Science/Engineering/Technical forums

Doug,

I seem to recall you put up a scan of a book with materials ordered by their relative sputtering susceptibility. (Or did I dream that!?!)

Could you please pin that up again in this thread, so it is easy to find?

thanks,

Here's the link. It was on the second page of results from typing "sputtering" into the search box (which BTW, works a lot better now).
viewtopic.php?f=12&t=245&p=1209&hilit=sputtering#p1209

Chris,
Here is a link to some sputtering information that JohnF has posted previously, also.

Thanks, both (plus John for the fusor post!). This plot was particularly informative!;

http://www.fusor.net/board/getfile.php? ... tt_id=7176

(Yes, I did use search but too many for 'sputtering' and didn't spot the one with the info in. As per the motto; if you want to hide a grain of sand, put it in a desert!)

OK, the next associated question; now I admit I might not understand the actual question this time(!), but here goes; is there any data on secondary electron emission rates from ion bombardment for different materials? (Does that question make sense?)

Chris
From where I'm at it seems that secondary electron emission has more to do with electric field and surface construction (smoothness) than from what material it is made from with a few exceptions that help electron emission like thoriated tungsten, Hafnium, and a few other rare elements

I may be totally wrong on this, so maybe someone can straighten me out because I was looking for the same thing a while back. Anyway, I didn't have any luck finding anything specific to ion bombardment, but I got the impression that secondary emission is essentially the same whether the primary is electrons or ions.

There's a ton of data on secondary emission in the Kohl book, maybe some in the older version in the library, but definitely in the new one. It has a lot to do with work functions. I have no idea if ions vs electrons is a big difference or not -- have seen zero data on that one -- I'd suspect velocity is a big one, it is within just electrons and most materials have a peak secondary emission vs input energy (from electrons). There's little mention on surface finish in Kohl, but he's the vacuum tube guy and they tend to be real smooth and uniform. Deliberate secondary emission is of course used in phototubes, and even in some older super high GM pentodes, as well as some gas tubes. There's often a correlation between primary thermionic emission and secondary emission, and many elements can have a multiplier up in the 3-4 range, while special oxides etc can get into the 20's at least. Pure carbon is a good choice for low secondary emission, which is one reason I've used it as grid parts here - and it really does reduce it over most other things you could make a grid from.

As John says, pointy stuff is best if you want to emit electrons by field emission. Too much surface roughness tends to "catch" the secondaries before they can get away, per Kohl. Obviously a lot depends on the field proximate to the thing -- and what you're trying to do.

It would be more helpful here if you said why you wanted this or that bit of info. You get better answers and teach others more that way.