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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Determination of the pure silicon monocarbide content of silicon carbide and products based on silicon carbide

Experience has shown that different methods of analysis of SiC products give different results. Methods identified as AFNOR, FEPA, and manufacturer P, currently used to detect SiC, free C, free Si, free Fe, and SiO2 are reviewed. The AFNOR method gives lower SiC content, attributed to destruction of SiC by grinding. Two products sent to independent labs for analysis by the AFNOR and FEPA methods showed somewhat different results, especially for SiC, SiO2, and Al2O3 content, whereas an X-ray analysis showed a SiC content approximately 10 points lower than by chemical methods.

Prost, L.↗
NASA NTRS1978

Continuous Czochralski growth: Silicon sheet growth development of the large area silicon sheet task of the Low Cost Silicon Solar Array project

The primary objective of this contract is to develop equipment and methods for the economic production of single crystal ingot material by the continuous Czochralski (CZ) process. Continuous CZ is defined for the purpose of this work as the growth of at least 100 kilograms of ingot from only one melt container. During the reporting period (October, 1977 - September, 1978), a modified grower was made fully functional and several recharge runs were performed. The largest run lasted 44 hours and over 42 kg of ingot was produced. Little, if any, degradation in efficiency was observed as a result of pulling multiple crystals from one crucible. Solar efficiencies observed were between 9.3 and 10.4% AMO (13.0 and 14.6% AMI) compared to 10.5% (14.7% AMI) for optimum CZ material control samples. Using the SAMICS/IPEG format, economic analysis of continuous CZ suggests that 1986 DoE cost goals can only be met by the growth of large diameter, large mass crystals.

Source record↗
NASA NTRS1979

Silicon-on-ceramic Process: Silicon Sheet Growth and Device Development for the Large-area Silicon Sheet and Cell Development Tasks of the Low-cost Solar Array Project

Significant progress is reported in fabricating a 4 sq cm cell having a 10.1 percent conversion efficiency and a 10 sq cm cell having a 9.2 percent conversion efficiency. The continuous (SCIM) coater succeeded in producing a 16 sq cm coating exhibiting unidirectional solidification and large grain size. A layer was grown at 0.2 cm/sec in the experimental coater which was partially dendritic but also contained a large smooth area approximately 100 micron m thick. The dark characteristic measurements of a typical SCC solar cell yield shunt resistance values of 10K ohms and series resistance values and 0.4 ohm. The production dip-coater is operating at over 50 percent yield in terms of good cell quality material. The most recent run yielded 13 good substrates out of 15.

Chapman, P. W.↗
NASA NTRS1979

Continuous Czochralski Growth. Silicon Sheet Growth Development of the Large Area Silicon Sheet Task of the Low Cost Silicon Solar Array Project

During the reporting period, a successful 100 kilogram run was performed. Six ingots of 13 cm diameter were grown, ranging in size from 15.5 kg to 17.7 kg. Melt replenishment methods included both poly rod and lump feed material. Samples from each ingot were prepared for solar cell fabrication and analyses, impurity analysis, and structural studies. The furnace was converted to the 14-inch hot zone and preliminary heat runs were performed. Two sucessful runs were demonstrated, by growing 25 kg ingots from 30 kg melts. Also, a 100 kg run was attempted, utilizing the 14 inch crucible hot zone, but was prematurely terminated due to excessive monoxide which accumulated on the viewports and a seed failure.

Merz, F.↗
NASA NTRS1983

Analysis of defect structure in silicon. Characterization of SEMIX material. Silicon sheet growth development for the large area silicon sheet task of the low-cost solar array project

Statistically significant quantitative structural imperfection measurements were made on samples from ubiquitous crystalline process (UCP) Ingot 5848 - 13C. Important correlation was obtained between defect densities, cell efficiency, and diffusion length. Grain boundary substructure displayed a strong influence on the conversion efficiency of solar cells from Semix material. Quantitative microscopy measurements gave statistically significant information compared to other microanalytical techniques. A surface preparation technique to obtain proper contrast of structural defects suitable for quantimet quantitative image analyzer (QTM) analysis was perfected and is used routinely. The relationships between hole mobility and grain boundary density was determined. Mobility was measured using the van der Pauw technique, and grain boundary density was measured using quantitative microscopy technique. Mobility was found to decrease with increasing grain boundary density.

Natesh, R.↗
DOE OSTI2025

Solid‐State Prealkylation of Electrode Architectures (SPEAR): Direct Control of Prelithiation Levels in Silicon Anodes and Electrochemical Cycling

The Solid-state Prealkylation of Electrode ARchitectures (SPEAR) is different than traditional electrochemical prealkylation processes. Through SPEAR, alkylation is driven by solid-state diffusion without the simultaneous SEI formation concomitant with polarization. Here, we investigate the prelithiation of 80 wt. % Si-based anodes to varying amounts (up to Li 1.38 Si) to understand the trade-off between improved Li capacity and expansion-induced stress. Through dilatometry, we found that solid-state lithiation led to filling of the electrode pores through silicon expansion. This swelling changed the SEI formation process and accessibility of the silicon compared to an electrochemically lithiated electrode. Indeed, optimal prelithiation to Li 0.82 Si increases the initial C/3 cycling capacity post-SEI formation up to 43%, consistent with deeper Si activation through the electrode bulk. Prelithiation and cycling cells prelithiated beyond Li 0.82 Si results in a state of charge (SOC) close to 100% which facilitates parasitic degradation mechanisms and volume expansion of the Si electrode. The results demonstrate a pathway to modify silicon activation/SEI formation to enable high-energy electrodes.

Musgrove, Amanda L. [Oak Ridge National Laboratory↗
DOE OSTI2024

Silicon-On-Silicon Carbide Platform for Integrated Photonics

Silicon carbide (SiC)'s nonlinear optical properties and applications to quantum information have recently brought attention to its potential as an integrated photonics platform. However, despite its many excellent material properties, such as large thermal conductivity, wide transparency window, and strong optical nonlinearities, it is generally a difficult material for microfabrication. Here, it is shown that directly bonded silicon-on-silicon carbide can be a high-performing hybrid photonics platform that does not require the need to form SiC membranes or directly pattern in SiC. The optimized bonding method yields defect-free, uniform films with minimal oxide at the silicon–silicon–carbide interface. Ring resonators are patterned into the silicon layer with standard, complimentary metal–oxide–semiconductor (CMOS) compatible (Si) fabrication and measure room-temperature, near-infrared quality factors exceeding 10 5 . The corresponding propagation loss is 5.7 dB cm -1 . The process offers a wafer-scalable pathway to the integration of SiC photonics into CMOS devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Cosmogenic activation of silicon

In the production of 3 H, 7 Be, and 22 Na by interactions of cosmic-ray particles with silicon can produce radioactive backgrounds in detectors used to search for rare events. Through controlled irradiation of silicon CCDs and wafers with a neutron beam that mimics the cosmic-ray neutron spectrum, followed by direct counting, we determined that the production rate from cosmic-ray neutrons at sea level is (112 ± 24) atoms/( kg day ) for 3 H, (8.1 ± 1.9) atoms/( kg day ) for 7 Be, and (43.0 ± 7.2) atoms/( kg day ) for 22 Na . Complementing these results with the current best estimates of activation cross sections for cosmic-ray particles other than neutrons, we obtain a total sea-level cosmic-ray production rate of (124 ± 25) atoms/(kg day) for 3 H, (9.4 ± 2.0) atoms/( kg day ) for 7 Be, and (49.6 ± 7.4) atoms/( kg day ) for 22 Na. These measurements will help constrain background estimates and determine the maximum time that silicon-based detectors can remain unshielded during detector fabrication before cosmogenic backgrounds impact the sensitivity of next-generation rare-event searches.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Thermo-optic properties of silicon-rich silicon nitride for on-chip applications

We demonstrate the thermo-optic properties of silicon-rich silicon nitride (SRN) films deposited using plasma-enhanced chemical vapor deposition (PECVD). Shifts in the spectral response of Mach-Zehnder interferometers (MZIs) as a function of temperature were used to characterize the thermo-optic coefficients of silicon nitride films with varying silicon contents. A clear relation is demonstrated between the silicon content and the exhibited thermo-optic coefficient in silicon nitride films, with the highest achievable coefficient being as high as (1.65±0.08) ×10 −4 K -1 . Furthermore, we realize an SRN multi-mode interferometer (MMI) based thermo-optic switch with over 20 dB extinction ratio and total power consumption for two-port switching of 50 mW.

Nejadriahi, Hani↗
NASA NTRS1979

Silicon halide-alkali metal flames as a source of solar grade silicon

The feasibility of using alkali metal-silicon halide diffusion flames to produce solar-grade silicon in large quantities and at low cost is demonstrated. Prior work shows that these flames are stable and that relatively high purity silicon can be produced using Na + SiCl4 flames. Silicon of similar purity is obtained from Na + SiF4 flames although yields are lower and product separation and collection are less thermochemically favored. Continuous separation of silicon from the byproduct alkali salt was demonstrated in a heated graphite reactor. The process was scaled up to reduce heat losses and to produce larger samples of silicon. Reagent delivery systems, scaled by a factor of 25, were built and operated at a production rate of 0.5 kg Si/h. Very rapid reactor heating rates are observed with wall temperatures reaching greater than 2000 K. Heat release parameters were measured using a cooled stainless steel reactor tube. A new reactor was designed.

Olsen, D. B.↗
NASA NTRS1979

Develop Silicone Encapsulation Systems for Terrestrial Silicon Solar Arrays

The results for Task 3 of the Low Cost Solar Array Project are presented. Task 3 is directed toward the development of a cost effective encapsulating system for photovoltaic modules using silicon based materials. The technical approach of the contract effort is divided into four special tasks: (1) technology review; (2) generation of concepts for screening and processing silicon encapsulation systems; (3) assessment of encapsulation concepts; and (4) evaluation of encapsulation concepts. The candidate silicon materials are reviewed. The silicon and modified silicon resins were chosen on the basis of similarity to materials with known weatherability, cost, initial tangential modulus, accelerated dirt pick-up test results and the ratio of the content of organic phenyl substitution of methyl substitution on the backbone of the silicon resin.

Source record↗
NASA NTRS1984

Powder containing 2H-type silicon carbide produced by reacting silicon dioxide and carbon powder in nitrogen atmosphere in the presence of aluminum

The production of powder which contains silicon carbide consisting of 40% of 2H-type silicon carbide, beta type silicon carbide and less than 3% of nitrogen is discussed. The reaction temperature to produce the powder containing 40% of 2H-type silicon carbide is set at above 1550 degrees C in an atmosphere of aluminum or aluminum compounds and nitrogen gas or an antioxidation atmosphere containing nitrogen gas. The mixture ratio of silicon dioxide and carbon powder is 0.55 - 1:2.0 and the contents of aluminum or aluminum compounds within silicon dioxide is less than 3% in weight.

Kuramoto, N.↗
NASA NTRS1986

Area Reports. Advanced materials and devices research area. Silicon materials research task, and advanced silicon sheet task

The objectives of the Silicon Materials Task and the Advanced Silicon Sheet Task are to identify the critical technical barriers to low-cost silicon purification and sheet growth that must be overcome to produce a PV cell substrate material at a price consistent with Flat-plate Solar Array (FSA) Project objectives and to overcome these barriers by performing and supporting appropriate R&D. Progress reports are given on silicon refinement using silane, a chemical vapor transport process for purifying metallurgical grade silicon, silicon particle growth research, and modeling of silane pyrolysis in fluidized-bed reactors.

Source record↗
NASA NTRS1987

Stability and rheology of dispersions of silicon nitride and silicon carbide

The relationship between the surface and colloid chemistry of commercial ultra-fine silicon carbide and silicon nitride powders was examined by a variety of standard characterization techniques and by methodologies especially developed for ceramic dispersions. These include electrokinetic measurement, surface titration, and surface spectroscopies. The effects of powder pretreatment and modification strategies, which can be utilized to augment control of processing characteristics, were monitored with these technologies. Both silicon carbide and nitride were found to exhibit silica-like surface chemistries, but silicon nitride powders possess an additional amine surface functionality. Colloidal characteristics of the various nitride powders in aqueous suspension is believed to be highly dependent on the relative amounts of the two types of surface groups, which in turn is determined by the powder synthesis route. The differences in the apparent colloidal characteristics for silicon nitride powders cannot be attributed to the specific absorption of ammonium ions. Development of a model for the prediction of double-layer characteristics of materials with a hybrid site interface facilitated understanding and prediction of the behavior of both surface charge and surface potential for these materials. The utility of the model in application to silicon nitride powders was demonstrated.

Feke, Donald L.↗