Making a Sample Filament (STM)

The wire used for the filament is in the wire drawer downstairs (it's on a green spool labeled "STM wire") and should be .1mm thick.

1. Find a small rod. Typically, I've used one of the needles from upstairs to wind the wire around.
2. You want to coil the wire so that you can generate a lot of heat in a localized place. The final length should be a little more than an inch long, but use the old filament as a guide for length.
3. There should be a clip on the back side of the sample holder that you can slip your newly made filament through. This will pin down the filament close to the sample at half its length.
4. Spot weld each end of the filament to the cylinders on the sample holder (these are the ones that the fork slide through).

Optional: Use an electrical feedthrough flange to connect to the sample holder. Test the filament in UHV by using the pump cart and a thermocouple (place on the side of the copper for good contact and appropriate measurement). Then you can know how hot the sample gets at varying power.

Opening the STM Shields

Notes from Wenhao Lu.

Parts update from after machining the inner shield.

STM Electrode Test

The electrode test tells you if you electronic components are working correctly. The principle is that by stimulating the inner electrode of a piezo with a square wave signal from the oscilloscope, you can see a square-like charge/discharge response (~2V) on the outer electrodes of the same piezo.

• Because all of the outer piezos have their inner electrodes connected, you can stimulate their common input ABCZ and check the response of each outer piezo's outer electrodes (AX-, AX+, AY-, AY+; BX-, BX+, BY-, BY+; CX-, CX+, CY-, CY+). 
• Similarly, you can stimulate the inner piezo's inner electrode Z, and measure the inner piezo's outer electrodes. These outer electrodes are daisy chained together inside the STM, and so you can measure the X-X+Y-Y+ BNC plug.
• If you stimulate the inner piezo's inner electrode (Z) and measure the outer pizeos' outer electrodes (AX-, AX+, AY-, AY+; BX-, BX+, BY-, BY+; CX-, CX+, CY-, CY+), you should see no response (in reality a smaller response of ~300mV).
• Conversly, you should see the same response (or lack thereof) if you stimulate the outer piezos' inner electrode (ABCZ) and measure the inner piezo's outer electrodes (X-X+Y-Y+).
• (Optional) If you stimulate an outer electrode and measure the other outer electrodes on the same piezo, you'll see a square-ish charge/discharge response that's smaller than if I stimulate the piezo's inner electrode.

STM Wiring

Here are a few different diagrams that show how the STM is currently wired up. I'd suggest looking at the powerpoint so that you can see things in higher resolution and move object around or even un-crop pictures to get a good idea of how things are placed.

Wiring is made using a very thin insulated wire (actually pacemaker wire use in heart monitors). You will need to either scrape or burn away the insulation (using a lighter). Then you will need to crimp connectors on the end. I use a method that involves sandwiching the exposed wire between two connector pieces, but play around with what works for you.

(Left: Original connection with insulation. Right: New connector with a front piece that can insert into a socket and a back piece that pushes the wire in for electrical contact, clamping it in place.)

A note on the Z electrode (inner piezo's inner electrode): The original socket for this somehow fell out. I used a worked around this issues by creating a connector piece with some copper braiding sticking out of the end. I made an extra, and it's in the STM wire box in case you need it later. (But you will still need to crimp that piece to some wire.)

A note on the bias electrode: This broke off during repairs and had to be reattached with silver paste (must be UHV safe). Stuff like this happens, and you can figure out from instructions online how to use the silver paste, I just thought I'd include a snap of the setup I used for curing. I used a solder iron to locally cure the epoxy, propping up the iron with clamps and clips.

Etching an STM Tip

1. Set up a 1M solution of KOH (.5 L of DI water and 56 g of KOH pellets).
2. Find tungsten wire of a diameter that matches your tip holder.
3. You want to make a stand with some sort of fine adjustment for holding the tungsten wire.
4. Using an AC power supply, connect one voltage to the wire you will etch. Connect the other to a metal/wire loop you will dip in solution.
5. Barely just dip with tip into the solution by using the fine adjustment and back out of the solution a bit so that the tip is just barely submersed in the surface (pulled upwards via capillary action).
6. Turn the voltage on (4-14V, but you can play around with this to see what works) and leave for about 4 minutes.
7. When the wire breaks, turn off the voltage. Collect the bottom tip using tweezer to pick it up from the solution.  Snip the top tip off with cutters.

Setup (from http://goliath.emt.inrs.ca/surfsci/docs/sc04/Olfert.pdf)

More information than you could ever really want here.

Opening the STM Chamber

1. Turn off the STM controller box completely (software off, HV off, LV off, capacitors off).






2. Turn off other items such as mass spec or sputter gun controller.
3. Turn off both ion pumps (located on the bottom shelf of the cart).
   
4. Turn off both ion gauges (flip off back switch on controller (top of cart)).
   
   
   
   
5. Close the turbo/chamber valve and the turbo/rough valve (both are electrically controlled so just unplug the appropriate power cords).
6. Turn off the turbo (unplug) and allow to spin down.
7. Turn off the rough pump.
8. Give some time to allow filaments to cool.
9. Leak a low pressure of nitrogen gas into the chamber via the vent valve. The bellow below the STM will deflate appropriately when the chamber reaches ambient pressure.
10. Open the bottom flange to unhook the STM chains. Cover with foil when not in use.
    
11. Disconnect the electrical connectors atop the STM.
    
12. Open the STM flange on the table.
13. Use three wire cables and attach to the ceiling crank. Slowly lift up the STM and place to rest on the STM holder.

Extra Notes: Always store the bolts and nuts in a place so that you will not have to search later to replace them. When possible, cover opened flanges with foil so as to minimize chamber contamination.

Dosing Molybdenum for MoS2

1. Prepare the Evaporator
• Open the turbo corner valve and pump the evaporator with the pump cart. You will have two turbos in series.
• Overnight, bake the evaporator at 70-80 V to reach >100 C. Be careful with the baking tape and make sure to wrap the evaporator with fiber glass.
• The next morning, stop the bake, set up the water cooling lines, and degas the filament for the evaporator. You should go to 5.6 A and 5 V for 15 minutes. At the same time, make sure to watch the temperature and pressure. You do not want to exceed 150 C or overpower the turbos.
2. Dummy Dose
• Insert the thickness monitor so that it is in front of the evaporator. Twist the knob until sleeve reaches the label which marks the correct position. You can double check the location is correct by opening the evaporator valve and looking through the view port on the other side.
• Set the thickness monitor controller to have a density setting at 10.2 and a Z-factor setting at .25. Watch the monitor a bit to check that it is stable.
• Apply the 3kV high voltage power supply. This is an external unit which is home built and directly connected to the evaporator source rod.
• Increase the filament current to around 5 A such that the dosing rate is ~2 angstroms/min. The dosing rate is related to V, I, high voltage (HV), and the Mo rod position, so you can fiddle with all of these.
3. Real Dose
• Quickly take the sample out of the STM chamber and align it visually (using the view port) so that the sample is in front of the evaporator.
• Retracted the thickness monitor.
• Introduce BT at ~3*10^-9 torr (this will not be a very stable value) and at the same time, anneal the sample at 10 W.
• Open the evaporator valve to begin dosing. You will dose for about 1 hour, while keeping an eye on temperature and maintaining dosing with adjustments to rod position and current. Although flux and emission current are imperfect measurements, you would like for them to be somewhat steady values.
• Stop dosing the Mo by closing the evaporator valve. Close the BT leak valve. 
• Anneal the sample at ~20 W. While waiting for good pressure to restore, turn off the evaporator. 
• Let the sample cool before putting back in the STM.