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NASA NTRS1990

Thin film characterization using spectroscopic ellipsometry

The application of the multiple angle and wavelength (MAW) technique to measure the dielectric function of semiconducting films is discussed. This technique evaluates unambiguously the complex dielectric function, epsilon (E), of the film without any pre-assumptions. In some cases the effective medium approximation (EMA) was used to determine the volume fraction of the film components. Application of the MAW technique to several semiconducting films was published previously. Different applications and examples are given, including metal and insulator films.

Alterovitz, Samuel A.↗

NASA NTRS1987

A simplified CARS measurement system for rapid determination of temperature and oxygen concentration

A new spectroscopic concept for the rapid determination of temperature and oxygen concentration by CARS (Coherent Anti-Stokes Raman Spectroscopy) was described. The ratio of two spectral regions in the broadband Q-branch spectrum was detected by photomultipliers in a monochromator, which ratio depends on temperature and species concentration. The comparison of the measured data with theory was made using a flat flame burner and an electric furnace, with reasonable results. Various optical techniques for alignment were introduced including a highly efficient, stable dye oscillator. The combination of the spectroscopic concept and the optical techniques will make the CARS measurement system rapid in data processing and simple in optical parts.

Fujii, Shoichi↗

NASA NTRS1972

Infrared spectra of group III A metal oxides

The measurement of infrared frequencies of metal-oxygen species which could be formed in the matrix and to investigate with an oxygen-18 enrichment study the controversy on the vibrational assignments for the suboxide. Several new molecules, Al3O2, Ga3O, In3O, In4O2, IntaO, IntaO2, and In2WO4, were found by mass spectrometric sampling to exist in extremely minor concentrations in the vapor phase. The latter three species were formed by reaction with the crucible materials and were unimportant for an infrared analysis. The infrared spectroscopic measurements were obtained by the matrix isolation technique of molecular beam sampling. The MO2 species were formed by direct reaction between metal and O2 in the matrix. A C2v structure and an O-M-O bond angle near 40 deg was favored for these molecules by analogy with a similar investigation of the alkali metals. The vibrational frequencies which were determined are given.

Lynch, D. A., Jr.↗

NASA NTRS1979

Nondispersive spectroscopy of celestial X-ray sources

The spectroscope aboard the Einstein Observatory which utilizes nondispersive techniques is presented. Examples of kinds of thermal and nonthermal features that can be seen as well as the possibility of seeing small traces of thermal features in either much higher temperature objects or nonthermal objects are considered.

Holt, S. S.↗

NASA NTRS1987

The production of low-energy neutral oxygen beams by grazing-incidence neutralization

The Vanderbilt University neutral oxygen facility produces beams of low-energy neutral oxygen atoms by means of grazing-incidence collisions between ion beams and metal surfaces. Residual ions are reflected by applied electric fields. This method can utilize initial ion beams of either O(+) or O2(+) since a very large percentage of molecular oxygen ions are dissociated when they undergo grazing-incidence neutralization. The method of neutralization is applicable to low-energy beams and to all ions. Particular emphasis is on O and N2 beams for simulation of the low Earth orbit space environment. Since the beam is a pure O-neutral beam and since measurements of the interaction of the beam with solid surfaces are made spectroscopically, absolute reaction rates can be determined. The technique permits the beams to be used in conjunction with electron and photon irradiation for studies of synergistic effects. Comparisons of optical spectra of Kapton excited by 2.5-keV O, O(+), and O2(+) show significant differences. Optical spectra of Kapton excited by neutral oxygen beams of less than 1 keV have been recorded.

Albridge, R. G.↗

NASA NTRS1987

Electrical properties of polyimides containing a near-surface deposit of silver

Films containing a surface or near-surface deposit of palladium, gold or copper metal as well as tin, cobalt, copper, or lithium oxides have been prepared by dissolving appropriate metal salts into poly(amide-acid)/N,N-dimethylacetamide solutions and curing the solvent cast films to temperatures up to 300 C. This preparation technique has been extended to evaluate the thermal, spectroscopic, and electrical characteristics of condensation polyimide films modified with silver nitrate. A near-surface deposit of metallic silver results but the reflective surface has high electrical resistivity (sheet resistivity) due to a polymer coating or overlayer above the metal. Details pertaining to the silver nitrate modified condensation polyimides are presented. Also, the applicability of the structural model and electrical model previously proposed for the cobalt oxide system are assessed.

Rancourt, J. D.↗

NASA NTRS2000

MACS, An Instrument, and a Methodology for Simulations and Global Measurements of the Coronal Electron Temperature and the Solar Wind Velocity on the Solar Corona

The determination of the radial and latitudinal temperature and wind profiles of the solar corona is of great importance in understanding the coronal heating mechanism and the dynamics of coronal expansion. Cram presented the theory for the formation of the K-coronal spectrum and identified two important observations. He observed the existence of temperature sensitive anti-nodes at certain wavelengths in the theoretical K-coronal spectra. The anti-nodes are separated by temperature-insensitive nodes. Remarkably, Cram showed that the wavelengths of the nodes and anti-nodes are almost independent of altitude above the solar limb. Because of these features, Cram suggested that the intensity ratios at two anti-nodes could be used as a diagnostic of the electron temperature in the K-corona. Based on this temperature diagnostic technique prescribed by Cram a slit-based spectroscopic study was performed by Ichimoto et al. on the solar corona in conjunction with the total solar eclipse of 3 Nov 1994 in Putre, Chile to determine the temperature profile of the solar corona. In this thesis Cram's theory has been extended to incorporate the role of the solar wind in the formation of the K-corona, and we have identified both temperature and wind sensitive intensity ratios. The instrument, MACS, for Multi Aperture Coronal Spectrometer, a fiber optic based spectrograph, was designed for global and simultaneous measurement of the thermal electron temperature and the solar wind velocity in the solar corona. The first ever experiment of this nature was conducted in conjunction with the total solar eclipse of 11 Aug 1999 in Elazig, Turkey. In this instrument one end of each of twenty fiber optic tips were positioned in the focal plane of the telescope in such a way that we could observe conditions simultaneously at many different latitudes and two different radial distances in the solar corona. The other ends of the fibers were vertically aligned and placed at the primary focus of the collimating lens of the spectrograph to obtain simultaneous and global spectra on the solar corona. By isolating the K-coronal spectrum from the spectrum recorded by each fiber the temperature and the wind sensitive intensity ratios were calculated to obtain simultaneous and global measurements of the thermal electron temperature and the solar wind velocity. We were successful in obtaining reliable estimates of the coronal temperature at many positions in the corona. This is the first time that simultaneous measurements of coronal temperatures have been obtained at so many points. However due to instrumental scattering encountered during observations, reliable estimates of the wind velocity turned out to be impossible to obtain. Although remedial measures were taken prior to observation, this task proved to be difficult owing to the inability to replicate the conditions expected during an eclipse in the laboratory. The full extent of the instrumental scattering was apparent only when we analyzed the observational sequence. Nevertheless the experience obtained from this very first attempt to simultaneously and globally measure both the wind velocity and the temperature on the solar corona have provided valuable information to conduct any future observations successfully.

Reginald, Nelson L.↗

NASA NTRS1995

Hydroxycinnamic acid-derived polymers constitute the polyaromatic domain of suberin

Suberin is an abundant, complex, intractable, plant cell wall polymeric network that forms both protective and wound-healing layers. Its function is, therefore, critical to the survival of all vascular plants. Its chemical structure and biosynthesis are poorly defined, although it is known to consist of both aromatic and aliphatic domains. While the composition of the aliphatic component has been fairly well characterized, that of the phenolic component has not. Using a combination of specific carbon-13 labeling techniques, and in situ solid state 13C NMR spectroscopic analysis, we now provide the first direct evidence for the nature of the phenolic domain of suberin and report here that it is almost exclusively comprised of a covalently linked, hydroxycinnamic acid-derived polymeric matrix.

NASA Discipline Plant Biology↗

NASA NTRS1980

Review of spectroscopic data for measurement of stratospheric species

The role of various infrared techniques in measurements of trace gases in the stratosphere were surveyed. Particular emphasis was placed on the role of instruments exhibiting ultrahigh resolution (i.e., less than or equal to 0.00/cm) such as laser heterodyne spectrometers.

Goldman, A.↗

NASA NTRS2000

Effective utilization of quantum-cascade distributed-feedback lasers in absorption spectroscopy

A variable duty cycle quasi-cw frequency scanning technique was applied to reduce thermal effects resulting from the high heat dissipation of type I quantum-cascade lasers. This technique was combined with a 100-m path-length multipass cell and a zero-air background-subtraction technique to enhance detection sensitivity to a parts-in-10(9) (ppb) concentration level for spectroscopic trace-gas detection of CH4, N2O, H2O, and C2H5OH in ambient air at 7.9 micrometers. A new technique for analysis of dense high resolution absorption spectra was applied to detection of ethanol in ambient air, yielding a 125-ppb detection limit.

NASA Discipline Environmental Health↗

NASA NTRS1980

Far infrared measurement of stratospheric HCl

Thermal emission from three rotational lines of H(Cl-35) and H(Cl-37) was observed with a Fourier transform spectrometer from a balloon platform at 28.9 km. The measured HCl line-of-sight density at 1.9 deg elevation above 28.9 km is 4.7 + or - 1.3 x 10 to the 15th/sq cm, implying an average volume mixing ratio of 0.8 + or - 0.2 x 10 to the -9th at the mean sampling altitude of 32.5 km. For a uniform mixing ratio model, this corresponds to a vertical column density of 2.4 + or - 0.6 x 10 to the 14th/sq cm. This result is in reasonable agreement with near infrared spectroscopic determinations and an abundance from a chemical sampling technique of HCl at this altitude; a pressure modulator radiometer measurement yields a significantly higher amount of HCl.

Chance, K. V.↗

NASA NTRS1990

Ellipsometric study of cubic SiC

Variable angle spectroscopic ellipsometry (VASE) was applied to cubic SiC. This technique gives absolute values of the refractive index (n) and the extinction coefficient (k) of a substrate and/or a thin film of unknown material. The samples were grown by chemical vapor deposition (CVD) on p-type silicon. The substrate was aligned either on the (001) axis or 1 degree of (001). Several growth temperatures and growth durations were used. The samples were divided into two groups: (1) thick films of order 10 microns grown near optimal conditions of temperature, flow, and gas ratio; and (2) thin films of order 100 A grown at various temperatures. The ellipsometric results for samples in group 1 were analyzed using a two-phase model (substrate and ambient). Results show that for wavelengths in the visible, the refractive index of these CVD samples is equal to that reported for single crystal cubic SiC, within the experimental error, which is on the order of 1 percent. However, the extinction coefficient has a relatively large value, even above the band gap. The absorption is sample dependent and has a broad peak in the visible. The results for samples in group 2 were analyzed using a three-phase model (substrate, film, and ambient). The dielectric functions of the film, deducted from the measured n and k, were further analyzed using the effective medium approximation. The results show that the films contain 30 to 40 vol. percent amorphous silicon, i.e., silicon with only short-range order.

Alterovitz, Samuel A.↗

NASA NTRS2000

Theoretical Calculations of Atomic Data for Spectroscopy

Several different approximations and techniques have been developed for the calculation of atomic structure, ionization, and excitation of atoms and ions. These techniques have been used to compute large amounts of spectroscopic data of various levels of accuracy. This paper presents a review of these theoretical methods to help non-experts in atomic physics to better understand the qualities and limitations of various data sources and assess how reliable are spectral models based on those data.

Bautista, Manuel A.↗

NASA NTRS1992

Speckle and spectroscopic orbits of the early A-type triple system Eta Virginis

Eta Virginis is a bright (V = 3.89) triple system of composite spectral type A2 IV that has been observed for over a dozen years with both spectroscopy and speckle interferometry. Analysis of the speckle observations results in a long period of 13.1 yr. This period is also detected in residuals from the spectroscopic observations of the 71.7919 day short-period orbit. Elements of the long-period orbit were determined separately using the observations of both techniques. The more accurate elements from the speckle solution have been assumed in a simultaneous spectroscopic determination of the short- and long-period orbital elements. The magnitude difference of the speckle components suggests that lines of the third star should be visible in the spectrum.

Hartkopf, William I.↗

NASA NTRS1990

Spectroscopic Analysis Of Insulating Crystal Fibers

New method provides rapid characterization of optical properties. Technique for determining optical properties of insulating single-crystal fibers developed and applied to sapphire, spinel, and YAIO crystalline host fibers doped with triply ionized titanium. Crystal fibers grown more rapidly and less expensively.

Buoncristiani, A. M.↗

NASA NTRS1986

Spectroscopic planetary detection

The Sun-as-a-star was monitored using the McMath Fourier transform spectometer (FTS) on Kitt Peak in 1983. In 1985 the first measurement was made using the laser heterodyne technique. The FTS measurements now extend for three years, with errors of order 3 meters/sec at a given epoch. Over this 3 year period, a 33 meter/sec change was measured in the apparent velocity of integrated sunlight. The sense of the effect is that a greater blueshift is seen near solar minimum, which is consistent with expectations based on considering the changing morphology of solar granular convection. Presuming this effect is solar-cycle-related, it will mimic the Doppler reflex produced by a planetary companion of approximately two Jupiter masses, with an 11 year orbital period. Thus, Jupiter itself is below the threshold for detection by spectroscopic means, without an additional technique for discrimination. However, for planetary companions in shorter period orbits (P approx. 3 years) the threshold for unambiguous detection is well below one Jupiter mass.

Deming, D.↗

NASA NTRS2001

Vibrational Spectroscopy and Astrobiology

Role of vibrational spectroscopy in solving problems related to astrobiology will be discussed. Vibrational (infrared) spectroscopy is a very sensitive tool for identifying molecules. Theoretical approach used in this work is based on direct computation of anharmonic vibrational frequencies and intensities from electronic structure codes. One of the applications of this computational technique is possible identification of biological building blocks (amino acids, small peptides, DNA bases) in the interstellar medium (ISM). Identifying small biological molecules in the ISM is very important from the point of view of origin of life. Hybrid (quantum mechanics/molecular mechanics) theoretical techniques will be discussed that may allow to obtain accurate vibrational spectra of biomolecular building blocks and to create a database of spectroscopic signatures that can assist observations of these molecules in space. Another application of the direct computational spectroscopy technique is to help to design and analyze experimental observations of ice surfaces of one of the Jupiter's moons, Europa, that possibly contains hydrated salts. The presence of hydrated salts on the surface can be an indication of a subsurface ocean and the possible existence of life forms inhabiting such an ocean.

Chaban, Galina M.↗

NASA NTRS1984

Analysis of glow discharges for understanding the process of film formation

The physical and chemical processes which occur during the formation of different types of films in a variety of glow discharge plasmas are discussed. Emphasis is placed on plasma diagnostic experiments using spectroscopic methods, probe analysis, mass spectrometric sampling and magnetic resonance techniques which are well suited to investigate the neutral and ionized gas phase species as well as some aspects of plasma surface interactions. The results on metallic, semi-conducting and insulating films are reviewed in conjunction with proposed models and the problem encountered under film deposition conditions. It is concluded that the understanding of film deposition process requires additional experimental information on plasma surface interactions of free radicals and the synergetic effects where photon, electron and ion bombardment change the reactivity of the incident radical with the surface.

Venugopalan, M.↗