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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

3-D Atomic-Scale Mapping of Manganese Dopants in Lead Sulfide Nanowires

Dopants in nanowires, whether intentional or unintentional, can ultimately control the material's properties and therefore need to be understood on the atomic scale. We study vapor-liquid-solid grown manganese-doped lead sulfide nanowires by atom-probe tomography for the first time for lead salt materials. The three-dimensional chemical concentration maps at the atomic scale demonstrate a radial distribution profile of Mn ions, with a concentration of only 0.18 at.% and 0.01 at.% for MnCl2 and Mn-acetate precursors, respectively. The ability to characterize these small concentrations of dopant atoms in Pb1-xMnxS nanowires (x = 0.0036 and 0.0002), important for spintronic and thermoelectric devices, sets a platform for similar analyses for all nanostructures. First-principles calculations confirm that Mn atoms substitute for Pb in the PbS structure.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Gallium-Doped Poly-Si:Ga/SiO 2 Passivated Emitters to n-Cz Wafers With iV oc >730 mV

Here, we form gallium-doped poly-Si:Ga/SiO 2 passivated contacts on n-type Czochralski (n-Cz) wafers using ion implantation of Ga and Ga-containing spin-on dopants. After annealing and passivation with Al 2 O 3 , the contacts exhibit i Voc values of >730 mV with corresponding Joe values of <5 fA/cm 2 . These are among the best-reported values for p-type poly-Si/SiO 2 contacts. Secondary ion mass spectroscopic depth profile data show that, in contrast to B, Ga does not pileup at the SiO 2 interface in agreement with its known high diffusivity in SiO 2 . This lack of Ga pileup may imply fewer dopant-related defects in the SiO 2 , compared with B dopants, and account for the excellent passivation.

14 SOLAR ENERGY↗
DOE OSTI2021

Polymer Stabilized Paraboloid Liquid Crystal Microlenses with Integrated Pancharatnam–Berry Phase

Aspheric lenses reduce aberration and provide sharper images with improved spot size compared to spherical lenses. Here this paper demonstrates that applying shear flow can produce plano-concave liquid crystal (LC) lens arrays with paraboloid aspheric profiles. The focal length of individual lenses, with a 0.2 mm aperture, decreases from 0.67 to 0.45 mm as the chiral dopant increases from 0 to 6 wt%. The focal length is also sensitive to the polarization state of the incoming light. The lenses are stabilized by photopolymerizing with 6 wt% of reactive monomer added to the LC. A qualitative explanation for the flow-induced lens formation and the optical properties of the lenses is provided. The potential tunability of the lenses in various fields and their use as paraboloid reflectors are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Development of arsenic doped Cd(Se,Te) absorbers by MOCVD for thin film solar cells

Recent developments in CdTe solar cell technology have included the incorporation of ternary alloy Cd(Se,Te) in the devices. CdTe absorber band gap grading due to Se alloying contributes to current density enhancement and can result in device performance improvement. Here we report Cd(Se,Te) polycrystalline thin films grown by a chamberless inline atmospheric pressure metal organic chemical vapour deposition technique, with subsequent incorporation in CdTe solar cells. The compositional dependence of the crystal structure and optical properties of Cd(Se,Te) are examined. Selenium graded Cd(Se,Te)/CdTe absorber structure in devices are demonstrated using either a single CdSe layer or CdSe/Cd(Se,Te) bilayer (with or without As doping in the Cd(Se,Te) layer). Cross-sectional TEM/EDS, photoluminescence spectra and secondary ion mass spectroscopy analysis confirmed the formation of a graded Se profile toward the back contact with a diffusion length of ~1.5 um and revealed back-diffusion of Group V (As) dopants from the CdTe layer into Cd(Se,Te) grains. Due to the strong Se/Te interdiffusion, CdSe in the Se bilayer configuration was unable to form an n-type emitter layer in processed devices. In situ As doping of the Cd(Se,Te) layer benefited the device junction quality with current density reaching 28.3 mA/cm 2 . The results provide useful insights for the optimisation of Cd(Se,Te)/CdTe solar cells.

14 SOLAR ENERGY↗
DOE OSTI2014

Band engineering of GaN/AlN quantum wells by Si dopants

The electronic properties of GaN/AlN quantum wells are engineered by Si doped in different positions with the aid of the first-principle calculations. The local potential where the dopant located is dragged down as a result of negative center induced by the Si atom, leading to a different shift of the potential, and further affects the band bending and carrier distribution. The band profiles are depicted by analyzing the projected densities of states, it is found that the different positions of Si doping lead to a different band bending owing to the modified polarization fields. The spatial distributions of electrons and holes plotted by the partial charge densities reveal that electrons and holes experience redistribution by Si dopant in different positions. The above results demonstrate that the effect of polarization on the band bending has been significantly modulated by Si doped in different positions. Such modification of electronic structure is especially valuable for the fabrication of GaN/AlN QWs under desired control.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Increasing stagnation pressure and thermonuclear performance of inertial confinement fusion capsules by the introduction of a high-Z dopant

Inertial confinement fusion requires the inertia of the imploding mass to provide the necessary confinement such that the core reaches adequate high density, temperature, and pressure. Studies utilize low-Z capsules filled with hydrogenic fuel, which are subject to multiple instabilities at the interfaces during the implosion. To improve the stability of the fuel:capsule interface and narrow the imploding shell profile, capsules are doped with a small atomic percentage of a high-Z material. A series of recent indirect-drive experiments executed at the National Ignition Facility with tungsten-doped high density carbon capsules has demonstrated that the presence of this dopant serves to increase the in-flight aspect ratio of the shell and increase the compression and neutron yield performance of both gas-filled and deuterium-tritium cryogenically layered targets. These experiments definitively show that benefits accrued by the introduction of a high-Z dopant into the capsule can outweigh the detrimentally reduced stability of the ablation front, avoiding shell breakup or significant radiative cooling of the hot spot. Future experiments will utilize these types of capsules to additionally increase nuclear performance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2020

Selective acetylene hydrogenation over single metal atoms supported on Fe 3 O 4 (001): A first-principle study

Supported single-atom catalysts (SACs) have gained increasing attention for improved catalytic activity and selectivity for industrially-relevant reactions. In this study, we explore the hydrogenation of acetylene over single Pt, Ru, Rh, Pd, and Ir atoms supported on the Fe 3 O 4 (001) surface using density functional theory (DFT) calculations. The thermodynamic profile of H diffusion is significantly changed with the type of single metal atoms used and suggests that H spillover from the single atom dopant to the Fe 3 O 4 (001) surface is favored and will likely lead to high H coverages in the functioning catalyst. Correspondingly, as the surface H coverage increases, the important desorption step of ethylene becomes energetically competitive against the detrimental hydrogenation steps of ethylene to ethane. Overall, we show herein that the selectivity of SACs towards ethylene production can be tuned by considering the proper type of metal and controlling the redox state of the support.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Investigation of Donor and Acceptor Ion Implantation in AlN

AlGaN alloys with high Al composition and AlN based electronic devices are attractive for high voltage, high temperature applications, including microwave power sources, power switches and communication systems. AlN is of particular interest because of its wide bandgap of ~6.1eV which is ideal for power electronic device applications in extreme environments which requires high dose ion implantation. One of the major challenges that need to be addressed to achieve full utilization of AlN for opto and microelectronic applications is the development of a doping strategy for both donors and acceptors. Ion implantation is a particularly attractive approach since it allows for selected-area doping of semiconductors due to its high spatial and dose control and its high throughput capability. Active layers in the semiconductor are created by implanting a dopant species followed by very high temperature annealing to reduce defects and thereby activate the dopants. Recovery of implant damage in AlN requires excessively high temperature. In this SBIR program we began the investigation by simulation of ion beam implantation profiles for Mg, Ge and Si in AlN over wide dose and energy ranges. Si and Ge are implanted to achieve the n-type doping, Mg is investigated as a p-type doping. The simulation of implantation profiles were performed in collaboration between NRL and Agnitron using a commercial software known as Stopping and Range of Ions in Matter (SRIM). The simulation results were then used as the basis for ion implantation of AlN samples. The implanted samples were annealed by an innovative technique under different conditions and evaluated along the way. Raman spectroscopy and XRD were used to determine the crystal quality of the implanted samples, demonstrating the effectiveness of annealing in removing implant induced damage. Additionally, SIMS was used to verify that a nearly uniform doping profile was achieved near the sample surface. The electrical characteristics of the implanted samples were evaluated by TLM and Hall techniques. Generally, the implanted samples before and after annealing were found to be very resistive. Further work is required before the superior properties of AlN can be fully utilized.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS1988

Material growth and characterization for solid state devices

During the period of this research grant, the process of liquid phase electroepitaxy (LPEE) was used to grow ternary and quaternary alloy III-V semiconductor thin films. Selective area growth of InGaAs was performed on InP substrates using a patterned sputtered quartz or spin-on glass layer. The etch back and growth characteristics with respect to substrate orientation were investigated. The etch back behavior is somewhat different from wet chemical etching with respect to the sidewall profiles which are observed. LPEE was also employed to grow epitaxial layers of InGaAsP alloys on InP substrates. The behavior of Mn as an acceptor dopant was investigated with low temperature Hall coefficient and photoluminescence measurements. A metal-organic vapor phase epitaxy system was partially complete within the grant period. This atmospheric pressure system will be used to deposit III-V compound and alloy semiconductor layers in future research efforts.

Collis, Ward J.↗
DOE OSTI2018

Stable, High Efficiency White Electrophosphorescent Organic Light Emitting Devices (OLED) by Reduced Molecular Dissociation (Final Report)

We shall pursue radically new strategies for increasing the lifetime of blue phosphorescent light emitting devices (PHOLEDs). Systematically seek robust dopant and host molecular pairs whose energy gaps allow both to participate in charge conduction in the PHOLED Emissive Layer (EML). By tailoring the host/dopant grading profile and extending the emission zone, it is anticipated that these approaches may significantly increase device lifetime while simultaneously increasing its efficiency.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2025

Ion implantation of magnesium guests into type II silicon clathrate films: an alternate approach to doping a cage-like silicon allotrope

Type II silicon clathrates, with their unique cage-like structure, offer exciting potential for applications in thermoelectrics, photovoltaics, and quantum materials due to their tunable electronic and thermal properties. This study investigates the use of ion implantation to introduce targeted guest atoms, which act as dopants, into type II Si clathrate films. The focus is on Mg as a test case for implantation, a dopant previously unreported in type II Si clathrates. The effects of ion implantation on the metastable Si clathrate structure were examined through systematic investigation of implant parameters. Time-of-flight secondary ion mass spectrometry depth profiling confirmed the successful implantation of Mg, while X-ray diffraction and confocal Raman spectroscopy demonstrated minimal structural damage at lower fluences, with the clathrate framework retaining its integrity without converting to other phases. At the higher end of the fluence range implantation caused localized transitions from clathrate to amorphous silicon. Implant activation using rapid thermal annealing was examined with the clathrate structure stable up to 500 °C and being converted to diamond silicon above this temperature. Post-implantation and activation structural characterization showed evidence of damage reversal. Electron paramagnetic resonance studies provided indirect evidence of dopant incorporation. These findings establish a foundation for introducing alternative guests/dopants into the Si clathrate cages through ion implantation, advancing their tunability for next-generation quantum and optoelectronic devices.

36 MATERIALS SCIENCE↗
NASA NTRS1985

Directed-energy process technology efforts

A summary of directed-energy process technology for solar cells was presented. This technology is defined as directing energy or mass to specific areas on solar cells to produce a desired effect in contrast to exposing a cell to a thermal or mass flow environment. Some of these second generation processing techniques are: ion implantation; microwave-enhanced chemical vapor deposition; rapid thermal processing; and the use of lasers for cutting, assisting in metallization, assisting in deposition, and drive-in of liquid dopants. Advantages of directed energy techniques are: surface heating resulting in the bulk of the cell material being cooler and unchanged; better process control yields; better junction profiles, junction depths, and metal sintering; lower energy consumption during processing and smaller factory space requirements. These advantages should result in higher-efficiency cells at lower costs. The results of the numerous contracted efforts were presented as well as the application potentials of these new technologies.

Alexander, P.↗
DOE OSTI2017

Simultaneous diagnosis of radial profiles and mix in NIF ignition-scale implosions via X-ray spectroscopy

In a National Ignition Facility implosion, hydrodynamic instabilities may cause the cold material from the imploding shell to be injected into the hot-spot (hot-spot mix), enhancing the radiative and conductive losses, which in turn may lead to a quenching of the ignition process. The bound-bound features of the spectrum emitted by high-Z ablator dopants that get mixed into the hot-spot have been previously used to infer the total amount of mixed mass; however, the typical errorbars are larger than the maximum tolerable mix. We present in this paper an improved 2D model for mix spectroscopy which can be used to retrieve information on both the amount of mixed mass and the full imploded plasma profile. By performing radiation transfer and simultaneously fitting all of the features exhibited by the spectra, we are able to constrain self-consistently the effect of the opacity of the external layers of the target on the emission, thus improving the accuracy of the inferred mixed mass. The model's predictive capabilities are first validated by fitting simulated spectra arising from fully characterized hydrodynamic simulations, and then, the model is applied to previously published experimental results, providing values of mix mass in agreement with previous estimates. Finally, we show that the new self consistent procedure leads to better constrained estimates of mix and also provides insight into the sensitivity of the hot-spot spectroscopy to the spatial properties of the imploded capsule, such as the in-flight aspect ratio of the cold fuel surrounding the hotspot.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Dopant Compensation within the Intrinsic Poly-Si Isolation Region in Poly-Si/SiOx Passivated IBC Si Solar Cells

We report on the effect of dopant compensation within intrinsic poly-Si regions between p- and n-type fingers of poly-Si/SiOx passivated interdigitated back contact (IBC) solar cells using intrinsic poly-Si as the isolation region between the doped poly-Si fingers. First, we show that dopants from the doped fingers contaminate the intrinsic gap, resulting in doping of the entire intrinsic gap and overlap of the dopant tails from each finger. Next, we show that despite this doping across the gap, shunting between the doped fingers does not occur. We show that this is a result of trap-assisted compensation creating a highly resistive intrinsic region, preventing shunt. We simulate shunt resistance across the gap based on local carrier concentration and deep trap density. We show that trap defects within the poly-Si enhance compensation between the dopant tails. We experimentally confirm these predictions by scanning spreading resistance microscopy of the gap showing ~20 um domain with resistivity ~10^7 ..omega.. cm. Additionally, Kelvin probe force microscopy are compared to finite element simulations which result in the same approximate shape for potential profile, indicating diode behavior across the isolation region. These results demonstrate the powerful effect that trap defects have within the poly-Si isolation region and suggest that precision patterning is not as essential as once thought.

dopant compensation↗
DOE OSTI2012

Modeling boron profiles in silicon after pulsed excimer laser annealing

In this work, we investigated four possible mechanisms which were candidates to explain the shape of boron profiles after ion implantation and melting excimer laser annealing in silicon. A laser with a wavelength of 308 nm and a pulse duration of {approx}180 ns was used. To simulate this process, an existing model for the temperature and phase evolution was complemented with equations for the migration of dopants. Outdiffusion, thermodiffusion, segregation, and adsorption were investigated as possible mechanisms. As a result, we found that outdiffusion and segregation can be excluded as major mechanisms. Thermodiffusion as well as adsorption could both reproduce the build-up at low melt depths, but only adsorption the one at deeper melt depths. In both cases, ion beam mixing during SIMS measurement had to be taken into account to reproduce the measured profiles.

36 MATERIALS SCIENCE↗
DOE OSTI2014

High-fluence Ga-implanted silicon—The effect of annealing and cover layers

The influence of SiO{sub 2} and SiN{sub x} cover layers on the dopant distribution as well as microstructure of high fluence Ga implanted Si after thermal processing is investigated. The annealing temperature determines the layer microstructure and the cover layers influence the obtained Ga profile. Rapid thermal annealing at temperatures up to 750 °C leads to a polycrystalline layer structure containing amorphous Ga-rich precipitates. Already after a short 20 ms flash lamp annealing, a Ga-rich interface layer is observed for implantation through the cover layers. This effect can partly be suppressed by annealing temperatures of at least 900 °C. However, in this case, Ga accumulates in larger, cone-like precipitates without disturbing the surrounding Si lattice parameters. Such a Ga-rich crystalline Si phase does not exist in the equilibrium phase diagram according to which the Ga solubility in Si is less than 0.1 at. %. The Ga-rich areas are capped with SiO{sub x} grown during annealing which only can be avoided by the usage of SiN{sub x} cover layers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Impurity and defect interactions during laser thermal annealing in Ge

The microscopic mechanisms involving dopants, contaminants, and defects in Ge during pulsed melting laser thermal annealing (LTA) are investigated in detail. Samples both un-implanted and implanted with As or B are processed by LTA as well as characterized in terms of chemical (1D and 3D), electrical, and strain profiling. The clustering of As is directly measured by 3D chemical profiling and correlated with its partial electrical activation along with a reduction of the lattice strain induced by As atoms. A semi-quantitative microscopic model involving the interaction with mobile As-vacancy (AsV) complexes is proposed to describe the clustering mechanism. Boron is shown to follow different clustering behavior that changes with depth and marked by completely different strain levels. Oxygen penetrates from the surface into all the samples as a result of LTA and, only in un-implanted Ge, it occupies an interstitial position inducing also positive strain in the lattice. On the contrary, data suggest that the presence of As or B forces O to assume different configurations with negligible strain, through O-V or O-B interactions for the two dopant species, respectively. These data suggest that LTA does not inject a significant amount of vacancies in Ge, at variance with Si, unless As atoms or possibly other n-type dopants are present. These results have to be carefully considered for modeling the LTA process in Ge and its implementation in technology.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Enhanced visible light activity of nano-titanium dioxide doped with multiple ions: Effect of crystal defects

Titanium dioxide photocatalysts co-doped with iron(III) and lanthanum(III) have been prepared through a modified sol-gel method. Doping with Fe{sup 3+} resulted in a relatively lower anatase to rutile phase transformation temperature, while La{sup 3+} addition reduced the crystal growth and thus retarded the phase transformation of titania nanoparticles. The presence of Fe{sup 3+} ions shifted the absorption profile of titania to the longer wavelength side of the spectrum and enhanced the visible light activity. On the other hand, La{sup 3+} addition improved the optical absorption of titania nanoparticles. Both the dopants improved the life time of excitons by proper transferring and trapping of photoexcited charges. In the present work, considerable enhancement in photocatalytic activity under visible light was achieved through synergistic effect of optimum concentrations of the two dopants and associated crystal defects. - Graphical abstract: Photocatalytic activity studies indicate a synergistic effect of dopants and crystal defects leading to an enhanced photochemical activity. Highlights: Black-Right-Pointing-Pointer An aqueous sol-gel synthesis of Fe{sup 3+} and La{sup 3+} co-doped TiO{sub 2} is being reported. Black-Right-Pointing-Pointer Optical and microstructural properties of titania were modified by co-doping. Black-Right-Pointing-Pointer Enhanced activity of titania by the crystal defects is being reported.

36 MATERIALS SCIENCE↗