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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Algae-based sorbents for removal of gallium from semiconductor manufacturing wastewater

Gallium is increasingly used in industry, and particularly as a component of new materials that have entered semiconductor manufacturing. The release of gallium in factory’s wastewater is potentially an environmental issue and a human health concern. Utilization of algae-based sorbents in the treatment of wastewater polluted by heavy metals has been regarded as a potentially efficient and environmentally-friendly technology. Removal of gallium from simulated wastewater using dead freshwater green algae, ( Chlorella sorokiniana ), as a sorbent was studied. Both batch and continuous flow operations were investigated. Mass balance-based process models were developed and validated for both batch and flow systems. These models were found to be valuable for both understanding the process steps as well as for analyzing the experimental data and determining the fundamental kinetics and thermodynamic parameters. Adsorption capacity was found to be 14.1 mg/g at pH of 2.3, increasing to 38.5 mg/g when the pH is raised to 2.8. The effect of pH is attributed to the surface charge interactions between biomass and gallium and indicates that gallium can be acid-washed and desorbed from the biomass. This property allows for capture followed by recovery of gallium from wastewater using algae based biosorbents.

09 BIOMASS FUELS↗
DOE OSTI2019

Photo‐/Thermal‐Responsive Field‐Effect Transistor upon Blending Polymeric Semiconductor with Hexaarylbiimidazole toward Photonically Programmable and Thermally Erasable Memory Device

Abstract It is shown that the semiconducting performance of field‐effect transistors (FETs) with PDPP4T (poly(diketopyrrolopyrrole‐quaterthiophene)) can be reversibly tuned by UV light irradiation and thermal heating after blending with the photochromic hexaarylbiimidazole compound ( p ‐NO 2 ‐HABI). A photo‐/thermal‐responsive FET with a blend thin film of PDPP4T and p ‐NO 2 ‐HABI is successfully fabricated. The transfer characteristics are altered significantly with current enhanced up to 10 6 ‐fold at V G = 0 V after UV light irradiation. However, further heating results in the recovery of the transfer curve. This approach can be extended to other semiconducting polymers such as P3HT (poly(3‐hexyl thiophene)), PBTTT (poly(2,5‐bis(3‐tetradecylthiophen‐2‐yl)thieno[3,2‐b] thiophene)) and PDPPDTT (poly(diketopyrrolopyrrole‐dithienothiophene)). It is hypothesized that TPIRs (2,4,5‐triphenylimidazolyl radicals) formed from p ‐NO 2 ‐HABI after UV light irradiation can interact with charge defects at the gate dielectric–semiconductor interface and those in the semiconducting layer to induce more hole carriers in the semiconducting channel. The application of the blend thin film of PDPP4T and p ‐NO 2 ‐HABI is further demonstrated to fabricate the photonically programmable and thermally erasable FET‐based nonvolatile memory devices that are advantageous in terms of i) high ON/OFF current ratio, ii) nondestructive reading at low electrical bias, and iii) reasonably highly stable ON‐state and OFF‐state.

Liu, Yidong↗
DOE OSTI2018

Air-Stable Direct Bandgap Perovskite Semiconductors: All-Inorganic Tin-Based Heteroleptic Halides A x SnCl y I z (A = Cs, Rb)

Semiconducting halide perovskites are a group of materials with exciting photoelectronic properties. Compared to the widely studied hybrid organic–inorganic perovskites, the all-inorganic derivatives are less well understood even as they promise high inherent stability. At the moment, such materials are limited due to the fact that there is a very narrow choice of inorganic cations that can stabilize the desirable perovskite structure. Herein we report on the synthesis and characterization of novel all-inorganic tin-based perovskites and perovskitoids that can be stabilized by the heteroleptic coordination of chloride and iodide anions, Cs 2 SnCl 2 I 2 ( 1 ) and Cs 2.38 Rb 1.62 Sn 3 Cl 8 I 2 ( 2 ), consist of two-dimensional (2D) layers of [SnCl 4 I 2 ] 4– octahedra with different connectivity modes. Compound 1 is an n = 1 Ruddlesden–Popper type perovskite adopting the tetragonal archetype structure ( I 4/ mmm space group; a = 5.5905(3) Å, c = 18.8982(13) Å), while compound 2 crystallizes as an orthorhombic modification ( Cmcm space group; a = 5.6730(11) Å, b = 25.973(5) Å, c = 16.587(3) Å) with corrugated layers. The crystal chemistry changes drastically when Cs + is replaced by the smaller Rb + cation which leads to the isolation of the low dimensional compounds Rb 3 SnCl 3 I 2 ( 3a ), Rb 3 SnCl 2.33 I 2.67 ( 3b ) and Rb 7 Sn 4.25 Cl 12 I 3.5 ( 4 ), thus illustrating the importance of the A-cation size in the formation of perovskites. The 2D perovskites show wide band gaps and relatively large resistivities, associated with their chemical stability against the oxidation of Sn 2+ . The chemical stability is coupled with remarkable electronic properties that derive from the perovskite structure. DFT calculations suggest that both compounds are direct band gap semiconductors with large bandwidths, consistently with the experimentally determined band gaps of E g = 2.62 and 2.81 eV for 1 and 2 , respectively. The combination of stability and favorable electronic structure in heteroleptic-halide perovskites presents a new direction toward the realization of functional devices made exclusively from inorganic perovskites.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Controlling Catalyst–Semiconductor Contacts: Interfacial Charge Separation in p-InP Photocathodes

Charge-carrier-selective interfaces between electrocatalyst particles and semiconductor light absorbers are critical for solar photochemistry but controlling their properties is challenging. Using thin films and nanoparticle arrays of Pt hydrogen-evolution catalysts on p-InP (a high-performance photocathode material), along with macroscopic and nanoscopic electrical and chemical analysis, we show how hydrogen alloying, the pinch-off effect for nanoscale contacts, and the formation of a native surface oxides all play different roles in creating charge-carrier-selective junctions. As a result, the new insights can be broadly applied to photocathodes, photoanodes, and overall water-splitting systems to control charge-carrier selectivity and improve performance.

14 SOLAR ENERGY↗
DOE OSTI2019

Stable Unassisted Solar Water Splitting on Semiconductor Photocathodes Protected by Multifunctional GaN Nanostructures

Producing hydrogen by unassisted solar water splitting is one essential step to make direct solar fuel conversion a viable energy source. To date, however, there has been no demonstration of stable photoelectrodes for high efficiency photoelectrochemical water splitting. In this work, we report that a GaInP2/GaAs/Ge triple-junction (3J) photocathode protected by multi-functional GaN nanostructures can enable both efficient and relatively stable solar water splitting. A 12.6% solar-to-hydrogen (STH) efficiency is measured without any external bias. Of particular importance, we demonstrate relatively stable solar water splitting for 80 hours in three-electrode configuration and 57 hours in two-electrode measurement at zero bias. This is the best reported stability for multi-junction semiconductor photocathodes in two-electrode configuration to our knowledge. Here, the multifunctional GaN nanostructure significantly reduces the charge transfer resistance at semiconductor/electrolyte interface and protects III-V materials against corrosion. Such multi-functional GaN photocatalytic nanostructures provide a new pathway to improve the performance of conventional photoelectrodes to achieve both efficient and stable unassisted solar water splitting.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Semiconductor Hyperbolic Metamaterials at the Quantum Limit

We study semiconductor hyperbolic metamaterials (SHMs) at the quantum limit experimentally using spectroscopic ellipsometry as well as theoretically using a new microscopic theory. The theory is a combination of microscopic density matrix approach for the material response and Green’s function approach for the propagating electric field. Our approach predicts absorptivity of the full multilayer system and for the first time allows the prediction of in-plane and out-of-plane dielectric functions for every individual layer constructing the SHM as well as effective dielectric functions that can be used to describe a homogenized SHM.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Electron-ion coupling in semiconductors beyond Fermi's Golden Rule [On the electron-ion coupling in semiconductors beyond Fermi's Golden Rule]

In the present study, a theoretical study of electron-phonon (electron-ion) coupling rates in semiconductors driven out of equilibrium is performed. Transient change of optical coefficients reflects the band gap shrinkage in covalently bonded materials, and thus, the heating of atomic lattice. Utilizing this dependence, we test various models of electron-ion coupling. The simulation technique is based on tight-binding molecular dynamics. Our simulations with the dedicated hybrid approach (XTANT) indicate that the widely used Fermi's golden rule can break down describing material excitation on femtosecond time scales. In contrast, dynamical coupling proposed in this work yields a reasonably good agreement of simulation results with available experimental data.

36 MATERIALS SCIENCE↗
DOE OSTI2017

BC8 Silicon (Si-III) is a Narrow-Gap Semiconductor

Large-volume, phase-pure synthesis of BC8 silicon ($Ia\bar{3}$, cI16) has allowed bulk measurements of optical, electronic, and thermal properties. Unlike previous reports that conclude BC8-Si is semimetallic, we demonstrate that this phase is a direct band gap semiconductor with a very small energy gap and moderate carrier concentration and mobility at room temperature, based on far- and midinfrared optical spectroscopy, temperature-dependent electrical conductivity, Seebeck and heat capacity measurements. Samples exhibit a plasma wavelength near 11 μm, indicating potential for infrared plasmonic applications. Thermal conductivity is reduced by 1–2 orders of magnitude depending on temperature as compared with the diamond cubic (DC-Si) phase. The electronic structure and dielectric properties can be reproduced by first-principles calculations with hybrid functionals after adjusting the level of exact Hartree–Fock (HF) exchange mixing. These results clarify existing limited and controversial experimental data sets and ab initio calculations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Furthermore, thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region.

14 SOLAR ENERGY↗
DOE OSTI2016

Electrical and photoelectric properties of Si-based metal–insulator–semiconductor structures with Au nanoparticles at the insulator–semiconductor interface

It is shown that the formation of Au nanoparticles at the insulator–silicon interface in structures with a high density of surface states results in a shift of the Fermi-level pinning energy at this interface towards the valence-band ceiling in silicon and in increasing the surface-state density at energies close to the Fermi level. In this case, a band with a peak at 0.85 eV arises on the photosensivity curves of the capacitor photovoltage, which is explained by the photoemission of electrons from the formed Au-nanoparticle electron states near the valence-band ceiling in silicon.

36 MATERIALS SCIENCE↗