At the end of the week we took our gold samples out of the x-ray beam and looked at them with an atomic force microscope.

The sample above is actually a bit junky looking, but has some interesting features. Anyhow, I thought it made a fun enough picture to post. Though the sample appears both flat and clean to the eye (even under a high powered optical microscope), the AFM gives a great deal of detail and features. The terraces are clearly visible in this picture showing that the sample is indeed not extremely flat. There are also small bumps and nodules over the surface and some curious looking little sticks.

We're doing something rather ambitious and, for the moment, it's working. Usually to perform our experiments we need to run at the synchrotron. However, we have our own x-ray source in our lab. It's dismally dim compared to the synchrotron, but it's ours. And as far as rotating anode x-ray sources are concerned, it's actually not too shabby. Our goal : successful surface scattering from our rotating anode.

We've had a huge number of problems in this process. I'd hoped to start taking data on Saturday, however it wasn't until today that we actually got really started. In all honesty, the solution to our final problem turned out to be double-sticky tape. Don't ask.

And so... here it is :



The smallish bump on the left indicates a well ordered surface, though it doesn't tell us exactly what the surface is. The bump on the right is a little more important. The only reason it should be there, and so strong, is if there is a hexagonal surface layer of gold on top. The fact that we're able to get both signals at once, from our little rotating anode x-ray machine, is very nice. The fact that we've got it will let us do further experiments without actually having to go to the Advanced Photon Source (well, as much).

In order to get this signal we have to run our machine at full power (12 kWatts), optimize all the positions and slits to minimize noise, flood the entire beampath with Helium gas to cut down on parasitic air scattering, and more. And of course... we've got to have a reasonably well prepared sample in the first place. The fact that we're using gold, where each atom has a large number of electrons, also helps us a great deal.

I've been a bit busy with things at the lab since we returned from our road trip last month. Many things have been unattended, and while I've actually written a few entries for the blog, they've never actually been posted. So kind readers (both of you), please excuse a few back dated posts.

We've been trying to wrap up our experiments with gold surfaces, at least to the point of having a good story worth writing. It's there, we just need a little extra work to have it all tied together nicely. There's usually some question of where to draw the line and write up your results. It would always be better to have and know more about what you're studying, but it also would never get published. The reverse of writing up every little step of progress is also to be avoided. In the words of Pliny the Elder, "...do what is worth being written, and write what is worth being read." (or something to that affect).

So we have decided on exactly what we need to put in our current paper and are attempting just such an experiment. The really exciting thing is that we've figured out a way to do it in our own lab! We have a rotating anode x-ray source set up with a full 4-circle diffractometer. Normally this is used to test things out before running at the synchrotron and provides us a nice way to characterize our sample quality ahead of time. However despite this being a very bright rotating anode source, it is still dismally dim compared to the synchrotron (ballpark, let's say a million times less photons). It also is essentially only capable of making a handful of different photon energies and changing between the energies requires a few days of effort.

But, let's say you already know almost everything you need to know. AND you've figured out exactly what you want to study, knowing exactly where you should find it. At the beamline this could be done with a scan that takes... let's say a minute. While synchrotron time is expensive, rare, and better used for other things, we can run our own dim x-ray source as long as we wish. So, that 1 minute stretches to an hour, which stretches to days, and ultimately let's say a week. That puts us at a factor of 1/10 the signal we could get during one of our beamline experiments and is entirely within acceptable limits!

We tested it this weekend and were successful at seeing the signal on a test sample! So at this point we need to get a good sample in the our beam. I prepared a sample all weekend and then tragedy struck this morning. While making the final adjustments before putting the sample in the experiment, I shattered the quartz and dropped the sample. Gold single crystals have a consistency very similar to butter. The fall from a few feet was enough to obliterate my precious (golum!). So, sadly, I'm preparing a new sample. Hopefully we can try tomorrow to start the experiment here.

Once we've done this, we're fairly confident that we can write up our results well enough. We've also been doing some very different experiments that confirm what we've already seen. It's certainly nice to have the extra proof, we're hoping to extend this in a new direction not previously possible. The new experiments involve a great deal of vacuum work. Instead of x-ray diffraction and scanning microscopy, I've been trying electron diffraction and photo-electron spectroscopy! Both are quite nice and deserve a bit of explanation, though I'm afraid that will have to wait a bit. However, you can see an example of the electron diffraction in the titlebar-mosaic above. It's the first picture on the far left.