly clamped when fully inserted. Avoid running the coarse motors on the spot, e.g. at their limits, for longer periods of time. When changing temperatures with the tip in tunneling distance there is an increased danger of tip crash. Constantly observe the Z-position and be prepared to retract the tip with the coarse motion drive.

Setup Electronics Switch off all units, disconnect mains and wait for a few minutes (for discharge of the power supplies) before connecting or disconnecting any cables. Never connect or disconnect the preamplifier supply voltage with the MATRIX CU switched on. Never have the LT STM connected to the electronics in the corona pressure region, i.e. between to mbar so as to avoid damage due to corona discharge.

Data Management When scanning: – To save space, attempt to not save bad images – pressing start and stop for the experiment seems to work well. – Make a note in the notebook for every image that is saved, including the scan cycle number. It saves time when the Image Metrology Explorer is not opened. Instead open files through D:drive/OmicronNanotechnology/Matrix/default/Results Images are saved with the following file names: – User_date-time_project-experiment_count.mtrx where the user is default, the project-experiment is STM- STM _Spectroscopy, and the count is the run number_scan cycle. Each time start and stop is pushed (a new experiment is started), the run number increases by one.

Data Management cont. Each scan cycle is saved (up/forward, up/backward, down/forward, down/backward) and when one of those images is deleted, the others could be corrupted. Rather than deleting, files will be moved to different folders on a biweekly or monthly basis, sorted by date. It seems however, that images need to be moved back to the Results folder in order to be opened correctly in SPIP. (Upon opening a file with the Heuristic File Importer, the parameters of the image are guessed, and if we know the parameters, the image should open correctly.) Files currently can not be opened with WSxM program.