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    • Good question! The problem is that the oxygen concentration in the chamber really does need to be extremely small. The nitrogen would have to be so pure that the density of oxygen contaminant is less than the oxygen density in air pumped down to UHV. At atmospheric pressure, there are about 10^25 molecules/m^3. At UHV, this drops to about 10^13 molecules/m^3. This means you’d need nitrogen that’s around 99.9999999999% pure! I’d imagine that trying to flush out/purge all the air from the chamber would also be extremely difficult.


  1. Pingback: A home-built scanning tunneling microscope with atomic resolution | Dan Berard



      • Dan, First I’d like to thank you for posting such comprehensive work that easily translates to the home/hobby shop tech. My Question is did you also make a High Vacuum Chamber to inspect samples that readily oxidize?
        if not, what are some off the top of your head ideas one should look at before beginning on a design concept. can you readily identify any of your components that would fail under vacuum? I see one area of caution in; The adhesives being used cannot contain ensonified gasses. (solution: perhaps curing under vacuum?)


      • The trouble is, high vacuum isn’t good enough, it really needs to be ultra-high vacuum. There’s an excellent explanation of why that is here:
        Higher vacuum levels reduce the time it takes for a surface to oxidize by reducing the number of gas molecules colliding with the surface. In high vacuum, a surface like silicon will still oxidize in a matter of seconds. In UHV, it will last much longer.
        UHV typically requires at least 3 pumps: a roughing pump, high vacuum pump (like a turbopump or diffusion pump), and a UHV pump (like an ion pump). Pumping to UHV can be very time consuming, which makes tip and sample changes much more complicated.
        As for adhesives, the ones I used (e.g. super glue) aren’t UHV compatible, but there are epoxies available that are. I’ve never worked with UHV before so I’m no expert on this stuff.


      • On the other hand, if you just wanted to obtain low temperatures (e.g. LN2 cooling) and didn’t care about oxidation, then UHV probably isn’t needed. In that case, you’d just need some level of vacuum for thermal insulation and to prevent condensation/frost forming on the sample.


  3. So awesome!
    Will you be able to flip out atoms from the lattice, aplying a higher voltage spike? I bet that if you can and draw HaD logo…you will be an epic win of the decade. XD


    • Good idea! I’ll definitely try to figure out a way to draw patterns on the surface! Might not work with graphite though, since all the atoms on the top layer are covalently bonded to each other, but it’s worth a try.


  4. Here from HAD – one suggestion to damp out high frequency vibration is simply … an inner tube. We’ve done some holography work (very vibration sensitive) using high mass steel plates and placing them on small inner tubes. Gets rid of all but the very low frequency stuff.


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