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--- e-beam_evaporator [2025/05/21 15:29] – [Manual mode] wigbout
+++ e-beam_evaporator [2025/06/13 13:54] (current) – [Aftermath] wigbout
@@ Line 199: / 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.
-==== Chamber Conditioning ====
+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
-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.
+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..
+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.
+=== 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.