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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 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Hydrogen Species Motion in Piezoelectrics: A Quasi-Elastic Neutron Scattering Study

Hydrogen is known to damage or degrade piezoelectric materials, at low pressure for ferroelectric random access memory applications, and at high pressure for hydrogen powered vehicle applications. The piezoelectric degradation is in part governed by the motion of hydrogen species within the piezoelectric materials. We present here Quasi-Elastic Neutron Scattering (QENS) measurements of the local hydrogen species motion within lead zirconate titanate (PZT) and barium titanate (BTO) on samples charged by gaseous exposure to high-pressure gaseous hydrogen {approx}17 MPa. Filter Analyzed Neutron Spectroscopy (FANS) studies of the hydrogen enhanced vibrational modes are presented as well. Results are discussed in context of theoretically predicted interstitial hydrogen lattice sites and compared to comparable bulk diffusion studies of hydrogen diffusion in lead zirconate titanate.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Lithiation of Silica through Partial Reduction

We demonstrate the reversible lithiation of SiO{sub 2} up to 2/3 Li per Si, and propose a mechanism for it based on molecular dynamics and density functional theory simulations. Our calculations show that neither interstitial Li (no reduction), nor the formation of Li{sub 2}O clusters and Si-Si bonds (full reduction) are energetically favorable. Rather, two Li effectively break a Si-O bond and become stabilized by oxygen, thus partially reducing the SiO{sub 2} anode: this leads to increased anode capacity when the reduction occurs at the Si/SiO{sub 2} interface. The resulting Li{sub x}SiO{sub 2} (x < 2/3) compounds have band-gaps in the range of 2.0-3.4 eV.

25 ENERGY STORAGE↗
DOE OSTI2012

Annealing studies of heteroepitaxial InSbN on GaAs grown by molecular beam epitaxy for long-wavelength infrared detectors

We report the effect of annealing on the structural, vibrational, electrical, and optical properties of heteropepitaxially grown InSbN epilayers on GaAs substrate by molecular beam epitaxy for long-wavelength infrared detector applications. As-grown epilayers exhibited high N incorporation in the both substitutional and interstitial sites, with N induced defects as evidenced from high resolution x-ray diffraction, secondary ion mass spectroscopy, and room temperature (RT) micro-Raman studies. The as-grown optical band gap was observed at 0.132 eV ({approx}9.4 {mu}m) and the epilayer exhibited high background carrier concentration at {approx}10{sup 18} cm{sup -3} range with corresponding mobility of {approx}10{sup 3} cm{sup 2}/Vs. Ex situ and in situ annealing at 430 Degree-Sign C though led to the loss of N but improved InSb quality due to effective annihilation of N related defects and other lattice defects attested to enhanced InSb LO phonon modes in the corresponding Raman spectra. Further, annealing resulted in the optical absorption edge red shifting to 0.12 eV ({approx}10.3 {mu}m) and the layers were characterized by reduced background carrier concentration in the {approx}10{sup 16} cm{sup -3} range with enhanced mobility in {approx}10{sup 4} cm{sup 2}/Vs range.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Incoherent twin boundary migration induced by ion irradiation in Cu

Grain boundaries can act as sinks for radiation-induced point defects. The sink capability is dependent on the atomic structures and varies with the type of point defects. Using high-resolution transmission electron microscopy, we observed that {Sigma}3{l_brace}112{r_brace} incoherent twin boundary (ITB) in Cu films migrates under Cu{sup 3+} ion irradiation. Using atomistic modeling, we found that {Sigma}3{l_brace}112{r_brace} ITB has the preferred sites for adsorbing interstitials and the preferential diffusion channels along the Shockley partial dislocations. Coupling with the high mobility of grain boundary Shockley dislocations within {Sigma}3{l_brace}112{r_brace} ITB, we infer that {Sigma}3{l_brace}112{r_brace} ITB migrates through the collective glide of grain boundary Shockley dislocations, driven by a concurrent reduction in the density of radiation-induced defects, which is demonstrated by the distribution of nearby radiation-induced defects.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Resolving the EH{sub 6/7} level in 4H-SiC by Laplace-transform deep level transient spectroscopy

We show that Laplace transform deep level transient spectroscopy (LDLTS) is an effective technique for the separation of the overlapping emission rates of the EH{sub 6} and EH{sub 7} levels, which are known to constitute EH{sub 6/7}, a mid-gap level in n-type 4H-SiC. The analysis of the electron irradiation dose, electric field dependence, and the effects of carbon interstitials injection on the emission rates of EH{sub 6} and EH{sub 7} shows that EH{sub 7} is dominant over EH{sub 6} and confirms that their nature is related to a carbon vacancy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Electrical characterisation and predictive simulation of defects induced by keV Si{sup +} implantation in n-type Si

In this work, we focused on the analysis of implantation-induced defects, mainly small interstitial clusters (ICs) and {l_brace} 311{r_brace} defects introduced in n-type Si after ion implantation using deep level transient spectroscopy (DLTS). Silicon ions (at 160 keV or 190 keV) of fluences ranging from (0.1-8.0) Multiplication-Sign 10{sup 13} cm{sup -2} have been implanted into n-type Si and annealed at temperatures between 500 Degree-Sign C and 800 Degree-Sign C specifically to create small ICs or {l_brace} 311{r_brace} s rod-like defects. In samples dominated by small ICs, DLTS spectra show prominent deep levels at Ec - 0.24 eV and Ec - 0.54 eV. After increasing the fluence and temperature, i.e., reducing the number of small ICs and forming {l_brace} 311{r_brace} defects, the peak Ec - 0.54 eV is still dominant while other electron traps Ec - 0.26 eV and Ec - 0.46 eV are introduced. There were no observable deep levels in reference, non-implanted samples. The identity and origin of all these traps are interpreted in conjunction with recently developed predictive defect simulation models.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

KrF- and ArF-excimer-laser-induced absorption in silica glasses produced by melting synthetic silica powder

KrF- and ArF-excimer-laser-induced absorption of silica glasses produced by electric melting and flame fusion of synthetic silica powder were investigated. The growth of KrF-laser-induced absorption was more gradual than that of ArF-laser-induced absorption. Induced absorption spectra exhibited a peak at about 5.8 eV, of which the position and width differed slightly among samples and laser species. Widths of ArF-laser-induced absorption spectra were wider than those of KrF-laser-induced spectra. KrF-laser-induced absorption is reproducible by two Gaussian absorption bands peaking at 5.80 eV with full width at half maximum (FWHM) of 0.62 eV and at 6.50 eV with FWHM of 0.74 eV. For reproduction of ArF-laser-induced absorption, Gaussian bands at 5.41 eV with FWHM of 0.62 eV was necessary in addition to components used for reproducing KrF-laser-induced absorption. Based on the discussion of the change of defect structures evaluated from change of absorption components, we proposed that the precursor of the 5.8-eV band ascribed to E Prime center ({identical_to}Si{center_dot}) is {identical_to}Si-H HO-Si{identical_to} structures formed by the reaction between strained Si-O-Si bonds and interstitial H{sub 2} molecules during the irradiation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Tuning the formation of p-type defects by peroxidation of CuAlO{sub 2} films

p-type conduction of CuAlO{sub 2} thin films was realized by the rf sputtering method. Combining with Hall, X-ray photoelectron spectroscopy, energy dispersive spectrometer, and X-ray diffraction results, a direct link between the hole concentration, Cu vacancy (V{sub Cu}), and interstitial oxygen (O{sub i}) was established. It is shown that peroxidation of CuAlO{sub 2} films may lead to the increased formation probability of acceptors (V{sub Cu} and O{sub i}), thus, increasing the hole concentration. The dependence of the V{sub Cu} density on growth conditions was identified for providing a guide to tune the formation of p-type defects in CuAlO{sub 2}. Understanding the defect-related p-type conductivity of CuAlO{sub 2} is essential for designing optoelectronic devices and improving their performance.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Electrical characterization of ensemble of GaN nanowires grown by the molecular beam epitaxy technique

High quality Schottky contacts are formed on GaN nanowires (NWs) structures grown by the molecular beam epitaxy technique on Si(111) substrate. The current-voltage characteristics show the rectification ratio of about 10{sup 3} and the leakage current of about 10{sup −4} A/cm{sup 2} at room temperature. From the capacitance-voltage measurements the free carrier concentration in GaN NWs is determined as about 10{sup 16} cm{sup −3}. Two deep levels (H200 and E280) are found in the structures containing GaN NWs. H200 is attributed to an extended defect located at the interface between the substrate and SiN{sub x} or near the sidewalls at the bottom of the NWs whereas E280 is tentatively assigned to a gallium-vacancy- or nitrogen interstitials-related defect.

36 MATERIALS SCIENCE↗
DOE OSTI2013

The role of ZrN capping layer deposited on ultra-thin high-k Zr-doped yttrium oxide for metal-gate metal–insulator–semiconductor applications

Metal-gate MIS structures with and without ZrN capping layer on high-k Y{sub 2}O{sub 3}:Zr/Y{sub 2}O{sub 3} stack were fabricated. The binding energies and depth profiles were investigated by x-ray photoelectron spectroscopy (XPS). The x-ray diffraction (XRD) patterns were compared. It is found that Ti out-diffusion into Zr-based high-k dielectric becomes lesser with the insertion of ZrN capping layer. The electrical properties of current-voltage (I-V) and capacitance-voltage (C-V) characteristics were measured in the postannealing temperature range of 550–850 °C. According to the defect reaction model, Zr cation vacancies are associated with the concentration of Ti ion by a transition from +3 to +2 states. The amount of Zr cation vacancies is quantified and equal to a half of Ti substitution amount at Zr site. The reduction in cation vacancies at high temperatures can well explain the decrease in ΔV{sub FB} for samples with ZrN layer. In contrast, an excess of Ti outdiffusion will produce the interstitial defects in high-k films without ZrN capping.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Investigation of activated oxygen molecules on the surface of Y{sub 2}O{sub 3} nanocrystals by Raman scattering

Activation of surface oxygen molecules on cubic Y{sub 2}O{sub 3} nanocrystals (NCs) is investigated. As the annealing temperature under O{sub 2} is increased, the strong Raman band at 965 cm{sup −1} previously never assigned weakens gradually, while the intensity of the 378 cm{sup −1} Raman band arising from Y{sup 3+}-O{sup 2−} vibration increases. X-ray diffraction reveals no structural change during annealing and energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and theoretical calculation suggest that the interstitial oxygen O{sub 2}{sup 2−} connected to the F centers gives rise to the 965 cm{sup −1} Raman band. The results provide direct evidence of the existence of activated oxygen ions on Y{sub 2}O{sub 3} NCs.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Irradiation-induced composition patterns in binary solid solutions

A theoretical/computational model for the irradiation-driven compositional instabilities in binary solid solutions has been developed. The model is suitable for investigating the behavior of structural alloys and metallic nuclear fuels in a reactor environment as well as the response of alloy thin films to ion beam irradiation. The model is based on a set of reaction-diffusion equations for the dynamics of vacancies, interstitials, and lattice atoms under irradiation. The dynamics of these species includes the stochastic generation of defects by collision cascades as well as the defect reactions and diffusion. The atomic fluxes in this model are derived based on the transitions of lattice defects. The set of reaction-diffusion equations are stiff, hence a stiffly stable method, also known as the Gear method, has been used to numerically approximate the equations. For the Cu-Au alloy in the solid solution regime, the model results demonstrate the formation of compositional patterns under high-temperature particle irradiation, with Fourier space properties (Fourier spectrum, average wavelength, and wavevector) depending on the cascade damage characteristics, average composition, and irradiation temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2013

First-principles DFT+U modeling of defect behaviors in anti-ferromagnetic uranium mononitride

A series of point defects in uranium mononitride (UN) have been studied by first-principles DFT+U calculations. The influence of intrinsic defects on the properties of UN was explored by considering the anti-ferromagnetic (AFM) order along the [001] direction. Our results show that all the point defects lead to obvious volume swelling of UN crystal. Energetically, the interstitial nitrogen defect is the most favorable one among single-point defects in UN crystal with the formation energy of 4.539 eV, while the N-Frenkel pair becomes the most preferable one among double-point defects. The AFM order induces obvious electron spin polarization of uranium towards neighboring uranium atoms with opposite spin orientations in UN crystal.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2014

Boron deactivation in heavily boron-doped Czochralski silicon during rapid thermal anneal: Atomic level understanding

The changes in hole concentration of heavily boron (B)-doped Czochralski silicon subjected to high temperature rapid thermal anneal (RTA) and following conventional furnace anneal (CFA) have been investigated. It is found that decrease in hole concentration, namely, B deactivation, is observed starting from 1050 °C and increases with RTA temperature. The following CFA at 300–500 °C leads to further B deactivation, while that at 600–800 °C results in B reactivation. It is supposed that the interaction between B atoms and silicon interstitials (I) thus forming BI pairs leads to the B deactivation during the high temperature RTA, and, moreover, the formation of extended B{sub 2}I complexes results in further B deactivation in the following CFA at 300–500 °C. On the contrary, the dissociation of BI pairs during the following CFA at 600–800 °C enables the B reactivation. Importantly, the first-principles calculation results can soundly account for the above-mentioned supposition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Structural defects induced by Fe-ion implantation in TiO{sub 2}

X-ray photoelectron spectroscopy and resonant x-ray emission spectroscopy measurements of pellet and thin film forms of TiO{sub 2} with implanted Fe ions are presented and discussed. The findings indicate that Fe-implantation in a TiO{sub 2} pellet sample induces heterovalent cation substitution (Fe{sup 2+} → Ti{sup 4+}) beneath the surface region. But in thin film samples, the clustering of Fe atoms is primarily detected. In addition to this, significant amounts of secondary phases of Fe{sup 3+} are detected on the surface of all doped samples due to oxygen exposure. These experimental findings are compared with density functional theory calculations of formation energies for different configurations of structural defects in the implanted TiO{sub 2}:Fe system. According to our calculations, the clustering of Fe-atoms in TiO{sub 2}:Fe thin films can be attributed to the formation of combined substitutional and interstitial defects. Further, the differences due to Fe doping in pellet and thin film samples can ultimately be attributed to different surface to volume ratios.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

The E3 center in zinc oxide: Evidence for involvement of hydrogen

Proton implantation is shown to increase the concentration of the so called and commonly observed E3 defect level in zinc oxide (ZnO). Box and single profiles of protons with doses ranging from 6×10{sup 10} cm{sup −2} to 4.3×10{sup 12} cm{sup −2} were implanted into hydrothermally grown ZnO samples with original concentrations of E3 below 5×10{sup 14} cm{sup −3}. Capacitance-Voltage profiling and junction spectroscopy measurements showed that the charge carrier concentration and absolute concentration of E3 centers increase by more than one order of magnitude compared to the as-grown samples as well as control samples implanted with He ions. The results provide strong evidence for the involvement of H in the formation of the E3 center, and a complex involving interstitial H and an oxygen sub-lattice primary defect are discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Synthesis of highly efficient antibacterial agent Ag doped ZnO nanorods: Structural, Raman and optical properties

Here, synthesis, structural, morphological, Raman, optical properties and antibacterial activity of undoped and Ag doped ZnO nanorods by chemical co-precipitation technique have been reported. Structural analysis has revealed that Ag doping cannot deteriorate the structure of ZnO and wurtzite phase is maintained. Lattice constants are found to be decreased with the Ag doping. Fourier transform infrared and Raman spectroscopy also confirm the X-ray diffraction results. Scanning electron microscopy results have demonstrated the formation of ZnO nanorods with average diameter and length of 96 nm and 700 nm, respectively. Raman spectroscopy results suggest that the Ag doping enhances the number of defects in ZnO crystal. It has been found from optical study that Ag doping results in positional shift of band edge absorption peak. This is attributed to the successful incorporation of Ag dopant into ZnO host matrix. The antibacterial activity of prepared nanorods has been determined by two different methods and compared to that of undoped ZnO nanorods. Ag doped ZnO nanorods exhibit excellent antibacterial activity as compared to that of undoped ZnO nanorods. This excellent antibacterial activity may be attributed to the presence of oxygen vacancies and Zn{sup 2+} interstitial defects. Our preliminary findings suggest that Ag doped ZnO nanorods can be used externally to control the spreading of infections related with tested bacterial strains.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Hydrogen removal from e-beam deposited alumina thin films by oxygen ion beam

Hydrogen interstitials and oxygen vacancies defects create energy levels in the band gap of alumina. This limits the application of alumina as a high-k dielectric. A low thermal budget method for removal of hydrogen from alumina is discussed. It is shown that bombardment of alumina films with low energy oxygen ion beam during electron beam evaporation deposition decreases the hydrogen concentration in the film significantly.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗