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Photo Engineer
01-06-2009, 04:21 PM
Basically a microdensitometer is a regular densitometer recalibrated to have a high intensity beam with a small aperture. It must be smaller than the smallest line you wish to scan. We typically used 1000, 100, 10 and 1 micron lines.

Usually, 10 microns is small enough, and therefore a 1 micron or 0.5 micron aperture would be OK.

PE

Alan Johnson
01-06-2009, 05:26 PM
Objects 3-4 microns can be measured with quality optical microscope, this is about the size of grain clumps I believe,but it sounds expensive.
www.microbiologyprocedure.com/microscopy-methods-in-microbiology/measurements-with-optical-microscope.html

Photo Engineer
01-06-2009, 05:51 PM
Grain clumps are smaller, and appear as noise in photomicrographs of edges. This is how RMSG is calculated, by analyzing the noise.

PE

archphoto
01-06-2009, 06:12 PM
By all means get yourself a better microscope !
The type depends on what you want to see: butterfly wings can be seen with low magnification, filmgrain at verry high.
I know this is a bit on the side-line of this forum, but still, you can allways send me a personal message.

Good luck !
Peter

patrickjames
01-06-2009, 09:48 PM
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. I can only imagine the size they can make them now!

Kirk Keyes
01-07-2009, 12:12 AM
Scientific American published instructions for making an electron microscope at home. Martin Gardner's column, I believe. Check the indexes from 30 to 40 years ago.

Most likely "Amatuer Scientist" and not Martin Gardner.

I happen to have all the Amatuer Scientist articles on CD - it was $30 at Fry's several years ago and I could not pass that up. I have a whole basement full of Scientific Americans, most every issue from 1950 up to 1990.

It's September, 1973 - "A High School Physics Club Builds Electron Microscopes" and has a difficulty level of "4 - possibly lethal"! I wonder what level 5 is - "may blow entire world"?

It's a transmission electron microscope. it will take some glass-blowing, a good vacuum system, and it has a nice vacuum tube power supply.

totalamateur
01-07-2009, 06:05 PM
I looked into having a friend of mine TEM my samples, if I ever made any worth while (which I have not- yet).

The local machine is for rent at $175 per hour, and apparently he'd be stretched to do 3 an hour (maybe up to 7 if he was doing a bunch, but apparently set up time takes a while, something about a perfect vacum and charging the flux capacitor) On the flip side, the TEM at the local U is used for taking pictures of bucky balls and nano tubes, so I'm pretty sure it could fill a frame with a halide crystal if I wanted to.

PE, if you have time, it would be useful to know the specific issues of preparing an emulsion sample for a TEM, since at some of us might hand samples of to the local universities for grain portrature, and it'd probably be advantageous to also hand a list of things to watch for when preparing the sample. (I'm assuming that no one here is actually going to try to run one themselves, the Nano geeks I know spend about 2 weeks on how to learn the machine badly, and it apparently takes months to learn how to use it well)

Photo Engineer
01-07-2009, 07:24 PM
I've never done TEMs, just SEMs and EMs. The prep method requires making a carbon replica. That should be enough for your friend to get started. You make the carbon replica of the crystal, and then use about the same conditions as for the buckyballs.

PE

Kirk Keyes
01-08-2009, 12:10 AM
I took a class in college in the mid-80s and it was on operating electron microscopes, both TEM and SEM. You can also make chrome replicas of items in addition to PE's mention of carbon replicas. That involved coating the subject/object with a plastic film, peeling/removing the film from the original, and then sputtering chromium metal at an angle onto the plastic replica. It was put on at an angle so that it cast a "shadow" of the object. The plastic was then removed by dissolving it with solvent. The chrome replica was then mounted in a frame and placed into the TEM.

SEM was much easier - the object was sputtered with silver metal and then it was placed into the SEM. The silver was there to allow the electrons to disappate from the surface of the object otherwise it could become charged and then it would repel the electrons the SEM shoots at it.

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?

AgX
02-23-2009, 10:17 AM
Electronic microscopy seems to have evolved to such a degree that even a company as Agfa contracts work of that kind to universities due to the sophisticated hardware to be found there.

Kirk Keyes
02-23-2009, 11:32 AM
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
02-26-2009, 01:25 PM
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
02-26-2009, 06:20 PM
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
02-26-2009, 09:41 PM
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
02-27-2009, 06:53 AM
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
02-27-2009, 08:34 AM
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
02-27-2009, 11:21 AM
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
02-27-2009, 11:22 AM
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
02-27-2009, 11:51 AM
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