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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Surface Immobilization of a Re(I) Tricarbonyl Phenanthroline Complex to Si(111) through Sonochemical Hydrosilylation

A sonochemical-based hydrosilylation method was employed to covalently attach a rhenium tricarbonyl phenanthroline complex to silicon(111). fac-Re(5-(p-Styrene)-phen)(CO) 3 Cl (5-(p-styrene)-phen = 5-(4-vinylphenyl)-1,10-phenanthroline) was reacted with hydrogen-terminated silicon(111) in an ultrasonic bath to generate a hybrid photoelectrode. Subsequent reaction with 1-hexene enabled functionalization of remaining atop Si sites. Attenuated total reflectance–Fourier transform infrared spectroscopy confirms attachment of the organometallic complex to silicon without degradation of the organometallic core, supporting hydrosilylation as a strategy for installing coordination complexes that retain their molecular integrity. Detection of Re(I) and nitrogen by X-ray photoelectron spectroscopy (XPS) further support immobilization of fac-Re(5-(p-styrene)-phen)(CO) 3 Cl. Cyclic voltammetry and electrochemical impedance spectroscopy under white light illumination indicate that fac-Re(5-(p-styrene)-phen)(CO) 3 Cl undergoes two electron reductions. Mott–Schottky analysis indicates that the flat band potential is 239 mV more positive for p-Si(111) co-functionalized with both fac-Re(5-(p-styrene)-phen)(CO) 3 Cl and 1-hexene than when functionalized with 1-hexene alone. XPS, ultraviolet photoelectron spectroscopy, and Mott–Schottky analysis show that functionalization with fac-Re(5-(p-styrene)-phen)(CO) 3 Cl and 1-hexene introduces a negative interfacial dipole, facilitating reductive photoelectrochemistry.

X-ray photoelectron spectroscopy↗
DOE OSTI2022

Revisiting the K-edge X-ray absorption fine structure of Si, Ge–Si alloys, and the isoelectronic series: CuBr, ZnSe, GaAs, and Ge

Extended X-ray absorption fine structure (EXAFS) has evolved into an unprecedented local-structure technique that is routinely used to study materials’ problems in the biological, chemical, and physical sciences. Like many other experimental techniques, EXAFS also requires that several key atomic parameters must be known a priori before structural information can be quantitatively determined. Utilizing current analytical methods, we revisit the isoelectronic series CuBr, ZnSe, GaAs, and Ge originally studied by Stern et al. during the early development of EXAFS. We demonstrate that the ab initio EXAFS code FEFF accurately predicts the atomic phase shifts and backscattering amplitudes that are primarily functions of the sum of atomic numbers Z along an EXAFS scattering path. We also investigate quantitative fitting and first- and second-shell phase transferability together with problems that arise if a backscattering atom is identified incorrectly in an EXAFS fitting model. Features in the near-edge region, on the other hand, are shown to require a comprehensive treatment of the band structure and density-of-states, including effects of the screened Coulomb interaction between the photoelectron and core hole. Here, we demonstrate that the Bethe–Salpeter equation (BSE) accurately captures the NEXAFS (or XANES) portion of the spectrum for the isoelectronic series in addition to Si and Ge–Si alloys, including within a few eV of the absorption edge, where band structure and excitonic effects are most important.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Low-Frequency Noise and Deep Level Transient Spectroscopy in n-p-n Si Bipolar Junction Transistors Irradiated with Si Ions

The properties of defects in n-p-n Si bipolar junction transistors (BJTs) caused by 17 MeV Si ions are investigated via current-voltage, low-frequency noise, and deep-level transient spectroscopy (DLTS) measurements. Four prominent radiation-induced defects in the base-collector junction of these transistors are identified via DLTS. At least two defect levels are observed in temperature-dependent low-frequency 1/ f noise measurements, one that is similar to a prominent defect in DLTS and another that is not. Defect microstructures are discussed. Here our results show that DLTS and 1/ f noise measurements can provide complementary information about defects in linear bipolar devices.

42 ENGINEERING↗
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↗
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↗
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↗
DOE OSTI2022

CLARION2-TRINITY: A Compton-suppressed HPGe and GAGG:Ce-Si-Si array for absolute cross-section measurements with heavy ions

The design and performance of a new Compton-suppressed HPGe and charged-particle array, CLARION2-TRINITY, are described. The TRINITY charged-particle array is comprised of 64 Cerium-doped Gadolinium Aluminum Gallium Garnet (GAGG:Ce) crystals configured into five rings spanning 7–54 degrees, and two annular silicon detectors that can shadow or extend the angular coverage to backward angles with minimal $\gamma$-ray attenuation. GAGG:Ce is a non-hygroscopic, bright, and relatively fast scintillator with a light distribution well matched to SiPMs. Count rates up to 40 kHz per crystal are sustainable. Fundamental characteristics of GAGG:Ce are measured and presented, including light- and heavy-ion particle identification (PID) capability, pulse-height defects, radiation hardness, and emission spectra. The CLARION2 array consists of up to 16 Compton-suppressed HPGe Clover detectors (efficiency at 1 MeV) configured into four rings (eight HPGe crystal rings) using a non-Archimedean geometry that suppresses back-to-back coincident 511-keV gamma rays. The entire array is instrumented with 100- and 500-MHz (14 bit) waveform digitizers which enable triggerless operation, pulse-shape discrimination, fast timing, and pileup correction. Lastly, two examples of experimental data taken during the commissioning of the CLARION2-TRINITY system are given: a PID spectrum from 16 O + 18 O fusion-evaporation, and PID and Doppler-corrected -ray spectra from 48 Ti + 12 C Coulomb excitation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗