I do not have any experience with the omicron EFM evaporator, however I know that several other e-beam evaporators have a quite "strange" wiring which you would not expect on a first glance: Those setups ground the evaporant (the iron source) and put a negative high voltage on the electron emitter. Maybe you should check this in the manual of your device? Are you sure that the iron rod should be on positive HV and the electron emitter grounded?

Good luck, Dirk

Hi Dirk,

thanks for the reply - but unfortunately, there's no mistake in the wiring that I can detect without breaking vacuum. Referring to the manual was one of the first things I did :) and connections look to be set up properly, and geometry is as described (the evaporant is positive).

Thanks for your input anyways

Regards

N

Hi Nikolay,

All I could think off is that there is problem with your HV power supply or the iron rod is not perfectly insulated. Good luck!

Dear Sir,

we are using the very same type of evaporator and usually it works very well.

Maybe, it would be a good choice to test the three other pockets (if equipped with any other rods).

In case that these pockets work, you can exclude all errors related to HV and focus

on errors related to this particular pocket, i.e. either flux monitor of this pocket or the

filament of this pocket. Does your setup allow to see the filament glowing (at least

indirectly)?

Of course, electron beam evaporation from metals with oxide skin is not as

straightforward as from clean metal surfaces. I just can refer to our experience

witl Al rods. The oxide layer sometimes acts as a kind of pressure cooker: The

metal inside is boiling and suddenly the oxide skin is "exploding".

Since you are experienced with this type of evaporator, it may be useless to

point to the general fact, that there is a steep onset of emission current depending on

filament current.

If it was my decission: I would remove the evaporator from the recipient for

checking it in detail on the desk. Maybe there is a Fe rod in this pocket, but the

connection is poor (since the original clamps have a very bad performance).

Spending a few days for annealing the UHV setup afterwards would be a smaller

loss of time than blind troubleshooting without any real concept ...

Regards, FM

I have some experience with these; oxidation should not play a role once you reach operation conditions. The position of the rod is extremely critical and emission current and even more the monitored flux react very nervous on a position-change.

Some of these evaporators can be damaged by the holder of the rod if it is advanced too much. If you have no idea where the tip of the rod is located the optimization can be a lengthy procedure. The best is to be slightly behind the filament and then progress slowly ( about less than 1 mm and then 5 minutes of trying to get emission current and hence flux). Of course this requires a proper setting of the filament current. the polarity is alright as you send the electrons on the tip of your rod.

Hi all, thank you for your suggestions.

Violeta, I have checked the HV output of the power supply as well as the HV wire. It seems to be fine...

Franck, sorry if I have confused you with the name of the evaporator, but this one is a single-port model (I believe it's called EFM3). No other pockets. Yes, I can see the reflection of the filament glowing, and the current through the filament is reasonable as well as the (expected) readings of flux monitor - indeed, if we are not attracting the electron cloud from the filament, it would end up on the flux monitor, and show a negative value. Unfortunately breaking vacuum is not an option at the moment, due to numerous reasons. (But this might be the only solution in the end, to find out the real cause).

Tobias, thank you for your suggestion, that's what I was trying to do, but I have moved the rod in by around 12 mm without any reaction from either emission current monitor/flux monitor, and this did not affect the pressure either (which I would expect if I wa bombarding not-annealed surface of the rod). I am starting to be sure there is no rod, which might be the case, if it has fallen out for some reason (however cannot see it in the chamber, neither anywhere around).

I'll post the answer once it is clear, if you are interested ;)

Regards

Nikolay

It hapenned to me once (some many years ago) a similar problem, and if I remeber right, the issue was a slight loose contact inside the source, at the fixation of the central rod (evaporating material) via the clamping screws. Unfortunately, to investigate it and then to fix this, the break of the UHV was necessary.

But before, I would sugest you to try thoroughly the procedure suggested by Tobias; you can start with the rod completely retracted, set some filament and HV parameters for which it should work (hopefully you have them noted from some previous experiments), and then VERY SLOWLY advanvce the rod (less than 1mm every 5 min is good) and try to get the flux

Goodluck and hoopefully you'll not have to break the vacuum

cristian

UPD

While I was following the route suggested by Tobias, the linear translator of the evaporator has got stuck (at still ~14mm to go to the end) This leads me to a conclusion that indeed the rod has fallen out from the barrel connector and is left inside the copper shrouds... Somehow weird that if it has fallen, it is not touching the central transfer rod of the evaporator, which is at HV, thus not grounding the central pin, neither it touches the filament, since the latter is not grounded either... Weird experience, anyhow. :)

UPD2 and (hopefully) final:

For those of you who are interested in what the problem finally turned out to be - the problem was a faulty barrel connector on the central rod, which holds the evaporant. The barrel connector turned out to be completely loose on the side where it attaches to the central rod. The evaporator was facing down, so, the barrel connector with the iron rod has slide down into the copper shroud. Fortunately it didn't break the filament, neither grounded the HV... That was a very strange problem...