viewing emulsion under a microscope

[Kirk Keyes]

That could be. But the university I went to in the early '80s had a TEM from the early '70s that we used. They did have a brand new SEM that we got to use too, so that was cool.

[Ray Rogers]

the object was sputtered with silver metal

Kirk, can you describe sputtering... and sputtering silver...
How its done and what actually is being done/used ?

TIA,

Ray

[Kirk Keyes]

Sure. I think it goes like this:

You put something (our target) into a vacuum chamber and hook it to electrical ground, pump the chamber down and then introduce a little inert gas, often argon. This gas is heated to give it some momentum, and some of the gas atoms crash into the material to be sputtered. (In my case for what we were doing it was silver metal.) The block of silver that was used was postively charged. That is, there is a DC potential between the silver and the thing you want to coat, often around 100 to 150VDC.

Silver atoms get knocked out of the chunk of silver metal by the momentum of the collision with the heated gas, and since they have an electrical charge on them (they are ions at this point), they go flying over to the target. The silver atoms crash into the taret and they loose their charge and they are left sitting on the
surface of our target.

It's a way to deposit material onto items.

Although it uses silver, it's not something that's really useful in emulsion making...

[Hans2008]

This is a little off topic, but about 15 years ago I know a rather brilliant fellow who was making an electron microscope the size of a sugar cube as his doctoral thesis. At the time it blew my mind that it was so small

Are you sure that this was not a Scanning Tunneling Microscope? They can be made this small. In fact, hobbyists make these at home.

[Ray Rogers]

Sure. I think it goes like this:

You put something (our target) into a vacuum chamber and hook it to electrical ground, pump the chamber down and then introduce a little inert gas, often argon. This gas is heated to give it some momentum, and some of the gas atoms crash into the material to be sputtered. (In my case for what we were doing it was silver metal.) The block of silver that was used was postively charged. That is, there is a DC potential between the silver and the thing you want to coat, often around 100 to 150VDC.

Silver atoms get knocked out of the chunk of silver metal by the momentum of the collision with the heated gas, and since they have an electrical charge on them (they are ions at this point), they go flying over to the target. The silver atoms crash into the taret and they loose their charge and they are left sitting on the surface of our target.

It's a way to deposit material onto items.

Although it uses silver, it's not something that's really useful in emulsion making...

Just to clarify, the object is connected to ground (earth), silver block connected to positive lead ... (is there a negative in there somewhere?) and
then in vacumm, an inert heated gas (what temperature?) knocks some silver atoms up up and away....

What are the orientations, or does it matter?

How far apart are the object and the metal?

What sort of times are involved?

Thanks, Kirk!

[Ray Rogers]

How you make replicas objects on the scale of film grain, I'd like to know. Put a thin coating of the emulsion onto glass and then sputter carbon onto it, and then dissolve the emulsion back off the carbon?

Kirk, I found this while looking for something else
"The Electron Microscopy of Photographic Grains. Specimen Preparation Techniques and Applications" Journal of Applied Physics, 1953

Too many pages and not enough sleep to look for something more concrete.

Ray

[Kirk Keyes]

Just to clarify, the object is connected to ground (earth), silver block connected to positive lead ... (is there a negative in there somewhere?) and
then in vacumm, an inert heated gas (what temperature?) knocks some silver atoms up up and away....

That's about it, and the silver atoms have a charge to they are pushed by the potential difference to go from the positive side of the potential to the negative side. And in this case, ground/earth is negative, as it's in reference to the positive side.

What are the orientations, or does it matter?

How far apart are the object and the metal?

What sort of times are involved?

It's a line of sight arrangement. You are just using the potential to repel the positive charged silver atoms away from the rest of the positively charges silver block and then it zips over to the other side where the item you are trying to coat is sitting on top of the negative plate.

It's been some 25+ years, but I seem to remember the vaccuum chamber about a foot in diameter, the silver source held in the top of the dome of the chamber, and the items to coat sitting on a metal ground plate. The item I was coating was a fossilized tree branch (a cedar from about 40 million years old), so it was not electrically conductive when it was first placed in there. So even though I said the item needed to be on the ground side, it's the metal plate under the item that's at ground, and that's good enough to get the potential difference for the sputtered silver to fly over to the target. And then it's just in the way as the silver tries to get to the negative plate. It lands on the target and then coats it.

How long, I don't know - over night I think. We closed it up at the end of class and then two days later when the next class met, we opened it up and they were done. I think someone turned it off in between then though.

It's not a thick layer of silver that's needed. For the SEM, it needs to be able to dissappate the electrons the SEM is shooting at the item being scanned. And to get elemental analysis from X-ray fluorescence, the electrons need to fly through the silver and down into the item so the electrons can bounce off the atoms in the items surface.

[Kirk Keyes]

Kirk, I found this while looking for something else
"The Electron Microscopy of Photographic Grains. Specimen Preparation Techniques and Applications" Journal of Applied Physics, 1953

Is this something online? I don't really have ready access to scientific journals.

[Ray Rogers]

Is this something online? I don't really have ready access to scientific journals.

I have no idea. I was in the stacks today when I found it.

ps: Thanks for the sputtering overview...

Ray