by Doug Coulter » Sat Jul 23, 2011 6:33 pm
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.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.