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All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

The Gas Composition and Deep Cloud Structure of Jupiter's Great Red Spot

We have obtained high-resolution spectra of Jupiter's Great Red Spot (GRS) between 4.6-5.4 microns using telescopes on Mauna Kea to derive gas abundances and to constrain its cloud structure between 0.5-5 bars. We used line profiles of deuterated methane (CH3D) at 4.66 microns to infer the presence of an opaque cloud at 5 plus or minus 1 bars. From thermochemical models, this is almost certainly a water cloud. We also used the strength of Fraunhofer lines in the GRS to obtain the ratio of reflected sunlight to thermal emission. The level of the reflecting layer was constrained to be at 570 plus or minus 30 millibars based on fitting strong NH3 lines at 5.32 microns. We identify this layer as an ammonia cloud based on the temperature where gaseous NH3 condenses. We found evidence for a strongly absorbing but not totally opaque cloud layer at pressures deeper than 1.3 bars by combining Cassini/CIRS (Composite Infrared Spectrometer) spectra of the GRS at 7.18 microns with ground-based spectra at 5 microns. This is consistent with the predicted level of an NH4SH cloud. We also constrained the vertical profile of H2O and NH3. The GRS spectrum is matched by a saturated H2O profile above an opaque water cloud at 5 bars. The pressure of the water cloud constrains Jupiter's O/H ratio to be at least 1.1 times solar. The NH3 mole fraction is 200 plus or minus 50 ppm (parts per million) for pressures between 0.7-5 bars. Its abundance is 40 ppm at the estimated pressure of the reflecting layer. We obtained 0.8 plus or minus 0.2 ppm for PH3, which is a factor of 2 higher than in the warm collar surrounding the GRS. We detected all five naturally occurring isotopes ofgermanium in GeH4 in the GRS. We obtained an average value of 0.35 plus or minus 0.05 ppb (parts per billion) for GeH4. Finally, we measured 0.8 plus or minus 0.2 ppb for CO in the deep atmosphere.

Bjoraker, G. L.↗
DOE OSTI2020

Oxide-Free Three-Dimensional Germanium/Silicon Core–Shell Metalattice Made by High-Pressure Confined Chemical Vapor Deposition

Metalattices are crystalline arrays of uniform particles in which the period of the crystal is close to some characteristic physical length scale of the material. In this work, we explore the synthesis and properties of a germanium metalattice in which the similar to 70 nm periodicity of a silica colloidal crystal template is close to the similar to 24 nm Bohr exciton radius of the nanocrystalline Ge replica. The problem of Ge surface oxidation can be significant when exploring quantum confinement effects or designing electronically coupled nanostructures because of the high surface area to volume ratio at the nanoscale. To eliminate surface oxidation, we developed a coreshell synthesis in which the Ge metalattice is protected by an oxide-free Si interfacial layer, and we explore its properties by transmission electron microscopy (TEM), Raman spectroscopy, and electron energy loss spectroscopy (EELS). The interstices of a colloidal crystal film grown from 69 nm diameter spherical silica particles were filled with polycrystalline Ge by high-pressure confined chemical vapor deposition (HPcCVD) from GeH4. After the SiO2 template was etched away with aqueous HF, the Ge replica was uniformly coated with an amorphous Si shell by HPcCVD as confirmed by TEM-EDS (energy-dispersive X-ray spectroscopy) and Raman spectroscopy. Formation of the shell prevents oxidation of the Ge core within the detection limit of XPS. The electronic properties of the core-shell structure were studied by accessing the Ge 3d edge onset using STEM-EELS. A blue shift in the edge onset with decreasing size of Ge sites in the metalattices suggests quantum confinement of the Ge core. The degree of quantum confinement of the Ge core depends on the void sizes in the template, which is tunable by using silica particles of varying size. The edge onset also shows a shift to higher energy near the shell in comparison with the Ge core. This shift along with the observation of Ge-Si vibrational modes in the Raman spectrum indicate interdiffusion of Ge and Si. Both the size of the voids in the template and core-shell interdiffusion of Si and Ge can in principle be tuned to modify the electronic properties of the Ge metalattice.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Metalorganic chemical vapor deposition of ZnGeN 2 films on GaN: effects of cation stoichiometry on surface morphology and crystallinity

Novel optoelectronic device designs based on the heterostructures of III-N and II-IV-N 2 are promising to advance device performance significantly. For example, by utilizing InGaN-ZnGeN 2 quantum well (QW) structures instead of pure InGaN, the band structure engineering in the QW active region can lead to improved electron-hole wavefunction overlap, and thus enhance the radiative efficiency for photon generation. These novel heterostructures have great potential to address the current challenge of low quantum efficiency in InGaN QW based light emitting diodes emitting in green and beyond. The materials development of ZnGeN 2 is still at an early stage as compared to the much matured GaN material system. In an ideal octet rule preserving ordered structure of ZnGeN 2 , every N atom is coordinated by exactly two Zn and two Ge atoms. However, local violation of octet rule can be caused by non-ideal coordination of N by the cations. The disordered structure is thermodynamically less favorable but can still be achieved, for example, in kinetics-limited growth regime. The ordered ZnGeN 2 has a bandgap very close to that of GaN (~3.4 eV) and a lattice mismatch of <0.1% with GaN. Interestingly, the valence band of ZnGeN 2 has been predicted to be ~1 eV above that of GaN, which has inspired novel designs for high efficiency light emitters. In this work, we investigated the metalorganic chemical vapor deposition (MOCVD) of ZnGeN 2 films on GaN/c-sapphire templates. Diethylzinc (DEZn), germane (GeH4) and ammonia were used as the precursors for Zn, Ge and N, respectively. A systematic study was conducted to investigate the cation stoichiometry as a function of growth temperature (TG), total reactor pressure (P) and DEZn/GeH 4 molar flow rate ratio (RII/IV). Under the investigated growth window, the Zn/(Zn+Ge) composition in the films, determined from energy dispersive X-ray spectroscopy, decreased monotonically with increase in TG but increased with increase in P and RII/IV. Atom probe tomography data did not indicate the presence of any secondary phases such as Zn 3 N 2 or Ge 3 N 4 . The surface morphology and crystallinity of the grown films had strong correlation with the Zn/(Zn+Ge) composition. The scanning electron microscopy images showed that the near-stoichiometric films have planar surfaces whereas Zn-rich films had crystallites on their surface and the Zn-poor films had faceted surface. Scanning transmission electron microscopy (STEM) imaging revealed that the Zn-rich and Zn-poor films have columnar and filament-like morphology, respectively, whereas the near-stoichiometric films have continuous film-like cross-sectional morphology. TEM nano-diffraction patterns as well as X-ray diffraction 2θ-ω scan profiles indicate that the near stoichiometric films are single crystalline. Nano-diffraction pattern of the stoichiometric films resembled that of a disordered ZnGeN 2 structure. Room temperature Raman spectra of near-stoichiometric films showed only the phonon density of states like features of a cation disordered ZnGeN 2 . Cathodoluminescence and photoluminescence spectra measured at different temperatures had similar features with peak emission wavelength at ~ 2 eV. In conclusion, the stoichiometry of ZnGeN 2 films can be widely tuned by tuning the MOCVD growth parameters. The surface morphology and the crystallinity of the films were found to have strong correlation with the Zn/(Zn+Ge) composition. The stoichiometric ZnGeN 2 films grown on GaN were demonstrated with uniform surface morphology and high crystalline quality. The results from this work will provide pathway to implement ZnGeN 2 in device structures.

Karim, Md Rezaul↗
NASA NTRS1978

Evidence for CO in Jupiter's atmosphere from airborne spectroscopic observations at 5 microns

High-altitude (12.4 km) spectra of Jupiter recorded at the Kuiper Airborne Observatory are analyzed for the presence of CO absorption lines. A line-by-line comparison of Jupiter's spectrum with that of carbon monoxide is presented, as well as a correlation analysis that includes the influence of other gases present in Jupiter's atmosphere (CH4, NH3, H2O, PH3, and GeH4). The resulting evidence points strongly to the presence of carbon monoxide in Jupiter's atmosphere, thus strengthening Beer's evidence for it. Possible explanations for the existence and observability of Jovian CO, including convection from hotter, deeper layers or decomposition of organic molecules, are explored. A recent suggestion that the Jovian CO is restricted to stratospheric levels is not supported by the observations.

Larson, H. P.↗
NASA NTRS1978

Chemical structure of the deep atmosphere of Jupiter

Equilibrium abundances calculated for a system of over 500 compounds of 27 selected elements along a nominal Jupiter adiabat are reported. Several species predicted to be of negligible abundance in the visible upper troposphere if chemical equilibrium is exactly attained are found to be potential tracers of rapid vertical motions. Vertical mixing of certain species, especially CO, PH3, AsH3, GeS, and GeH4, may provide detectable quantities of these species near the visible cloudtops due to quenching and incomplete equilibration of the rapidly rising, rapidly cooling gas. Observational prospects for detecting such tracers of deep circulation are discussed in the light of the spectroscopic detection of CO in the 5-micron window on Jupiter and the confirmation of PH3 on both Jupiter and Saturn.

Barshay, S. S.↗
NASA NTRS1978

Upper limits to trace constituents in Jupiter's atmosphere from an analysis of its 5 micrometer spectrum

A high-resolution spectrum of Jupiter at 5 micrometers recorded at the Kuiper Airborne Observatory is used to determine upper limits to the column density of 19 molecules. The upper limits to the mixing ratios of SiH4, H2S, HCN, and simple hydrocarbons are discussed with respect to current models of Jupiter's atmosphere. These upper limits are compared to expectations based upon the solar abundance of the elements. This analysis permits upper limit measurements (SiH4), or actual detections (GeH4) of molecules with mixing ratios with hydrogen as low as 10 to the minus 9th power. In future observations at 5 micrometers the sensitivity of remote spectroscopic analyses should permit the study of constituents with mixing ratios as low as 10 to the minus 10th power, which would include the hydrides of such elements as Sn and As as well as numerous organic molecules.

Treffers, R. R.↗
NASA NTRS1979

Infrared observations of the Jovian system from Voyager 1

The infrared spectroscopy and radiometry investigation has obtained spectra of Jupiter and its satellites between approximately 180 and 2500 kayser with a spectral resolution of 4.3 kayser. The Jupiter spectra show clear evidence of H2, CH4, C2H2, C2H6, CH3D, NH3, PH3, H2O, and GeH4. A helium concentration of 0.11 plus or minus 0.03 by volume is obtained. Meridional temperature cross sections show considerable structure. At high latitudes, the stratosphere is warmer in the north than in the south. The upper troposphere and lower stratosphere are locally cold over the Great Red Spot. Amalthea is warmer than expected. Considerable thermal structure is observed on Io, including a relatively hot region in the vicinity of a volcanic feature.

Hanel, R.↗
NASA NTRS1980

The middle-infrared spectrum of Saturn - Evidence for phosphine and upper limits to other trace atmospheric constituents

Observations of Saturn at high spectral resolution in the middle-IR spectral region (2.5-5.6 microns) were obtained using a Fourier spectrometer at ground-based and airborne observatories. These spectra establish that PH3 exists on Saturn with an abundance at least equal to the solar P/H value, and probably enhanced by about a factor of 2. No evidence is found for gaseous or solid NH3 on Saturn throughout this spectral region, and upper limits to several other molecules (H2O, HCN, SiH4, and GeH4) are determined. Frequent comparisons of the spectral data for Saturn with observations and interpretations of IR studies of Jupiter show that these two planetary atmospheres are chemically similar, with major observational differences accounted for by reduced H2O and NH3 abundances in Saturn's colder atmosphere.

Larson, H. P.↗
NASA NTRS1981

High efficiency thin-film GaAs solar cells

The paper demonstrates the feasibility of producing high-efficiency GaAs solar cells with high power-to-weight ratios by organic metallic chemical vapor deposition (OM-CVD) growth of thin epi-layers on suitable substrates. An AM1 conversion efficiency of 18% (14% AM0), or 17% (13% AM0) with a 5% grid coverage is achieved for a single-crystal GaAs n(+)/p cell grown by OM-CVD on a Ge wafer. Thin GaAs epi-layers OM-CVD grown can be fabricated with good crystallographic quality using a Si-substrate on which a thin Ge epi-interlayer is first deposited by CVD from GeH4 and processed for improved surface morphology

Zwerdling, S.↗
NASA NTRS1984

Lower atmospheric composition of Jupiter from Voyager infrared measurements

The observed spectrum of Jovian atmosphere exhibits spectral features of H2, CH4, C2H6, NH3, H2O, GeH4 and CH3D. Analytical programs were developed for radiative transfer calculations and for retrieval of lower atmospheric composition of Jupiter from the observed infrared spectrum. The program models developed are based line by line transmittance calculations with appropriate convolution of the instrument function. The constituent inversion programs were evaluated for accuracy by analyzing synthetic data for retrievals of NH3 profiles. The inversion programs were employed for retrieval of NH3 profiles from the Voyager infared data with results generally in agreement with the accepted values.

Abbas, M. M.↗
NASA NTRS1985

Infrared and far-infrared laser magnetic resonance spectroscopy of the GeH radical - Determination of ground state parameters

The GeH radical has been detected in its ground 2 Pi state in the gas phase reaction of fluorine atoms with GeH4 by laser magnetic resonance techniques. Rotational transitions within both 2 Pi 1/2 and 2 Pi 3/2 manifolds have been observed at far-infrared wavelengths and rotational transitions between the two fine structure components have been detected at infrared wavelengths (10 microns). Signals have been observed for all five naturally occurring isotopes of germanium. Nuclear hyperfine structure for H-1 and Ge-73 has also been observed. The data for the dominant isotope (/Ge-74/H) have been fitted to within experimental error by an effective Hamiltonian to give a set of molecular parameters for the X 2 Pi state which is very nearly complete. In addition, the dipole moment of GeH in its ground state has been estimated from the relative intensities of electric and magnetic dipole transitions in the 10 micron spectrum to be 1.24(+ or - 0.10) D.

Brown, J. M.↗
NASA NTRS1986

The gas composition of Jupiter derived from 5 micron airborne spectroscopic observations

It is pointed out that Jupiter's 5-micron spectrum is a very diagnostic observational tool to probe the troposphere of this giant planet. A report is presented of abundance analyses of NH3, PH3, CH4, CH3D, CO, and GeH4 in the 1- to 6-bar pressure range in Jupiter's troposphere. All the considered molecules have been previously detected in ground-based, airborne, and spacecraft observations of Jupiter. The contribution made by the present study is related to a self-consistent simultaneous determination of the abundances of all of these molecules at the same physical level in Jupiter's atmosphere using one high spectral resolution dataset and a radiative transfer model. It is found that most abundances deviate significantly from expectations based upon an atmospheric model assuming solar composition and chemical equilibrium. The D/H ratio in Jupiter is comparable to that measured in the interstellar medium.

Bjoraker, G. L.↗
NASA NTRS1987

Intensities and H2-broadened half-widths of germane lines around 4.7 microns at temperatures relevant to Jupiter's atmosphere

Absolute intensities and H2-broadened half-widths of R(0) and R(1) of Ge-72H4 have been measured at 119.5, 150.3, 199.0, 250.0, and 296.0 K using a tunable diode laser and the sweep integration technique. The combined intensity of the nu3 bands of all of the five isotopic species of GeH4 as well as that of the Q-branches alone have been measured independently at 294 K using the Wilson-Wells-Penner-Weber technique.

Varanasi, P.↗
NASA NTRS1988

Evidence for germane in Saturn

Observations in Saturn have prompted the development of an 0.4 + or - 0.2 ppb mole fraction for germane (GeH4) on the basis of the P- and R-branch lines' spectra. The presence of germane in Saturn implies a disequilibrium of the upper atmosphere by rapid vertical convection. It is suggested that future, more realistic radiative transfer models that include the effects of scattering within a cloud layer will probably only reduce the mole fraction presently derived for germane, by increasing the effective path length in a given atmospheric layer.

Noll, Keith S.↗
NASA NTRS1988

Infrared spectroscopy of Jupiter and Saturn

High resolution infrared spectoscopy provides unique insights into the chemistry and dynamics of the atmospheres of Jupiter and Saturn. The 5 micrometer spectral region, which is transparent to deep levels, is particularly useful for the identification of molecules that are present at very low (parts per billion) concentrations. These are tracers of convective and strongly non-equilibrium processes in the atmosphere. High resolution ground-based spectroscopy complements Voyager and Galileo measurements. Spectroscopy is sensitive to lower mixing levels for selected molecules, while the on-board mass spectrometers probe molecules that are spectroscopically inaccessible. Analysis and modeling of the 4.7 micrometer carbon monoxide in Jupiter was completed. CO is present at a mole fraction of 1.6 plus or minus 0.3 x 10 to the 9th power and concentrated in the troposphere. At this abundance, it must be convected upward from much deeper levels in Jupiter where the temperature is near 1100 K. Thus CO is a tracer of the deep atmosphere which is otherwise unobservable. The oxygen abundance in Jupiter (as measured by the CO abundance) is near solar. Chemical or physical process must deplete the major oxygen carrier, water. Germane, GeH4, was discovered on Saturn at amole fraction of 4 plus or minus 2 x 10 to the 10th power.

Knacke, Roger↗
NASA NTRS1988

Planetary astronomy and supporting laboratory research

The aim was to obtain form laboratory measurements the molecular parameters needed to interpret observations of planetary and cometary spectra, and to develop the analytical and computational techniques to interpret the observed spectra in terms of planetary atmospheres including solids and cometary ices. The gas phase molecular parameters measured include the intensities and half-widths of vib-rotational lines, total intensities of absorption bands, temperature dependencies, and absorption and pressure parameters in random-band models of absorption bands. Computation of line shapes of H2 quadrupole lines from quantum mechanical first principles for comparison with laboratory data and use in modeling of planetary atmospheres was accomplished. The solid phase measurements include band profile and quantitative intensity measurements and dependence on composition as well as thermal and photolytic processing which mimics the particular astrophysical environments. Work on GeH4, PH3, has made significant progress.

Valero, F. P. J.↗
NASA NTRS1990

Rate constant for reaction of atomic hydrogen with germane

Due to the interest in the chemistry of germane in the atmospheres of Jupiter and Saturn, and because previously reported kinetic reaction rate studies at 298 K gave results differing by a factor of 200, laboratory measurements were performed to determine the reaction rate constant for H + GeH4. Results of the study at 298 K, obtained via the direct technique of flash photolysis-resonance fluorescence, yield the reaction rate constant, k = (4.08 + or - 0.22) x 10(exp -12) cu cm/s.

Nava, David F.↗
NASA NTRS1991

Studies of electron collisions with polyatomic molecules using distributed-memory parallel computers

Elastic electron scattering cross sections from 5-30 eV are reported for the molecules C2H4, C2H6, C3H8, Si2H6, and GeH4, obtained using an implementation of the Schwinger multichannel method for distributed-memory parallel computer architectures. These results, obtained within the static-exchange approximation, are in generally good agreement with the available experimental data. These calculations demonstrate the potential of highly parallel computation in the study of collisions between low-energy electrons and polyatomic gases. The computational methodology discussed is also directly applicable to the calculation of elastic cross sections at higher levels of approximation (target polarization) and of electronic excitation cross sections.

Winstead, C.↗