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[Sandia Lab News]

Vol. 56, Special Issue        March 2004
[Sandia National Laboratories]

Albuquerque, New Mexico 87185-0165    ||   Livermore, California 94550-0969
Tonopah, Nevada; Nevada Test Site; Amarillo, Texas

Back to Lab News Sandia Labs Accomplishments 2004 index

Materials, physics, and chemistry; bio/nano/cogno; electronics

Materials

Recrystallization removes damage and defects from a deformed piece of metal, leaving tough, ductile, perfect crystals behind. What recrystallization does is well-known, but how it begins is a long-standing mystery. Using advanced mesoscale computer models, we performed the first full-physics simulations of a deformed aluminum substructure. We find that one in a million tiny, pre-existing crystallites grows quickly and large, supplying the nucleus for recrystallization. These observations provide the basis for a new, physically based understanding of this pervasive metallurgical process. (1800)

Stress in mixed silicon/germanium films, grown under precisely controlled conditions, causes the spontaneous formation of remarkable nanoscale quantum dot molecules in square fortress-like shapes with highly uniform sizes. The special electronic properties of such solid-state "molecules" could lead to revolutionary quantum computing devices with logic, storage, and wiring elements that actually build themselves. Furthermore, a focused ion beam can selectively seed the self-assembly process, demonstrating the potential to create complex nanoscale circuits exactly where we want them. (1100)

Metallic photonic crystals were fabricated at Sandia's Microelectronics Development Laboratory that experimentally demonstrated that thermally excited emission from metallic 3-D photonic crystals can exceed the values predicted by Planck's law for planar emitters over particular temperature ranges and for a relatively narrow band of wavelengths. Potential applications could include thermal to electric energy-conversion devices. (1700, 1100)

We have adopted a novel approach using engineered defects and newly developed analytical techniques to unravel the mysteries of how localized corrosion initiates in aluminum. We're generating mechanistic information by comparing the characteristics of nanometer-length scale degradation processes in synthesized protective oxide structures with that in actual alloy systems. The knowledge we're gaining is a critical component in our ongoing effort to develop predictive models of materials aging. (1800, 1100)

Using a crossed molecular beam apparatus, Sandia scientists, in collaboration with Prof. James Valentini of Columbia University, have cooled molecules by collisions. A single collision between an atom and a molecule moving at supersonic velocities has produced molecules almost stationary in the laboratory. By picking the appropriate collision energy, a cloud of molecules having a temperature of approximately 30 millikelvin has been produced. This achievement opens the possibility of trapping and evaporatively cooling a large number of molecules to even lower temperatures where their wave nature can be investigated. (8300)

We have made significant improvements in ultra-high-temperature ceramics for use in advanced thermal protection systems. We made fully dense ZrB2-SiC and HfB2-SiC ceramics in composition ranges not previously available. These materials melt above 3,200C and are strong and resistant to thermal shock. Such materials are needed to manage the 2,000C temperatures expected from aerothermal heating of maneuverable, hypersonic vehicles that are proposed for a number of defense, surveillance, and space missions. (1800)

Historically, the complexity of glassy polymer behavior made it nearly impossible to evaluate design changes or reliability in encapsulated components without extensive experimental testing. Based on molecular simulations (conducted with New Mexico Tech) linking a polymer's viscoelastic friction to its potential energy, we developed a thermodynamically consistent theory and 3-D analysis code requiring no adjustable parameters to predict quantitatively the wide range of glassy polymer response. Our new methodology has been reported in a series of four recent journal articles. (1800, 9100)

We have devised a general, environmentally benign, chemical-synthesis approach to build complex nanostructures that are strikingly similar to those observed in biominerals (seashells and diatoms). The key to this new approach is to control nucleation and growth events and crystalline surface chemistry. We hope this new class of nanomaterials will lead not only to novel applications in microdevices, sensing, energy storage and conversion, catalysis, etc., but will also add to our understanding of how complex biomaterials are formed. (1800)

Bio/Nano/Cogno

Electronic and mechanical parts often contain interfaces between dissimilar materials. Such interfaces often crucially affect overall materials strength of a part. We have discovered a totally new structure for such interfaces, with perfect metal on both sides separated by a single layer of specially arranged metal atoms. This single layer contains an intricate perfect array of nanoscale dislocations that mate to the two different bulk metals. This structure promises to provide an extremely strong shear-resistant bond. (8700)

Motor proteins are molecular machines that enable many materials-assembly and actuation functions in living organisms, including cell division, organelle transport, and muscle contraction. We are exploring the use of these active proteins to assemble and reconfigure nanomaterials in artificial systems. As a first step toward creating programmable nanomaterials, we have demonstrated that the motor protein kinesin can transport inorganic materials such as gold nanoparticles and quantum dots in lithographically patterned microfluidic channels. (1100, 1700, 1800)

We have developed a novel computational and experimental approach to the determination of membrane protein structures and dynamics in a native membrane environment. The approach employed chemical crosslinking, proteolysis, and mass spectrometry to determine a set of nine pairwise interatomic distances in rhodopsin, a membrane protein critical to the vertebrate visual signal transduction pathway. These pairwise distances were used in conjunction with computational tools developed at Sandia for the construction, optimization, and simulation of membrane protein structures to determine the transmembrane domain structure of rhodopsin at moderate resolution. (8100, 1100, 1800, 8300, 9200)

Electronics

Our breakthrough in deep ultraviolet (UV) solid-state, light emitting diodes (LEDs) has led to continuous optical powers of 1.3 mW at 290 nm and 0.5 mW at 275 nm, and peak output power exceeding 8 mW at 290 nm under pulsed operation. These LEDs have been used in demonstrations of bio-agent detection and a non-line-of-sight communication system. Further development could enable water purification, decontamination, and thin-film curing. Team members received an award for excellence from DARPA. (1100)

Two-Dimensional Metal: Fact or Fiction? We have studied the physics of electrons confined to two dimensions (as seen in silicon transistors) to determine whether this system is a metal or insulator at temperatures near absolute zero. Metallic behavior would mean radical new physics and perhaps even new technology. While experiments by other groups over the last two decades have shown indirect evidence for a metallic state, our experiments and associated theory reveal insulating behavior, upholding conventional ideas. There is no true metallic state. (1100)

With MIT, we have achieved world-record long-wavelength lasing from quantum cascade lasers (QCLs). We have generated wavelengths as long as 141 microns (frequency >2 THz) and record operating temperatures in this regime (137K pulsed and 93K continuous operation). THz spectroscopy has potential for rapidly identifying chemical and biological agents and for imaging applications. Sandia is one of only three laboratories worldwide that has demonstrated the sophisticated compound semiconductor growth required for these structures. (1100)

Last modified: March 25, 2004


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