Not much to say here, just that we’ve managed to get speckled scattering patterns from a surface monolayer of gold atoms.



The speckle is not very well developed, the contrast isn’t great. But it’s clearly there and very static at room temperature.

Often it is nessecary to perform an experiment where there are very few impuritiies present. Impurities can be anything, but most often they are water, air, and hydrocarbons. That’s the case for my currently little experiment. The standard approach is first not to put anything in (no bubblegum, sticky fingerprints, spare change, etc) and subsequently to “bake” your system.

Baking really is quite similar to what the name implies. You literally heat everything up to a certain temperature (depending upon what you want to do) and then let it cook for a day or two. The high temperature encourages the water molecules and other junk to come off the walls of the chamber and into the ambient vacuum. In effect this makes the vacuum much worse, but only while it’s hot. During the heating the mechanical pumps are working over-time to pull the “junk” out of the vacuum. After a couple of days you slowly bring the temperature down and the vacuum is in general much cleaner than when you started.

First, here’s a professional system in “bakeout” mode. There are large custom made fiberglass insulation plates that wrap the chamber. There are heaters with fans built into the chamber. Most importantly, everything is controlled by the computer racks next to the machine. They monitor the temperature inside and adjust the heat depending upon the conditions. Notice how nice everything looks. It’s all been designed and functions quite well as a whole.




Now you have mine (and truly, most all custom chambers). The vacuum chamber is wrapped inside a giant ball of aluminum foil. Right next to the chamber walls are strips of heater tape to provide the temperature. Home-made thermocouples are in the best places I could think to stick them and none of it is controlled by computer. I get to sit by the machine, turn the dials and see what happens. And who couldn’t love a giant aluminum foil ball that’s cooking at 150 degrees celcius?







The only real “appendages” left that are visible are inlet/exit valves for the gas dosing into the system. The base of the turbo pump (the cylinder containing a giant set of spinning blades that’s pulling incredibly hard to make the vacuum) is also visible at the very top of the aluminum foil ball. I’ve had a little difficulty in getting the top-half of the chamber to maintain the correct temperature. The turbo pump is water cooled (keeping those blades spinning at 830 revolutions per second takes some effort) and needs to maintain a reasonable temperature to operate. Since the rest of the chamber needs to be hot for the cleaning process, there’s quite a bit of additional “heat loss” from the turbo pump cooling and a stiff heat gradient from the hot to cold regions.

You might wonder how much aluminum foil I wasted while wrapping this creature... The answer is actually none. We have a box of aluminum foil that has been passed down from post-doc to post-doc for exactly this purpose. It’s fully reusable for this (and many other functions). Once I’m done it is all carefully unwrapped and stored for the next time we need to bake something.

With the advent of the new version of Rapidweaver, along with progression in the (slow) transition from my old laptop to my new one, the website has changed appearances. Eventually I’d like to make it look similar to the old style, but for now a plan “vanilla” has some appeal if for no other reason that it looks reasonable with little effort. So there you go.

Part of the reason for the lack of entries lately has also been this transition between computers as well as a very busy time at work. More about that soon.