SEM Buildblog

BRB playing with rockets

Mon, 25 Feb 2013 20:33:00 -0700

Sad and excited to say that the HSL SEM project is on the back burner (but not on hold! Big difference!) while I send some things to the ISS.

BRB. (Go Antares!)

My talk at EHSM 2012 Berlin!

Sun, 30 Dec 2012 18:45:00 -0700

My talk at EHSM 2012 Berlin!

TIG Welding for Fun and Profit

Thu, 13 Dec 2012 22:48:00 -0700

So I recently championed the acquisition of a nice TIG welder at the Heatsync Labs hackerspace (special thanks to Karl at K-Zell Metals for getting us such a good deal). I want us to always be able to make anything, even space ships, so I want us to have the tools we need, be it laser cutters or TIG welders. However, my real reason for wanting a good welder was to weld vacuum chambers, fittings, tee’s, etc.

I’ve since discovered that I’m not very good at welding. But I’m trying. Which illustrates exactly my passion for this project! The SEM project truly encompasses every conceivable form of fabrication that I can think of. Digital electronics, power electronics, high voltage, RF, analog front ends, welding, machining, vacuum physics, mechanical assembly, materials science, particle physics, electromagnetic software design, human interface systems… the list goes on and on and on!!

Literally everyone who walks into the hackerspace has something, or more realistically, multiple things to offer this project. I have learned so many skills by passionately chasing this dream around for the past two years and for that I am so thankful! I am thankful that a creative community such as Heatsync Labs, and the entire maker movement in general, exists. This is something that didn’t exist when I was little, and to be a part of it is awe inspiring.

Whew! Yeah ok I’m done, for now ;)

EHSM! on Flickr.http://ehsm.eu

Wed, 12 Dec 2012 11:45:02 -0700

EHSM! on Flickr.

http://ehsm.eu

it happens on Flickr. Sh— er Crap. Electron gun Mark II...

Sat, 15 Sep 2012 09:04:00 -0700

it happens on Flickr.

Sh— er Crap. Electron gun Mark II bit the dust because someone forgot to tell me that glass is brittle and not at all flexible. Who knew? But we just utter some colorful words and smile and make it again, amirite?

Electron Gun Mark II

Fri, 14 Sep 2012 11:02:00 -0700

I kicked around a few ideas about how to build a free standing “developmental” version of the gun, with an improved rigid support structure. Also shows is an all-metal version which should prove to be better as a final version, though it sadly hides the entire discharge tube from sight and therefore is not a good candidate for a “development” item. Call it future idea #7633…

HDPE is not the best material for a high vacuum, but it does OK under low vacuum… conditions. It seems to be the best readily available material except teflon, which I admit I was lazy about acquiring. Having huge blocks of HDPE at the hackerspace already…. well at 2 AM sometimes you just need to hack!!

A quick search on http://outgassing.nasa.gov/ shows that HDPE is actually not bad at all, total mass loss (TML) is 0.22% per day and condensate (CVCM) was 0.04% of that. Low outgassing is defined as TML < 1% and CVCM < 0.1% and HDPE certainly qualifies for this, though its thermal properties leave much to be desired. Bake-out is not really possible with HDPE, but I am OK with this for now.

A quick lathing operation and a cleanse with some brake degreaser and the gun is ready to go. Except I don’t have a pic of the finished gun. Why don’t I have a pic of that…. Hang on…

Electron Gun Mark I on Flickr. yes, I realize the tungsten...

Thu, 13 Sep 2012 10:50:00 -0700

Electron Gun Mark I on Flickr.

yes, I realize the tungsten electrode is off center. You try precisely lathe boring natural rubber! It kinda moves all over!

A Better Cold Cathode Electron Gun

Wed, 12 Sep 2012 09:01:00 -0700

Time to make things better. The first prototype cold cathode electron gun used a piece of aluminum foil as a beam aperture. Talk about a not at all precise piece of optics. The new Mark I gun uses a lathe turned rubber stopper to support a piece of lathe turned tungsten and a small peiece of #32 AWG wire to bias a lathe turned aluminum anode with a 0.46mm aperture.

Interestingly enough the electron spot is much larger even though the length of the exit aperture is longer (more tunnel, less hole in foil) but it IS larger in diameter. Not to worry because a larger divergence (high optical numerical aperture or N.A.) actually means a smaller spot size once we start using the lenses to focus things down. But it makes me wonder if there is some scattering off of the inside walls of the aperture bore. Hmm…

But there are still problems. The rubber stopper is very difficult to center and likes to wobble. Its impossible to keep the electron gun on center and the spot wanders because of this. More than once the glass tube supporting the gas discharge fell off inside the beamline and had to be fished out after damaging the phosphor coated detector. Also, the aperture is jam fit to the glass and has caused the glass to crack more than once. Its a bad idea, the whole assembly really needs the be rigidly attached. Mark II is on its way already… But its still progress, and its still really pretty to see!

Oh, and please ignore my crappy attempt at a beam current detector. It really didn’t work at all. Which makes sense considering how low the beam current is.

An Awful Horrible Deliciously Hacked Up Electron Lens

Wed, 12 Sep 2012 08:39:11 -0700

Its not pretty. (Is… is she using a… harbor freight clamp to hold the lens at the focal point? yikes…) I’m sorry, because, it is in fact indeed awful and horrible and hideous. Its arguably uglier than my current divorce… (hilarious! … *crickets* …*clears throat*) But you know what it is?

Its a gap-solenoid electron lens! Its a baby step, and I might even go so far as to say that it is even more than just a baby step because it is an electron spot, and an electron spot is exactly what an SEM needs to be… well… an SEM! But its also a low-vacuum electron spot and totally affordable and hackable electron spot. Its.. its progress!

The lens consists of a piece of lathe turned 1018 steel. Its a spool shaped central piece which is cut in half to allow for a small 1mm thick brass washer to be inserted. The 500 turns of #20 AWG magnet wire is wrapped around either side of the gap washer and a sleeve of lathe turned 1018 steel is slid over and clamped onto the spool shape. The end result is a bit like a hollow donut with 0.070” thick walls and a rectangular cross section instead of the familiar circular one we all know and love and dip in coffee. Except its steel.

The resulting focal length is about 6 inches with 800mA of lens current at the 10kV acceleration voltage. The actual beam energy has yet to be measured and is surely less than this due to the voltage drop across the plasma used to create the beam. This is probably somewhat excessive and the number of turns should be doubled to reduce lens heating. But it works for now so I don’t really want to touch it.

Happy Accidents

Sun, 10 Jun 2012 20:03:48 -0700

What happens when water gets into the beamline during a leak check? Amazing accidental plasma art!!

Cold Cathode Electron Gun Part 1

Sun, 10 Jun 2012 19:54:00 -0700

Please bare with me, this narration is coming from the past. I try to always take pics and document everything but life happens and the blarg doesn’t get updated and then I have to do this :)

Using what I saw on Mr Styner’s amazing and truly humbling website, I constructed a simple experimental electron gun using a copper wire in a capillary tube, a rubber stopper, and a turned stainless steel needle. Its really not even worth describing what I did because it looked horrible and didn’t even work. It did make a nice discharge tube tough. Mmmm delicious nitrogen plasma… Several things were wrong, the polarity of the chamber vs the gun caused the plasma to extend all the way down the beamline. Also, it was an unfocused electron spray, not really a directional spot.

With try number 2 I decided to actually put a little work into it. Ugh! You know how lazy I am… ;) I attempted to create an inverted design, so instead of shielding the accelerating anode wire I shielded the discharge area, with the tube within a tube design shown above. One of the huge problems with the stainless steel needle was the rate of sputter coat. The glass was almost black with metalization after only a short period of time, tens of minutes if that. I used a 1/16th inch TIG welding tungsten electrode for the cathode, and a piece of aluminum foil with a pinhole poked into it for the anode. The pinhole wasn’t very round and I really didn’t measure it… But oh well.

The supporting structure is a lathe turned rubber stopper. Yes, to my surprise you really can lathe natural rubber stoppers quite well! Go figure! I lathed a nipple for the small glass tube and a shoulder for the beamline tube. A 5C collet was used to hold the rubber stopper (mostly centered.. it is squishy rubber) and a hole was drilled for the main centered tungsten cathode. a small 30 gauge wire was pushed through the stopper for the anode. No epoxy was used, the rubber made its own seal which didn’t seem to leak horribly.

I applied about 10kV using a flyback transformer driving from a 12V 1.5A laptop power supply through a 10 megaohm 5 watt resistor to the cathode and I grounded the anode. A target was constructed using a stainless steel rod coated with powder from the inside of a CFL and placed into the beamline tube.

I was nervous as all hell during pumpdown using only the roughing pump.. I could see the Faraday space of the discharge tube getting longer and longer and longer until it touched the anode… then I looked down and saw a faint orange (orange? what the hull? everyone knows electrons are green…) spot appear on the target!! It was… really off center, but who cares. As I watched it grew brighter and brighter and brighter until it winked out all together as the discharge went out. Oh no did I blow a power supply?!?! Nope, the vacuum just became too deep. No worries, shut off the pump, wait 5 minutes, hey its back again!

ELECTRON BEAM SUCCESS

(Shh, I know its not focused yet, we’ll get to that later!)

Inspiration From an Old Hacker Hero

Sun, 10 Jun 2012 16:13:00 -0700

More about the cold cathode low pressure electron gun I spoke of in the last post.

The inspiration to even try a low pressure electron gun came randomly, through the usual exploratory google search. However, I wasn’t searching SEMs, electron guns, or even vacuum physics…

I was helping Erica build a theremin, and randomly stumbled across Mr Nyles Styner and his EWI (Electronic Wind Instrument). Now I’m familiar with Mr Styner’s amazing musical and electronic work. However, I was not familiar with his physics and vacuum science work. I somehow stumbled across this page http://www.sparkbangbuzz.com/crt/crt6.htm and of course I’m not going to distract from his work so PLEASE VISIT THIS LINK TO UNDERSTAND HOW AMAZING THIS MAN REALLY IS!!!!

After getting very excited and watery eyed and letting my more girly side show for a moment, I realized that THIS WAS THE ANSWERR! The PERFECT way to generate an ebeam that could be focused down and rasterized across a sample without drawing a deep vacuum and without needing fancy high current superimposed power supplies!! Demystify technology! Come on people lets do it! Awe crap I’m getting tears in my eyes again <3 <3

Science and hacking is all about collaboration and empowerment and that my friends is the ENTIRE POINT of this ENTIRE SEM PROJECT as well as the hackerspace movement in general. Community, inspiration and circular creativity. My heart just melts away and tears come to my eyes with the realization of and truth behind this latest sparkle of a twist in the direction of this SEM… Maybe I shouldn’t blog when I’m near my period?? *wipes tears*

Why is this such a good idea? This is a good idea because this does NOT require the use of a turbomolecular pump. Turbo-molecular pumps are not hack-able. Turbo-molecular pumps are not cheap and they are not replaceable. Frankly, even the roughing pump we currently have will draw too deep of a vacuum for this method.

Onward!!!

Completed Vacuum System on Flickr. Hey look, its a fully...

Sat, 09 Jun 2012 17:12:00 -0700

Completed Vacuum System on Flickr.

Hey look, its a fully functional vacuum system!

What does that mean? That means that the turbo-pump and the backing pump have their own lines into the chamber. The chamber can be roughed, then switched over to turbopump control if needed.

So what’s the plan from here? The plan is to develop two beamlines. The first beamline will use a cold cathode emission system which operates at low pressures and uses the residual air in the chamber and a HV DC source to form a plasma from which electrons are harvested and injected down into the optical system.

The second beamline will be a standard thermionic emitter using a tungsten hairpin filament and a high current DC source. The downside of this is that the system needs to be running at high vacuum which means turbopump. Turbopumps are nice, but they are not hackable. We can’t go get one for less than the price of the entire completed system, and that’s just not the point!

DV-6M with turbopump calibration and leak test on...

Sat, 09 Jun 2012 16:37:37 -0700

DV-6M with turbopump calibration and leak test on Flickr.

That’s the power of ~~pinesol~~ turbomolucular pumps!

This plot shows the leak rate of the chamber over a 100 minute period after a quick pumpdown using the turbopump. It leaves much to be desired, but its not bad for never having been baked out or electropolished.

Steel machined Vacuum Valve Knob by hslphotosync on Flickr. The...

Sat, 09 Jun 2012 15:49:00 -0700

Steel machined Vacuum Valve Knob by hslphotosync on Flickr.

The Art of Scrounging and Hacking or Time vs Money.

It just so happened that these cheap high vacuum pneumatic valves were on ebay for $60 apiece. What a steal. Let’s convert them to manual by adding a lathe turned knurled steel knob!

And of course, should you ever want to do this yourself here’s what the steel knobbie looks like drawing on purple engineering paper.

Scanning Electron Microscope Project Update

Tue, 27 Dec 2011 10:54:00 -0700

Scanning Electron Microscope Project Update:

As presented to Heatsync Labs, the home of the HSL SEM!

Turbomolecular porn by hslphotosync on Flickr. The...

Fri, 23 Dec 2011 22:56:00 -0700

Turbomolecular porn by hslphotosync on Flickr.

The turbomolecular pump has been attached! The largest flange on the chamber is a KF-50 for various reasons including cost of fitting hardware. Above this size, ISO fittings must be used and these are much more expensive than the KF style.

The turbopump that was donated to the project uses a 4.5” CFF conflat style metal knife gasket mount. 4.5”CFF to KF-50 adapters are several hundred dollars so it was decided instead to machine an adapter out of aluminum and use a square lathe-cut viton gasket instead of the soft metal gasket. The gasket was purchased from ANCorp for $14.50. The 3x5” aluminum stock was purchased from Industrial Metal Supply for $22. But of course nothing is free, the 10 hours or so it took to machine the piece is worth something right?! Luckily time IS free!

The profile of the piece was turned first, with the KF-50 end on one side and a square shoulder on the other.

Though I suppose its not completely necessary when using viton rubber instead of metal as a gasket material, I attempted to machine the knife edge into the face of the CFF half. The circular sawtooth would normally bite into a soft copper gasket but of course that’s not possible when using aluminum for the flange material as the aluminum is too easily deformed. Stainless is too expensive and I’m not sure I have the skill required to pull it off just yet… The knife edge came out OK, though slightly over sized. I must’ve been tired or something.

Finally the hole pattern was added using a mill and a (horribly undersized) rotary table. A very long day at the lathe, and a somewhat tired yet nonetheless glorious victory!

Edit: If I made this piece again, I would probably have attempted to make it tapered from the CFF bore to the KF-50 bore. If I ever come across enough free time and another hunk of metal I might just try to machine another one and compare the pumping speed between the two.

Compression Fitting Assembled with BA Gauge The BA gauge which I...

Fri, 23 Dec 2011 19:46:00 -0700

Compression Fitting Assembled with BA Gauge

The BA gauge which I want to use to measure the ultimate vacuum level is a glass tube type and lacks a flange. The solution is either to torch a metal fitting out of kovar (expensive) or to use a simple viton O-ring compression fitting. Since the latter isn’t destructive and I don’t yet trust my glassblowing skills, I went with the compression fitting.

Instead of buying a compression fitting from a vacuum supplier, I decided to go ahead and turn one on the lathe for practice. The combination of threading, tight tolerances, dissimilar materials and knurling made this the most advanced lathe project I have yet taken on.

An exploded view of the pieces is shown below

In order to prevent any burrs in the threads of the steel nut, a thread form was turned and is shown below. Made from the same steel, the threads were worked against the nut threads under force for multiple mate demate cycles until the motion was smooth.

And finally a photo of the gauge connected to the chamber. Just one step closer :)

Edit: If I made this piece again I would have added a small internal shoulder for the neck of the gauge to sit on so that it couldn’t be pushed all the way into the flange and potentially hit things inside the chamber.

High Voltage Feedthrough Experiment on Flickr. So it turns out...

Sun, 25 Sep 2011 23:20:00 -0700

High Voltage Feedthrough Experiment on Flickr.

So it turns out that spark plugs make terrible high vacuum devices, and this became quite apparent before even introducing one into the chamber. While attempting to “alter” one on the lathe, the metal sheath became very loose and it was evident that there was neither an o-ring nor any sort of sealant nor braze connecting the ceramic core to the metal jacket which contains the threads.

A couple of lathe-hours later…

“Yo dawg, I heard you liked holding work-pieces so I put a chuck in your chuck so you could use inner jaws while you use outer jaws”

Upon discovering this I simply removed the entire jacket and turned the profile of the Al2O3 core into a custom KF-25 flange. The fit was so snug it required a special jig just to remove once I had “test fit” the part.

Add in some hysol 0151 low out-gassing epoxy and viola! A high voltage feedthrough :)

Vacuum Leak Plot annotated on Flickr. The HSL SEM Chamber has...

Thu, 08 Sep 2011 17:30:00 -0700

Vacuum Leak Plot annotated on Flickr.

The HSL SEM Chamber has several tiny pinhole leaks in the welds. The pinholes were detected by spraying the welds with isopropanol from a spray bottle and watching the response as the alcohol leaked through and then vaporized (and spoiled the vacuum momentarily).

Here I stand, mighty spray bottle in one hand, and determination in the other :) (Photo by Erica Weems)

As you can tell from the plot above, painting the holes with clear nail polish (nitrocellulose laquer) while under vacuum made a nice seal as the liquid was pulled through the leaks and solidified. The DV-6M gauge was brought to 10mV which indicates ~10^-3 Torr.

The next step involves getting cheap surplus valves to seal off the chamber and estimate leak rate in prep for attaching the turbomolecular pump to the system for an ever deeper vacuum. WE NEED TO GO DEEPER!