Scanning Electron Microscope Subject Stage Assembly update

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Moderators: rjlittlefield, ChrisR, Chris S., Pau

Pizzazz
Posts: 583
Joined: Thu Nov 28, 2013 7:39 pm

Scanning Electron Microscope Subject Stage Assembly update

Post by Pizzazz »

Hi

I just got to play with this and experiment with the motorized rotational
stage. Here are two shots showing the unit. I have it bolted to a small
optical bread board and I eventually will add more support towards the
mechanical side.

Mike


Image



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Harald
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Post by Harald »

Hi,
That is some great piece of machinery.
Looking forward to see some great results from you
Kind Regards
Harald

Lier Fotoklubb / NSFF
AFIAP / CPS
BGF / GMV
http://www.500px.com/blender11

Pizzazz
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Joined: Thu Nov 28, 2013 7:39 pm

Post by Pizzazz »

Harald

What? Results? Kidding, right?

I have been away for quite some time and hope to get back into the
swing of things soon.

Mike

Pau
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Post by Pau »

IMO you want a shorter sample holder to put the subject in the device axis and fully profiting its rotational capabilities
Pau

Pizzazz
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Joined: Thu Nov 28, 2013 7:39 pm

Post by Pizzazz »

Pau

OK, the stage has a 5.5 inch diameter acrylic plate that I placed on top
of the rotating turret. I have plenty of room with this as it does not
interfere with any mechanics.

So, being confused, would you explain what you mean?

Mike

Pau
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Post by Pau »

I'm referring to the device horizontal rotating axis.
The typical SEM sample holders are much lower, allowing to put the sample at the centre of all axis, so when you rotate it doesn't traslate
Pau

Pizzazz
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Post by Pizzazz »

Pau

Please bear with me. Looking at the photo, the wasp and nest are on
an alligator clamp which as you can see, is attached to a small wood block.

I did take a movie of this, and shifted the wasp off-center to align as
much as possible, the subject in the vertical plane.

Now, the placement of the wasp, are you saying that should be as close as
possible to the rotating stage?

Help me Obi Wan Pau .... You're my only hope.

Pau
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Post by Pau »

Sorry, right now I'm traveling with just a phone and poor or no internet connection, so I can't make drawings or make long posts. Will be back in ten days.
Pau

Chris S.
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Post by Chris S. »

Mike,

As Pau is away, I'll attempt an explanation of his point. Please refer back to the picture of my goniometric stage. In that picture, the three red-arrowed lines represent the three rotational movements of the goniometric stage. Just below the middle of the fern leaf, these three rotational movements coincide on a single point of rotation.

While my goniometric stage and yours look different, both have the same function. This is to move a subject around three orthogonal axes, in such a way that during rotational motion on any axis, the subject's orientation to that axis does not change, and that all three axes of rotation intersect. At this intersection--the center of rotation for all axes--your subject can turn (nearly) any way you want it, without leaving your camera's frame. From the viewpoint of your camera, the effect is like flying around your specimen.

Said another way, if you mount your subject at this intersection point, it will be centered within any rotational movement you dial in, no matter in which dimension that rotation is conducted. This makes it easier to take pictures in different rotational positions without having to adjust the subject, or having your subject rotate out of your camera frame.

On my goniometric stage, the axis of rotation exists one inch above the top of my upper stage. This means that about half-way up the fern leaf is the sweet spot. Looking at your stage, the center of rotation appears to be much lower than your wasp nest--perhaps about where the clip meets the wood block. But this just a guess, as I've never had a chance to examine a goniometric stage from an SEM.

To be sure, it's not always necessary to place a subject at the three-axis rotational center when using a goniometer. Sometimes you don't use all the movements, or don't mind a making an adjustment if you do. At low magnifications, I tend not to worry if I'm not working in exact center of rotation. In these cases, I'm using the stage as a simple multi-axis stage, ignoring its ability to precisely spin a subject around a designated sweet spot. At higher mags, such as 100x--where a subject can disappear due to small fields of view and tiny depth of field--here is where I tend to be much more careful about mounting a subject in the center of rotation.

Still, knowing where the center of rotation is, for your stage, will reward you in pretty much all use. Even when you are not centering your subject in the sweet spot, your awareness of how far it is from the sweet spot will help you form useful intuitions as you juggle your rods and dials.

I'd enjoy seeing more documentation about your stage, as SEM stages are a solution to a problem I solved rather differently. I've longed to get an SEM goniometric stage in my hands, and see what I could learn from it. Goniometric stages similar to mine are now used rather widely. But could we kick this design up a notch by learning from SEM goniometers?

Mike, if you've absorbed all this, you are now our Obi Wan Mikey, as you have the only SEM goniometer on the forum available for study (so far as I'm aware)! Please show us lots of details about this technology. :D

Questions:
  • 1.) Mechanically, how is each axis of rotation implemented? Are there mechanical differences between the axes?

    2.) Mechanically, how is movement actuated for each axis of rotation? Are there differences between the axes?

    3.) What angular range of movement is available for each axis?

    4) Getting back to basics, where do the axes of rotation intersect? How high is this above the top of your stage?
--Chris S.

Pizzazz
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Post by Pizzazz »

Chris and all

I need to take some detailed shots of my device and try to answer the
questions you ask.

I did take a quick movie of the wasp and nest, and I attempted to
center the subject on the rotational axis, and I get close to your
description of "flying around the subject".

I will post more later today.

Mike

Pizzazz
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Post by Pizzazz »

Chris and all

Here are a few detailed shot of the assembly. Note that the subject stage
is motor driven so it can rotate 360 degrees, and the entire assembly can
be rotated, but there are limit stops to prevent it from going too far in
either direction.

I will submit photos in two replies.


Mike



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Pizzazz
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Post by Pizzazz »

Here are the rest of the shots.


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Pizzazz
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Joined: Thu Nov 28, 2013 7:39 pm

Post by Pizzazz »

Chris and all

So, except for the motor driven rotating subject stage, all adjustments
are done manually with high precision controls.

The complete stage is under tension with springs to prevent backlash.

For the Z axis, there are stops to "park" the assembly in a preset max/min
location.


My friend has another SEM, and it is interesting that it has the same
features but is implemented differently. For example, the subject stage is
simply a metal rod that has a small plate to place the subject, and when
you adjust the X or Y axis, the base of the rod moves almost like a ball
joint. However the assembly rotation has a much larger capability than
the one I have shown.

Pau
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Post by Pau »

Mike, Chris S. has provided a very good explanation of the concepts and a clear comparison with his much simpler -and so easier to understand- positioner.

I have very limited knowledge and experience with SEM and the only two instruments I've used were very different (chamber size, mechanics, electronics...) but both allowed X-Y-Z rotations and translations.
The sample holders are metal disks not higher than 5mm and the sample was glued just over them with conductive double sided adhesive tape.

If you need I could attempt to draw schemes (with lots of uncertainty)
Pau

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