Publications

Abstract not provided.

Tethered supramolecular machines represent a new class of active self-assembled monolayers in which molecular configurations can be reversibly programmed using electrochemical stimuli. We are using these machines to address the chemistry of substrate surfaces for integrated microfluidic systems. Interactions between the tethered tetracationic cyclophane host cyclobis(paraquat-p-phenylene) and dissolved {pi}-electron-rich guest molecules, such as tetrathiafulvalene, have been reversibly switched by oxidative electrochemistry. The results demonstrate that surface-bound supramolecular machines can be programmed to adsorb or release appropriately designed solution species for manipulating surface chemistry.

Parabolic trough power systems that utilize concentrated solar energy to generate electricity are a proven technology. Industry and laboratory research efforts are now focusing on integration of thermal energy storage as a viable means to enhance dispatchability of concentrated solar energy. One option to significantly reduce costs is to use thermocline storage systems, low-cost filler materials as the primary thermal storage medium, and molten nitrate salts as the direct heat transfer fluid. Prior thermocline evaluations and thermal cycling tests at the Sandia National Laboratories' National Solar Thermal Test Facility identified quartzite rock and silica sand as potential filler materials. An expanded series of isothermal and thermal cycling experiments were planned and implemented to extend those studies in order to demonstrate the durability of these filler materials in molten nitrate salts over a range of operating temperatures for extended timeframes. Upon test completion, careful analyses of filler material samples, as well as the molten salt, were conducted to assess long-term durability and degradation mechanisms in these test conditions. Analysis results demonstrate that the quartzite rock and silica sand appear able to withstand the molten salt environment quite well. No significant deterioration that would impact the performance or operability of a thermocline thermal energy storage system was evident. Therefore, additional studies of the thermocline concept can continue armed with confidence that appropriate filler materials have been identified for the intended application.

Sandia National Laboratories has sponsored an LDRD (Laboratory Directed Research and Development) project to investigate and develop micro-chemical sensors for in-situ monitoring of subsurface contaminants. As part of this project, a literature search has been conducted to survey available technologies and identify the most promising methods for sensing and monitoring subsurface contaminants of interest. Specific sensor technologies are categorized into several broad groups, and these groups are then evaluated for use in subsurface, long-term applications. This report introduces the background and specific scope of the problem being addressed by this LDRD project, and it provides a summary of the advantages and disadvantages of each sensor technology identified from the literature search.

This LDRD is aimed to place Sandia at the forefront of GaN-based technologies. Two important themes of this LDRD are: (1) The demonstration of novel GaN-based devices which have not yet been much explored and yet are coherent with Sandia's and DOE's mission objectives. UV optoelectronic and piezoelectric devices are just two examples. (2) To demonstrate front-end monolithic integration of GaN with Si-based microelectronics. Key issues pertinent to the successful completion of this LDRD have been identified to be (1) The growth and defect control of AlGaN and GaN, and (2) strain relief during/after the heteroepitaxy of GaN on Si and the separation/transfer of GaN layers to different wafer templates.

Grating light reflection spectroscopy (GLRS) is an emerging technique for spectroscopic analysis and sensing. A transmission diffraction grating is placed in contact with the sample to be analyzed, and an incident light beam is directed onto the grating. At certain angles of incidence, some of the diffracted orders are transformed from traveling waves to evanescent waves. This occurs at a specific wavelength that is a function of the grating period and the complex index of refraction of the sample. The intensities of diffracted orders are also dependent on the sample's complex index of refraction. The authors describe the use of GLRS, in combination with electrochemical modulation of the grating, for the detection of trace amounts of aromatic hydrocarbons. The diffraction grating consisted of chromium lines on a fused silica substrate. The depth of the grating lines was 1 {micro}m, the grating period was 1 {micro}m, and the duty cycle was 50%. Since chromium was not suitable for electrochemical modulation of the analyte concentration, a 200 nm gold layer was deposited over the entire grating. This gold layer slightly degraded the transmission of the grating, but provided satisfactory optical transparency for the spectroelectrochemical experiments. The grating was configured as the working electrode in an electrochemical cell containing water plus trace amounts of the aromatic hydrocarbon analytes. The grating was then electrochemically modulated via cyclic voltammetry waveforms, and the normalized intensity of the zero order reflection was simultaneously measured. The authors discuss the lower limits of detection (LLD) for two analytes, 7-dimethylamino-1,2-benzophenoxazine (Meldola's Blue dye) and 2,4,6-trinitrotoluene (TNT), probed with an incident HeNe laser beam ({lambda} = 543.5 nm) at an incident angle of 52.5{degree}. The LLD for 7-dimethylamino-1,2-benzophenoxazine is approximately 50 parts per billion (ppb), while the LLD for TNT is approximately 50 parts per million (ppm). The possible factors contributing to the differences in LLD for these analytes are discussed. This is the final report for a Sandia National Laboratories Laboratory Directed Research and Development (LDRD) project conducted during fiscal years 1998 and 1999 (case number 3518.190).