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A systematic approach for multidimensional, closed-form analytic modeling: Effective intrinsic carrier concentrations in Ga1-xAlxAs heterostructures
No full textA critical issue identified in both the technology roadmap from the Optoelectronics Industry Development Association and the roadmaps from the National Electronics Manufacturing Initiative, Inc. is the need for predictive computer simulations of processes, devices, and circuits. The goal of this paper is to respond to this need by representing the extensive amounts of theoretical data for transport properties in the multi-dimensional space of mole fractions of AlAs in Ga1-xAlxAs, dopant densities, and carrier densities in terms of closed form analytic expressions. Representing such data in terms of closed-form analytic expressions is a significant challenge that arises in developing computationally efficient simulations of microelectronic and optoelectronic devices. In this paper, we present a methodology to achieve the above goal for a class of numerical data in the bounded two-dimensional space of mole fraction of AlAs and dopant density. We then apply this methodology to obtain closed-form analytic expressions for the effective intrinsic carrier concentrations at 300 K in n-type and p-type Ga1-xAlxAs as functions of the mole fraction x of AlAs between 0.0 and 0.3. In these calculations, the donor density N-D for n-type material varies between 10(16) cm(-3) and 10(19) cm(-3) and the acceptor density N-A for p-type materials varies between 10(16) cm(-3) and 10(20) cm(-3).We find that p-type Ga1-xAlxAs presents much greater challenges for obtaining acceptable analytic fits whenever acceptor densities are sufficiently near the Mott transition because of increased scatter in the numerical computer results for solutions to the theoretical equations. The Mott transition region in p-type Ga1-xAlxAs is of technological significance for mobile wireless communications systems. This methodology and its associated principles, strategies, regression analyses, and graphics are expected to be applicable to other problems beyond the specific case of effective intrinsic carrier concentrations such as interpreting scanning capacitance microscopy data to obtain two-dimensional doping profiles
Implications of polishing techniques in quantitative x-ray microanalysis
No full textSpecimen preparation using abrasives results in surface and subsurface mechanical (stresses, strains), geometrical (roughness), chemical (contaminants, reaction products) and physical modifications (structure, texture, lattice defects). The mechanisms involved in polishing with abrasives are presented to illustrate the effects of surface topography, surface and subsurface composition and induced lattice defects on the accuracy of quantitative x-ray microanalysis of mineral materials with the electron probe microanalyzer (EPMA)
X-ray microanalyses in the variable pressure (environmental) scanning electron microscope
No full textElectron-excited x-ray microanalysis performed in the variable pressure and environmental scanning electron microscopes is subject to additional artifacts beyond those encountered in the conventional scanning electron microscope. Gas scattering leads to direct contributions to the spectrum from the environmental gas, as well as remote generation of x rays by electrons scattered out of the focussed beam. The analyst can exert some degree of control over these artifacts, but depending on the exact situation, spurious elements can appear at the trace ( 0.1 mass fraction) levels. Dispersed particle samples give the least compromised results, while fine scale microstructures are the most severely compromised. Procedures to optimize the situation based upon specimen preparation as well as spectral processing are described
Richard N. Wright
No full textRICHARD N. WRIGHT
Inducted: 2002
Citation:
For sustained leadership in building research, for the development of standards, and for representing the U.S. building industry and research community worldwide
Tenure: 1971-1999
Birth: 1932
Education:
Syracuse University: BS (civil engineering) 1953; MS (civil engineering) 1955
University of Illinois: PhD (civil engineering) 1962
Positions held:
Chief, Structures Section, Building Research Division
Deputy Director-Technical, Center for Building Technology
Director, Center for Building Technology
Director, Building and Fire Research Laboratory
Honors:
U.S. Department of Commerce Gold Medal, 1982
Nat. Soc. of Professional Engineers, Federal Engineer of the Year, 1988
Meritorious Executive Rank Award, 1988
National Conference of States on Building Codes and Standards, Mahaffey Award, 1998
Civil Engineering Research Foundation, Michel Award for Industry Advancement of Research, 1999
American Society of Civil Engineers, Honorary Member, 2002
Memberships:
American Society of Civil Engineers, Fellow
American Association for the Advancement of Science, Fellow
National Society of Professional Engineers
Earthquake Engineering Research Institute
President, International Council for Research and Innovation in Building and Construction
Publications:
Over 100 publications on topics in building and fire research, including:
Construction and Building: Federal Research and Development in Support of the U.S.Construction Industry; (with co-authors), Subcommittee on Construction and Building, Committee on Civilian Industrial Technology, National Science and Technology Council, (September 1995)
Assessment: U.S. Embassy Office Building in Moscow, (with co-authors), J. Performance of Constructed Facilities, American Society of Civil Engineers, (February 1989)
Computer Integrated Construction, IABSE Proceedings, P-123/88, International Association for Bridge and Structural Engineering, (February 1988
William C. Martin
No full textWILLIAM C. MARTIN
Inducted: 2002
Citation:
For many publications concerned with measurement and energy-level analysis of atomic spectra and for direction of the Atomic Energy Levels Data Center.
Tenure: 1957 - 1998
Birth: 1929, Cullman, Alabama
Education:
University of Richmond, BS (physics), 1951
Princeton University, MA (physics), 1953; PhD (physics), 1956
Positions held:
Chief, Spectroscopy Section, Atomic Physics Division
Director, Atomic Energy Levels Data Center
Leader, Atomic Spectroscopy
NIST Scientist Emeritus
Honors:
U.S. Department of Commerce Silver Medal, 1968; Gold Medal, 1981
NIST Allen V. Astin Measurement Science Award, 1992
Office of Measurement Services Award, 1997
Optical Society of America William F. Meggers Award, 1983
Memberships:
Optical Society of America, Fellow
American Physical Society, Fellow
American Association for the Advancement of Science, Fellow
International Astronomical Union
Chair of Working Group on Atomic Spectra and Wavelength Standards
American Astronomical Society
Associate Editor and Topical Editor, Journal of the Optical Society of America
Feature Editor, Journal of the Optical Society of America, 1988
Publications:
Over 65 published papers on atomic spectroscopy, including:
Value of the Rydberg Constant, Phys. Rev., (1956)
NIST Atomic Spectroscopic Database, Version 1.0 (with co-authors). Released on World Wide Web in March, 1995; Version 2.0 released in March, 1999
Atomic Spectroscopy, ( with W. L. Wiese) in Atomic, Molecular, and Optical Physics Handbook, AIP Press, New York, (1996)
Ionization Energies and Quantum Electrodynamic Effects in the Lower lsns and lsnp Levels of Neutral Helium (4He I), (coauthor), Can. J. Phys., (1998
Through measurement to knowledge: The inaugural lecture of Heike Kamerlingh Onnes (1882)
No full textThis paper is a contribution to the NIST Centennial 2001. It presents the first complete English translation of the inaugural speech of Heike Kamerlingh Onnes on the occasion of his appointment as Professor at the University of Leiden (The Netherlands) in 1882. The speech is a snapshot of the scientific landscape of that time and lays out a vision. It advocates with enthusiasm the significance of quantitative measurements and the development of metrology standards. Although science and technology have advanced since then by orders of magnitude, a number of interesting parallels between then and now appear
Donald G. Fletcher
No full textDONALD G. FLETCHER
NBS: 1952-1986
Birth: May 19, 1922, Rushville, Indiana
Education:
Clark College, BS (chemistry), 1950
Howard University (chemistry), 1950-1951
Principal Field:
Product and Process Development of Paper, Plastic, and Textile Materials
Positions Held at NBS:
Charter Member, Senior Executive Service, 1979
Research Chemist, Paper Section, Polymers Division
Chief, Synthetic Fibers Section
Chief, Paper Section, Polymers Division
Chief, Fibrous Systems Group, Institute for Materials Research
NBS Equal Employment Officer
Member, Human Resources Ethics Committee at NIST
NBS Representative, Congressional Paper Standards and Testing Committee, U.S. Congress
NBS Representative, Technical Association of the Pulp and Paper Industry
Honors:
NBS Supervisor of the Year, 1965
U.S. Department of Commerce Silver Medal, 1970; Gold Medal, 1975
U.S. Department of Commerce Science Fellow, 1970-71
Sandy Hill Award (Papermaker Award), 1983
Memberships:
Technical Association of the Pulp and Paper Industry
American Association of Textile Chemists and Colorists
American Chemical Society
Washington Academy of Science
The Visible Cement Data Set
No full textWith advances in x-ray microtomography, it is now possible to obtain three-dimensional representations of a material's microstructure with a voxel size of less than one micrometer. The Visible Cement Data Set represents a collection of 3-D data sets obtained using the European Synchrotron Radiation Facility in Grenoble, France in September 2000. Most of the images obtained are for hydrating portland cement pastes, with a few data sets representing hydrating Plaster of Paris and a common building brick. All of these data sets are being made available on the Visible Cement Data Set website at http://visiblecement.nist.gov. The website includes the raw 3-D datafiles, a description of the material imaged for each data set, example two-dimensional images and visualizations for each data set, and a collection of C language computer programs that will be of use in processing and analyzing the 3-D microstructural images. This paper provides the details of the experiments performed at the ESRF, the analysis procedures utilized in obtaining the data set files, and a few representative example images for each of the three materials investigated
Quantitating fluorescence intensity from fluorophores: Practical use of MESF values
No full textThe present work uses fluorescein as the model fluorophore and points out critical steps in the use of MESF (Molecules of Equivalent Soluble Fluorophores) values for quantitative flow cytometric measurements. It has been found that emission spectrum matching between a reference solution and an analyte and normalization by the corresponding extinction coefficient are required for quantifying fluorescence signals using flow cytometers. Because of the use of fluorescein, the pH value of the medium is also critical for accurate MESF assignments. Given that the emission spectrum shapes of microbead suspensions and stained biological cells are not significantly different, the percentage of error due to spectrum mismatch is estimated. We have also found that the emission spectrum of a microbead with a seven-methylene linker between the fluorescein and the bead surface (bead7) provides the best match with the spectra from biological cells. Therefore, bead7 is potentially a better calibration standard for flow cytometers than the existing one that is commercially available and used in the present study
Electron-impact total ionization cross sections of hydrocarbon ions
No full textThe Binary-Encounter-Bethe (BEB) model for electron-impact total ionization cross sections has been applied to CH2+,CH3+, CH4+, C2H2+, C2H4+, C2H6+, and H3O+. The cross sections for the hydrocarbon ions are needed for modeling cool plasmas in fusion devices. No experimental data are available for direct comparison. Molecular constants to generate total ionization cross sections at arbitrary incident electron energies using the BEB formula are presented. A recent experimental result on the ionization of H3O+ is found to be almost 1/20 of the present theory at the cross section peak