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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Low Threshold Lasing in InP/GaInP Quantum Dot Microdisks

We report a realization of room temperature lasing threshold of 1 μW in GaInP microdisk containing a few self-aggregated InP/GaInP quantum dots (QDs) grown by metal-organic vapor phase epitaxy. InP/GaInP QD microdisk cavities emitting in the spectral range of 700–800 nm and having the size of ~2 μm, free spectral range of ~35 nm and quality factors Q ~ 4000 were formed by wet chemical etching. Low dot density (~2 μm{sup –2}) and large dot size (~150 nm), suggesting a single dot lasing and maximum overlap of QD and cavity mode, were achieved using deposition of 3 ML of InP layer at 700°C.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of the Conductive Channel Cut-Off on Operation of n{sup +}–n–n{sup +} GaN NW-Based Gunn Diode

Nowadays modern science and technology require development of efficient electromagnetic emitters covering far GHz and THz ranges. Semiconductor elements with negative differential resistance (NDR) such as Gunn diodes based on GaAs and InP are well-established powerful microwave emitters. In this work the Gunn diode structure based on single GaN nanowire with the potential of THz device development was proposed and investigated both theoretically and experimentally. According to the results of the numerical modeling, the Gunn generation can be obtained in the proposed geometry. Dependence of the doping concentration on the NW length necessary for the electrons domain formation was obtained. The nanostructures were grown via molecular beam epitaxy technique. Contacts to single nanowires were fabricated with the combination of e-beam lithography and thermal evaporation. It was shown experimentally that the volt-ampere characteristics of the GaN nanowire structure possess current saturation region. Experimental results correspond well to proposed numerical model.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

A Search for Asymmetric Barrier Layers for 1550 nm Al-Free Diode Lasers

A search for materials suitable for implementation of 1.55 µm Al-free diode lasers based on InP with asymmetric barrier (AB) layers is conducted. It is shown that a very high (over 10{sup 6}) suppression ratio of the parasitic electron flux can be achieved using common III–V alloys for the ABs. Hence placing such ABs in the immediate vicinity of the active region should completely suppress the parasitic recombination in the waveguide. Several optimal AB designs are proposed that are based on one of the following alloys: Al-free GaInPSb, ternary AlInAs, or quaternary AlGaInAs with a low Al-content. As an important and beneficial byproduct of utilization of such ABs, an improvement of majority carrier capture into the active region occurs.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Spontaneous Emission and Lasing of a Two-Wavelength Quantum-Cascade Laser

The results of experiments on the fabrication (by molecular-beam epitaxy) and investigation of the heterostructures of a two-frequency quantum-cascade laser produced on the basis of a heteropair of In{sub 0.53}Ga{sub 0.47}As/Al{sub 0.48}In{sub 0.52}As solid solutions on an InP substrate are presented. The heterostructures contained quantum cascades emitting at a wavelength of 9.6 μm and cascades emitting at a wavelength of 7.6 μm. The high structural quality of the fabricated heterostructures is shown. The spontaneous emission and lasing spectra are investigated and the multimodal laser generation of stripe lasers at a wavelength of 7.6 μm is demonstrated.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Comparative Studies of AlGaAs/InGaAs Enhancement/Depletion-Mode High Electron Mobility Transistors with Virtual Channel Layers by Hybrid Gate Recesses Approaches

Unlike the conventional GaAs- and InP-based enhancement/depletion-mode (E/D-mode) transistors, the improved gate characteristics of the AlGaAs/InGaAs E-mode high electron mobility transistors (HEMTs) by way of hybrid gate recesses to remove the n-AlAs/i-GaAs/n-AlGaAs virtual channel layers upon 2DEG channels are demonstrated. As compared to the D-mode device (sample A), the gate reverse currents are effectively reduced by 45 and 102 times for the E-mode devices with additional gate recess time of 24 s (sample B) and 30 s (sample C) to remove part of the virtual channel layers, respectively. Under gate forward bias, the hybrid gate recesses also enable the gate turn-on voltages to increase. Furthermore, the threshold voltages of –1.25, 0.09, and 0.22 V are observed in the samples A, B, and C, respectively. The maximum transconductances of 187.3, 209.2, and 243.4 mS/mm and saturation current density of 482.8, 410.6, and 347.4 mA/mm are obtained in the samples A, B, and C, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

High-Power Nano- and Picosecond Optoelectronic Switches Based on High-Voltage Silicon Structures with p–n Junctions. III. Self-Heating Effects

The self-heating effects of optoelectronic switches based on vertical high-voltage structures with p–n junctions (Vertical Photoactivated Semiconductor Switches, VPSS) operating in the high-frequency mode are theoretically studied for the first time. It is shown that the strong temperature dependence of the control-radiation absorbance κ(T) is a major factor controlling the maximum switching frequency f{sub max} and the corresponding maximum crystal temperature T{sub max}, as well as the temperature T and current density j distributions over the device area. Two-dimensional analysis of the simplest electrothermal model of a VPSS embedded into a double coaxial forming line shows that an increase in the switching frequency f leads to current displacement to the device periphery where the temperature is minimum. However, the T and j distributions over the device area remain stable at f < f{sub max} and T < T{sub max}. Certainly, f{sub max} and T{sub max} depend on the control-radiation pulse energy, pulse switching power, and heat-removal conditions. For the VPSS based on indirect-gap semiconductors (Si, SiC), they vary within 20–120 kHz and 120–160°C which is quite sufficient for practical applications. However, VPSSs based on direct-gap semiconductors (GaAs, InP) are in fact inapplicable to operation in high-frequency modes due to the fact that the dependence κ(T) is too sharp.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Nonradiative Energy Transfer in Hybrid Nanostructures with Varied Dimensionality

A composite nanostructure based on quasi-one-dimensional InP nanowires with an InAsP nanoinsert, grown on a Si(111) substrate by the method of molecular-beam epitaxy, and CdSe/ZnS zero-dimensional colloidal quantum dots is reported for the first time. The nonradiative resonance energy transfer between components of the hybrid nanostructure, namely, between the colloidal quantum dots and the nanoinsert, is experimentally confirmed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Quantum-Cascade Lasers Generating at the 4.8-μm Wavelength at Room Temperature

We report on room-temperature generation at the 4.8-μm wavelength in a lattice-matched structure of a quantum cascade laser (QCL) grown on indium phosphide (InP) substrate. Laser heterostructures grown by molecular beam epitaxy (MBE) comprised 30 cascades and were designed to generate at the 4.80 μm wavelength corresponding to an atmospheric transparency window. Experiments demonstrated effective lasing at temperatures from 80 to 300 K on a wavelength coinciding with the calculated value, which confirmed the high quality of interfaces, high precision of layer thicknesses, and high accuracy of active region doping.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

The Influence of the InAlAs Layer Surface Morphology on the Temperature Dependence of Parameters of Au/Ti/n-InAlAs(001) Schottky Diodes

Growth-related structural defects present on the surface of InAlAs layers grown by molecular beam epitaxy on InP(001) substrates influence the temperature dependences of the current–voltage characteristics of Au/Ti/InAlAs Schottky barriers. It is established that these defects in the form of pits cause the appearance of regions with reduced barrier height. At a surface density of ≥10{sup 7} cm{sup –2}, these defects significantly influence the parameters of the Schottky barriers at temperatures below 200 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Heterobarrier Varactors with Nonuniformly Doped Modulation Layers

Optimum shape of the capacitance–voltage (C–V) characteristic is a critical parameter determining the efficiency of frequency multiplication in heterobarrier varactors (HBVs) operating in the millimeter and submillimeter frequency ranges. A numerical model for calculating the C–V characteristics and leakage currents of HBV heterostructures with arbitrary composition and doping profiles has been verified on the basis of published and original experimental data. A specially designed HBV heterostructure with three undoped InAlAs/AlAs/InAlAs barriers surrounded by nonuniformly doped n-InGaAs modulation layers has been grown by molecular beam epitaxy on InP substrate. Prototype HBVs manufactured using the proposed heterostructure demonstrated a nearly cosine shape of the C–V curve at bias voltages up to 2 V, increased overlap capacitance, and low leakage currents.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

WaterSystems.jl

WaterSystems.jl is a Julia package for defining water delivery infrastructure system data and problem definitions. The WaterSystems.jl package enables parsing from the EPANET *.inp file format and the expression of data for WaterSimulations.jl models. WaterSystems.jl defines a data schema for water infrastructure networks.

Barrows, Clayton↗
DOE OSTI2021

inp2cjw

inp2cjw is a utility program for hierarchical finite element analysis which converts Abaqus formatted (inp) model output from CUBIT to a format (cjw) for HFEM and HFEM-Hydro modeling codes while introducing volume, facet, and edge material properties into the model. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2021-4551 O

Weiss, ChesterJ↗
DOE OSTI2024

TAMU TRACER: Targeted Mobile Measurements to Isolate the Impacts of Aerosols and Meteorology on Deep Convection

Difficulty in using observations to isolate the impacts of aerosols from meteorology on deep convection often stems from inability to resolve the spatiotemporal variations in the environment serving as the storm’s inflow region. During the DOE TRacking Aerosol Convection interactions ExpeRiment (TRACER) in June-September 2022, a Texas A&M University (TAMU) team conducted a mobile field campaign to characterize the meteorological and aerosol variability in airmasses that serve as inflow to convection across the ubiquitous mesoscale boundaries associated with the sea- and bay-breezes in the Houston, Texas, region. These boundaries propagate inland over the fixed DOE Atmospheric Radiation Measurement (ARM) sites. However, convection occurs on either or both the continental or maritime sides or along the boundary. The maritime and continental airmasses serving as convection inflow may be quite distinct, with different meteorological and aerosol characteristics that fixed-site measurements cannot simultaneously sample. Thus, a primary objective of TAMU TRACER was to provide mobile measurements similar to those at the fixed sites, but in the opposite airmass across these moving mesoscale boundaries. TAMU TRACER collected radiosonde, lidar, aerosol, cloud condensation nuclei (CCN), and ice nucleating particle (INP) measurements on 29 enhanced operations days covering a variety of maritime, continental, outflow, and pre-frontal airmasses. This paper summarizes the TAMU TRACER deployment and measurement strategy, instruments, available datasets, and provides sample cases highlighting differences between these mobile measurements and those made at the ARM sites. We also highlight the exceptional TAMU TRACER undergraduate student participation in high impact learning activities through forecasting and field deployment opportunities.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Dependencies of Four Mechanisms of Secondary Ice Production on Cloud-Top Temperature in a Continental Convective Storm

Various mechanisms of secondary ice production (SIP) cause multiplication of numbers of ice particle, after the onset of primary ice. A measure of SIP is the ice enhancement ratio (“IE ratio”) defined here as the ratio between number concentrations of total ice (excluding homogeneously nucleated ice) and active ice-nucleating particles (INPs). A convective line observed on 11 May 2011 over the Southern Great Plains in the Mesoscale Continental Convective Cloud Experiment (MC3E) campaign was simulated with the “Aerosol–Cloud” (AC) model. AC is validated against coincident MC3E observations by aircraft, ground-based instruments, and satellite. Four SIP mechanisms are represented in AC: the Hallett–Mossop (HM) process of rime splintering, and fragmentation during ice–ice collisions, raindrop freezing, and sublimation. The vertical profile of the IE ratio, averaged over the entire simulation, is almost uniform (10 2 to 10 3 ) because fragmentation in ice–ice collisions dominates at long time scales, driving the ice concentration toward a theoretical maximum. The IE ratio increases with both the updraft (HM process, fragmentation during raindrop freezing, and ice–ice collisions) and downdraft speed (fragmentation during ice–ice collisions and sublimation). As reported historically in aircraft sampling, IE ratios were predicted to peak near 10 3 for cloud-top temperatures close to the −12°C level, mostly due to the HM process in typically young clouds with their age less than 15 min. Here, at higher altitudes with temperatures of −20° to −30°C, the predicted IE ratios were smaller, ranging from 10 to 10 2 , and mainly resulted from fragmentation in ice–ice collisions.

Aerosols↗
DOE OSTI2017

Quantifying engineered nanomaterial toxicity: comparison of common cytotoxicity and gene expression measurements

When evaluating the toxicity of engineered nanomaterials (ENMS) it is important to use multiple bioassays based on different mechanisms of action. In this regard we evaluated the use of gene expression and common cytotoxicity measurements using as test materials, two selected nanoparticles with known differences in toxicity, 5 nm mercaptoundecanoic acid (MUA)-capped InP and CdSe quantum dots (QDs). We tested the effects of these QDs at concentrations ranging from 0.5 to 160 µg/mL on cultured normal human bronchial epithelial (NHBE) cells using four common cytotoxicity assays: the dichlorofluorescein assay for reactive oxygen species (ROS), the lactate dehydrogenase assay for membrane viability (LDH), the mitochondrial dehydrogenase assay for mitochondrial function, and the Comet assay for DNA strand breaks.

Biomarkers↗
DOE OSTI2021

Hybrid integrated photonic platforms: opinion

While photonic integration has made remarkable progress in recent years, there is no one integrated photonic platform that offers all desired functionalities and manufacturability on the same platform. GaAs and InP-based optoelectronic integrated circuits (OEICs) were very popular in the past decades; however, silicon photonics has recently emerged as a preferred platform due to its high-density and high-yield manufacturability leveraging the CMOS ecosystem, although it lacks optical gain, the Pockels effect, and other characteristics. On the other hand, hybrid photonic integration adds new and diverse functionalities to the host materials like silicon. This opinion paper investigates hybrid integrated photonic platforms, and discusses the new functionalities added to the silicon CMOS photonic platform.

42 ENGINEERING↗
DOE OSTI2025

automesh: Automatic mesh generation in Rust

automesh is an open-source Rust software program that uses a segmentation, typically generated from a 3D image stack, to create a finite element mesh, composed either of hexahedral (volumetric) or triangular (isosurface) elements. automesh converts between segmentation formats (.npy, .spn) and mesh formats (.exo, .inp, .mesh, .stl, .vtk). automesh can defeature voxel domains, apply Laplacian and Taubin smoothing, and output mesh quality metrics. automesh uses an internal octree for fast performance.

Hovey, Chad Brian [Sandia National Laboratories (S↗
DOE OSTI2013

Truchas Reference Manual (V.2.8)

Truchas is executed in serial using a command of the form truchas [-h] [-d[:n ]] [-t] [-o:outdir ] [-r:rstfile ] infile assuming truchas is the name of the executable. The brackets denote optional arguments that are described in Table 1.1. The only required argument is the path to the input file infile . This file name must end with the extension “.inp" (without the quotes). The general format of the input file is described in the next section, and the following chapters describe the various Fortran namelists that go into the input file to describe the problem to be simulated. All of the output files are written to directory whose name is generated from the base name of the input file. For example, if the input file is myprob.inp, the output directory will be named myprob_output. The name of the output directory can be overridden using the -o option. The directory will be created if necessary. The precise manner of executing Truchas in parallel depends on the MPI implementation being used. This may be as simple as prefixing the serial invocation above with “mpirun -np n”, where n is the number of processes. But this varies widely and providing specific instructions is beyond the scope of this document. There is no difference in the Truchas arguments between serial and parallel, however.

36 MATERIALS SCIENCE↗