Sunday, August 2, 2015

Sulfur X-Ray Spectroscopy at the Stanford Synchrotron Radiation Lightsource

The Stanford Synchrotron Radiation Lightsource at dusk (credit: SSRL/SLAC)
My lab mates and I are once again back at the Stanford Synchrotron Radiation Lightsource (SSRL), a synchrotron particle accelerator in Menlo Park, California. We're here to conduct some x-ray microprobe mapping and x-ray absorption spectroscopy on samples from our various research projects (and to sleep very little while working all day and night, but that's just how we roll at synchrotrons). I've been to three synchrotrons so far in my life: the Swiss Light Source (SLS) at the Paul Scherrer Institut near Villagen, Switzerland; the Canadian Light Source (CLS) in Saskatoon, Canada; and, of course, here at SSRL.

SSRL is a particle accelerator where a storage ring (the rough shape of which you can see in the image above) holds electrons that are traveling at close to the speed of light. Synchrotrons are awesome laboratories full of a wide array of instruments that make use of the infrared, visible, ultraviolet, and, especially, x-ray radiation produced when these relativistic electrons spin around the ring. Each of the individual experimental stations at synchrotrons are called Beamlines (BLs). Four of us from our lab group, the Templeton Geomicrobiology Lab, are working on three of these beamlines here at SSRL this weekend. Two of our beamlines are made for x-ray microprobe mapping and microscale x-ray spectroscopy while the other beamline is designed for bulk x-ray absorption spectroscopy.

I wrote a post entitled "Sulfur X-Ray Microprobe and XAS at SSRL: A First Look Into My Beamline Science" back in 2013 where I first introduced some of the work that I've done here at SSRL for my graduate research. That's back when Beamline 14-3 at SSRL was first getting up and running. I'm now conducting more of that work on BL 14-3 (actually, this may be the last time I come to SSRL, at least as a graduate student).

BL 14-3 is an x-ray microprobe beamline. An x-ray microprobe is based on the concept that each element can absorb x-rays of a very specific energy. When the x-rays are absorbed, one thing that can happen is the emission of light. With the sulfur x-ray microprobe on BL 14-3, I'm scanning across polished surfaces of material that I collected at Borup Fiord Pass last summer. The x-ray microprobe can tell me how much sulfur is present in an area that I've mapped this way. Here's an image showing a rough map that I just collected:

The image on the left is a reflected light micrograph (a microscope image) of one of my samples. The inset is a tricolored map image showing where sulfide (red/orange), elemental sulfur (green/yellow), and sulfate (blue) can all be spatially resolved in this sample. Pretty awesome!

Once I've mapped the sample, I can conduct x-ray absorption spectroscopy on the most interesting spots in the sample. This will allow me to figure out not only what kinds of sulfur are in my sample, but also how those types of sulfur are distributed throughout the material. Fantastical!

Of course, being that I'm at a synchrotron, I imagine this has not been my best writing. There's this thing about synchrotron work, where many of us will be working most of the day and night and taking our sleep in little bouts when we can get it. The time we get on synchrotrons is always limited and we like to make the most of it, so we end up driving ourselves into a bit of zombie mode toward the end of our time at these facilities (especially for those of us who caffeinate heavily while here).

I'm very hopeful for the data I'm collecting this weekend. These data, along with the rest of my work from this summer, should drive my research into its last leg as I look toward the last year or so of my graduate work. Using sulfur x-ray micropobe mapping and x-ray spectroscopy here at SSRL should give me some of the key pieces of data that will help me to build my dissertation.

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