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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Prototyping and Development of Commercial Nanocrystalline and Thin Film Silicon for Photovoltaic Manufacturing

The College of Nanoscale Science and Engineering (CNSE) at the University at Albany received funding from the Department of Energy for its proposal Prototyping and Development of Commercial Nanocrystalline and Thin Film Si for Photovoltaic Manufacturing. This project was created to identify growth rate, texture uniformity, process window, economics, composition and thickness uniformity solutions related to fabricating large area, high efficiency thin film silicon based solar cells. This document serves as a final report for the closure of this program and details the deliverables from CNSE against its original scope of work. Thin-film silicon solar cells are a promising candidate for electricity generation applications because of a combination of advantages. Nanocrystalline and poly-Si based thin films, reduces the use of expensive semiconductor material content, can be deposited onto a foreign substrate (e.g. glass or flexible stainless steel) and enables use of the cells in wide variety of applications. In addition, nano and poly-Si films have higher carrier mobility as well as reduce recombination effects, relative to traditional amorphous-silicon films. They can be mass-produced at low cost, and expected to have a strong position in the international photovoltaic industry, which is experiencing a compounded annual growth of 25%. The objectives included: Demonstration of high rate VHF (Very High Frequency) growth of nc-Si over large areas with uniform thickness. Demonstration of single chamber device growth that allows mass production processing. Demonstration of uniform segmented electrodes. Development of computer models to accelerate efforts. Demonstration of large grain thin film polycrystalline silicon films fabrication. Utilizing the AIC (Aluminum Induced Crystallization) process for large grain silicon film fabrication. Demonstration of 12% efficient nanocrystalline and polycrystalline thin film devices. The end result expected was the production of high-efficiency, low-cost thin film Si devices with reduced cost per watt, allowing dramatically increased market penetration. While further research is required to meet these ultimate goals, this project proved its feasibility.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Scaling effects in sodium zirconium silicate phosphate (Na 1+ x Zr 2 Si x P 3- x O 12 ) ion-conducting thin films

Preparation of sodium zirconium silicate phosphate (NaSICon), Na 1+x Zr 2 Si x P 3–x O 12 (0.25 ≤ x ≤ 1.0), thin films has been investigated via a chemical solution approach on platinized silicon substrates. Increasing the silicon content resulted in a reduction in the crystallite size and a reduction in the measured ionic conductivity. Processing temperature was also found to affect microstructure and ionic conductivity with higher processing temperatures resulting in larger crystallite sizes and higher ionic conductivities. The highest room temperature sodium ion conductivity was measured for an x = 0.25 composition at 2.3 × 10 –5 S/cm. In conclusion, the decreasing ionic conductivity trends with increasing silicon content and decreasing processing temperature are consistent with grain boundary and defect scattering of conducting ions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Mesoporous silicon synthesis and applications in Li-ion batteries and solar hydrogen fuel cells

We provide a mesoporous silicon material (PSi) prepared via a template-free and HF-free process. The production process is facile and scalable, and it may be conducted under mild reaction conditions. The silicon may be produced directly by the reduction of a silicon-halogenide precursor (for example, SiCl.sub.4) with an alkaline alloy (for example, NaK alloy). The resulting Si-salt matrix is then annealed for the pore formation and crystallite growth. Final product is obtained by removal of the salt by-products with water.

25 ENERGY STORAGE↗
DOE OSTI2017

Effect of wheel speed on the magnetic and mechanical properties of melt spun Fe-6.5 wt.% electric steel

Fe-Si electric steel is the most widely used soft magnetic materials in electric mahines and motors, transformers and generators. Improving the surperior magnetic and electric properties of 6.5 wt.% high silicon steel is essential for higher may improve energy efficiency and power density of electric machines. However, the brittleness due to the formation of B2 and D03 ordered phases in high silicon steel make it difficult forbids for the application of high silicon steel. It is known that these ordered phases can be fully or partially suppressed by rapid cooling. However, further study is needed to understand the extend of cooling on the magnetic and mechanical properties of 6.5 wt.% silicon steel with various degree of ordering. By tuning the wheel speed from 1m/s to 30m/s with several intervals of the melt spinning process, varying degrees of cooling were achieved on 6.5 wt.% silicon steel ribbons. The cooling rate significant altered the ordering, microstructure size scale, and thus the mechanical and magnetic properties. TEM results showed that D03 ordering can be fully suppressed at high wheel speed, but started to nucleate at 5m/s and below, which correlates with the hardness and Young’s modulus increase towards low wheel speeds as tested by micro and nano indentation. The grain sizes of the ribbons on the wheel side decreased with increasing wheel speeds being ~100 micron at 1m/s and ~8 micron at 30m/s, which led to the change in coercivity. Saturation magnetization and electric resistivity of the ribbons remained about 190 emu/g and 84 microhm *cm, which appeared to be mainly depend on the chemistry.

Fe-6.5%Si Steel↗
DOE OSTI2015

Effects of laser fluence on silicon modification by four-beam laser interference

This paper discusses the effects of laser fluence on silicon modification by four-beam laser interference. In this work, four-beam laser interference was used to pattern single crystal silicon wafers for the fabrication of surface structures, and the number of laser pulses was applied to the process in air. By controlling the parameters of laser irradiation, different shapes of silicon structures were fabricated. The results were obtained with the single laser fluence of 354 mJ/cm{sup 2}, 495 mJ/cm{sup 2}, and 637 mJ/cm{sup 2}, the pulse repetition rate of 10 Hz, the laser exposure pulses of 30, 100, and 300, the laser wavelength of 1064 nm, and the pulse duration of 7–9 ns. The effects of the heat transfer and the radiation of laser interference plasma on silicon wafer surfaces were investigated. The equations of heat flow and radiation effects of laser plasma of interfering patterns in a four-beam laser interference distribution were proposed to describe their impacts on silicon wafer surfaces. The experimental results have shown that the laser fluence has to be properly selected for the fabrication of well-defined surface structures in a four-beam laser interference process. Laser interference patterns can directly fabricate different shape structures for their corresponding applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Thin, Flexible Sensors and Actuators as ‘Instrumented’ Surgical Sutures for Targeted Wound Monitoring and Therapy

Proper healing of incised skin is critical to the natural processes of tissue repair. Concepts in flexible silicon electronics enable integration of actuators, sensors and a variety of semiconductor devices onto thin strips of plastic or biopolymers, to yield ‘instrumented’ suture threads for monitoring and accelerating the wound healing in this context. Bifacial systems of this type demonstrate various classes of functionality, in live animal models. Furthermore, detailed modelling of the mechanics reveals stress and strain distributions in such applications, to support design strategies for robust operation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2024

Mechanical Design Guidelines to Inhibit Fracture in Perovskite Solar Cells

Perovskite (PVSK) solar cells offer significant benefits over conventional silicon cells including low-cost solution processibility, minimal materials usage related to strong photon absorption in thin-film cell architectures, and a tunable bandgap. However, PVSK films are mechanically fragile, and fracture of PVSK layers and adjacent interfaces are a significant concern during fabrication, encapsulation, and operation. Herein, a thin-film mechanics fracture analysis tailored for p–i–n and n–i–p PVSK solar cells on both soda lime glass and polyimide substrates fabricated with three PVSK crystallization methods is presented. Here, the role of thermal processing of each cell layer is explored to determine the maximum allowable temperature below which fracture is inhibited. In the analysis, the mechanics basis for processing and materials selection guidelines for preventing fracture in PVSK solar cells is provided.

adhesion↗
DOE OSTI2020

Impurity Levels in Cerium Oxide Microspheres Prepared by Internal Gelation Sol-Gel Methods

Impurity levels were measured in cerium oxide microspheres fabricated by modified internal gelation sol-gel methods. A combination of glow discharge mass spectrometry, electron impact mass spectrometry, combustion gas analysis and instrumental gas analysis were used to assess a wide range of potential elemental impurities. Low concentrations of carbon, nitrogen, and hydrogen impurities in microspheres showed a dependence on how microspheres were washed. Silicon impurities are believed to derive from silicone oil used during sol-gel processing. Spheres washed by the preferred approach had impurity levels below 100 ppm for all elements tested. For applications such as nuclear fuels, sol-gel methods could meet purity specifications as long as metal nitrate feed solutions of sufficient purity are used and microspheres are washed appropriately. In this study, cerium was used as a surrogate for plutonium-238, which is used in radioisotope power systems as a heat source, to determine whether carbon or other impurities were concentrated during internal gelation processing and remained after heat treatments. Analyses indicated low concentrations of impurities in cerium oxide microspheres after sintering steps that were well below documented limits for plutonium-238 oxide fuels. Modified washing methods, combined with a pressurized water treatment, resulted in sintered cerium oxide sol-gel microspheres with low impurity levels.

cerium oxide, sol-gel, internal gelation, microsph↗
DOE OSTI2018

Dephosphorization of Levitated Silicon-Iron Droplets for Production of Solar-Grade Silicon

The treatment of relatively inexpensive silicon-iron alloys is a potential refining route in order to generate solar-grade silicon. Phosphorus is one of the more difficult impurity elements to remove by conventional processing. In this study, electromagnetic levitation was used to investigate phosphorus behavior in silicon-iron alloy droplets exposed to H{sub 2}-Ar gas mixtures under various experimental conditions including, refining time, temperature (1723 K to 1993 K), gas flow rate, iron content, and initial phosphorus concentration in the alloy. Thermodynamic modeling of the dephosphorization reaction permitted prediction of the various gaseous products and indicated that diatomic phosphorus is the dominant species formed.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Nanoscale friction properties of graphene and graphene oxide

Achieving superlow friction and wear at the micro/nano-scales through the uses of solid and liquid lubricants may allow superior performance and long-lasting operations in a range of micromechanical system including micro-electro mechanical systems (MEMS). Previous studies have indicated that conventional solid lubricants such as highly ordered pyrolitic graphite (HOPG) can only afford low friction in humid environments at micro/macro scales; but, HOPG is not suitable for practical micro-scale applications. Here, we explored the nano-scale frictional properties of multi-layered graphene films as a potential solid lubricant for such applications. Atomic force microscopy (AFM) measurements have revealed that for high-purity multilayered graphene (7–9 layers), the friction force is significantly lower than what can be achieved by the use of HOPG, regardless of the counterpart AFM tip material. We have demonstrated that the quality and purity of multilayered graphene plays an important role in reducing lateral forces, while oxidation of graphene results in dramatically increased friction values. Furthermore, for the first time, we demonstrated the possibility of achieving ultralow friction for CVD grown single layer graphene on silicon dioxide. This confirms that the deposition process insures a stronger adhesion to substrate and hence enables superior tribological performance than the previously reported mechanical exfoliation processes.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Selection and properties of alternative forming fluids for TRISO fuel kernel production

Current Very High Temperature Reactor (VHTR) designs incorporate TRi-structural ISOtropic (TRISO) fuel, which consists of a spherical fissile fuel kernel surrounded by layers of pyrolytic carbon and silicon carbide. An internal sol-gel process forms the fuel kernel using wet chemistry to produce uranium oxyhydroxide gel spheres by dropping a cold precursor solution into a hot column of trichloroethylene (TCE). Over time, gelation byproducts inhibit complete gelation, and the TCE must be purified or discarded. The resulting TCE waste stream contains both radioactive and hazardous materials and is thus considered a mixed hazardous waste. Changing the forming fluid to a non-hazardous alternative could greatly improve the economics of TRISO fuel kernel production. Selection criteria for a replacement forming fluid narrowed a list of ~10,800 chemicals to yield ten potential replacement forming fluids: 1-bromododecane, 1- bromotetradecane, 1-bromoundecane, 1-chlorooctadecane, 1-chlorotetradecane, 1-iododecane, 1-iodododecane, 1-iodohexadecane, 1-iodooctadecane, and squalane. The density, viscosity, and surface tension for each potential replacement forming fluid were measured as a function of temperature between 25 °C and 80 °C. Calculated settling velocities and heat transfer rates give an overall column height approximation. 1-bromotetradecane, 1-chlorooctadecane, and 1-iodododecane show the greatest promise as replacements, and future tests will verify their ability to form satisfactory fuel kernels.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Thermal stability of dopants in boron carbide

Undoped (B 4 C), B rich (B 5.5 C), and B/Si co-doped (Si-B 6.5 C) boron carbides were annealed at 500 °C for up to 21 days to investigate the thermal stability of primary dopants, B and Si. Structural changes associated with dedoping were investigated by X-ray diffraction (XRD) and Raman spectroscopy. The stable phase B 4 C showed no microstructural or lattice parameter changes. Similarly, lattice parameters of B 5.5 C remained constant, suggesting that B dopant is stable at the given conditions. However, the shortened lattice parameters and reduced Si content of Si-B 6.5 C over the annealing time indicated that Si dopant was in a metastable state at the annealing temperature. Consequently, Si dedoping led to an increase in amorphization (a loss of local crystalline order) which degrades the ballistic performance of boron carbide. The insight highlights the importance of Si dopant in boron carbide and suggests that rapid processing may be necessary to retain more silicon for better performance.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Photovoltaics: Separating Multiple Excitons

Scientists have demonstrated an efficient process for generating multiple excitons in adjacent silicon nanocrystals from a single high-energy photon. Their findings could prove useful for a wide range of photovoltaic applications.

14 SOLAR ENERGY↗
DOE OSTI2012

A Model for Phosphosilicate Glass Deposition via POCl3 for Control of Phosphorus Dose in Si

Effective control of diffused phosphorus profiles in crystalline silicon requires detailed understanding of the doping process. We develop a model and analyze concentration profiles within the deposited phosphosilicate glass (PSG) for a range of POCl3 conditions. During predeposition, a PSG layer with composition nearly independent of process conditions forms. This layer is separated from Si by a thin SiO2 layer. There is also strong accumulation of P at the SiO2-Si interface. A simple linear-parabolic model cannot fully explain the kinetics of thickness and dose; while an improved model including oxygen dependence and dose saturation gives better fits to the experiments.

Control↗
DOE OSTI2015

Nonlinear electronic excitations in crystalline solids using meta-generalized gradient approximation and hybrid functional in time-dependent density functional theory

We develop methods to calculate electron dynamics in crystalline solids in real-time time-dependent density functional theory employing exchange-correlation potentials which reproduce band gap energies of dielectrics; a meta-generalized gradient approximation was proposed by Tran and Blaha [Phys. Rev. Lett. 102, 226401 (2009)] (TBm-BJ) and a hybrid functional was proposed by Heyd, Scuseria, and Ernzerhof [J. Chem. Phys. 118, 8207 (2003)] (HSE). In time evolution calculations employing the TB-mBJ potential, we have found it necessary to adopt the predictor-corrector step for a stable time evolution. We have developed a method to evaluate electronic excitation energy without referring to the energy functional which is unknown for the TB-mBJ potential. For the HSE functional, we have developed a method for the operation of the Fock-like term in Fourier space to facilitate efficient use of massive parallel computers equipped with graphic processing units. We compare electronic excitations in silicon and germanium induced by femtosecond laser pulses using the TB-mBJ, HSE, and a simple local density approximation (LDA). At low laser intensities, electronic excitations are found to be sensitive to the band gap energy: they are close to each other using TB-mBJ and HSE and are much smaller in LDA. At high laser intensities close to the damage threshold, electronic excitation energies do not differ much among the three cases.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

A high bandwidth microelectromechanical system-based nanopositioner for scanning tunneling microscopy

Limited Z-axis bandwidth of piezotube scanners used in conventional Scanning Tunneling Microscopes (STMs) has been a major limiting factor in achieving high scan speeds in STM applications. Slow Z-axis dynamics of typical piezotube scanners combined with the weight of the STM tip/tip holder assembly, that the scanner has to carry, substantially limit the achievable Z-axis bandwidth in both imaging and lithography modes. To tackle this issue, we introduce a high bandwidth microelectromechanical-system-based nanopositioner to be integrated into an existing STM scanner. The device is designed to replace the STM tip and fine Z-positioning mechanisms in the conventional STM setup, while providing an order of magnitude higher bandwidth in Z axis. The device is microfabricated using double silicon-on-isolator technology, and standard cleanroom processes. Experiments show that tunneling current between the device tip and a highly ordered pyrolytic graphite sample can be successfully established and maintained in air using the proposed device in a feedback loop. Results suggest that the proposed device uniquely combines a very high resolution and a large stroke with a substantially larger Z-axis bandwidth compared to that of conventional STM piezotube scanners, enabling higher scanning speeds in STM operations.

42 ENGINEERING↗
DOE OSTI2017

HOLE-BLOCKING LAYERS FOR SILICON/ORGANIC HETEROJUNCTIONS: A NEW CLASS OF HIGH-EFFICIENCY LOW-COST PV

This project is the first investigation of the use of thin titanium dioxide layers on silicon as a hole-blocking / electron-transparent selective contact to silicon. The work was motivated by the goal of a high-efficiency low-cost silicon-based solar cells that could be processed entirely at low temperature (300 Degree Celsius) or less, without requiring plasma-processing.

Sturm, James↗