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At least 1,495 records · Page 83

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DOE OSTI2024

Characterization of n-Type Iodine-Doped and Indium-Doped CdTe/Cd-Se-Te Thin Films Fabricated by Close-Spaced Sublimation Epitaxy

In this study, n-type CdTe thin films, specifically iodine-doped CdTe (CdTe:I), indium-doped CdTe (CdTe:In), and indium-doped Cd-Se-Te (CST:In), were synthesized using close-spaced sublimation epitaxy (CSSE). Characterization techniques secondary ion mass spectrometry (SIMS), electron backscatter diffraction (EBSD), Hall-effect measurements, and time-resolved photoluminescence (TRPL) were employed to analyze the chemical, structural, and electronic properties of these materials. The results indicated epitaxial single crystal CSSE films grew on the single crystal substrates, with carrier density ranging from 10^14 - 10^16 cm -3 , and after post-annealing, the minority-carrier lifetimes reach near the radiative limit. Additionally, a preliminary exploration of homojunction structures with an n- type (CdTe:In /CST:In /CdTe:I) /CdTe:P /Cu /Mo configuration was performed. The best device performance was achieved with CdTe:I including CdS aiding in band alignment, resulting in a power conversion efficiency (..eta..) of 2.61% with open circuit voltage (Voc) of 850 mV, fill factor (FF) of 47.8%, and short-circuit current (Jsc) of 6.44 mA/cm 2 . The observed low Jsc and efficiency may be attributed to a buried junction and a poor interface, due to dopant interdiffusion. Consequently, further investigations focusing on interface optimization, diffusion blocking, and reduced recombination through passivation, are crucial to enhancing the efficiency of CSSE CdTe homojunction devices in the future.

cadmium compounds↗

DOE OSTI2022

Demonstration of >6.0-kV Breakdown Voltage in Large Area Vertical GaN p-n Diodes With Step-Etched Junction Termination Extensions

Vertical gallium nitride (GaN) p-n diodes have garnered significant interest for use in power electronics where high-voltage blocking and high-power efficiency are of concern. In this article, we detail the growth and fabrication methods used to develop a large area (1 mm 2 ) vertical GaN p-n diode capable of a 6.0-kV breakdown. We also demonstrate a large area diode with a forward pulsed current of 3.5 A, an 8.3-mΩ$\cdot$cm 2 differential specific ON-resistance, and a 5.3-kV reverse breakdown. In addition, we report on a smaller area diode (0.063 mm 2 ) that is capable of 6.4-kV breakdown with a differential specific ON-resistance of 10.2 mΩ$\cdot$cm 2 , when accounting for current spreading through the drift region at a 45° angle. Finally, the demonstration of avalanche breakdown is shown for a 0.063-mm 2 diode with a room temperature breakdown of 5.6 kV. In this work, these results were achieved via epitaxial growth of a 50-μm drift region with a very low carrier concentration of <1×10 15 cm –3 and a carefully designed four-zone junction termination extension.

42 ENGINEERING↗

DOE OSTI2020

Creation of skyrmions in van der Waals ferromagnet Fe 3 GeTe 2 on (Co/Pd) n superlattice

Magnetic skyrmions are topological spin textures, which usually exist in noncentrosymmetric materials where the crystal inversion symmetry breaking generates the so-called Dzyaloshinskii-Moriya interaction. This requirement unfortunately excludes many important magnetic material classes, including the recently found two-dimensional van der Waals (vdW) magnetic materials, which offer unprecedented opportunities for spintronic technology. Using photoemission electron microscopy and Lorentz transmission electron microscopy, we investigated and stabilized Néel-type magnetic skyrmion in vdW ferromagnetic Fe 3 GeTe 2 on top of (Co/Pd) n in which the Fe 3 GeTe 2 has a centrosymmetric crystal structure. We demonstrate that the magnetic coupling between the Fe 3 GeTe 2 and the (Co/Pd) n could create skyrmions in Fe 3 GeTe 2 without the need of an external magnetic field. Our results open exciting opportunities in spintronic research and the engineering of topologically protected nanoscale features by expanding the group of skyrmion host materials to include these previously unknown vdW magnets.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

N-Glycolylneuraminic Acid Binding of Avian and Equine H7 Influenza A Viruses

Influenza A viruses (IAV) initiate infection by binding to glycans with terminal sialic acids on the cell surface. Hosts of IAV variably express two major forms of sialic acid, N-acetylneuraminic acid (NeuAc) and N-glycolylneuraminic acid (NeuGc). NeuGc is produced in most mammals, including horses and pigs, but is absent in humans, ferrets, and birds. The only known naturally occurring IAV that exclusively bind NeuGc are extinct highly pathogenic equine H7N7 viruses. We determined the crystal structure of a representative equine H7 hemagglutinin (HA) in complex with NeuGc and observed high similarity in the receptor-binding domain with an avian H7 HA. To determine the molecular basis for NeuAc and NeuGc specificity, we performed systematic mutational analyses, based on the structural insights, on two distant avian H7 HAs and an H15 HA. We found that the A135E mutation is key for binding α2,3-linked NeuGc but does not abolish NeuAc binding. The additional mutations S128T, I130V, T189A, and K193R converted the specificity from NeuAc to NeuGc. We investigated the residues at positions 128, 130, 135, 189, and 193 in a phylogenetic analysis of avian and equine H7 HAs. This analysis revealed a clear distinction between equine and avian residues. The highest variability was observed at key position 135, of which only the equine glutamic acid led to NeuGc binding. These results demonstrate that genetically distinct H7 and H15 HAs can be switched from NeuAc to NeuGc binding and vice versa after the introduction of several mutations, providing insights into the adaptation of H7 viruses to NeuGc receptors.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2025

1 × 1 km maps of abundances of eight enzyme functional classes for soil C, N, and P cycling across the CONUS

This dataset includes eight 1 × 1 km maps of the abundances of eight enzyme functional classes (EFC) for soil C, N, and P cycling across the CONUS. These mappings are predicted by the machine learning model trained using metagenomics and the corresponding environmental data. This item corresponds to our article: Fan, C., Song, Y., Mishra, U., Gautam, S., & Mayes, M. A. (2025). Harnessing the Power of Machine Learning and Omics to Identify Environmental Regulation on Microbial Functional Composition for Soil C, N, and P Cycling. Journal of Geophysical Research: Biogeosciences, 130(10).

1 × 1 km↗

DOE OSTI2024

Effects of N -glycans on the structure of human IgA2

The transition of IgA antibodies into clinical development is crucial because they have the potential to create a new class of therapeutics with superior pathogen neutralization, cancer cell killing, and immunomodulation capacity compared to IgG. However, the biological role of IgA glycans in these processes needs to be better understood. This study provides a detailed biochemical, biophysical, and structural characterization of recombinant monomeric human IgA2, which varies in the amount/locations of attached glycans. Monomeric IgA2 antibodies were produced by removing the N-linked glycans in the CH1 and CH2 domains. The impact of glycans on oligomer formation, thermal stability, and receptor binding was evaluated. In addition, we performed a structural analysis of recombinant IgA2 in solution using Small Angle X-Ray Scattering (SAXS) to examine the effect of glycans on protein structure and flexibility. Our results indicate that the absence of glycans in the Fc tail region leads to higher-order aggregates. SAXS, combined with atomistic modeling, showed that the lack of glycans in the CH2 domain results in increased flexibility between the Fab and Fc domains and a different distribution of open and closed conformations in solution. When binding with the Fcα-receptor, the dissociation constant remains unaltered in the absence of glycans in the CH1 or CH2 domain, compared to the fully glycosylated protein. These results provide insights into N-glycans’ function on IgA2, which could have important implications for developing more effective IgA-based therapeutics in the future.

59 BASIC BIOLOGICAL SCIENCES↗

NASA NTRS1965

Epitaxial process development for monolithic complementary MOS-FET structures with P-N JUNCTION isolation Final report, 1 Feb. - 15 Jul. 1965

Epitaxial deposition of P-type silicon into etche grooves in N-type silicon for P-N junction for complimentary MOS-FET devices

P-N JUNCTION↗

NASA NTRS1975

Semi-empirical calculation of depletion region width in n+-p silicon solar cells

An extension of the width calculation for impurity distributions of complementary error function and the Gaussian function, in addition to the exponential function is used in combination with experimental width values deduced from capacitance measurements at zero bias to numerically determine the width occurring in both the n+ and p junctions. The total possible error o the semi-empirical calculation is less than plus or minus 3%. Results show considerable variation in the depletion widths occurring in the n+ and p regions for different impurity profiles.

Wang, E. Y.↗

NASA NTRS1983

Development of a segmented n-type germanium detector, and its application to astronomical gamma-ray spectroscopy

Extensive calculations and simulations have shown that the instrumental background in a coaxial germanium photon detector flown at balloon altitudes or in space, can be substantially reduced by segmenting the outer contact. The contact is divided into horizontal strips around the side of the detector, giving it many characteristics similar to that of a stack of planar detectors. By choosing different segment coincidence requirements in different energy ranges, one can obtain a factor of approx. 2 increase in sensitivity to spectral lines between 40 keV and 1 MeV, compared with an unsegmented detector. The reverse electrode configuration (using n-type germanium), with the p contact outside, is preferred for this application due to its thin dead layer and resistance to radiation damage in space. A small two segment n type detector is being developed to serve as a prototype for larger multisegment devices. Results of this development effort and of detector tests are presented.

Gehrels, N.↗

NASA NTRS1984

The development of a segmented N-type germanium detector, and its application to astronomical gamma-ray spectroscopy

Gehrels, N.↗

NASA NTRS1988

Modified reaction mechanism of aerated n-dodecane liquid flowing over heated metal tubes

The degradation mechanism of the n-dodecane was studied using a modified jet fuel thermal oxidation tester containing a sample withdrawal system as a reaction vessel. The reaction products were identified using gas chromatography and mass spectorometry. The soluble products were found to consist mainly of C5-C10 n-alkanes and 1-alkenes, C7-C10 aldehydes, tetrahydrofuran derivatives, dodecanol and dodecanone isomers, dodecyl hydroperoxide (ROOH) decomposition products, and C24 alkane isomers. The data from the experiments agreed with those of Hazlett et al. (1977). It was found that alkyl peroxide radical reactions dominate in the autooxidation temperature regime (at T not above 300 C); the dominant path is for the alkyl peroxyl radical to react bimolecularly with fuel to yield primarily alkyl hydroperoxides. The alkyl peroxide radical also undergoes self-termination and unimolecular isomerization and decomposition reactions, to yield smaller amounts of C12 alcohol plus ketone products and tetrahydrofuran derivatives, respectively.

Reddy, K. T.↗

NASA NTRS1992

Improved electrical properties of n-type SiGe alloys

The effect of changes in the carrier concentration and mobility for heavily doped n-type SiGe on the electrical power factor has been investigated. It has been shown that power factors of 37-40 microV/cm-K-squared can be achieved with carrier concentrations of 2.0 - 2.5 x 10 exp 20/cu cm and mobilities of 38-40 sq cm/V-sec. Many samples with suitable carrier concentration do not have high mobilities and some rationale for this behavior is presented. Initial results are presented on fabrication of n-type samples from ultrafine powders. The emphasis in this work is to achieve thermal conductivity reductions by adding inert particles to scatter midfrequency phonons.

Scoville, A. N.↗

NASA NTRS1993

Electronic passivation of n- and p-type GaAs using chemical vapor deposited GaS

We report on the electronic passivation of n- and p-type GaAs using CVD cubic GaS. Au/GaS/GaAs-fabricated metal-insulator-semiconductor (MIS) structures exhibit classical high-frequency capacitor vs voltage (C-V) behavior with well-defined accumulation and inversion regions. Using high- and low-frequency C-V, the interface trap densities of about 10 exp 11/eV per sq cm on both n- and p-type GaAs are determined. The electronic condition of GaS/GaAs interface did not show any deterioration after a six week time period.

Tabib-Azar, Massood↗

NASA NTRS1994

Status of diffused junction p+n InP solar cells for space applications

Recently, we have succeeded in fabricating diffused junction p(sup +)n(Cd,S) InP solar cells with measured AMO, 25 C open circuit voltage (V(sub OC)) of 887.6 mV, which, to the best of our knowledge, is higher than previously reported V(sub OC) values for any InP homojunction solar cells. The experiment-based projected achievable efficiency of these cells using LEC grown substrates is 21.3 percent. The maximum AMO, 25 C internal losses due to date on bare cells is, however, only 13.2 percent. This is because of large external and internal losses due to non-optimized front grid design, antireflection (AR) coating and emitter thickness. This paper summarizes recent advances in the technology of fabrication of p(sup +)n InP diffused structures and solar cells, resulted from a study undertaken in an effort to increase the cell efficiency. The topics discussed in this paper include advances in: (1) the formation on thin p(sup +) InP:Cd emitter layers, (2) electroplated front contacts, (3) surface passivation and (4) the design of a new native oxide/Al2O3/MgF2 tree layer AR coating using a chemically-grown P-rich passivating oxide as a first layer. Based on the high radiation resistance and the excellent post-irradiation annealing and recovery demonstrated in the early tests done to date, as well as the projected high efficiency and low-cost high-volume fabricability, these cells show a very good potential for space photovoltaic applications.

Faur, Mircea↗

NASA NTRS1995

Thermally stable, low resistance contact systems for use with shallow junction p(+) nn(+) and n(+)pp(+) InP solar cells

Two contact systems for use on shallow junction InP solar cells are described. The feature shared by these two contact systems is the absence of the metallurgical intermixing that normally takes place between the semiconductor and the contact metallization during the sintering process. The n(+)pp(+) cell contact system, consisting of a combination of Au and Ge, not only exhibits very low resistance in the as-fabricated state, but also yields post-sinter resistivity values of 1(exp -7) ohms-sq cm, with effectively no metal-InP interdiffusion. The n(+)pp(+)cell contact system, consisting of a combination of Ag and Zn, permits low resistance ohmic contact to be made directly to a shallow junction p/n InP device without harming the device itself during the contacting process.

Weizer, V. G.↗

NASA NTRS1998

The [N II] Kinematics of R Aquarii

We report a kinematic study of the symbiotic star system R Aqr derived from [N H]lambda 6584 emission observations with a Fabry-Perot imaging spectrometer. The [N II] spatial structure of the R Aqr jet, first observed circa 1977, and surrounding hourglass-shaped nebulosity, due to an explosion approximately 660 years ago, are derived from 41 velocity planes spaced at approximately 12 km/s intervals. Fabry-Perot imagery shows the elliptical nebulosity comprising the waist of the hourglass shell is consistent with a circular ring expanding radially at 55 km/s as seen at an inclination angle, i approximately 70 deg. Fabry-Perot imagery shows the two-sided R Aqr jet is collimated flow in opposite directions. The intensity-velocity structure of the strong NE jet component is shown in contrast to the amorphous SW jet component. We offer a idealized schematic model for the R Aqr jet motion which results in a small-scale helical structure forming around a larger-scale helical path. The implications of such a jet model are discussed. We present a movie showing a side-by-side comparison of the spatial structure of the model and the data as a function of the 41 velocity planes.

Hollis, J. M.↗

NASA NTRS1994

Status of Diffused Junction p(+)n InP Solar Cells for Space Applications

Recently, we have succeeded in fabricating diffused junction p(+)n(Cd,S) InP solar cells with measured AMO, 25 C open circuit voltage (V(sub OC)) of 887.6 mV, which, to the best of our knowledge, is higher than previously reported V(sub OC) values for any InP homojunction solar cells. The experiment-based projected achievable efficiency of these cells using LEC grown substrates is 21.3%. The maximum AMO, 25 C efficiency recorded to date on bare cells is, however, only 13.2%. This is because of large external and internal losses due to non-optimized front grid design, antireflection (AR) coating and emitter thickness. This paper summarizes recent advances in the technology of fabrication of p(+)n InP diffused structures and solar cells, resulted from a study undertaken in an effort to increase the cell efficiency. The topics discussed in this paper include advances in: 1) the formation of thin p(+) InP:Cd emitter layers, 2) electroplated front contacts, 3) surface passivation and 4) the design of a new native oxide/AI203/MgF2 three layer AR coating using a chemically-grown P-rich passivating oxide as a first layer. Based on the high radiation resistance and the excellent post-irradiation annealing and recovery demonstrated in the early tests done to date, as well as the projected high efficiency and low-cost high-volume fabricability, these cells show a very good potential for space photovoltaic applications.

Faur, Mircea↗

NASA NTRS2000

A DNA enzyme with N-glycosylase activity

In vitro evolution was used to develop a DNA enzyme that catalyzes the site-specific depurination of DNA with a catalytic rate enhancement of about 10(6)-fold. The reaction involves hydrolysis of the N-glycosidic bond of a particular deoxyguanosine residue, leading to DNA strand scission at the apurinic site. The DNA enzyme contains 93 nucleotides and is structurally complex. It has an absolute requirement for a divalent metal cation and exhibits optimal activity at about pH 5. The mechanism of the reaction was confirmed by analysis of the cleavage products by using HPLC and mass spectrometry. The isolation and characterization of an N-glycosylase DNA enzyme demonstrates that single-stranded DNA, like RNA and proteins, can form a complex tertiary structure and catalyze a difficult biochemical transformation. This DNA enzyme provides a new approach for the site-specific cleavage of DNA molecules.

Non-NASA Center↗