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--- e-beam_evaporator [2025/04/11 08:25] – [Introduction] wigbout
+++ e-beam_evaporator [2025/06/13 13:54] (current) – [Aftermath] wigbout
@@ Line 12: / Line 12: @@
   * If you wish to evaporate specific materials, let the technicians know (a few weeks) in advance.
   * New materials are usually loaded on Friday afternoon, so please avoid booking the system on the Friday afternoon.
-  * Ordering new materials (that have not been used in the system) and setting up the evaporator for specific processes takes a long time, as the interaction between liner and material, the evaporation rates at specific e-beam emission currents, and the sensitivity of the QCM measurement is usually ill-documented, and as of then, unknown to us.
+  * Ordering new materials (that have not been used in the system) and setting up the evaporator for specific processes takes a long time. (Liner choice is far from trivial, because there is a lot of interaction between the liner and the new material. The evaporation rates at specific e-beam emission currents have to be checked. The sensitivity of the QCM measurement for specific materials is not well-documented.)
 ----
@@ Line 29: / Line 29: @@
 Every material has their own preferred liner-material (e.g. Nb prefers tungsten liners over graphite due to contaminations; Au will stick to molybdenum liners, but it will form droplets in a graphite liner).
 Liners can come in all sorts of types: different materials((Common liner materials are a.o.: graphite, Al2O3, vitreous carbide, FABMATE, reinfiltred graphite, tungsten, molybdenum, copper)) and sizes((Common sizes that we use are 15cc, 4cc)). If we use 4cc liners, usually there is some adapter piece involved.
-The wide variation in liners is because every evaporant material will behave differently in a different liner. Not only the thermal conductivity is different for every liner (which is important for the rate at which heat is dissipated from the materials), but also the interplay between liquid metal and solid liner is important (effects such as wetting, spitting, etc.)
+The wide variation in liners is because every evaporant material will behave differently in a different liner. Not only the thermal conductivity is different for every liner (which is important for the rate at which heat is dissipated from the materials), but also the interplay between liquid metal and solid liner is important (effects such as [[https://en.wikipedia.org/wiki/Wetting|wetting]], [[https://www.london-nano.com/sites/default/files/u29/DevelopingaFundamentalUnderstandingofGoldSpitting.pdf|spitting]], etc.)
 It is good to be aware that it is very easy to burn through a liner (especially a graphite liner). Once a liner is burnt through, both the liner and the leftover material can be thrown away.
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    * Pump the loadlock down.
    * Leave after you see that the pressure is <1e-5.
+   * In the mean time, you can stop the log. As soon as you stop it, you will see in which directory it is saved. You have to open the utilities page again, and click the stripes (third button).
+   * Click File > Open, and select your logfile.
+   * Click All, click Trace.
+   * Now a graph with all the traced log data appears, which you can copy using the copy-icon.
+   * Create a new text-file and press CTRL+V to paste. (It can take a while to paste a big logfile.)
+   * Good luck with plotting this. It's a tab-separated file. (FIXME if there is a Python code available)
 ^  Material  ^  Setpoint  ^  Max Emission  ^ notes? ^ (date) ^
-|  Ti   |  40  |  < 200  |  | (18 dec. '24) |
+|  Ti   |  40  |  < 200  |  | (18 Dec. '24) |
-|  Cu   |  40  |  < 200  |  | (18 dec. '24) |
+|  Cu   |  40  |  < 200  |  | (18 Dec. '24) |
-|  Au   |  20  |  <  40  | [[Graphite liners vs. Mo liners for Au]] FIXME | (18 dec. '24) |
+|  Au   |  20  |  <  40  | [[Graphite liners vs. Mo liners for Au]] FIXME | (18 Dec. '24) |
-|  Co   |  65  |  < 120  |  | (18 dec. '24) |
+|  Co   |  35  |  < 70  | The melting takes a while, you could increase emission to 50 mA, but the deposition rate will likely overshoot. | (21 May '25) |
-|  Nb   |  150  |  < 400  | [[Evaporating superconducting Nb]] FIXME | (18 dec. '24) |
+|  Nb   |  150  |  < 400  | [[Evaporating superconducting Nb]] FIXME | (18 Dec. '24) |
-|  Pt   |  130  |  < 150  | [[Prevent burning through 4cc-graphite liner]] FIXME | (10 feb. '25) |
+|  Pt   |  65  |  < 85  | [[Prevent burning through 4cc-graphite liner]] FIXME | (10 Feb. '25) |
-|  Al   |  50  |  <  80  |  | (18 dec. '24) |
+|  Al   |  50  |  <  80  |  | (18 Dec. '24) |
@@ Line 165: / Line 171: @@
 ----
-==== Manual mode ====
-The manual mode actually is a kind-of-manual mode, in which you operate the computer - you don't have to manually open and close the valves, the computer will control these subprocesses.
-The following instructions can be followed after you have loaded your sample.
-   - First, we transfer the sample from the loadlock to the evaporation chamber. Click the ''LL >> Evap'' button in the Process Diagram.
-   - Once the sampleholder is in the chamber and the valve to the loadlock is closed, change the tilt, rotation and/or angular velocity of the sample stage if necessary.
-   - Select the e-beam gun process.
-   - Now we turn to the Xtal Monitor. Select the correct crucible (i.e. the required material).
-   - Enter your desired thin film thickness.
-   - Enter a target deposition rate, a common value is 0.10 nm/s.
-   - Turn on the 10 kV high voltage.
-   - Check your material's setpoint in the table below.
-   - After waiting for a 1 minute, the high voltage switches on, and you can click on the arrows of the horizontal scrolling bar to //slowly// increase the emission current of the electron beam until you have reached the desired setpoint.((It is important to increase the emission current slowly, because we want to prevent liners from cracking due to thermal stress induced by local hotspots from the electron beam.))
-   - Close the lower viewport to prevent getting welding eyes (especially when evaporating materials with high melting points, such as Nb).
-   - When the deposition rate is roughly two-thirds towards the desired deposition rate, turn the Rate Control on.((For expensive materials (Au, Pt), you want to prevent an overshoot in the deposition rate that wastes a lot of material.))
-   - Once your required deposition rate is reached, click the Start button to initiate deposition.
-   - Write the process pressure, deposition rate and thickness in the log book.
-   - Once the thickness is acquired, the shutter will be closed, emission current will drop, and the HV will turn off automatically.
-   - Wait for 2 minutes, so that the evaporated source can cool down.
-   - You can either
-    * Deposit another layer (go back to step 2).
-    * Transfer your sample to the loadlock, and unload (continue steps).
-   - In the Process Diagram, click the ''LL << Evap'' button.
-   - After your sample is back in the loadlock, you can vent the loadlock.
-   - Take the sampleholder out, using gloves.
-   - Remove your samples, and place the sampleholder in the loadlock.
-   - Pump the loadlock down.
-^  Material  ^  Setpoint  ^  Max Emission  ^
-|  Ti   |  200  |  < 300  |
-|  Cu   |  20   |  < 100  |
-|  Au   |  20   |  <  40  |
-|  Ni   |  100  |  < 150  |
-|  Co   |  65   |  < 120  |
-|  Nb   |  100  |  < 400  |
-|  Pt   |  20   |  < 125  |
-|  Cr   |  10   |  <  35  |
-|  Py   |  20   |  < 150  |
-|  Al   |  50   |  <  80  |
-|  Ag   |  20   |  < 320  |
-|  Ge   |  45   |  < 100  |
-----
 ==== Ion Beam Gun ====
@@ Line 238: / Line 199: @@
 ===== Maintaining High Quality Materials =====
-Because the system is used by a lot of users, we strongly urge every user to be aware of others' needs. After a bake-out, the system can be booked to condition the chamber. In that case, Nb will be evaporated without a sample, but for the sake of obtaining a ultra-high vacuum.
+Because the system is used by a lot of users, we strongly urge every user to be aware of others' needs. After a bake-out, the pressure will be around 8e-8 mbar. After opening, the chamber always needs to be conditioned in order to obtain high quality Nb.
+When materials are refilled, they need to be molten. Why do you want to melt materials loaded into the e-beam evaporator? The metals are loaded in the form of tiny pellets.
+These are often:
+  * Oxidized
+  * Dirty
+  * Thermally not well connected to each other or the liner
+In the case of Nb, poor quality can be disastrous to the Tc and its applications in sample/probe fabrication. Melting it and then conditioning out the oxygen and other impurities is imperative.
+Increasing the heat conductance of the pellets by melting them into a single large blob makes evaporation easier and more consistent.
+==== Melting ====
+Different materials have different melting points, so it is important to start with a low emission current and increase it gradually depending on the targeted metal. Melting must be done homogeneously over the entire area of the liner filled with pellets, which avoids the trapping of impurities and ensures that all pellets can be combined into a single amalgamation. So the steps are:
+  - Write in the logbook.
+  - Start at 1 mA and allow the material time to heat up. The goal is to achieve a glow such that you can see where the beam aims at. (At very low currents, it is safe to remove the mask on the window for better sight). Once this is achieved at 1mA (or higher for some materials, e.g.: Nb), constantly monitor the chamber pressure. You should see a sharp increase when the material is first exposed to the beam (this is mostly oxides and dirt), which is expected.
+  - Now that the glow allows for orientation, you can move around with the beam. This can again result in a pressure increase. Wait until the pressure stabilizes and repeat until you have passed all the pellets. Once the chamber pressure is reduced and stabilized, you can slightly increase the current until you observe a rise in chamber pressure again (the amount you increase will likely be larger as you approach the material’s setpoint).
+  - Scan over all the pallets until the pressure is once again stabilized.
+  - Go back to step 3 and repeat until you have started evaporating some material (check the material's setpoint to get an idea of when this will happen). \\ \\ :!: Don't forget to put polarization mask on the viewport and/or welding glasses on when reaching higher currents to protect your eyes! \\ \\
+  - The mA step size should start slowly and increase in the latter stages of the process. Use the logbook to gauge what a reasonable step should be, as melting is done with lower currents than evaporation.
+Tips and tricks:
+  * The movement of the controller does not perfectly align with the actual movement of the beam. This results in the lower regions being unreachable via e-beam. To address this, we spend more time at the lowest point we can reach, aiming to utilize thermal conductance to melt the unreachable regions as well.
+  * Patience is key! Do not melt in a hurry, but relax with some nice music or company.
+  * In the beginning, some pallets are badly thermally connected, which sometimes causes them to be much brighter than the nearby regions. Take good care of safety for your eyes!
+  * Melting is done at ~e-8 mbar. During melting, it sometimes goes to e-6, but the start should have a good enough pressure to avoid more impurities.
+  * Throughout the melting process, the chamber pressure should never reach the ~e-5 regime. If it does, you’re either using too high of a current or melting too fast.
+==== Aftermath ====
+After melting, there are two important things to do:
+  - The conditioning of the chamber.
+  - The conditioning of the Nb.
+=== Conditioning the chamber: ===
+Evaporate a getter-material, such as Nb or Ti. These materials bond with dirt and oxygen in the chamber and end up sticking to the walls, improving pressure after pumping down again. The aim is to achieve e-9 to 1e-8 chamber base pressure..
-==== Chamber Conditioning ====
+In order to get to better pressures, one could evaporate a getter-material (e.g. Ti, Nb). This type of material will absorb vaporous hydrogen, oxygen molecules and other dirty molecules in the chamber, thus reducing the pressure further.
+By evaporating 5 - 10 nm of getter-material, and waiting for one hour, the chamber pressure will decrease. The aim is to achieve ~1e-8 or ~5e-9 mbar. In the first step, after some time, the getter will stop working as efficiently as in the beginning. So, when the pressure is stabilized, one can evaporate more.
-After the materials are refilled or replaced, or the quartz crystal has been replaced, the chamber needs to be pumped down. Typically, this type of maintenance is done on a Friday, so that the system can be baked out for 48 hours during the weekend. After the bake-out, the pressure will be around 8e-8 mbar.
+=== Conditioning Nb: ===
+There is still a lot of dirt in Nb after melting. This can be seen if there is a good base pressure but a very bad Nb evaporation pressure. To solve this, we evaporate a lot of Nb the get rid of the impurities. This has the double effect of also conditioning the chamber.
-In order to get to better pressures, one could evaporate a getter-material (e.g. Ti, Nb). This type of material will 'catch' vaporous hydrogen or oxygen molecules in the chamber, thus reducing the pressure further.
-By simply evaporating 5 - 10 nm of getter-material, and waiting for one hour, the chamber pressure will decrease. After some time, the getter will stop working as efficiently as in the beginning. So, when the pressure is stabilized, one can evaporate more.
-If the pressure does not decrease any further, the best pressure is obtained. If this pressure is still too high, there might be a (virtual) leak.