Getting gold onto diaphragm

Today was my first attempt at gold deposition. It almost worked. I got the vacuum pump working, though probably not quite enough vacuum... after having a diaphragm in vacuum for a couple of hours, I turned on the heater for the nickel, and after a few seconds everything around the filament was covered in a silver-black layer. Next, I turned on the gold filament. Opps... the power transformer burned out. The epoxy vacuum seal for the filament power feed-throughs melted, there was the unmistakable suck of air, and that transformer gave its dying gasp and a big puff of smoke. Resistance of the mylar film with the nickel is about 1k over a 1" gap, resistance of the bit of glass with gold on it is about 45 ohms for the same distance. It almost worked...

Desired modifications: modify the vacuum feedthroughs to handle more serious current (100 amps or so), and add better clamps for the filaments. Add a good sample holder to put the diaphragm straight up from the filament. It's getting there.... maybe in a week or two I'll have it working. I think there was still some contamination in the vacuum chamber - I need to probably let it sit for 24 hours under the vacuum pump to decontaminate the system before trying this again. Likely I'll get a chance to try again in a couple of weeks, after fabricating the new parts.

I love hearing about people doing this sort of thing!
:thumb:


-jay

Dale,

I've heard of people doing gold-evaporating for electron-microscopy that used argon gas to "clean out" the vacuum.

It's something like evacuating, letting in argon, and evacuating again.

This ensures that whatever gas you have left because of imperfect vacuum is at least chemically inert, and won't influence your processes much.

Process can be repeated a couple of times to "thin out" the non-argon content.

Jakob E.

hey Dale, this sounds like you are doing some pretty intense DIY there! If it will help you, I have an AKG 414 that was sounding a bit crackly now and then, so I got the capsule replaced with a new one. The old capsule was returned to me, if it is of use to you I will post it over to you. Perhaps you can re-diaphragm it and use it?

[quote author="dale116dot7"]I got the vacuum pump working, though probably not quite enough vacuum... [/quote]
I have also problems with vacuum pump and the air going into it.
I have cookbook to make vacuum fill-in fett.
It is mixture of pure Lanolin and "ground wax".
I have not that "ground wax." Can I use pure lanolin as substitute for the
fett. ?

xvlk

I think my problem is not waiting long enough after turning the pump on - even an accidental fingerprint may take hours to purge., but Jakob's suggestion of using Argon to purge the system is probably worth doing. I use Dow Corning silicone vacuum grease for all of my joints. I need to get some proper vacuum hose as well - the hose I have will likely off-gas too much.

Look for The Amateur Scientist collection on CDROM. All kinds of cool DIY stuff build your own vacuum pump, sputtering etc.....


I think I bought my copy from surplus shed. I think alot of people here will like the collection There is also a very good telescope CDROM.

Dale....its cool that you've got this going now. What kind of pump are you using? The pump/purge idea with some inert gas is a good idea. You might want to think about an oil trap to stop back-streaming from the pump as well. How are you supporting the metal? Are you just clamping directly onto the Ni and Au or are you using a W or Mo boat? Maybe a boat would help with the high current problem...I have a few extra if you want.

Our old JEOL thermal evaporator just died.....got a hole in the cooling water line for the diffusion pump and burned a bunch of oil and sprayed water all over the electronics. Not sure what we are going to do with it yet. I'm going to be doing electron beam evaporation on my diaphragms this week and see how that goes.

Hi Ebeam!

Welcome to "The Lab"!

Jakob E.

It's a Precision Scientific pump, it's supposed to pull down to 10-3 torr or something like that, it's a smaller pump - 1/2 hp. I am using W boats, though with my fiddling (and the fact that they get brittle after use), I've wrecked a few. I've been getting my supplies from Structure Probe, Inc. They even had 6 micron mylar. I also got a new power supply - a car battery charger with a 150 amp 'boost' mode. I tried it again to make sure I could get things to seal and work properly, and everything did work though the air left in the chamber prevented proper deposition. I got a blue deposit all over everything. It was just a check to see if I was going to have more meltdowns or that sort of thing. After I get a new vacuum hose and maybe an argon purge system going I'll try again. I was looking at the Neumann pictures http://www.omnipressor.com/Other/NeumannBookPix/ and thought the setup looked like thermal evaporation, not sputtering. The other thing is a proper bell jar setup would be much easier to work with - I'm using an old dessicator jar, and everything is located in a 'dish' so it's harder to work in there with big farmer hands. Maybe I'll borrow a digital camera and post a photo or two.

Jakob- Thanks...I've been lurking a while, but my electronics knowledge is so deficient that I haven't had much to contribute. But if you have electron microscopy questions......

Dale- Definitely looks like thermal evaporation in the Neumann pics.

The ultimate vacuum you can achieve is going to depend a lot on how you set up the system, size of tubing, pumping speed vs. leak rate etc. For that pressure range, you might be able to rig up a vacuum gauge of some sort fairly easily....maybe a thermocouple gauge.

I actually bought the mylar from SPI as well...I think 92m should last me a while.

> Resistance of the mylar film with the nickel is about 1k over a 1" gap

You don't need high conductance on a condenser diaphragm. Remember you are going into a 100-Meg Grid, and the total capsule impedance is over 100K at the top of the audio band. Another K in series with that is no big deal.

High vacuum is a perfectionist art, as you know.

Get some duct seal and a vacuum gauge. Go around and look for leaks by pressing the duct seal around any suspect seams. You can check the vacuum by "feel" by placing your hand over a valve and opening the valve. If you have a good hard vacuum, you will put a pretty good ring on your palm. Close the valve and listen for a good snap when you remove your palm.

Duct seal is a grey clay like substance that you can but at the hardware store. It is handy also for putting on the end of a stick and retrieving lost bolts down intake maniflds, etc.

The vacuum pump will make more noise when it has really pulled down a lot.
Leave it on overnight to get a real good vauum, provided you have no leaks.

The vacuum already is enough that you can't measure it with a normal gauge - I'm using a thermistor gauge, the type used by air conditioning people to see if the vacuum is enough in their systems, the problem is that under those low pressures, the hydrocarbons in the rubber hose between the pump and the jar evaporate, leaving air at that partial pressure still in the jar. I'm for sure getting below 1 torr, but I need more like 10-3 torr.

This is getting interesting. Dale, Can you post some pix of your rig? We have vacuum lines here at work which I might be able to hijack for a while.
Cheers!
Stewart

I was reading an article on sputtering from the Amateur Scientist collection. In the article using the glow discharge to clean the part was mentioned, I believe it is at about 1 tor.

IIRC the article also stated that you need 10 -5 torr for evaporation.

Apparently so; I'm getting around 10-1 torr, but that's not enough. I'm getting a gold coloured but non-conductive deposit on the bell jar, and a very light non-conductive blue deposit on the mylar. It looks as though the light blue deposit would likely be tungsten oxide, and the non-conductive gold coloured deposit is likely gold oxide. Not the desired effect, I'm afraid. I don't have the argon purge stuff available yet, I'll need to order it in a month or two when my DIY budget allows. I'll order argon, valves, and some tubing at the same time. I don't see much point in wasting gold wire or tungsten boats 'till I get the rig fixed up. The other issue I think I've got is the hole size going into the jar makes it hard to pump the system down to the vacuum level I need. In the meantime, I have capsule backplates to machine and drill (and drill and drill...). I'll try to get photos of the deposition setup next week.

I doubt that it's tungsten oxide - I think you would have to get VERY hot before tungsten has sufficient vapor pressure. The color of the gold deposit will change with thickness and won't really look gold until you get a thicker film (also depends on the substrate). I just deposited about 20nm sputtered gold on glass and it looks green/blue. I seriously doubt that you have gold oxide as that compound isn't stable. You probably just have a lot of contaminants trapped in the film decreasing the conductivity.

I have to delay this project a bit... not enough vacuum. I am getting a diffusion pump, but I need to get some high vacuum valves, a bigger (more expensive) mechanical pump (I need about ten times my current capacity for a backing pump), a new vacuum baseplate with a bigger outlet, and some diffusion pump oil ($275 for 100mL - expensive). Likely I'll have the funds to get the bits and pieces early next year, in the meantime I'm going to work on building capsule backplates. I am leaning towards a KK47-like capsule except a glued diaphragm like on a M7.

I've got the bigger backing pump and the diffusion pump, as well as a set of nice vacuum gauges. They left oil in the diff pump so I've got to clean it out and replace it. Maybe mid November will be the next attempt at metalizing.