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.

December 2002
Katharina Lüning, Sean Brennan, Piero Pianetta

Increasing the speed and complexity of semiconductor integrated circuits requires advanced processes that put extreme constraints on the level of metal contamination allowed on the surfaces of silicon wafers. Such contamination degrades for example the performance of the ultra thin SiO2 gate dielectrics (< 4nm) that form the heart of the individual transistors. Ultimately, reliability and yield are reduced to levels that must be improved before new processes can be put into production. Much of this metal contamination occurs during the wet chemical etching and rinsing steps required for the manufacture of integrated circuits and industry is actively developing new processes that have already brought the metal contamination to levels beyond the detection capabilities of conventional analytical techniques.

November 2002
Hope Ishii, Sean Brennan, Arthur Bienenstock
Figure 1.

Attempting to determine and describe the atomic arrangements in an amorphous material is a daunting prospect. A considerable advance has been made in the anomalous X-ray scattering approach to determining these arrangements in materials containing two atomic species.

X-ray scattering, X-ray Absorption Spectroscopy
October 2002
M. Greven, L. Zhou, S. Larochelle
Figure 1.

Many condensed matter systems can be described as large collections of microscopic entities, each of which can be in one of two possible states. For example, in many anisotropic magnets spins can point in one of two directions along a unique crystalline axis.  In a liquid-gas phase transition, molecules will be in either the gas or liquid phase.  When the microscopic entities interact, they may exhibit collective long-range order.  A collection of two-state particles with near-neigh bor interactions is known as an Ising system.  This simple system is very important because the behavior that an Ising system displays as it undergoes a transition to long-range order has universal features that are independent of the details of the two-state particles or their interaction.

September 2002
Douglas C. Rees, California Institute of Technology
Figure 1.

The Research group of Douglas Rees at the California Institute of Technology collected X-ray crystallographic data to a resolution of 1.16 Å at SSRL Beam Line 9-2 using the new Quantum-315 CCD detector from crystals of Nitrogenase MoFe-Protein, an extremely efficient enzyme found in bacteria that catalyzes the production of ammonia from dinitrogen. Bacteria produce about half of the world’s bio-nitrogen available for agriculture, the rest comes from nitrogenous fertilizer produced chemically at extreme temperature and pressure, consuming about 1% of the world's total annual energy supply. 

Macromolecular Crystallography
August 2002
Kaspar P. Locher, Allen T. Lee, Douglas C. Rees, Caltech
Figure 1.

Transport proteins, embedded in lipid membranes, facilitate the import of nutrients into cells or the release of toxic products into the surrounding medium. The largest and arguably the most important family of membrane transport proteins are the ABC transporters. They are ubiquitous in biology and power the translocation of substrates across the membrane, often against a concentration gradient, by hydrolyzing ATP (Higgins, 1992). 

Macromolecular Crystallography
July 2002
Figure 1.

In the well-known Greek legend the touch of King Midas would convert anything to metallic gold. Recently, a team working at SSRL lead by Professor Jorge Gardea-Torresdey from the University of Texas at El Paso have shown that ordinary alfalfa plants can accumulate very small particles (nanoparticles) of metallic gold (1). The best-known materials that contain nanoparticles of metallic gold are gold colloids. These lack the familiar metallic luster, but show bright colors which range from red, violet or blue, depending upon the size of the nanoparticles (2,3). 

X-ray Absorption Spectroscopy
June 2002
M. Cornacchia (SSRL), H.-D. Nuhn (SSRL), C. Pellegrini (UCLA)
Figure 1.

Advances in accelerator technology and in the theoretical understanding of collective instabilities and production of coherent radiation, have been the driving forces of the progress toward brighter synchrotron radiation sources, with scientific applications developing in response to the availability of new sources. The rate of improvement in source capability has been tremendous: for 30 years x-ray source brightness has been increasing exponentially with a doubling time of about 10 months. A modern synchrotron source is eleven orders of magnitude brighter than a 1960s laboratory x-ray source. Seldom, if ever, in history (perhaps only in the field of visible laser optics and colliders for high energy physics) has a scientific discipline seen its tools change so dramatically within the active life of a single generation of scientists.

May 2002
David L. Clark, Los Alamos National Laboratory
Figure 1.

The Rocky Flats Environmental Technology Site (RFETS) is an environmental cleanup site located about 16 miles northwest of downtown Denver (Fig 1).  Two decades of routine monitoring have shown that the environment around RFETS is contaminated with actinide elements (U, Pu, Am) from site operations, [1] and RFETS has been designated by the U.S. Environmental Protection Agency (EPA) as a Superfund cleanup site.  Until December 1989, the Rocky Flats Plant made components for nuclear weapons using various radioactive and hazardous materials, including plutonium, uranium and beryllium. Nearly 40 years of nuclear weapons production left behind a legacy of contaminated facilities, soils, and ground water.  More than 2.5 million people live within a 50 mile radius of the site; 300,000 of those live in the Rocky Flats watershed.

April 2002
Thiang Yian Wong, Robert Schwarzenbacher, Robert C. Liddington
Figure 1.

Anthrax Toxin is a major virulence factor in the infectious disease, Anthrax (1). This toxin is produced by Bacillus anthracis, which is an encapsulated, spore-forming, rod-shaped bacterium. Inhalation anthrax, the most deadly form, is contracted through breathing spores. Once spores germinate within cells of the immune system called macrophages (2), bacterial cells are released into the bloodstream. There they proliferate rapidly and secrete Anthrax Toxin, ultimately leading to septic shock and death. Although antibiotics may be used to kill the bacteria, the level of toxin has often become so high in the bloodstream that removing the bacteria alone is not sufficient to prevent death.

Macromolecular Crystallography
BL7-1, BL9-1
March 2002
Satish C. B. Myneni, Department of Geosciences, Princeton University, Princeton, NJ 08544
Figure 1.

When we think of chlorine, we often relate it to the salt used in food preparation, chloride in the oceans, chlorine gas from swimming pools, and gaseous chlorofluorocarbons that have close links to the depletion of stratospheric ozone. We rarely think of thousands of chlorinated hydrocarbons that exist in the natural systems, several of which are highly toxic to humans (1). The C-Cl bond, common to all organo-Cl compounds, is strong and gives high stability to organo-Cl compounds. For this reason, several organo-Cl compounds have been synthesized and used extensively for years in agricultural and industrial applications.



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