SSRL Science Highlights Archive

Approximately 1,700 scientists visit SSRL annually to conduct experiments in broad disciplines including life sciences, materials, environmental science, and accelerator physics. Science highlights featured here and in our monthly newsletter, Headlines, increase the visibility of user science as well as the important contribution of SSRL in facilitating basic and applied scientific research. Many of these scientific highlights have been included in reports to funding agencies and have been picked up by other media. Users are strongly encouraged to contact us when exciting results are about to be published. We can work with users and the SLAC Office of Communication to develop the story and to communicate user research findings to a much broader audience. Visit SSRL Publications for a list of the hundreds of SSRL-related scientific papers published annually. Contact us to add your most recent publications to this collection.


January 2002
I. J. Pickering, G. N. George
Figure 1.

Sulfur is essential for all life, but it plays a particularly central role in the metabolism of many anaerobic microorganisms. Prominent among these are the sulfide-oxidizing bacteria that oxidize sulfide (S2-) to sulfate (SO42-). Many of these organisms can store elemental sulfur (S0) in "globules" for use when food is in short supply (Fig. 1). The chemical nature of the sulfur in these globules has been an enigma since they were first described as far back as 1887 (1); all known forms (or allotropes) of elemental sulfur are solid at room temperature, but globule sulfur has been described as "liquid", and it apparently has a low density – 1.3 compared to 2.1 for the common yellow allotrope α-sulfur.

X-ray Absorption Spectroscopy
December 2001
J. Stöhr, H. Ohldag, J. Lüning

Computer hard drives and other advanced electronic devices depend on layered stacks of magnetic and non-magnetic materials, but researchers don't fully understand why such layered materials exhibit new properties that cannot be predicted from the properties of the individual layers. In a recent publication a team working at SSRL and the ALS describes new methods, based on x-ray spectroscopy and x-ray microscopy, that reveal the magnetic structures at the boundaries between these layers. Their data show that the boundaries are not as clean as previously assumed but a new ultrathin interface layer may be formed by a chemical reaction. The thickness of the interfacial layer is found to change with temperature and this change can be directly correlated with the magnetic properties of the multilayer stack. The work provides the first magnetic images of a buried interface and gives direct experimental evidence for the existence and long-assumed importance of interfacial magnetic spins.

November 2001
Alexis S. Templeton, Thomas P. Trainor, Gordon E. Brown, Jr.
Figure 1.

Sorption reactions on particle surfaces can dramatically affect the speciation, cycling and bioavailability of essential micronutrients (i.e. PO43-, Cu, Zn etc.) and toxic metals and metalloids (i.e. Pb, Hg, Se, As) in soils and aquatic environments. Considerable attention has been focused on understanding metal sorption reactions at a molecular/mechanistic level and the effects of metal concentration, pH, ionic strength, and complexing ligands on the ways in which metal ions bind to the surfaces of common mineral phases such as Fe-, Mn- and Al-(hydr)oxides and clays. However, a significant fraction of mineral surfaces in natural environments are extensively colonized by microbial organisms, which can also be potent sorbents for metals due to the large number of reactive functional groups that decorate the cell walls and outer membranes of bacterial surfaces. 

X-ray Absorption Spectroscopy
September 2001
Martin Greven, John Arthur
(a) Superlattice wave vector (±e, 0, 0)o as a function of x for La1-xSr1+xMnO4. The dashed line for x > 0.5 is e = 2(1 - x) = 2ne. (b) Linear-scale contour map (10% contours) of the scattering intensity around (10, 6, 0)o for x = 0.525.

The strong electron correlations in transition metal oxides give rise to such phenomena as high-temperature superconductivity in layered cuprates and to stripe-like order in layered cuprates and nickelates. In the case of the manganites, an additional strong electron-lattice interaction leads to a very rich phase diagram in which structural, magnetic, and transport properties are intimately related. Colossal magnetoresistance (CMR) has been observed in the perovskite and double-layer manganites, but not in the single-layer system La1-xSr1+xMnO4 (Mn214). 

X-ray scattering
August 2001
John Miao, Keith Hodgson
3D Structures of Biomolecules

Protein crystallography can routinely determine the 3D structure of protein molecules at near atomic or atomic resolution. The bottleneck of this methodology is to obtain sizable and good quality protein crystals. Overcoming the crystallization difficulty requires the development of the new methodologies. One approach is to use NMR to image protein molecules in solvent. However, it is only applicable primarily to macromolecules in the lower molecular weight range. Another approach under rapid development is single molecule imaging using cryo electron microscopy (cryo-EM). The highest resolution currently achievable by this technique is ~ 7 Å for highly symmetrical viruses (1) and 11.5 Å for the asymmetrical ribosome (2). The main limitations to achieving better resolution by cryo-EM are radiation damage, specimen movement and low contrast.

July 2001
C. Kim (SSRL), D. H. Lu (Stanford), K. M. Shen (Stanford), Z.-X. Shen (Stanford/SSRL)
High Tc Superconductivity

Extensive research efforts to study the novel electronic properties of high-Tc superconductors and their related materials by angle-resolved photoemission spectroscopy at a recently commissioned Beam Line 5-4 (led by Z.-X. Shen) continue to be successful, producing many important results. These results, which are highlighted by five articles recently published in Physical Review Letters and one in Science, brought our understanding steps closer to solving the mystery of the high-Tc superconductivity.

Angle-resolved photoelectron spectroscopy
June 2001
J. Stöhr (SSRL), M. Samant (IBM), J. Lüning (SSRL)
Flat Panel Displays

Today's laptop computers utilize flat panel displays where the light  transmission from the back to the front of the display is modulated by orientation changes in liquid crystal (LC) molecules.  Details are discussed in Ref. 2 below.  One of the key steps in the manufacture of the displays is the alignment of the LC molecules in the display.   Today this is done by mechanical rubbing of two polymer surfaces and then sandwiching the LC between two such surfaces with orthogonal rubbing directions. Over the past years a great challenge of this $20 billion/year industry has been to devise an alternative method of liquid crystal alignment.   The rubbing process is plagued with contamination issues and the polymer film is deposited by a wet process that is incompatible with high-tech manufacturing techniques.

May 2001
Hiro Tsuruta

The combined use of x-ray crystallography and solution small angle x-ray scattering has enabled a research collaboration involving scientists from Boston College and SSRL  to provide structural evidence supporting a 30-year old model accounting for the cooperative binding of ligands to allosteric proteins and enzymes - a function central to physiology and cellular processes.

Biological Small-angle X-ray Scattering (BioSAXS)
April 2001
Structure of RNA Polymerase II

RNA Polymerase transcribes genetic information into a message that can be read by the ribosome to produce protein The research group of Professor Roger Kornberg of Stanford University has studied the structure of this 12-subunit and half-megadalton size macromolecular machine using diffraction data collected at SSRL.

Macromolecular Crystallography


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