MBMS Standard Operating Procedure
1. Turn on the two oil vacuum pumps on the ground (plug and switch).
2. Turn on the water chiller for the turbo pump (behind the blue cabinet, under the table) and make sure the chiller is filled with water.
Open the black MDC valve (top of instrument) and black Speedivalve (in front of the diffusion pump) to evacuate the sample chamber.
3. Once you have good vacuum (after around 1 h), turn on the turbo pump (press Start on the black Leybold-Heraeus turbotronik NT 150/360 controller above the computer). IG1 and IG2 on the ion gauge controller (white box) show the pressure of the backing pump of the turbopump and the sample chamber, respectively (PG1 and PG2 should be around 10^-3 if the sample chamber is under vacuum). You can check the pressure of the detection chamber by pressing IG1 on the same ion gauge controller. The pressure should be around 10–7 Torr. Do not leave IG1 on unless you’re collecting data.
4. Close the black MDC valve (top of instrument) and black Speedivalve (in front of the diffusion pump) and vent the sample chamber (green knob at the top).
5. Wrap the sample holder with the heating tape and attach the power supply via the two purple wires. The heating tape is secured using the orange, transparent thermal tape. The thermocouple (grey cord) is also attached to the sample holder using a screw. See photos below.
I suggest to test whether the heating tape works by slightly increasing the current using the white instrument (see step 16). It is pretty annoying to see that you cannot heat up the sample holder (e.g. because of a loose wire) after you waited an eternity until the diffusion pump is hot (see later steps).
6. The sample can be carefully attached to the sample holder using one or two screws, as depicted in the photo below. Note that the position of the sample holder can be adjusted using the metal rod on the right side of the instrument. Also keep in mind that you only need around 5-10 mg of sample, otherwise you’ll overload the detector and have to stop your experiment early.
7. After securing the sample, it should be adjusted so that it’s around 1 cm away from the skimmer using the metal rod on the right side of the instrument.
8. Close the sample chamber and open the MDC and the Speedi valves.
9. Once the sample chamber is evacuated (when PG2 reaches around 10–1 Torr), open the house water valves that are connected to the diffusion pump and plug in the diffusion pump (make sure you twist). The cord is on the ground and is labeled DIFF PUMP. You will plug this into the outlet labeled diffusion. Note that the valve for the diffusion pump (metal block with a handle in the middle of the instrument) is broken, so you have to load your sample before turning on the diffusion pump. Check the tubing that connects the house water supply and the diffusion pump. I have replaced one of the hoses that leaked constantly, however, you should place a bucket beneath the hose to prevent the lab from flooding.
10. Wait for the diffusion pump oil to get hot (180 °C). The temperature of the oil is shown on the programmable temperature controller (white box on top of the shelf) under diff hot. The pressure of the chamber will initially raise but then drop over time. Then, close the MDC valve again. This step might take about 30 to 45 minutes.
11. Open the gate valve connecting the sample chamber to the detection chamber to where the sharpie line is drawn. Turn on the ion gauge (IG1) and make sure it’s around 10–7 Torr.
12. Turn on the MS (two devices that are stacked on top of each other). These instruments are located on the top shelf on the opposite site of the bench. Both switches show a green light when the devices are on. Log into the computer (password: MolecularBeam) and open Merlin Automation Data System.
13. Go to define scan methods (top left, below toolbar) and change the mass range (for example, 10-200) and go to the window labeled real time centroid. Here, you will click on collect centroid spectrum and adjust scale, which allows you to adjust the mass range. The bar on the right side of the window gives you an idea of the ion count. Before collecting data, this bar should be green or, at least, very short and blue. If the mass spec is not connecting to the computer, you may need to change the IP address (see attached ‘Device Driver Installation Guide’).
14. Open the temperature logger application (NI USB-TC01). This can be found in Computer, under devices. We have fixed the thermocouple recently. Handle everything with care, especially when you place the sample holder in the chamber. All the wires and cables are rather fragile.
15. To start collecting mass spec data, hit the green traffic light on the top left corner of the Merlin application. You’ll want to start logging the temperature of the sample at the same time.
16. To heat up the sample, you’ll increase the current of the power supply. Keep the voltage at maximum. Currents of 0.6 A and 0.9 A correspond to roughly 70 oC and 120 oC, respectively. The heating tape will degrade if you go above 0.9 A.
17. Closely monitor IG1 and make sure that it does not exceed 10–5 Torr. If it approaches this value, immediately close the gate valve connecting the sample chamber to the detection chamber.
18. Once you are done collecting data, close the gate valve connecting the sample chamber to the detection chamber.
19. After 1 h, the ion gauge (IG1) can be turned off (we are burning off any material that got onto the IG by leaving it on after the experiment).
20. Unplug the diffusion pump, and after ‘diff hot’ reaches room temperature, the water supply for the diffusion pump can be closed. Cooling of the diffusion pump to room temperature also takes about 60 to 90 minutes.
21. To export your data from Merlin, go to the bottom of the program and type in chro_to_file filename. Then, another window opens that asks you to type in filename.txt. The data can be found on the Desktop under MS_Data.
Some important things to remember:
- DO NOT open the MS/sample chamber gate valve until everything is fully evacuated.
- DO NOT turn on the mass spec unless the detection chamber is below 10–5 Torr (IG1).
- DO NOT turn on the diffusion pump before the house water valves are opened.