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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Performance of direct injected propane and gasoline in a high stroke-to-bore ratio SI engine: Pathways to diesel efficiency parity with ultra low soot

This work explores pathways to achieve diesel-like, high-efficiency combustion with stoichiometric 3-way catalyst compatible combustion in a single-cylinder spark ignition (SI) research engine. A unique high stroke-to-bore engine design (1.5:1) with cooled exhaust gas recirculation (EGR) and high compression ratio ( r c ) was used to improve engine efficiency by up to 30% compared with a production turbocharged gasoline direct injection spark ignition engine. Engine experiments were conducted with both 91 RON E10 gasoline and liquified petroleum gas (LPG) (i.e. autogas) and were compared to legacy gasoline data on the production engine. Geometric compression ratio ( r c ) of 13.3:1 was used for both fuels with additional experiments at 16.8:1 for LPG only. Measurements of exhaust soot particle size and number concentrations were made with both fuels. Significant reduction in soot particles across the whole particle size range were achieved with LPG due to the elimination of in-cylinder liquid films. The effects of EGR, late intake valve closing (IVC) and fuel characteristics were investigated through their effects on efficiency, combustion stability and soot production. Results of 47% gross thermal efficiency, and 45% net thermal efficiency at stoichiometric engine operation, at up to 17 bar IMEP and 2000 r/min with 16.8:1 r c were achieved with LPG. Estimated brake efficiency values were compared to a contemporary medium duty diesel engine illustrating the benefits of the chosen path for achieving diesel efficiency parity.

33 ADVANCED PROPULSION SYSTEMS↗
NASA NTRS1978

Limb-brightening observations from the OSO-7 satellite. III - Comparison of EUV line intensities of Fe XII, Fe XI, Fe XV, Si X and S XII, Si IX and S XI with predictions

Continuing a study of heliocentric dependence of EUV emission line intensities observed by the Goddard OSO-7 spectroheliograph in 1972, the variation of lines of the ions Fe XII, Fe XI, Fe XV, Si X and S XII, Si IX and S XI is compared with the results of individual calculations for these ions, including theoretical intensities presented for Fe XII and Fe XI. Agreement is found to be good for Fe XII and reasonable for some of the lines of the other ions which in general are weaker in intensity. Several apparent anomalies are found however which may be due to unknown line components near the wavelengths observed.

Kastner, S. O.↗
NASA NTRS1985

New adatom model for Si(11) 7X7 and Si(111)Ge 5X5 reconstructed surfaces

A new adatom model differing from the conventional model by a reconstruction of the substrate is proposed. The new adatom structure provides an explanation for the 7x7 and 5x5 size of the unit cells seen on annealed Si(111) and Si(111)-Ge surfaces, respectively. The model is consistent with structural information from vacuum-tunneling microscopy. It also provides simple explanations for stacking-fault-type features expected from Rutherford backscattering experiments and for similarities in the LEED and photoemission spectra of 2x1 and 7x7 surfaces.

Chadi, D. J.↗
NASA NTRS1990

A technique for determining Urbach edge, midgap states and electric field in a-Si:H and a-(Si,Ge):H devices

A technique for measuring the Urbach energy of valence band tail states and midgap defect densities in a-Si:H and a-(Si,Ge):H devices is described. The Urbach energy is determined by measuring the quantum efficiency (QE) of delocalized holes in the devices, whereas the midgap state density (DOS) is estimated by measuring the QE of localized holes. The distinction between delocalized and localized holes is obtained from the behavior of the QE upon the application of reverse bias to the device. The QE of holes localized in midgap states increases significantly upon the application of reverse bias because of Frenkel-Poole tunneling, whereas the QE of holes in tail states does not show such an increase. It is shown that upon light soaking the Urbach edge does not change, but the midgap DOS does increase significantly. A primary consequence of the increase in DOS is a decrease in electric field in the low-field middle i region of the p-i-n cell. The decrease in electric field is experimentally estimated by fitting the increase in the reverse bias QE to Frenkel-Poole tunneling.

Dalal, Vikram L.↗
NASA NTRS1991

Sputtered Ta-Si-N diffusion barriers in Cu metallizations for Si

Electrical measurements on shallow Si n+-p junction diodes with a 30-nm TiSi2 contacting layer demonstrate that an 80-nm-thick amorphous Ta36Si14N50 film prepared by reactive RF sputtering of a Ta5Si3 target in an Ar/N2 plasma very effectively prevents the interaction between the Si substrate with the TiSi2 contacting layer and a 500-nm Cu overlayer. The Ta36Si14N50 diffusion barrier maintains the integrity of the I-V characteristics up to 900 C for 30-min annealing in vacuum. It is concluded that the amorphous Ta36Si14N50 alloy is not only a material with a very low reactivity for copper, titanium, and silicon, but must have a small diffusivity for copper as well.

Kolawa, E.↗
NASA NTRS1992

Bose-Einstein correlations in Si + Al and Si + Au collisions at 14.6A GeV/c

The E802 Spectrometer at the Brookhaven Alternating Gradient Synchrotron has been used to measure the correlation in relative momentum between like-sign pions emitted in central Si + Al and Si + Au collisions at 14.6A GeV/c. Data are presented in terms of the correlation function for both identified pi(-) and pi(+) pairs near the nucleon-nucleon center-of-mass rapidity. All parametrizations of the correlation function are consistent with a spherically symmetric source of rms radius 3.5 +/- 0.4 fm and lifetime fm/c.

Abbott, T.↗
NASA NTRS1994

Pourous Si(x)Ge(1-x) Layers Within Single Crystals Of Si

Layers of porous Si(x)Ge(1-x) buried within single crystals of Si formed by epitaxial growth of Si/Si(x)Ge(1-x)/Si structures followed by etching in solutions of HF:HNO3:H2O. Electroluminescence from these layers utilized in novel optoelectronic devices.

Fathauer, Robert W.↗
DOE OSTI2021

Pinhole Formation in Poly-Si/SiOx Passivating Contacts on Si(111)-Oriented Textures

Poly-Si/SiOx passivating contacts were grown on inverted pyramid and random pyramid textured wafers to investigate the hypothesis that pinhole formation is most susceptible at the valleys and edges of a textured surface. Tetramethylammonium hydroxide (TMAH) etching and electron beam induced current (EBIC) were used to assess pinhole formation and charge-carrier transport. Scanning electron microscopy revealed that TMAH etching can expose pinhole locations on textured surfaces. We show that pinholes may preferentially form at the vertices of inverted pyramids. Our TMAH and EBIC analyses on random pyramids show no preferential oxide breakup at the pyramid valleys.

41 EE - Solar Energy Technologies Office (EE-4S)↗
DOE OSTI2020

Electronic structure of the Si-containing topological Dirac semimetal CaAl 2 Si 2

There has been an upsurge in the discovery of topological quantum materials, where various topological insulators and semimetals have been theoretically predicted and experimentally observed. However, very few of them contain silicon, the most widely used element in the electronics industry. Recently, ternary compound CaA l 2 S i 2 has been predicted to be a topological Dirac semimetal, hosting Lorentz-symmetry-violating quasiparticles with a strongly tilted conical band dispersion. In this work, by using high-resolution angle-resolved photoemission spectroscopy, we investigated the comprehensive electronic structure of CaA l 2 S i 2 . A pair of topological Dirac crossings is observed along the k z direction, in good agreement with the ab initio calculations, confirming the topological Dirac semimetal nature of the compound. Our study expands the topological material family on Si-containing compounds, which have great application potential in realizing low-cost, nontoxic electronic devices with topological quantum states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1993

An investigation on the rheological behavior of metallic semi-solid slurries of Al-6.5 pct Si and semi-solid composite slurries of SiC particulates in an Al-6.5 pct Si alloy matrix

The rheology of SiC particulate/Al-6.5 pct Si composite slurries was explored. The rheological behavior of the composite slurries shows both thixotropic and pseudoplastic behaviors. Isostructural experiments on the composite slurries revealed a Newtonian behavior beyond a high shear rate limit. The rheology of fully molten composite slurries over the low to high shear rate range indicates the existence of a low shear rate Newtonian region, an intermediate pseudoplastic region and a high shear rate Newtonian region. The isostructural studies indicate that the viscosity of a composite slurry depends upon the shearing history of a given volume of material. An unexpected shear thinning was noted for SiC particulate + alpha slurries as compared to semi-solid metallic slurries at the same fraction solid. The implications of these findings for the processing of slurries into cast components is discussed.

Moon, H.-K.↗
DOE OSTI2021

Fabrication of Poly-Si on Locally Etched SiOx as Passivating Contacts for c-Si Solar Cells

Proof-of-concept for polysilicon on locally etched oxide (PLEO) contacts. Room temperature approach (via MACE) to engineer pinholes decouples charge-carrier transport across contact from passivation scheme of choice. 19 and 17% PLEO devices fabricated on double-side textured and saw-damage etched n Cz wafers, respectively. Preliminary work on polysilicon on locally etched nitride/oxide (PLENO) contacts. 0.2 fA/cm2 achieved with p PLENO; contact displays Ohmic behavior but still very resistive due to low pinhole density.

c-Si↗
DOE OSTI2020

Materials Data on Si by Materials Project

Si is Clathrate-like structured and crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are twenty-one inequivalent Si sites. In the first Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.35–2.45 Å. In the second Si site, Si is bonded to four Si atoms to form a mixture of edge and corner-sharing SiSi4 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.34–2.36 Å. In the third Si site, Si is bonded to four Si atoms to form a mixture of edge and corner-sharing SiSi4 tetrahedra. There are two shorter (2.36 Å) and one longer (2.38 Å) Si–Si bond lengths. In the fourth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are one shorter (2.35 Å) and two longer (2.39 Å) Si–Si bond lengths. In the fifth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are one shorter (2.38 Å) and one longer (2.40 Å) Si–Si bond lengths. In the sixth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.37–2.39 Å. In the seventh Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. Both Si–Si bond lengths are 2.36 Å. In the eighth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are one shorter (2.35 Å) and two longer (2.39 Å) Si–Si bond lengths. In the ninth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. The Si–Si bond length is 2.33 Å. In the tenth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.34–2.42 Å. In the eleventh Si site, Si is bonded to four Si atoms to form a mixture of edge and corner-sharing SiSi4 tetrahedra. The Si–Si bond length is 2.35 Å. In the twelfth Si site, Si is bonded to four Si atoms to form a mixture of edge and corner-sharing SiSi4 tetrahedra. There are one shorter (2.34 Å) and one longer (2.36 Å) Si–Si bond lengths. In the thirteenth Si site, Si is bonded to four Si atoms to form a mixture of edge and corner-sharing SiSi4 tetrahedra. Both Si–Si bond lengths are 2.38 Å. In the fourteenth Si site, Si is bonded to four Si atoms to form a mixture of edge and corner-sharing SiSi4 tetrahedra. The Si–Si bond length is 2.37 Å. In the fifteenth Si site, Si is bonded to four Si atoms to form a mixture of edge and corner-sharing SiSi4 tetrahedra. The Si–Si bond length is 2.38 Å. In the sixteenth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are one shorter (2.38 Å) and one longer (2.41 Å) Si–Si bond lengths. In the seventeenth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. The Si–Si bond length is 2.39 Å. In the eighteenth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are one shorter (2.36 Å) and one longer (2.39 Å) Si–Si bond lengths. In the nineteenth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. The Si–Si bond length is 2.37 Å. In the twentieth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. In the twenty-first Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Si by Materials Project

Si is Clathrate-like structured and crystallizes in the hexagonal P6/mmm space group. The structure is three-dimensional. there are seventeen inequivalent Si sites. In the first Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.33–2.38 Å. In the second Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.33–2.38 Å. In the third Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.33–2.37 Å. In the fourth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.33–2.38 Å. In the fifth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are two shorter (2.35 Å) and one longer (2.37 Å) Si–Si bond lengths. In the sixth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are two shorter (2.34 Å) and one longer (2.38 Å) Si–Si bond lengths. In the seventh Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are one shorter (2.33 Å) and two longer (2.36 Å) Si–Si bond lengths. In the eighth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are one shorter (2.33 Å) and two longer (2.36 Å) Si–Si bond lengths. In the ninth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are one shorter (2.40 Å) and one longer (2.45 Å) Si–Si bond lengths. In the tenth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. The Si–Si bond length is 2.40 Å. In the eleventh Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. Both Si–Si bond lengths are 2.48 Å. In the twelfth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. There are a spread of Si–Si bond distances ranging from 2.36–2.45 Å. In the thirteenth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. The Si–Si bond length is 2.34 Å. In the fourteenth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. In the fifteenth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. The Si–Si bond length is 2.33 Å. In the sixteenth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. The Si–Si bond length is 2.33 Å. In the seventeenth Si site, Si is bonded to four Si atoms to form corner-sharing SiSi4 tetrahedra. Both Si–Si bond lengths are 2.33 Å.

36 MATERIALS SCIENCE↗