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Future Directions

• Space-Based Calibration Program. The possibility of using the International Space Station (ISS) to provide a platform for NIST-traceable standard sensors in the ultraviolet, visible, IR, and microwave spectral regions is being pursued. On-orbit instruments, periodically returned to NIST for recalibration, would provide long-term assurance of the accuracy of other space-borne instrumentation used for remote sensing and environmental monitoring. Division staff are currently coordinating an interdisciplinary and interagency Ad Hoc Committee for ISS Radiometric Calibration Utilization to study the feasibility and benefits of such a program.

• Infrared Spectral Emittance Metrology. A new facility is being built to meet the emerging demand for measurements of infrared emittance of opaque and semi-transparent materials at elevated temperatures. The facility expands existing capabilities in the FTIR Spectrophotometry Laboratory for measuring the optical properties of solid materials at cryogenic and near-ambient temperatures. For elevated temperatures (> 600 K), new instrumentation for direct measurements of emittance will be developed. Using this facility, the spectral regular reflectance and transmittance scales will be compared with those of the National Physical Laboratory of the United Kingdom. Additional comparisons of regular transmittance and diffuse reflectance will be undertaken with the National Physical Laboratory of India as part of an Indo-U.S. collaborative project.

• Submillimeter Plasma Chemical Imaging. In response to the needs of the semiconductor industry, we plan to develop high-resolution (_source < 100 kHz) submillimeter absorption spectroscopy (1000 GHz > _source > 300 GHz) for plasma chemical diagnostics. With the semiconductor industry standard wafer size increasing to 300 mm and feature size decreasing to sub 0.18 µm, there is increasing demand for better uniformity and image fidelity in plasma etching processes. To achieve these goals requires the development of new diagnostic tools that can be implemented on industrial test stations to provide feedback on the critical plasma and surface-plasma chemistry driving the etching process. This information is used by itself or in concert with plasma models to optimize the plasma chemistry for the desired result. With submillimeter absorption spectroscopy, mean chemical concentrations along the submillimeter beam path through the plasma are obtained from the degree of attenuation of the radiation when its frequency is coincident with a rotational transition of the molecule of interest. Submillimeter radiation achieves high sensitivity by probing near the peak of the thermal rotational distribution in the nominally 400 K plasmas. Additionally, the high spectral resolution of the technique allows the detailed analysis of the Doppler line shapes of the molecules, giving direct information on the translational temperature of the plasma. Also, for the same species, measurement of the relative intensity of two rotational lines or of the same rotational line for two different vibrational states provides information on the rotational and vibrational temperatures in the plasma and their degree of disequilibrium. Ideally, this information will accelerate the development of reliable plasma etching computer models, which ultimately will be used to program the plasma conditions to achieve the desired etch. This project will be done in collaboration with the Atomic Physics Division and EEEL.

• Qualitative Secondary and Tertiary Structural Determination from the Raman Spectroscopy of Proteins Aligned in Bicelles. We plan to initiate an effort to simplify the determination of the secondary structural elements in membrane proteins by binding the proteins to synthetic lipid bilayers and aligning the bilayers and thus the proteins in a high magnetic field for study by polarized Raman spectroscopy. The alignment, similar to what can be done with liquid crystals with electric or magnetic fields, adds symmetry to the system, which simplifies the analysis and provides additional structural information. It is our anticipation that this technique will accelerate our knowledge of the structure and function of membrane proteins. This knowledge is presently limited by the difficulty of crystallizing membrane proteins for traditional X-ray crystallography studies and by the fact that NMR techniques are limited to polypeptides or small proteins. Indeed, the utility of such studies has been recently demonstrated in NMR measurements; however, no attempt has yet been made to explore the potential of other spectroscopic techniques, such as Raman spectroscopy, which has a throughput advantage over NMR for qualitative structural determinations. Raman spectroscopy is also applicable to the study of large noncrystalline proteins not accessible by NMR.

• Ultraviolet Radiometry and Material Characterization at SURF III. The recent upgrade of SURF II to SURF III and the continuous effort to improve the performance of SURF III have resulted in a synchrotron source with the potential for world-leading research in UV radiometry and materials characterization. One of the new synchrotron beamlines is equipped with a normal-incidence monochromator that operates between 125 nm and 320 nm and is dedicated to UV detector calibrations and the characterization of photodiode damage by UV-excimer-laser radiation. A second beamline is dedicated to experiments in source-based radiometry. These experiments are made possible by a new beam-current monitor that provides accurate storage-ring current measurements necessary for the calculation of the absolute irradiance of SURF. The beamline will be used to calibrate Deuterium and FEL lamps in the spectral region from 200 nm to 400 nm with an accuracy of better than 2 %. A third beamline is presently under construction for interferrometric measurements of the refractive index of materials to a few parts per million an UV Fourier-transform spectrometer with input radiation from SURF III. Such measurements are critical to the development of the next-generation lithography tools for the semiconductor industry. This beamline will also be capable of characterizing and calibrating UV sources.

• Noncontact Microthermometry. Micron-resolution, high-accuracy, noncontact thermometry is being developed to improve the understanding of the microscale processes important in the development and application of MEMS, MOEMS, and micro chemical and biosensors. In addition, advances in microscale thermometry can substantially improve our ability to predict and optimize the performance of macroscale processes, such as machining of materials. The goals of this effort include accurate non-contact temperature measurements with µm spatial and µs temporal resolution along with predictive modeling of the measured spatial distributions of temperatures. It is desirable to make such measurements using noncontact optical sensing of radiance temperatures, however, such an approach requires that the emissivity of the system be known at a spatial resolution of microns or better, which will be particularly challenging when the composition and shape of the device varies over the same scale. The increasing use of microheater arrays in such areas as combinatorial DNA screening and in microchemical reactors is further indication of the need for the proposed effort. The work will make use of time-gated thermal-imaging arrays to determine the contact or the thermodynamic temperatures of materials so that accurate modeling and understanding of the chemical and thermo-mechanical processes are possible.