We’ve got an interesting experiment almost ready to run. But what I’m finding the most fun about it (at the moment) isn’t so much the subject being studied. Rather it’s that we’re doing it in our own x-ray lab and without a visit to a synchrotron.

In truth, that’s not entirely fair. The question that we’re looking to answer has to do with something we saw during a beamrun at the Advanced Photon Source (or more precisely, something we didn’t see while we were looking for it). However, I think it is something we can resolve with the tools available in our own lab. Even if it’s an anomaly we cannot explain, we can at least investigate it a bit further.

So, what is fun about it? Well, it’s a full experiment complete with vacuum chamber mounted on a diffractometer, lots of diagnostic equipment and it’s all going to run with our “little” x-ray machine downstairs. The little x-ray machine is in fact not so little. It is still a 200 kiloWatt monster. In december a couple of my colleagues expended a great deal of effort to set things up and get it running.

We’re now almost at the point where we can begin doing the actual experiment. There are still a few bugs to be worked out. We’ve suffered the loss of 3 different computers within the space of a month (2 hard disk failures and 1 unknown). This has given us a bit of difficulty maintaining proper control over the instruments. We’ve also had a small problem keeping the diffractometer aligned properly, though that appears fixed for the moment.

Yesterday I began bringing the x-ray source online and checked it out. This morning it looks ready to go. I also checked most of our sample preparation and modification equipment and that seemed ok. The only thing left to bring online is a piece of equipment that measures various gas concentrations. Once that is done, it will be time to try to establish the conditions over the sample surface identical to those that we had in November. When we’ve achieved that, then we can measure some of the surface properties with the x-ray machine and see what they tell us.

... well, for the physics world anyways.

Last week our latest paper was published in Physical Review Letter (PRL) and I promised to write more, though I wasn’t quite expecting to say this. Our letter was used as the cover article for that issue. So if you go look at Vol 103, Issue 16, then you’ll see two little hexagons at the top of the page. That’s from our article and is part of Figure 1.

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Surface X-Ray Speckles: Coherent Surface Diffraction from Au(001)
M. S. Pierce, K. C. Chang, D. Hennessy, V. Komanicky, M. Sprung, A. Sandy, and H. You

Published 15 October 2009
165501  Full Text: PDF (526 kB)  | Buy Article

We present coherent speckled x-ray diffraction patterns obtained from a monolayer of surface atoms. We measured both the specular anti-Bragg reflection and the off-specular hexagonal reconstruction peak for the Au(001) surface reconstruction. We observed fluctuations of the speckle patterns even when the integrated intensity appears static. By autocorrelating the speckle patterns, we were able to identify two qualitatively different surface dynamic behaviors of the hex reconstruction depending on the sample temperature.

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First, I am ecstatic about this news. In fact, I’m ecstatic just to have another paper published in PRL. Making on the cover is something else! This is my third PRL, but it’s significant for another reason as well. This is solely from my work at Argonne and, while a “coherent x-ray scattering experiment,” it is significantly different from my first two which came from my thesis work. It’s an important step to show that my publication record and potential is not totally tied to just one thing (be it thesis or post-doc). My choice to switch fields so drastically from my thesis work has been a hard decision to bear (both for me as well as those that I work with). It was a gamble, but I believe it has paid off.

Now about that figure. I’ve posted similar versions of it before on this website to help explain some of the features of the surfaces we study.

The figure is a representation of the two possible orientations of the surface atoms on a gold crystal cut along one of the cubic directions. Instead of maintaining the underlying face-centered-cubic structure, the surface atoms rearrange (reconstruct is the term we use) into a hexagonal pattern. Now, if you think about it, you there’s not a single preferred way to lay down a hexagon over a square. Cut out a square and hexagon and see for yourself. If you try to align two of the hexagon sides with two of the square sides, you’ll be left with points of the hexagon protruding over the other two sides of the square. Now, rotate the hexagon by 90 degrees (1 quarter of a turn). The hexagon sides that used to overlap will now have points over the square edges and the sides which used to be points will now be aligned with the square. So you can see, there are two equivalent ways to lay down hexagons over squares. Nature is no fool and so naturally our crystals contain surface regions with each of the different orientations. In a nutshell, that’s what the figure is meant to show (or remind the scientists reading the article).

Perhaps it’s easier to see if I rotate the entire figure by 45 degrees.

The only detracting thing here is that all of the above is not new. In fact, it’s 30 years old more or less. What we did was to observe changes in those hexagons in a clever way. But we were not establishing the existence of the hexagons.

In truth I did lobby a bit for a different figure. We were informed earlier in the week that our paper was being considered for the cover art. “Considered” is still a long shot and I was gratified to have the article be up for consideration, but wasn’t hoping for too much. They requested high resolution copies of our Figure 1 (which I sent). But I also included higher quality versions of some of our other figures which I thought were quite aesthetically pleasing, but also show cased some of the newer results. Figure 1 was just too pedagogical for my tastes. But in the end I was only willing to push so much for fear that it would remove our slim chance.



This is the basic figure I was lobbying to be modified for use. Right now it still has too many labels and numbers to be cover art, but ignore those for a second. The vertical “component” of each is collection of speckles. Where a speckle is bright, the plot is red. Where it is dim (or absent), the figure is blue. The horizontal direction in each of the 3 plots is time. So, if a speckle is bright (red) and unchanging with time, then there will be a red streak in the horizontal direction. If the speckle is changing, then the red will change to some other color and other places, not previously bright will begin to show red. If it’s rapidly changing then there will be only short periods of persistence of the speckles. That’s what you see in the 3 figures. What could be labeled, hot, hotter, and really hot. On the left the speckle is not changing very rapidly. On the right you see very rapid fluctuation. The middle is well, somewhere in the middle.

Anyhow, get rid of the numbers, massage them a bit, and you’d have an aesthetically pleasing image that contains the core of the new science that we did.

That aside, figure 1 is a nice graphic and I’m of course very happy they decided to use it. The “atoms” are raytraced using the open-source POVRAY package. In fact, coupling the graphical rendering power of POVRAY with the mathematical ability of Matlab can make for some very beautiful (and complicated) images. By ray-tracing standards my little pictures are not anything special. In fact, compared to some of the computer rendered artwork out there, these images are plain bland. However, they’re still pretty in their own right, and have some content to them. They’re also much nicer than any of the normal simple chemical rendering programs out there. So thank you to the people that wrote POVRAY.

Wow! I am simply giddy at the moment.

Our new paper has just been published in Physical Review Letters : Surface X-Ray Speckles: Coherent Surface Diffraction from Au(001).

This is just wonderful news. I’ll write more later about it, but for now I’m just giddy.

Welcome to another installment of “Michael likes to make graphs, plots, and figures.” Here’s one of my latest:

It’s latest in an unusual sense. It’s not the research work that I’ve been doing recently and is not even data taken in the last couple of years. But it is data left over from my thesis work. We’ve had a paper that’s been, well... languishing, for some time now. However, there’s been a nice little lull over the past weekend and I’m very excited to finish off this paper.

So what are you looking at above? Basically our friends Olav and Eric grew a series of 6 magnetic samples with increasing roughness (disorder), but otherwise identical. The higher the pressure during sample growth, the more disorder in the samples. On the left you can see reflectivity curves (literally measuring x-rays reflected specularly from the sample) for a few of the samples. The two low pressure (3 and 7) show nice fringe structure, well defined peaks, and slower decay. The two shown high pressure samples show no (or little) fringes, weak peaks, and quick decay in the scattering. All of that tells us some of properties as the disorder increases. On the top right is a plot of the magnetic domain structure imaged using a magnetic force microscope for all 6 samples. For the lowest disorder samples there is a well defined domain structure and for the high pressure samples the domains get more disordered. The bottom right is a plot of the surface roughness of the samples. Those data points are actually determined from the plot on the right hand side.

Actually the above figure is one of the “background” figures that we use to explain the basics of what went into the experiment. So there’s not anything new in it. Nonetheless the figure came out nicely and I thought it deserved to be immortalized here.

We’ve just gotten word that one of our papers has been accepted to Physical Review Letters. The preprint is available here on the arXiv servers : cond-mat : 0909.2273. The paper deals with our work on studying the surface reconstruction of gold using coherent scattering techniques.

The short story is that we’re able to get access to how quickly the microstate (the microscopic configuration and profile of the surface) is evolving even when the average properties of the surface are not changing. We’ve been able to collect speckled scattering patterns and, by comparing how fast the speckles evolve, determine some new information about the surface dynamics. This was principally a demonstration experiment that happened to have some nice results along with it. We’re now working to extend this technique to a few new samples and system combinations.

Surprisingly I did not have my usual multi-hour fight with the arXiv server either. Usually it takes countless attempts, anger, meditation, bribery, and some things I should not admit in order to get through the automated paper submission process. But for some reason this time it happened without a hitch.

One of the fun things about papers is creating the figures. Well, sometimes it is fun, and sometimes it is tedium. However, the results are sometimes quite nice. The little thing above is a ray-tracing example or ``cartoon” of the two different surface orientations of a hexagonal arrangement over the square facet of a face centered cubic arrangement.

Actually, that’s a nice way to begin to explain the header graphic for the blog (at least the current one). If you notice the two hexagons are offset from each other by a rotation of 30 degrees (it’s actually a 90 deg rotation, but 30, 90, 150, etc... are all the same. That is called symmetry, but it takes too much digression for the moment). Each hexagon has 6 corners. Though for our purpose, it’s better to think of each hexagon as having 6 possible orientations. But since there are two was of laying the hexagons down over the squares, you get 12 total possible orientations. These orientations can all be made to satisfy a diffraction condition.

The graphic below is an example (albeit a computer generated one) of what such a diffraction patter would look like.

There’s a bright region in the center, but let’s ignore that for a moment. Instead, count the number of bright spots going around in a large circle. There are 12, one for each of the possible orientations. To be fair, this picture is as if we are diffracting photons through the sample, instead of off of the sample (we reflect them).

Wow... well, we’re done for now.

My project was running at beamline 8 and we took an enormous amount of data. It was very hard work, but I think we got some very interesting results. It’s not going to be easy to analyze, but it should be quite rewarding when finished. We managed to get a very exhaustive look at our two primary objective samples in a variety of different conditions. With our remaining two days we managed to do some exploratory work on even a couple of our backup samples. Usually the backup samples only come out with the primary things don’t work. In this case we managed to get so much done during the first 5 days that we could call the most important things “finished” (at least until a complete data analysis can be done) and that it would be worth it to look at a couple of new things.

I’d prefer not to discuss any of the details at the moment as it’s both very new and not understood. But we managed to continue to extend coherent scattering work onto new surfaces and new/different systems. The above picture is no secret though. The glowing white hot thing is a platinum single crystal being prepared. It is annealing at a temperature of ~1700K, hence the glowing so brightly. If you look carefully you can see that the top of the crystal is flat. That’s the surface of interest for this sample and it’s been cut and polished along a particular crystal facet. You can also see the heating mechanism (the 2 turns of a copper coil) and the quartz pedestal holding the sample.

We’ve seen some interesting features with Zinc oxide, but it’s way too early to tell if they’re meaningful or not. We’ve had a small issue with some of the ZnO samples and while those are being reprepared we’ll switch back to Au for a bit longer. There’s hope that maybe we can get something from it. I wish I could be more descriptive about what’s going on, but I’m more than just a little tired at the moment.

Today has been frustrating as well. We’ve switched to looking at Zinc oxide surfaces while we consider what’s going on with my gold samples. However, things have not gone as planned. Getting a properly prepared surface on a metal oxide is considerably more difficult (in my opinion) than my metal crystals. That struggle has taken quite a bit of effort.

For a while I thought I’d found something really cool. I had weak diffraction peaks at forbidden locations which is (sometimes) and indication that there’s a small ordered surface layer or adsorbate. Sadly in this case it was not that, rather it was just higher energy x-rays playing havoc.

We use a device called a “mono-chromator” to select out a particular wavelength of light. In principle it works great. It uses crystal lattices to diffract the initial beam. Only photons with the correct wavelength make it through the reflections from the crystals. However there is a problem... It can’t tell the difference between photons of the correct wavelength and photons with only half that wavelength and other integer fractions of smaller and smaller wavelength x-rays. These phonies get through the monochromator and also hit our samples. Now, the real problem is that the same mechanism that let them through the monochromator also diffractors them up at times into our detector. The detector can be set to not count them, but very often they can get counted anyways as things are not perfect. So instead of finding something new, all I really saw for an hour were peaks due to these rogue photons of shorter wavelength.

Things like that happen in science. It’s not an easy process. Often at first when you think you’ve found something interesting it later turns out to be some artifact of something else. The best you can really hope and aim for is to make fewer of those mistakes (though they’ll happen) and to correct them early before you waste entire experiments on them.

No one said this would be easy... In fact, we often say just the opposite. If it was easy, someone else would’ve done it.

Sigh...

It’s been a rather unfortunate day for my little experiment. We’ve encountered a problem without a real solution, at least in the short term.

In short, the beamline has been upgraded since the last time I tried this kind of experiment. In general terms this is a great thing. The beamline now produces more light and is focused to a smaller area. Unfortunately it’s too much light... or at least too much in too small of an area. If we could spread it out more (defocus the beam) over more of the sample area, then it might still work. But for now any part of my sample the beam hits becomes fried very quickly.

So... thankfully we have plenty of quality back-up experiments that can be done and we’ll shift over to them. But it means the one I wanted to do will need to be re-thought or get the “two suns in the sunset” solution. It’s too bad... We have been so close to having the data to finish this paper and now we find ourselves unable to do the experiment anymore. If it were simply a “problem” of having too much light it would be ok, but the central part of the problem is having all of that light (and hence radiation) deposited on such a small part of the sample surface.

Things have no started particularly well. We’ve had problems with both the sample and the beam. My first sample doesn’t look at all “right” when put in the beam. It looks like gold, it feels like gold, it smells like gold (does gold really smell?), but put it in a beam and it doesn’t really behave like a duck should, ermmm... like a gold crystal should. That’s been frustrating enough, but the beamline may be giving us trouble in a new way.

Anyhow, there has been some progress. The big piece of equipment that moves our samples around is aligned and calibrated (the diffractometer). The heating equipment functions, the gas flow controllers function, and the plumbing is done for the water. Now we just need to get the sample to behave. Hopefully that shouldn’t be too hard. On a normal day that means just heating the sample up to around 1200 degrees Kelvin. At that temperature most anything that’s not gold will have left the surface and the atoms themselves will have enough heat energy to rearrange. The atoms in the bulk usually “repair” their arrangement to some extent. Gold is so soft that virtually any time it is handled the crystal begins to suffer from the forces and the crystal loses some of its regular atomic lattice. High temperatures help remove those internal clumps, stresses, twists, bunches, etc... and restore the more highly ordered spacing. However, for us the most important thing is that the high temperatures provide enough energy for the surface atoms to rearrange into the interesting patterns we hope to observe and manipulate.

Unfortunately things have not ended well for the day. As I leave the APS, turning the experiment over to the night crew, the beam has been lost and we have no light. No light = no experiment. We’ve done about all we can do without light, so it’s a matter of waiting.

and Yes, yes... it’s still October. In fact it’s not even Halloween yet. But since most of the run will occur in November, I’ll keep this as November.

I’ve got a busy month ahead. In fact, all the members in our group will be busy. We’ve got 3 weeks of beamtime at the Advanced Photon Source. The time will be split pretty evenly between the three post-docs. Happily for me, my project runs first. This should see an increase in blog entries as I tend to get wordy while sitting at the beamline.

This project will see a return to my earlier project to tidy up some loose ends for a second paper. We’re going to be studying various gas phase interactions with gold surfaces, greatly extending our first paper on the subject. We’ve almost had enough to write a paper for a while. That is we’ve seen some very interesting behavior that we just didn’t have enough time to get fully characterized with systems other than what we’ve been talking about. It’s taken a little while for us to get beamtime to finish the second part of the project (and hopefully open up a third part!). That’s due in part to two different things. First, I’ve had another project (the speckle experiment!) that took precedence in terms of my own effort. But we’ve also had a little trouble getting the time scheduled. Anyhow, that’s behind us at the moment and we’ve got time to finish this up.

It’s going to be fun in another aspect. We’re going to try an experimental technique that’s new to me : resonant surface scattering. I suppose it is similar in many respects to more traditional “in the neighborhood of a resonance” scattering techniques. But there are some subtleties here that should make for an interesting time. Modeling the data to figure out what it does in fact tell us may be the most difficult portion of the process. The other post-docs all have projects that will run too. So in general we’re going to be doing quite a wide variety of surface science experiments in the coming month.

Today was a day spent in reciprocal space. A day for diffraction.

I suppose that's not so uncommon around here, but it was still a day full of experiments. My time was divided between x-ray diffraction on a coworker's metal-oxide crystals and electron diffraction from the surface of my own samples. It's been a long day and I'll be glad to have a little rest. Tomorrow I'll come back to swap in my own sample to the x-ray beam for (hopefully) the last repeat of this particular process.

The data looks interesting, though it's not actually anything new.



These are low energy electron diffraction (LEED) patterns. I should explain what that means, but for now I'm just going to leave the pictures on their own. I should also explain what the dots themselves mean, but again... I'm tired and lazy at the moment.

The modifications I made to the diffractometer (xray detector device) seem to have worked. We took data both yesterday and today and everything seems to have held together. It's always a good feeling when some of your effort has the intended effect of improving the situation instead of breaking it further.

Sometimes things end up looking like something completely unintended.

For my recent experiments I had to put together the little x-ray scattering vacuum chamber again. The last time we used it there didn’t seem to be anything special about its appearance. However, this time there seemed something quite peculiar as I put things together. It looked very similar to an elephant or an insect.

Here I’ve removed the long hose from the front “snout,” but the effect is still there. The two largest ports where the x-rays come in and go out (which above are glass, but replaced by Beryllium windows) make the eyes. It’s got ears and a nose, along with a couple of dangling arms/appendages. In truth it really was not intended to look like something else. It’s a surface scattering chamber complete with vacuum hardware and measurement pieces, an RF induction heating system, rotating sample stage feedthrough, fine-adjust gas flow leak-valves, burst-disk, and enough windows that I can see the sample positions during the experiment.

One of my friends took one look at it and said, “Ganesh!” The name stuck. So we have a vacuum chamber named after a Hindu deity. Stranger things have happened (I recall the himalayan pray flags that routinely went up during experiments at one beamline at the ALS), but it is a little odd to have my surface scattering experiment refereed to with the proper name of a god. “How is Ganesha today? Is Ganesha’s pressure ok? Is Ganesha’s thermocouple measuring the temperature accurately?”

It turns out that Ganesha the deity is often seen as a patron of science (among many other things). So perhaps the little vacuum chamber Ganesha is not without some obtuse justification beyond mere appearance. For better or worse, the name has stuck and I surely hope that it’s not seen as offensive.

One further thought... Most of our samples involve at least some (if not large) parts made from precious metals such as gold and platinum. So there have ben several occasions where such precious metals have been “offered” to Ganesha. Thankfully he’s always returned them to us intact.

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.

Things are progressing in many ways better than expected, though we're still struggling to get to the point of doing science.

By the start of the second day, we had the sample in the diffractometer, and everything was aligned. The surface was even "kind of" located. Not bad for doing an experiment at a place where such kinds of experiments are not common.

This afternoon we made the first attempt at in-situ heating our sample. It both worked and didn't work. It worked in that things got hot. It didn't work in that I ended up melting the grounding wire. Without a grounding wire a charge will build up on the sample from the x-rays ionizing the metal atoms. A charged sample is a bad sample, hence the grounding wire.

After some discussion about how best to fix it, we settled on wrapping a small Pt wire around the sample and its pedestal. The wire then connects onto the rotation stage. This took an hour to do and a few more hours to re position the sample from the effort.

Howdy again,

We're back running at the APS doing another set of experiments. This time, however, the experiment is my own baby. We're attempting a different kind diffraction experiment from metal surfaces.

I don't have time to write much. More or less all I can say is that we're extremely busy. This is a rather new kind of an experiment, it's being done with a new chamber, and being done at a beamline where we've never worked before. Top it off with the fact that the beamline isn't optimized for a full diffraction experiment (it is however highly optimized for coherent x-ray scattering!). All together, this is somewhat ambitious.

The experiment began a few days ago in fact. The initial work had to be done in our own lab. It also means that we're going to get one shot at this, maybe two. There is a fair amount of risk involved in that statement. Preparation began with the sample and chamber in the materials science division. Aside from the usual work of preparing a sample (cleaning, degreasing, annealing) and getting equipment together (debugging, writing code, packing, testing), we actually assembled the chamber and its essential elements in our own lab. This included actually getting the sample in the chamber.

Why, might you ask, did we do all this?

In order for this experiment to work, we have to arrive at the beamline with a fully oriented sample. Or at least oriented to within a few degrees. So the whole chamber (sample and all), must be mounted on our diffractometer prior to our APS visit. It must then be removed from MSD and transported intact to the APS. This was not exactly easy. However, we made it.

Here you can see the chamber (the silver ball that has some glowing orange parts)mounted on our diffractometer(the green-blue thing). This allows us to scatter x-rays (from a source off to the right side) through our sample. By correctly positioning the sample and observing where the x-rays are scattered, we can determine the relative position of the crystal sample.




Here's something of a closer look at the inside of the chamber. The crystal is held, inverted on a long quartz pedestal. Yes, it really is held upside down. The erie glow just happens to be the light behind the chamber.

Things are.... well at least they're going.

The problems we had last night eventually required replacement and realigning of the flight path. That was taken care of and the day crew took a nice several nice sets of scans at room temperature. Our goal for the evening was to take a series of the same scans at elevated temperature. Unfortunately the heating element obliterated the sample. sigh... So we're just about to finish a second set of room temperature data before being fully recovered and taking the high temperature data. But at least everything else seems to be working.

Welcome to another "installment" of beamrun news from the APS.

Our group has a week of time at beamline 12 and will be performing a series of x-ray reflectivity experiments from various materials.

What follows is a rather dry post. However, it's one of the parts of this work and serves to justify how unglamorous some of this can be.

Currently we are suffering the virtually inevitable problem of alignment, or in other words getting the tiny beam of light conditioned and in exactly the correct place. Depending upon the kind of experiment you wish to perform, the alignment (or geometry) needs varying degrees of rigor. For some experiments, with a large sample and where the angle of the scattered light is not very important, the experiment can be done without careful alignment. Our experiments tend to be very sensitive to the various angles and positions, making us spend a good deal of effort to align everything. All of this is further complicated because every piece of equipment that interacts with the beam sits on something. Each piece may not be firmly attached, or may not be completely centered. Even the concrete floor can occasionally give a little shift (I've heard stories of the operators "detecting" earthquakes by variation in the electron beam).

What all has to be aligned and how do we do it you might ask...

The first part is largely out of control of the users (which isn't always a bad thing) and that is the light source itself. In this case we have a very large magnetic field bending the flight path of the electrons. As they follow a curve they release a continuous spectrum of light. This light tends to be brightest in the forward direction of the beam and already fairly small and tight. By changing the magnetic fields on the electron stream we could alter the initial direction of the small spotlight of photons coming out. However, direct manipulation of the electron beam by users (especially in some cases) can be a very bad idea leading to all sorts of problems. The worst of these would be total electron beam loss effecting all the other users in the facility.

So we have little control over the light source itself. It brings a beam of light down a pipe to a monochromator. This ingenious device allows us to select out a particular photon energy, or at least a very narrow band of photon energies, eliminating all the unwanted light. It also can (and does) serve a second purpose in most cases by acting as a focusing element for the beam. All of this sits down from us by about 20 meters. From there the light travels down a long pipe and into the experimental hutch.

Inside the hutch are the last few meters of the photon flight path, and incidentally the most important ones. The beam is conditioned further by a secondary focusing element and then narrowed by the use of several slits. The focusing serves to get the most light in the area of interest and the slits further work to eliminate unwanted stray photons. It also allows is to correct for minor the beam intensity variation.

So from the light source the photons travel first through the monochromator, then 20 meters and through more focusing elements and slits before all before arriving at the sample. It would be simple if we just had a place saying "put sample here," however that doesn't quite work. First there is the inevitable drift and change that occurs in the position of the beam from adjusting any of the previous instruments I mentioned. So "center" is a moving target every time (virtually) that an experiment is set up. We locate the approximate center by placing a small piece of paper that "burns" in the x-ray beam. By seeing where the make is made on the paper we can then get the diffractometer(the device that holds both the sample and the detector in place) into approximate position. From there is gets a little tricky.

Remember, we can't just see any of the photons with our eyes and being inside the hutch with the x-rays is right out. And even having the sample sitting in the center isn't enough. Each axis that the sample rotates about must be aligned and centered. We have various jigs and pins, precisely machined, that are used to position and align each axis. And since there is no definitive starting point, once we've aligned each axis and positioned everything once, it's still not fully aligned. Rather it is an iterative process with each step bringing us closer until we're within the tolerances of all the motor positions. Having such devices (which weigh well over a ton) move reliably, repeatably to within sub millimeters is something to behold... well, it is for me anyways.
At this point things should be good and all that's left is to define the detector aperture. This isn't terribly difficult as it only involves (you guessed it) more slits.

Once all this is done, we're then ready to actually move our experiment into the hutch and observe what happens. If we get lucky and things are reasonably placed from the pervious users, then it's only a few hours. Our record is around 4-5 hours I believe(and that's not because we're slow, but that's just how long it takes to systematically check everything and make minimal adjustments). At times we've gone a couple of days before working out all the problems. As that can be a couple of days out of our entire week without even placing our experiment in the hutch, it gets to be a major frustration and obstacle. I seriously wonder what the cost-benefit analysis would say regarding how much time and effort (which means money) that we waste each time because we have to take such pains (as many if not most users must do). Some of the equipment is certainly "top of the line" but much of it is "lowest bidder" equipment. How much could we have saved (and how much easier would it be for us) had the initial investment been higher?

Anyhow... We're reasonably lucky today and have an aligned diffractometer as of about 3am.

About the time I typed this we realized we might not be so lucky. I also left out a piece from the earlier writing... There is one other component in the flight path of the photons, a filter box. While for our experiments we need as many photons as possible, it is often necessary to eliminate some or most of the photons at various times for what I'll call diagnostic purposes. Usually this means checking our alignment or the orientation of a crystal or some such thing.
This little box of filters sits directly in the flight path and is capable of dropping pieces of aluminum of various thicknesses into the path. The problem is that they appear to be stuck.

The real problem is that we didn't notice this until everything else was already put together. The day shift had just finished aligning the slits down stream of this filter box when we came in. As we assumed that they'd already checked the filters up stream (everything proceeds in a down stream fashion in this business), we didn't bother attempting to use them. Or maybe they had been tested and were shown to have worked, but failed in the intervening time. Now that we're done with the alignment and ready to go we attempted to open things up and discovered this little problem. The part that really hurts and just makes me want to cry is that to fix the filterbox, we will probably end up destroying the careful positioning of the slits just downstream... and sadly, that will nuke the positioning of every subsequent piece of hardware.

It's still a little too early to imagine realigning again, so we're working as best as possible to attempt to diagnose and fix this little pneumatic filterbox. wish us luck.

We've got a beamrun scheduled to begin this Friday. As such, the blog will probably be updated fairly regularly. We've got a week of time at beamline 12-BM again. I'll post as we go to keep my dear readers (all 3 of you) up-to-date on our progress. It will again be an experiment where I assist. We will be performing some x-ray scattering/electro-chemistry experiments and possibly more metal-oxide surface experiments.

My own beamtime comes up the second week of April. We were initially to have another week in April for a different experiment (where I would again be assisting though not the principle person). We've lost that week due to equipment failure and will try to make up for it a bit in this coming week (by attempting two things instead of just one). The current science budget has further reduced our hopes as we're expecting the APS to be shutdown several weeks later in the year. This will make the available beamtime even more precious and the competition even tighter.

Our paper, "CO-Induced Lifting of Au(001) Surface Reconstruction " has finally been published! It is in Journal of Physical Chemistry C as a letter and I am very happy about it. The article is the first one listed on that page, complete with a nice graphic that all the letters are allowed to include. This was quite a process, longer than I'd hoped, but it's done. However, I'm not aware of any of my papers ever being "quick" or "easy." It never seems to be so easy as "just writing up what we've found," making a figure or two and sending it off for someone to publish.

One of the fun things is when science ends up (inadvertently in this case) looking like art.

It has become necessary to my upcoming experiment to simulate what our scattering patterns might look like. Below is the result :




It's the kind of picture I want to make in higher quality and then print up on giant poster sized paper.

It's not exactly what we'll see when we do our experiments, but it's something similar. In fact, the pattern is calculated in a geometry that we'll never observe (ie orientation of the crystal, beam, detector, etc), but I find it a rather striking pattern. The pattern is representative of scattering light (x-rays) through a monolayer of gold atoms. In this case, the atoms are arrange in a hexagonal pattern as you would find on top of a cubicly cut gold crystal. Instead of remaining in the cubic arrangement the atoms "reconstruct" into hexagonal patterns. Now... if you've ever tried to lay down a hexagon on top of a square, you may have noticed that there is no unique way to place the hexagon. There are two possible and equivalent ways to lay down the hexagonals. Nature is aware of this and so we end up with hexagonal arrays of atoms that are oriented 90 degrees away from each other.

What this means in the scattering pattern above, is that instead of just a single array of 6 hexagonal peaks in reciprocal space we instead find a total of 12 peaks, or two arrays rotated 90 degrees (or equivalently 30 degrees) from each other. The central bright region is from the unscattered light and the scattering due to the large scale structure of the pattern. The first set of higher ordered hexagonal peaks is also visible around the bright set of 12. Also visible is some "random" variation and faint signals. This noise is, in this case, due to the random shapes of the hexagonal domains I used (the atoms are still arrayed in hexagons, just the larger shape made by all the hexagons is a little random.

It's another reasonably slow night at the APS. We're taking data comfortably and able to work on other things for about 30 minutes at a time.

I think our research, particularly our study of Au surfaces under different conditions, got a huge boost today. Gerhard Ertl just won the Nobel prize in chemistry for his surface science work, primarily on understanding electrochemistry and chemical adsorption on Platinum surfaces. As we've been comparing our work, favorably, as an additional system not previously known to exhibit these behaviors, it will help our cause that at least a few other people think this kind of thing is pretty important.

In fact, upon learning the news my thought process went something like this :

For a second I had the scheming thought of, "maybe I should rework our latest paper to cite Ertl. That would help it get published."

Next came a short pause of guilt as I try to be above things despite the occasional impulse.

However, within another second came the moment of clarity where I realized that I actually didn't need to feel bad about that as I wouldn't have to change anything. It turns out we're already citing his work, 4 times in fact.

It's been a remarkably slow night. We're taking data at regular intervals and in between there's not much to do with the experiment. It's almost able to be unattended for 30 minutes at a time. That's rather useful as it allows me to work on other things in the interim.

Someone has been making good coffee in the evenings. Every night I come in to find a freshly brewed, almost full pot of coffee in the LOM adjacent to the beamline we're running at. Every night a new pot is brewed, like magic. So I suppose I need to find out who this kind soul is that has been making me coffee. I should like to endow them with some of my own favorite beans.

A couple of days ago we just finished out metal-oxide surface experiments and picked up to go to a different experimental station to study platinum nanoparticles under electrochemical control. This experiment has actually started fairly quickly. It's with a system we've used many times before, indeed the cell predates me here at the lab), which means most of the bugs have already been worked out of it. So even on our first night we're actually taking useful (we hope) data. After our last experience this is a welcome change. If things go well enough, we may even have some time left for one of my ideas. But for the moment I'm happy we're just taking data early on in the run.

The official wildlife report, at least thus far today, is one skunk out in the midnight hours happily scavenging in the grass. Was it the same guy I saw before...? I don't know. I don't get close enough to them to tell.

All in all it's been a pretty easy day for the start of a beam run. I'm already giving thought as to how to automate certain portions of the experiment so it can run without constant attention. It's also been a good day as I've gotten to learn a little more about this kind of experiment. I set up some of the conventional analysis software for XAFS and got some very preliminary plots of the behavior of the nano-particles. A proper analysis, with full modeling fitting and bells and whistles, will do better and be needed. But it's at least enough to tell us roughly what's going on. And to think that yesterday I didn't know how to do it!

It's about 6:30 in the morning here. You can always tell when you're working on a weekday/night as the coffee cart comes blasting music around the storage ring. That and there will be a few cars in the parking lot, not just mine.

Thus far today we're actually doing a little bit of science. Or at least we're trying to do science. There's no assurance that what we want to do will actually work, however at least we're not struggling just to get the beamline functional. It's really sad that we had to spend 50% of our beamtime just getting the light in the proper place.

What we're doing at the moment is watching how water behaves on metal-oxide surface as we freeze and thaw the water. We're seeing some interesting crystalization of the water molecules which we believe is actually occurring on the surface. We will spend much of the rest of this shift ensuring that what we're seeing really is on the surface of the metal-oxide and not elsewhere. But thus far it's repeatable and seems to be in interesting places.

We have also, thankfully, reached the stage of data collection. It means that we can pause and catch our breath while the experiment is running. Or, in this case, it should allow me enough time to walk around the storage ring for some welcome exercise. Hopefully I'll also finish the next blog entry.

We've reached the last day for this beamrun. Thankfully we're doing science and getting some really interesting results. It's been more painful than I recall as being normal to get here.

We're following some very interesting behavior as we get water to freeze on our surface. I say it's interesting, because it's freezing in two completely different configurations of ice. It's even more interesting as the ice appears to be freezing somewhat in patterns. Unfortunately we're having to do this without moving some of the motors on the diffractometer which limits our ability to really scan to determine fully the structure and orientation of all the ice crystals.

It's exciting to have a science question to actually ponder. We're not sure of exactly how the ice crystals are going onto the surface. Is it purely epitaxial (ie lining up with the metal atoms underneath) or does it have some variation, perhaps random? More importantly... how can we test for this with our remaining time? And how can we test for it with a buggy instrument and still have a reliable result? So we forge ahead, not knowing exactly what we'll find and trying our best to figure out ways to tell us what we're seeing.

As per Kerri's request, the wildlife sightings are as follows. Tonight was quiet with no one about. Yesterday was quite active with 2 raccoons and a skunk out during the night hours. During the morning there was a large hawk on a post. The previous two nights saw a small herd of white deer grazing contentedly. Among them were two yearlings and the buck.

We basically got no where last night, and basically the day shift didn't make it any further either. We've lost now fully 3/8ths of our beamtime because we the beam of photons and the diffractometer refuse to line up. Sadly, this is not something that users should be doing. In an ideal world, we would just come in, set up our experiment, and do science. That's not really the case in practice, but usually things go smoother than this. We still have to struggle, but usually we're struggling with the experiment and not basic beamline function.

Regrettably the diffractometer motors frequently lose their positions. And by frequently, I mean that two of them seem to lose track every time they move.

This is further complicated by the fact that the photon energy, the wavelength of the light, is A) not as advertised, B) not constant, and C) drifts in position. The beam of x-rays that comes from the storage ring has lots of different energies, most of which we don't need. So there is a device called a monochromator that selects out a particular energy that we want. The x-rays dump an enormous amount of heat on the monochromator mirrors. Usually there's a fairly reliable cooling system that adjusts the angles, correcting for aberation due to the heating. Unfortunately this is not the case. So we suffer from a beam of photons that is not the energy we request. The energy of the beam fluctuates and its position at the diffractometer also change. Such problems may be fatal to the experiment at hand...

So we're not very happy at the moment.

We'll try to make the best of it.

Hello dear readers (both of you),

Things have not started on a particularly good note. The beamline we're doing our first set of measurements on has had some.... problems. In fact, despite it now being a little past midnight we've been working 16 hours and have yet to achieve alignment on the diffraction instrument. If we cannot get the beam through the diffractometer properly, get the instrument aligned, and get it all together, well, then there's nowhere to put our experiment. Ideally the previous users would not leave the hutch in such poor shape, but that's part of the "shared" access problem at a facility like this. We've now spent a good 15% of our allotted time here doing absolutely nothing (except working our asses off).

But that is often the way of things. The night continues, though without much success. It's 3am and we still have not gotten a sample even mounted in the beamline. We are certainly close, but still not there.

Our primary data collection tool this time is an x-ray CCD camera. Usually we have a point detector that we sweep past the area of interest. The CCD camera has the distinct advantage of having a large area with high resolution. It allows us to collect all the scattering from a particular peak in one place without having to move the sample.

There are some disadvantages however. Most of the area (ie the camera) vs. point detector debates focus on resolution, count rates, efficiency, and things like that. For the moment we''l leave all that discussion to the experts. My major problem with CCD detectors is the company that manufactures them, Roper Scientific/Princeton Instruments. I had to use one of their cameras during graduate school and I detested the foul piece of equipment. I produced an extremely long laundry list of complaints about the camera and the software that controlled it. By the time I came into possession of it, the camera was already quite old. So you'd think, you'd hope, that some of the problems would have been solved in the 10 years between that old piece of junk and a brand spanking new one today. However, you'd be wrong.

So many of the same communications and software bugs that caused problems for me with the decade old camera are also present in this camera as well.
It's been 10 years and they still can't design a camera system that will work and "play nice" with anything else in the computer. sigh.....

Such is the way of things at times.

If you'd asked me earlier today to predict what I would've done for the day, I would have been totally wrong.

Today was certainly a difficult day at the beamline. Finally we got all the problems with the beamline and hutch under control. This moved us on to the problems we needed to solve with our experiments. As I said earlier, I hate Roper Scientific. These people are not even the least bit afraid that there might be a hell. Anyhow, we've had nightmarish problems with our computer talking to the ccd camera. The eventual solution was to take out the high-end digital electronics and fiber optic cable. This solved our last communication problem, but left us with a new one.... Our cables are a bit short.

In fact all USB cables are a bit short as they just do not make anything long enough for what we need. The problem is that the CCD camera needs to be inside the hutch with the x-rays and the computer needs to be outside the hutch with us. Humans and x-rays don't play well in the same room together. That's something you learn being an x-ray physicist. They teach you that in school.... never go in the hutch with the x-rays.

The eventual solution has the CCD and its electronics in the hutch with a long cable on the floor to our computer (inside the hutch still). However, the computer is close to a "rabbit hole" to the outside. In fact, it's close enough that I got the cables for the monitor, keyboard, and mouse through the hole and intro the hutch. It just means that the "control" center for the experiment sits on the concrete floor. So be it.

Our next problem, still not 100% solved, has been temperature control of the sample. The stage has a heat sink, but it does not dissipate heat quickly enough to be useful. I salvaged a few computer fans from trashed/junked computers, powered them, and stuck them under the stage. That sort of worked but not enough... So I got a liquid nitrogen dewar, filled it after only 2 minor fiascos, and took copper cord to the sample block to act as a sink for the heat. That also worked, though still only sort of... and not enough...

At this point we pulled the entire stage off in favor of putting an older cryostat assembly into the diffractometer. One entertaining bit is that it uses high pressure helium lines for the cooling. Anyhow, the cryostat didn't fit well into the diffractometer as at some point, someone had smashed the threads. We spent another hour fixing some rather onerous screw threads before the new/old stage could be assembled. But now it's there and sort of working. we'll see...

Another day at the beamline...

During the down time I've been trying to learn a bit about making computer generated pictures using ray tracing programs.

The reason for this is simple. Often a great deal can be communicated through nice pictures that would be awkward or opaque through spoken word or text alone. At the same time poor quality pictures or representations of what you're attempting to explain can also obfuscate. So I decided that I'd had enough of making simple little pictures in MS-powerpoint. I wanted something more.

I downloaded POV-Ray and set to work. With a modest amount of mathematics and programming already under my belt, this turned out to be rather straight forward to use. Perhaps the simplest thing to make is a sphere, so I set about learning how to render pictures of a few spheres :

So there's my first attempt. A nicely colored row of spheres. It wasn't too hard to make actually. And to be honest, all I really need to know how to make are spheres. lots of them. LOTS AND LOTS OF THEM.

One of the systems near and dear to me is the surface of a particular gold crystal facet (though to be sure, the other facets are interesting too as are plenty of other crystals). It's a square cut through the face-centered-cubic lattice of gold atoms. The top row of atoms the rearranges itself into a hexagonal pattern. The hexagonal pattern can then be one of two possible orientations (rotated 90 degrees from each other). Furthermore because the surface atoms do not line-up perfectly with the atoms underneath, the surface ends up rippled and crumpled in a particular way.... See? I could keep going and going about the positions and so forth, but a simple picture would be sooooo much better.

Ah to be in Paris and in love...


Finally... Finally... we submitted my first paper from my work as a post-doc. It's been a little over a year now (and was a large leap in terms of science), but we've got our first paper sent off. It's far from time to really celebrate though. It will be a month or two before it comes back from the referees and they'll certainly have some things we need to fix. I say "certainly" because we submitted the paper to Physical Review Letters. This essentially assures us of having negative comments from the referees. It's almost a given. The question is how negative and how we respond.

The trade off is that this is (aside from perhaps Nature) about the best place for a physicist to publish research. Because of that, they're pretty selective about what makes it through and the referees are supposed to be tough on the authors. The converse is that we've got (I think) a really good paper with some very interesting results (interesting to a wide variety of people). Nothing is certain, except that it will never get published if it's never submitted.

This is particularly exciting for me as it will be my first paper with Hoydoo and my first in the realm of surface physics. It's been quite a big jump between my thesis project in graduate school and the research I'm doing here. However, I'm glad to have made the transition and be contributing in a second field. I suppose that's part of what I like about being a physicist. Despite some difficulty it's very possible to switch between different interests with some degree of fluidity.

We had some extra time today when one of the facility scientists abruptly (and obscenely) took the beam down. He needed to do some work on a piece of equipment we use and that required us to stop working. The best situation would have been if he'd informed us in the morning that he'd need to do his work in the afternoon. Or... since he didn't warn us at all, to allow us a few minutes to finish our work (ball-park, at most 30 minutes of time). Or... he could have stressed the urgency of what needed to be done and apologized, but taken it away. Instead he got in a fit, stormed off to get a supervisor/coordinator person, and came back to curse and yell at us.

You know... if you're going to curse, you've got to do it well enough that people will be impressed by your ability curse instead of being offended. His... eloquence with 4-letter words was somewhat lacking. Anyhow, he acted quite childish and then took the beam down. sigh... So we used the spare time to finish our paper and send it off!

Today was quite a day and follows on the heels of "quite a day."

This was my first chance to host a visit for a guest scientist, in this case Paul G. Evans from the University of Wisconsin at Madison. I recently joined the colloquium committee for the Materials Science Division. The committee selects and invites speakers to give our weekly colloquium (no self nominations!). I met Paul a couple of months ago at a workshop and wanted to learn more about his work (something I'm a bit unfamiliar with). One of the best ways to do that is have someone come out to give a talk! I enjoyed putting this together and, so long as I'm not in charge of it every week, it's something I'll probably continue to enjoy in the future.

It's been a rather long day because we're also currently running our experiments. Two of mine are actively running in the Materials Science building, while one of the other post-docs has an experiment running at the Advanced Photon Source. Being in so many places at once is difficult. It's not easy to violate causality.

This all comes after the day before which gave me one of the best experimental results we've gotten thus far. It was one of those rare days where everything worked (including the experimenter!). We went to look for something we'd seen indirectly with our other experiments and found it. Having an independent confirmation (in this case, a radically different experimental technique) of a result is very, very reassuring. In particular it's coming at a good time as we're ready to submit a paper on the first set of experiments. Now that we're in "phase 2" and the results are confirmed it goes quite a ways to setting my mind at ease. If you're going to make a rather interesting, potentially controversial claim, then it really helps to have several different pieces of evidence. ie...the bigger the claim, then the better the evidence.

The experiment we're running at the APS is on "free" beamtime. There is a new device (x-ray source) that needs to be tested. The scientists in charge have it set up, and nominally working. However, the real test for them is if people can come in and do science with it. We're that group of people (we hope).

The reality is of course that nothing is free. As the x-ray source is new, it has some issues and problems that must be solved before we have a hope of doing good science. And part of our effort will be spent helping the beamline scientists solve these problems. Ideally everything will work rather quickly and we'll get to take some nice data. But for now there are no promises. We've got some oddities in the photons coming down the pipe and we're not quite sure what to make of it. Conversely, at the moment these oddities don't really have an adverse effect on our measurements. However, it's something that needs to be worked out.

One of the worst things in experimental science is having data that is inconclusive. However, something more insidious is when you equipment fails and conspires against you. I say "conspires" because at times I think we'd all swear there's some evil genius inside the machine purposefully twarting our efforts.

The current manifestation of this "entity" was causing us to lose the motor positions and alignment of our diffractometer (the giant green-aqua thing we use to take x-ray scattering data).

These are the works of man, this is the sum of our ambition : To make this little motor turn (in a known, reliable, repeatable fashion.






I spent much (too much) of the last day getting this little motor to spin properly. In the end we had two different mistakes compounding each other. Having two issues concurrently makes life more difficult because the cause becomes more difficult to identify. A typical problem solving approach to this is to first ask, "is there anything known to commonly fail that we should check first, or does the way it's failing indicate a particular problem?" Assuming that doesn't work (it didn't), the next phase is to proceed methodically through the rest of the parts, removing them from the list of possibilities. The problem here, is that with failure in two different areas, the above method doesn't exactly work.

Eventually we figured things out, but it was painfully long. I'll spare you the details, but we were running our motor at too high of a power, causing occasional jams, and our connection coupling from the motor would occasionally lose contact when one of the other motors was in motion. sigh...

For posterity's sake I should reproduce something here. After checking all over the web I could not find this information for the wiring of a particular model/kind of motor. So, after figuring out how a 4-phase motor should work, plenty of measurements with a multi-meter, and a bit of cursing similar (but different) wiring identification schemes, I finally got it. For a 4-phase (four-phase) Slo Syn synchronous stepping motor, model M061 - CE08 (made by Superior Electric) the connection wiring is as follows.

Label on the Motor : A,B,C,D,E,F,G,H
Matching common female connector : 1,2,3,4,5,6,7,8 (there's only one orientation here)
Using the standard 8 wire bundle (though any will do)
Connecting to a standard stepper-motor plug connector (male).


Motor Letter, Motor Connector (wire color) - stepper male connector plug letter
B,2 (red) - to A
H,8 (red/white) - B
D,4 (green) - C
F,6 (green/white) -D
G,7 (black) - E
A,1 (white) - F
E,5 (orange) - H
C,3 (black/white) - J

W & T short together
U & X short together

We short W&T, U&X because we use software limits on the motors, not hardware limits on the machine.

On the motor itself, the phase pulse out/return pairs are :
A/H - phase 2
B/G - phase 1
C/F - phase 3
D/E - phase 4

Hopefully google will pick that up for the next time someone needs that information.

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.