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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 901 records · Page 50
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Prediction of plasma-induced damage distribution during silicon nitride etching using advanced three-dimensional voxel model

The authors modeled SiN film etching with hydrofluorocarbon (CH{sub x}F{sub y}/Ar/O{sub 2}) plasma considering physical (ion bombardment) and chemical reactions in detail, including the reactivity of radicals (C, F, O, N, and H), the area ratio of Si dangling bonds, the outflux of N and H, the dependence of the H/N ratio on the polymer layer, and generation of by-products (HCN, C{sub 2}N{sub 2}, NH, HF, OH, and CH, in addition to CO, CF{sub 2}, SiF{sub 2}, and SiF{sub 4}) as ion assistance process parameters for the first time. The model was consistent with the measured C-F polymer layer thickness, etch rate, and selectivity dependence on process variation for SiN, SiO{sub 2}, and Si film etching. To analyze the three-dimensional (3D) damage distribution affected by the etched profile, the authors developed an advanced 3D voxel model that can predict the time-evolution of the etched profile and damage distribution. The model includes some new concepts for gas transportation in the pattern using a fluid model and the property of voxels called “smart voxels,” which contain details of the history of the etching situation. Using this 3D model, the authors demonstrated metal–oxide–semiconductor field-effect transistor SiN side-wall etching that consisted of the main-etch step with CF{sub 4}/Ar/O{sub 2} plasma and an over-etch step with CH{sub 3}F/Ar/O{sub 2} plasma under the assumption of a realistic process and pattern size. A large amount of Si damage induced by irradiated hydrogen occurred in the source/drain region, a Si recess depth of 5 nm was generated, and the dislocated Si was distributed in a 10 nm deeper region than the Si recess, which was consistent with experimental data for a capacitively coupled plasma. An especially large amount of Si damage was also found at the bottom edge region of the metal–oxide–semiconductor field-effect transistors. Furthermore, our simulation results for bulk fin-type field-effect transistor side-wall etching showed that the Si fin (source/drain region) was directly damaged by high energy hydrogen and had local variations in the damage distribution, which may lead to a shift in the threshold voltage and the off-state leakage current. Therefore, side-wall etching and ion implantation processes must be carefully designed by considering the Si damage distribution to achieve low damage and high transistor performance for complementary metal–oxide–semiconductor devices.

42 ENGINEERING↗
DOE OSTI2017

Review Article: Advanced nanoscale patterning and material synthesis with gas field helium and neon ion beams

Focused ion beam nanoscale synthesis has emerged as a critical tool for selected area nanofabrication. Helium and neon ion beams from the gas field ion source have recently demonstrated unparalleled resolution among other scanning ion beams. In this review, the authors focus on the nanoscale synthesis applications for these ion species which have been demonstrated to date. The applications and recent work can broadly be grouped into the following categories: (1) Monte Carlo simulations, (2) direct-write milling or sputtering, (3) ion beam lithography, (4) selective ion implantation or defect introduction, and (5) gas-assisted processing. A special emphasis is given toward using He+ and Ne+ for the processing of two dimensional materials, as several groups have demonstrated promising results. Finally, the authors will discuss the future outlook of He+ and Ne+ nanoprocessing techniques and applications.

Stanford, Michael G.↗
DOE OSTI2020

Toward ultrafast, ultra-stable imaging arrays: Superlattice doping to enhance the performance of backside-illuminated 3D-hybridized silicon photodetectors

In this paper, the authors report the latest results on their development of superlattice-doped, thinned, backside-illuminated (BSI), 3D-integrated photodiode detectors—a step toward their ultimate goal of demonstrating ultrafast, ultrastable CMOS imaging arrays. As with most silicon-based photodetectors, backside-illumination and backside surface passivation are keys to achieve the highest performance capability. The two-dimensional (2D) doping technique developed at the Jet Propulsion Laboratory (JPL) has proved to result in a highly efficient, highly stable detector response when combined with a variety of detectors. Here, JPL's 2D-doping has been combined with Sandia's BSI photodetectors hybridized with custom fanout wafer via copper Direct Bond Interconnect (DBI®), a technology that is rapidly becoming industry standard for BSI CMOS imaging arrays. The prototype detectors were packaged and evaluated with respect to their response to low energy electrons. The authors find that the responsivity of 2D-doped BSI detectors is higher than devices prepared using other surface passivation techniques (i.e., ion implantation). The success of the work described herein verifies that the 2D-doping processes previously developed for Sandia's frontside-illuminated photodetectors are generally applicable to BSI detectors and demonstrates for the first time that JPL's 2D-doping process is compatible with the Cu-DBI® technology.

Jewell, April D.↗
DOE OSTI2015

WE-AB-BRB-04: A Novel Monolithic Silicon 2D Detector Array for Use in Stereotactic Applications

Purpose: To assess the capability of a novel 2D monolithic silicon detector array in measuring stereotactic photon fields. Methods: The silicon array detector used in this work, named Magic Plate-512 (MP512), is a thin monolithic silicon wafer (52 × 52 × 0.47 mm{sup 3}) with 512 ion-implanted diodes (0.5 × 0.5 mm{sup 2}). Adjacent pixels are spaced evenly with 2 mm pitch, covering a maximum detection area 46 mm wide. Its fast, FPGA based read-out system is synchronised with the linac to allow readout of all pixels pulse-by-pulse. A clinical SABR lung plan (consisting of 9 single segment beams, 6MV) was measured with the array at 1.5 cm depth in a solid water phantom (100 cm SSD). The typical field size was in the range of 3 × 3 cm{sup 2} to 4 × 4 cm{sup 2}. Each beam was delivered at perpendicular incidence to the detector plane so as to avoid the need for angular dependence corrections. The fields were measured under the same conditions using Gafchromic EBT3 film for comparison. The film was scanned at 72 dpi resolution, with the red channel data used for analysis. Results: Average gamma passing rates of (92.3 ± 1.8) % for 2%/2mm criteria, and (86.6 ± 2.3) % for 1%/2mm criteria were achieved for MP512, using EBT3 film as the reference distribution. The detector array was able to accurately measure the full-width-at-half-maximum (FWHM), to within (0.77 ± 0.01) mm accuracy when compared to film. The penumbral widths (80%-20%) were measured to within (0.30 ± 0.01) mm accuracy to film. Conclusion: The MP512 is a feasible option for measurement of stereotactic photon fields, with its high density of detection points making it useful for small field applications. The prototype array has demonstrated merit; in the future the development of a larger array detection area would be beneficial for clinical applications.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Applications of Nuclear and Particle Physics Technology: Particles & Detection — A Brief Overview

Here, a brief overview of the technology applications with significant societal benefit that have their origins in nuclear and particle physics research is presented. It is shown through representative examples that applications of nuclear physics can be classified into two basic areas: 1) applying the results of experimental nuclear physics and 2) applying the tools of experimental nuclear physics. Examples of the application of the tools of experimental nuclear and particle physics research are provided in the fields of accelerator and detector based technologies namely synchrotron light sources, nuclear medicine, ion implantation and radiation therapy.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

In-situ 3D characterization of He bubble and displacement damage in dense and nanoporous thin films.

This initial work attempted to determine the feasibility of using advanced in-situ, electron tomography, and precession electron diffraction techniques to determine the structural evolution that occurs during advanced aging of Pd films with nanometer resolution. To date, significant progress has been made in studying the cavity structures in sputtered, evaporated, and pulsed-laser deposited Pd films that result from both the deposition parameters, as well as from He ion implantation. In addition, preliminary work has been done to determine the feasibility of performing precession electron diffraction (PED) and electron tomography in these type of systems. Significant future work is needed to determine the proper conditions such that relevant advanced aging protocols can be developed.

Hattar, Khalid Mikhiel↗
DOE OSTI2016

Author Contribution to the Pu Handbook II: Chapter 37 LLNL Integrated Sample Preparation Glovebox (TEM) Section

The development of our Integrated Actinide Sample Preparation Laboratory (IASPL) commenced in 1998 driven by the need to perform transmission electron microscopy studies on naturally aged plutonium and its alloys looking for the microstructural effects of the radiological decay process (1). Remodeling and construction of a laboratory within the Chemistry and Materials Science Directorate facilities at LLNL was required to turn a standard radiological laboratory into a Radiological Materials Area (RMA) and Radiological Buffer Area (RBA) containing type I, II and III workplaces. Two inert atmosphere dry-train glove boxes with antechambers and entry/exit fumehoods (Figure 1), having a baseline atmosphere of 1 ppm oxygen and 1 ppm water vapor, a utility fumehood and a portable, and a third double-walled enclosure have been installed and commissioned. These capabilities, along with highly trained technical staff, facilitate the safe operation of sample preparation processes and instrumentation, and sample handling while minimizing oxidation or corrosion of the plutonium. In addition, we are currently developing the capability to safely transfer small metallographically prepared samples to a mini-SEM for microstructural imaging and chemical analysis. The gloveboxes continue to be the most crucial element of the laboratory allowing nearly oxide-free sample preparation for a wide variety of LLNL-based characterization experiments, which includes transmission electron microscopy, electron energy loss spectroscopy, optical microscopy, electrical resistivity, ion implantation, X-ray diffraction and absorption, magnetometry, metrological surface measurements, high-pressure diamond anvil cell equation-of-state, phonon dispersion measurements, X-ray absorption and emission spectroscopy, and differential scanning calorimetry. The sample preparation and materials processing capabilities in the IASPL have also facilitated experimentation at world-class facilities such as the Advanced Photon Source at Argonne National Laboratory, the European Synchrotron Radiation Facility in Grenoble, France, the Stanford Synchrotron Radiation Facility, the National Synchrotron Light Source at Brookhaven National Laboratory, the Advanced Light Source at Lawrence Berkeley National Laboratory, and the Triumph Accelerator in Canada.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2017

CZT DTRA final report

The objective of the project is to understand the physical origin of electronic noise injected by the electrical contacts in CZT and CdTe, and moreover to understand how it impacts the current- voltage (IV) relationships of these materials. This understanding is critical to enabling the next crucial enhancement in the performance of CZT radiation detectors, as there have recently been impressive advancements in the growth of CZT crystals, particularly at our commercial partner Redlen Technologies. Redlen scientists have successfully reduced the size of the transport-inhibiting tellurium precipitates to be <3 micrometers, such that, with sufficiently high fields, it is possible to achieve resolution of <1% at 662 keV using suitable electrode geometries. In contrast to the excellent progress in crystal growth, practitioners in the field of radiation detection have been fabricating rather routine contacts on CZT for nearly two decades; there is no basic understanding of the semiconductor physics of the contacts, and consequently no breakthrough progress in this area. Our objective is to resolve this inadequacy in CZT diode fabrication on the basis of a science-based study, such that CZT detectors can achieve their full promise in performance as superior contacts will enable use of higher fields with lower leakage current – thereby enhancing the resolution that is possible while eliminating the well-known “tailing” effect suffered by the photopeak. Our approach is to develop methods that reduce or eliminate leakage currents in CZT devices through “engineering” the surfaces with novel treatments and structures. This includes using high density plasma etching, doping via ion implantation and metal diffusion, rapid thermal annealing, amorphous semiconductor and dielectric films, and controlled oxide growth. Using these methods, sources of injected and generated noise at the surface can be eliminated via plasma etching and film deposition or oxide growth, while advanced junctions (both homo- and heterojunctions) can be created to eliminate current injection from the metal contacts. The work involves the fabrication and characterization of CZT having a variety of contact structures. Tools capable of evaporating and sputtering metals, together with the usual lithographic and chemical processing methods, are employed. The CZT material employed will be of the highest quality available (Redlen Technologies), and we are engaging Prof. Burger of Fisk University, who is internationally recognized as one of the most accomplished materials physicists in the field on radiation detectors. We have also begun collaborating with Prof. Nicholas Kioussis of Cal State Northridge, Srivananthan Labs (Bolingbrook, IL), and Mark Amman of Lawrence Berkeley National Laboratory, all funded separately by DTRA.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2018

Status of Metallic Structural Materials for Molten Salt Reactors

In the US and around the world, significant interest surrounds development and deployment of nuclear systems using molten salts to transfer heat. Several configurations are being explored, including the use of fluoride salts either as the primary coolant of a reactor with solid fuel or with the fissile material dissolved in the salt. Molten Salt Reactors (MSRs) with fluoride salt typically have a thermal neutron spectrum. There are also fast-spectrum reactors that could use chloride salts to transfer heat. As a result of operation of the Molten Salt Reactor Experiment (MSRE) at Oak Ridge National Laboratory during the 1960s, a system with uranium fuel dissolved in a fluoride-salt medium is the most well-established technology. A nickel alloy with about 6%Cr and molybdenum as a solid solution strengthening agent was developed and deployed for all structural applications in this reactor. The alloy was commercialized as Hastelloy N. During these experiments and in post-decommissioning characterization of material behavior, it was determined that the most significant challenges for structural materials are embrittlement, from helium introduced by transmutation of Ni, and corrosion and grain boundary embrittlement from the fission product tellurium. The MSRE had an outlet temperature of approximately 650°C. The mechanical properties of Hastelloy N are not sufficient to support long-term operation of an MSR above this temperature. Qualification of a material for use in the ASME Boiler and Pressure Vessel Code, Section III, “Rules for Construction of Nuclear Facility Components,” Division 5, “High Temperature Reactors,” will facilitate licensing with the Nuclear Regulatory Commission. Hastelloy N has not been qualified for use in nuclear construction, and significant additional characterization would be required for Code qualification. Given that this alloy is susceptible to He embrittlement and has limited high-temperature strength, it is not recommended that Code qualification be pursued. Instead, it is recommended that a systematic development program be initiated to develop new nickel alloys that contain a fine, stable dispersion of intermetallic particles to trap He at the interface between the matrix and particle and with increased solid solution strengthening from addition of refractory elements. Extensive screening of attractive alloy compositions for elevated temperature strength, microstructural stability, weldability, and resistance to He embrittlement (characterized using ion implantation) will lead to an alloy down-selection for commercialization and Code qualification.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Geranium Photodiodes for Hard Xray Detection

This report summarizes the investigations engaged at UC Davis under subcontract B632083, as related to the LLNL-LDRD Project “High-Speed X-Ray Imager Arrays.” The first section entails work done within the Electrical and Computer Engineering (ECE) Department. The purpose of the work done so far is to understand photodiode design and which parameters are conducive to the design goals, which are: I: Maximize the detector quantum efficiency. The device must have a quantum efficiency of roughly 5% at 80 keV. II: Minimize temporal response. Collection time is limited to 1ns. All charge must be collected in that time. III: Minimize dark current. In this document, various photodiode parameters and designs are explored, and their impact on these goals are tabulated. In addition to these, various instruments that have been constructed for either testing these parameters or helping teammates with their experiments. The second section entails work done with the Materials Science Engineering (MSE) Department. In accordance with the proposed development of the germanium ROIC backside imagers, a critical step in the micromachining of these devices was the removal of the substrate on which the PIN junctions were epitaxially grown. A common technique for the micromachining of silicon wafers is the use of chemical etching alongside an “etch-stop” layer. In this technique, a chemical etchant will remove material until it reaches the etch-stop layer, at which the etch rate will drop significantly. This high selectivity (ratio of etch rates) allows any unevenness in the initial etching to be effectively smoothed away in the event that part of the wafer surface reaches the etch-stop layer sooner than another. An initial literature review found a paper by Divan et al. in which the authors used ion implantation to dope germanium wafers and achieve selectivity on the order of 100, sufficient for a reliable etch-stop.

42 ENGINEERING↗
DOE OSTI2024

Assessment of the literature about Be-W mixed material layer formation in the fusion reactor environment

All plasma facing surfaces in a fusion reactor, whether initially pure or an alloy, will rapidly evolve into a mixed material due to plasma-induced erosion, migration and redeposition. Beryllium (Be) erosion from the main chamber, and its transport and deposition on to a tungsten (W) divertor results in the growth of mixed Be-W layers, which can evolve to form beryllides. These Be-W mixed materials exhibit generally less desirable properties than pure tungsten or pure beryllium, such as lower melting points. In order to better understand the parameter space for growth of these alloys, this paper reviews the literature on Be-W mixed material formation experiments—in magnetically confined fusion reactors, in linear plasma test stands, and during thin-film deposition—and on computational modeling of Be-W interactions, as well as briefly assesses the Be-W growth kinetics. We conclude that the following kinetic steps drive the material mixing: adsorption of the implanted/deposited ion on the metal surface; diffusion of the implanted/deposited ion from surface into the bulk, which is accelerated by defects; and loss of deposited material through erosion. Adsorption dominates (or prevents) material mixing in thin-film deposition experiments, whereas diffusion drives material mixing in plasma exposures due to the energetic ion implantation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2022

Fabrication of Nb3Sn by Magnetron Sputtering for Superconducting Radiofrequency Application

Particle accelerators are considered as an important device that has wide applications in cancer treatment, sterilizing waste, preserving foods, ion implantation in semiconductor industry, and in production of isotopes for medical applications. Superconducting radiofrequency (SRF) cavities are the building blocks of a linear particle accelerator. Current particle accelerators use niobium (Nb) superconductors as the sheet material to fabricate a single SRF cavity for particle acceleration. With better superconducting properties (critical temperature Tc ~ 18.3 K, superheating field Hsh~ 400 mT), Nb3Sn is considered a potential candidate in SRF technology. Magnetron sputtering is a promising deposition method to fabricate Nb3Sn thin films inside SRF cavities. Superconducting Nb3Sn films were fabricated on Nb and sapphire substrates by magnetron sputtering from a single stoichiometric Nb3Sn target, by multilayer sputtering of Nb and Sn followed by annealing, and by co-sputtering of Nb and Sn followed by annealing. The variation of morphological and superconducting properties was investigated for different substrate temperatures, annealing temperatures, annealing durations, and thicknesses. The film properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray spectroscopy (EDS). The films had crystalline Nb3Sn structure without any presence of poor superconducting Nb6Sn5 and NbSn2 phases. The highest Tc of the films fabricated from the stoichiometric target, multilayer sputtering and co-sputtering were 17.44, 17.93, and 17.66 K respectively. Finally, a cylindrical sputter coater with two identical magnetrons was designed and commissioned to fabricate Nb3Sn films inside a 2.6 GHz SRF cavity. The magnetrons were installed facing opposite to each other in a custom designed vacuum chamber and multilayers of Nb and Sn films on 1 cm2 Nb substrates replicating the beam tubes and equator locations of the cavity and the coated multilayered films were annealed at 950 °C for 3 h. The XRD of the as?deposited and annealed films confirmed the formation of Nb3Sn after the annealing. The dissertation discusses the fabrication process, characterized results of the fabricated films, the design of the cylindrical sputter coater and the preliminary data obtained from the sputter coater.

Sayeed, Md Nizam↗
DOE OSTI2017

In Situ TEM Multi-Beam Ion Irradiation as a Technique for Elucidating Synergistic Radiation Effects

Materials designed for nuclear reactors undergo microstructural changes resulting from a combination of several environmental factors, including neutron irradiation damage, gas accumulation and elevated temperatures. Typical ion beam irradiation experiments designed for simulating a neutron irradiation environment involve irradiating the sample with a single ion beam and subsequent characterization of the resulting microstructure, often by transmission electron microscopy (TEM). This method does not allow for examination of microstructural effects due to simultaneous gas accumulation and displacement cascade damage, which occurs in a reactor. Sandia’s in situ ion irradiation TEM (I3TEM) offers the unique ability to observe microstructural changes due to irradiation damage caused by concurrent multi-beam ion irradiation in real time. This allows for time-dependent microstructure analysis. A plethora of additional in situ stages can be coupled with these experiments, e.g., for more accurately simulating defect kinetics at elevated reactor temperatures. This work outlines experiments showing synergistic effects in Au using in situ ion irradiation with various combinations of helium, deuterium and Au ions, as well as some initial work on materials utilized in tritium-producing burnable absorber rods (TPBARs): zirconium alloys and LiAlO2.

Taylor, Caitlin↗
DOE OSTI2021

Helium Bubbles and Blistering in a Nanolayered Metal/Hydride Composite

Helium is insoluble in most metals and precipitates out to form nanoscale bubbles when the concentration is greater than 1 at.%, which can alter the material properties. Introducing controlled defects such as multilayer interfaces may offer some level of helium bubble management. This study investigates the effects of multilayered composites on helium behavior in ion-implanted, multilayered ErD 2 /Mo thin film composites. Following in-situ and ex-situ helium implantation, scanning and transmission electron microscopy showed the development of spherical helium bubbles within the matrix, but primarily at the layer interfaces. Bubble linkage and surface blistering is observed after high fluence ex-situ helium implantation. These results show the ability of metallic multilayers to alter helium bubble distributions even in the presence of a hydride layer, increasing the lifetime of materials in helium environments.

36 MATERIALS SCIENCE↗
NASA NTRS1971

Air Force/Ion Physics hardened lithium doped solar cell development

Introduction of lithium by ion implantation eliminates reproducibility and surface problem deficiencies of other introduction techniques. Implantation has been demonstrated to make possible a degree of control over the cell lithium content which has not previously been available. Front barrier development remains to be completed. Successful development of the barrier will make available the freedom to select optimum lithium concentration throughout the cell, including in the vicinity of the junction.

Kirkpatrick, A.↗
NASA NTRS1972

Development of GaAs solar cells

Calculations of GaAs solar cell output parameters were refined and a computer model was developed for parameter optimization. The results were analyzed to determine the material characteristics required for a high efficiency solar cell. Calculated efficiencies for a P/N cell polarity are higher than an N/P cell. Both cell polarities show efficiency to have a larger dependence on short circuit current than an open circuit voltage under nearly all conditions considered. The tolerances and requirements of a cell fabrication process are more critical for an N/P type than for a P/N type cell. Several solar cell fabrication considerations relative to junction formation using ion implantation are also discussed.

Mcnally, P. J.↗