On the interplay between phonon-boundary scattering and phonon-point-defect scattering in SiGe thin films

NASA Astrophysics Data System (ADS)

Iskandar, A.; Abou-Khalil, A.; Kazan, M.; Kassem, W.; Volz, S.

2015-03-01

This paper provides theoretical understanding of the interplay between the scattering of phonons by the boundaries and point-defects in SiGe thin films. It also provides a tool for the design of SiGe-based high-efficiency thermoelectric devices. The contributions of the alloy composition, grain size, and film thickness to the phonon scattering rate are described by a model for the thermal conductivity based on the single-mode relaxation time approximation. The exact Boltzmann equation including spatial dependence of phonon distribution function is solved to yield an expression for the rate at which phonons scatter by the thin film boundaries in the presence of the other phonon scattering mechanisms. The rates at which phonons scatter via normal and resistive three-phonon processes are calculated by using perturbation theories with taking into account dispersion of confined acoustic phonons in a two dimensional structure. The vibrational parameters of the model are deduced from the dispersion of confined acoustic phonons as functions of temperature and crystallographic direction. The accuracy of the model is demonstrated with reference to recent experimental investigations regarding the thermal conductivity of single-crystal and polycrystalline SiGe films. The paper describes the strength of each of the phonon scattering mechanisms in the full temperature range. Furthermore, it predicts the alloy composition and film thickness that lead to minimum thermal conductivity in a single-crystal SiGe film, and the alloy composition and grain size that lead to minimum thermal conductivity in a polycrystalline SiGe film.

Healing X-ray scattering images

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jiliang; Lhermitte, Julien; Tian, Ye

X-ray scattering images contain numerous gaps and defects arising from detector limitations and experimental configuration. Here, we present a method to heal X-ray scattering images, filling gaps in the data and removing defects in a physically meaningful manner. Unlike generic inpainting methods, this method is closely tuned to the expected structure of reciprocal-space data. In particular, we exploit statistical tests and symmetry analysis to identify the structure of an image; we then copy, average and interpolate measured data into gaps in a way that respects the identified structure and symmetry. Importantly, the underlying analysis methods provide useful characterization of structuresmore » present in the image, including the identification of diffuseversussharp features, anisotropy and symmetry. The presented method leverages known characteristics of reciprocal space, enabling physically reasonable reconstruction even with large image gaps. The method will correspondingly fail for images that violate these underlying assumptions. The method assumes point symmetry and is thus applicable to small-angle X-ray scattering (SAXS) data, but only to a subset of wide-angle data. Our method succeeds in filling gaps and healing defects in experimental images, including extending data beyond the original detector borders.« less

Healing X-ray scattering images

DOE PAGES

Liu, Jiliang; Lhermitte, Julien; Tian, Ye; ...

2017-05-24

X-ray scattering images contain numerous gaps and defects arising from detector limitations and experimental configuration. Here, we present a method to heal X-ray scattering images, filling gaps in the data and removing defects in a physically meaningful manner. Unlike generic inpainting methods, this method is closely tuned to the expected structure of reciprocal-space data. In particular, we exploit statistical tests and symmetry analysis to identify the structure of an image; we then copy, average and interpolate measured data into gaps in a way that respects the identified structure and symmetry. Importantly, the underlying analysis methods provide useful characterization of structuresmore » present in the image, including the identification of diffuseversussharp features, anisotropy and symmetry. The presented method leverages known characteristics of reciprocal space, enabling physically reasonable reconstruction even with large image gaps. The method will correspondingly fail for images that violate these underlying assumptions. The method assumes point symmetry and is thus applicable to small-angle X-ray scattering (SAXS) data, but only to a subset of wide-angle data. Our method succeeds in filling gaps and healing defects in experimental images, including extending data beyond the original detector borders.« less

Complete p-type activation in vertical-gradient freeze GaAs co-implanted with gallium and carbon

NASA Astrophysics Data System (ADS)

Horng, S. T.; Goorsky, M. S.

1996-03-01

High-resolution triple-axis x-ray diffractometry and Hall-effect measurements were used to characterize damage evolution and electrical activation in gallium arsenide co-implanted with gallium and carbon ions. Complete p-type activation of GaAs co-implanted with 5×1014 Ga cm-2 and 5×1014 C cm-2 was achieved after rapid thermal annealing at 1100 °C for 10 s. X-ray diffuse scattering was found to increase after rapid thermal annealing at 600-900 °C due to the aggregation of implantation-induced point defects. In this annealing range, there was ˜10%-72% activation. After annealing at higher annealing temperatures, the diffuse scattered intensity decreased drastically; samples that had been annealed at 1000 °C (80% activated) and 1100 °C (˜100% activated) exhibited reciprocal space maps that were indicative of high crystallinity. The hole mobility was about 60 cm2/V s for all samples annealed at 800 °C and above, indicating that the crystal perfection influences dopant activation more strongly than it influences mobility. Since the high-temperature annealing simultaneously increases dopant activation and reduces x-ray diffuse scattering, we conclude that point defect complexes which form at lower annealing temperatures are responsible for both the diffuse scatter and the reduced activation.

Influence of defect distribution on the thermoelectric properties of FeNbSb based materials.

PubMed

Guo, Shuping; Yang, Kaishuai; Zeng, Zhi; Zhang, Yongsheng

2018-05-21

Doping and alloying are important methodologies to improve the thermoelectric performance of FeNbSb based materials. To fully understand the influence of point defects on the thermoelectric properties, we have used density functional calculations in combination with the cluster expansion and Monte Carlo methods to examine the defect distribution behaviors in the mesoscopic FeNb1-xVxSb and FeNb1-xTixSb systems. We find that V and Ti exhibit different distribution behaviors in FeNbSb at low temperature: forming the FeNbSb-FeVSb phase separations in the FeNb1-xVxSb system but two thermodynamically stable phases in FeNb1-xTixSb. Based on the calculated effective mass and band degeneracy, it seems the doping concentration of V or Ti in FeNbSb has little effect on the electrical properties, except for one of the theoretically predicted stable Ti phases (Fe6Nb5Ti1Sb6). Thus, an essential methodology to improve the thermoelectric performance of FeNbSb should rely on phonon scattering to decrease the thermal conductivity. According to the theoretically determined phase diagrams of Fe(Nb,V)Sb and Fe(Nb,Ti)Sb, we propose the (composition, temperature) conditions for the experimental synthesis to improve the thermoelectric performance of FeNbSb based materials: lowering the experimental preparation temperature to around the phase boundary to form a mixture of the solid solution and phase separation. The point defects in the solid solution effectively scatter the short-wavelength phonons and the (coherent or incoherent) interfaces introduced by the phase separation can additionally scatter the middle-wavelength phonons to further decrease the thermal conductivity. Moreover, the induced interfaces could enhance the Seebeck coefficient as well, through the energy filtering effect. Our results give insight into the understanding of the impact of the defect distribution on the thermoelectric performance of materials and strengthen the connection between theoretical predictions and experimental measurements.

Surface defects evaluation system based on electromagnetic model simulation and inverse-recognition calibration method

NASA Astrophysics Data System (ADS)

Yang, Yongying; Chai, Huiting; Li, Chen; Zhang, Yihui; Wu, Fan; Bai, Jian; Shen, Yibing

2017-05-01

Digitized evaluation of micro sparse defects on large fine optical surfaces is one of the challenges in the field of optical manufacturing and inspection. The surface defects evaluation system (SDES) for large fine optical surfaces is developed based on our previously reported work. In this paper, the electromagnetic simulation model based on Finite-Difference Time-Domain (FDTD) for vector diffraction theory is firstly established to study the law of microscopic scattering dark-field imaging. Given the aberration in actual optical systems, point spread function (PSF) approximated by a Gaussian function is introduced in the extrapolation from the near field to the far field and the scatter intensity distribution in the image plane is deduced. Analysis shows that both diffraction-broadening imaging and geometrical imaging should be considered in precise size evaluation of defects. Thus, a novel inverse-recognition calibration method is put forward to avoid confusion caused by diffraction-broadening effect. The evaluation method is applied to quantitative evaluation of defects information. The evaluation results of samples of many materials by SDES are compared with those by OLYMPUS microscope to verify the micron-scale resolution and precision. The established system has been applied to inspect defects on large fine optical surfaces and can achieve defects inspection of surfaces as large as 850 mm×500 mm with the resolution of 0.5 μm.

The influence of point defects on the thermal conductivity of AlN crystals

NASA Astrophysics Data System (ADS)

Rounds, Robert; Sarkar, Biplab; Alden, Dorian; Guo, Qiang; Klump, Andrew; Hartmann, Carsten; Nagashima, Toru; Kirste, Ronny; Franke, Alexander; Bickermann, Matthias; Kumagai, Yoshinao; Sitar, Zlatko; Collazo, Ramón

2018-05-01

The average bulk thermal conductivity of free-standing physical vapor transport and hydride vapor phase epitaxy single crystal AlN samples with different impurity concentrations is analyzed using the 3ω method in the temperature range of 30-325 K. AlN wafers grown by physical vapor transport show significant variation in thermal conductivity at room temperature with values ranging between 268 W/m K and 339 W/m K. AlN crystals grown by hydride vapor phase epitaxy yield values between 298 W/m K and 341 W/m K at room temperature, suggesting that the same fundamental mechanisms limit the thermal conductivity of AlN grown by both techniques. All samples in this work show phonon resonance behavior resulting from incorporated point defects. Samples shown by optical analysis to contain carbon-silicon complexes exhibit higher thermal conductivity above 100 K. Phonon scattering by point defects is determined to be the main limiting factor for thermal conductivity of AlN within the investigated temperature range.

Diagnostics for the detection and evaluation of laser induced damage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheehan, L.; Kozlowski, M.; Rainer, F.

1995-12-31

The Laser Damage and Conditioning Group at LLNL is evaluating diagnostics which will help make damage testing more efficient and reduce the risk of damage during laser conditioning. The work to date has focused on photoacoustic and scattered light measurements on 1064-nm wavelength HfO{sub 2}/SiO{sub 2} multilayer mirror and polarizer coatings. Both the acoustic and scatter diagnostics have resolved 10 {mu}m diameter damage points in these coatings. Using a scanning stage, the scatter diagnostic can map both intrinsic and laser-induced scatter. Damage threshold measurements obtained using scatter diagnostics compare within experimental error with those measured using 100x Nomarski microscopy. Scattermore » signals measured during laser conditioning can be used to detect damage related to nodular defects.« less

Diagnostics for the detection and evaluation of laser induced damage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheehan, L.; Kozlowski, M.; Rainer, F.

1995-01-03

The Laser Damage and Conditioning Group at LLNL is evaluating diagnostics which will help make damage testing more efficient and reduce the risk of damage during laser conditioning. The work to date has focused on photoacoustic and scattered light measurements on 1064-nm wavelength HfO{sub 2}/SiO{sub 2} multilayer mirror and polarizer coatings. Both the acoustic and scatter diagnostics have resolved 10 {mu}m diameter damage points in these coatings. Using a scanning stage, the scatter diagnostic can map both intrinsic and laser-induced scatter. Damage threshold measurements obtained using scatter diagnostics compare within experimental error with those measured using 100x Nomarski microscopy. Scattermore » signals measured during laser conditioning can be used to detect damage related to nodular defects.« less

Detection of single nano-defects in photonic crystals between crossed polarizers.

PubMed

Grepstad, Jon Olav; Kaspar, Peter; Johansen, Ib-Rune; Solgaard, Olav; Sudbø, Aasmund

2013-12-16

We investigate, by simulations and experiments, the light scattering of small particles trapped in photonic crystal membranes supporting guided resonance modes. Our results show that, due to amplified Rayleigh small particle scattering, such membranes can be utilized to make a sensor that can detect single nano-particles. We have designed a biomolecule sensor that uses cross-polarized excitation and detection for increased sensitivity. Estimated using Rayleigh scattering theory and simulation results, the current fabricated sensor has a detection limit of 26 nm, corresponding to the size of a single virus. The sensor can potentially be made both cheap and compact, to facilitate use at point-of-care.

Defect-induced ferromagnetism in ZnO nanoparticles prepared by mechanical milling

NASA Astrophysics Data System (ADS)

Phan, The-Long; Zhang, Y. D.; Yang, D. S.; Nghia, N. X.; Thanh, T. D.; Yu, S. C.

2013-02-01

Though ZnO is known as a diamagnetic material, recent studies have revealed that its nanostructures can be ferromagnetic (FM). The FM origin has been ascribed to intrinsic defects. This work shines light on an alternate method based on mechanical milling to induce defect-related ferromagnetism in ZnO nanoparticles (NPs) from initial diamagnetic ZnO powders. Our idea is motivated by the fact that mechanical milling introduces more defects to a ground material. We point out that the FM order increases with increasing the density of defects in ZnO NPs. The experimental results obtained from analyzing X-ray absorption, electron spin resonance, and Raman scattering spectra demonstrate that the ferromagnetism in ZnO NPs is due to intrinsic defects mainly related to oxygen and zinc vacancies. Among these, zinc vacancies play a decisive role in introducing a high FM order in ZnO NPs.

Correlation between He-Ne scatter and 2.7-microm pulsed laser damage at coating defects.

PubMed

Porteus, J O; Spiker, C J; Franck, J B

1986-11-01

A reported correlation between defect-initiated pulsed laser damage and local predamage scatter in multilayer infrared mirror coatings has been analyzed in detail. Examination of a much larger data base confirms the previous result on dielectric-enhanced reflectors with polished substrates over a wide range of energy densities above the damage onset. Scatter signals from individual undamaged defects were detected using a He-Ne scatter probe with a focal spot that nearly coincides with the 150-microm-diam (D1/e(2)) focal spot of the damage-probe beam. Subsequent damage frequency measurements (1-on-1) were made near normal or at 45 degrees incidence with 100-ns pulses at 2.7-microm wavelength. The correlation is characterized by an increase in damage frequency with increasing predamage scatter signal and by equivalence of the defect densities indicated by the two probes. Characteristics of the correlation are compared with a simple model based on focal spot intensity profiles. Conditions that limit correlation are discussed, including variable scatter from defects and background scatter from diamond-turned substrates. Results have implication for nondestructive defect detection and coating quality control.

Distribution of point defects in Si(100)/Si grown by low-temperature molecular-beam epitaxy and solid-phase epitaxy

NASA Astrophysics Data System (ADS)

Asoka-Kumar, P.; Gossmann, H.-J.; Unterwald, F. C.; Feldman, L. C.; Leung, T. C.; Au, H. L.; Talyanski, V.; Nielsen, B.; Lynn, K. G.

1993-08-01

Positron annihilation in Si is a quantitaive, depth-sensitive technique for the detection of vacancylike defects or voids. A sensitivity of 5×1015 cm-3 for voidlike defects is easily achieved. The technique has been applied to a study of point-defect distributions in thin films of Si grown by molecular-beam epitaxy. A special procedure was developed to remove the influence of the native oxide on the positron measurement. 200-nm-thick films grown at temperatures between 475 and 560 °C show no defects below the sensitivity limit and are indistinguishable from the bulk substrate. So are films grown at 220 °C, provided a 2-min high-temperature anneal to a peak temperature of >=500 °C is executed every ~=30 nm during growth. If TRTA=450 °C, part of the film contains vacancylike defects to a concentration of ~=1018 cm-3. These results correlate well with current-voltage characteristics of p-n junctions grown with different rapid thermal anneal (RTA) temperatures. Ion scattering, with a defect sensitivity of ~=1%, shows no difference between films grown with different TRTA. Recrystallization of amorphous films, deposited at room temperature and annealed in situ at 550 °C, always leaves a significant defect concentration of ~=2×1018 cm-3; those defects are reduced but still present even after a 2-h 800 °C furnace anneal.

Effect of void shape in Czochralski-Si wafers on the intensity of laser-scattering

NASA Astrophysics Data System (ADS)

Takahashi, J.; Kawakami, K.; Nakai, K.

2001-06-01

The shape effect of anisotropic-shaped microvoid defects in Czochralski-grown silicon wafers on the intensity of laser scattering has been investigated. The size and shape of the defects were examined by means of transmission electron microscopy. Octahedral voids in conventional (nitrogen-undoped) wafers showed an almost isotropic scattering property under the incident condition of a p-polarization beam. On the other hand, parallelepiped-plate-shaped voids in nitrogen-doped wafers showed an anisotropic scattering property on both p- and s-polarized components of scattered light, depending strongly on the incident laser direction. The measured results were explained not by scattering calculation using Born approximation but by calculation based on Rayleigh scattering. It was found that the s component is explained by an inclination of a dipole moment induced on a defect from the scattering plane. Furthermore, using numerical electromagnetic analysis it was shown that the asymmetric behavior of the s component on the parallelepiped-plate voids is ascribed to the parallelepiped shape effect. These results suggest that correction of the scattering intensity is necessary to evaluate the size and volume of anisotropic-shaped defects from the scattered intensity.

Four-probe electrical-transport measurements on single indium tin oxide nanowires between 1.5 and 300 K

NASA Astrophysics Data System (ADS)

Chiu, Shao-Pin; Chung, Hui-Fang; Lin, Yong-Han; Kai, Ji-Jung; Chen, Fu-Rong; Lin, Juhn-Jong

2009-03-01

Single-crystalline indium tin oxide (ITO) nanowires (NWs) were grown by the standard thermal evaporation method. The as-grown NWs were typically 100-300 nm in diameter and a few µm long. Four-probe submicron Ti/Au electrodes on individual NWs were fabricated by the electron-beam lithography technique. The resistivities of several single NWs have been measured from 300 down to 1.5 K. The results indicate that the as-grown ITO NWs are metallic, but disordered. The overall temperature behavior of resistivity can be described by the Bloch-Grüneisen law plus a low-temperature correction due to the scattering of electrons off dynamic point defects. This observation suggests the existence of numerous dynamic point defects in as-grown ITO NWs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smylie, M. P.; Willa, K.; Claus, H.

We present resistivity and magnetization measurements on proton-irradiated crystals demonstrating that the superconducting state in the doped topological insulator Nb xBi 2Se 3 (x = 0.25) is surprisingly robust against disorder-induced electron scattering. The superconducting transition temperature Tc decreases without indication of saturation with increasing defect concentration, and the corresponding scattering rates far surpass expectations based on conventional theory. The low-temperature variation of the London penetration depth Δλ(T) follows a power law [Δλ(T)~T 2] indicating the presence of symmetry-protected point nodes. Lastly, our results are consistent with the proposed robust nematic E u pairing state in this material.

Thermal conductivity of graphene with defects induced by electron beam irradiation

NASA Astrophysics Data System (ADS)

Malekpour, Hoda; Ramnani, Pankaj; Srinivasan, Srilok; Balasubramanian, Ganesh; Nika, Denis L.; Mulchandani, Ashok; Lake, Roger K.; Balandin, Alexander A.

2016-07-01

We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ~7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 1010 cm-2 to 1.8 × 1011 cm-2 the thermal conductivity decreases from ~(1.8 +/- 0.2) × 103 W mK-1 to ~(4.0 +/- 0.2) × 102 W mK-1 near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ~400 W mK-1. The thermal conductivity dependence on the defect density is analyzed using the Boltzmann transport equation and molecular dynamics simulations. The results are important for understanding phonon - point defect scattering in two-dimensional systems and for practical applications of graphene in thermal management.We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ~7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 1010 cm-2 to 1.8 × 1011 cm-2 the thermal conductivity decreases from ~(1.8 +/- 0.2) × 103 W mK-1 to ~(4.0 +/- 0.2) × 102 W mK-1 near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ~400 W mK-1. The thermal conductivity dependence on the defect density is analyzed using the Boltzmann transport equation and molecular dynamics simulations. The results are important for understanding phonon - point defect scattering in two-dimensional systems and for practical applications of graphene in thermal management. Electronic supplementary information (ESI) available: Additional thermal conductivity measurements data. See DOI: 10.1039/c6nr03470e

Depth resolved investigations of boron implanted silicon

NASA Astrophysics Data System (ADS)

Sztucki, M.; Metzger, T. H.; Milita, S.; Berberich, F.; Schell, N.; Rouvière, J. L.; Patel, J.

2003-01-01

We have studied the depth distribution and structure of defects in boron implanted silicon (0 0 1). Silicon wafers were implanted with a boron dose of 6×10 15 ions/cm -2 at 32 keV and went through different annealing treatments. Using diffuse X-ray scattering at grazing incidence and exit angles we are able to distinguish between different kinds of defects (point defect clusters and extrinsic stacking faults on {1 1 1} planes) and to determine their depth distribution as a function of the thermal budget. Cross-section transmission electron microscopy was used to gain complementary information. In addition we have determined the strain distribution caused by the boron implantation as a function of depth from rocking curve measurements.

X-ray analysis of temperature induced defect structures in boron implanted silicon

NASA Astrophysics Data System (ADS)

Sztucki, M.; Metzger, T. H.; Kegel, I.; Tilke, A.; Rouvière, J. L.; Lübbert, D.; Arthur, J.; Patel, J. R.

2002-10-01

We demonstrate the application of surface sensitive diffuse x-ray scattering under the condition of grazing incidence and exit angles to investigate growth and dissolution of near-surface defects after boron implantation in silicon(001) and annealing. Silicon wafers were implanted with a boron dose of 6×1015 ions/cm2 at 32 keV and went through different annealing treatments. From the diffuse intensity close to the (220) surface Bragg peak we reveal the nature and kinetic behavior of the implantation induced defects. Analyzing the q dependence of the diffuse scattering, we are able to distinguish between point defect clusters and extrinsic stacking faults on {111} planes. Characteristic for stacking faults are diffuse x-ray intensity streaks along <111> directions, which allow for the determination of their growth and dissolution kinetics. For the annealing conditions of our crystals, we conclude that the kinetics of growth can be described by an Ostwald ripening model in which smaller faults shrink at the expense of the larger stacking faults. The growth is found to be limited by the self-diffusion of silicon interstitials. After longer rapid thermal annealing the stacking faults disappear almost completely without shrinking, most likely by transformation into perfect loops via a dislocation reaction. This model is confirmed by complementary cross-sectional transmission electron microscopy.

Analysis of composite/difference field scattering properties between a slightly rough optical surface and multi-body defects.

PubMed

Gong, Lei; Wu, Zhensen; Gao, Ming; Qu, Tan

2018-03-20

The effective extraction of optical surface roughness and defect characteristic provide important realistic values to improve optical system efficiency. Based on finite difference time domain/multi-resolution time domain (FDTD/MRTD) mixed approach, composite scattering between a slightly rough optical surface and multi-body defect particles with different positions is investigated. The scattering contribution of defect particles or the slightly rough optical surface is presented. Our study provides a theoretical and technological basis for the nondestructive examination and optical performance design of nanometer structures.

Anti-resonance scattering at defect levels in the quantum conductance of a one-dimensional system

NASA Astrophysics Data System (ADS)

Sun, Z. Z.; Wang, Y. P.; Wang, X. R.

2002-03-01

For the ballistic quantum transport, the conductance of one channel is quantized to a value of 2e^2/h described by the Landauer formula. In the presence of defects, electrons will be scattered by these defects. Thus the conductance will deviate from the values of the quantized conductance. We show that an anti-resonance scattering can occur when an extra defect level is introduced into a conduction band. At the anti-resonance scattering, exact one quantum conductance is destroyed. The conductance takes a non-zero value when the Fermi energy is away from the anti-resonance scattering. The result is consistent with recent numerical calculations given by H. J. Choi et al. (Phys. Rev. Lett. 84, 2917(2000)) and P. L. McEuen et al. (Phys. Rev. Lett. 83, 5098(1999)).

Phonons, defects and optical damage in crystalline acetanilide

NASA Astrophysics Data System (ADS)

Kosic, Thomas J.; Hill, Jeffrey R.; Dlott, Dana D.

1986-04-01

Intense picosecond pulses cause accumulated optical damage in acetanilide crystals at low temperature. Catastrophic damage to the irradiated volume occurs after an incubation period where defects accumulate. The optical damage is monitored with subanosecond time resolution. The generation of defects is studied with damage-detected picosecond spectroscopy. The accumulation of defects is studied by time-resolved coherent Raman scattering, which is used to measure optical phonon scattering from the accumulating defects.

Modelling NDE pulse-echo inspection of misorientated planar rough defects using an elastic finite element method

NASA Astrophysics Data System (ADS)

Pettit, J. R.; Walker, A. E.; Lowe, M. J. S.

2015-03-01

Pulse-echo ultrasonic NDE examination of large pressure vessel forgings is a design and construction code requirement in the power generation industry. Such inspections aim to size and characterise potential defects that may have formed during the forging process. Typically these defects have a range of orientations and surface roughnesses which can greatly affect ultrasonic wave scattering behaviour. Ultrasonic modelling techniques can provide insight into defect response and therefore aid in characterisation. However, analytical approaches to solving these scattering problems can become inaccurate, especially when applied to increasingly complex defect geometries. To overcome these limitations a elastic Finite Element (FE) method has been developed to simulate pulse-echo inspections of embedded planar defects. The FE model comprises a significantly reduced spatial domain allowing for a Monte-Carlo based approach to consider multiple realisations of defect orientation and surface roughness. The results confirm that defects aligned perpendicular to the path of beam propagation attenuate ultrasonic signals according to the level of surface roughness. However, for defects orientated away from this plane, surface roughness can increase the magnitude of the scattered component propagating back along the path of the incident beam. This study therefore highlights instances where defect roughness increases the magnitude of ultrasonic scattered signals, as opposed to attenuation which is more often assumed.

Investigation of defect clusters in ion-irradiated Ni and NiCo using diffuse X-ray scattering and electron microscopy

DOE PAGES

Olsen, Raina J.; Jin, Ke; Lu, Chenyang; ...

2015-11-23

The nature of defect clusters in Ni and Nimore » $$_{50}$$Co$$_{50}$$ (NiCo) irradiated at room temperature with 2–16 MeV Ni ions is studied using asymptotic diffuse X-ray scattering and transmission electron microscopy (TEM). Analysis of the scattering data provides separate size distributions for vacancy and interstitial type defect clusters, showing that both types of defect clusters have a smaller size and higher density in NiCo than in Ni. Diffuse scattering results show good quantitative agreement with TEM results for cluster sizes greater than 4 nm diameter, but find that the majority of vacancy clusters are under 2 nm in NiCo, which, if not detected, would lead to the conclusion that defect density was actually lower in the alloy. Interstitial dislocation loops and stacking fault tetrahedra are identified by TEM. Lastly comparison of diffuse scattering lineshapes to those calculated for dislocation loops and SFTs indicates that most of the vacancy clusters are SFTs.« less

Simulation and analysis on ultrasonic testing for the cement grouting defects of the corrugated pipe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qingbang, Han; Ling, Chen; Changping, Zhu

2014-02-18

The defects exist in the cement grouting process of prestressed corrugated pipe may directly impair the bridge safety. In this paper, sound fields propagation in concrete structures with corrugated pipes and the influence of various different defects are simulated and analyzed using finite element method. The simulation results demonstrate a much complex propagation characteristic due to multiple reflection, refraction and scattering, where the scattering signals caused by metal are very strong, while the signals scattered by an air bubble are weaker. The influence of defect both in time and frequency domain are found through deconvolution treatment. In the time domain,more » the deconvolution signals correspond to larger defect display a larger head wave amplitude and shorter arrive time than those of smaller defects; in the frequency domain, larger defect also shows a stronger amplitude, lower center frequency and lower cutoff frequency.« less

Modelling NDE pulse-echo inspection of misorientated planar rough defects using an elastic finite element method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pettit, J. R.; Lowe, M. J. S.; Walker, A. E.

2015-03-31

Pulse-echo ultrasonic NDE examination of large pressure vessel forgings is a design and construction code requirement in the power generation industry. Such inspections aim to size and characterise potential defects that may have formed during the forging process. Typically these defects have a range of orientations and surface roughnesses which can greatly affect ultrasonic wave scattering behaviour. Ultrasonic modelling techniques can provide insight into defect response and therefore aid in characterisation. However, analytical approaches to solving these scattering problems can become inaccurate, especially when applied to increasingly complex defect geometries. To overcome these limitations a elastic Finite Element (FE) methodmore » has been developed to simulate pulse-echo inspections of embedded planar defects. The FE model comprises a significantly reduced spatial domain allowing for a Monte-Carlo based approach to consider multiple realisations of defect orientation and surface roughness. The results confirm that defects aligned perpendicular to the path of beam propagation attenuate ultrasonic signals according to the level of surface roughness. However, for defects orientated away from this plane, surface roughness can increase the magnitude of the scattered component propagating back along the path of the incident beam. This study therefore highlights instances where defect roughness increases the magnitude of ultrasonic scattered signals, as opposed to attenuation which is more often assumed.« less

Characterization of GaSb/InAs type II infrared detectors at very long wavelengths: carrier scattering at defect clusters

NASA Astrophysics Data System (ADS)

Kitchin, M. R.; Jaros, M.

2003-06-01

We report a systematic study into carrier scattering by isovalent defects within GaSb/InAs superlattices. The heterostructure system which we investigate has attracted recent interest as the active region of a photodetector for very long wavelength infrared (VLWIR) (⩾12 μm) radiation. To achieve our objective, we employed models of the electronic band structure and scattering cross-section. We considered isolated, substitutional defects at each atom site throughout the unit cell in turn and found that the scattering magnitude generally follows the carrier envelope function, being greatest where the overlap of charge with the defect is highest. We scrutinized the contribution of lattice relaxation around defects to the overall scattering, by comparing calculations where this effect was, in turn, included and excluded. We identified some anomalous contributions of relaxation to both qualitative and quantitative features of the cross-section. Physical mechanisms to explain these effects must be arrived at in order to attain satisfactory characterization of these materials, highlighting the need for both microscopic models and further research. Additional modelling of islands of such defects indicated that the cross-section is proportional to the square of the number of constituent atoms, for both carrier types (holes and electrons) and each defect type. This article demonstrates important links between key growth issues and the dynamical properties of these novel semiconductor devices.

Optical method and apparatus for detection of surface and near-subsurface defects in dense ceramics

DOEpatents

Ellingson, William A.; Brada, Mark P.

1995-01-01

A laser is used in a non-destructive manner to detect surface and near-subsurface defects in dense ceramics and particularly in ceramic bodies with complex shapes such as ceramic bearings, turbine blades, races, and the like. The laser's wavelength is selected based upon the composition of the ceramic sample and the laser can be directed on the sample while the sample is static or in dynamic rotate or translate motion. Light is scattered off surface and subsurface defects using a preselected polarization. The change in polarization angle is used to select the depth and characteristics of surface/subsurface defects. The scattered light is detected by an optical train consisting of a charge coupled device (CCD), or vidicon, television camera which, in turn, is coupled to a video monitor and a computer for digitizing the image. An analyzing polarizer in the optical train allows scattered light at a given polarization angle to be observed for enhancing sensitivity to either surface or near-subsurface defects. Application of digital image processing allows subtraction of digitized images in near real-time providing enhanced sensitivity to subsurface defects. Storing known "feature masks" of identified defects in the computer and comparing the detected scatter pattern (Fourier images) with the stored feature masks allows for automatic classification of detected defects.

Singular lensing from the scattering on special space-time defects

NASA Astrophysics Data System (ADS)

Mavromatos, Nick E.; Papavassiliou, Joannis

2018-01-01

It is well known that certain special classes of self-gravitating point-like defects, such as global (non gauged) monopoles, give rise to non-asymptotically flat space-times characterized by solid angle deficits, whose size depends on the details of the underlying microscopic models. The scattering of electrically neutral particles on such space-times is described by amplitudes that exhibit resonant behaviour when thescattering and deficit angles coincide. This, in turn, leads to ring-like structures where the cross sections are formally divergent ("singular lensing"). In this work, we revisit this particular phenomenon, with the twofold purpose of placing it in a contemporary and more general context, in view of renewed interest in the theory and general phenomenology of such defects, and, more importantly, of addressing certain subtleties that appear in the particular computation that leads to the aforementioned effect. In particular, by adopting a specific regularization procedure for the formally infinite Legendre series encountered, we manage to ensure the recovery of the Minkowski space-time, and thus the disappearance of the lensing phenomenon, in the no-defect limit, and the validity of the optical theorem for the elastic total cross section. In addition, the singular nature of the phenomenon is confirmed by means of an alternative calculation, which, unlike the original approach, makes no use of the generating function of the Legendre polynomials, but rather exploits the asymptotic properties of the Fresnel integrals.

Microstructure-Induced Phonon Focusing Effects and Opportunities for Improved Material Quantification (Postprint)

DTIC Science & Technology

2012-02-01

phonon interactions with electrons , electron -hole pairs, defects, super- lattices, and interfaces [1-4]. As pointed out by Hauser et. al. [3], and...phonon-phonon and electron - phonon scattering processes placed limits on the methods applicability. More recently, the advantages of using lower...texture effects. In particular, the elongated grains result in colonies that are largely cigar -shaped or cylindrical in their form, where elastic

Extraordinary Thermoelectric Performance Realized in Hierarchically Structured AgSbSe2 with Ultralow Thermal Conductivity.

PubMed

Gao, Weihong; Wang, Zhenyou; Huang, Jin; Liu, Zihang

2018-05-24

Thermoelectric conversion from low-grade heat to electricity is regarded as the highly reliable and environmentally friendly technology in energy-harvesting area. However, how to develop efficient thermoelectric materials using a simple fabrication method is still a critical challenge in thermoelectric community. Here, we first fabricate the high thermoelectric performance of Ca-doped AgSbSe 2 with a hierarchical microstructure using a facile approach, namely, mechanical alloying (for only 30 min) and a quick hot-pressing method. The hierarchical microstructure, including point defects (atomic scale), dislocations, and nanoprecipitates (nanoscale) as well as grain boundaries (microscale), strongly scatters phonons with comparable sizes without deterioration of carrier mobility. Because of the higher carrier concentration of nanostructured AgSbSe 2 than that of coarse-grain AgSbSe 2 , power factor can also be improved slightly after nanostructuring. Ca doping further optimizes the carrier concentration and creates the point-defect scattering of phonons, leading to the ultralow lattice thermal conductivity ∼0.27 W m -1 K -1 at 673 K and thus largely improving the peak ZT up to 1.2. The high thermoelectric performance in combination with a facile fabrication method highlights AgSbSe 2 -based materials as robust thermoelectric candidates for energy harvesting.

Impact of defects on the electrical transport, optical properties and failure mechanisms of GaN nanowires.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Armstrong, Andrew M.; Aubry, Sylvie; Shaner, Eric Arthur

2010-09-01

We present the results of a three year LDRD project that focused on understanding the impact of defects on the electrical, optical and thermal properties of GaN-based nanowires (NWs). We describe the development and application of a host of experimental techniques to quantify and understand the physics of defects and thermal transport in GaN NWs. We also present the development of analytical models and computational studies of thermal conductivity in GaN NWs. Finally, we present an atomistic model for GaN NW electrical breakdown supported with experimental evidence. GaN-based nanowires are attractive for applications requiring compact, high-current density devices such asmore » ultraviolet laser arrays. Understanding GaN nanowire failure at high-current density is crucial to developing nanowire (NW) devices. Nanowire device failure is likely more complex than thin film due to the prominence of surface effects and enhanced interaction among point defects. Understanding the impact of surfaces and point defects on nanowire thermal and electrical transport is the first step toward rational control and mitigation of device failure mechanisms. However, investigating defects in GaN NWs is extremely challenging because conventional defect spectroscopy techniques are unsuitable for wide-bandgap nanostructures. To understand NW breakdown, the influence of pre-existing and emergent defects during high current stress on NW properties will be investigated. Acute sensitivity of NW thermal conductivity to point-defect density is expected due to the lack of threading dislocation (TD) gettering sites, and enhanced phonon-surface scattering further inhibits thermal transport. Excess defect creation during Joule heating could further degrade thermal conductivity, producing a viscous cycle culminating in catastrophic breakdown. To investigate these issues, a unique combination of electron microscopy, scanning luminescence and photoconductivity implemented at the nanoscale will be used in concert with sophisticated molecular-dynamics calculations of surface and defect-mediated NW thermal transport. This proposal seeks to elucidate long standing material science questions for GaN while addressing issues critical to realizing reliable GaN NW devices.« less

Temperature-dependent thermal conductivities of 1D semiconducting nanowires via four-point-probe 3-ω method.

PubMed

Lee, Seung-Yong; Lee, Mi-Ri; Park, No-Won; Kim, Gil-Sung; Choi, Heon-Jin; Choi, Tae-Youl; Lee, Sang-Kwon

2013-12-13

We report on a systematic study of the thermal transport characteristics of both as-grown zinc oxide and gallium nitride nanowires (NWs) via the four-point-probe 3-ω method in the temperature range 130-300 K. Both as-grown NWs were synthesized by a vapor-liquid-solid growth mechanism, and show clear n-type semiconducting behavior without any defects, which enables both the NWs to be promising candidates for thermoelectric materials. To measure the thermal conductivities of both NWs with lower heat loss and measurement errors, the suspended structures were formed by a combination of an e-beam lithography process and a random dispersion method. The measured thermal conductivities of both NWs are greatly reduced compared to their bulk materials due to the enhanced phonon scattering via the size effect and dopants (impurities). Furthermore, we observed that the Umklapp peaks of both NWs are shifted to a higher temperature than those of their bulk counterparts, indicating that phonon-boundary scattering dominates over other phonon scattering due to the size effect.

Imaging atomic-scale effects of high-energy ion irradiation on superconductivity and vortex pinning in Fe(Se,Te).

PubMed

Massee, Freek; Sprau, Peter Oliver; Wang, Yong-Lei; Davis, J C Séamus; Ghigo, Gianluca; Gu, Genda D; Kwok, Wai-Kwong

2015-05-01

Maximizing the sustainable supercurrent density, J C, is crucial to high-current applications of superconductivity. To achieve this, preventing dissipative motion of quantized vortices is key. Irradiation of superconductors with high-energy heavy ions can be used to create nanoscale defects that act as deep pinning potentials for vortices. This approach holds unique promise for high-current applications of iron-based superconductors because J C amplification persists to much higher radiation doses than in cuprate superconductors without significantly altering the superconducting critical temperature. However, for these compounds, virtually nothing is known about the atomic-scale interplay of the crystal damage from the high-energy ions, the superconducting order parameter, and the vortex pinning processes. We visualize the atomic-scale effects of irradiating FeSe x Te1-x with 249-MeV Au ions and find two distinct effects: compact nanometer-sized regions of crystal disruption or "columnar defects," plus a higher density of single atomic site "point" defects probably from secondary scattering. We directly show that the superconducting order is virtually annihilated within the former and suppressed by the latter. Simultaneous atomically resolved images of the columnar crystal defects, the superconductivity, and the vortex configurations then reveal how a mixed pinning landscape is created, with the strongest vortex pinning occurring at metallic core columnar defects and secondary pinning at clusters of point-like defects, followed by collective pinning at higher fields.

Temperature-dependent thermal conductivity and diffusivity of a Mg-doped insulating β-Ga2O3 single crystal along [100], [010] and [001

NASA Astrophysics Data System (ADS)

Handwerg, M.; Mitdank, R.; Galazka, Z.; Fischer, S. F.

2016-12-01

The monoclinic crystal structure of β-{{Ga}}2{{{O}}}3 leads to significant anisotropy of the thermal properties. The 2ω-method is used to measure the thermal diffusivity D in [010] and [001] direction respectively and to determine the thermal conductivity values λ of the [100], [010] and [001] direction from the same insulating Mg-doped β-{{Ga}}2{{{O}}}3 single crystal. We detect a temperature independent anisotropy factor of both the thermal diffusivity and conductivity values of {D}[010]/{D}[001]={λ }[010]/{λ }[001]=1.4+/- 0.1. The temperature dependence is in accord with phonon-phonon-Umklapp-scattering processes from 300 K down to 150 K. Below 150 K point-defect-scattering lowers the estimated phonon-phonon-Umklapp-scattering values.

Thermal conductivity of graphene with defects induced by electron beam irradiation.

PubMed

Malekpour, Hoda; Ramnani, Pankaj; Srinivasan, Srilok; Balasubramanian, Ganesh; Nika, Denis L; Mulchandani, Ashok; Lake, Roger K; Balandin, Alexander A

2016-08-14

We investigate the thermal conductivity of suspended graphene as a function of the density of defects, ND, introduced in a controllable way. High-quality graphene layers are synthesized using chemical vapor deposition, transferred onto a transmission electron microscopy grid, and suspended over ∼7.5 μm size square holes. Defects are induced by irradiation of graphene with the low-energy electron beam (20 keV) and quantified by the Raman D-to-G peak intensity ratio. As the defect density changes from 2.0 × 10(10) cm(-2) to 1.8 × 10(11) cm(-2) the thermal conductivity decreases from ∼(1.8 ± 0.2) × 10(3) W mK(-1) to ∼(4.0 ± 0.2) × 10(2) W mK(-1) near room temperature. At higher defect densities, the thermal conductivity reveals an intriguing saturation-type behavior at a relatively high value of ∼400 W mK(-1). The thermal conductivity dependence on the defect density is analyzed using the Boltzmann transport equation and molecular dynamics simulations. The results are important for understanding phonon - point defect scattering in two-dimensional systems and for practical applications of graphene in thermal management.

Optical method and apparatus for detection of surface and near-subsurface defects in dense ceramics

DOEpatents

Ellingson, W.A.; Brada, M.P.

1995-06-20

A laser is used in a non-destructive manner to detect surface and near-subsurface defects in dense ceramics and particularly in ceramic bodies with complex shapes such as ceramic bearings, turbine blades, races, and the like. The laser`s wavelength is selected based upon the composition of the ceramic sample and the laser can be directed on the sample while the sample is static or in dynamic rotate or translate motion. Light is scattered off surface and subsurface defects using a preselected polarization. The change in polarization angle is used to select the depth and characteristics of surface/subsurface defects. The scattered light is detected by an optical train consisting of a charge coupled device (CCD), or vidicon, television camera which, in turn, is coupled to a video monitor and a computer for digitizing the image. An analyzing polarizer in the optical train allows scattered light at a given polarization angle to be observed for enhancing sensitivity to either surface or near-subsurface defects. Application of digital image processing allows subtraction of digitized images in near real-time providing enhanced sensitivity to subsurface defects. Storing known ``feature masks`` of identified defects in the computer and comparing the detected scatter pattern (Fourier images) with the stored feature masks allows for automatic classification of detected defects. 29 figs.

Robust odd-parity superconductivity in the doped topological insulator Nb x Bi 2 Se 3

DOE PAGES

Smylie, M. P.; Willa, K.; Claus, H.; ...

2017-09-15

We present resistivity and magnetization measurements on proton-irradiated crystals demonstrating that the superconducting state in the doped topological insulator Nb xBi 2Se 3 (x = 0.25) is surprisingly robust against disorder-induced electron scattering. The superconducting transition temperature Tc decreases without indication of saturation with increasing defect concentration, and the corresponding scattering rates far surpass expectations based on conventional theory. The low-temperature variation of the London penetration depth Δλ(T) follows a power law [Δλ(T)~T 2] indicating the presence of symmetry-protected point nodes. Lastly, our results are consistent with the proposed robust nematic E u pairing state in this material.

Robust odd-parity superconductivity in the doped topological insulator NbxBi2Se3

NASA Astrophysics Data System (ADS)

Smylie, M. P.; Willa, K.; Claus, H.; Snezhko, A.; Martin, I.; Kwok, W.-K.; Qiu, Y.; Hor, Y. S.; Bokari, E.; Niraula, P.; Kayani, A.; Mishra, V.; Welp, U.

2017-09-01

We present resistivity and magnetization measurements on proton-irradiated crystals demonstrating that the superconducting state in the doped topological insulator NbxBi2Se3 (x =0.25 ) is surprisingly robust against disorder-induced electron scattering. The superconducting transition temperature Tc decreases without indication of saturation with increasing defect concentration, and the corresponding scattering rates far surpass expectations based on conventional theory. The low-temperature variation of the London penetration depth Δ λ (T ) follows a power law [Δ λ (T ) ˜T2] indicating the presence of symmetry-protected point nodes. Our results are consistent with the proposed robust nematic Eu pairing state in this material.

A scanning defect mapping system for semiconductor characterization

NASA Technical Reports Server (NTRS)

Sopori, Bushnan L.

1994-01-01

We have developed an optical scanning system that generates maps of the spatial distributions of defects in single and polycrystalline silicon wafers. This instrument, called Scanning Defect Mapping System, utilizes differences in the scattering characteristics of dislocation etch pits and grain boundaries from a defect-etched sample to identify and count them. This system simultaneously operates in the dislocation mode and the grain boundary (GB) mode. In the 'dislocation mode,' the optical scattering from the etch pits is used to statistically count dislocations, while ignoring the GB's. Likewise, in the 'grain boundary mode' the system only recognizes the local scattering from the GB's to generate grain boundary distributions. The information generated by this instrument is valuable for material quality control, identifying mechanisms of defect generation and the nature of thermal stresses during the crystal growth, and the solar cell process design.

High-speed mapping of grown-in defects and their influence in large-area silicon photovoltaic devices

NASA Astrophysics Data System (ADS)

Sopori, Bhushan; Wei, Chen; Yi, Zhang; Madjdpour, Jamal

2000-03-01

A scanning system for mapping defects, and for measuring their influence on the photovoltaic of Si solar cells, is described. The system uses optical scattering patterns to identify the nature of defects. The local density of the defects is statistically determined from the integrated scattered light. The optical system can also measure the reflectance and the light-induced current which is then used to yield maps of the internal photoresponse of the device.

Defect mapping system

DOEpatents

Sopori, Bhushan L.

1995-01-01

Apparatus for detecting and mapping defects in the surfaces of polycrystalline materials in a manner that distinguishes dislocation pits from grain boundaries includes a laser for illuminating a wide spot on the surface of the material, a light integrating sphere with apertures for capturing light scattered by etched dislocation pits in an intermediate range away from specular reflection while allowing light scattered by etched grain boundaries in a near range from specular reflection to pass through, and optical detection devices for detecting and measuring intensities of the respective intermediate scattered light and near specular scattered light. A center blocking aperture or filter can be used to screen out specular reflected light, which would be reflected by nondefect portions of the polycrystalline material surface. An X-Y translation stage for mounting the polycrystalline material and signal processing and computer equipment accommodate rastor mapping, recording, and displaying of respective dislocation and grain boundary defect densities. A special etch procedure is included, which prepares the polycrystalline material surface to produce distinguishable intermediate and near specular light scattering in patterns that have statistical relevance to the dislocation and grain boundary defect densities.

Defect mapping system

DOEpatents

Sopori, B.L.

1995-04-11

Apparatus for detecting and mapping defects in the surfaces of polycrystalline materials in a manner that distinguishes dislocation pits from grain boundaries includes a laser for illuminating a wide spot on the surface of the material, a light integrating sphere with apertures for capturing light scattered by etched dislocation pits in an intermediate range away from specular reflection while allowing light scattered by etched grain boundaries in a near range from specular reflection to pass through, and optical detection devices for detecting and measuring intensities of the respective intermediate scattered light and near specular scattered light. A center blocking aperture or filter can be used to screen out specular reflected light, which would be reflected by nondefect portions of the polycrystalline material surface. An X-Y translation stage for mounting the polycrystalline material and signal processing and computer equipment accommodate rastor mapping, recording, and displaying of respective dislocation and grain boundary defect densities. A special etch procedure is included, which prepares the polycrystalline material surface to produce distinguishable intermediate and near specular light scattering in patterns that have statistical relevance to the dislocation and grain boundary defect densities. 20 figures.

Scattering of Lamb waves in a composite plate

NASA Technical Reports Server (NTRS)

Bratton, Robert; Datta, Subhendu; Shah, Arvind

1991-01-01

A combined analytical and finite element technique is developed to gain a better understanding of the scattering of elastic waves by defects. This hybrid method is capable of predicting scattered displacements from arbitrary shaped defects as well as inclusions of different material. The continuity of traction and displacements at the boundaries of the two areas provided the necessary equations to find the nodal displacements and expansion coefficients. Results clearly illustrate the influence of increasing crack depth on the scattered signal.

Anomalous satellite inductive peaks in alternating current response of defective carbon nanotubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirai, Daisuke; Watanabe, Satoshi; Yamamoto, Takahiro

2014-05-07

AC response of defective metallic carbon nanotubes is investigated from first principles. We found that capacitive peaks appear at electron scattering states. Moreover, we show that satellite inductive peaks are seen adjacent to a main capacitive peak, which is in contrast to the conductance spectra having no satellite features. The appearance of satellite inductive peaks seems to depend on the scattering states. Our analysis with a simple resonant scattering model reveals that the origin of the satellite inductive peaks can be understood by just one parameter, i.e., the lifetime of electrons at a defect state.

Laser Scattering Tomography for the Study of Defects in Protein Crystals

NASA Technical Reports Server (NTRS)

Feigelson, Robert S.; DeLucas, Lawrence; DeMattei, R. C.

1997-01-01

The goal of this research is to explore the application of the non-destructive technique of Laser Scattering Tomography (LST) to study the defects in protein crystals and relate them to the x-ray diffraction performance of the crystals. LST has been used successfully for the study of defects in inorganic crystals and. in the case of lysozyme, for protein crystals.

Thermoelectrics. Dense dislocation arrays embedded in grain boundaries for high-performance bulk thermoelectrics.

PubMed

Kim, Sang Il; Lee, Kyu Hyoung; Mun, Hyeon A; Kim, Hyun Sik; Hwang, Sung Woo; Roh, Jong Wook; Yang, Dae Jin; Shin, Weon Ho; Li, Xiang Shu; Lee, Young Hee; Snyder, G Jeffrey; Kim, Sung Wng

2015-04-03

The widespread use of thermoelectric technology is constrained by a relatively low conversion efficiency of the bulk alloys, which is evaluated in terms of a dimensionless figure of merit (zT). The zT of bulk alloys can be improved by reducing lattice thermal conductivity through grain boundary and point-defect scattering, which target low- and high-frequency phonons. Dense dislocation arrays formed at low-energy grain boundaries by liquid-phase compaction in Bi(0.5)Sb(1.5)Te3 (bismuth antimony telluride) effectively scatter midfrequency phonons, leading to a substantially lower lattice thermal conductivity. Full-spectrum phonon scattering with minimal charge-carrier scattering dramatically improved the zT to 1.86 ± 0.15 at 320 kelvin (K). Further, a thermoelectric cooler confirmed the performance with a maximum temperature difference of 81 K, which is much higher than current commercial Peltier cooling devices. Copyright © 2015, American Association for the Advancement of Science.

Changing of optical absorption and scattering coefficients in nonlinear-optical crystal lithium triborate before and after interaction with UV-radiation

NASA Astrophysics Data System (ADS)

Demkin, Artem S.; Nikitin, Dmitriy G.; Ryabushkin, Oleg A.

2016-04-01

In current work optical properties of LiB3O5 (LBO) crystal with ultraviolet (UV) (λ= 266 nm) induced volume macroscopic defect (track) are investigated using novel piezoelectric resonance laser calorimetry technique. Pulsed laser radiation of 10 W average power at 532 nm wavelength, is consecutively focused into spatial regions with and without optical defect. For these cases exponential fitting of crystal temperature kinetics measured during its irradiation gives different optical absorption coefficients α1 = 8.1 • 10-4 cm-1 (region with defect) and α =3.9ṡ10-4 cm-1 (non-defected region). Optical scattering coefficient is determined as the difference between optical absorption coefficients measured for opaque and transparent lateral facets of the crystal respectively. Measurements reveal that scattering coefficient of LBO in the region with defect is three times higher than the optical absorption coefficient.

Studying post-etching silicon crystal defects on 300mm wafer by automatic defect review AFM

NASA Astrophysics Data System (ADS)

Zandiatashbar, Ardavan; Taylor, Patrick A.; Kim, Byong; Yoo, Young-kook; Lee, Keibock; Jo, Ahjin; Lee, Ju Suk; Cho, Sang-Joon; Park, Sang-il

2016-03-01

Single crystal silicon wafers are the fundamental elements of semiconductor manufacturing industry. The wafers produced by Czochralski (CZ) process are very high quality single crystalline materials with known defects that are formed during the crystal growth or modified by further processing. While defects can be unfavorable for yield for some manufactured electrical devices, a group of defects like oxide precipitates can have both positive and negative impacts on the final device. The spatial distribution of these defects may be found by scattering techniques. However, due to limitations of scattering (i.e. light wavelength), many crystal defects are either poorly classified or not detected. Therefore a high throughput and accurate characterization of their shape and dimension is essential for reviewing the defects and proper classification. While scanning electron microscopy (SEM) can provide high resolution twodimensional images, atomic force microscopy (AFM) is essential for obtaining three-dimensional information of the defects of interest (DOI) as it is known to provide the highest vertical resolution among all techniques [1]. However AFM's low throughput, limited tip life, and laborious efforts for locating the DOI have been the limitations of this technique for defect review for 300 mm wafers. To address these limitations of AFM, automatic defect review AFM has been introduced recently [2], and is utilized in this work for studying DOI on 300 mm silicon wafer. In this work, we carefully etched a 300 mm silicon wafer with a gaseous acid in a reducing atmosphere at a temperature and for a sufficient duration to decorate and grow the crystal defects to a size capable of being detected as light scattering defects [3]. The etched defects form a shallow structure and their distribution and relative size are inspected by laser light scattering (LLS). However, several groups of defects couldn't be properly sized by the LLS due to the very shallow depth and low light scattering. Likewise, SEM cannot be used effectively for post-inspection defect review and classification of these very shallow types of defects. To verify and obtain accurate shape and three-dimensional information of those defects, automatic defect review AFM (ADR AFM) is utilized for accurate locating and imaging of DOI. In ADR AFM, non-contact mode imaging is used for non-destructive characterization and preserving tip sharpness for data repeatability and reproducibility. Locating DOI and imaging are performed automatically with a throughput of many defects per hour. Topography images of DOI has been collected and compared with SEM images. The ADR AFM has been shown as a non-destructive metrology tool for defect review and obtaining three-dimensional topography information.

Identification of dominant scattering mechanism in epitaxial graphene on SiC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Jingjing; Guo, Liwei, E-mail: lwguo@iphy.ac.cn, E-mail: chenx29@aphy.iphy.ac.cn; Jia, Yuping

2014-05-05

A scheme of identification of scattering mechanisms in epitaxial graphene (EG) on SiC substrate is developed and applied to three EG samples grown on SiC (0001), (112{sup ¯}0), and (101{sup ¯}0) substrates. Hall measurements combined with defect detection technique enable us to evaluate the individual contributions to the carrier scatterings by defects and by substrates. It is found that the dominant scatterings can be due to either substrate or defects, dependent on the substrate orientations. The EG on SiC (112{sup ¯}0) exhibits a better control over the two major scattering mechanisms and achieves the highest mobility even with a highmore » carrier concentration, promising for high performance graphene-based electronic devices. The method developed here will shed light on major aspects in governing carrier transport in EG to harness it effectively.« less

Use of the reciprocity theorem for a closed form solution of scattering of the lowest axially symmetric torsional wave mode by a defect in a pipe.

PubMed

Lee, Jaesun; Achenbach, Jan D; Cho, Younho

2018-03-01

Guided waves can effectively be used for inspection of large scale structures. Surface corrosion is often found as major defect type in large scale structures such as pipelines. Guided wave interaction with surface corrosion can provide useful information for sizing and classification. In this paper, the elastodynamic reciprocity theorem is used to formulate and solve complicated scattering problems in a simple manner. The approach has already been applied to scattering of Rayleigh and Lamb waves by defects to produce closed form solutions of amplitude of scattered waves. In this paper, the scattering of the lowest axially symmetric torsional mode, which is widely used in commercial applications, is analyzed by the reciprocity theorem. In the present paper, the theorem is used to determine the scattering of the lowest torsional mode by a tapered defect that was earlier considered experimentally and numerically by the finite element method. It is shown that by the presented method it is simple to obtain the ratio of amplitudes of scattered torsional modes for a tapered notch. The results show a good agreement with earlier numerical results. The wave field superposition technique in conjunction with the reciprocity theorem simplifies the solution of the scattering problem to yield a closed form solution which can play a significant role in quantitative signal interpretation. Copyright © 2017 Elsevier B.V. All rights reserved.

Improved spatial resolution of luminescence images acquired with a silicon line scanning camera

NASA Astrophysics Data System (ADS)

Teal, Anthony; Mitchell, Bernhard; Juhl, Mattias K.

2018-04-01

Luminescence imaging is currently being used to provide spatially resolved defect in high volume silicon solar cell production. One option to obtain the high throughput required for on the fly detection is the use a silicon line scan cameras. However, when using a silicon based camera, the spatial resolution is reduced as a result of the weakly absorbed light scattering within the camera's chip. This paper address this issue by applying deconvolution from a measured point spread function. This paper extends the methods for determining the point spread function of a silicon area camera to a line scan camera with charge transfer. The improvement in resolution is quantified in the Fourier domain and in spatial domain on an image of a multicrystalline silicon brick. It is found that light spreading beyond the active sensor area is significant in line scan sensors, but can be corrected for through normalization of the point spread function. The application of this method improves the raw data, allowing effective detection of the spatial resolution of defects in manufacturing.

Multimodal sparse reconstruction in guided wave imaging of defects in plates

NASA Astrophysics Data System (ADS)

Golato, Andrew; Santhanam, Sridhar; Ahmad, Fauzia; Amin, Moeness G.

2016-07-01

A multimodal sparse reconstruction approach is proposed for localizing defects in thin plates in Lamb wave-based structural health monitoring. The proposed approach exploits both the sparsity of the defects and the multimodal nature of Lamb wave propagation in plates. It takes into account the variation of the defects' aspect angles across the various transducer pairs. At low operating frequencies, only the fundamental symmetric and antisymmetric Lamb modes emanate from a transmitting transducer. Asymmetric defects scatter these modes and spawn additional converted fundamental modes. Propagation models are developed for each of these scattered and spawned modes arriving at the various receiving transducers. This enables the construction of modal dictionary matrices spanning a two-dimensional array of pixels representing potential defect locations in the region of interest. Reconstruction of the region of interest is achieved by inverting the resulting linear model using the group sparsity constraint, where the groups extend across the various transducer pairs and the different modes. The effectiveness of the proposed approach is established with finite-element scattering simulations of the fundamental Lamb wave modes by crack-like defects in a plate. The approach is subsequently validated with experimental results obtained from an aluminum plate with asymmetric defects.

A comparison of angle-beam shear wave scattering from hidden defects in single-and double-layer plates

NASA Astrophysics Data System (ADS)

Maki, Carson T.; Michaels, Jennifer E.; Weng, Yu

2018-04-01

Quantification of shear wave scattering from hidden defects is challenging because it is difficult to separate defect-scattered waves from waves that are scattered from benign structural features such as interfaces and fastener holes. It is even more difficult for the case of a crack emanating from a through-hole because there is complicated scattering from both the hole and the crack. This present work reports the results of a study that considers measurements from several far-surface notches emanating from through-holes in an aluminum plate both before and after a second plate is bonded to the back surface of the first plate. Measurements are also made of scattering from just a through-hole in both the single and bonded plates as a basis for comparison. The presence of the second layer provides a path for energy to leak out of the first plate, which can reduce the scattered energy. The recorded data show that notch scattering is clearly visible in the wavefield data for all of the notched holes. This scattering is quantified by first applying frequency-wavenumber filtering to extract shear waves of interest, and then computing scattered energy as a function of direction. Results for the different specimens are reported and compared to show the differences in scattering caused by the presence of the second layer.

Scatter and crosstalk corrections for {sup 99m}Tc/{sup 123}I dual-radionuclide imaging using a CZT SPECT system with pinhole collimators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, Peng; Hutton, Brian F.; Holstensson, Maria

2015-12-15

Purpose: The energy spectrum for a cadmium zinc telluride (CZT) detector has a low energy tail due to incomplete charge collection and intercrystal scattering. Due to these solid-state detector effects, scatter would be overestimated if the conventional triple-energy window (TEW) method is used for scatter and crosstalk corrections in CZT-based imaging systems. The objective of this work is to develop a scatter and crosstalk correction method for {sup 99m}Tc/{sup 123}I dual-radionuclide imaging for a CZT-based dedicated cardiac SPECT system with pinhole collimators (GE Discovery NM 530c/570c). Methods: A tailing model was developed to account for the low energy tail effectsmore » of the CZT detector. The parameters of the model were obtained using {sup 99m}Tc and {sup 123}I point source measurements. A scatter model was defined to characterize the relationship between down-scatter and self-scatter projections. The parameters for this model were obtained from Monte Carlo simulation using SIMIND. The tailing and scatter models were further incorporated into a projection count model, and the primary and self-scatter projections of each radionuclide were determined with a maximum likelihood expectation maximization (MLEM) iterative estimation approach. The extracted scatter and crosstalk projections were then incorporated into MLEM image reconstruction as an additive term in forward projection to obtain scatter- and crosstalk-corrected images. The proposed method was validated using Monte Carlo simulation, line source experiment, anthropomorphic torso phantom studies, and patient studies. The performance of the proposed method was also compared to that obtained with the conventional TEW method. Results: Monte Carlo simulations and line source experiment demonstrated that the TEW method overestimated scatter while their proposed method provided more accurate scatter estimation by considering the low energy tail effect. In the phantom study, improved defect contrasts were observed with both correction methods compared to no correction, especially for the images of {sup 99m}Tc in dual-radionuclide imaging where there is heavy contamination from {sup 123}I. In this case, the nontransmural defect contrast was improved from 0.39 to 0.47 with the TEW method and to 0.51 with their proposed method and the transmural defect contrast was improved from 0.62 to 0.74 with the TEW method and to 0.73 with their proposed method. In the patient study, the proposed method provided higher myocardium-to-blood pool contrast than that of the TEW method. Similar to the phantom experiment, the improvement was the most substantial for the images of {sup 99m}Tc in dual-radionuclide imaging. In this case, the myocardium-to-blood pool ratio was improved from 7.0 to 38.3 with the TEW method and to 63.6 with their proposed method. Compared to the TEW method, the proposed method also provided higher count levels in the reconstructed images in both phantom and patient studies, indicating reduced overestimation of scatter. Using the proposed method, consistent reconstruction results were obtained for both single-radionuclide data with scatter correction and dual-radionuclide data with scatter and crosstalk corrections, in both phantom and human studies. Conclusions: The authors demonstrate that the TEW method leads to overestimation in scatter and crosstalk for the CZT-based imaging system while the proposed scatter and crosstalk correction method can provide more accurate self-scatter and down-scatter estimations for quantitative single-radionuclide and dual-radionuclide imaging.« less

Oscillations of kinks on dislocation lines in crystals and low-temperature transport anomalies as a ``passport'' of newly-induced defects

NASA Astrophysics Data System (ADS)

Mezhov-Deglin, L. P.; Mukhin, S. I.

2011-10-01

The possible interpretation of experimental data on low-temperature anomalies in weakly deformed metallic crystals prepared form ultra-pure lead, copper, and silver, as well as in crystals of 4He is discussed within the previously proposed theoretical picture of dislocations with dynamical kinks. In the case of pure metals the theoretical predictions give a general picture of interaction of conduction electrons in a sample with newly-introduced dislocations, containing dynamic kinks in the Peierls potential relief. In the field of random stresses appearing due to plastic deformation of a sample, kinks on the dislocation line form a set of one-dimensional oscillators in potential wells of different shapes. In the low temperature region at low enough density of defects pinning kinks the inelastic scattering of electrons on kinks should lead to deviations from the Wiedemann-Franz law. In particular, the inelastic scattering on kinks should result in a quadratic temperature dependence of the thermal conductivity in a metallic sample along preferential directions of dislocation axes. In the plane normal to the dislocation axis the elastic large-angle scattering of electrons is prevalent. The kink pinning by a point defect or by additional dislocations as well as the sample annealing leading to the disappearance of kinks should induce suppression of transport anomalies. Thus, the energy interval for the spectrum of kink oscillations restricted by characteristic amplitude of the Peierls relief is a "passport of deformation history" for each specific sample. For instance, in copper the temperature/energy region of the order of 1 K corresponds to it. It is also planned to discuss in the other publication applicability of mechanism of phonon scattering on mobile dislocation kinks and pinning of kinks by impurities in order to explain anomalies of phonon thermal conductivity of 4He crystals and deformed crystals of pure lead in a superconducting state.

Noncontact measurement of guided ultrasonic wave scattering for fatigue crack characterization

NASA Astrophysics Data System (ADS)

Fromme, P.

2013-04-01

Fatigue cracks can develop in aerospace structures at locations of stress concentration such as fasteners. For the safe operation of the aircraft fatigue cracks need to be detected before reaching a critical length. Guided ultrasonic waves offer an efficient method for the detection and characterization of fatigue cracks in large aerospace structures. Noncontact excitation of guided waves was achieved using electromagnetic acoustic transducers (EMAT). The transducers were developed for the specific excitation of the A0 Lamb mode. Based on the induced eddy currents in the plate a simple theoretical model was developed and reasonably good agreement with the measurements was achieved. However, the detection sensitivity for fatigue cracks depends on the location and orientation of the crack relative to the measurement locations. Crack-like defects have a directionality pattern of the scattered field depending on the angle of the incident wave relative to the defect orientation and on the ratio of the characteristic defect size to wavelength. The detailed angular dependency of the guided wave field scattered at crack-like defects in plate structures has been measured using a noncontact laser interferometer. Good agreement with 3D Finite Element simulation predictions was achieved for machined part-through and through-thickness notches. The amplitude of the scattered wave was quantified for a variation of angle of the incident wave relative to the defect orientation and the defect depth. These results provide the basis for the defect characterization in aerospace structures using guided wave sensors.

On the failure load and mechanism of polycrystalline graphene by nanoindentation

PubMed Central

Sha, Z. D.; Wan, Q.; Pei, Q. X.; Quek, S. S.; Liu, Z. S.; Zhang, Y. W.; Shenoy, V. B.

2014-01-01

Nanoindentation has been recently used to measure the mechanical properties of polycrystalline graphene. However, the measured failure loads are found to be scattered widely and vary from lab to lab. We perform molecular dynamics simulations of nanoindentation on polycrystalline graphene at different sites including grain center, grain boundary (GB), GB triple junction, and holes. Depending on the relative position between the indenter tip and defects, significant scattering in failure load is observed. This scattering is found to arise from a combination of the non-uniform stress state, varied and weakened strengths of different defects, and the relative location between the indenter tip and the defects in polycrystalline graphene. Consequently, the failure behavior of polycrystalline graphene by nanoindentation is critically dependent on the indentation site, and is thus distinct from uniaxial tensile loading. Our work highlights the importance of the interaction between the indentation tip and defects, and the need to explicitly consider the defect characteristics at and near the indentation site in polycrystalline graphene during nanoindentation. PMID:25500732

The impact of defect scattering on the quasi-ballistic transport of nanoscale conductors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Esqueda, I. S., E-mail: isanchez@isi.edu; Fritze, M.; Cress, C. D.

2015-02-28

Using the Landauer approach for carrier transport, we analyze the impact of defects induced by ion irradiation on the transport properties of nanoscale conductors that operate in the quasi-ballistic regime. Degradation of conductance results from a reduction of carrier mean free path due to the introduction of defects in the conducting channel. We incorporate scattering mechanisms from radiation-induced defects into calculations of the transmission coefficient and present a technique for extracting modeling parameters from near-equilibrium transport measurements. These parameters are used to describe degradation in the transport properties of nanoscale devices using a formalism that is valid under quasi-ballistic operation.more » The analysis includes the effects of bandstructure and dimensionality on the impact of defect scattering and discusses transport properties of nanoscale devices from the diffusive to the ballistic limit. We compare calculations with recently published measurements of irradiated nanoscale devices such as single-walled carbon nanotubes, graphene, and deep-submicron Si metal-oxide-semiconductor field-effect transistors.« less

The critical role of point defects in improving the specific capacitance of δ-MnO 2 nanosheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Peng; Metz, Peter; Hey, Trevyn

3D porous nanostructures built from 2D δ-MnO 2 nanosheets are an environmentally friendly and industrially scalable class of supercapacitor electrode material. While both the electrochemistry and defects of this material have been studied, the role of defects in improving the energy storage density of these materials has not been addressed. In this work, δ-MnO 2 nanosheet assemblies with 150 m 2 g -1 specific surface area are prepared by exfoliation of crystalline K xMnO 2 and subsequent reassembly. Equilibration at different pH introduces intentional Mn vacancies into the nanosheets, increasing pseudocapacitance to over 300 F g -1, reducing charge transfermore » resistance as low as 3 Ω, and providing a 50% improvement in cycling stability. X-ray absorption spectroscopy and high-energy X-ray scattering demonstrate a correlation between the defect content and the improved electrochemical performance. The results show that Mn vacancies provide ion intercalation sites which concurrently improve specific capacitance, charge transfer resistance and cycling stability.« less

First-principles studies of electron transport in Ga2O3

NASA Astrophysics Data System (ADS)

Kang, Youngho; Krishnaswamy, Karthik; Peelaers, Hartwin; van de Walle, Chris G.

Ga2O3 is a wide-gap semiconductor with a monoclinic crystal structure and a band gap of 4.8 eV. Its high carrier mobility and large band gap have attracted a lot of attention for use in high power electronics and transparent conductors. Despite its potential for adoption in these applications, an understanding of its carrier transport properties is still lacking. In this study we use first-principles calculations to analyze and compute the electron scattering rates in Ga2O3. Scattering due to ionized impurities and polar longitudinal-optical (LO) phonon is taken into account. We find that the electron mobility is nearly isotropic, despite the low-symmetry monoclinic structure of Ga2O3. At low carrier densities ( 1017 cm-3), the mobility is limited by LO phonon scattering. Scattering by ionized impurities becomes increasingly important at higher carrier densities. This type of scattering is enhanced when compensating native point defects are present; in particular, gallium vacancies, which are triply negatively charged, can have a strong effect on mobility. These effects explain the downturn in mobility observed in experiments at high carrier densities. This work was supported by ARO and NSF.

Direct Observation of Sink-Dependent Defect Evolution in Nanocrystalline Iron under Irradiation

DOE PAGES

El Atwani, Osman; Nathaniel, James; Leff, Asher C.; ...

2017-05-12

Crystal defects generated during irradiation can result in severe changes in morphology and an overall degradation of mechanical properties in a given material. Nanomaterials have been proposed as radiation damage tolerant materials, due to the hypothesis that defect density decreases with grain size refinement due to the increase in grain boundary surface area. The lower defect density should arise from grain boundary-point defect absorption and enhancement of interstitial-vacancy annihilation. In this study, low energy helium ion irradiation on free-standing iron thin films were performed at 573 K. Interstitial loops of a 0 /2 [111] Burgers vector were directly observed asmore » a result of the displacement damage. Loop density trends with grain size demonstrated an increase in the nanocrystalline (<100 nm) regime, but scattered behavior in the transition from the nanocrystalline to the ultra-fine regime (100–500 nm). To examine the validity of such trends, loop density and area for different grains at various irradiation doses were compared and revealed efficient defect absorption in the nanocrystalline grain size regime, but loop coalescence in the ultra-fine grain size regime. Lastly, a relationship between the denuded zone formation, a measure of grain boundary absorption efficiency, grain size, grain boundary type and misorientation angle is determined.« less

Direct Observation of Sink-Dependent Defect Evolution in Nanocrystalline Iron under Irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

El Atwani, Osman; Nathaniel, James; Leff, Asher C.

Crystal defects generated during irradiation can result in severe changes in morphology and an overall degradation of mechanical properties in a given material. Nanomaterials have been proposed as radiation damage tolerant materials, due to the hypothesis that defect density decreases with grain size refinement due to the increase in grain boundary surface area. The lower defect density should arise from grain boundary-point defect absorption and enhancement of interstitial-vacancy annihilation. In this study, low energy helium ion irradiation on free-standing iron thin films were performed at 573 K. Interstitial loops of a 0 /2 [111] Burgers vector were directly observed asmore » a result of the displacement damage. Loop density trends with grain size demonstrated an increase in the nanocrystalline (<100 nm) regime, but scattered behavior in the transition from the nanocrystalline to the ultra-fine regime (100–500 nm). To examine the validity of such trends, loop density and area for different grains at various irradiation doses were compared and revealed efficient defect absorption in the nanocrystalline grain size regime, but loop coalescence in the ultra-fine grain size regime. Lastly, a relationship between the denuded zone formation, a measure of grain boundary absorption efficiency, grain size, grain boundary type and misorientation angle is determined.« less

Electron-phonon coupling and thermal transport in the thermoelectric compound Mo 3Sb 7–xTe x

DOE PAGES

Bansal, Dipanshu; Li, Chen W.; Said, Ayman H.; ...

2015-12-07

Phonon properties of Mo 3Sb 7–xTe x (x = 0, 1.5, 1.7), a potential high-temperature thermoelectric material, have been studied with inelastic neutron and x-ray scattering, and with first-principles simulations. The substitution of Te for Sb leads to pronounced changes in the electronic struc- ture, local bonding, phonon density of states (DOS), dispersions, and phonon lifetimes. Alloying with tellurium shifts the Fermi level upward, near the top of the valence band, resulting in a strong suppression of electron-phonon screening, and a large overall stiffening of interatomic force- constants. The suppression in electron-phonon coupling concomitantly increases group velocities and suppresses phononmore » scattering rates, surpassing the effects of alloy-disorder scattering, and re- sulting in a surprising increased lattice thermal conductivity in the alloy. We also identify that the local bonding environment changes non-uniformly around different atoms, leading to variable perturbation strengths for different optical phonon branches. The respective roles of changes in phonon group velocities and phonon lifetimes on the lattice thermal conductivity are quantified. Lastly, our results highlight the importance of the electron-phonon coupling on phonon mean-free-paths in this compound, and also estimates the contributions from boundary scattering, umklapp scattering, and point-defect scattering.« less

Light scattering techniques for the characterization of optical components

NASA Astrophysics Data System (ADS)

Hauptvogel, M.; Schröder, S.; Herffurth, T.; Trost, M.; von Finck, A.; Duparré, A.; Weigel, T.

2017-11-01

The rapid developments in optical technologies generate increasingly higher and sometimes completely new demands on the quality of materials, surfaces, components, and systems. Examples for such driving applications are the steadily shrinking feature sizes in semiconductor lithography, nanostructured functional surfaces for consumer optics, and advanced optical systems for astronomy and space applications. The reduction of surface defects as well as the minimization of roughness and other scatter-relevant irregularities are essential factors in all these areas of application. Quality-monitoring for analysing and improving those properties must ensure that even minimal defects and roughness values can be detected reliably. Light scattering methods have a high potential for a non-contact, rapid, efficient, and sensitive determination of roughness, surface structures, and defects.

Mapping crystal defects with a digital scanning ultramicroscope

NASA Astrophysics Data System (ADS)

Springer, John M., Jr.; Silberman, Enrique; Kroes, Roger L.; Reiss, Don

1991-12-01

A computer controlled scanning ultramicroscope has been built to assist in the characterization of transparent crystals. The device measures the scattering of a focused He-Ne laser beam by crystalline defects. As an XYZ translation table moves the crystal under the ultramicroscope, the scattered light is measured by a photodetector whose output is digitized and recorded. From this data, contour maps or 3-D perspective plots of the scattering regions of the crystal can be generated to assist in finding patterns of defects which might be correlated with perturbations in the growth process. The verified resolution of the present instrument is about 1 micrometers , which is limited by the minimum step of the stepper-motor driven translation stages, optical diffraction effects, and the sensitivity of the detector at the laser light frequency. The instrument was used to build a database of defects patterns in commercial laboratory grown triglycine sulphate (TGS) crystals, and to map defects in a TGS crystal grown from aqueous solution during the flight of Spacelab 3. This crystal shows indications of a reduction both in the generation of defects at the seed-new growth interface and in their propagation into the new crystal.

Mapping crystal defects with a digital scanning ultramicroscope

NASA Astrophysics Data System (ADS)

Springer, J. M.; Silberman, E.; Kroes, Roger; Reiss, D.

A computer controlled scanning ultramicroscope has been built to assist in the characterization of transparent crystals. The device measures the scattering of a focused He-Ne laser beam by crystalline defects. As an XYZ translation table moves the crystal under the ultramicroscope, the scattered light is measured by a photodetector whose output is digitized and recorded. From this data, contour maps or three dimensional perspective plots of the scattering regions of the crystal can be generated to assist in finding patterns of defects which might be correlated with perturbations in the growth process. The verified resolution of the present instrument is about 1 micrometer, which is limited by the minimum step of the stepper-motor driven translation stages, optical diffraction effects and the sensitivity of the detector at the laser light frequency. The instrument was used to build a database of defects patterns in commercial laboratory grown triglycine sulphate (TGS) crystals, and to map defects in a TGS crystal grown from aqueous solution during the flight of Spacelab 3. This crystal shows indications of a reduction both in the generation of defects at the seed-new growth interface and in their propagation into the new crystal.

Mapping crystal defects with a digital scanning ultramicroscope

NASA Technical Reports Server (NTRS)

Springer, J. M.; Silberman, E.; Kroes, Roger; Reiss, D.

1991-01-01

A computer controlled scanning ultramicroscope has been built to assist in the characterization of transparent crystals. The device measures the scattering of a focused He-Ne laser beam by crystalline defects. As an XYZ translation table moves the crystal under the ultramicroscope, the scattered light is measured by a photodetector whose output is digitized and recorded. From this data, contour maps or three dimensional perspective plots of the scattering regions of the crystal can be generated to assist in finding patterns of defects which might be correlated with perturbations in the growth process. The verified resolution of the present instrument is about 1 micrometer, which is limited by the minimum step of the stepper-motor driven translation stages, optical diffraction effects and the sensitivity of the detector at the laser light frequency. The instrument was used to build a database of defects patterns in commercial laboratory grown triglycine sulphate (TGS) crystals, and to map defects in a TGS crystal grown from aqueous solution during the flight of Spacelab 3. This crystal shows indications of a reduction both in the generation of defects at the seed-new growth interface and in their propagation into the new crystal.

Optical method and apparatus for detection of defects and microstructural changes in ceramics and ceramic coatings

DOEpatents

Ellingson, William A.; Todd, Judith A.; Sun, Jiangang

2001-01-01

Apparatus detects defects and microstructural changes in hard translucent materials such as ceramic bulk compositions and ceramic coatings such as after use under load conditions. The beam from a tunable laser is directed onto the sample under study and light reflected by the sample is directed to two detectors, with light scattered with a small scatter angle directed to a first detector and light scattered with a larger scatter angle directed to a second detector for monitoring the scattering surface. The sum and ratio of the two detector outputs respectively provide a gray-scale, or "sum" image, and an indication of the lateral spread of the subsurface scatter, or "ratio" image. This two detector system allows for very high speed crack detection for on-line, real-time inspection of damage in ceramic components. Statistical image processing using a digital image processing approach allows for the quantative discrimination of the presence and distribution of small flaws in a sample while improving detection reliability. The tunable laser allows for the penetration of the sample to detect defects from the sample's surface to the laser's maximum depth of penetration. A layered optical fiber directs the incoming laser beam to the sample and transmits each scattered signal to a respective one of the two detectors.

Space-time windowing of angle-beam wavefield data to characterize scattering from defects

NASA Astrophysics Data System (ADS)

Weng, Yu; Michaels, Jennifer E.

2018-04-01

The primary focus of ultrasonic nondestructive evaluation is defect detection and characterization. In particular, fatigue cracks emanating from fastener holes are commonly found in aerospace structures. Therefore, scattering of ultrasonic waves from crack-like notches is of practical interest. Here, angle-beam shear waves are used to interrogate notches in aluminum plates. In prior work, notch-scattering was characterized and quantified in the frequency-wavenumber domain, which has the undesirable effect of lumping all scattered shear wave energy from notches into a single energy curve. This present work focuses on developing space-time windowing methods to quantify notch-scattered energy directly in the time-space domain. Two strategies are developed. The first is to indirectly characterize notch-scattering via the change in scattering as compared to the undamaged through-hole. The second strategy is to directly track notch-scattered waves in the time-space domain and then quantify scattered energy by constructing energy-versus-direction curves. Both strategies provide a group of energy difference curves, which show how notch-scattering evolves as time progresses. Notch-scattering quantification results for different notch lengths are shown and discussed.

Point Defects in Two-Dimensional Layered Semiconductors: Physics and Its Applications

NASA Astrophysics Data System (ADS)

Suh, Joonki

Recent advances in material science and semiconductor processing have been achieved largely based on in-depth understanding, efficient management and advanced application of point defects in host semiconductors, thus finding the relevant techniques such as doping and defect engineering as a traditional scientific and technological solution. Meanwhile, two- dimensional (2D) layered semiconductors currently draw tremendous attentions due to industrial needs and their rich physics at the nanoscale; as we approach the end of critical device dimensions in silicon-based technology, ultra-thin semiconductors have the potential as next- generation channel materials, and new physics also emerges at such reduced dimensions where confinement of electrons, phonons, and other quasi-particles is significant. It is therefore rewarding and interesting to understand and redefine the impact of lattice defects by investigating their interactions with energy/charge carriers of the host matter. Potentially, the established understanding will provide unprecedented opportunities for realizing new functionalities and enhancing the performance of energy harvesting and optoelectronic devices. In this thesis, multiple novel 2D layered semiconductors, such as bismuth and transition- metal chalcogenides, are explored. Following an introduction of conventional effects induced by point defects in semiconductors, the related physics of electronically active amphoteric defects is revisited in greater details. This can elucidate the complication of a two-dimensional electron gas coexisting with the topological states on the surface of bismuth chalcogenides, recently suggested as topological insulators. Therefore, native point defects are still one of the keys to understand and exploit topological insulators. In addition to from a fundamental science point of view, the effects of point defects on the integrated thermal-electrical transport, as well as the entropy-transporting process in thermoelectric materials are thoroughly investigated. Point defects can potentially beat the undesired coupling, often term "thermoelectric Bermuda triangle", among electrical conductivity, thermal conductivity and thermopower. The maximum thermoelectric performance is demonstrated with an intermediate density of defects when they beneficially and multi-functionally act as electron donors, as well as strongly energy-dependent electron and phonon scatterers. Therefore, this is a good example of how fundamental defect physics can be applied for practical devices toward renewable energy technology. Another interesting field of layered nanomaterials is on transition-metal dichalcogenides (TMDs), sensational candidates for 2D semiconductor physics and applications. At the reduced dimensionality of 2D where a far stronger correlation between point defects and charge carriers is expected, it is studied how chalcogen vacancies alter optical properties of monolayer TMDs. A new, sub-bandgap broad emission lines as well as increase in the overall photoluminescence intensity at low temperatures are reported as a result of high quantum efficiency of excitons, i.e., bound electron-hole pairs, localized at defect sites. On electrical transport, both n- and p-type materials are needed to form junctions and support bipolar carrier conduction while typically only one type of doping is stable for a particular TMD. For example, MoS2 is natively n-type, thus the lack of p-type doping hampers the development of charge-splitting p-n junctions of MoS2. To address this issue, we demonstrate stable p-type conduction in MoS2 by substitutional Nb doping up to the degenerate level. Proof-of-concept, van der Waals p-n homo-junctions based on vertically stacked MoS2 layers are also fabricated which enable gate-tuneable current rectification. Various electronic devices fabricated are stable in ambient air even without additional treatment such as capping layer protection, thanks to the substitutionality nature of the doping; this is in stark contrast to the existing approach of using molecular doping, which usually suffers from volatility and reactivity with air and/or water molecules.

Vacancy-induced dislocations within grains for high-performance PbSe thermoelectrics

DOE PAGES

Chen, Zhiwei; Ge, Binghui; Li, Wen; ...

2017-01-04

To minimize the lattice thermal conductivity in thermoelectrics, strategies typically focus on the scattering of low-frequency phonons by interfaces and high-frequency phonons by point defects. In addition, scattering of mid-frequency phonons by dense dislocations, localized at the grain boundaries, has been shown to reduce the lattice thermal conductivity and improve the thermoelectric performance. Here we propose a vacancy engineering strategy to create dense dislocations in the grains. In Pb 1$-$xSb 2x/3Se solid solutions, cation vacancies are intentionally introduced, where after thermal annealing the vacancies can annihilate through a number of mechanisms creating the desired dislocations homogeneously distributed within the grains.more » This leads to a lattice thermal conductivity as low as 0.4Wm -1 K -1 and a high thermoelectric figure of merit, which can be explained by a dislocation scattering model. As a result, the vacancy engineering strategy used here should be equally applicable for solid solution thermoelectrics and provides a strategy for improving zT.« less

Surface-plasmon polariton scattering from a finite array of nanogrooves/ridges: Efficient mirrors

NASA Astrophysics Data System (ADS)

Sánchez-Gil, José A.; Maradudin, Alexei A.

2005-06-01

The scattering of surface-plasmon polaritons (SPP) by finite arrays of one-dimensional nanodefects on metal surfaces is theoretically investigated on the basis of the reduced Rayleigh equation. Numerical calculations are carried out that rigorously account for all the scattering channels: SPP reflection and transmission, and radiative leakage. We analyze the range of parameters (defect size and number) for which high SPP reflection efficiency (low radiative losses) is achieved within a SPP band gap (negligible SPP transmission), neglecting ohmic losses (justified for array lengths significantly shorter than the SPP inelastic length): Smaller defects play better as SPP mirrors (e.g., efficiency >90% at λ ˜650nm for Gaussian ridges/grooves with sub-30nm height and half-width) than larger defects, since the latter yield significant radiative losses.

Characterization of Subsurface Defects in Ceramic Rods by Laser Scattering and Fractography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, J. M.; Sun, J. G.; Andrews, M. J.

2006-03-06

Silicon nitride ceramics are leading materials being evaluated for valve train components in diesel engine applications. The surface and subsurface defects and damage induced by surface machining can significantly affect component strength and lifetime. In this study, a nondestructive evaluation (NDE) technique based upon laser scattering has been utilized to analyze eight transversely ground silicon nitride cylindrical rods before fracture tests. The fracture origins (machining cracks or material-inherent flaws) identified by fractography after fracture testing were correlated with laser scattering images. The results indicate that laser scattering is able to identify possible fracture origin in the silicon nitride subsurface withoutmore » the need for destructive fracture tests.« less

The relationship between the retinal image quality and the refractive index of defects arising in IOL: numerical analysis

NASA Astrophysics Data System (ADS)

Geniusz, Malwina

2017-09-01

The best treatment for cataract patients, which allows to restore clear vision is implanting an artificial intraocular lens (IOL). The image quality of the lens has a significant impact on the quality of patient's vision. After a long exposure the implant to aqueous environment some defects appear in the artificial lenses. The defects generated in the IOL have different refractive indices. For example, glistening phenomenon is based on light scattering on the oval microvacuoles filled with an aqueous humor which refractive index value is about 1.34. Calcium deposits are another example of lens defects and they can be characterized by the refractive index 1.63. In the presented studies it was calculated how the difference between the refractive indices of the defect and the refractive index of the lens material affects the quality of image. The OpticStudio Professional program (from Radiant Zemax, LLC) was used for the construction of the numerical model of the eye with IOL and to calculate the characteristics of the retinal image. Retinal image quality was described in such characteristics as Point Spread Function (PSF) and the Optical Transfer Function with amplitude and phase. The results show a strong correlation between the refractive indices difference and retinal image quality.

Scattering matrices of Lamb waves at irregular surface and void defects.

PubMed

Feng, Feilong; Shen, Jianzhong; Lin, Shuyu

2012-08-01

Time-harmonic solution of Lamb wave scattering in a plane-strain waveguide with irregular thickness is investigated based on stair-step discretization and stepwise mode matching. The transfer relations of the transmission matrices and reflection matrices are derived in both directions of the waveguide. With these, an explicit expression of the scattering matrix is derived. When the scattering region of an inner irregular defect is geometrically divided into several parts composed of sub-waveguides with variable thicknesses and void regions with vertical free edges corresponding to the plate surfaces, the scattering matrix of the whole region could then be derived by modal matching along the artificial boundaries, as explicit functions of all the scattering matrices of the sub-waveguides and reflection matrices of the free edges. The effectiveness of the formulation is examined by numerical examples; the calculated scattering coefficients are in good accordance with those obtained from numerical simulation models. Copyright © 2012 Elsevier B.V. All rights reserved.

Layer-dependent second-order Raman intensity of Mo S2 and WS e2 : Influence of intervalley scattering

NASA Astrophysics Data System (ADS)

Qian, Qingkai; Zhang, Zhaofu; Chen, Kevin J.

2018-04-01

Acoustic-phonon Raman scattering, as a defect-induced second-order Raman scattering process (with incident photon scattered by one acoustic phonon at the Brillouin-zone edge and the momentum conservation fulfilled by defect scattering), is used as a sensitive tool to study the defects of transition-metal dichalcogenides (TMDs). Moreover, second-order Raman scattering processes are closely related to the valley depolarization of single-layer TMDs in potential valleytronic applications. Here, the layer dependence of second-order Raman intensity of Mo S2 and WS e2 is studied. The electronic band structures of Mo S2 and WS e2 are modified by the layer thicknesses; hence, the resonance conditions for both first-order and second-order Raman scattering processes are tuned. In contrast to the first-order Raman scattering, second-order Raman scattering of Mo S2 and WS e2 involves additional intervalley scattering of electrons by phonons with large momenta. As a result, the electron states that contribute most to the second-order Raman intensity are different from that to first-order process. A weaker layer-tuned resonance enhancement of second-order Raman intensity is observed for both Mo S2 and WS e2 . Specifically, when the incident laser has photon energy close to the optical band gap and the Raman spectra are normalized by the first-order Raman peaks, single-layer Mo S2 or WS e2 has the strongest second-order Raman intensity. This layer-dependent second-order Raman intensity can be further utilized as an indicator to identify the layer number of Mo S2 and WS e2 .

Investigating the Defect Structures in Transparent Conducting Oxides Using X-ray and Neutron Scattering Techniques

PubMed Central

González, Gabriela B.

2012-01-01

Transparent conducting oxide (TCO) materials are implemented into a wide variety of commercial devices because they possess a unique combination of high optical transparency and high electrical conductivity. Created during the processing of the TCOs, defects within the atomic-scale structure are responsible for their desirable optical and electrical properties. Therefore, studying the defect structure is essential to a better understanding of the behavior of transparent conductors. X-ray and neutron scattering techniques are powerful tools to investigate the atomic lattice structural defects in these materials. This review paper presents some of the current developments in the study of structural defects in n-type TCOs using x-ray diffraction (XRD), neutron diffraction, extended x-ray absorption fine structure (EXAFS), pair distribution functions (PDFs), and x-ray fluorescence (XRF). PMID:28817010

Angle-Beam Shear Wave Scattering from Buried Crack-like Defects in Bonded Specimens (Postprint)

DTIC Science & Technology

2017-02-01

wavenumber filtering and spatial windowing is proposed and implemented as an alternative approach to quantify scattering from damage. 15. SUBJECT...TERMS Backscattering . Ultrasonography . Spatial filtering . Ultrasonic scattering . Scattering measurement 16. SECURITY CLASSIFICATION OF: 17...of frequency- wavenumber filtering and spatial windowing is proposed and implemented as an alternative approach to quantify scattering from damage

Topological Defects in Topological Insulators and Bound States at Topological Superconductor Vortices

PubMed Central

Parente, Vincenzo; Campagnano, Gabriele; Giuliano, Domenico; Tagliacozzo, Arturo; Guinea, Francisco

2014-01-01

The scattering of Dirac electrons by topological defects could be one of the most relevant sources of resistance in graphene and at the boundary surfaces of a three-dimensional topological insulator (3D TI). In the long wavelength, continuous limit of the Dirac equation, the topological defect can be described as a distortion of the metric in curved space, which can be accounted for by a rotation of the Gamma matrices and by a spin connection inherited with the curvature. These features modify the scattering properties of the carriers. We discuss the self-energy of defect formation with this approach and the electron cross-section for intra-valley scattering at an edge dislocation in graphene, including corrections coming from the local stress. The cross-section contribution to the resistivity, ρ, is derived within the Boltzmann theory of transport. On the same lines, we discuss the scattering of a screw dislocation in a two-band 3D TI, like Bi1−xSbx, and we present the analytical simplified form of the wavefunction for gapless helical states bound at the defect. When a 3D TI is sandwiched between two even-parity superconductors, Dirac boundary states acquire superconductive correlations by proximity. In the presence of a magnetic vortex piercing the heterostructure, two Majorana states are localized at the two interfaces and bound to the vortex core. They have a half integer total angular momentum each, to match with the unitary orbital angular momentum of the vortex charge. PMID:28788537

Topological Defects in Topological Insulators and Bound States at Topological Superconductor Vortices.

PubMed

Parente, Vincenzo; Campagnano, Gabriele; Giuliano, Domenico; Tagliacozzo, Arturo; Guinea, Francisco

2014-03-04

The scattering of Dirac electrons by topological defects could be one of the most relevant sources of resistance in graphene and at the boundary surfaces of a three-dimensional topological insulator (3D TI). In the long wavelength, continuous limit of the Dirac equation, the topological defect can be described as a distortion of the metric in curved space, which can be accounted for by a rotation of the Gamma matrices and by a spin connection inherited with the curvature. These features modify the scattering properties of the carriers. We discuss the self-energy of defect formation with this approach and the electron cross-section for intra-valley scattering at an edge dislocation in graphene, including corrections coming from the local stress. The cross-section contribution to the resistivity, ρ, is derived within the Boltzmann theory of transport. On the same lines, we discuss the scattering of a screw dislocation in a two-band 3D TI, like Bi 1-x Sb x , and we present the analytical simplified form of the wavefunction for gapless helical states bound at the defect. When a 3D TI is sandwiched between two even-parity superconductors, Dirac boundary states acquire superconductive correlations by proximity. In the presence of a magnetic vortex piercing the heterostructure, two Majorana states are localized at the two interfaces and bound to the vortex core. They have a half integer total angular momentum each, to match with the unitary orbital angular momentum of the vortex charge.

Universal scattering response across the type-II Weyl semimetal phase diagram

NASA Astrophysics Data System (ADS)

Rüßmann, P.; Weber, A. P.; Glott, F.; Xu, N.; Fanciulli, M.; Muff, S.; Magrez, A.; Bugnon, P.; Berger, H.; Bode, M.; Dil, J. H.; Blügel, S.; Mavropoulos, P.; Sessi, P.

2018-02-01

The discovery of Weyl semimetals represents a significant advance in topological band theory. They paradigmatically enlarged the classification of topological materials to gapless systems while simultaneously providing experimental evidence for the long-sought Weyl fermions. Beyond fundamental relevance, their high mobility, strong magnetoresistance, and the possible existence of even more exotic effects, such as the chiral anomaly, make Weyl semimetals a promising platform to develop radically new technology. Fully exploiting their potential requires going beyond the mere identification of materials and calls for a detailed characterization of their functional response, which is severely complicated by the coexistence of surface- and bulk-derived topologically protected quasiparticles, i.e., Fermi arcs and Weyl points, respectively. Here, we focus on the type-II Weyl semimetal class in which we find a stoichiometry-dependent phase transition from a trivial to a nontrivial regime. By exploring the two extreme cases of the phase diagram, we demonstrate the existence of a universal response of both surface and bulk states to perturbations. We show that quasiparticle interference patterns originate from scattering events among surface arcs. Analysis reveals that topologically nontrivial contributions are strongly suppressed by spin texture. We also show that scattering at localized impurities can generate defect-induced quasiparticles sitting close to the Weyl point energy. These give rise to strong peaks in the local density of states, which lift the Weyl node, significantly altering the pristine low-energy spectrum. Remarkably, by comparing the WTe2 and the MoTe2 cases we found that scattering response and topological transition are not directly linked. Visualizing the existence of a universal microscopic response to scattering has important consequences for understanding the unusual transport properties of this class of materials. Overall, our observations provide a unifying picture of the type-II Weyl phase diagram.

Multiscale modeling of thermal conductivity of high burnup structures in UO 2 fuels

DOE PAGES

Bai, Xian -Ming; Tonks, Michael R.; Zhang, Yongfeng; ...

2015-12-22

The high burnup structure forming at the rim region in UO 2 based nuclear fuel pellets has interesting physical properties such as improved thermal conductivity, even though it contains a high density of grain boundaries and micron-size gas bubbles. To understand this counterintuitive phenomenon, mesoscale heat conduction simulations with inputs from atomistic simulations and experiments were conducted to study the thermal conductivities of a small-grain high burnup microstructure and two large-grain unrestructured microstructures. We concluded that the phonon scattering effects caused by small point defects such as dispersed Xe atoms in the grain interior must be included in order tomore » correctly predict the thermal transport properties of these microstructures. In extreme cases, even a small concentration of dispersed Xe atoms such as 10 -5 can result in a lower thermal conductivity in the large-grain unrestructured microstructures than in the small-grain high burnup structure. The high-density grain boundaries in a high burnup structure act as defect sinks and can reduce the concentration of point defects in its grain interior and improve its thermal conductivity in comparison with its large-grain counterparts. Furthermore, an analytical model was developed to describe the thermal conductivity at different concentrations of dispersed Xe, bubble porosities, and grain sizes. Upon calibration, the model is robust and agrees well with independent heat conduction modeling over a wide range of microstructural parameters.« less

Method and apparatus for inspecting reflection masks for defects

DOEpatents

Bokor, Jeffrey; Lin, Yun

2003-04-29

An at-wavelength system for extreme ultraviolet lithography mask blank defect detection is provided. When a focused beam of wavelength 13 nm is incident on a defective region of a mask blank, three possible phenomena can occur. The defect will induce an intensity reduction in the specularly reflected beam, scatter incoming photons into an off-specular direction, and change the amplitude and phase of the electric field at the surface which can be monitored through the change in the photoemission current. The magnitude of these changes will depend on the incident beam size, and the nature, extent and size of the defect. Inspection of the mask blank is performed by scanning the mask blank with 13 nm light focused to a spot a few .mu.m in diameter, while measuring the reflected beam intensity (bright field detection), the scattered beam intensity (dark-field detection) and/or the change in the photoemission current.

Phononic thermal conductivity in silicene: the role of vacancy defects and boundary scattering

NASA Astrophysics Data System (ADS)

Barati, M.; Vazifehshenas, T.; Salavati-fard, T.; Farmanbar, M.

2018-04-01

We calculate the thermal conductivity of free-standing silicene using the phonon Boltzmann transport equation within the relaxation time approximation. In this calculation, we investigate the effects of sample size and different scattering mechanisms such as phonon–phonon, phonon-boundary, phonon-isotope and phonon-vacancy defect. We obtain some similar results to earlier works using a different model and provide a more detailed analysis of the phonon conduction behavior and various mode contributions. We show that the dominant contribution to the thermal conductivity of silicene, which originates from the in-plane acoustic branches, is about 70% at room temperature and this contribution becomes larger by considering vacancy defects. Our results indicate that while the thermal conductivity of silicene is significantly suppressed by the vacancy defects, the effect of isotopes on the phononic transport is small. Our calculations demonstrate that by removing only one of every 400 silicon atoms, a substantial reduction of about 58% in thermal conductivity is achieved. Furthermore, we find that the phonon-boundary scattering is important in defectless and small-size silicene samples, especially at low temperatures.

Nondestructive monitoring damage in composites using scanning laser acoustic microscopy

NASA Technical Reports Server (NTRS)

Wey, A. C.; Kessler, L. W.; Dos Reis, H. L. M.

1992-01-01

Several Nicalon fiber reinforced LAS (lithium alumino-silicate) glass matrix composites were tested to study the relation between the residual strength and the different amounts of damage. The samples were fatigued by four-point cyclic loading at a 5 Hz rate at 500 C for a different number of cycles. 10 MHz scanning laser acoustic microscope (SLAM) images were taken to monitor damage on the samples. Our SLAM results indicate that there were defects already existing throughout the sample before fatigue, and the resultant damage pattern from fatigue could be related to the initial defect distribution in the sample. Finally, the fatigued samples were fractured and the residual strength data could not be explained by the cyclic fatigue alone. Rather, the damage patterns evident in the SLAM images were needed to explain the scatter in the data. The results show that SLAM is useful in nondestructively monitoring damage and estimating residual strength of fatigued ceramic composites.

Towards Improved Finite Element Modelling of the Interaction of Elastic Waves with Complex Defect Geometries

NASA Astrophysics Data System (ADS)

Rajagopal, P.; Drozdz, M.; Lowe, M. J. S.

2009-03-01

A solution to the problem of improving the finite element (FE) modeling of elastic wave-defect interaction is sought by reconsidering the conventional opinion on meshing strategy. The standard approach using uniform square elements imposes severe limitations in representing complex defect outlines but this is thought to improve when the mesh is made finer. Free meshing algorithms available widely in commercial packages of late can cope with difficult features well but they are thought to cause scattering by the irregular mesh itself. This paper examines whether the benefits offered by free meshing in representing defects better outweigh the inaccuracies due to mesh scattering. If using the standard mesh, the questions whether mesh refinement leads to improved results and whether a practical strategy can be constructed are considered.

A model for the high-temperature transport properties of heavily doped n-type silicon-germanium alloys

NASA Technical Reports Server (NTRS)

Vining, Cronin B.

1991-01-01

A model is presented for the high-temperature transport properties of large-grain-size, heavily doped n-type silicon-germanium alloys. Electron and phonon transport coefficients are calculated using standard Boltzmann equation expressions in the relaxation time approximation. Good agreement with experiment is found by considering acoustic phonon and ionized impurity scattering for electrons, and phonon-phonon, point defect, and electron-phonon scattering for phonons. The parameters describing electron transport in heavily doped and lightly doped materials are significantly different and suggest that most carriers in heavily doped materials are in a band formed largely from impurity states. The maximum dimensionless thermoelectric figure of merit for single-crystal, n-type Si(0.8)Ge(0.2) at 1300 K is estimated at ZT about 1.13 with an optimum carrier concentration of n about 2.9 x 10 to the 20th/cu cm.

Lattice dynamics and the nature of structural transitions in organolead halide perovskites

DOE PAGES

Comin, Riccardo; Crawford, Michael K.; Said, Ayman H.; ...

2016-09-09

Organolead halide perovskites are a family of hybrid organic-inorganic compounds whose remark- able optoelectronic properties have been under intensive scrutiny in recent years. Here we use inelastic X-ray scattering to study low-energy lattice excitations in single crystals of methylammonium lead iodide and bromide perovskites. Our ndings conrm the displacive nature of the cubic-to- tetragonal phase transition, which is further shown, using neutron and x-ray diraction, to be close to a tricritical point. The experimental sound speed, around 100-200 m/s, suggests that electron- phonon scattering is likely a limiting factor for further improvements in carrier mobility. Lastly, we detect quasistatic symmetry-breakingmore » nanodomains persisting well into the high-temperature cubic phase, possibly stabilized by local defects. These ndings reveal key structural properties of these materials, but also bear important implications for carrier dynamics across an extended temperature range relevant for photovoltaic applications.« less

Some Remarks on GMRES for Transport Theory

NASA Technical Reports Server (NTRS)

Patton, Bruce W.; Holloway, James Paul

2003-01-01

We review some work on the application of GMRES to the solution of the discrete ordinates transport equation in one-dimension. We note that GMRES can be applied directly to the angular flux vector, or it can be applied to only a vector of flux moments as needed to compute the scattering operator of the transport equation. In the former case we illustrate both the delights and defects of ILU right-preconditioners for problems with anisotropic scatter and for problems with upscatter. When working with flux moments we note that GMRES can be used as an accelerator for any existing transport code whose solver is based on a stationary fixed-point iteration, including transport sweeps and DSA transport sweeps. We also provide some numerical illustrations of this idea. We finally show how space can be traded for speed by taking multiple transport sweeps per GMRES iteration. Key Words: transport equation, GMRES, Krylov subspace

Lattice dynamics and the nature of structural transitions in organolead halide perovskites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Comin, Riccardo; Crawford, Michael K.; Said, Ayman H.

Organolead halide perovskites are a family of hybrid organic-inorganic compounds whose remark- able optoelectronic properties have been under intensive scrutiny in recent years. Here we use inelastic X-ray scattering to study low-energy lattice excitations in single crystals of methylammonium lead iodide and bromide perovskites. Our ndings conrm the displacive nature of the cubic-to- tetragonal phase transition, which is further shown, using neutron and x-ray diraction, to be close to a tricritical point. The experimental sound speed, around 100-200 m/s, suggests that electron- phonon scattering is likely a limiting factor for further improvements in carrier mobility. Lastly, we detect quasistatic symmetry-breakingmore » nanodomains persisting well into the high-temperature cubic phase, possibly stabilized by local defects. These ndings reveal key structural properties of these materials, but also bear important implications for carrier dynamics across an extended temperature range relevant for photovoltaic applications.« less

Viewing Integrated-Circuit Interconnections By SEM

NASA Technical Reports Server (NTRS)

Lawton, Russel A.; Gauldin, Robert E.; Ruiz, Ronald P.

1990-01-01

Back-scattering of energetic electrons reveals hidden metal layers. Experiment shows that with suitable operating adjustments, scanning electron microscopy (SEM) used to look for defects in aluminum interconnections in integrated circuits. Enables monitoring, in situ, of changes in defects caused by changes in temperature. Gives truer picture of defects, as etching can change stress field of metal-and-passivation pattern, causing changes in defects.

Imaging atomic-scale effects of high-energy ion irradiation on superconductivity and vortex pinning in Fe(Se,Te)

PubMed Central

Massee, Freek; Sprau, Peter Oliver; Wang, Yong-Lei; Davis, J. C. Séamus; Ghigo, Gianluca; Gu, Genda D.; Kwok, Wai-Kwong

2015-01-01

Maximizing the sustainable supercurrent density, JC, is crucial to high-current applications of superconductivity. To achieve this, preventing dissipative motion of quantized vortices is key. Irradiation of superconductors with high-energy heavy ions can be used to create nanoscale defects that act as deep pinning potentials for vortices. This approach holds unique promise for high-current applications of iron-based superconductors because JC amplification persists to much higher radiation doses than in cuprate superconductors without significantly altering the superconducting critical temperature. However, for these compounds, virtually nothing is known about the atomic-scale interplay of the crystal damage from the high-energy ions, the superconducting order parameter, and the vortex pinning processes. We visualize the atomic-scale effects of irradiating FeSexTe1−x with 249-MeV Au ions and find two distinct effects: compact nanometer-sized regions of crystal disruption or “columnar defects,” plus a higher density of single atomic site “point” defects probably from secondary scattering. We directly show that the superconducting order is virtually annihilated within the former and suppressed by the latter. Simultaneous atomically resolved images of the columnar crystal defects, the superconductivity, and the vortex configurations then reveal how a mixed pinning landscape is created, with the strongest vortex pinning occurring at metallic core columnar defects and secondary pinning at clusters of point-like defects, followed by collective pinning at higher fields. PMID:26601180

Acoustic Coherent Backscatter Enhancement from Aggregations of Point Scatterers

DTIC Science & Technology

2015-09-30

and far-field acoustic multiple scattering from two- and now three-dimensional aggregations of omnidirectional point scatterers to determine the...an aggregation of omnidirectional point scatterers [1]. If ψ(r) is the harmonic acoustic pressure field at frequency ω at the point r and ψ0(r) is... scattered field and is given by the sum in (1), N is the number of scatterers , gn is the scattering coefficient of the nth scatterer , ψn(rn) is the field

Impact of vacancy ordering on thermal transport in crystalline phase-change materials.

PubMed

Siegert, K S; Lange, F R L; Sittner, E R; Volker, H; Schlockermann, C; Siegrist, T; Wuttig, M

2015-01-01

Controlling thermal transport in solids is of paramount importance for many applications. Often thermal management is crucial for a device's performance, as it affects both reliability and power consumption. A number of intricate concepts have been developed to address this challenge, such as diamond-like coatings to enhance the thermal conductivity or low symmetry complex super-structures to reduce it. Here, a different approach is pursued, where we explore the potential of solids with a high yet controllable degree of disorder. Recently, it has been demonstrated that an unconventionally high degree of structural disorder characterizes a number of crystalline phase-change materials (PCMs). This disorder strongly impacts electronic transport and even leads to disorder induced localization (Anderson localization). This raises the question how thermal transport is affected by such conditions. Here thermal transport in highly disordered crystalline Ge-Sb-Te (GST) based PCMs is investigated. Glass-like thermal properties are observed for several crystalline PCMs, which are attributed to strong scattering by disordered point defects. A systematic study of different compounds along the pseudo-binary line between GeTe and Sb2Te3 reveals that disordered vacancies act as point defects responsible for pronounced phonon scattering. Annealing causes a gradual ordering of the vacancies and leads to a more 'crystal-like' thermal conductivity. While both vibrational and electronic degrees of freedom are affected by disorder, the consequences differ for different stoichiometries. This opens up a pathway to tune electrical and thermal transport by controlling the degree of disorder. Materials with tailored transport properties may not only help to improve power efficiency and scaling in upcoming phase-change memories but are also of fundamental interest in the field of thermoelectric materials.

Impact of vacancy ordering on thermal transport in crystalline phase-change materials

NASA Astrophysics Data System (ADS)

Siegert, K. S.; Lange, F. R. L.; Sittner, E. R.; Volker, H.; Schlockermann, C.; Siegrist, T.; Wuttig, M.

2015-01-01

Controlling thermal transport in solids is of paramount importance for many applications. Often thermal management is crucial for a device's performance, as it affects both reliability and power consumption. A number of intricate concepts have been developed to address this challenge, such as diamond-like coatings to enhance the thermal conductivity or low symmetry complex super-structures to reduce it. Here, a different approach is pursued, where we explore the potential of solids with a high yet controllable degree of disorder. Recently, it has been demonstrated that an unconventionally high degree of structural disorder characterizes a number of crystalline phase-change materials (PCMs). This disorder strongly impacts electronic transport and even leads to disorder induced localization (Anderson localization). This raises the question how thermal transport is affected by such conditions. Here thermal transport in highly disordered crystalline Ge-Sb-Te (GST) based PCMs is investigated. Glass-like thermal properties are observed for several crystalline PCMs, which are attributed to strong scattering by disordered point defects. A systematic study of different compounds along the pseudo-binary line between GeTe and Sb2Te3 reveals that disordered vacancies act as point defects responsible for pronounced phonon scattering. Annealing causes a gradual ordering of the vacancies and leads to a more ‘crystal-like’ thermal conductivity. While both vibrational and electronic degrees of freedom are affected by disorder, the consequences differ for different stoichiometries. This opens up a pathway to tune electrical and thermal transport by controlling the degree of disorder. Materials with tailored transport properties may not only help to improve power efficiency and scaling in upcoming phase-change memories but are also of fundamental interest in the field of thermoelectric materials.

Laser scatter feature of surface defect on apples

NASA Astrophysics Data System (ADS)

Rao, Xiuqin; Ying, Yibin; Cen, YiKe; Huang, Haibo

2006-10-01

A machine vision system for real-time fruit quality inspection was developed. The system consists of a chamber, a laser projector, a TMS-7DSP CCD camera (PULNIX Inc.), and a computer. A Meteor-II/MC frame grabber (Matrox Graphics Inc.) was inserted into the slot of the computer to grab fruit images. The laser projector and the camera were mounted at the ceiling of the chamber. An apple was put in the chamber, the spot of the laser projector was projected on the surface of the fruit, and an image was grabbed. 2 breed of apples was test, Each apple was imaged twice, one was imaged for the normal surface, and the other for the defect. The red component of the images was used to get the feature of the defect and the sound surface of the fruits. The average value, STD value and comentropy Value of red component of the laser scatter image were analyzed. The Standard Deviation value of red component of normal is more suitable to separate the defect surface from sound surface for the ShuijinFuji apples, but for bintang apples, there is more work need to do to separate the different surface with laser scatter image.

Nondestructive defect detection in laser optical coatings

NASA Astrophysics Data System (ADS)

Marrs, C. D.; Porteus, J. O.; Palmer, J. R.

1985-03-01

Defects responsible for laser damage in visible-wavelength mirrors are observed at nondamaging intensities using a new video microscope system. Studies suggest that a defect scattering phenomenon combined with lag characteristics of video cameras makes this possible. Properties of the video-imaged light are described for multilayer dielectric coatings and diamond-turned metals.

Inspection of lithographic mask blanks for defects

DOEpatents

Sommargren, Gary E.

2001-01-01

A visible light method for detecting sub-100 nm size defects on mask blanks used for lithography. By using optical heterodyne techniques, detection of the scattered light can be significantly enhanced as compared to standard intensity detection methods. The invention is useful in the inspection of super-polished surfaces for isolated surface defects or particulate contamination and in the inspection of lithographic mask or reticle blanks for surface defects or bulk defects or for surface particulate contamination.

Characterization of Oxygen Defect Clusters in UO2+ x Using Neutron Scattering and PDF Analysis.

PubMed

Ma, Yue; Garcia, Philippe; Lechelle, Jacques; Miard, Audrey; Desgranges, Lionel; Baldinozzi, Gianguido; Simeone, David; Fischer, Henry E

2018-06-18

In hyper-stoichiometric uranium oxide, both neutron diffraction work and, more recently, theoretical analyses report the existence of clusters such as the 2:2:2 cluster, comprising two anion vacancies and two types of anion interstitials. However, little is known about whether there exists a region of low deviation-from-stoichiometry in which defects remain isolated, or indeed whether at high deviation-from-stoichiometry defect clusters prevail that contain more excess oxygen atoms than the di-interstitial cluster. In this study, we report pair distribution function (PDF) analyses of UO 2 and UO 2+ x ( x ≈ 0.007 and x ≈ 0.16) samples obtained from high-temperature in situ neutron scattering experiments. PDF refinement for the lower deviation from stoichiometry sample suggests the system is too dilute to differentiate between isolated defects and di-interstitial clusters. For the UO 2.16 sample, several defect structures are tested, and it is found that the data are best represented assuming the presence of center-occupied cuboctahedra.

Extended bidirectional reflectance distribution function for polarized light scattering from subsurface defects under a smooth surface.

PubMed

Shen, Jian; Deng, Degang; Kong, Weijin; Liu, Shijie; Shen, Zicai; Wei, Chaoyang; He, Hongbo; Shao, Jianda; Fan, Zhengxiu

2006-11-01

By introducing the scattering probability of a subsurface defect (SSD) and statistical distribution functions of SSD radius, refractive index, and position, we derive an extended bidirectional reflectance distribution function (BRDF) from the Jones scattering matrix. This function is applicable to the calculation for comparison with measurement of polarized light-scattering resulting from a SSD. A numerical calculation of the extended BRDF for the case of p-polarized incident light was performed by means of the Monte Carlo method. Our numerical results indicate that the extended BRDF strongly depends on the light incidence angle, the light scattering angle, and the out-of-plane azimuth angle. We observe a 180 degrees symmetry with respect to the azimuth angle. We further investigate the influence of the SSD density, the substrate refractive index, and the statistical distributions of the SSD radius and refractive index on the extended BRDF. For transparent substrates, we also find the dependence of the extended BRDF on the SSD positions.

The Influence of Inspection Angle, Wave Type and Beam Shape on Signal-to-Noise Ratios in Ultrasonic Pitch-Catch Inspections

NASA Astrophysics Data System (ADS)

Margetan, F. J.; Li, Anxiang; Thompson, R. B.

2007-03-01

Grain noise, which arises from the scattering of sound waves by microstructure, can limit the detection of small internal defects in metal components. Signal-to-noise (S/N) ratios for ultrasonic pitch/catch inspections are primarily determined by three factors: the scattering ability of the defect; the inherent noisiness of the microstructure (per unit volume); and finite-beam effects. An approximate single-scattering model has been formulated which contains terms representing each of these factors. In this paper the model is applied to a representative pitch/catch inspection problem, namely, the detection of a circular crack in a nickel cylinder. The object is to estimate S/N ratios for various choices of the inspection angle and sonic wave types, and to demonstrate how S/N is determined by the interplay of the defect, microstructure, and finite-beam factors. We also explore how S/N is influenced by the sizes, shapes, and orientations of the transmitter and receiver sound beams.

Diffusive charge transport in graphene

NASA Astrophysics Data System (ADS)

Chen, Jianhao

The physical mechanisms limiting the mobility of graphene on SiO 2 are studied and printed graphene devices on a flexible substrate are realized. Intentional addition of charged scattering impurities is used to study the effects of charged impurities. Atomic-scale defects are created by noble-gas ions irradiation to study the effect of unitary scatterers. The results show that charged impurities and atomic-scale defects both lead to conductivity linear in density in graphene, with a scattering magnitude that agrees quantitatively with theoretical estimates. While charged impurities cause intravalley scattering and induce a small change in the minimum conductivity, defects in graphene scatter electrons between the valleys and suppress the minimum conductivity below the metallic limit. Temperature-dependent measurements show that longitudinal acoustic phonons in graphene produce a small resistivity which is linear in temperature and independent of carrier density; at higher temperatures, polar optical phonons of the SiO2 substrate give rise to an activated, carrier density-dependent resistivity. Graphene is also made into high mobility transparent and flexible field effect device via the transfer-printing method. Together the results paint a complete picture of charge carrier transport in graphene on SiO2 in the diffusive regime, and show the promise of graphene as a novel electronic material that have potential applications not only on conventional inorganic substrates, but also on flexible substrates.

Neutron-scattering-based evidence for interacting magnetic excitons in LaCo O 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

El-Khatib, S.; Phelan, D.; Barker, J. G.

Recent progress with the thermally-driven spin-state crossover in LaCoO3 has made it increasingly apparent that the nominally non-magnetic low spin ground state of this material actually hosts novel defect-'based magnetism. This is investigated here via a small-angle neutron scattering (SANS) study of LaCoO3-s crystals. The results provide: (i) the surprising finding that the spin-state crossover is clearly reflected in SANS via quasielastic/inelastic scattering from paramagnetic spin fluctuations/excitations, and (ii) evidence for the formation, likely around oxygen defects, of local entities known as magnetic excitons. The latter generate distinct magnetic scattering below 60 K, providing valuable quantitative information on exciton densitiesmore » and interactions. Potential relevance to the unexpected ferromagnetism recently discovered in epitaxial LaCoO3 films is discussed.« less

The defect level and ideal thermal conductivity of graphene uncovered by residual thermal reffusivity at the 0 K limit

NASA Astrophysics Data System (ADS)

Xie, Yangsu; Xu, Zaoli; Xu, Shen; Cheng, Zhe; Hashemi, Nastaran; Deng, Cheng; Wang, Xinwei

2015-05-01

Due to its intriguing thermal and electrical properties, graphene has been widely studied for potential applications in sensor and energy devices. However, the reported value for its thermal conductivity spans from dozens to thousands of W m-1 K-1 due to different levels of alternations and defects in graphene samples. In this work, the thermal diffusivity of suspended four-layered graphene foam (GF) is characterized from room temperature (RT) down to 17 K. For the first time, we identify the defect level in graphene by evaluating the inverse of thermal diffusivity (termed ``thermal reffusivity'': Θ) at the 0 K limit. By using the Debye model of Θ = Θ0 + C × e-θ/2T and fitting the Θ-T curve to the point of T = 0 K, we identify the defect level (Θ0) and determine the Debye temperature of graphene. Θ0 is found to be 1878 s m-2 for the studied GF and 43-112 s m-2 for three highly crystalline graphite materials. This uncovers a 16-43-fold higher defect level in GF than that in pyrolytic graphite. In GF, the phonon mean free path solely induced by defects and boundary scattering is determined as 166 nm. The Debye temperature of graphene is determined to be 1813 K, which is very close to the average theoretical Debye temperature (1911 K) of the three acoustic phonon modes in graphene. By subtracting the defect effect, we report the ideal thermal diffusivity and conductivity (κideal) of graphene presented in the 3D foam structure in the range of 33-299 K. Detailed physics based on chemical composition and structure analysis are given to explain the κideal-T profile by comparing with those reported for suspended graphene.Due to its intriguing thermal and electrical properties, graphene has been widely studied for potential applications in sensor and energy devices. However, the reported value for its thermal conductivity spans from dozens to thousands of W m-1 K-1 due to different levels of alternations and defects in graphene samples. In this work, the thermal diffusivity of suspended four-layered graphene foam (GF) is characterized from room temperature (RT) down to 17 K. For the first time, we identify the defect level in graphene by evaluating the inverse of thermal diffusivity (termed ``thermal reffusivity'': Θ) at the 0 K limit. By using the Debye model of Θ = Θ0 + C × e-θ/2T and fitting the Θ-T curve to the point of T = 0 K, we identify the defect level (Θ0) and determine the Debye temperature of graphene. Θ0 is found to be 1878 s m-2 for the studied GF and 43-112 s m-2 for three highly crystalline graphite materials. This uncovers a 16-43-fold higher defect level in GF than that in pyrolytic graphite. In GF, the phonon mean free path solely induced by defects and boundary scattering is determined as 166 nm. The Debye temperature of graphene is determined to be 1813 K, which is very close to the average theoretical Debye temperature (1911 K) of the three acoustic phonon modes in graphene. By subtracting the defect effect, we report the ideal thermal diffusivity and conductivity (κideal) of graphene presented in the 3D foam structure in the range of 33-299 K. Detailed physics based on chemical composition and structure analysis are given to explain the κideal-T profile by comparing with those reported for suspended graphene. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02012c

Two-dimensional PSF prediction of multiple-reflection optical systems with rough surfaces

NASA Astrophysics Data System (ADS)

Tayabaly, Kashmira; Spiga, Daniele; Sironi, Giorgia; Pareschi, Giovani; Lavagna, Michele

2016-09-01

The focusing accuracy in reflective optical systems, usually expressed in terms of the Point Spread Function (PSF) is chiefly determined by two factors: the deviation of the mirror shape from the nominal design and the surface finishing. While the effects of the former are usually well described by the geometrical optics, the latter is diffractive/interferential in nature and determined by a distribution of defects that cover several decades in the lateral scale (from a few millimeters to a few microns). Clearly, reducing the level of scattered light is crucial to improve the focusing of the collected radiation, particularly for astronomical telescopes that aim to detect faint light signals from our Universe. Telescopes are typically arranged in multiple reflections configuration and the behavior of the multiply-scattered radiation becomes difficult to predict and control. Also it is difficult to disentangle the effect of surface scattering from the PSF degradation caused by the shape deformation of the optical elements. This paper presents a simple and unifying method for evaluating the contribution of optical surfaces defects to the two-dimensional PSF of a multi-reflections system, regardless of the classification of a spectral range as "geometry" or "roughness". This method, entirely based on Huygens-Fresnel principle in the far-field approximation, was already applied in grazing-incidence X-ray mirrors and experimentally validated for a single reflection system, accounting for the real surface topography of the optics. In this work we show the extension of this formalism to a double reflection system and introducing real microroughness data. The formalism is applied to a MAGIC-I panel mirror that was fully characterized, allowing us to predict the PSF and the validation with real measurements of the double reflection ASTRI telescope, a prototype of CTA-SST telescope.

Influence of Casting Defects on S- N Fatigue Behavior of Ni-Al Bronze

NASA Astrophysics Data System (ADS)

Sarkar, Aritra; Chakrabarti, Abhishek; Nagesha, A.; Saravanan, T.; Arunmuthu, K.; Sandhya, R.; Philip, John; Mathew, M. D.; Jayakumar, T.

2015-02-01

Nickel-aluminum bronze (NAB) alloys have been used extensively in marine applications such as propellers, couplings, pump casings, and pump impellers due to their good mechanical properties such as tensile strength, creep resistance, and corrosion resistance. However, there have been several instances of in-service failure of the alloy due to high cycle fatigue (HCF). The present paper aims at characterizing the casting defects in this alloy through X-ray radiography and X-ray computed tomography into distinct defect groups having particular defect size and location. HCF tests were carried out on each defect group of as-cast NAB at room temperature by varying the mean stress. A significant decrease in the HCF life was observed with an increase in the tensile mean stress, irrespective of the defect size. Further, a considerable drop in the HCF life was observed with an increase in the size of defects and proximity of the defects to the surface. However, the surface proximity indicated by location of the defect in the sample was seen to override the influence of defect size and maximum cyclic stress. This leads to huge scatter in S- N curve. For a detailed quantitative analysis of defect size and location, an empirical model is developed which was able to minimize the scatter to a significant extent. Further, a concept of critical distance is proposed, beyond which the defect would not have a deleterious consequence on the fatigue behavior. Such an approach was found to be suitable for generating S- N curves for cast NAB.

The defect level and ideal thermal conductivity of graphene uncovered by residual thermal reffusivity at the 0 K limit.

PubMed

Xie, Yangsu; Xu, Zaoli; Xu, Shen; Cheng, Zhe; Hashemi, Nastaran; Deng, Cheng; Wang, Xinwei

2015-06-14

Due to its intriguing thermal and electrical properties, graphene has been widely studied for potential applications in sensor and energy devices. However, the reported value for its thermal conductivity spans from dozens to thousands of W m(-1) K(-1) due to different levels of alternations and defects in graphene samples. In this work, the thermal diffusivity of suspended four-layered graphene foam (GF) is characterized from room temperature (RT) down to 17 K. For the first time, we identify the defect level in graphene by evaluating the inverse of thermal diffusivity (termed "thermal reffusivity": Θ) at the 0 K limit. By using the Debye model of Θ = Θ0 + C× e(-θ/2T) and fitting the Θ-T curve to the point of T = 0 K, we identify the defect level (Θ0) and determine the Debye temperature of graphene. Θ0 is found to be 1878 s m(-2) for the studied GF and 43-112 s m(-2) for three highly crystalline graphite materials. This uncovers a 16-43-fold higher defect level in GF than that in pyrolytic graphite. In GF, the phonon mean free path solely induced by defects and boundary scattering is determined as 166 nm. The Debye temperature of graphene is determined to be 1813 K, which is very close to the average theoretical Debye temperature (1911 K) of the three acoustic phonon modes in graphene. By subtracting the defect effect, we report the ideal thermal diffusivity and conductivity (κideal) of graphene presented in the 3D foam structure in the range of 33-299 K. Detailed physics based on chemical composition and structure analysis are given to explain the κideal-T profile by comparing with those reported for suspended graphene.

Characterization and analysis of thermoelectric transport using SPB model in nanostructured aluminum doped zinc tellurium

NASA Astrophysics Data System (ADS)

Bhaskar, Ankam; Pai, Yi-Hsuan; Liu, Chia-Jyi

2017-11-01

Low-temperature electronic and thermal transport measurements are carried out on nanostructured Zn1-x Al x Te (0  ⩽  x  ⩽  0.15) fabricated using hydrothermal synthesis followed by evacuated-and-encapsulated sintering. A single parabolic band with acoustic phonon scattering is used to analyze thermoelectric transport data. It is found that reduced Fermi energy gets closer to the valence band edge and density of states effective mass, effective density of states, and Hall factor decrease with increasing x in doped samples. The chemical carrier concentration, carrier density independent mobility, β, and theoretical zT values increase with increasing x in doped samples. The nanostructured Zn1-x Al x Te exhibits significant reduction of thermal conductivity at 300 K (1.82-3.71 W m-1 K-1) as compared to bulk ZnTe (18 W m-1 K-1). The point-defect scattering and phonon-grain scattering play an important role in reducing the lattice thermal conductivity. In addition, partial substitution of Al3+ for Zn2+ significantly improves both the power factor and zT values.

Thermal and thermoelectric transport measurements of an individual boron arsenide microstructure

NASA Astrophysics Data System (ADS)

Kim, Jaehyun; Evans, Daniel A.; Sellan, Daniel P.; Williams, Owen M.; Ou, Eric; Cowley, Alan H.; Shi, Li

2016-05-01

Recent first principles calculations have predicted that boron arsenide (BAs) can possess an unexpectedly high thermal conductivity that depends sensitively on the crystal size and defect concentration. However, few experimental results have been obtained to verify these predictions. In the present work, we report four-probe thermal and thermoelectric transport measurements of an individual BAs microstructure that was synthesized via a vapor transport method. The measured thermal conductivity was found to decrease slightly with temperature in the range between 250 K and 350 K. The temperature dependence suggests that the extrinsic phonon scattering processes play an important role in addition to intrinsic phonon-phonon scattering. The room temperature value of (186 ± 46) W m-1 K-1 is higher than that of bulk silicon but still a factor of four lower than the calculated result for a defect-free, non-degenerate BAs rod with a similar diameter of 1.15 μm. The measured p-type Seebeck coefficient and thermoelectric power factor are comparable to those of bismuth telluride, which is a commonly used thermoelectric material. The foregoing results also suggest that it is necessary to not only reduce defect and boundary scatterings but also to better understand and control the electron scattering of phonons in order to achieve the predicted ultrahigh intrinsic lattice thermal conductivity of BAs.

An efficient algorithm for the generalized Foldy-Lax formulation

NASA Astrophysics Data System (ADS)

Huang, Kai; Li, Peijun; Zhao, Hongkai

2013-02-01

Consider the scattering of a time-harmonic plane wave incident on a two-scale heterogeneous medium, which consists of scatterers that are much smaller than the wavelength and extended scatterers that are comparable to the wavelength. In this work we treat those small scatterers as isotropic point scatterers and use a generalized Foldy-Lax formulation to model wave propagation and capture multiple scattering among point scatterers and extended scatterers. Our formulation is given as a coupled system, which combines the original Foldy-Lax formulation for the point scatterers and the regular boundary integral equation for the extended obstacle scatterers. The existence and uniqueness of the solution for the formulation is established in terms of physical parameters such as the scattering coefficient and the separation distances. Computationally, an efficient physically motivated Gauss-Seidel iterative method is proposed to solve the coupled system, where only a linear system of algebraic equations for point scatterers or a boundary integral equation for a single extended obstacle scatterer is required to solve at each step of iteration. The convergence of the iterative method is also characterized in terms of physical parameters. Numerical tests for the far-field patterns of scattered fields arising from uniformly or randomly distributed point scatterers and single or multiple extended obstacle scatterers are presented.

Study on the intrinsic defects in tin oxide with first-principles method

NASA Astrophysics Data System (ADS)

Sun, Yu; Liu, Tingyu; Chang, Qiuxiang; Ma, Changmin

2018-04-01

First-principles and thermodynamic methods are used to study the contribution of vibrational entropy to defect formation energy and the stability of the intrinsic point defects in SnO2 crystal. According to thermodynamic calculation results, the contribution of vibrational entropy to defect formation energy is significant and should not be neglected, especially at high temperatures. The calculated results indicate that the oxygen vacancy is the major point defect in undoped SnO2 crystal, which has a higher concentration than that of the other point defect. The property of negative-U is put forward in SnO2 crystal. In order to determine the most stable defects much clearer under different conditions, the most stable intrinsic defect as a function of Fermi level, oxygen partial pressure and temperature are described in the three-dimensional defect formation enthalpy diagrams. The diagram visually provides the most stable point defects under different conditions.

Higgs transition from a magnetic Coulomb liquid to a ferromagnet in Yb₂Ti₂O₇.

PubMed

Chang, Lieh-Jeng; Onoda, Shigeki; Su, Yixi; Kao, Ying-Jer; Tsuei, Ku-Ding; Yasui, Yukio; Kakurai, Kazuhisa; Lees, Martin Richard

2012-01-01

In a class of frustrated magnets known as spin ice, magnetic monopoles emerge as classical defects and interact via the magnetic Coulomb law. With quantum-mechanical interactions, these magnetic charges are carried by fractionalized bosonic quasi-particles, spinons, which can undergo Bose-Einstein condensation through a first-order transition via the Higgs mechanism. Here, we report evidence of a Higgs transition from a magnetic Coulomb liquid to a ferromagnet in single-crystal Yb(2)Ti(2)O(7). Polarized neutron scattering experiments show that the diffuse [111]-rod scattering and pinch-point features, which develop on cooling are suddenly suppressed below T(C)~0.21 K, where magnetic Bragg peaks and a full depolarization of the neutron spins are observed with thermal hysteresis, indicating a first-order ferromagnetic transition. Our results are explained on the basis of a quantum spin-ice model, whose high-temperature phase is effectively described as a magnetic Coulomb liquid, whereas the ground state shows a nearly collinear ferromagnetism with gapped spin excitations.

Microstructural study of Mg-doped p-type GaN: Correlation between high-resolution electron microscopy and Raman spectroscopy

NASA Astrophysics Data System (ADS)

Tsen, S.-C. Y.; Smith, David J.; Tsen, K. T.; Kim, W.; Morkoç, H.

1997-12-01

A series of Mg-doped GaN films (˜1-1.3 μm) grown by reactive molecular beam epitaxy at substrate temperatures of 750 and 800 °C has been studied by high-resolution electron microscopy (HREM) and Raman spectroscopy. Stacking defects parallel to the substrate surface were observed in samples grown on sapphire substrates at 750 °C with AlN buffer layers (60-70 nm) at low Mg concentration. A transition region with mixed zinc-blende cubic (c) and wurtzite hexagonal (h) phases having the relative orientations of (111)c//(00.1)h and (11¯0)c//(10.0)h was observed for increased Mg concentration. The top surfaces of highly doped samples were rough and assumed a completely zinc-blende phase with some inclined stacking faults. Samples grown with a Mg cell temperature of 350 °C and high doping levels were highly disordered with many small crystals having inclined stacking faults, microtwins, and defective wurtzite and zinc-blende phases. Correlation between HREM and Raman scattering results points towards the presence of compressive lattice distortion along the growth direction which might be attributable to structural defects. The films grown at 800 °C had better quality with less observable defects and less yellow luminescence than samples grown at 750 °C.

Investigation of the effect of scattering centers on low dimensional nanowire channel

NASA Astrophysics Data System (ADS)

Cariappa, K. S.; Shukla, Raja; Sarkar, Niladri

2018-05-01

In this work, we studied the effect of scattering centers on the electron density profiles of a one dimensional Nanowire channel. Density Matrix Formalism is used for calculating the local electron densities at room temperature. Various scattering centers have been simulated in the channel. The nearest neighbor tight binding method is applied to construct the Hamiltonian of nanoscale devices. We invoke scattering centers by adding local scattering potentials to the Hamiltonian. This analysis could give an insight into the understanding and utilization of defects for device engineering.

Magnetic penetration-depth measurements of a suppressed superfluid density of superconducting Ca0.5Na0.5Fe2As2 single crystals by proton irradiation

NASA Astrophysics Data System (ADS)

Kim, Jeehoon; Haberkorn, N.; Graf, M. J.; Usov, I.; Ronning, F.; Civale, L.; Nazaretski, E.; Chen, G. F.; Yu, W.; Thompson, J. D.; Movshovich, R.

2012-10-01

We report on the dramatic effect of random point defects, produced by proton irradiation, on the superfluid density ρs in superconducting Ca0.5Na0.5Fe2As2 single crystals. The magnitude of the suppression is inferred from measurements of the temperature-dependent magnetic penetration depth λ(T) using magnetic force microscopy. Our findings indicate that a radiation dose of 2×1016 cm-2 produced by 3 MeV protons results in a reduction of the superconducting critical temperature Tc by approximately 10%. In contrast, ρs(0) is suppressed by approximately 60%. This breakdown of the Abrikosov-Gorkov theory may be explained by the so-called “Swiss cheese model,” which accounts for the spatial suppression of the order parameter near point defects similar to holes in Swiss cheese. Both the slope of the upper critical field and the penetration depth λ(T/Tc)/λ(0) exhibit similar temperature dependences before and after irradiation. This may be due to a combination of the highly disordered nature of Ca0.5Na0.5Fe2As2 with large intraband and simultaneous interband scattering as well as the s±-wave nature of short coherence length superconductivity.

IR calibrations for water determination in olivine, r-GeO2, and SiO2 polymorphs

NASA Astrophysics Data System (ADS)

Thomas, Sylvia-Monique; Koch-Müller, Monika; Reichart, Patrick; Rhede, Dieter; Thomas, Rainer; Wirth, Richard; Matsyuk, Stanislav

2009-10-01

Mineral-specific IR absorption coefficients were calculated for natural and synthetic olivine, SiO2 polymorphs, and GeO2 with specific isolated OH point defects using quantitative data from independent techniques such as proton-proton scattering, confocal Raman spectroscopy, and secondary ion mass spectrometry. Moreover, we present a routine to detect OH traces in anisotropic minerals using Raman spectroscopy combined with the “Comparator Technique”. In case of olivine and the SiO2 system, it turns out that the magnitude of ɛ for one structure is independent of the type of OH point defect and therewith the peak position (quartz ɛ = 89,000 ± 15,000 text{l} text{mol}_{{text{H}_2}text{O}}^{-1} text{cm}^{-2}), but it varies as a function of structure (coesite ɛ = 214,000 ± 14,000 text{l} text{mol}_{{text{H}_2}text{O}}^{-1} text{cm}^{-2}; stishovite ɛ = 485,000 ± 109,000 text{l} text{mol}_{{text{H}_2}text{O}}^{-1} text{cm}^{-2}). Evaluation of data from this study confirms that not using mineral-specific IR calibrations for the OH quantification in nominally anhydrous minerals leads to inaccurate estimations of OH concentrations, which constitute the basis for modeling the Earth’s deep water cycle.

Defect quasi Fermi level control-based CN reduction in GaN: Evidence for the role of minority carriers

NASA Astrophysics Data System (ADS)

Reddy, Pramod; Kaess, Felix; Tweedie, James; Kirste, Ronny; Mita, Seiji; Collazo, Ramon; Sitar, Zlatko

2017-10-01

Compensating point defect reduction in wide bandgap semiconductors is possible by above bandgap illumination based defect quasi Fermi level (dQFL) control. The point defect control technique employs excess minority carriers that influence the dQFL of the compensator, increase the corresponding defect formation energy, and consequently are responsible for point defect reduction. Previous studies on various defects in GaN and AlGaN have shown good agreement with the theoretical model, but no direct evidence for the role of minority carriers was provided. In this work, we provide direct evidence for the role of minority carriers in reducing point defects by studying the predicted increase in work done against defect (CN-1) formation with the decrease in the Fermi level (free carrier concentration) in Si doped GaN at a constant illumination intensity. Comparative defect photoluminescence measurements on illuminated and dark regions of GaN show an excellent quantitative agreement with the theory by exhibiting a greater reduction in yellow luminescence attributed to CN-1 at lower doping, thereby providing conclusive evidence for the role of the minority carriers in Fermi level control-based point defect reduction.

Guided wave crack detection and size estimation in stiffened structures

NASA Astrophysics Data System (ADS)

Bhuiyan, Md Yeasin; Faisal Haider, Mohammad; Poddar, Banibrata; Giurgiutiu, Victor

2018-03-01

Structural health monitoring (SHM) and nondestructive evaluation (NDE) deals with the nondestructive inspection of defects, corrosion, leaks in engineering structures by using ultrasonic guided waves. In the past, simplistic structures were often considered for analyzing the guided wave interaction with the defects. In this study, we focused on more realistic and relatively complicated structure for detecting any defect by using a non-contact sensing approach. A plate with a stiffener was considered for analyzing the guided wave interactions. Piezoelectric wafer active transducers were used to produce excitation in the structures. The excitation generated the multimodal guided waves (aka Lamb waves) that propagate in the plate with stiffener. The presence of stiffener in the plate generated scattered waves. The direct wave and the additional scattered waves from the stiffener were experimentally recorded and studied. These waves were considered as a pristine case in this research. A fine horizontal semi-circular crack was manufactured by using electric discharge machining in the same stiffener. The presence of crack in the stiffener produces additional scattered waves as well as trapped waves. These scattered waves and trapped wave modes from the cracked stiffener were experimentally measured by using a scanning laser Doppler vibrometer (SLDV). These waves were analyzed and compared with that from the pristine case. The analyses suggested that both size and shape of the horizontal crack may be predicted from the pattern of the scattered waves. Different features (reflection, transmission, and mode-conversion) of the scattered wave signals are analyzed. We found direct transmission feature for incident A0 wave mode and modeconversion feature for incident S0 mode are most suitable for detecting the crack in the stiffener. The reflection feature may give a better idea of sizing the crack.

Formation Energies of Native Point Defects in Strained-Layer Superlattices (Postprint)

DTIC Science & Technology

2017-06-05

AFRL-RX-WP-JA-2017-0217 FORMATION ENERGIES OF NATIVE POINT DEFECTS IN STRAINED-LAYER SUPERLATTICES (POSTPRINT) Zhi-Gang Yu...2016 Interim 11 September 2013 – 5 November 2016 4. TITLE AND SUBTITLE FORMATION ENERGIES OF NATIVE POINT DEFECTS IN STRAINED-LAYER SUPERLATTICES...native point defect (NPD) formation energies and absence of mid-gap levels. In this Letter we use first-principles calculations to study the formation

Formation Energies of Native Point Defects in Strained layer Superlattices (Postprint)

DTIC Science & Technology

2017-06-05

AFRL-RX-WP-JA-2017-0440 FORMATION ENERGIES OF NATIVE POINT DEFECTS IN STRAINED-LAYER SUPERLATTICES (POSTPRINT) Zhi Gang Yu...2017 Interim 11 September 2013 – 31 May 2017 4. TITLE AND SUBTITLE FORMATION ENERGIES OF NATIVE POINT DEFECTS IN STRAINED-LAYER SUPERLATTICES...Hamiltonian, tight-binding Hamiltonian, and Green’s function techniques to obtain energy levels arising from native point defects (NPDs) in InAs-GaSb and

Glassy behavior and dynamic tweed in defect-free multiferroics

NASA Astrophysics Data System (ADS)

Wang, Xiaofei; Salje, Ekhard K. H.; Sun, Jun; Ding, Xiangdong

2018-01-01

Multiferroics often show significant elastic fluctuations even when the transition is strongly stepwise. Molecular dynamics simulations of a generic toy model show the appearance of tweed nanostructures (cross hatched patterns) in the paraelastic phase just above the transition point. This tweed lowers the elastic modulus C12 when approaching the transition temperature. The spatial and temporal correlations of the tweed structure follow the Vogel-Fulcher relationship, and the Vogel-Fulcher temperature is slightly below the transition temperature Ttrans, preventing this glassy state to freeze completely. Spatial correlations of shear strain show that the size of tweed patches reaches about eight lattice spacings near Ttrans. Cross- and rod-shaped diffuse scattering, similar to that in relaxors, emerges around {hh0}* and {h00}* Bragg reflections. The viscosity of the sample increases dramatically at the transition point with a significant precursor increase in the tweed regime.

Lithium-ion drifting: Application to the study of point defects in floating-zone silicon

NASA Technical Reports Server (NTRS)

Walton, J. T.; Wong, Y. K.; Zulehner, W.

1997-01-01

The use of lithium-ion (Li(+)) drifting to study the properties of point defects in p-type Floating-Zone (FZ) silicon crystals is reported. The Li(+) drift technique is used to detect the presence of vacancy-related defects (D defects) in certain p-type FZ silicon crystals. SUPREM-IV modeling suggests that the silicon point defect diffusivities are considerably higher than those commonly accepted, but are in reasonable agreement with values recently proposed. These results demonstrate the utility of Li(+) drifting in the study of silicon point defect properties in p-type FZ crystals. Finally, a straightforward measurement of the Li(+) compensation depth is shown to yield estimates of the vacancy-related defect concentration in p-type FZ crystals.

Solid-State Division progress report for period ending March 31, 1983

DOE Office of Scientific and Technical Information (OSTI.GOV)

Green, P.H.; Watson, D.M.

1983-09-01

Progress and activities are reported on: theoretical solid-state physics (surfaces; electronic, vibrational, and magnetic properties; particle-solid interactions; laser annealing), surface and near-surface properties of solids (surface, plasma-material interactions, ion implantation and ion-beam mixing, pulsed-laser and thermal processing), defects in solids (radiation effects, fracture, impurities and defects, semiconductor physics and photovoltaic conversion), transport properties of solids (fast-ion conductors, superconductivity, mass and charge transport in materials), neutron scattering (small-angle scattering, lattice dynamics, magnetic properties, structure and instrumentation), and preparation and characterization of research materials (growth and preparative methods, nuclear waste forms, special materials). (DLC)

Point defects in Cd(Zn)Te and TlBr: Theory

NASA Astrophysics Data System (ADS)

Lordi, Vincenzo

2013-09-01

The effects of various crystal defects on the performances of CdTe, CdZnxTe (CZT), and TlBr for room-temperature high-energy radiation detection are examined using first-principles theoretical methods. The predictive, parameter-free, atomistic approaches used provide fundamental understanding of defect properties that are difficult to measure and also allow rapid screening of possibilities for material engineering, such as optimal doping and annealing conditions. Several recent examples from the author's work are reviewed, including: (i) accurate calculations of the thermodynamic and electronic properties of native point defects and point defect complexes in CdTe and CZT; (ii) the effects of Zn alloying on the native point defect properties in CZT; (iii) point defect diffusion and binding leading to Te clustering in Cd(Zn)Te; (iv) the profound effect of native point defects—principally vacancies—on the intrinsic material properties of TlBr, particularly its electronic and ionic conductivity; and (v) a study on doping TlBr to independently control the electronic and ionic conductivity.

Optical probe for porosity defect detection on inner diameter surfaces of machined bores

NASA Astrophysics Data System (ADS)

Kulkarni, Ojas P.; Islam, Mohammed N.; Terry, Fred L.

2010-12-01

We demonstrate an optical probe for detection of porosity inside spool bores of a transmission valve body with diameters down to 5 mm. The probe consists of a graded-index relay rod that focuses a laser beam spot onto the inner surface of the bore. Detectors, placed in the specular and grazing directions with respect to the incident beam, measure the change in scattered intensity when a surface defect is encountered. Based on the scattering signatures in the two directions, the system can also validate the depth of the defect and distinguish porosity from bump-type defects coming out of the metal surface. The system can detect porosity down to a 50-μm lateral dimension and ~40 μm in depth with >3-dB contrast over the background intensity fluctuations. Porosity detection systems currently use manual inspection techniques on the plant floor, and the demonstrated probe provides a noncontact technique that can help automotive manufacturers meet high-quality standards during production.

Relationship between the Amplitude and Phase of a Signal Scattered by a Point-Like Acoustic Inhomogeneity

NASA Astrophysics Data System (ADS)

Burov, V. A.; Morozov, S. A.

2001-11-01

Wave scattering by a point-like inhomogeneity, i.e., a strong inhomogeneity with infinitesimal dimensions, is described. This type of inhomogeneity model is used in investigating the point-spread functions of different algorithms and systems. Two approaches are used to derive the rigorous relationship between the amplitude and phase of a signal scattered by a point-like acoustic inhomogeneity. The first approach is based on a Marchenko-type equation. The second approach uses the scattering by a scatterer whose size decreases simultaneously with an increase in its contrast. It is shown that the retarded and advanced waves are scattered differently despite the relationship between the phases of the corresponding scattered waves.

Interface with weakly singular points always scatter

NASA Astrophysics Data System (ADS)

Li, Long; Hu, Guanghui; Yang, Jiansheng

2018-07-01

Assume that a bounded scatterer is embedded into an infinite homogeneous isotropic background medium in two dimensions. The refractive index function is supposed to be piecewise constant. If the scattering interface contains a weakly singular point, we prove that the scattered field cannot vanish identically. This implies the absence of non-scattering energies for piecewise analytic interfaces with one singular point. Local uniqueness is obtained for shape identification problems in inverse medium scattering with a single far-field pattern.

Effect of C and N Addition on Thermoelectric Properties of TiNiSn Half-Heusler Compounds.

PubMed

Dow, Hwan Soo; Kim, Woo Sik; Shin, Weon Ho

2018-02-08

We investigated the thermoelectric properties of the ternary half-Heusler compound, TiNiSn, when introducing C and N. The addition of C or N to TiNiSn leads to an enhanced power factor and a decreasing lattice thermal conductivity by point defect phonon scattering. The thermoelectric performances of TiNiSn alloys are significantly improved by adding 1 at. % TiN, TiC, and figure of merit ( ZT ) values of 0.43 and 0.34, respectively, can be obtained at 723 K. This increase in thermoelectric performance is very helpful in the commercialization of thermoelectric power generation in the mid-temperature range.

In vacancies in InN grown by plasma-assisted molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Reurings, Floris; Tuomisto, Filip; Gallinat, Chad S.; Koblmüller, Gregor; Speck, James S.

2010-12-01

The authors have applied positron annihilation spectroscopy to study the effect of different growth conditions on vacancy formation in In- and N-polar InN grown by plasma-assisted molecular beam epitaxy. The results suggest that the structural quality of the material and limited diffusion of surface adatoms during growth dictate the In vacancy formation in low electron-density undoped epitaxial InN, while growth conditions and thermodynamics have a less important role, contrary to what is observed in, e.g., GaN. Furthermore, the results imply that in high quality InN, the electron mobility is likely limited not by ionized point defect scattering, but rather by threading dislocations.

Tuneable dielectric films having low electrical losses

DOEpatents

Dimos, Duane Brian; Schwartz, Robert William; Raymond, Mark Victor; Al-Shareef, Husam Niman; Mueller, Carl; Galt, David

2000-01-01

The present invention is directed to a method for forming dielectric thin films having substantially reduced electrical losses at microwave and millimeter wave frequencies relative to conventional dielectric thin films. The reduction in losses is realized by dramatically increasing the grain sizes of the dielectric films, thereby minimizing intergranular scattering of the microwave signal due to grain boundaries and point defects. The increase in grain size is realized by heating the film to a temperature at which the grains experience regrowth. The grain size of the films can be further increased by first depositing the films with an excess of one of the compoents, such that a highly mobile grain boundary phase is formed.

Localised surface plasmon-like resonance generated by microwave electromagnetic waves in pipe defects

NASA Astrophysics Data System (ADS)

Alobaidi, Wissam M.; Nima, Zeid A.; Sandgren, Eric

2018-01-01

Localised surface plasmon (LSP)-like resonance phenomena were simulated in COMSOL Multiphysics™, and the electric field enhancement was evaluated in eight pipe defects using the microwave band from 1.80 to 3.00 GHz and analysed by finite element analysis (FEA). The simulation was carried out, in each defect case, on a pipe that has 762 mm length and 152.4 mm inner diameter, and 12.7 mm pipe wall thickness. Defects were positioned in the middle of the pipe and were named as follows; SD: Square Defect, FCD: fillet corner defect, FD: fillet defect, HCD: half circle defect, TCD: triangle corner defect, TD: triangle defect, ZD: zigzag defect, GD: gear defect. The LSP electric field, and scattering parametric (S21, and S11) waves were evaluated in all cases and found to be strongly dependent on the size and the shape of the defect rather than the pipe and or the medium materials.

Thermal and thermoelectric transport measurements of an individual boron arsenide microstructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, Jaehyun; Sellan, Daniel P.; Ou, Eric

2016-05-16

Recent first principles calculations have predicted that boron arsenide (BAs) can possess an unexpectedly high thermal conductivity that depends sensitively on the crystal size and defect concentration. However, few experimental results have been obtained to verify these predictions. In the present work, we report four-probe thermal and thermoelectric transport measurements of an individual BAs microstructure that was synthesized via a vapor transport method. The measured thermal conductivity was found to decrease slightly with temperature in the range between 250 K and 350 K. The temperature dependence suggests that the extrinsic phonon scattering processes play an important role in addition to intrinsic phonon-phononmore » scattering. The room temperature value of (186 ± 46) W m{sup −1 }K{sup −1} is higher than that of bulk silicon but still a factor of four lower than the calculated result for a defect-free, non-degenerate BAs rod with a similar diameter of 1.15 μm. The measured p-type Seebeck coefficient and thermoelectric power factor are comparable to those of bismuth telluride, which is a commonly used thermoelectric material. The foregoing results also suggest that it is necessary to not only reduce defect and boundary scatterings but also to better understand and control the electron scattering of phonons in order to achieve the predicted ultrahigh intrinsic lattice thermal conductivity of BAs.« less

On the scattering of elastic waves from a non-axisymmetric defect in a coated pipe.

PubMed

Duan, Wenbo; Kirby, Ray; Mudge, Peter

2016-02-01

Viscoelastic coatings are often used to protect pipelines in the oil and gas industry. However, over time defects and areas of corrosion often form in these pipelines and so it is desirable to monitor the structural integrity of these coated pipes using techniques similar to those used on uncoated pipelines. A common approach is to use ultrasonic guided waves that work on the pulse-echo principle; however, the energy in the guided waves can be heavily attenuated by the coating and so significantly reduce the effective range of these techniques. Accordingly, it is desirable to develop a better understanding of how these waves propagate in coated pipes with a view to optimising test methodologies, and so this article uses a hybrid SAFE-finite element approach to model scattering from non-axisymmetric defects in coated pipes. Predictions are generated in the time and frequency domain and it is shown that the longitudinal family of modes is likely to have a longer range in coated pipes when compared to torsional modes. Moreover, it is observed that the energy velocity of modes in a coated pipe is very similar to the group velocity of equivalent modes in uncoated pipes. It is also observed that the coating does not induce any additional mode conversion over and above that seen for an uncoated pipe when an incident wave is scattered by a defect. Accordingly, it is shown that when studying coated pipes one need account only for the attenuation imparted by the coating so that one may normally neglect the effect of coating on modal dispersion and scattering. Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

Multiple scattered radiation emerging from Rayleigh and continental haze layers. I - Radiance, polarization, and neutral points

NASA Technical Reports Server (NTRS)

Kattawar, G. W.; Plass, G. N.; Hitzfelder, S. J.

1976-01-01

The matrix operator method was used to calculate the polarization of radiation scattered on layers of various optical thicknesses, with results compared for Rayleigh scattering and for scattering from a continental haze. In both cases, there are neutral points arising from the zeros of the polarization of single scattered photons at scattering angles of zero and 180 degrees. The angular position of these Rayleigh-like neutral points (RNP) in the sky shows appreciable variation with the optical thickness of the scattering layer for a Rayleigh phase matrix, but only a small variation for haze L phase matrix. Another type of neutral point exists for non-Rayleigh phase functions that is associated with the zeros of the polarization for single scattering which occurs between the end points of the curve. A comparison of radiances calculated from the complete theory of radiative transfer using Stokes vectors with those obtained from the scalar theory shows that differences of the order of 23% may be obtained for Rayleigh scattering, while the largest difference found for a haze L phase function was of the order of 0.1%.

Multiple scattered radiation emerging from continental haze layers. 1: Radiance, polarization, and neutral points

NASA Technical Reports Server (NTRS)

Kattawar, G. W.; Plass, G. N.; Hitzfelder, S. J.

1975-01-01

The complete radiation field is calculated for scattering layers of various optical thicknesses. Results obtained for Rayleigh and haze scattering are compared. Calculated radiances show differences as large as 23% compared to the approximate scalar theory of radiative transfer, while the same differences are approximately 0.1% for a continental haze phase function. The polarization of reflected and transmitted radiation is given for various optical thicknesses, solar zenith angles, and surface albedos. Two types of neutral points occur for aerosol phase functions. Rayleigh-like neutral points arise from zero polarization that occurs at scattering angles of 0 deg and 180 deg. For Rayleigh phase functions, the position of these points varies with the optical thickness of the scattering layer. Non-Rayleigh neutral points are associated with the zeros of polarization which occur between the end points of the single scattering curve, and are found over a wide range of azimuthal angles.

Effective scheme to determine accurate defect formation energies and charge transition levels of point defects in semiconductors

NASA Astrophysics Data System (ADS)

Yao, Cang Lang; Li, Jian Chen; Gao, Wang; Tkatchenko, Alexandre; Jiang, Qing

2017-12-01

We propose an effective method to accurately determine the defect formation energy Ef and charge transition level ɛ of the point defects using exclusively cohesive energy Ecoh and the fundamental band gap Eg of pristine host materials. We find that Ef of the point defects can be effectively separated into geometric and electronic contributions with a functional form: Ef=χ Ecoh+λ Eg , where χ and λ are dictated by the geometric and electronic factors of the point defects (χ and λ are defect dependent). Such a linear combination of Ecoh and Eg reproduces Ef with an accuracy better than 5% for electronic structure methods ranging from hybrid density-functional theory (DFT) to many-body random-phase approximation (RPA) and experiments. Accordingly, ɛ is also determined by Ecoh/Eg and the defect geometric/electronic factors. The identified correlation is rather general for monovacancies and interstitials, which holds in a wide variety of semiconductors covering Si, Ge, phosphorenes, ZnO, GaAs, and InP, and enables one to obtain reliable values of Ef and ɛ of the point defects for RPA and experiments based on semilocal DFT calculations.

Elastic dipoles of point defects from atomistic simulations

NASA Astrophysics Data System (ADS)

Varvenne, Céline; Clouet, Emmanuel

2017-12-01

The interaction of point defects with an external stress field or with other structural defects is usually well described within continuum elasticity by the elastic dipole approximation. Extraction of the elastic dipoles from atomistic simulations is therefore a fundamental step to connect an atomistic description of the defect with continuum models. This can be done either by a fitting of the point-defect displacement field, by a summation of the Kanzaki forces, or by a linking equation to the residual stress. We perform here a detailed comparison of these different available methods to extract elastic dipoles, and show that they all lead to the same values when the supercell of the atomistic simulations is large enough and when the anharmonic region around the point defect is correctly handled. But, for small simulation cells compatible with ab initio calculations, only the definition through the residual stress appears tractable. The approach is illustrated by considering various point defects (vacancy, self-interstitial, and hydrogen solute atom) in zirconium, using both empirical potentials and ab initio calculations.

On the interplay of point defects and Cd in non-polar ZnCdO films

NASA Astrophysics Data System (ADS)

Zubiaga, A.; Reurings, F.; Tuomisto, F.; Plazaola, F.; García, J. A.; Kuznetsov, A. Yu.; Egger, W.; Zúñiga-Pérez, J.; Muñoz-Sanjosé, V.

2013-01-01

Non-polar ZnCdO films, grown over m- and r-sapphire with a Cd concentration ranging between 0.8% and 5%, have been studied by means of slow positron annihilation spectroscopy (PAS) combined with chemical depth profiling by secondary ion mass spectroscopy and Rutherford back-scattering. Vacancy clusters and Zn vacancies with concentrations up to 1017 cm-3 and 1018 cm-3, respectively, have been measured inside the films. Secondary ion mass spectroscopy results show that most Cd stays inside the ZnCdO film but the diffused atoms can penetrate up to 1.3 μm inside the ZnO buffer. PAS results give an insight to the structure of the meta-stable ZnCdO above the thermodynamical solubility limit of 2%. A correlation between the concentration of vacancy clusters and Cd has been measured. The concentration of Zn vacancies is one order of magnitude larger than in as-grown non-polar ZnO films and the vacancy cluster are, at least partly, created by the aggregation of smaller Zn vacancy related defects. The Zn vacancy related defects and the vacancy clusters accumulate around the Cd atoms as a way to release the strain induced by the substitutional CdZn in the ZnO crystal.

Ultra-low Thermal Conductivity in Si/Ge Hierarchical Superlattice Nanowire.

PubMed

Mu, Xin; Wang, Lili; Yang, Xueming; Zhang, Pu; To, Albert C; Luo, Tengfei

2015-11-16

Due to interfacial phonon scattering and nanoscale size effect, silicon/germanium (Si/Ge) superlattice nanowire (SNW) can have very low thermal conductivity, which is very attractive for thermoelectrics. In this paper, we demonstrate using molecular dynamics simulations that the already low thermal conductivity of Si/Ge SNW can be further reduced by introducing hierarchical structure to form Si/Ge hierarchical superlattice nanowire (H-SNW). The structural hierarchy introduces defects to disrupt the periodicity of regular SNW and scatters coherent phonons, which are the key contributors to thermal transport in regular SNW. Our simulation results show that periodically arranged defects in Si/Ge H-SNW lead to a ~38% reduction of the already low thermal conductivity of regular Si/Ge SNW. By randomizing the arrangement of defects and imposing additional surface complexities to enhance phonon scattering, further reduction in thermal conductivity can be achieved. Compared to pure Si nanowire, the thermal conductivity reduction of Si/Ge H-SNW can be as large as ~95%. It is concluded that the hierarchical structuring is an effective way of reducing thermal conductivity significantly in SNW, which can be a promising path for improving the efficiency of Si/Ge-based SNW thermoelectrics.

Ultra-low Thermal Conductivity in Si/Ge Hierarchical Superlattice Nanowire

PubMed Central

Mu, Xin; Wang, Lili; Yang, Xueming; Zhang, Pu; To, Albert C.; Luo, Tengfei

2015-01-01

Due to interfacial phonon scattering and nanoscale size effect, silicon/germanium (Si/Ge) superlattice nanowire (SNW) can have very low thermal conductivity, which is very attractive for thermoelectrics. In this paper, we demonstrate using molecular dynamics simulations that the already low thermal conductivity of Si/Ge SNW can be further reduced by introducing hierarchical structure to form Si/Ge hierarchical superlattice nanowire (H-SNW). The structural hierarchy introduces defects to disrupt the periodicity of regular SNW and scatters coherent phonons, which are the key contributors to thermal transport in regular SNW. Our simulation results show that periodically arranged defects in Si/Ge H-SNW lead to a ~38% reduction of the already low thermal conductivity of regular Si/Ge SNW. By randomizing the arrangement of defects and imposing additional surface complexities to enhance phonon scattering, further reduction in thermal conductivity can be achieved. Compared to pure Si nanowire, the thermal conductivity reduction of Si/Ge H-SNW can be as large as ~95%. It is concluded that the hierarchical structuring is an effective way of reducing thermal conductivity significantly in SNW, which can be a promising path for improving the efficiency of Si/Ge-based SNW thermoelectrics. PMID:26568511

Developing a more useful surface quality metric for laser optics

NASA Astrophysics Data System (ADS)

Turchette, Quentin; Turner, Trey

2011-02-01

Light scatter due to surface defects on laser resonator optics produces losses which lower system efficiency and output power. The traditional methodology for surface quality inspection involves visual comparison of a component to scratch and dig (SAD) standards under controlled lighting and viewing conditions. Unfortunately, this process is subjective and operator dependent. Also, there is no clear correlation between inspection results and the actual performance impact of the optic in a laser resonator. As a result, laser manufacturers often overspecify surface quality in order to ensure that optics will not degrade laser performance due to scatter. This can drive up component costs and lengthen lead times. Alternatively, an objective test system for measuring optical scatter from defects can be constructed with a microscope, calibrated lighting, a CCD detector and image processing software. This approach is quantitative, highly repeatable and totally operator independent. Furthermore, it is flexible, allowing the user to set threshold levels as to what will or will not constitute a defect. This paper details how this automated, quantitative type of surface quality measurement can be constructed, and shows how its results correlate against conventional loss measurement techniques such as cavity ringdown times.

Actinic defect counting statistics over 1-cm2 area of EUVL mask blank

NASA Astrophysics Data System (ADS)

Jeong, Seongtae; Lai, Chih-wei; Rekawa, Senajith; Walton, Christopher C.; Bokor, Jeffrey

2000-07-01

As a continuation of comparison experiments between EUV inspection and visible inspection of defects on EUVL mask blanks, we report on the result of an experiment where the EUV defect inspection tool is used to perform at-wavelength defect counting over 1 cm2 of EUVL mask blank. Initial EUV inspection found five defects over the scanned area and the subsequent optical scattering inspection was able to detect all of the five defects. Therefore, if there are any defects that are only detectable by EUV inspection, the density is lower than the order of unity per cm2. An upgrade path to substantially increase the overall throughput of the EUV inspection system is also identified in the manuscript.

Invisible defects in complex crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Longhi, Stefano, E-mail: stefano.longhi@fisi.polimi.it; Della Valle, Giuseppe

2013-07-15

We show that invisible localized defects, i.e. defects that cannot be detected by an outside observer, can be realized in a crystal with an engineered imaginary potential at the defect site. The invisible defects are synthesized by means of supersymmetric (Darboux) transformations of an ordinary crystal using band-edge wavefunctions to construct the superpotential. The complex crystal has an entire real-valued energy spectrum and Bragg scattering is not influenced by the defects. An example of complex crystal synthesis is presented for the Mathieu potential. -- Highlights: •We show the existence of invisible localized defects in complex crystals. •They turn out tomore » be fully invisible to Bloch waves belonging to any lattice band. •An example of invisible defect is presented for a PT-symmetric Mathieu crystal.« less

Nanoscale structure in AgSbTe2 determined by diffuse elastic neutron scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Specht, Eliot D; Ma, Jie; Delaire, Olivier A

2015-01-01

Diffuse elastic neutron scattering measurements confirm that AgSbTe2 has a hierarchical structure, with defects on length scales from nanometers to microns. While scattering from mesoscale structure is consistent with previously-proposed structures in which Ag and Sb order on a NaCl lattice, more diffuse scattering from nanoscale structure suggests a structural rearrangement in which hexagonal layers form a combination of (ABC), (ABA), and (AAB) stacking sequences. The AgCrSe2 structure is the best-fitting model for the local atomic arrangements.

Decision-Level Fusion of Spatially Scattered Multi-Modal Data for Nondestructive Inspection of Surface Defects

PubMed Central

Heideklang, René; Shokouhi, Parisa

2016-01-01

This article focuses on the fusion of flaw indications from multi-sensor nondestructive materials testing. Because each testing method makes use of a different physical principle, a multi-method approach has the potential of effectively differentiating actual defect indications from the many false alarms, thus enhancing detection reliability. In this study, we propose a new technique for aggregating scattered two- or three-dimensional sensory data. Using a density-based approach, the proposed method explicitly addresses localization uncertainties such as registration errors. This feature marks one of the major of advantages of this approach over pixel-based image fusion techniques. We provide guidelines on how to set all the key parameters and demonstrate the technique’s robustness. Finally, we apply our fusion approach to experimental data and demonstrate its capability to locate small defects by substantially reducing false alarms under conditions where no single-sensor method is adequate. PMID:26784200

Nanoscale electron transport at the surface of a topological insulator.

PubMed

Bauer, Sebastian; Bobisch, Christian A

2016-04-21

The use of three-dimensional topological insulators for disruptive technologies critically depends on the dissipationless transport of electrons at the surface, because of the suppression of backscattering at defects. However, in real devices, defects are unavoidable and scattering at angles other than 180° is allowed for such materials. Until now, this has been studied indirectly by bulk measurements and by the analysis of the local density of states in close vicinity to defect sites. Here, we directly measure the nanoscale voltage drop caused by the scattering at step edges, which occurs if a lateral current flows along a three-dimensional topological insulator. The experiments were performed using scanning tunnelling potentiometry for thin Bi2Se3 films. So far, the observed voltage drops are small because of large contributions of the bulk to the electronic transport. However, for the use of ideal topological insulating thin films in devices, these contributions would play a significant role.

Nanoscale electron transport at the surface of a topological insulator

NASA Astrophysics Data System (ADS)

Bauer, Sebastian; Bobisch, Christian A.

2016-04-01

The use of three-dimensional topological insulators for disruptive technologies critically depends on the dissipationless transport of electrons at the surface, because of the suppression of backscattering at defects. However, in real devices, defects are unavoidable and scattering at angles other than 180° is allowed for such materials. Until now, this has been studied indirectly by bulk measurements and by the analysis of the local density of states in close vicinity to defect sites. Here, we directly measure the nanoscale voltage drop caused by the scattering at step edges, which occurs if a lateral current flows along a three-dimensional topological insulator. The experiments were performed using scanning tunnelling potentiometry for thin Bi2Se3 films. So far, the observed voltage drops are small because of large contributions of the bulk to the electronic transport. However, for the use of ideal topological insulating thin films in devices, these contributions would play a significant role.

Effect of heavy-ion and electron irradiation on properties of Fe-based superconductors

NASA Astrophysics Data System (ADS)

Konczykowski, Marcin

2013-03-01

The introduction of defects by particle irradiation is used to reveal the role of disorder in matter, which is unavoidable in all crystalline solids. In superconductors defects introduce flux pinning, controlling critical current, Jc; as well as pair-breaking scattering, limiting the critical temperature, Tc. To elucidate defect related properties of Fe-based superconductors (FBS) we precede in two types of irradiation: heavy ion (6GeV Pb) to create disorder in the form of amorphous tracks and low temperature electron irradiation (2.5MeV at 20K) to create point like defects. Substantial increase of irreversible magnetization and an upward shift of the irreversibility line are observed after heavy ion irradiation of all FBS investigated to date. In BaK 122 , signatures of a Bose-glass vortex state; angular dependence and variable-range hopping flux creep are revealed. Remarkably, heavy ion irradiation does not depress Tc, however, point-like disorder introduced by electron irradiation does substantially. In isovalently substituted Ba(FeAs1 - xPx) 2 and Ba(Fe1 - x Rux As) 2 crystals, Tc decreases linearly with dose. Suppression to 40 % of initial value of Tc was achieved in Ba(FeAs1 - xPx) 2 . An increase of normal state resistivity is observed and correlated to depression of Tc. Change of superconducting gap structure with disorder was determined from penetration depth measurements, λ (T) dependence, at various stages of irradiation. Linear in T variation of pristine samples, indicative of the presence of nodes in gap, turned at low irradiation dose to exponential T variation, indicative of a fully gaped state. T2 variation of λ is observed at higher doses. This behaviour is incompatible with symmetry-imposed nodes of d-wave pairing but consistent with S + / - , S + / + mechanisms. This is the first observation of the impurity-induced node lifting expected in anisotropic s-wave superconductors

Point Defect Properties of Cd(Zn)Te and TlBr for Room-Temperature Gamma Radiation Detectors

NASA Astrophysics Data System (ADS)

Lordi, Vincenzo

2013-03-01

The effects of various crystal defects in CdTe, Cd1-xZnxTe (CZT), and TlBr are critical for their performance as room-temperature gamma radiation detectors. We use predictive first principles theoretical methods to provide fundamental, atomic scale understanding of the defect properties of these materials to enable design of optimal growth and processing conditions, such as doping, annealing, and stoichiometry. Several recent cases will be reviewed, including (i) accurate calculations of the thermodynamic and electronic properties of native point defects and point defect complexes in CdTe and CZT; (ii) the effects of Zn alloying on the native point defect properties of CZT; (iii) point defect diffusion and binding related to Te clustering in Cd(Zn)Te; (iv) the profound effect of native point defects--principally vacancies--on the intrinsic material properties of TlBr, particularly electronic and ionic conductivity; (v) tailored doping of TlBr to independently control the electronic and ionic conductivity; and (vi) the effects of metal impurities on the electronic properties and device performance of TlBr detectors. Prepared by LLNL under Contract DE-AC52-07NA27344 with support from the National Nuclear Security Administration Office of Nonproliferation and Verification Research and Development NA-22.

Scanning Tunneling Microscopy Observation of Phonon Condensate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Altfeder, Igor; Balatsky, Alexander V.; Voevodin, Andrey A.

Using quantum tunneling of electrons into vibrating surface atoms, phonon oscillations can be observed on the atomic scale. Phonon interference patterns with unusually large signal amplitudes have been revealed by scanning tunneling microscopy in intercalated van der Waals heterostructures. Our results show that the effective radius of these phonon quasi-bound states, the real-space distribution of phonon standing wave amplitudes, the scattering phase shifts, and the nonlinear intermode coupling strongly depend on the presence of defect-induced scattering resonance. The observed coherence of these quasi-bound states most likely arises from phase- and frequency-synchronized dynamics of all phonon modes, and indicates the formationmore » of many-body condensate of optical phonons around resonant defects. We found that increasing the strength of the scattering resonance causes the increase of the condensate droplet radius without affecting the condensate fraction inside it. The condensate can be observed at room temperature.« less

Scanning Tunneling Microscopy Observation of Phonon Condensate

PubMed Central

Altfeder, Igor; Voevodin, Andrey A.; Check, Michael H.; Eichfeld, Sarah M.; Robinson, Joshua A.; Balatsky, Alexander V.

2017-01-01

Using quantum tunneling of electrons into vibrating surface atoms, phonon oscillations can be observed on the atomic scale. Phonon interference patterns with unusually large signal amplitudes have been revealed by scanning tunneling microscopy in intercalated van der Waals heterostructures. Our results show that the effective radius of these phonon quasi-bound states, the real-space distribution of phonon standing wave amplitudes, the scattering phase shifts, and the nonlinear intermode coupling strongly depend on the presence of defect-induced scattering resonance. The observed coherence of these quasi-bound states most likely arises from phase- and frequency-synchronized dynamics of all phonon modes, and indicates the formation of many-body condensate of optical phonons around resonant defects. We found that increasing the strength of the scattering resonance causes the increase of the condensate droplet radius without affecting the condensate fraction inside it. The condensate can be observed at room temperature. PMID:28225066

Scanning Tunneling Microscopy Observation of Phonon Condensate

DOE PAGES

Altfeder, Igor; Balatsky, Alexander V.; Voevodin, Andrey A.; ...

2017-02-22

Using quantum tunneling of electrons into vibrating surface atoms, phonon oscillations can be observed on the atomic scale. Phonon interference patterns with unusually large signal amplitudes have been revealed by scanning tunneling microscopy in intercalated van der Waals heterostructures. Our results show that the effective radius of these phonon quasi-bound states, the real-space distribution of phonon standing wave amplitudes, the scattering phase shifts, and the nonlinear intermode coupling strongly depend on the presence of defect-induced scattering resonance. The observed coherence of these quasi-bound states most likely arises from phase- and frequency-synchronized dynamics of all phonon modes, and indicates the formationmore » of many-body condensate of optical phonons around resonant defects. We found that increasing the strength of the scattering resonance causes the increase of the condensate droplet radius without affecting the condensate fraction inside it. The condensate can be observed at room temperature.« less

Accurate modeling of defects in graphene transport calculations

NASA Astrophysics Data System (ADS)

Linhart, Lukas; Burgdörfer, Joachim; Libisch, Florian

2018-01-01

We present an approach for embedding defect structures modeled by density functional theory into large-scale tight-binding simulations. We extract local tight-binding parameters for the vicinity of the defect site using Wannier functions. In the transition region between the bulk lattice and the defect the tight-binding parameters are continuously adjusted to approach the bulk limit far away from the defect. This embedding approach allows for an accurate high-level treatment of the defect orbitals using as many as ten nearest neighbors while keeping a small number of nearest neighbors in the bulk to render the overall computational cost reasonable. As an example of our approach, we consider an extended graphene lattice decorated with Stone-Wales defects, flower defects, double vacancies, or silicon substitutes. We predict distinct scattering patterns mirroring the defect symmetries and magnitude that should be experimentally accessible.

Role of pre-existing point defects on primary damage production and amorphization in silicon carbide (β-SiC)

NASA Astrophysics Data System (ADS)

Sahoo, Deepak Ranjan; Szlufarska, Izabela; Morgan, Dane; Swaminathan, Narasimhan

2018-01-01

Molecular dynamics simulations of displacement cascades were conducted to study the effect of point defects on the primary damage production in β-SiC. Although all types of point defects and Frenkel pairs were considered, Si interstitials and Si Frenkel pairs were unstable and hence excluded from the cascade studies. Si (C) vacancies had the maximum influence, enhancing C (Si) antisites and suppressing C interstitial production, when compared to the sample without any defects. The intracascade recombination mechanisms, in the presence of pre-existing defects, is explored by examining the evolution of point defects during the cascade. To ascertain the role of the unstable Si defects on amorphization, simulations involving explicit displacements of Si atoms were conducted. The dose to amorphization with only Si displacements was much lower than what was observed with only C displacements. The release of elastic energy accumulated due to Si defects, is found to be the amorphizing mechanism.

Effects of Defect Size and Number Density on the Transmission and Reflection of Guided Elastic Waves

DTIC Science & Technology

2016-04-22

localized region, a photoacoustic source generates elastic waves on one side of the damaged region, and then two ultrasound transducers measure the...where the defects are of the same order as the wavelength of the ultrasound , we find ourselves confronted with Mie scattering, which has weaker

Identifying and counting point defects in carbon nanotubes.

PubMed

Fan, Yuwei; Goldsmith, Brett R; Collins, Philip G

2005-12-01

The prevailing conception of carbon nanotubes and particularly single-walled carbon nanotubes (SWNTs) continues to be one of perfectly crystalline wires. Here, we demonstrate a selective electrochemical method that labels point defects and makes them easily visible for quantitative analysis. High-quality SWNTs are confirmed to contain one defect per 4 microm on average, with a distribution weighted towards areas of SWNT curvature. Although this defect density compares favourably to high-quality, silicon single-crystals, the presence of a single defect can have tremendous electronic effects in one-dimensional conductors such as SWNTs. We demonstrate a one-to-one correspondence between chemically active point defects and sites of local electronic sensitivity in SWNT circuits, confirming the expectation that individual defects may be critical to understanding and controlling variability, noise and chemical sensitivity in SWNT electronic devices. By varying the SWNT synthesis technique, we further show that the defect spacing can be varied over orders of magnitude. The ability to detect and analyse point defects, especially at very low concentrations, indicates the promise of this technique for quantitative process analysis, especially in nanoelectronics development.

Slow Noncollinear Coulomb Scattering in the Vicinity of the Dirac Point in Graphene.

PubMed

König-Otto, J C; Mittendorff, M; Winzer, T; Kadi, F; Malic, E; Knorr, A; Berger, C; de Heer, W A; Pashkin, A; Schneider, H; Helm, M; Winnerl, S

2016-08-19

The Coulomb scattering dynamics in graphene in energetic proximity to the Dirac point is investigated by polarization resolved pump-probe spectroscopy and microscopic theory. Collinear Coulomb scattering rapidly thermalizes the carrier distribution in k directions pointing radially away from the Dirac point. Our study reveals, however, that, in almost intrinsic graphene, full thermalization in all directions relying on noncollinear scattering is much slower. For low photon energies, carrier-optical-phonon processes are strongly suppressed and Coulomb mediated noncollinear scattering is remarkably slow, namely on a ps time scale. This effect is very promising for infrared and THz devices based on hot carrier effects.

System for characterizing semiconductor materials and photovoltaic device

DOEpatents

Sopori, B.L.

1996-12-03

Apparatus for detecting and mapping defects in the surfaces of polycrystalline material in a manner that distinguishes dislocation pits from grain boundaries includes a first laser of a first wavelength for illuminating a wide spot on the surface of the material, a second laser of a second relatively shorter wavelength for illuminating a relatively narrower spot on the surface of the material, a light integrating sphere with apertures for capturing light scattered by etched dislocation pits in an intermediate range away from specular reflection while allowing light scattered by etched grain boundaries in a near range from specular reflection to pass through, and optical detection devices for detecting and measuring intensities of the respective intermediate scattered light and near specular scattered light. A center blocking aperture or filter can be used to screen out specular reflected light, which would be reflected by nondefect portions of the polycrystalline material surface. An X-Y translation stage for mounting the polycrystalline material and signal processing and computer equipment accommodate raster mapping, recording, and displaying of respective dislocation and grain boundary defect densities. A special etch procedure is included, which prepares the polycrystalline material surface to produce distinguishable intermediate and near specular light scattering in patterns that have statistical relevance to the dislocation and grain boundary defect densities. A reflectance measurement of the piece of material is obtained by adding together the signals from the optical detection devices. In the case where the piece of material includes a photovoltaic device, the current induced in the device by the illuminating light can be measured with a current sensing amplifier after the light integrating sphere is moved away from the device. 22 figs.

System for characterizing semiconductor materials and photovoltaic device

DOEpatents

Sopori, Bhushan L.

1996-01-01

Apparatus for detecting and mapping defects in the surfaces of polycrystalline material in a manner that distinguishes dislocation pits from grain boundaries includes a first laser of a first wavelength for illuminating a wide spot on the surface of the material, a second laser of a second relatively shorter wavelength for illuminating a relatively narrower spot on the surface of the material, a light integrating sphere with apertures for capturing light scattered by etched dislocation pits in an intermediate range away from specular reflection while allowing light scattered by etched grain boundaries in a near range from specular reflection to pass through, and optical detection devices for detecting and measuring intensities of the respective intermediate scattered light and near specular scattered light. A center blocking aperture or filter can be used to screen out specular reflected light, which would be reflected by nondefect portions of the polycrystalline material surface. An X-Y translation stage for mounting the polycrystalline material and signal processing and computer equipment accommodate raster mapping, recording, and displaying of respective dislocation and grain boundary defect densities. A special etch procedure is included, which prepares the polycrystalline material surface to produce distinguishable intermediate and near specular light scattering in patterns that have statistical relevance to the dislocation and grain boundary defect densities. A reflectance measurement of the piece of material is obtained by adding together the signals from the optical detection devices. In the case where the piece of material includes a photovoltaic device, the current induced in the device by the illuminating light can be measured with a current sensing amplifier after the light integrating sphere is moved away from the device.

Bound states, scattering states, and resonant states in PT -symmetric open quantum systems

NASA Astrophysics Data System (ADS)

Garmon, Savannah; Gianfreda, Mariagiovanna; Hatano, Naomichi

2015-08-01

We study a simple open quantum system with a PT -symmetric defect potential as a prototype in order to illustrate a number of general features of PT -symmetric open quantum systems; however, the potential itself could be mimicked by a number of PT systems that have been experimentally studied quite recently. One key feature is the resonance in continuum (RIC), which appears in both the discrete spectrum and the scattering spectrum of such systems. The RIC wave function forms a standing wave extending throughout the spatial extent of the system and in this sense represents a resonance between the open environment associated with the leads of our model and the central PT -symmetric potential. We also illustrate that as one deforms the system parameters, the RIC may exit the continuum by splitting into a bound state and a virtual bound state at the band edge, a process which should be experimentally observable. We also study the exceptional points appearing in the discrete spectrum at which two eigenvalues coalesce; we categorize these as either EP2As, at which two real-valued solutions coalesce before becoming complex-valued, and EP2Bs, for which the two solutions are complex on either side of the exceptional point. The EP2As are associated with PT -symmetry breaking; we argue that these are more stable against parameter perturbation than the EP2Bs. We also study complex-valued solutions of the discrete spectrum for which the wave function is nevertheless spatially localized, something that is not allowed in traditional open quantum systems; we illustrate that these may form quasibound states in continuum under some circumstances. We also study the scattering properties of the system, including states that support invisible propagation and some general features of perfect transmission states. We finally use our model as a prototype for the construction of scattering states that satisfy PT -symmetric boundary conditions; while these states do not conserve the traditional probability current, we introduce the PT current which is preserved. The perfect transmission states appear as a special case of the PT -symmetric scattering states.

New Insights into Intrinsic Point Defects in V2VI3 Thermoelectric Materials.

PubMed

Zhu, Tiejun; Hu, Lipeng; Zhao, Xinbing; He, Jian

2016-07-01

Defects and defect engineering are at the core of many regimes of material research, including the field of thermoelectric study. The 60-year history of V 2 VI 3 thermoelectric materials is a prime example of how a class of semiconductor material, considered mature several times, can be rejuvenated by better understanding and manipulation of defects. This review aims to provide a systematic account of the underexplored intrinsic point defects in V 2 VI 3 compounds, with regard to (i) their formation and control, and (ii) their interplay with other types of defects towards higher thermoelectric performance. We herein present a convincing case that intrinsic point defects can be actively controlled by extrinsic doping and also via compositional, mechanical, and thermal control at various stages of material synthesis. An up-to-date understanding of intrinsic point defects in V 2 VI 3 compounds is summarized in a (χ, r)-model and applied to elucidating the donor-like effect. These new insights not only enable more innovative defect engineering in other thermoelectric materials but also, in a broad context, contribute to rational defect design in advanced functional materials at large.

Acquisition and analysis of angle-beam wavefield data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dawson, Alexander J.; Michaels, Jennifer E.; Levine, Ross M.

2014-02-18

Angle-beam ultrasonic testing is a common practical technique used for nondestructive evaluation to detect, locate, and characterize a variety of material defects and damage. Greater understanding of the both the incident wavefield produced by an angle-beam transducer and the subsequent scattering from a variety of defects and geometrical features is anticipated to increase the reliability of data interpretation. The focus of this paper is on acquiring and analyzing propagating waves from angle-beam transducers in simple, defect-free plates as a first step in the development of methods for flaw characterization. Unlike guided waves, which excite the plate throughout its thickness, angle-beammore » bulk waves bounce back and forth between the plate surfaces, resulting in the well-known multiple “skips” or “V-paths.” The experimental setup consists of a laser vibrometer mounted on an XYZ scanning stage, which is programmed to move point-to-point on a rectilinear grid to acquire waveform data. Although laser vibrometry is now routinely used to record guided waves for which the frequency content is below 1 MHz, it is more challenging to acquire higher frequency bulk waves in the 1–10 MHz range. Signals are recorded on the surface of an aluminum plate that were generated from a 5 MHz, 65° refracted angle, shear wave transducer-wedge combination. Data are analyzed directly in the x-t domain, via a slant stack Radon transform in the τ-p (offset time-slowness) domain, and via a 2-D Fourier transform in the ω-k domain, thereby enabling identification of specific arrivals and modes. Results compare well to those expected from a simple ray tracing analysis except for the unexpected presence of a strong Rayleigh wave.« less

Adsorption and Photodesorption of CO from Charged Point Defects on TiO 2 (110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mu, Rentao; Dahal, Arjun; Wang, Zhi-Tao

Adsorption and photodesorption of weakly-bound carbon monoxide, CO, from reduced and hydroxylated rutile TiO2(110) (r- and h- TiO2(110)) at sub-monolayer coverages is studied with atomically-resolved scanning tunneling microscopy (STM) along with ensemble-averaged temperature-programmed desorption (TPD) and angle-resolved photon-stimulated desorption (PSD) at low temperatures ( 50 K). STM data weighted by the concentration of each kind of adsorption sites on r-TiO2(110) give an adsorption probability which is the highest for the bridging oxygen vacancies (VO) and very low for the Ti5c sites closest to VO. Occupancy of the remaining Ti5c sites with CO is significant, but smaller than for VO. Themore » probability distribution for the different adsorption sites corresponds to a very small difference in CO adsorption energies: < 0.02 eV. We also find that UV irradiation stimulates both diffusion and desorption of CO at low temperature. CO photodesorbs primarily from the vacancies with a bi-modal angular distribution. In addition to a major, normal to the surface component, there is a broader cosine component indicating scattering from the surface which likely also leads to photo-stimulated diffusion. Hydroxylation of VO’s does not significantly change the CO PSD yield and angular distribution, indicating that not atomic but rather electronic surface defects are involved in the site-specific PSD process. We suggest that photodesorption can be initiated by recombination of photo-generated holes with excess unpaired electrons localized near the surface point-defect (either VO or bridging hydroxyl), leading to the surface atoms rearrangement and ejection of the weakly-bound CO molecules.« less

Experimental evaluation of the ring focus test for X-ray telescopes using AXAF's technology mirror assembly, MSFC CDDF Project No. H20

NASA Technical Reports Server (NTRS)

Zissa, D. E.; Korsch, D.

1986-01-01

A test method particularly suited for X-ray telescopes was evaluated experimentally. The method makes use of a focused ring formed by an annular aperture when using a point source at a finite distance. This would supplement measurements of the best focus image which is blurred when the test source is at a finite distance. The telescope used was the Technology Mirror Assembly of the Advanced X-ray Astrophysis Facility (AXAF) program. Observed ring image defects could be related to the azimuthal location of their sources in the telescope even though in this case the predicted sharp ring was obscured by scattering, finite source size, and residual figure errors.

Tailoring plasmonic properties of gold nanohole arrays for surface-enhanced Raman scattering

PubMed Central

Zheng, Peng; Cushing, Scott K.; Suri, Savan; Wu, Nianqiang

2015-01-01

The wide plasmonic tuning range of nanotriangle and nanohole array patterns fabricated by nanosphere lithography makes them promising in surface-enhanced Raman scattering (SERS) sensors. Unfortunately, it is challenging to optimize these patterns for SERS sensing because their optical response is a complex mixture of localized and propagating surface plasmons. In this paper, transmission and reflection measurements are combined with finite difference time domain simulations to identify and separate each plasmonic mode, discerning which resonance leads to the electromagnetic field enhancement. The SERS enhancement is found to be dominated by the absorption, which is shifted from the transmission and reflection dips usually used as tuning points, and by the ‘gap’ defects formed within the pattern. These effects have different spectral and geometric dependences, forming two optimization curves which can be used to predict the best performance for a given excitation wavelength. The developed model is verified with experimental SERS measurements for several nanohole sizes and periodicities, and then used to give optimal fabrication parameters for a range of measurement conditions. The results will promote the application of two-dimensional plasmonic nanoarrays in SERS sensors. PMID:25586930

Higgs transition from a magnetic Coulomb liquid to a ferromagnet in Yb2Ti2O7

PubMed Central

Chang, Lieh-Jeng; Onoda, Shigeki; Su, Yixi; Kao, Ying-Jer; Tsuei, Ku-Ding; Yasui, Yukio; Kakurai, Kazuhisa; Lees, Martin Richard

2012-01-01

In a class of frustrated magnets known as spin ice, magnetic monopoles emerge as classical defects and interact via the magnetic Coulomb law. With quantum-mechanical interactions, these magnetic charges are carried by fractionalized bosonic quasi-particles, spinons, which can undergo Bose–Einstein condensation through a first-order transition via the Higgs mechanism. Here, we report evidence of a Higgs transition from a magnetic Coulomb liquid to a ferromagnet in single-crystal Yb2Ti2O7. Polarized neutron scattering experiments show that the diffuse [111]-rod scattering and pinch-point features, which develop on cooling are suddenly suppressed below TC~0.21 K, where magnetic Bragg peaks and a full depolarization of the neutron spins are observed with thermal hysteresis, indicating a first-order ferromagnetic transition. Our results are explained on the basis of a quantum spin-ice model, whose high-temperature phase is effectively described as a magnetic Coulomb liquid, whereas the ground state shows a nearly collinear ferromagnetism with gapped spin excitations. PMID:22871811

Scaling of graphene field-effect transistors supported on hexagonal boron nitride: radio-frequency stability as a limiting factor

NASA Astrophysics Data System (ADS)

Feijoo, Pedro C.; Pasadas, Francisco; Iglesias, José M.; Martín, María J.; Rengel, Raúl; Li, Changfeng; Kim, Wonjae; Riikonen, Juha; Lipsanen, Harri; Jiménez, David

2017-12-01

The quality of graphene in nanodevices has increased hugely thanks to the use of hexagonal boron nitride as a supporting layer. This paper studies to which extent hBN together with channel length scaling can be exploited in graphene field-effect transistors (GFETs) to get a competitive radio-frequency (RF) performance. Carrier mobility and saturation velocity were obtained from an ensemble Monte Carlo simulator that accounted for the relevant scattering mechanisms (intrinsic phonons, scattering with impurities and defects, etc). This information is fed into a self-consistent simulator, which solves the drift-diffusion equation coupled with the two-dimensional Poisson’s equation to take full account of short channel effects. Simulated GFET characteristics were benchmarked against experimental data from our fabricated devices. Our simulations show that scalability is supposed to bring to RF performance an improvement that is, however, highly limited by instability. Despite the possibility of a lower performance, a careful choice of the bias point can avoid instability. Nevertheless, maximum oscillation frequencies are still achievable in the THz region for channel lengths of a few hundreds of nanometers.

Quantum walks with an anisotropic coin II: scattering theory

NASA Astrophysics Data System (ADS)

Richard, S.; Suzuki, A.; de Aldecoa, R. Tiedra

2018-05-01

We perform the scattering analysis of the evolution operator of quantum walks with an anisotropic coin, and we prove a weak limit theorem for their asymptotic velocity. The quantum walks that we consider include one-defect models, two-phase quantum walks, and topological phase quantum walks as special cases. Our analysis is based on an abstract framework for the scattering theory of unitary operators in a two-Hilbert spaces setting, which is of independent interest.

Recipe creation for automated defect classification with a 450mm surface scanning inspection system based on the bidirectional reflectance distribution function of native defects

NASA Astrophysics Data System (ADS)

Yathapu, Nithin; McGarvey, Steve; Brown, Justin; Zhivotovsky, Alexander

2016-03-01

This study explores the feasibility of Automated Defect Classification (ADC) with a Surface Scanning Inspection System (SSIS). The defect classification was based upon scattering sensitivity sizing curves created via modeling of the Bidirectional Reflectance Distribution Function (BRDF). The BRDF allowed for the creation of SSIS sensitivity/sizing curves based upon the optical properties of both the filmed wafer samples and the optical architecture of the SSIS. The elimination of Polystyrene Latex Sphere (PSL) and Silica deposition on both filmed and bare Silicon wafers prior to SSIS recipe creation and ADC creates a challenge for light scattering surface intensity based defect binning. This study explored the theoretical maximal SSIS sensitivity based on native defect recipe creation in conjunction with the maximal sensitivity derived from BRDF modeling recipe creation. Single film and film stack wafers were inspected with recipes based upon BRDF modeling. Following SSIS recipe creation, initially targeting maximal sensitivity, selected recipes were optimized to classify defects commonly found on non-patterned wafers. The results were utilized to determine the ADC binning accuracy of the native defects and evaluate the SSIS recipe creation methodology. A statistically valid sample of defects from the final inspection results of each SSIS recipe and filmed substrate were reviewed post SSIS ADC processing on a Defect Review Scanning Electron Microscope (SEM). Native defect images were collected from each statistically valid defect bin category/size for SEM Review. The data collected from the Defect Review SEM was utilized to determine the statistical purity and accuracy of each SSIS defect classification bin. This paper explores both, commercial and technical, considerations of the elimination of PSL and Silica deposition as a precursor to SSIS recipe creation targeted towards ADC. Successful integration of SSIS ADC in conjunction with recipes created via BRDF modeling has the potential to dramatically reduce the workload requirements of a Defect Review SEM and save a significant amount of capital expenditure for 450mm SSIS recipe creation.

Self healing of defected graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Jianhui; Shi, Tuwan; Cai, Tuocheng

For electronics applications, defects in graphene are usually undesirable because of their ability to scatter charge carriers, thereby reduce the carrier mobility. It would be extremely useful if the damage can be repaired. In this work, we employ Raman spectroscopy, X-ray photoemission spectroscopy, transmission electron microscopy, and electrical measurements to study defects in graphene introduced by argon plasma bombardment. We have found that majority of these defects can be cured by a simple thermal annealing process. The self-healing is attributed to recombination of mobile carbon adatoms with vacancies. With increasing level of plasma induced damage, the self-healing becomes less effective.

Effect of point defects and disorder on structural phase transitions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Toulouse, J.

1997-06-01

Since the beginning in 1986, the object of this project has been Structural Phase Transitions (SPT) in real as opposed to ideal materials. The first stage of the study has been centered around the role of Point Defects in SPT`s. Our intent was to use the previous knowledge we had acquired in the study of point defects in non-transforming insulators and apply it to the study of point defects in insulators undergoing phase transitions. In non-transforming insulators, point defects, in low concentrations, marginally affect the bulk properties of the host. It is nevertheless possible by resonance or relaxation methods tomore » study the point defects themselves via their local motion. In transforming solids, however, close to a phase transition, atomic motions become correlated over very large distances; there, even point defects far removed from one another can undergo correlated motions which may strongly affect the transition behavior of the host. Near a structural transition, the elastic properties win be most strongly affected so as to either raise or decrease the transition temperature, prevent the transition from taking place altogether, or simply modify its nature and the microstructure or domain structure of the resulting phase. One of the well known practical examples is calcium-stabilized zirconia in which the high temperature cubic phase is stabilized at room temperature with greatly improved mechanical properties.« less

Optical absorption and scattering spectra of pathological stomach tissues

NASA Astrophysics Data System (ADS)

Giraev, K. M.; Ashurbekov, N. A.; Lakhina, M. A.

2011-03-01

Diffuse reflection spectra of biotissues in vivo and transmission and reflection coefficients for biotissues in vitro are measured over 300-800 nm. These data are used to determine the spectral absorption and scattering indices and the scattering anisotropy factor for stomach mucous membranes under normal and various pathological conditions (chronic atrophic and ulcerous defects, malignant neoplasms). The most importan tphysiological (hemodynamic and oxygenation levels) and structural-morphological (scatterer size and density) parameters are also determined. The results of a morphofunctional study correlate well with the optical properties and are consistent with data from a histomorphological analysis of the corresponding tissues.

Tuning thermal conduction via extended defects in graphene

NASA Astrophysics Data System (ADS)

Huang, Huaqing; Xu, Yong; Zou, Xiaolong; Wu, Jian; Duan, Wenhui

2013-05-01

Designing materials for desired thermal conduction can be achieved via extended defects. We theoretically demonstrate the concept by investigating thermal transport in graphene nanoribbons (GNRs) with the extended line defects observed by recent experiments. Our nonequilibrium Green's function study excluding phonon-phonon interactions finds that thermal conductance can be tuned over wide ranges (more than 50% at room temperature), by controlling the orientation and the bond configuration of the embedded extended defect. Further transmission analysis reveals that the thermal-conduction tuning is attributed to two fundamentally different mechanisms, via modifying the phonon dispersion and/or tailoring the strength of defect scattering. The finding, applicable to other materials, provides useful guidance for designing materials with desired thermal conduction.

Multiple scattered radiation emerging from Rayleigh and continental haze layers. 1: Radiance, polarization, and neutral points.

PubMed

Kattawar, G W; Plass, G N; Hitzfelder, S J

1976-03-01

The complete radiation field including polarization is calculated by the matrix operator method for scattering layers of various optical thicknesses. Results obtained for Rayleigh scattering are compared with those for scattering from a continental haze. Radiances calculated using Stokes vectors show differences as large as 23% compared to the approximate scalar theory of radiative transfer, while the same differences are only of the order of 0.1% for a continental haze phase function. The polarization of the reflected and transmitted radiation is given for a wide range of optical thicknesses of the scattering layer, for various solar zenith angles, and various surface albedos. Two entirely different types of neutral points occur for aerosol phase functions. Rayleigh-like neutral points (RNP) arise from the zero polarization in single scattering that occurs for all phase functions at scattering angles of 0 degrees and 180 degrees . For Rayleigh phase functions, the position of the RNP varies appreciably with the optical thickness of the scattering layer. At low solar elevations there may be four RNP. For a continental haze phase function the position of the RNP in the reflected radiation shows only a small variation with the optical thickness, and the RNP exists in the transmitted radiation only for extremely small optical thicknesses. Another type of neutral point (NRNP) exists for aerosol phase functions. It is associated with the zeros of the single scattered polarization, which occur between the end points of the curve; these are called non-Rayleigh neutral points (NRNP). There may be from zero to four of these neutral points associated with each zero of the single scattering curve. They occur over a range of azimuthal angles, unlike the RNP that are in the principal plane only. The position of these neutral points is given as a function of solar angle and optical thickness.

Identification of dopant-induced point defects and their effect on the performance of CZT detectors (Conference Presentation)

NASA Astrophysics Data System (ADS)

Gul, Rubi; Bolotnikov, Aleksey E.; Camarda, Giuseppe S.; Cui, Yonggang; Didic, Václav; Egarievwe, Stephen U.; Hossain, Anwar; Roy, Utpal N.; Yang, Ge; James, Ralph B.

2016-09-01

In our prior research we investigated room-temperature radiation detectors (CZT, CMT, CdMgTe, CTS, among other compound semiconductors) for point defects related to different dopants and impurities. In this talk we will report on our most recent research on newly grown CZT crystals doped with In, In+Al, In+Ni, and In+Sn. The main focus will be on the study of dopant-induced point defects using deep-level current transient spectroscopy (i-DLTS). In addition the performance, ? product, gamma-ray spectral response and internal electric field of the detectors were measured and correlated with the dopant-induced point defects and their concentrations. Characterization of the detectors was carried out using i-DLTS for the point defects, Pockels effect for the internal electric-field distribution, and γ-ray spectroscopy for the spectral properties.

Analysis of Ultrasonic Wave Scattering for Characterization of Defects in Solids

DTIC Science & Technology

1976-05-01

embedded in a solid matrix.’ The results of this work have been partially reported in a paper sub- mitted to the "Journal of the Acoustical Society of...America." The abstract of this paper is presented here: a. "Scattering of Longitudinal Waves Incident on a Spherical Cavity in a Solid," B. R. Tittmann...F I 7 ... .OCT..9 UM... ... .. . ... U SCS7g. 31R 2. Scattering by a Spherical Inclusion During this past year the experimental portion of the

Study of point- and cluster-defects in radiation-damaged silicon

NASA Astrophysics Data System (ADS)

Donegani, Elena M.; Fretwurst, Eckhart; Garutti, Erika; Klanner, Robert; Lindstroem, Gunnar; Pintilie, Ioana; Radu, Roxana; Schwandt, Joern

2018-08-01

Non-ionising energy loss of radiation produces point defects and defect clusters in silicon, which result in a significant degradation of sensor performance. In this contribution results from TSC (Thermally Stimulated Current) defect spectroscopy for silicon pad diodes irradiated by electrons to fluences of a few 1014 cm-2 and energies between 3.5 and 27 MeV for isochronal annealing between 80 and 280∘C, are presented. A method based on SRH (Shockley-Read-Hall) statistics is introduced, which assumes that the ionisation energy of the defects in a cluster depends on the fraction of occupied traps. The difference of ionisation energy of an isolated point defect and a fully occupied cluster, ΔEa, is extracted from the TSC data. For the VOi (vacancy-oxygen interstitial) defect ΔEa = 0 is found, which confirms that it is a point defect, and validates the method for point defects. For clusters made of deep acceptors the ΔEa values for different defects are determined after annealing at 80∘C as a function of electron energy, and for the irradiation with 15 MeV electrons as a function of annealing temperature. For the irradiation with 3.5 MeV electrons the value ΔEa = 0 is found, whereas for the electron energies of 6-27 MeV ΔEa > 0. This agrees with the expected threshold of about 5 MeV for cluster formation by electrons. The ΔEa values determined as a function of annealing temperature show that the annealing rate is different for different defects. A naive diffusion model is used to estimate the temperature dependencies of the diffusion of the defects in the clusters.

Nonequilibrium Steady State Generated by a Moving Defect: The Supersonic Threshold

NASA Astrophysics Data System (ADS)

Bastianello, Alvise; De Luca, Andrea

2018-02-01

We consider the dynamics of a system of free fermions on a 1D lattice in the presence of a defect moving at constant velocity. The defect has the form of a localized time-dependent variation of the chemical potential and induces at long times a nonequilibrium steady state (NESS), which spreads around the defect. We present a general formulation that allows recasting the time-dependent protocol in a scattering problem on a static potential. We obtain a complete characterization of the NESS. In particular, we show a strong dependence on the defect velocity and the existence of a sharp threshold when such velocity exceeds the speed of sound. Beyond this value, the NESS is not produced and, remarkably, the defect travels without significantly perturbing the system. We present an exact solution for a δ -like defect traveling with an arbitrary velocity and we develop a semiclassical approximation that provides accurate results for smooth defects.

Luminescence Properties of Surface Radiation-Induced Defects in Lithium Fluoride

NASA Astrophysics Data System (ADS)

Voitovich, A. P.; Kalinov, V. S.; Martynovich, E. F.; Novikov, A. N.; Runets, L. P.; Stupak, A. P.

2013-11-01

Luminescence and luminescence excitation spectra are recorded for surface radiation-induced defects in lithium fluoride at temperatures of 77 and 293 K. The presence of three bands with relatively small intensity differences is a distinctive feature of the excitation spectrum. These bands are found to belong to the same type of defects. The positions of the peaks and the widths of the absorption and luminescence bands for these defects are determined. The luminescence decay time is measured. All the measured characteristics of these surface defects differ from those of previously known defects induced by radiation in the bulk of the crystals. It is found that the luminescence of surface defects in an ensemble of nanocrystals with different orientations is not polarized. The number of anion vacancies in the surface defects is estimated using the polarization measurements. It is shown that radiative scattering distorts the intensity ratios of the luminescence excitation bands located in different spectral regions.

Quality Control System using Simple Implementation of Seven Tools for Batik Textile Manufacturing

NASA Astrophysics Data System (ADS)

Ragil Suryoputro, Muhammad; Sugarindra, Muchamad; Erfaisalsyah, Hendy

2017-06-01

In order to produce better products and mitigate defect in products, every company must implement a quality control system. Company will find means to implement a quality control system that is capable and reliable. One of the methods is using the simple implementation of the seven tools in quality control defects. The case studied in this research was the level of disability xyz grey fabric on a shuttle loom 2 on the Batik manufacturing company. The seven tools that include: flowchart, check sheet, histogram, scatter diagram combined with control charts, Pareto diagrams and fishbone diagrams (causal diagram). Check sheet results obtained types of defects in the grey fabric was woven xyz is warp, double warp, the warp break, double warp, empty warp, warp tenuous, ugly edges, thick warp, and rust. Based on the analysis of control chart indicates that the process is out of control. This can be seen in the graph control where there is still a lot of outlier data. Based on a scatter diagram shows a positive correlation between the percentage of disability and the number of production. Based on Pareto diagram, repair needs priority is for the dominant type of defect is warp (44%) and based on double warp value histogram is also the highest with a value of 23635.11 m. In addition, based on the analysis of the factors causing defect by fishbone diagram double warp or other types of defects originating from the materials, methods, machines, measurements, man and environment. Thus the company can take to minimize the prevention and repair of defects and improve product quality.

The generation and accumulation of interstitial atoms and vacancies in alloys with L1{sub 2} superstructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pantyukhova, Olga, E-mail: Pantyukhova@list.ru; Starenchenko, Vladimir, E-mail: star@tsuab.ru; Starenchenko, Svetlana, E-mail: sve-starenchenko@yandex.ru

2016-01-15

The dependences of the point defect concentration (interstitial atoms and vacancies) on the deformation degree were calculated for the L1{sub 2} alloys with the high and low antiphase boundaries (APB) energy in terms of the mathematical model of the work and thermal strengthening of the alloys with the L1{sub 2} structure; the concentration of the point defects generated and annihilated in the process of deformation was estimated. It was found that the main part of the point defects generating during plastic deformation annihilates, the residual density of the deformation point defects does not exceed 10{sup −5}.

Native point defects in MoS2 and their influences on optical properties by first principles calculations

NASA Astrophysics Data System (ADS)

Saha, Ashim Kumar; Yoshiya, Masato

2018-03-01

Stability of native point defect species and optical properties are quantitatively examined through first principles calculations in order to identify possible native point defect species in MoS2 and its influences on electronic structures and resultant optical properties. Possible native point defect species are identified as functions of thermodynamic environment and location of Fermi-level in MoS2. It is found that sulphur vacancies can be introduced more easily than other point defect species which will create impurity levels both in bandgap and in valence band. Additionally, antisite Mo and/or Mo vacancies can be created depending on chemical potential of sulphur, both of which will create impurity levels in bandgap and in valence band. Those impurity levels result in pronounced photon absorption in visible light region, though each of these point defects alone has limited impact on the optical properties unless their concentration remained low. Thus, attention must be paid when intentional impurity doping is made to MoS2 to avoid unwanted modification of optical properties of MoS2. Those impurity may enable further exploitation of photovoltaic energy conversion at longer wavelength.

Using high pressure to study thermal transport and phonon scattering mechanisms

NASA Astrophysics Data System (ADS)

Hohensee, Gregory Thomas

The aerospace industry studies nanocomposites for heat dissipation and moderation of thermal expansion, and the semiconductor industry faces a Joule heating barrier in devices with high power density. My primary experimental tools are the diamond anvil cell (DAC) coupled with time-domain thermoreflectance (TDTR). TDTR is a precise optical method well-suited to measuring thermal conductivities and conductances at the nanoscale and across interfaces. The DAC-TDTR method yields thermal property data as a function of pressure, rather than temperature. This relatively unexplored independent variable can separate the components of thermal conductance and serve as an independent test for phonon-defect scattering models. I studied the effect of non-equilibrium thermal transport at the aluminum-coated surface of an exotic cuprate material Ca9La5Cu 24O41, which boasts a tenfold enhanced thermal conductivity along one crystalline axis where two-leg copper-oxygen spin-ladder structures carry heat in the form of thermalized magnetic excitations. Highly anisotropic materials are of interest for controlled thermal management applications, and the spin-ladder magnetic heat carriers ("magnons") are not well understood. I found that below room temperature, the apparent thermal conductivity of Ca9La5Cu24O41 depends on the frequency of the applied surface heating in TDTR. This occurs because the thermal penetration depth in the TDTR experiment is comparable to the length-scale for the equilibration of the magnons that are the dominant channel for heat conduction and the phonons that dominate the heat capacity. I applied a two-temperature model to analyze the TDTR data and extracted an effective volumetric magnon-phonon coupling parameter g for Ca9La5Cu24O 41 at temperatures from 75 K to 300 K; g varies by approximately two orders of magnitude over this range of temperature and has the value g = 1015 W m-3 K-1 near the peak of the thermal conductivity at T ≈ 180 K. To examine intrinsic phonon-mediated interface conductance between dissimilar materials, I applied DAC-TDTR to measure the thermal conductance of a series of metal-diamond interfaces as a function of pressure up to 50 GPa. The thermal conductance of interfaces between metals and diamond, which has a comparatively high Debye temperature, is often greater than can be accounted for by two phonon-processes, and the nature of heat transport between such dissimilar materials is central to the thermal design of composite materials. The high pressures achievable in a diamond anvil cell can significantly extend the metal phonon density of states to higher frequencies, and can also suppress extrinsic effects by greatly stiffening interface bonding. I measured the interface thermal conductances of Pb, Au0.95Pd0.05, Pt, and Al films deposited on Type 1A natural [100] and Type 2A synthetic [110] diamond anvils, from ambient pressure to 50 GPa. In all cases, the thermal conductances increase weakly or saturate to similar values at high pressure. My results suggest that anharmonic conductance at metal-diamond interfaces is controlled by partial transmission processes, where a diamond phonon that inelastically scatters at the interface absorbs or emits a metal phonon. The thermal conductivity and absolute electrical resistivity of metallic silicon have not been measured previously. I performed regular and beam-offset TDTR to establish the thermal conductivities of Si and Si0.991Ge 0.009 across the semiconductor-metal phase transition and up to 45 GPa. The thermal conductivities of metallic Si and Si(Ge) are comparable to aluminum and indicative of predominantly electronic heat carriers. Metallic Si and Si(Ge) have a transport anisotropy of approximately 1.4, similar to that of beryllium, due to the primitive hexagonal crystal structure. I used the Wiedemann-Franz law to derive the associated electrical resistivity, and found it consistent with the Bloch-Gruneisen model. Not all crystalline point defects are alike in how they scatter phonons and reduce the thermal conductivity of mixed crystals. Heat-carrying phonons in iron (Fe) doped MgO, or [Mg,Fe]O ferropericlase, are known to be resonantly scattered by interaction with a 3.3 THz electronic transition in the high-spin state of the Fe impurities. At sufficiently high pressures, the Fe atoms transition from a high-spin to a low-spin state, which eliminates the resonant interaction and reduces the Fe atoms to simpler point defect phonon scatterers. To study the behavior of phonon-defect scattering with and without this resonant scattering process, I measured the thermal conductivity of Mg0.92Fe0.08 O ferropericlase up to and above the 40--60 GPa spin transition. Fe-doped MgO (ferropericlase) is also a model system relevant to geophysical modeling of the Earth's core-mantle boundary, so data on its thermal transport under pressure is valuable in itself. (Abstract shortened by UMI.).

Optical spectroscopy and microscopy of radiation-induced light-emitting point defects in lithium fluoride crystals and films

NASA Astrophysics Data System (ADS)

Montereali, R. M.; Bonfigli, F.; Menchini, F.; Vincenti, M. A.

2012-08-01

Broad-band light-emitting radiation-induced F2 and F3+ electronic point defects, which are stable and laser-active at room temperature in lithium fluoride crystals and films, are used in dosimeters, tuneable color-center lasers, broad-band miniaturized light sources and novel radiation imaging detectors. A brief review of their photoemission properties is presented, and their behavior at liquid nitrogen temperatures is discussed. Some experimental data from optical spectroscopy and fluorescence microscopy of these radiation-induced point defects in LiF crystals and thin films are used to obtain information about the coloration curves, the efficiency of point defect formation, the effects of photo-bleaching processes, etc. Control of the local formation, stabilization, and transformation of radiation-induced light-emitting defect centers is crucial for the development of optically active micro-components and nanostructures. Some of the advantages of low temperature measurements for novel confocal laser scanning fluorescence microscopy techniques, widely used for spatial mapping of these point defects through the optical reading of their visible photoluminescence, are highlighted.

On the validity of the amphoteric-defect model in gallium arsenide and a criterion for Fermi-level pinning by defects

NASA Astrophysics Data System (ADS)

Chen, C.-H.; Tan, T. Y.

1995-10-01

Using the theoretically calculated point-defect total-energy values of Baraff and Schlüter in GaAs, an amphoteric-defect model has been proposed by Walukiewicz to explain a large number of experimental results. The suggested amphoteric-defect system consists of two point-defect species capable of transforming into each other: the doubly negatively charged Ga vacancy V {Ga/2-} and the triply positively charged defect complex (ASGa+ V As)3+, with AsGa being the antisite defect of an As atom occupying a Ga site and V As being an As vacancy. When present in sufficiently high concentrations, the amphoteric defect system V {Ga/2-}/(AsGa+ V As)3+ is supposed to be able to pin the GaAs Fermi level at approximately the E v +0.6 eV level position, which requires that the net free energy of the V Ga/(AsGa+ V As) defect system to be minimum at the same Fermi-level position. We have carried out a quantitative study of the net energy of this defect system in accordance with the individual point-defect total-energy results of Baraff and Schlüter, and found that the minimum net defect-system-energy position is located at about the E v +1.2 eV level position instead of the needed E v +0.6 eV position. Therefore, the validity of the amphoteric-defect model is in doubt. We have proposed a simple criterion for determining the Fermi-level pinning position in the deeper part of the GaAs band gap due to two oppositely charged point-defect species, which should be useful in the future.

A novel full-angle scanning light scattering profiler to quantitatively evaluate forward and backward light scattering from intraocular lenses

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walker, Bennett N., E-mail: bennett.walker@fda.hhs.gov; Office of Device Evaluation, Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, Maryland 20993; James, Robert H.

Glare, glistenings, optical defects, dysphotopsia, and poor image quality are a few of the known deficiencies of intraocular lenses (IOLs). All of these optical phenomena are related to light scatter. However, the specific direction that light scatters makes a critical difference between debilitating glare and a slightly noticeable decrease in image quality. Consequently, quantifying the magnitude and direction of scattered light is essential to appropriately evaluate the safety and efficacy of IOLs. In this study, we introduce a full-angle scanning light scattering profiler (SLSP) as a novel approach capable of quantitatively evaluating the light scattering from IOLs with a nearlymore » 360° view. The SLSP method can simulate in situ conditions by controlling the parameters of the light source including angle of incidence. This testing strategy will provide a more effective nonclinical approach for the evaluation of IOL light scatter.« less

Direct detection of light dark matter and solar neutrinos via color center production in crystals

NASA Astrophysics Data System (ADS)

Budnik, Ranny; Cheshnovsky, Ori; Slone, Oren; Volansky, Tomer

2018-07-01

We propose a new low-threshold direct-detection concept for dark matter and for coherent nuclear scattering of solar neutrinos, based on the dissociation of atoms and subsequent creation of color center type defects within a lattice. The novelty in our approach lies in its ability to detect single defects in a macroscopic bulk of material. This class of experiments features ultra-low energy thresholds which allows for the probing of dark matter as light as O (10) MeV through nuclear scattering. Another feature of defect creation in crystals is directional information, which presents as a spectacular signal and a handle on background reduction in the form of daily modulation of the interaction rate. We discuss the envisioned setup and detection technique, as well as background reduction. We further calculate the expected rates for dark matter and solar neutrinos in two example crystals for which available data exists, demonstrating the prospective sensitivity of such experiments.

A 3D Laser Profiling System for Rail Surface Defect Detection

PubMed Central

Li, Qingquan; Mao, Qingzhou; Zou, Qin

2017-01-01

Rail surface defects such as the abrasion, scratch and peeling often cause damages to the train wheels and rail bearings. An efficient and accurate detection of rail defects is of vital importance for the safety of railway transportation. In the past few decades, automatic rail defect detection has been studied; however, most developed methods use optic-imaging techniques to collect the rail surface data and are still suffering from a high false recognition rate. In this paper, a novel 3D laser profiling system (3D-LPS) is proposed, which integrates a laser scanner, odometer, inertial measurement unit (IMU) and global position system (GPS) to capture the rail surface profile data. For automatic defect detection, first, the deviation between the measured profile and a standard rail model profile is computed for each laser-imaging profile, and the points with large deviations are marked as candidate defect points. Specifically, an adaptive iterative closest point (AICP) algorithm is proposed to register the point sets of the measured profile with the standard rail model profile, and the registration precision is improved to the sub-millimeter level. Second, all of the measured profiles are combined together to form the rail surface through a high-precision positioning process with the IMU, odometer and GPS data. Third, the candidate defect points are merged into candidate defect regions using the K-means clustering. At last, the candidate defect regions are classified by a decision tree classifier. Experimental results demonstrate the effectiveness of the proposed laser-profiling system in rail surface defect detection and classification. PMID:28777323

Regular scattering patterns from near-cloaking devices and their implications for invisibility cloaking

NASA Astrophysics Data System (ADS)

Kocyigit, Ilker; Liu, Hongyu; Sun, Hongpeng

2013-04-01

In this paper, we consider invisibility cloaking via the transformation optics approach through a ‘blow-up’ construction. An ideal cloak makes use of singular cloaking material. ‘Blow-up-a-small-region’ construction and ‘truncation-of-singularity’ construction are introduced to avoid the singular structure, however, giving only near-cloaks. The study in the literature is to develop various mechanisms in order to achieve high-accuracy approximate near-cloaking devices, and also from a practical viewpoint to nearly cloak an arbitrary content. We study the problem from a different viewpoint. It is shown that for those regularized cloaking devices, the corresponding scattering wave fields due to an incident plane wave have regular patterns. The regular patterns are both a curse and a blessing. On the one hand, the regular wave pattern betrays the location of a cloaking device which is an intrinsic defect due to the ‘blow-up’ construction, and this is particularly the case for the construction by employing a high-loss layer lining. Indeed, our numerical experiments show robust reconstructions of the location, even by implementing the phaseless cross-section data. The construction by employing a high-density layer lining shows a certain promising feature. On the other hand, it is shown that one can introduce an internal point source to produce the canceling scattering pattern to achieve a near-cloak of an arbitrary order of accuracy.

Raman Scattering by Crystals of Rare-Earth Hexaborides with Different Isotopes of Boron

NASA Astrophysics Data System (ADS)

Markov, Yu. F.; Gurin, V. N.; Ponkratov, K. V.

2018-04-01

Monocrystals of lanthanum hexaboride LaB6 containing both natural boron and its isotopes 10B and 11B have been produced using the solution-melt method. Polyelement hexaboride rare-earths have been grown and the corresponding ceramics have been synthesized for the first time. All these crystals have been studied by means of various techniques, generally using Raman scattering. The Raman spectra attributed to various spectral lines corresponding to nonanalyzable representations have been obtained and interpreted. Frequencies and half-widths of spectral lines have been obtained, the removal of degeneracy and the development of respective splitting of degenerate oscillations induced by defects, mainly by boron isotope inclusions, have been identified. The influence of defects on the Raman spectra has been determined.

Study of the degradation and recovery of the optical properties of H+-implanted ZnO pigments

NASA Astrophysics Data System (ADS)

Li, Chundong; Lv, Jinpeng; Yao, Shulong; Hu, Jiangang; Liang, Zhiqiang

2013-01-01

We studied the influences of proton implantation and oxygen post-annealing on the optical properties of ZnO pigments using a combination of Raman scattering, positron annihilation and photoluminescence techniques. Raman scattering results indicated that oxygen vacancies and interstitial zinc defects were produced after proton implantation. Positron annihilation spectroscopy and photoluminescence measurements demonstrated that the zinc vacancies do not contribute to the optical absorption, but give rise to the visible band emission. Interestingly, the proton implantation induced optical degradation can be annealed out at 800 °C in an O2 atmosphere. We conclude that the defect centers responsible for the optical absorption are primarily composed of VO+, ionized Zni and ionized Oi.

Solid State Division progress report, September 30, 1981

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1982-04-01

Progress made during the 19 months from March 1, 1980, through September 30, 1981, is reported in the following areas: theoretical solid state physics (surfaces, electronic and magnetic properties, particle-solid interactions, and laser annealing); surface and near-surface properties of solids (plasma materials interactions, ion-solid interactions, pulsed laser annealing, and semiconductor physics and photovoltaic conversion); defects in solids (radiation effects, fracture, and defects and impurities in insulating crystals); transport properties of solids (fast-ion conductors, superconductivity, and physical properties of insulating materials); neutron scattering (small-angle scattering, lattice dynamics, and magnetic properties); crystal growth and characterization (nuclear waste forms, ferroelectric mateirals, high-temperature materials,more » and special materials); and isotope research materials. Publications and papers are listed. (WHK)« less

A novel micro-Raman technique to detect and characterize 4H-SiC stacking faults

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piluso, N., E-mail: nicolo.piluso@imm.cnr.it; Camarda, M.; La Via, F.

A novel Micro-Raman technique was designed and used to detect extended defects in 4H-SiC homoepitaxy. The technique uses above band-gap high-power laser densities to induce a local increase of free carriers in undoped epitaxies (n < 10{sup 16} at/cm{sup −3}), creating an electronic plasma that couples with the longitudinal optical (LO) Raman mode. The Raman shift of the LO phonon-plasmon-coupled mode (LOPC) increases as the free carrier density increases. Crystallographic defects lead to scattering or recombination of the free carriers which results in a loss of coupling with the LOPC, and in a reduction of the Raman shift. Given that the LOmore » phonon-plasmon coupling is obtained thanks to the free carriers generated by the high injection level induced by the laser, we named this technique induced-LOPC (i-LOPC). This technique allows the simultaneous determination of both the carrier lifetime and carrier mobility. Taking advantage of the modifications on the carrier lifetime induced by extended defects, we were able to determine the spatial morphology of stacking faults; the obtained morphologies were found to be in excellent agreement with those provided by standard photoluminescence techniques. The results show that the detection of defects via i-LOPC spectroscopy is totally independent from the stacking fault photoluminescence signals that cover a large energy range up to 0.7 eV, thus allowing for a single-scan simultaneous determination of any kind of stacking fault. Combining the i-LOPC method with the analysis of the transverse optical mode, the micro-Raman characterization can determine the most important properties of unintentionally doped film, including the stress status of the wafer, lattice impurities (point defects, polytype inclusions) and a detailed analysis of crystallographic defects, with a high spectral and spatial resolution.« less

A Computational Framework for Automation of Point Defect Calculations

NASA Astrophysics Data System (ADS)

Goyal, Anuj; Gorai, Prashun; Peng, Haowei; Lany, Stephan; Stevanovic, Vladan; National Renewable Energy Laboratory, Golden, Colorado 80401 Collaboration

A complete and rigorously validated open-source Python framework to automate point defect calculations using density functional theory has been developed. The framework provides an effective and efficient method for defect structure generation, and creation of simple yet customizable workflows to analyze defect calculations. The package provides the capability to compute widely accepted correction schemes to overcome finite-size effects, including (1) potential alignment, (2) image-charge correction, and (3) band filling correction to shallow defects. Using Si, ZnO and In2O3as test examples, we demonstrate the package capabilities and validate the methodology. We believe that a robust automated tool like this will enable the materials by design community to assess the impact of point defects on materials performance. National Renewable Energy Laboratory, Golden, Colorado 80401.

Point defect weakened thermal contraction in monolayer graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zha, Xian-Hu; Department of Physics, University of Science and Technology of China, Hefei; USTC-CityU Joint Advanced Research Centre, Suzhou 215123

We investigate the thermal expansion behaviors of monolayer graphene and three configurations of graphene with point defects, namely the replacement of one carbon atom with a boron or nitrogen atom, or of two neighboring carbon atoms by boron-nitrogen atoms, based on calculations using first-principles density functional theory. It is found that the thermal contraction of monolayer graphene is significantly decreased by point defects. Moreover, the corresponding temperature for negative linear thermal expansion coefficient with the maximum absolute value is reduced. The cause is determined to be point defects that enhance the mechanical strength of graphene and then reduce the amplitudemore » and phonon frequency of the out-of-plane acoustic vibration mode. Such defect weakening of graphene thermal contraction will be useful in nanotechnology to diminish the mismatching or strain between the graphene and its substrate.« less

Optimization of thermoelectric performance of SrSi2-based alloys via the modification in band structure and phonon-point-defect scattering

PubMed Central

Kuo, Yung-Kang; Ramachandran, Balakrishnan; Lue, Chin-Shan

2014-01-01

Thermoelectric properties of alkaline-earth-metal disilicides are strongly dependent on their electronic band structure in the vicinity of the Fermi level. In particular, the strontium disilicide, SrSi2 with a narrow band gap of about few tens of meV is composed of non-toxic, naturally abundant elements, and its thermoelectric properties are very sensitive to the substitution/alloying with third elements. In this article, we summarize the thermoelectric performance of substituted and Sr-deficient/Sr-rich SrSi2 alloys to realize the high thermoelectric figure-of-merit (ZT) for practical applications in the electronic and thermoelectric aspects, and also to explore the alternative routes to further improve its ZT value. PMID:25505784

Lattice dynamics and the nature of structural transitions in organolead halide perovskites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Comin, Riccardo; Crawford, Michael K.; Said, Ayman H.

Organolead halide perovskites are a family of hybrid organic-inorganic compounds whose remarkable optoelectronic properties have been under intensive scrutiny in recent years. Here we use inelastic x-ray scattering to study low-energy lattice excitations in single crystals of methylammonium lead iodide and bromide perovskites. Our findings confirm the displacive nature of the cubic-to-tetragonal phase transition, which is further shown, using neutron and x-ray diffraction, to be close to a tricritical point. Lastly, we detect quasistatic symmetry-breaking nanodomains persisting well into the high-temperature cubic phase, possibly stabilized by local defects. These findings reveal key structural properties of these materials, and also bearmore » important implications for carrier dynamics across an extended temperature range relevant for photovoltaic applications.« less

Fe-Doping Effect on Thermoelectric Properties of p-Type Bi0.48Sb1.52Te₃.

PubMed

Mun, Hyeona; Lee, Kyu Hyoung; Kim, Suk Jun; Kim, Jong-Young; Lee, Jeong Hoon; Lim, Jae-Hong; Park, Hee Jung; Roh, Jong Wook; Kim, Sung Wng

2015-03-05

The substitutional doping approach has been shown to be an effective strategy to improve ZT of Bi₂Te₃-based thermoelectric raw materials. We herein report the Fe-doping effects on electronic and thermal transport properties of polycrystalline bulks of p -type Bi 0.48 Sb 1.52 Te₃. After a small amount of Fe-doping on Bi/Sb-sites, the power factor could be enhanced due to the optimization of carrier concentration. Additionally, lattice thermal conductivity was reduced by the intensified point-defect phonon scattering originating from the mass difference between the host atoms (Bi/Sb) and dopants (Fe). An enhanced ZT of 1.09 at 300 K was obtained in 1.0 at% Fe-doped Bi 0.48 Sb 1.52 Te₃ by these synergetic effects.

Interplay of point defects, biaxial strain, and thermal conductivity in homoepitaxial SrTiO3 thin films

NASA Astrophysics Data System (ADS)

Wiedigen, S.; Kramer, T.; Feuchter, M.; Knorr, I.; Nee, N.; Hoffmann, J.; Kamlah, M.; Volkert, C. A.; Jooss, Ch.

2012-02-01

Separating out effects of point defects and lattice strain on thermal conductivity is essential for improvement of thermoelectric properties of SrTiO3. We study relations between defects generated during deposition, induced lattice strain, and their impact on thermal conductivity κ in homoepitaxial SrTiO3 films prepared by ion-beam sputtering. Lowering the deposition temperature gives rise to lattice expansion by enhancement of point defect density which increases the hardness of the films. Due to a fully coherent substrate-film interface, the lattice misfit induces a large biaxial strain. However, we can show that the temperature dependence of κ is mainly sensitive on the defect concentration.

Nanoscale interfacial defect shedding in a growing nematic droplet.

PubMed

Gurevich, Sebastian; Provatas, Nikolas; Rey, Alejandro

2017-08-01

Interfacial defect shedding is the most recent known mechanism for defect formation in a thermally driven isotropic-to-nematic phase transition. It manifests in nematic-isotropic interfaces going through an anchoring switch. Numerical computations in planar geometry established that a growing nematic droplet can undergo interfacial defect shedding, nucleating interfacial defect structures that shed into the bulk as +1/2 point defects. By extending the study of interfacial defect shedding in a growing nematic droplet to larger length and time scales, and to three dimensions, we unveil an oscillatory growth mode involving shape and anchoring transitions that results in a controllable regular distributions of point defects in planar geometry, and complex structures of disclination lines in three dimensions.

Complex Interaction Mechanisms between Dislocations and Point Defects Studied in Pure Aluminium by a Two-Wave Acoustic Coupling Technique

NASA Astrophysics Data System (ADS)

Bremnes, O.; Progin, O.; Gremaud, G.; Benoit, W.

1997-04-01

Ultrasonic experiments using a two-wave coupling technique were performed on 99.999% pure Al in order to study the interaction mechanisms occurring between dislocations and point defects. The coupling technique consists in measuring the attenuation of ultrasonic waves during low-frequency stress cycles (t). One obtains closed curves () called signatures whose shape and evolution are characteristic of the interaction mechanism controlling the low-frequency dislocation motion. The signatures observed were attributed to the interaction of the dislocations with extrinsic point defects. A new interpretation of the evolution of the signatures measured below 200 K with respect to temperature and stress frequency had to be established: they are linked to depinning of immobile point defects, whereas a thermally activated depinning mechanism does not fit the observations. The signatures measured between 200 and 370 K were interpreted as dragging and depinning of extrinsic point defects which are increasingly mobile with temperature.

Asymmetric interaction of point defects and heterophase interfaces in ZrN/TaN multilayered nanofilms.

PubMed

Lao, Yuanxia; Hu, Shuanglin; Shi, Yunlong; Deng, Yu; Wang, Fei; Du, Hao; Zhang, Haibing; Wang, Yuan

2017-01-05

Materials with a high density of heterophase interfaces, which are capable of absorbing and annihilating radiation-induced point defects, can exhibit a superior radiation tolerance. In this paper, we investigated the interaction behaviors of point defects and heterophase interfaces by implanting helium atoms into the ZrN/TaN multilayered nanofilms. It was found that the point defect-interface interaction on the two sides of the ZrN/TaN interface was asymmetric, likely due to the difference in the vacancy formation energies of ZrN and TaN. The helium bubbles could migrate from the ZrN layers into the TaN layers through the heterophase interfaces, resulting in a better crystallinity of the ZrN layers and a complete amorphization of the TaN layers. The findings provided some clues to the fundamental behaviors of point defects near the heterophase interfaces, which make us re-examine the design rules of advanced radiation-tolerant materials.

Asymmetric interaction of point defects and heterophase interfaces in ZrN/TaN multilayered nanofilms

NASA Astrophysics Data System (ADS)

Lao, Yuanxia; Hu, Shuanglin; Shi, Yunlong; Deng, Yu; Wang, Fei; Du, Hao; Zhang, Haibing; Wang, Yuan

2017-01-01

Materials with a high density of heterophase interfaces, which are capable of absorbing and annihilating radiation-induced point defects, can exhibit a superior radiation tolerance. In this paper, we investigated the interaction behaviors of point defects and heterophase interfaces by implanting helium atoms into the ZrN/TaN multilayered nanofilms. It was found that the point defect-interface interaction on the two sides of the ZrN/TaN interface was asymmetric, likely due to the difference in the vacancy formation energies of ZrN and TaN. The helium bubbles could migrate from the ZrN layers into the TaN layers through the heterophase interfaces, resulting in a better crystallinity of the ZrN layers and a complete amorphization of the TaN layers. The findings provided some clues to the fundamental behaviors of point defects near the heterophase interfaces, which make us re-examine the design rules of advanced radiation-tolerant materials.

Asymmetric interaction of point defects and heterophase interfaces in ZrN/TaN multilayered nanofilms

PubMed Central

Lao, Yuanxia; Hu, Shuanglin; Shi, Yunlong; Deng, Yu; Wang, Fei; Du, Hao; Zhang, Haibing; Wang, Yuan

2017-01-01

Materials with a high density of heterophase interfaces, which are capable of absorbing and annihilating radiation-induced point defects, can exhibit a superior radiation tolerance. In this paper, we investigated the interaction behaviors of point defects and heterophase interfaces by implanting helium atoms into the ZrN/TaN multilayered nanofilms. It was found that the point defect-interface interaction on the two sides of the ZrN/TaN interface was asymmetric, likely due to the difference in the vacancy formation energies of ZrN and TaN. The helium bubbles could migrate from the ZrN layers into the TaN layers through the heterophase interfaces, resulting in a better crystallinity of the ZrN layers and a complete amorphization of the TaN layers. The findings provided some clues to the fundamental behaviors of point defects near the heterophase interfaces, which make us re-examine the design rules of advanced radiation-tolerant materials. PMID:28053307

A novel sampling method for multiple multiscale targets from scattering amplitudes at a fixed frequency

NASA Astrophysics Data System (ADS)

Liu, Xiaodong

2017-08-01

A sampling method by using scattering amplitude is proposed for shape and location reconstruction in inverse acoustic scattering problems. Only matrix multiplication is involved in the computation, thus the novel sampling method is very easy and simple to implement. With the help of the factorization of the far field operator, we establish an inf-criterion for characterization of underlying scatterers. This result is then used to give a lower bound of the proposed indicator functional for sampling points inside the scatterers. While for the sampling points outside the scatterers, we show that the indicator functional decays like the bessel functions as the sampling point goes away from the boundary of the scatterers. We also show that the proposed indicator functional continuously depends on the scattering amplitude, this further implies that the novel sampling method is extremely stable with respect to errors in the data. Different to the classical sampling method such as the linear sampling method or the factorization method, from the numerical point of view, the novel indicator takes its maximum near the boundary of the underlying target and decays like the bessel functions as the sampling points go away from the boundary. The numerical simulations also show that the proposed sampling method can deal with multiple multiscale case, even the different components are close to each other.

The Interface Influence in TiN/SiN x Multilayer Nanocomposite Under Irradiation

NASA Astrophysics Data System (ADS)

Uglov, V. V.; Safronov, I. V.; Kvasov, N. T.; Remnev, G. E.; Shimanski, V. I.

2018-01-01

The paper focuses on studying the kinetics of radiation-induced point defects formed in TiN/SiN x multilayer nanocomposites with account of their generation, diffusion recombination, and the influence of sinks functioning as interfaces. In order to describe the kinetics in nanocrystalline TiN and amorphous SiN x phases, a finite-difference method is used to solve the system of balance kinetic equations for absolute defect concentrations depending on the spatiotemporal variables. A model of the disclination-dislocation interface structure is used to study the absorption of radiation-induced point defects on the boundaries in created stress fields. It is shown that the interface effectively absorbs point defects in these phases of TiN/SiN x multilayer nanocomposite, thereby reducing their amount within the space between phases. This behavior of point defects partially explains a mechanism of the radiation resistance in this type of nanocomposites.

Defect Genome of Cubic Perovskites for Fuel Cell Applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balachandran, Janakiraman; Lin, Lianshan; Anchell, Jonathan S.

Heterogeneities such as point defects, inherent to material systems, can profoundly influence material functionalities critical for numerous energy applications. This influence in principle can be identified and quantified through development of large defect data sets which we call the defect genome, employing high-throughput ab initio calculations. However, high-throughput screening of material models with point defects dramatically increases the computational complexity and chemical search space, creating major impediments toward developing a defect genome. In this paper, we overcome these impediments by employing computationally tractable ab initio models driven by highly scalable workflows, to study formation and interaction of various point defectsmore » (e.g., O vacancies, H interstitials, and Y substitutional dopant), in over 80 cubic perovskites, for potential proton-conducting ceramic fuel cell (PCFC) applications. The resulting defect data sets identify several promising perovskite compounds that can exhibit high proton conductivity. Furthermore, the data sets also enable us to identify and explain, insightful and novel correlations among defect energies, material identities, and defect-induced local structural distortions. Finally, such defect data sets and resultant correlations are necessary to build statistical machine learning models, which are required to accelerate discovery of new materials.« less

Defect Genome of Cubic Perovskites for Fuel Cell Applications

DOE PAGES

Balachandran, Janakiraman; Lin, Lianshan; Anchell, Jonathan S.; ...

2017-10-10

Heterogeneities such as point defects, inherent to material systems, can profoundly influence material functionalities critical for numerous energy applications. This influence in principle can be identified and quantified through development of large defect data sets which we call the defect genome, employing high-throughput ab initio calculations. However, high-throughput screening of material models with point defects dramatically increases the computational complexity and chemical search space, creating major impediments toward developing a defect genome. In this paper, we overcome these impediments by employing computationally tractable ab initio models driven by highly scalable workflows, to study formation and interaction of various point defectsmore » (e.g., O vacancies, H interstitials, and Y substitutional dopant), in over 80 cubic perovskites, for potential proton-conducting ceramic fuel cell (PCFC) applications. The resulting defect data sets identify several promising perovskite compounds that can exhibit high proton conductivity. Furthermore, the data sets also enable us to identify and explain, insightful and novel correlations among defect energies, material identities, and defect-induced local structural distortions. Finally, such defect data sets and resultant correlations are necessary to build statistical machine learning models, which are required to accelerate discovery of new materials.« less

Point defects in CdTe xSe 1-x crystals grown from a Te-rich solution for applications in detecting radiation

DOE PAGES

Gul, R.; Roy, U. N.; Bolotnikov, A. E.; ...

2015-04-15

We investigated cadmium telluride selenide (CdTeSe) crystals, newly grown by the Traveling Heater Method (THM), for the presence and abundance of point defects. Deep Level Transient spectroscopy (I-DLTS) was used to determine the energies of the traps, their capture cross sections, and densities. The bias across the detectors was varied from (1–30) V. Four types of point defects were identified, ranging from 10 meV to 0.35 eV. Two dominant traps at energies of 0.18 eV and 0.14 eV were studied in depth. Cd vacancies are found at lower concentrations than other point defects present in the material.

Use of Isobestic and Isoemission Points in Absorption and Luminescence Spectra for Study of the Transformation of Radiation Defects in Lithium Fluoride

NASA Astrophysics Data System (ADS)

Voitovich, A. P.; Kalinov, V. S.; Stupak, A. P.; Runets, L. P.

2015-03-01

Isobestic and isoemission points are recorded in the combined absorption and luminescence spectra of two types of radiation defects involved in complex processes consisting of several simultaneous parallel and sequential reactions. These points are observed if a constant sum of two terms, each formed by the product of the concentration of the corresponding defect and a characteristic integral coefficient associated with it, is conserved. The complicated processes involved in the transformation of radiation defects in lithium fluoride are studied using these points. It is found that the ratio of the changes in the concentrations of one of the components and the reaction product remains constant in the course of several simultaneous reactions.

Flat band in disorder-driven non-Hermitian Weyl semimetals

NASA Astrophysics Data System (ADS)

Zyuzin, A. A.; Zyuzin, A. Yu.

2018-01-01

We study the interplay of disorder and band-structure topology in a Weyl semimetal with a tilted conical spectrum around the Weyl points. The spectrum of particles is given by the eigenvalues of a non-Hermitian matrix, which contains contributions from a Weyl Hamiltonian and complex self-energy due to electron elastic scattering on disorder. We find that the tilt-induced matrix structure of the self-energy gives rise to either a flat band or a nodal line segment at the interface of the electron and hole pockets in the bulk band structure of type-II Weyl semimetals depending on the Weyl cone inclination. For the tilt in a single direction in momentum space, each Weyl point expands into a flat band lying on the plane, which is transverse to the direction of the tilt. The spectrum of the flat band is fully imaginary and is separated from the in-plane dispersive part of the spectrum by the "exceptional nodal ring" where the matrix of the Green's function in momentum-frequency space is defective. The tilt in two directions might shrink a flat band into a nodal line segment with "exceptional edge points." We discuss the connection to the non-Hermitian topological theory.

Characterization of point defects in monolayer arsenene

NASA Astrophysics Data System (ADS)

Liang, Xiongyi; Ng, Siu-Pang; Ding, Ning; Wu, Chi-Man Lawrence

2018-06-01

Topological defects that are inevitably found in 2D materials can dramatically affect their properties. Using density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) method, the structural, thermodynamic, electronic and magnetic properties of six types of typical point defects in arsenene, i.e. the Stone-Wales defect, single and double vacancies and adatoms, were systemically studied. It was found that these defects were all more easily generated in arsenene with lower formation energies than those with graphene and silicene. Stone-Wales defects can be transformed from pristine arsenene by overcoming a barrier of 2.19 eV and single vacancy defects tend to coalesce into double vacancy defects by diffusion. However, a type of adatom defect does not exhibit kinetic stability at room temperature. In addition, SV defects and another type of adatom defect can remarkably affect the electronic and magnetic properties of arsenene, e.g. they can introduce localized states near the Fermi level, as well as a strongly local magnetic moment due to dangling bond and unpaired electron. Furthermore, the simulated scanning tunneling microscopy (STM) and Raman spectroscopy were computed and the types of point defects can be fully characterized by correlating the STM images and Raman spectra to the defective atomistic structures. The results provide significant insights to the effect of defects in arsenene for potential applications, as well as identifications of two helpful tools (STM and Raman spectroscopy) to distinguish the type of defects in arsenene for future experiments.

Effect of point defects on the electronic density states of SnC nanosheets: First-principles calculations

NASA Astrophysics Data System (ADS)

Majidi, Soleyman; Achour, Amine; Rai, D. P.; Nayebi, Payman; Solaymani, Shahram; Beryani Nezafat, Negin; Elahi, Seyed Mohammad

In this work, we investigated the electronic and structural properties of various defects including single Sn and C vacancies, double vacancy of the Sn and C atoms, anti-sites, position exchange and the Stone-Wales (SW) defects in SnC nanosheets by using density-functional theory (DFT). We found that various vacancy defects in the SnC monolayer can change the electronic and structural properties. Our results show that the SnC is an indirect band gap compound, with the band gap of 2.10 eV. The system turns into metal for both structure of the single Sn and C vacancies. However, for the double vacancy contained Sn and C atoms, the structure remains semiconductor with the direct band gap of 0.37 eV at the G point. We also found that for anti-site defects, the structure remains semiconductor and for the exchange defect, the structure becomes indirect semiconductor with the K-G point and the band gap of 0.74 eV. Finally, the structure of SW defect remains semiconductor with the direct band gap at K point with band gap of 0.54 eV.

Prediction of guided wave scattering by defects in rails using numerical modelling

NASA Astrophysics Data System (ADS)

Long, Craig S.; Loveday, Philip W.

2014-02-01

A guided wave based monitoring system for welded freight rail, has previously been developed. The current arrangement consists of alternating transmit and receive stations positioned roughly 1 km apart, and is designed to reliably detect complete breaks in a rail. Current research efforts are focused on extending this system to include a pulse-echo mode of operation in order to detect, locate, monitor and possibly characterize damage, before a complete break occurs. For monitoring and inspection applications, it is beneficial to be able to distinguish between scattering defects which do not represent damage (such as welds) and cracks which could result in rail breaks. In this paper we investigate the complex interaction between selected propagating modes and various weld and crack geometries in an attempt to relate scattering behaviour to defect geometry. An efficient hybrid method is employed which models the volume containing the defect with conventional solid finite elements, while the semi-infinite incoming and outgoing waveguides are accounted for using the SAFE method. Four candidate modes, suitable for long range propagation, are identified and evaluated. A weighted average reflection coefficient is used as a measure to quantify mode conversion between these four modes, and results are represented graphically in the form of reflection maps. The results show that it should be possible to distinguish between a large crack in the crown of the rail and a weld. We also show that there may be difficulties associated with reliably identifying cracks in the web as well as cracks in the crown which occur at a thermite weld. We suspect that it will be difficult to detect damage in the foot of the rail.

Direct observation of vast off-stoichiometric defects in single crystalline SnSe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Di; Wu, Lijun; He, Dongsheng

Single crystalline tin selenide (SnSe) recently emerged as a very promising thermoelectric material for waste heat harvesting and thermoelectric cooling, due to its record high figure of merit ZT in mediate temperature range. The most striking feature of SnSe lies in its extremely low lattice thermal conductivity as ascribed to the anisotropic and highly distorted Sn-Se bonds as well as the giant bond anharmonicity by previous studies, yet no theoretical models so far can give a quantitative explanation to such low a lattice thermal conductivity. Here, we presented direct observation of an astonishingly vast number of off-stoichiometric Sn vacancies andmore » Se interstitials, using sophisticated aberration corrected scanning transmission electron microscope; and credited the previously reported ultralow thermal conductivity of the SnSe single crystalline samples partly to their off-stoichiometric feature. In order to further validate the conclusion, we also synthesized stoichiometric SnSe single crystalline samples, and illustrated that the lattice thermal conductivity is deed much higher as compared with the off-stoichiometric single crystals. Finally, the scattering efficiency of individual point defect on heat-carrying phonons was then discussed in the state-of-art Debye-Callaway model.« less

Direct observation of vast off-stoichiometric defects in single crystalline SnSe

DOE PAGES

Wu, Di; Wu, Lijun; He, Dongsheng; ...

2017-04-06

Single crystalline tin selenide (SnSe) recently emerged as a very promising thermoelectric material for waste heat harvesting and thermoelectric cooling, due to its record high figure of merit ZT in mediate temperature range. The most striking feature of SnSe lies in its extremely low lattice thermal conductivity as ascribed to the anisotropic and highly distorted Sn-Se bonds as well as the giant bond anharmonicity by previous studies, yet no theoretical models so far can give a quantitative explanation to such low a lattice thermal conductivity. Here, we presented direct observation of an astonishingly vast number of off-stoichiometric Sn vacancies andmore » Se interstitials, using sophisticated aberration corrected scanning transmission electron microscope; and credited the previously reported ultralow thermal conductivity of the SnSe single crystalline samples partly to their off-stoichiometric feature. In order to further validate the conclusion, we also synthesized stoichiometric SnSe single crystalline samples, and illustrated that the lattice thermal conductivity is deed much higher as compared with the off-stoichiometric single crystals. Finally, the scattering efficiency of individual point defect on heat-carrying phonons was then discussed in the state-of-art Debye-Callaway model.« less

Influence of defects and doping on phonon transport properties of monolayer MoSe2

NASA Astrophysics Data System (ADS)

Yan, Zhequan; Yoon, Mina; Kumar, Satish

2018-07-01

The doping of monolayer MoSe2 by tungsten (W) can suppress the Se vacancy concentration, but how doping and resulting change in defect concentration can tune its thermal properties is not understood yet. We use first-principles density functional theory (DFT) along with the phonon Boltzmann transport equation (BTE) to study the phonon transport properties of pristine MoSe2 and W doped MoSe2 with and without the presence of Se vacancies. We found that for samples without Se vacancy, the W doping could enhance the thermal transport of monolayer MoSe2 due to reduced three-phonon scattering phase space. For example, we observed that the 16.7% W doping increases the thermal conductivity of the monolayer MoSe2 with 2% Se vacancy by 80% if all vacancies can be suppressed by W-doping. However, the W doping in the defective MoSe2 amplifies the influence of the phonon scattering caused by the Se vacancies, which results in a further decrease in thermal conductivity of monolayer MoSe2 with defects. This is found to be related with higher phonon density of states of Mo0.83W0.17Se2 and larger mass difference between W and Se atoms compared to Mo and Se atoms. This study deciphers the effect of defects and doping on the thermal conductivity of monolayer MoSe2, which helps us understand the mechanism of defect-induced phonon transport, and provides insights into enhancing the heat dissipation in MoSe2-based electronic devices.

A Baseline-Free Defect Imaging Technique in Plates Using Time Reversal of Lamb Waves

NASA Astrophysics Data System (ADS)

Hyunjo, Jeong; Sungjong, Cho; Wei, Wei

2011-06-01

We present an analytical investigation for a baseline-free imaging of a defect in plate-like structures using the time-reversal of Lamb waves. We first consider the flexural wave (A0 mode) propagation in a plate containing a defect, and reception and time reversal process of the output signal at the receiver. The received output signal is then composed of two parts: a directly propagated wave and a scattered wave from the defect. The time reversal of these waves recovers the original input signal, and produces two additional sidebands that contain the time-of-flight information on the defect location. One of the side-band signals is then extracted as a pure defect signal. A defect localization image is then constructed from a beamforming technique based on the time-frequency analysis of the side band signal for each transducer pair in a network of sensors. The simulation results show that the proposed scheme enables the accurate, baseline-free imaging of a defect.

Plant photonics: application of optical coherence tomography to monitor defects and rots in onion

NASA Astrophysics Data System (ADS)

Meglinski, I. V.; Buranachai, C.; Terry, L. A.

2010-04-01

The incidence of physiological and/or pathological defects in many fresh produce types is still unacceptably high and accounts for a large proportion of waste. With increasing interest in food security their remains strong demand in developing reliable and cost effective technologies for non-destructive screening of internal defects and rots, these being deemed unacceptable by consumers. It is well recognized that the internal defects and structure of turbid scattering media can be effectively visualized by using optical coherence tomography (OCT). In the present study, the high spatial resolution and advantages of OCT have been demonstrated for imaging the skins and outer laminae (concentric tissue layers) of intact whole onion bulbs with a view to non-invasively visualizing potential incidence/severity of internal defects.

A Method for Automatic Surface Inspection Using a Model-Based 3D Descriptor.

PubMed

Madrigal, Carlos A; Branch, John W; Restrepo, Alejandro; Mery, Domingo

2017-10-02

Automatic visual inspection allows for the identification of surface defects in manufactured parts. Nevertheless, when defects are on a sub-millimeter scale, detection and recognition are a challenge. This is particularly true when the defect generates topological deformations that are not shown with strong contrast in the 2D image. In this paper, we present a method for recognizing surface defects in 3D point clouds. Firstly, we propose a novel 3D local descriptor called the Model Point Feature Histogram (MPFH) for defect detection. Our descriptor is inspired from earlier descriptors such as the Point Feature Histogram (PFH). To construct the MPFH descriptor, the models that best fit the local surface and their normal vectors are estimated. For each surface model, its contribution weight to the formation of the surface region is calculated and from the relative difference between models of the same region a histogram is generated representing the underlying surface changes. Secondly, through a classification stage, the points on the surface are labeled according to five types of primitives and the defect is detected. Thirdly, the connected components of primitives are projected to a plane, forming a 2D image. Finally, 2D geometrical features are extracted and by a support vector machine, the defects are recognized. The database used is composed of 3D simulated surfaces and 3D reconstructions of defects in welding, artificial teeth, indentations in materials, ceramics and 3D models of defects. The quantitative and qualitative results showed that the proposed method of description is robust to noise and the scale factor, and it is sufficiently discriminative for detecting some surface defects. The performance evaluation of the proposed method was performed for a classification task of the 3D point cloud in primitives, reporting an accuracy of 95%, which is higher than for other state-of-art descriptors. The rate of recognition of defects was close to 94%.

A Method for Automatic Surface Inspection Using a Model-Based 3D Descriptor

PubMed Central

Branch, John W.

2017-01-01

Automatic visual inspection allows for the identification of surface defects in manufactured parts. Nevertheless, when defects are on a sub-millimeter scale, detection and recognition are a challenge. This is particularly true when the defect generates topological deformations that are not shown with strong contrast in the 2D image. In this paper, we present a method for recognizing surface defects in 3D point clouds. Firstly, we propose a novel 3D local descriptor called the Model Point Feature Histogram (MPFH) for defect detection. Our descriptor is inspired from earlier descriptors such as the Point Feature Histogram (PFH). To construct the MPFH descriptor, the models that best fit the local surface and their normal vectors are estimated. For each surface model, its contribution weight to the formation of the surface region is calculated and from the relative difference between models of the same region a histogram is generated representing the underlying surface changes. Secondly, through a classification stage, the points on the surface are labeled according to five types of primitives and the defect is detected. Thirdly, the connected components of primitives are projected to a plane, forming a 2D image. Finally, 2D geometrical features are extracted and by a support vector machine, the defects are recognized. The database used is composed of 3D simulated surfaces and 3D reconstructions of defects in welding, artificial teeth, indentations in materials, ceramics and 3D models of defects. The quantitative and qualitative results showed that the proposed method of description is robust to noise and the scale factor, and it is sufficiently discriminative for detecting some surface defects. The performance evaluation of the proposed method was performed for a classification task of the 3D point cloud in primitives, reporting an accuracy of 95%, which is higher than for other state-of-art descriptors. The rate of recognition of defects was close to 94%. PMID:28974037

Optically inactive defects in monolayer and bilayer phosphorene: A first-principles study

NASA Astrophysics Data System (ADS)

Huang, Ling-yi; Zhang, Xu; Zhang, Mingliang; Lu, Gang

2018-05-01

Many-body excitonic effect is crucial in two-dimensional (2D) materials and can significantly impact their optoelectronic properties. Because defects are inevitable in 2D materials, understanding how they influence the optical and excitonic properties of the 2D materials is of significant scientific and technological importance. Here we focus on intrinsic point defects in monolayer and bilayer phosphorene and examine whether and how their optoelectronic properties may be modified by the defects. Based on large-scale first-principles calculations, we have systematically explored the optical and excitonic properties of phosphorene in the presence and absence of the point defects. We find that the optical properties of bilayer phosphorene depend on the stacking order of the layers. More importantly, we reveal that the dominant point defects in few-layer phosphorene are optically inactive, which renders phosphorene particularly attractive in optoelectronic applications.

Characterization of Local Carrier Dynamics in AlN and AlGaN Films using High Spatial- and Time-resolution Cathodoluminescence Spectroscopy

DTIC Science & Technology

2012-10-12

21/2012 Abstract: In order to assess the impacts of structural and point defects on the local carrier (exciton) recombination dynamics in...quantitatively understood as functions of structural / point defect and impurity concentrations (crystal imperfections). However, only few papers [5...NOTES 14. ABSTRACT In order to assess the impacts of structural and point defects on the local carrier (exciton) recombination dynamics in wide bandgap

Dipole oscillations of a Bose-Einstein condensate in the presence of defects and disorder.

PubMed

Albert, M; Paul, T; Pavloff, N; Leboeuf, P

2008-06-27

We consider dipole oscillations of a trapped dilute Bose-Einstein condensate in the presence of a scattering potential consisting either in a localized defect or in an extended disordered potential. In both cases the breaking of superfluidity and the damping of the oscillations are shown to be related to the appearance of a nonlinear dissipative flow. At supersonic velocities the flow becomes asymptotically dissipationless.

Modeling a distribution of point defects as misfitting inclusions in stressed solids

NASA Astrophysics Data System (ADS)

Cai, W.; Sills, R. B.; Barnett, D. M.; Nix, W. D.

2014-05-01

The chemical equilibrium distribution of point defects modeled as non-overlapping, spherical inclusions with purely positive dilatational eigenstrain in an isotropically elastic solid is derived. The compressive self-stress inside existing inclusions must be excluded from the stress dependence of the equilibrium concentration of the point defects, because it does no work when a new inclusion is introduced. On the other hand, a tensile image stress field must be included to satisfy the boundary conditions in a finite solid. Through the image stress, existing inclusions promote the introduction of additional inclusions. This is contrary to the prevailing approach in the literature in which the equilibrium point defect concentration depends on a homogenized stress field that includes the compressive self-stress. The shear stress field generated by the equilibrium distribution of such inclusions is proved to be proportional to the pre-existing stress field in the solid, provided that the magnitude of the latter is small, so that a solid containing an equilibrium concentration of point defects can be described by a set of effective elastic constants in the small-stress limit.

Influence of multiple scattering and absorption on the full scattering profile and the isobaric point in tissue

NASA Astrophysics Data System (ADS)

Duadi, Hamootal; Fixler, Dror

2015-05-01

Light reflectance and transmission from soft tissue has been utilized in noninvasive clinical measurement devices such as the photoplethysmograph (PPG) and reflectance pulse oximeter. Incident light on the skin travels into the underlying layers and is in part reflected back to the surface, in part transferred and in part absorbed. Most methods of near infrared (NIR) spectroscopy focus on the volume reflectance from a semi-infinite sample, while very few measure transmission. We have previously shown that examining the full scattering profile (angular distribution of exiting photons) provides more comprehensive information when measuring from a cylindrical tissue. Furthermore, an isobaric point was found which is not dependent on changes in the reduced scattering coefficient. The angle corresponding to this isobaric point depends on the tissue diameter. We investigated the role of multiple scattering and absorption on the full scattering profile of a cylindrical tissue. First, we define the range in which multiple scattering occurs for different tissue diameters. Next, we examine the role of the absorption coefficient in the attenuation of the full scattering profile. We demonstrate that the absorption linearly influences the intensity at each angle of the full scattering profile and, more importantly, the absorption does not change the position of the isobaric point. The findings of this work demonstrate a realistic model for optical tissue measurements such as NIR spectroscopy, PPG, and pulse oximetery.

Luminescence properties of defects in GaN

NASA Astrophysics Data System (ADS)

Reshchikov, Michael A.; Morkoç, Hadis

2005-03-01

Gallium nitride (GaN) and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet (UV) emitters and detectors (in photon ranges inaccessible by other semiconductors) and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these nitride semiconductors. Even though GaN broke the long-standing paradigm that high density of dislocations precludes acceptable device performance, point defects have taken the center stage as they exacerbate efforts to increase the efficiency of emitters, increase laser operation lifetime, and lead to anomalies in electronic devices. The point defects include native isolated defects (vacancies, interstitial, and antisites), intentional or unintentional impurities, as well as complexes involving different combinations of the isolated defects. Further improvements in device performance and longevity hinge on an in-depth understanding of point defects and their reduction. In this review a comprehensive and critical analysis of point defects in GaN, particularly their manifestation in luminescence, is presented. In addition to a comprehensive analysis of native point defects, the signatures of intentionally and unintentionally introduced impurities are addressed. The review discusses in detail the characteristics and the origin of the major luminescence bands including the ultraviolet, blue, green, yellow, and red bands in undoped GaN. The effects of important group-II impurities, such as Zn and Mg on the photoluminescence of GaN, are treated in detail. Similarly, but to a lesser extent, the effects of other impurities, such as C, Si, H, O, Be, Mn, Cd, etc., on the luminescence properties of GaN are also reviewed. Further, atypical luminescence lines which are tentatively attributed to the surface and structural defects are discussed. The effect of surfaces and surface preparation, particularly wet and dry etching, exposure to UV light in vacuum or controlled gas ambient, annealing, and ion implantation on the characteristics of the defect-related emissions is described.

Optimization of the defects and the nonradiative lifetime of GaAs/AlGaAs double heterostructures

NASA Astrophysics Data System (ADS)

Cevher, Z.; Folkes, P. A.; Hier, H. S.; VanMil, B. L.; Connelly, B. C.; Beck, W. A.; Ren, Y. H.

2018-04-01

We used Raman scattering and time-resolved photoluminescence spectroscopy to investigate the molecular-beam-epitaxy (MBE) growth parameters that optimize the structural defects and therefore the internal radiative quantum efficiency of MBE-grown GaAs/AlGaAs double heterostructures (DH). The DH structures were grown at two different temperatures and three different As/Ga flux ratios to determine the conditions for an optimized structure with the longest nonradiative minority carrier lifetime. Raman scattering measurements show an improvement in the lattice disorder in the AlGaAs and GaAs layers as the As/Ga flux ratio is reduced from 40 to 15 and as the growth temperature is increased from 550 to 595 °C. The optimized structure is obtained with the As/Ga flux ratio equal to 15 and the substrate temperature 595 °C. This is consistent with the fact that the optimized structure has the longest minority carrier lifetime. Moreover, our Raman studies reveal that incorporation of a distributed Bragg reflector layer between the substrate and DH structures significantly reduces the defect density in the subsequent epitaxial layers.

Magnetic Modes in Rare Earth Perovskites: A Magnetic-Field-Dependent Inelastic Light Scattering study.

PubMed

Saha, Surajit; Cao, Bing-Chen; Motapothula, M; Cong, Chun-Xiao; Sarkar, Tarapada; Srivastava, Amar; Sarkar, Soumya; Patra, Abhijeet; Ghosh, Siddhartha; Ariando; Coey, J M D; Yu, Ting; Venkatesan, T

2016-11-15

Here, we report the presence of defect-related states with magnetic degrees of freedom in crystals of LaAlO 3 and several other rare-earth based perovskite oxides using inelastic light scattering (Raman spectroscopy) at low temperatures in applied magnetic fields of up to 9 T. Some of these states are at about 140 meV above the valence band maximum while others are mid-gap states at about 2.3 eV. No magnetic impurity could be detected in LaAlO 3 by Proton-Induced X-ray Emission Spectroscopy. We, therefore, attribute the angular momentum-like states in LaAlO 3 to cationic/anionic vacancies or anti-site defects. Comparison with the other rare earth perovskites leads to the empirical rule that the magnetic-field-sensitive transitions require planes of heavy elements (e.g. lanthanum) and oxygen without any other light cations in the same plane. These magnetic degrees of freedom in rare earth perovskites with useful dielectric properties may be tunable by appropriate defect engineering for magneto-optic applications.

System-size convergence of point defect properties: The case of the silicon vacancy

NASA Astrophysics Data System (ADS)

Corsetti, Fabiano; Mostofi, Arash A.

2011-07-01

We present a comprehensive study of the vacancy in bulk silicon in all its charge states from 2+ to 2-, using a supercell approach within plane-wave density-functional theory, and systematically quantify the various contributions to the well-known finite size errors associated with calculating formation energies and stable charge state transition levels of isolated defects with periodic boundary conditions. Furthermore, we find that transition levels converge faster with respect to supercell size when only the Γ-point is sampled in the Brillouin zone, as opposed to a dense k-point sampling. This arises from the fact that defect level at the Γ-point quickly converges to a fixed value which correctly describes the bonding at the defect center. Our calculated transition levels with 1000-atom supercells and Γ-point only sampling are in good agreement with available experimental results. We also demonstrate two simple and accurate approaches for calculating the valence band offsets that are required for computing formation energies of charged defects, one based on a potential averaging scheme and the other using maximally-localized Wannier functions (MLWFs). Finally, we show that MLWFs provide a clear description of the nature of the electronic bonding at the defect center that verifies the canonical Watkins model.

International Conference on Defects in Semiconductors (19th), ICDS-19, Held in Aveiro, Portugal on 21-25 July 1997, Part 1

DTIC Science & Technology

1998-01-23

scattering profiles. We note [CAs] ~ 1020 cm-3) foUomng anneals at ^ ^ symmetry of the defect can also be 850°C for up to 4h ( Kr+ ion laser source ...to be the source of n-type conductivity. Our first-principles investigations, however, indicate that nitrogen vacancies are high-energy defects in n...1996) [ 37 ] C. G. Van de Walle (to be published). [38] W. Götz, N. M. Johnson, J. Walker, D. P. Bour, and R. A. Street, Appl. Phys. Lett. 68, 667(1996

PyCDT: A Python toolkit for modeling point defects in semiconductors and insulators

DOE PAGES

Broberg, Danny; Medasani, Bharat; Zimmermann, Nils E. R.; ...

2018-02-13

Point defects have a strong impact on the performance of semiconductor and insulator materials used in technological applications, spanning microelectronics to energy conversion and storage. The nature of the dominant defect types, how they vary with processing conditions, and their impact on materials properties are central aspects that determine the performance of a material in a certain application. This information is, however, difficult to access directly from experimental measurements. Consequently, computational methods, based on electronic density functional theory (DFT), have found widespread use in the calculation of point-defect properties. Here we have developed the Python Charged Defect Toolkit (PyCDT) tomore » expedite the setup and post-processing of defect calculations with widely used DFT software. PyCDT has a user-friendly command-line interface and provides a direct interface with the Materials Project database. This allows for setting up many charged defect calculations for any material of interest, as well as post-processing and applying state-of-the-art electrostatic correction terms. Our paper serves as a documentation for PyCDT, and demonstrates its use in an application to the well-studied GaAs compound semiconductor. As a result, we anticipate that the PyCDT code will be useful as a framework for undertaking readily reproducible calculations of charged point-defect properties, and that it will provide a foundation for automated, high-throughput calculations.« less

PyCDT: A Python toolkit for modeling point defects in semiconductors and insulators

NASA Astrophysics Data System (ADS)

Broberg, Danny; Medasani, Bharat; Zimmermann, Nils E. R.; Yu, Guodong; Canning, Andrew; Haranczyk, Maciej; Asta, Mark; Hautier, Geoffroy

2018-05-01

Point defects have a strong impact on the performance of semiconductor and insulator materials used in technological applications, spanning microelectronics to energy conversion and storage. The nature of the dominant defect types, how they vary with processing conditions, and their impact on materials properties are central aspects that determine the performance of a material in a certain application. This information is, however, difficult to access directly from experimental measurements. Consequently, computational methods, based on electronic density functional theory (DFT), have found widespread use in the calculation of point-defect properties. Here we have developed the Python Charged Defect Toolkit (PyCDT) to expedite the setup and post-processing of defect calculations with widely used DFT software. PyCDT has a user-friendly command-line interface and provides a direct interface with the Materials Project database. This allows for setting up many charged defect calculations for any material of interest, as well as post-processing and applying state-of-the-art electrostatic correction terms. Our paper serves as a documentation for PyCDT, and demonstrates its use in an application to the well-studied GaAs compound semiconductor. We anticipate that the PyCDT code will be useful as a framework for undertaking readily reproducible calculations of charged point-defect properties, and that it will provide a foundation for automated, high-throughput calculations.

PyCDT: A Python toolkit for modeling point defects in semiconductors and insulators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Broberg, Danny; Medasani, Bharat; Zimmermann, Nils E. R.

Point defects have a strong impact on the performance of semiconductor and insulator materials used in technological applications, spanning microelectronics to energy conversion and storage. The nature of the dominant defect types, how they vary with processing conditions, and their impact on materials properties are central aspects that determine the performance of a material in a certain application. This information is, however, difficult to access directly from experimental measurements. Consequently, computational methods, based on electronic density functional theory DFT), have found widespread use in the calculation of point defect properties. Here we have developed the Python Charged Defect Toolkit (PyCDT)more » to expedite the setup and post-processing of defect calculations with widely used DFT software. PyCDT has a user-friendly command-line interface and provides a direct interface with the Materials Project database. This allows for setting up many charged defect calculations for any material of interest, as well as post-processing and applying state-of-the-art electrostatic correction terms. Our paper serves as a documentation for PyCDT, and demonstrates its use in an application to the well-studied GaAs compound semiconductor. We anticipate that the PyCDT code will be useful as a framework for undertaking readily reproducible calculations of charged point-defect properties, and that it will provide a foundation for automated, high-throughput calculations.« less

PyCDT: A Python toolkit for modeling point defects in semiconductors and insulators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Broberg, Danny; Medasani, Bharat; Zimmermann, Nils E. R.

Point defects have a strong impact on the performance of semiconductor and insulator materials used in technological applications, spanning microelectronics to energy conversion and storage. The nature of the dominant defect types, how they vary with processing conditions, and their impact on materials properties are central aspects that determine the performance of a material in a certain application. This information is, however, difficult to access directly from experimental measurements. Consequently, computational methods, based on electronic density functional theory (DFT), have found widespread use in the calculation of point-defect properties. Here we have developed the Python Charged Defect Toolkit (PyCDT) tomore » expedite the setup and post-processing of defect calculations with widely used DFT software. PyCDT has a user-friendly command-line interface and provides a direct interface with the Materials Project database. This allows for setting up many charged defect calculations for any material of interest, as well as post-processing and applying state-of-the-art electrostatic correction terms. Our paper serves as a documentation for PyCDT, and demonstrates its use in an application to the well-studied GaAs compound semiconductor. As a result, we anticipate that the PyCDT code will be useful as a framework for undertaking readily reproducible calculations of charged point-defect properties, and that it will provide a foundation for automated, high-throughput calculations.« less

Line and point defects in nonlinear anisotropic solids

NASA Astrophysics Data System (ADS)

Golgoon, Ashkan; Yavari, Arash

2018-06-01

In this paper, we present some analytical solutions for the stress fields of nonlinear anisotropic solids with distributed line and point defects. In particular, we determine the stress fields of (i) a parallel cylindrically symmetric distribution of screw dislocations in infinite orthotropic and monoclinic media, (ii) a cylindrically symmetric distribution of parallel wedge disclinations in an infinite orthotropic medium, (iii) a distribution of edge dislocations in an orthotropic medium, and (iv) a spherically symmetric distribution of point defects in a transversely isotropic spherical ball.

Brillouin light scattering from surface acoustic waves in a subwavelength-diameter optical fibre

PubMed Central

Beugnot, Jean-Charles; Lebrun, Sylvie; Pauliat, Gilles; Maillotte, Hervé; Laude, Vincent; Sylvestre, Thibaut

2014-01-01

Brillouin scattering in optical fibres is a fundamental interaction between light and sound with important implications ranging from optical sensors to slow and fast light. In usual optical fibres, light both excites and feels shear and longitudinal bulk elastic waves, giving rise to forward-guided acoustic wave Brillouin scattering and backward-stimulated Brillouin scattering. In a subwavelength-diameter optical fibre, the situation changes dramatically, as we here report with the first experimental observation of Brillouin light scattering from surface acoustic waves. These Rayleigh-type surface waves travel the wire surface at a specific velocity of 3,400 m s−1 and backscatter the light with a Doppler shift of about 6 GHz. As these acoustic resonances are sensitive to surface defects or features, surface acoustic wave Brillouin scattering opens new opportunities for various sensing applications, but also in other domains such as microwave photonics and nonlinear plasmonics. PMID:25341638

A DFT study on the failure mechanism of Al2O3 film by various point defects in solution

NASA Astrophysics Data System (ADS)

Zhang, Chuan-Hui; Chen, Bao; Jin, Ying; Sun, Dong-Bai

2018-03-01

The defects on oxide film surface are very important, and they would occur when the film is peeled or scratched. The periodic DFT calculations have been performed on Al2O3 surface to model the influences of various point-defects. Three kinds of point defect surfaces (vacancy, inversion, substitution) are considered, and the molecular H2O dissociation and the transition state are calculated. The predicted formation energy of O vacancy is 8.30 eV, whereas that corresponding to the formation of Al vacancy is found to be at least a 55% larger. On the vacancy point defect surfaces, upward H2O molecule surfaces prefer to occur chemical reaction, leading the surfaces to be hydroxylated. And then the D-Cl-substitution-Al surface is corroded, which suggests a Cl adsorption induced failure mechanism of the oxide film. At last, the process of H2O dissociation on the OH-substitution-Al surfaces with four or five transition paths are discussed.

Phonon conduction in GaN-diamond composite substrates

NASA Astrophysics Data System (ADS)

Cho, Jungwan; Francis, Daniel; Altman, David H.; Asheghi, Mehdi; Goodson, Kenneth E.

2017-02-01

The integration of strongly contrasting materials can enable performance benefits for semiconductor devices. One example is composite substrates of gallium nitride (GaN) and diamond, which promise dramatically improved conduction cooling of high-power GaN transistors. Here, we examine phonon conduction in GaN-diamond composite substrates fabricated using a GaN epilayer transfer process through transmission electron microscopy, measurements using time-domain thermoreflectance, and semiclassical transport theory for phonons interacting with interfaces and defects. Thermoreflectance amplitude and ratio signals are analyzed at multiple modulation frequencies to simultaneously extract the thermal conductivity of GaN layers and the thermal boundary resistance across GaN-diamond interfaces at room temperature. Uncertainties in the measurement of these two properties are estimated considering those of parameters, including the thickness of a topmost metal transducer layer, given as an input to a multilayer thermal model, as well as those associated with simultaneously fitting the two properties. The volume resistance of an intermediate, disordered SiN layer between the GaN and diamond, as well as a presence of near-interfacial defects in the GaN and diamond, dominates the measured GaN-diamond thermal boundary resistances as low as 17 m2 K GW-1. The GaN thermal conductivity data are consistent with the semiclassical phonon thermal conductivity integral model that accounts for the size effect as well as phonon scattering on point defects at concentrations near 3 × 1018 cm-3.

Crystal pathologies in macromolecular crystallography.

PubMed

Dauter, Zbigniew; Jaskólski, Mariusz

Macromolecules, such as proteins or nucleic acids, form crystals with a large volume fraction of water, ~50% on average. Apart from typical physical defects and rather trivial poor quality problems, macromolecular crystals, as essentially any crystals, can also suffer from several kinds of pathologies, in which everything seems to be perfect, except that from the structural point of view the interpretation may be very difficult, sometimes even impossible. A frequent nuisance is pseudosymmetry, or non-crystallographic symmetry (NCS), which is particularly nasty when it has translational character. Lattice-translocation defects, also called order-disorder twinning (OD-twinning), occur when molecules are packed regularly in layers but the layers are stacked (without rotation) in two (or more) discrete modes, with a unique translocation vector. Crystal twinning arises when twin domains have different orientations, incompatible with the symmetry of the crystal structure. There are also crystals in which the periodic (lattice) order is broken or absent altogether. When the strict short-range translational order from one unit cell to the next is lost but the long-range order is restored by a periodic modulation, we have a modulated crystal structure. In quasicrystals (not observed for macromolecules yet), the periodic order (in 3D space) is lost completely and the diffraction pattern (which is still discrete) cannot be even indexed using three hkl indices. In addition, there are other physical defects and phenomena (such as high mosaicity, diffraction anisotropy, diffuse scattering, etc.) which make diffraction data processing and structure solution difficult or even impossible.

Natural nanostructure and superlattice nanodomains in AgSbTe{sub 2}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carlton, Christopher E.; De Armas, Ricardo; Shao-Horn, Yang, E-mail: delaireoa@ornl.gov, E-mail: shaohorn@mit.edu

2014-04-14

AgSbTe{sub 2} has long been of interest for thermoelectric applications because of its favorable electronic properties and its low lattice thermal conductivity of ∼0.7 W/mK. In this work, we report new findings from a high-resolution transmission electron microscopy study revealing two nanostructures in single crystal Ag{sub 1−x}Sb{sub 1+x}Sb{sub 2+x} (with x = 0, 0.1, 0.2); (i) a rippled natural nanostructure with a period of ∼2.5–5 nm and (ii) superlattice ordered nanodomains consistent with cation ordering predicted in previous density functional theory studies. These nanostructures, combined with point-defects, probably serve as sources of scattering for phonons, thereby yielding a low lattice thermal conductivity over amore » wide temperature range.« less

Effect of optical damage resistant dopants on the dielectric properties of LiNbO3: Insight from broadband impedance spectroscopy and Raman scattering

NASA Astrophysics Data System (ADS)

Cochard, Charlotte; Guennou, Mael; Spielmann, Thiemo; van Hoof, Niels; Halpin, Alexei; Granzow, Torsten

2018-04-01

Optical damage limits the application range of congruent LiNbO3. This problem is commonly overcome by adding optical-damage-resistant cations. Here, the influence of doping with optical-damage-resistant Mg and Zn on the ionic and piezoelectric contributions to the dielectric permittivity is investigated in a broad frequency range (1 mHz-2 THz). It is shown that the two dopants have radically different influences on the variation of ionic permittivity with doping, in spite of their similarities with respect to the crystallographic structure. Raman spectroscopy reveals that the difference in permittivity can be traced to the effect of Mg and Zn doping on the susceptibility of the phonon modes. Both observations point to differences in the defect incorporation mechanisms.

Enhanced ZnO Thin-Film Transistor Performance Using Bilayer Gate Dielectrics.

PubMed

Alshammari, Fwzah H; Nayak, Pradipta K; Wang, Zhenwei; Alshareef, Husam N

2016-09-07

We report ZnO TFTs using Al2O3/Ta2O5 bilayer gate dielectrics grown by atomic layer deposition. The saturation mobility of single layer Ta2O5 dielectric TFT was 0.1 cm(2) V(-1) s(-1), but increased to 13.3 cm(2) V(-1) s(-1) using Al2O3/Ta2O5 bilayer dielectric with significantly lower leakage current and hysteresis. We show that point defects present in ZnO film, particularly VZn, are the main reason for the poor TFT performance with single layer dielectric, although interfacial roughness scattering effects cannot be ruled out. Our approach combines the high dielectric constant of Ta2O5 and the excellent Al2O3/ZnO interface quality, resulting in improved device performance.

Fe-Doping Effect on Thermoelectric Properties of p-Type Bi0.48Sb1.52Te3

PubMed Central

Mun, Hyeona; Lee, Kyu Hyoung; Kim, Suk Jun; Kim, Jong-Young; Lee, Jeong Hoon; Lim, Jae-Hong; Park, Hee Jung; Roh, Jong Wook; Kim, Sung Wng

2015-01-01

The substitutional doping approach has been shown to be an effective strategy to improve ZT of Bi2Te3-based thermoelectric raw materials. We herein report the Fe-doping effects on electronic and thermal transport properties of polycrystalline bulks of p-type Bi0.48Sb1.52Te3. After a small amount of Fe-doping on Bi/Sb-sites, the power factor could be enhanced due to the optimization of carrier concentration. Additionally, lattice thermal conductivity was reduced by the intensified point-defect phonon scattering originating from the mass difference between the host atoms (Bi/Sb) and dopants (Fe). An enhanced ZT of 1.09 at 300 K was obtained in 1.0 at% Fe-doped Bi0.48Sb1.52Te3 by these synergetic effects. PMID:28787981

Improvement in crystal quality and optical properties of n-type GaN employing nano-scale SiO2 patterned n-type GaN substrate.

PubMed

Jo, Min Sung; Sadasivam, Karthikeyan Giri; Tawfik, Wael Z; Yang, Seung Bea; Lee, Jung Ju; Ha, Jun Seok; Moon, Young Boo; Ryu, Sang Wan; Lee, June Key

2013-01-01

n-type GaN epitaxial layers were regrown on the patterned n-type GaN substrate (PNS) with different size of silicon dioxide (SiO2) nano dots to improve the crystal quality and optical properties. PNS with SiO2 nano dots promotes epitaxial lateral overgrowth (ELOG) for defect reduction and also acts as a light scattering point. Transmission electron microscopy (TEM) analysis suggested that PNS with SiO2 nano dots have superior crystalline properties. Hall measurements indicated that incrementing values in electron mobility were clear indication of reduction in threading dislocation and it was confirmed by TEM analysis. Photoluminescence (PL) intensity was enhanced by 2.0 times and 3.1 times for 1-step and 2-step PNS, respectively.

Point defect reduction in MOCVD (Al)GaN by chemical potential control and a comprehensive model of C incorporation in GaN

NASA Astrophysics Data System (ADS)

Reddy, Pramod; Washiyama, Shun; Kaess, Felix; Kirste, Ronny; Mita, Seiji; Collazo, Ramon; Sitar, Zlatko

2017-12-01

A theoretical framework that provides a quantitative relationship between point defect formation energies and growth process parameters is presented. It enables systematic point defect reduction by chemical potential control in metalorganic chemical vapor deposition (MOCVD) of III-nitrides. Experimental corroboration is provided by a case study of C incorporation in GaN. The theoretical model is shown to be successful in providing quantitative predictions of CN defect incorporation in GaN as a function of growth parameters and provides valuable insights into boundary phases and other impurity chemical reactions. The metal supersaturation is found to be the primary factor in determining the chemical potential of III/N and consequently incorporation or formation of point defects which involves exchange of III or N atoms with the reservoir. The framework is general and may be extended to other defect systems in (Al)GaN. The utility of equilibrium formalism typically employed in density functional theory in predicting defect incorporation in non-equilibrium and high temperature MOCVD growth is confirmed. Furthermore, the proposed theoretical framework may be used to determine optimal growth conditions to achieve minimum compensation within any given constraints such as growth rate, crystal quality, and other practical system limitations.

Unraveling energy conversion modeling in the intrinsic persistent upconverted luminescence of solids: a study of native point defects in antiferromagnetic Er2O3.

PubMed

Huang, Bolong

2016-05-11

We investigated the mechanism of the intrinsic persistent luminescence of Er2O3 in the A-type lattice based on first-principles calculations. We found that the native point defects were engaged in mutual subtle interactions in the form of chemical reactions between different charge states. The release of energy related to lattice distortion facilitates the conversion of energy for electrons to be transported between the valence band and the trap levels or even between the deep trap levels so as to generate persistent luminescence. The defect transitions that take place along the zero-phonon line release energy to enable optical transitions, with the exact amount of negative effective correlation energy determined by the lattice distortions. Our calculations on the thermodynamic transition levels confirm that both the visible and NIR experimentally observed intrinsic persistent luminescence (phosphor or afterglow) are related to the thermodynamic transition levels of oxygen-related defects, and the thermodynamic transition levels within different charge states for these defects are independent of the chemical potentials of the given species. Lattice distortion defects such as anion Frenkel (a-Fr) pair defects play an important role in transporting O-related defects between different lattice sites. To obtain red persistent luminescence that matches the biological therapeutic window, it is suggested to increase the electron transition levels between high-coordinated O vacancies and related metastable a-Fr defects; a close-packed core-shell structure is required to quench low-coordinated O-related defects so as to reduce the green band luminescence. We further established a conversed chain reaction (CCR) model to interpret the energy conversion process of persistent luminescence in terms of the inter-reactions of native point defects between different charge states. It is advantageous to use the study of defect levels combined with formation energies to suggest limits to doping energy and explain photostimulated luminescence in terms of native point defects.

Small-Angle Scatter Measurement.

NASA Astrophysics Data System (ADS)

Wein, Steven Jay

The design, analysis, and performance of a small -angle scatterometer are presented. The effects of the diffraction background, geometrical aberrations and system scatter at the small-angles are separated. Graphs are provided that quantify their contribution. The far-field irradiance distributions of weakly truncated and untruncated Gaussian beams are compared. The envelope of diffraction ringing is shown to decrease proportionately with the level of truncation in the pupil. Spherical aberration and defocus are shown to have little effect on the higher-order diffraction rings of Gaussian apertures and as such will have a negligible effect on most scatter measurements. A method is presented for determining the scattered irradiance level for a given BRDF in relation to the peak irradiance of the point spread function. A method of Gaussian apodization is presented and tested that allows the level of diffraction ringing to become a design parameter. Upon sufficient reduction of the diffraction background, the scattered light from the scatterometers' primary mirror is seen to be the limiting component of the small-angle instrument profile. The scatterometer described was able to make a meaningful measurement close enough to the specular direction at 0.6328mum in order to observe the characteristic height and width of the scatter function. This allowed the rms roughness and autocorrelation length of the surface to be determined from the scatter data at this wavelength. The inferred rms roughness agreed well with an independent optical profilometer measurement of the surface. The BRDF of the samples were also measured at 10.6mum. The rms roughness inferred from this scatter data did not agree with the other measurements. The BRDF did not scale in accordance with the scaler diffraction theory of microrough surfaces. The scattering in the visible was dominated by the effects of surface roughness whereas the scattering in the far-infrared was apparently dominated by the effects of contaminants and surface defects. The model for the surface statistics is investigated. A K_0 (modified Bessel function) autocorrelation function is shown to predict the scattered light distribution of these samples much better than the conventional negative -exponential function. Additionally, a sampling theory is developed that addresses the negative-exponentially correlated output of lock-in amplifiers, detectors, and electronic circuits in general. It is shown that the optimum sampling rate is approximately one sample per time constant and at this rate the improvement in SNR is sqrt {N/2} where N is the number of measurements.

A computational framework for automation of point defect calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goyal, Anuj; Gorai, Prashun; Peng, Haowei

We have developed a complete and rigorously validated open-source Python framework to automate point defect calculations using density functional theory. Furthermore, the framework provides an effective and efficient method for defect structure generation, and creation of simple yet customizable workflows to analyze defect calculations. This package provides the capability to compute widely-accepted correction schemes to overcome finite-size effects, including (1) potential alignment, (2) image-charge correction, and (3) band filling correction to shallow defects. Using Si, ZnO and In2O3 as test examples, we demonstrate the package capabilities and validate the methodology.

A computational framework for automation of point defect calculations

DOE PAGES

Goyal, Anuj; Gorai, Prashun; Peng, Haowei; ...

2017-01-13

We have developed a complete and rigorously validated open-source Python framework to automate point defect calculations using density functional theory. Furthermore, the framework provides an effective and efficient method for defect structure generation, and creation of simple yet customizable workflows to analyze defect calculations. This package provides the capability to compute widely-accepted correction schemes to overcome finite-size effects, including (1) potential alignment, (2) image-charge correction, and (3) band filling correction to shallow defects. Using Si, ZnO and In2O3 as test examples, we demonstrate the package capabilities and validate the methodology.

Defect interactions in GaAs single crystals

NASA Technical Reports Server (NTRS)

Gatos, H. C.; Lagowski, J.

1984-01-01

The two-sublattice structural configuration of GaAs and deviations from stoichiometry render the generation and interaction of electrically active point defects (and point defect complexes) critically important for device applications and very complex. Of the defect-induced energy levels, those lying deep into the energy band are very effective lifetime ""killers". The level 0.82 eV below the condition band, commonly referred to as EL2, is a major deep level, particularly in melt-grown GaAs. This level is associated with an antisite defect complex (AsGa - VAS). Possible mechanisms of its formation and its annihilation were further developed.

Diabolical points in multi-scatterer optomechanical systems

PubMed Central

Chesi, Stefano; Wang, Ying-Dan; Twamley, Jason

2015-01-01

Diabolical points, which originate from parameter-dependent accidental degeneracies of a system's energy levels, have played a fundamental role in the discovery of the Berry phase as well as in photonics (conical refraction), in chemical dynamics, and more recently in novel materials such as graphene, whose electronic band structure possess Dirac points. Here we discuss diabolical points in an optomechanical system formed by multiple scatterers in an optical cavity with periodic boundary conditions. Such configuration is close to experimental setups using micro-toroidal rings with indentations or near-field scatterers. We find that the optomechanical coupling is no longer an analytic function near the diabolical point and demonstrate the topological phase arising through the mechanical motion. Similar to a Fabry-Perot resonator, the optomechanical coupling can grow with the number of scatterers. We also introduce a minimal quantum model of a diabolical point, which establishes a connection to the motion of an arbitrary-spin particle in a 2D parabolic quantum dot with spin-orbit coupling. PMID:25588627

The parallel-sequential field subtraction techniques for nonlinear ultrasonic imaging

NASA Astrophysics Data System (ADS)

Cheng, Jingwei; Potter, Jack N.; Drinkwater, Bruce W.

2018-04-01

Nonlinear imaging techniques have recently emerged which have the potential to detect cracks at a much earlier stage and have sensitivity to particularly closed defects. This study utilizes two modes of focusing: parallel, in which the elements are fired together with a delay law, and sequential, in which elements are fired independently. In the parallel focusing, a high intensity ultrasonic beam is formed in the specimen at the focal point. However, in sequential focusing only low intensity signals from individual elements enter the sample and the full matrix of transmit-receive signals is recorded; with elastic assumptions, both parallel and sequential images are expected to be identical. Here we measure the difference between these images formed from the coherent component of the field and use this to characterize nonlinearity of closed fatigue cracks. In particular we monitor the reduction in amplitude at the fundamental frequency at each focal point and use this metric to form images of the spatial distribution of nonlinearity. The results suggest the subtracted image can suppress linear features (e.g., back wall or large scatters) and allow damage to be detected at an early stage.

Swiftly moving focus points and forming shapes through the scattering media

NASA Astrophysics Data System (ADS)

Tran, Vinh; Sahoo, Sujit Kumar; Tang, Dongliang; Dang, Cuong

2018-02-01

Propagation of light through scattering media such as ground glass or biological tissue limits the quality and intensity of focusing point. Wave front shaping technique which uses spatial light modulator (SLM) devices to reshape the field profile of incoming light, is considered as one of the most effective and convenient methods. Advanced biomedical or manufacturing applications require drawing various contours or shapes quickly and precisely. However, creating each shape behind the scattering medium needs different phase profiles, which are time consuming to optimize or measure. Here, we demonstrate a technique to draw various shapes or contours behind the scattering medium by swiftly moving the focus point without any mechanical movements. Our technique relies on the existence of speckle correlation property in scattering media, also known as optical memory effect. In our procedure, we first modulate the phase-only SLM to create the focus point on the other side of scattering medium. Then, we digitally shift the preoptimized phase profile on the SLM and ramp it to tilt the beam accordingly. Now, the incoming beam with identical phase profile shines on the same scattering region at a tilted angle to regenerate the focus point at the desired position due to memory effect. Moreover, with linear combination of different field patterns, we can generate a single phase profile on SLM to produce two, three or more focus points simultaneously on the other side of a turbid medium. Our method could provide a useful tool for prominent applications such as opto-genetic excitation, minimally invasive laser surgery and other related fields.

Acoustic Scattering from Corners, Edges and Circular Cones

NASA Astrophysics Data System (ADS)

Elschner, Johannes; Hu, Guanghui

2018-05-01

Consider the time-harmonic acoustic scattering from a bounded penetrable obstacle imbedded in an isotropic homogeneous medium. The obstacle is supposed to possess a circular conic point or an edge point on the boundary in three dimensions and a planar corner point in two dimensions. The opening angles of cones and edges are allowed to be any number in {(0,2π)π}. We prove that such an obstacle scatters any incoming wave non-trivially (that is, the far field patterns cannot vanish identically), leading to the absence of real non-scattering wavenumbers. Local and global uniqueness results for the inverse problem of recovering the shape of penetrable scatterers are also obtained using a single incoming wave. Our approach relies on the singularity analysis of the inhomogeneous Laplace equation in a cone.

Low-energy planar magnetic defects in BaFe2As2: Nanotwins, twins, antiphase, and domain boundaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khan, S. N.; Alam, A.; Johnson, Duane D.

2013-01-01

In BaFe2As2, structural and magnetic planar defects begin to proliferate below the structural phase transition, affecting descriptions of magnetism and superconductivity.We study, using density-functional theory, the stability and magnetic properties of competing antiphase and domain boundaries, twins and isolated nanotwins (twin nuclei), and spin excitations proposed and/or observed. These nanoscale defects have a very low surface energy (22 210 m Jm 2), with twins favorable to the mesoscale. Defects exhibit smaller moments confined near their boundaries making a uniform-moment picture inappropriate for long-range magnetic order in real samples. Nanotwins explain features in measured pair distribution functions so should be consideredmore » when analyzing scattering data. All these defects can be weakly mobile and/or can have fluctuations that lower« less

7 CFR 51.1565 - Internal defects.

Code of Federal Regulations, 2014 CFR

2014-01-01

..., Internal Discoloration, Vascular Browning, Fusarium Wilt, Net Necrosis, Other Necrosis, Stem End Browning 5... Discoloration (Heat Necrosis) Not more than the equivalent of 3 scattered spots 1/8 inch in diameter in a potato...

7 CFR 51.1565 - Internal defects.

Code of Federal Regulations, 2013 CFR

2013-01-01

..., Internal Discoloration, Vascular Browning, Fusarium Wilt, Net Necrosis, Other Necrosis, Stem End Browning 5... Discoloration (Heat Necrosis) Not more than the equivalent of 3 scattered spots 1/8 inch in diameter in a potato...

Surface scanning inspection system particle detection dependence on aluminum film morphology

NASA Astrophysics Data System (ADS)

Prater, Walter; Tran, Natalie; McGarvey, Steve

2012-03-01

Physical vapor deposition (PVD) aluminum films present unique challenges when detecting particulate defects with a Surface Scanning Inspection System (SSIS). Aluminum (Al) films 4500Å thick were deposited on 300mm particle grade bare Si wafers at two temperatures using a Novellus Systems INOVA® NExT,.. Film surface roughness and morphology measurements were performed using a Veeco Vx310® atomic force microscope (AFM). AFM characterization found the high deposition temperature (TD) Al roughness (Root Mean Square 16.5 nm) to be five-times rougher than the low-TD Al roughness (rms 3.7 nm). High-TD Al had grooves at the grain boundaries that were measured to be 20 to 80 nm deep. Scanning electron microscopy (SEM) examination, with a Hitachi RS6000 defect review SEM, confirmed the presence of pronounced grain grooves. SEM images established that the low-TD filmed wafers have fine grains (0.1 to 0.3 um diameter) and the high-TD film wafers have fifty-times larger equiaxed plateletshape grains (5 to 15 um diameter). Calibrated Poly-Styrene Latex (PSL) spheres ranging in size from 90 nm to 1 μm were deposited in circular patterns on the wafers using an aerosol deposition chamber. PSL sphere depositions at each spot were controlled to yield 2000 to 5000 counts. A Hitachi LS9100® dark field full wafer SSIS was used to experimentally determine the relationship of the PSL sphere scattered light intensity with S-polarized light, a measure of scattering cross-section, with respect to the calibrated PSL sphere diameter. Comparison of the SSIS scattered light versus PSL spot size calibration curves shows two distinct differences. Scattering cross-section (intensity) of the PSL spheres increased on the low-TD Al film with smooth surface roughness and the low-TD Al film defect detection sensitivity was 126 nm compared to 200 nm for the rougher high- TD Al film. This can be explained by the higher signal to noise attributed to the smooth low-TD Al. Dark field defect detection on surface scanning inspection systems is used to rapidly measure defectivity data. The user generates a calibration curve on the SSIS to plot the intensity of the light scattering derived at each National Institute of Standards and Technology (NIST) certified PSL deposition spot that was deposited. It is not uncommon for the end user to embark upon the time consuming process of attempting to "push" the maximal SSIS film specific sensitivity curve beyond the optical performance capability of the SSIS. Bidirectional reflectance distribution function (BRDF) light scattering modeling was utilized as a means of determining the most appropriate polarity prior to the SSIS recipe creation process. The modeling utilized the Al refractive index (n) and extinction coefficient (k) and the SSIS detector angles and laser wavelength. The modeling results allowed predetermination of the maximal sensitivity for each different Al thickness and eliminate unnecessary recipe modification trial-and-error in search of the SSIS maximal sensitivity. The modeling accurately forecasted the optimal polarization and maximal sensitivity of the SSIS recipe, which, by avoiding a trial and error approach, can result in a substantial savings in time and resources.

Steady distribution structure of point defects near crystal-melt interface under pulling stop of CZ Si crystal

NASA Astrophysics Data System (ADS)

Abe, T.; Takahashi, T.; Shirai, K.

2017-02-01

In order to reveal a steady distribution structure of point defects of no growing Si on the solid-liquid interface, the crystals were grown at a high pulling rate, which Vs becomes predominant, and the pulling was suddenly stopped. After restoring the variations of the crystal by the pulling-stop, the crystals were then left in prolonged contact with the melt. Finally, the crystals were detached and rapidly cooled to freeze point defects and then a distribution of the point defects of the as-grown crystals was observed. As a result, a dislocation loop (DL) region, which is formed by the aggregation of interstitials (Is), was formed over the solid-liquid interface and was surrounded with a Vs-and-Is-free recombination region (Rc-region), although the entire crystals had been Vs rich in the beginning. It was also revealed that the crystal on the solid-liquid interface after the prolonged contact with the melt can partially have a Rc-region to be directly in contact with the melt, unlike a defect distribution of a solid-liquid interface that has been growing. This experimental result contradicts a hypothesis of Voronkov's diffusion model, which always assumes the equilibrium concentrations of Vs and Is as the boundary condition for distribution of point defects on the growth interface. The results were disscussed from a qualitative point of view of temperature distribution and thermal stress by the pulling-stop.

Impact of iron-site defects on superconductivity in LiFeAs

DOE PAGES

Chi, Shun; Aluru, Ramakrishna; Singh, Udai Raj; ...

2016-10-19

In conventional s -wave superconductors, only magnetic impurities exhibit impurity bound states, whereas for an s ± order parameter they can occur for both magnetic and nonmagnetic impurities. Impurity bound states in superconductors can thus provide important insight into the order parameter. We present a combined experimental and theoretical study of native and engineered iron-site defects in LiFeAs. A detailed comparison of tunneling spectra measured on impurities with spin-fluctuation theory reveals a continuous evolution from negligible impurity-bound-state features for weaker scattering potential to clearly detectable states for somewhat stronger scattering potentials. Furthermore, all bound states for these intermediate strengthmore » potentials are pinned at or close to the gap edge of the smaller gap, a phenomenon that we explain and ascribe to multiorbital physics.« less

Quasiparticle Scattering off Defects and Possible Bound States in Charge-Ordered YBa_{2}Cu_{3}O_{y}.

PubMed

Zhou, R; Hirata, M; Wu, T; Vinograd, I; Mayaffre, H; Krämer, S; Horvatić, M; Berthier, C; Reyes, A P; Kuhns, P L; Liang, R; Hardy, W N; Bonn, D A; Julien, M-H

2017-01-06

We report the NMR observation of a skewed distribution of ^{17}O Knight shifts when a magnetic field quenches superconductivity and induces long-range charge-density-wave (CDW) order in YBa_{2}Cu_{3}O_{y}. This distribution is explained by an inhomogeneous pattern of the local density of states N(E_{F}) arising from quasiparticle scattering off, yet unidentified, defects in the CDW state. We argue that the effect is most likely related to the formation of quasiparticle bound states, as is known to occur, under specific circumstances, in some metals and superconductors (but not in the CDW state, in general, except for very few cases in 1D materials). These observations should provide insight into the microscopic nature of the CDW, especially regarding the reconstructed band structure and the sensitivity to disorder.

Intrinsic point defects in off-stoichiometric Cu2ZnSnSe4: A neutron diffraction study

NASA Astrophysics Data System (ADS)

Gurieva, Galina; Valle Rios, Laura Elisa; Franz, Alexandra; Whitfield, Pamela; Schorr, Susan

2018-04-01

This work is an experimental study of intrinsic point defects in off-stoichiometric kesterite type CZTSe by means of neutron powder diffraction. We revealed the existence of copper vacancies (VCu), various cation anti site defects (CuZn, ZnCu, ZnSn, SnZn, and CuZn), as well as interstitials (Cui, Zni) in a wide range of off-stoichiometric polycrystalline powder samples synthesized by the solid state reaction. The results show that the point defects present in off-stoichiometric CZTSe agree with the off-stoichiometry type model, assuming certain cation substitutions accounting for charge balance. In addition to the known off-stoichiometry types A-H, new types (I-L) have been introduced. For the very first time, a correlation between the chemical composition of the CZTSe kesterite type phase and the occurring intrinsic point defects is presented. In addition to the off-stoichiometry type specific defects, the Cu/Zn disorder is always present in the CZTSe phase. In Cu-poor/Zn-rich CZTSe, a composition considered as the one that delivers the best photovoltaic performance, mainly copper vacancies, ZnCu and ZnSn anti sites are present. Also, this compositional region shows the lowest degree of Cu/Zn disorder.

Process for sensing defects on a smooth cylindrical interior surface in tubing

DOEpatents

Dutton, G. Wayne

1987-11-17

The cylindrical interior surface of small diameter metal tubing is optically inspected to determine surface roughness by passing a slightly divergent light beam to illuminate the entire interior surface of the tubing. Impingement of the input light beam components on any rough spots on the interior surface generates forward and backward scattered radiation components. The forward scattered components can be measured by blocking direct and specular radiation components exiting the tubing while allowing the forward scattered radiation to travel past the blocking location. Collecting optics are employed to converge the forward scattered radiation onto a photodetector generating a signal indicative of surface roughness. In the back scattered mode, back scattered radiation exiting the tubing through the entrance opening is reflected 90.degree. by a beam splitter towards collecting optics and a photodetector. Alternatively, back scattered radiation can be transmitted through a fiber optic bundle towards the collecting optics. The input light beam can be supplied through a white light fiber optic bundle mounted coaxial with the first bundle.

Process for sensing defects on a smooth cylindrical interior surface in tubing

DOEpatents

Dutton, G.W.

1987-11-17

The cylindrical interior surface of small diameter metal tubing is optically inspected to determine surface roughness by passing a slightly divergent light beam to illuminate the entire interior surface of the tubing. Impingement of the input light beam components on any rough spots on the interior surface generates forward and backward scattered radiation components. The forward scattered components can be measured by blocking direct and specular radiation components exiting the tubing while allowing the forward scattered radiation to travel past the blocking location. Collecting optics are employed to converge the forward scattered radiation onto a photodetector generating a signal indicative of surface roughness. In the back scattered mode, back scattered radiation exiting the tubing through the entrance opening is reflected 90[degree] by a beam splitter towards collecting optics and a photodetector. Alternatively, back scattered radiation can be transmitted through a fiber optic bundle towards the collecting optics. The input light beam can be supplied through a white light fiber optic bundle mounted coaxial with the first bundle. 6 figs.

Process and apparatus for sensing defects on a smooth cylindrical surface in tubing

DOEpatents

Dutton, G.W.

1985-08-05

The cylindrical interior surface of small diameter metal tubing is optically inspected to determine surface roughness by passing a slightly divergent light beam to illuminate the entire interior surface of the tubing. Impingement of the input light beam components on any rough spots on the interior surface generates forward and backward scattered radiation components. The forward scattered components can be measured by blocking direct and specular radiation components exiting the tubing while allowing the forward scattered radiation to travel past the blocking location. Collecting optics are employed to converge the forward scattered radiation onto a photodetector generating a signal indicative of surface roughness. In the back scattered mode, back scattered radiation exiting the tubing through the entrance opening is reflected 90/sup 0/ by a beam splitter towards collecting optics and a photodetector. Alternatively, back scattered radiation can be transmitted through a fiber optic bundle towards the collecting optics. The input light beam can be supplied through a white light fiber optic bundle mounted coaxial with the first bundle.

Polarimetric ISAR: Simulation and image reconstruction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chambers, David H.

In polarimetric ISAR the illumination platform, typically airborne, carries a pair of antennas that are directed toward a fixed point on the surface as the platform moves. During platform motion, the antennas maintain their gaze on the point, creating an effective aperture for imaging any targets near that point. The interaction between the transmitted fields and targets (e.g. ships) is complicated since the targets are typically many wavelengths in size. Calculation of the field scattered from the target typically requires solving Maxwell’s equations on a large three-dimensional numerical grid. This is prohibitive to use in any real-world imaging algorithm, somore » the scattering process is typically simplified by assuming the target consists of a cloud of independent, non-interacting, scattering points (centers). Imaging algorithms based on this scattering model perform well in many applications. Since polarimetric radar is not very common, the scattering model is often derived for a scalar field (single polarization) where the individual scatterers are assumed to be small spheres. However, when polarization is important, we must generalize the model to explicitly account for the vector nature of the electromagnetic fields and its interaction with objects. In this note, we present a scattering model that explicitly includes the vector nature of the fields but retains the assumption that the individual scatterers are small. The response of the scatterers is described by electric and magnetic dipole moments induced by the incident fields. We show that the received voltages in the antennas are linearly related to the transmitting currents through a scattering impedance matrix that depends on the overall geometry of the problem and the nature of the scatterers.« less

MLFMA-accelerated Nyström method for ultrasonic scattering - Numerical results and experimental validation

NASA Astrophysics Data System (ADS)

Gurrala, Praveen; Downs, Andrew; Chen, Kun; Song, Jiming; Roberts, Ron

2018-04-01

Full wave scattering models for ultrasonic waves are necessary for the accurate prediction of voltage signals received from complex defects/flaws in practical nondestructive evaluation (NDE) measurements. We propose the high-order Nyström method accelerated by the multilevel fast multipole algorithm (MLFMA) as an improvement to the state-of-the-art full-wave scattering models that are based on boundary integral equations. We present numerical results demonstrating improvements in simulation time and memory requirement. Particularly, we demonstrate the need for higher order geom-etry and field approximation in modeling NDE measurements. Also, we illustrate the importance of full-wave scattering models using experimental pulse-echo data from a spherical inclusion in a solid, which cannot be modeled accurately by approximation-based scattering models such as the Kirchhoff approximation.

Vertical Root Fracture initiation in curved roots after root canal preparation: A dentinal micro-crack analysis with LED transillumination

PubMed Central

Martín-Biedma, Benjamín; Varela-Patiño, Purificación; Ruíz-Piñón, Manuel; Castelo-Baz, Pablo

2017-01-01

Background One of the causative factors of root defects is the increased friction produced by rotary instrumentation. A high canal curvature may increase stress, making the tooth more susceptible to dentinal cracks. The purpose of this study was to evaluate dentinal micro-crack formation with the ProTaper NEXT and ProTaper Universal systems using LED transillumination, and to analyze the micro-crack generated at the point of maximum canal curvature. Material and Methods 60 human mandibular premolars with curvatures between 30–49° and radii between 2–4 mm were used. The root canals were instrumented using the Protaper Universal® and Protaper NEXT® systems, with the aid of the Proglider® system. The obtained samples were sectioned transversely before subsequent analysis with LED transillumination at 2 mm and 8 mm from the apex and at the point of maximum canal curvature. Defects were scored: 0 for no defects; and 1 for micro-cracks. Results Root defects were not observed in the control group. The ProTaper NEXT system caused fewer defects (16.7%) than the ProTaper Universal system (40%) (P<0.05). The ProTaper Universal system caused significantly more micro-cracks at the point of maximum canal curvature than the ProTaper NEXT system (P<0.05). Conclusions Rotary instrumentation systems often generate root defects, but the ProTaper NEXT system generated fewer dentinal defects than the ProTaper Universal system. A higher prevalence of defects was found at the point of maximum curvature in the ProTaper Universal group. Key words:Curved root, Micro-crack, point of maximum canal curvature, ProTaper NEXT, ProTaper Universal, Vertical root fracture. PMID:29167712

Defect states of complexes involving a vacancy on the boron site in boronitrene

NASA Astrophysics Data System (ADS)

Ngwenya, T. B.; Ukpong, A. M.; Chetty, N.

2011-12-01

First principles calculations have been performed to investigate the ground state properties of freestanding monolayer hexagonal boronitrene (h-BN). We have considered monolayers that contain native point defects and their complexes, which form when the point defects bind with the boron vacancy on the nearest-neighbor position. The changes in the electronic structure are analyzed to show the extent of localization of the defect-induced midgap states. The variations in formation energies suggest that defective h-BN monolayers that contain carbon substitutional impurities are the most stable structures, irrespective of the changes in growth conditions. The high energies of formation of the boron vacancy complexes suggest that they are less stable, and their creation by ion bombardment would require high-energy ions compared to point defects. Using the relative positions of the derived midgap levels for the double vacancy complex, it is shown that the quasi-donor-acceptor pair interpretation of optical transitions is consistent with stimulated transitions between electron and hole states in boronitrene.

Accelerated defect visualization of microelectronic systems using binary search with fixed pitch-catch distance laser ultrasonic scanning

NASA Astrophysics Data System (ADS)

Park, Byeongjin; Sohn, Hoon

2018-04-01

The practicality of laser ultrasonic scanning is limited because scanning at a high spatial resolution demands a prohibitively long scanning time. Inspired by binary search, an accelerated defect visualization technique is developed to visualize defect with a reduced scanning time. The pitch-catch distance between the excitation point and the sensing point is also fixed during scanning to maintain a high signal-to-noise ratio of measured ultrasonic responses. The approximate defect boundary is identified by examining the interactions between ultrasonic waves and defect observed at the scanning points that are sparsely selected by a binary search algorithm. Here, a time-domain laser ultrasonic response is transformed into a spatial ultrasonic domain response using a basis pursuit approach so that the interactions between ultrasonic waves and defect can be better identified in the spatial ultrasonic domain. Then, the area inside the identified defect boundary is visualized as defect. The performance of the proposed defect visualization technique is validated through an experiment on a semiconductor chip. The proposed defect visualization technique accelerates the defect visualization process in three aspects: (1) The number of measurements that is necessary for defect visualization is dramatically reduced by a binary search algorithm; (2) The number of averaging that is necessary to achieve a high signal-to-noise ratio is reduced by maintaining the wave propagation distance short; and (3) With the proposed technique, defect can be identified with a lower spatial resolution than the spatial resolution required by full-field wave propagation imaging.

Dextrocardia

MedlinePlus

Cyanotic heart defect - dextrocardia; Congenital heart defect - dextrocardia; Birth defect - dextrocardia ... During the early weeks of pregnancy, the baby’s heart develops. Sometimes, it turns so that it points ...

Characterization of oxygen defects in diamond by means of density functional theory calculations

NASA Astrophysics Data System (ADS)

Thiering, Gergő; Gali, Adam

2016-09-01

Point defects in diamond are of high interest as candidates for realizing solid state quantum bits, bioimaging agents, or ultrasensitive electric or magnetic field sensors. Various artificial diamond synthesis methods should introduce oxygen contamination in diamond, however, the incorporation of oxygen into diamond crystal and the nature of oxygen-related point defects are largely unknown. Oxygen may be potentially interesting as a source of quantum bits or it may interact with other point defects which are well established solid state qubits. Here we employ plane-wave supercell calculations within density functional theory, in order to characterize the electronic and magneto-optical properties of various oxygen-related defects. Besides the trivial single interstitial and substitutional oxygen defects we also consider their complexes with vacancies and hydrogen atoms. We find that oxygen defects are mostly electrically active and introduce highly correlated orbitals that pose a challenge for density functional theory modeling. Nevertheless, we are able to identify the fingerprints of substitutional oxygen defect, the oxygen-vacancy and oxygen-vacancy-hydrogen complexes in the electron paramagnetic resonance spectrum. We demonstrate that first principles calculations can predict the motional averaging of the electron paramagnetic resonance spectrum of defects that are subject to Jahn-Teller distortion. We show that the high-spin neutral oxygen-vacancy defect exhibits very fast nonradiative decay from its optical excited state that might hinder applying it as a qubit.

FIBER OPTICS: Role of point defects in the photosensitivity of hydrogen-loaded phosphosilicate glass

NASA Astrophysics Data System (ADS)

Larionov, Yu V.

2010-08-01

It is shown that point defect modifications in hydrogen-loaded phosphosilicate glass (PSG) do not play a central role in determining its photosensitivity. Photochemical reactions that involve a two-step point defect modification and pre-exposure effect are incapable of accounting for photoinduced refractive index changes. It seems likely that a key role in UV-induced refractive index modifications is played by structural changes in the PSG network. Experimental data are presented that demonstrate intricate network rearrangement dynamics during UV exposure of PSG.

Imaging of a Defect in Thin Plates Using the Time Reversal of Single Mode Lamb Waves

NASA Astrophysics Data System (ADS)

Jeong, Hyunjo; Lee, Jung-Sik; Bae, Sung-Min

2011-06-01

This paper presents an analytical investigation for a baseline-free imaging of a defect in plate-like structures using the time-reversal of Lamb waves. We first consider the flexural wave (A0 mode) propagation in a plate containing a defect, and reception and time reversal process of the output signal at the receiver. The received output signal is then composed of two parts: a directly propagated wave and a scattered wave from the defect. The time reversal of these waves recovers the original input signal, and produces two additional sidebands that contain the time-of-flight information on the defect location. One of the side band signals is then extracted as a pure defect signal. A defect localization image is then constructed from a beamforming technique based on the time-frequency analysis of the side band signal for each transducer pair in a network of sensors. The simulation results show that the proposed scheme enables the accurate, baseline-free detection of a defect, so that experimental studies are needed to verify the proposed method and to be applied to real structure.

Molecular dynamics simulation of thermal transport in UO 2 containing uranium, oxygen, and fission-product defects

DOE PAGES

Liu, Xiang -Yang; Cooper, Michael William D.; McClellan, Kenneth James; ...

2016-10-25

Uranium dioxide (UO 2) is the most commonly used fuel in light-water nuclear reactors and thermal conductivity controls the removal of heat produced by fission, thereby governing fuel temperature during normal and accident conditions. The use of fuel performance codes by the industry to predict operational behavior is widespread. A primary source of uncertainty in these codes is thermal conductivity, and optimized fuel utilization may be possible if existing empirical models are replaced with models that incorporate explicit thermal-conductivity-degradation mechanisms during fuel burn up. This approach is able to represent the degradation of thermal conductivity due to each individual defectmore » type, rather than the overall burn-up measure typically used, which is not an accurate representation of the chemical or microstructure state of the fuel that actually governs thermal conductivity and other properties. To generate a mechanistic thermal conductivity model, molecular dynamics (MD) simulations of UO 2 thermal conductivity including representative uranium and oxygen defects and fission products are carried out. These calculations employ a standard Buckingham-type interatomic potential and a potential that combines the many-body embedded-atom-method potential with Morse-Buckingham pair potentials. Potential parameters for UO 2+x and ZrO 2 are developed for the latter potential. Physical insights from the resonant phonon-spin-scattering mechanism due to spins on the magnetic uranium ions are introduced into the treatment of the MD results, with the corresponding relaxation time derived from existing experimental data. High defect scattering is predicted for Xe atoms compared to that of La and Zr ions. Uranium defects reduce the thermal conductivity more than oxygen defects. For each defect and fission product, scattering parameters are derived for application in both a Callaway model and the corresponding high-temperature model typically used in fuel-performance codes. The model is validated by comparison to low-temperature experimental measurements on single-crystal hyperstoichiometric UO 2+x samples and high-temperature literature data. Furthermore, this work will enable more accurate fuel-performance simulations and will extend to new fuel types and operating conditions, all of which improve the fuel economics of nuclear energy and maintain high fuel reliability and safety.« less

Molecular dynamics simulation of thermal transport in UO 2 containing uranium, oxygen, and fission-product defects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xiang -Yang; Cooper, Michael William D.; McClellan, Kenneth James

Uranium dioxide (UO 2) is the most commonly used fuel in light-water nuclear reactors and thermal conductivity controls the removal of heat produced by fission, thereby governing fuel temperature during normal and accident conditions. The use of fuel performance codes by the industry to predict operational behavior is widespread. A primary source of uncertainty in these codes is thermal conductivity, and optimized fuel utilization may be possible if existing empirical models are replaced with models that incorporate explicit thermal-conductivity-degradation mechanisms during fuel burn up. This approach is able to represent the degradation of thermal conductivity due to each individual defectmore » type, rather than the overall burn-up measure typically used, which is not an accurate representation of the chemical or microstructure state of the fuel that actually governs thermal conductivity and other properties. To generate a mechanistic thermal conductivity model, molecular dynamics (MD) simulations of UO 2 thermal conductivity including representative uranium and oxygen defects and fission products are carried out. These calculations employ a standard Buckingham-type interatomic potential and a potential that combines the many-body embedded-atom-method potential with Morse-Buckingham pair potentials. Potential parameters for UO 2+x and ZrO 2 are developed for the latter potential. Physical insights from the resonant phonon-spin-scattering mechanism due to spins on the magnetic uranium ions are introduced into the treatment of the MD results, with the corresponding relaxation time derived from existing experimental data. High defect scattering is predicted for Xe atoms compared to that of La and Zr ions. Uranium defects reduce the thermal conductivity more than oxygen defects. For each defect and fission product, scattering parameters are derived for application in both a Callaway model and the corresponding high-temperature model typically used in fuel-performance codes. The model is validated by comparison to low-temperature experimental measurements on single-crystal hyperstoichiometric UO 2+x samples and high-temperature literature data. Furthermore, this work will enable more accurate fuel-performance simulations and will extend to new fuel types and operating conditions, all of which improve the fuel economics of nuclear energy and maintain high fuel reliability and safety.« less

Comparison of finite source and plane wave scattering from corrugated surfaces

NASA Technical Reports Server (NTRS)

Levine, D. M.

1977-01-01

The choice of a plane wave to represent incident radiation in the analysis of scatter from corrugated surfaces was examined. The physical optics solution obtained for the scattered fields due to an incident plane wave was compared with the solution obtained when the incident radiation is produced by a source of finite size and finite distance from the surface. The two solutions are equivalent if the observer is in the far field of the scatterer and the distance from observer to scatterer is large compared to the radius of curvature at the scatter points, condition not easily satisfied with extended scatterers such as rough surfaces. In general, the two solutions have essential differences such as in the location of the scatter points and the dependence of the scattered fields on the surface properties. The implication of these differences to the definition of a meaningful radar cross section was examined.

7 CFR 51.3416 - Classification of defects.

Code of Federal Regulations, 2013 CFR

2013-01-01

..., Fusarium Wilt, Net Necrosis, Other Necrosis, Stem End Browning 5% waste 10% waste. Occurring entirely... discoloration (Heat Necrosis) Not more than the equivalent of 3 scattered spots 1/8 inch in diameter in a potato...

7 CFR 51.3416 - Classification of defects.

Code of Federal Regulations, 2014 CFR

2014-01-01

..., Fusarium Wilt, Net Necrosis, Other Necrosis, Stem End Browning 5% waste 10% waste. Occurring entirely... discoloration (Heat Necrosis) Not more than the equivalent of 3 scattered spots 1/8 inch in diameter in a potato...

Solid state division progress report, period ending February 29, 1980

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1980-09-01

Research is reported concerning theoretical solid state physics; surface and near-surface properties of solids; defects in solids; transport properties of solids; neutron scattering; crystal growth and characterization; and isotope research materials.

Effects of artificially produced defects on film thickness distribution in sliding EHD point contacts

NASA Technical Reports Server (NTRS)

Cusano, C.; Wedeven, L. D.

1981-01-01

The effects of artificially produced dents and grooves on the elastohydrodynamic (EHD) film thickness profile in a sliding point contact were investigated by means of optical interferometry. The defects, formed on the surface of a highly polished ball, were held stationary at various locations within and in the vicinity of the contact region while the disk was rotating. It is shown that the defects, having a geometry similar to what can be expected in practice, can dramatically change the film thickness which exists when no defects are present in or near the contact. This change in film thickness is mainly a function of the position of the defects in the inlet region, the geometry of the defects, the orientation of the defects in the case of grooves, and the depth of the defect relative to the central film thickness.

Wavelength dependence in radio-wave scattering and specular-point theory

NASA Technical Reports Server (NTRS)

Tyler, G. L.

1976-01-01

Radio-wave scattering from natural surfaces contains a strong quasispecular component that at fixed wavelengths is consistent with specular-point theory, but often has a strong wavelength dependence that is not predicted by physical optics calculations under the usual limitations of specular-point models. Wavelength dependence can be introduced by a physical approximation that preserves the specular-point assumptions with respect to the radii of curvature of a fictitious, effective scattering surface obtained by smoothing the actual surface. A uniform low-pass filter model of the scattering process yields explicit results for the effective surface roughness versus wavelength. Interpretation of experimental results from planetary surfaces indicates that the asymptotic surface height spectral densities fall at least as fast as an inverse cube of spatial frequency. Asymptotic spectral densities for Mars and portions of the lunar surface evidently decrease more rapidly.

Analysis of a Spatial Point Pattern: Examining the Damage to Pavement and Pipes in Santa Clara Valley Resulting from the Loma Prieta Earthquake

USGS Publications Warehouse

Phelps, G.A.

2008-01-01

This report describes some simple spatial statistical methods to explore the relationships of scattered points to geologic or other features, represented by points, lines, or areas. It also describes statistical methods to search for linear trends and clustered patterns within the scattered point data. Scattered points are often contained within irregularly shaped study areas, necessitating the use of methods largely unexplored in the point pattern literature. The methods take advantage of the power of modern GIS toolkits to numerically approximate the null hypothesis of randomly located data within an irregular study area. Observed distributions can then be compared with the null distribution of a set of randomly located points. The methods are non-parametric and are applicable to irregularly shaped study areas. Patterns within the point data are examined by comparing the distribution of the orientation of the set of vectors defined by each pair of points within the data with the equivalent distribution for a random set of points within the study area. A simple model is proposed to describe linear or clustered structure within scattered data. A scattered data set of damage to pavement and pipes, recorded after the 1989 Loma Prieta earthquake, is used as an example to demonstrate the analytical techniques. The damage is found to be preferentially located nearer a set of mapped lineaments than randomly scattered damage, suggesting range-front faulting along the base of the Santa Cruz Mountains is related to both the earthquake damage and the mapped lineaments. The damage also exhibit two non-random patterns: a single cluster of damage centered in the town of Los Gatos, California, and a linear alignment of damage along the range front of the Santa Cruz Mountains, California. The linear alignment of damage is strongest between 45? and 50? northwest. This agrees well with the mean trend of the mapped lineaments, measured as 49? northwest.

Imaging atomic-level random walk of a point defect in graphene

NASA Astrophysics Data System (ADS)

Kotakoski, Jani; Mangler, Clemens; Meyer, Jannik C.

2014-05-01

Deviations from the perfect atomic arrangements in crystals play an important role in affecting their properties. Similarly, diffusion of such deviations is behind many microstructural changes in solids. However, observation of point defect diffusion is hindered both by the difficulties related to direct imaging of non-periodic structures and by the timescales involved in the diffusion process. Here, instead of imaging thermal diffusion, we stimulate and follow the migration of a divacancy through graphene lattice using a scanning transmission electron microscope operated at 60 kV. The beam-activated process happens on a timescale that allows us to capture a significant part of the structural transformations and trajectory of the defect. The low voltage combined with ultra-high vacuum conditions ensure that the defect remains stable over long image sequences, which allows us for the first time to directly follow the diffusion of a point defect in a crystalline material.

Insight into point defects and impurities in titanium from first principles

NASA Astrophysics Data System (ADS)

Nayak, Sanjeev K.; Hung, Cain J.; Sharma, Vinit; Alpay, S. Pamir; Dongare, Avinash M.; Brindley, William J.; Hebert, Rainer J.

2018-03-01

Titanium alloys find extensive use in the aerospace and biomedical industries due to a unique combination of strength, density, and corrosion resistance. Decades of mostly experimental research has led to a large body of knowledge of the processing-microstructure-properties linkages. But much of the existing understanding of point defects that play a significant role in the mechanical properties of titanium is based on semi-empirical rules. In this work, we present the results of a detailed self-consistent first-principles study that was developed to determine formation energies of intrinsic point defects including vacancies, self-interstitials, and extrinsic point defects, such as, interstitial and substitutional impurities/dopants. We find that most elements, regardless of size, prefer substitutional positions, but highly electronegative elements, such as C, N, O, F, S, and Cl, some of which are common impurities in Ti, occupy interstitial positions.

Ferromagnetism induced by point defect in Janus monolayer MoSSe regulated by strain engineering

NASA Astrophysics Data System (ADS)

Meng, Ming; Li, Tinghui; Li, Shaofeng; Liu, Kuili

2018-03-01

The formation and regulation of magnetism dependent on introduced defects in the Janus MoSSe monolayer has attracted much attention because of its potential application in spintronics. Here, we present a theoretical study of defect formation in the MoSSe monolayer and its introduced magnetism under external strain. The tensile deformation induced by external strain not only leads to decreases in defect formation energy, but also enhances magnetic characteristics. However, as compressed deformation increases, the magnetism in the structure induced by Se or S defects remains unchanged because this microstructural deformation adequately spin polarizes unpaired electrons of neighboring Mo atoms. Our results suggest the use of point defect and strain engineering in the Janus MoSSe monolayer for spintronics applications.

Native point defects in GaSb

NASA Astrophysics Data System (ADS)

Kujala, J.; Segercrantz, N.; Tuomisto, F.; Slotte, J.

2014-10-01

We have applied positron annihilation spectroscopy to study native point defects in Te-doped n-type and nominally undoped p-type GaSb single crystals. The results show that the dominant vacancy defect trapping positrons in bulk GaSb is the gallium monovacancy. The temperature dependence of the average positron lifetime in both p- and n-type GaSb indicates that negative ion type defects with no associated open volume compete with the Ga vacancies. Based on comparison with theoretical predictions, these negative ions are identified as Ga antisites. The concentrations of these negatively charged defects exceed the Ga vacancy concentrations nearly by an order of magnitude. We conclude that the Ga antisite is the native defect responsible for p-type conductivity in GaSb single crystals.

Neutron and x-ray scattering study of phonon dispersion and diffuse scattering in (Na ,Bi ) Ti O3-x BaTi O3 single crystals near the morphotropic phase boundary

NASA Astrophysics Data System (ADS)

Luo, Chengtao; Bansal, Dipanshu; Li, Jiefang; Viehland, Dwight; Winn, Barry; Ren, Yang; Li, Xiaobing; Luo, Haosu; Delaire, Olivier

2017-11-01

Neutron and x-ray scattering measurements were performed on (N a1 /2B i1 /2 ) Ti O3-x at %BaTi O3 (NBT-x BT ) single crystals (x =4 , 5, 6.5, and 7.5) across the morphotropic phase boundary (MPB), as a function of both composition and temperature, and probing both structural and dynamical aspects. In addition to the known diffuse scattering pattern near the Γ points, our measurements revealed new, faint superlattice peaks, as well as an extensive diffuse scattering network, revealing a short-range ordering of polar nanoregions (PNR) with a static stacking morphology. In samples with compositions closest to the MPB, our inelastic neutron scattering investigations of the phonon dynamics showed two unusual features in the acoustic phonon branches, between the superlattice points, and between the superlattice points and Γ points, respectively. These critical elements are not present in the other compositions away from the MPB, which suggests that these features may be related to the tilt modes coupling behavior near the MPB.

Splatterplots: overcoming overdraw in scatter plots.

PubMed

Mayorga, Adrian; Gleicher, Michael

2013-09-01

We introduce Splatterplots, a novel presentation of scattered data that enables visualizations that scale beyond standard scatter plots. Traditional scatter plots suffer from overdraw (overlapping glyphs) as the number of points per unit area increases. Overdraw obscures outliers, hides data distributions, and makes the relationship among subgroups of the data difficult to discern. To address these issues, Splatterplots abstract away information such that the density of data shown in any unit of screen space is bounded, while allowing continuous zoom to reveal abstracted details. Abstraction automatically groups dense data points into contours and samples remaining points. We combine techniques for abstraction with perceptually based color blending to reveal the relationship between data subgroups. The resulting visualizations represent the dense regions of each subgroup of the data set as smooth closed shapes and show representative outliers explicitly. We present techniques that leverage the GPU for Splatterplot computation and rendering, enabling interaction with massive data sets. We show how Splatterplots can be an effective alternative to traditional methods of displaying scatter data communicating data trends, outliers, and data set relationships much like traditional scatter plots, but scaling to data sets of higher density and up to millions of points on the screen.

Splatterplots: Overcoming Overdraw in Scatter Plots

PubMed Central

Mayorga, Adrian; Gleicher, Michael

2014-01-01

We introduce Splatterplots, a novel presentation of scattered data that enables visualizations that scale beyond standard scatter plots. Traditional scatter plots suffer from overdraw (overlapping glyphs) as the number of points per unit area increases. Overdraw obscures outliers, hides data distributions, and makes the relationship among subgroups of the data difficult to discern. To address these issues, Splatterplots abstract away information such that the density of data shown in any unit of screen space is bounded, while allowing continuous zoom to reveal abstracted details. Abstraction automatically groups dense data points into contours and samples remaining points. We combine techniques for abstraction with with perceptually based color blending to reveal the relationship between data subgroups. The resulting visualizations represent the dense regions of each subgroup of the dataset as smooth closed shapes and show representative outliers explicitly. We present techniques that leverage the GPU for Splatterplot computation and rendering, enabling interaction with massive data sets. We show how splatterplots can be an effective alternative to traditional methods of displaying scatter data communicating data trends, outliers, and data set relationships much like traditional scatter plots, but scaling to data sets of higher density and up to millions of points on the screen. PMID:23846097

Splatterplots: Overcoming Overdraw in Scatter Plots.

PubMed

Mayorga, Adrian; Gleicher, Michael

2013-03-20

We introduce Splatterplots, a novel presentation of scattered data that enables visualizations that scale beyond standard scatter plots. Traditional scatter plots suffer from overdraw (overlapping glyphs) as the number of points per unit area increases. Overdraw obscures outliers, hides data distributions, and makes the relationship among subgroups of the data difficult to discern. To address these issues, Splatterplots abstract away information such that the density of data shown in any unit of screen space is bounded, while allowing continuous zoom to reveal abstracted details. Abstraction automatically groups dense data points into contours and samples remaining points. We combine techniques for abstraction with with perceptually based color blending to reveal the relationship between data subgroups. The resulting visualizations represent the dense regions of each subgroup of the dataset as smooth closed shapes and show representative outliers explicitly. We present techniques that leverage the GPU for Splatterplot computation and rendering, enabling interaction with massive data sets. We show how splatterplots can be an effective alternative to traditional methods of displaying scatter data communicating data trends, outliers, and data set relationships much like traditional scatter plots, but scaling to data sets of higher density and up to millions of points on the screen.

Temperature dependent behavior of thermal conductivity of sub-5 nm Ir film: Defect-electron scattering quantified by residual thermal resistivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Zhe; Xu, Zaoli; Xu, Shen

2015-01-14

By studying the temperature-dependent behavior (300 K down to 43 K) of electron thermal conductivity (κ) in a 3.2 nm-thin Ir film, we quantify the extremely confined defect-electron scatterings and isolate the intrinsic phonon-electron scattering that is shared by the bulk Ir. At low temperatures below 50 K, κ of the film has almost two orders of magnitude reduction from that of bulk Ir. The film has ∂κ/∂T > 0, while the bulk Ir has ∂κ/∂T < 0. We introduce a unified thermal resistivity (Θ = T/κ) to interpret these completely different κ ∼ T relations. It is found that the film and the bulk Ir share a very similar Θ ∼ T trend,more » while they have a different residual part (Θ{sub 0}) at 0 K limit: Θ{sub 0} ∼ 0 for the bulk Ir, and Θ{sub 0} = 5.5 m·K{sup 2}/W for the film. The Ir film and the bulk Ir have very close ∂Θ/∂T (75–290 K): 6.33 × 10{sup −3} m K/W for the film and 7.62 × 10{sup −3} m K/W for the bulk Ir. This strongly confirms the similar phonon-electron scattering in them. Therefore, the residual thermal resistivity provides an unprecedented way to quantitatively evaluating defect-electron scattering (Θ{sub 0}) in heat conduction. Moreover, the interfacial thermal conductance across the grain boundaries is found larger than that of Al/Cu interface, and its value is proportional to temperature, largely due to the electron's specific heat. A unified interfacial thermal conductance is also defined and firmly proves this relation. Additionally, the electron reflection coefficient is found to be large (88%) and almost temperature independent.« less

Effects of LED phototherapy on bone defects grafted with MTA, bone morphogenetic proteins and guided bone regeneration: a Raman spectroscopic study.

PubMed

Pinheiro, Antonio L B; Soares, Luiz G P; Cangussú, Maria Cristina T; Santos, Nicole R S; Barbosa, Artur Felipe S; Silveira Júnior, Landulfo

2012-09-01

We studied peaks of calcium hydroxyapatite (CHA) and protein and lipid CH groups in defects grafted with mineral trioxide aggregate (MTA) treated or not with LED irradiation, bone morphogenetic proteins and guided bone regeneration. A total of 90 rats were divided into ten groups each of which was subdivided into three subgroups (evaluated at 15, 21 and 30 days after surgery). Defects were irradiated with LED light (wavelength 850 ± 10 nm) at 48-h intervals for 15 days. Raman readings were taken at the surface of the defects. There were no statistically significant differences in the CHA peaks among the nonirradiated defects at any of the experimental time-points. On the other hand, there were significant differences between the defects filled with blood clot and the irradiated defects at all time-points (p < 0.001, p = 0.02, p < 0.001). There were significant differences between the mean peak CHA in nonirradiated defects at all the experimental time-points (p < 0.01). The mean peak of the defects filled with blood clot was significantly different from that of the defects filled with MTA (p < 0.001). There were significant differences between the defects filled with blood clot and the irradiated defects (p < 0.001). The results of this study using Raman spectral analysis indicate that infrared LED light irradiation improves the deposition of CHA in healing bone grafted or not with MTA.

Plasmon-enhanced scattering and charge transfer in few-layer graphene interacting with buried printed 2D-pattern of silver nanoparticles

NASA Astrophysics Data System (ADS)

Carles, R.; Bayle, M.; Bonafos, C.

2018-04-01

Hybrid structures combing silver nanoparticles and few-layer graphene have been synthetized by combining low-energy ion beam synthesis and stencil techniques. A single plane of metallic nanoparticles plays the role of an embedded plasmonic enhancer located in dedicated areas at a controlled nanometer distance from deposited graphene layers. Optical imaging, reflectance and Raman scattering mapping are used to measure the enhancement of electronic and vibrational properties of these layers. In particular electronic Raman scattering is shown as notably efficient to analyze the optical transfer of charge carriers between the systems and the presence of intrinsic and extrinsic defects.

Plasmon-enhanced scattering and charge transfer in few-layer graphene interacting with buried printed 2D-pattern of silver nanoparticles.

PubMed

Carles, R; Bayle, M; Bonafos, C

2018-04-27

Hybrid structures combing silver nanoparticles and few-layer graphene have been synthetized by combining low-energy ion beam synthesis and stencil techniques. A single plane of metallic nanoparticles plays the role of an embedded plasmonic enhancer located in dedicated areas at a controlled nanometer distance from deposited graphene layers. Optical imaging, reflectance and Raman scattering mapping are used to measure the enhancement of electronic and vibrational properties of these layers. In particular electronic Raman scattering is shown as notably efficient to analyze the optical transfer of charge carriers between the systems and the presence of intrinsic and extrinsic defects.

Low-energy planar magnetic defects in BaFe 2 As 2 : Nanotwins, twins, antiphase, and domain boundaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khan, S. N.; Alam, Aftab; Johnson, Duane D.

2013-11-27

In BaFe 2As 2, structural and magnetic planar defects begin to proliferate below the structural phase transition, affecting descriptions of magnetism and superconductivity. We study, using density-functional theory, the stability and magnetic properties of competing antiphase and domain boundaries, twins and isolated nanotwins (twin nuclei), and spin excitations proposed and/or observed. These nanoscale defects have a very low surface energy (22–210 m Jm -2), with twins favorable to the mesoscale. Defects exhibit smaller moments confined near their boundaries—making a uniform-moment picture inappropriate for long-range magnetic order in real samples. Nanotwins explain features in measured pair distribution functions so should bemore » considered when analyzing scattering data. All these defects can be weakly mobile and/or can have fluctuations that lower assessed “ordered” moments from longer spatial and/or time averaging and should be considered directly.« less

Grazing-incidence X-ray diffraction from a crystal with subsurface defects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gaevskii, A. Yu., E-mail: transilv@mail.ru; Golentus, I. E.

2015-03-15

The diffraction of X rays incident on a crystal surface under grazing angles under conditions of total external reflection has been investigated. An approach is proposed in which exact solutions to the dynamic problem of grazing-incidence diffraction in an ideal crystal are used as initial functions to calculate the diffuse component of diffraction in a crystal with defects. The diffuse component of diffraction is calculated for a crystal with surface defects of a dilatation-center type. Exact formulas of the continuum theory which take into account the mirror-image forces are used for defect-induced atomic displacements. Scattering intensity maps near Bragg peaksmore » are constructed for different scan modes, and the conditions for detecting primarily the diffuse component are determined. The results of dynamic calculations of grazing-incidence diffraction in defect-containing crystals are compared with calculations in the kinematic approximation.« less

Defect stability in thorium monocarbide: An ab initio study

NASA Astrophysics Data System (ADS)

Wang, Chang-Ying; Han, Han; Shao, Kuan; Cheng, Cheng; Huai, Ping

2015-09-01

The elastic properties and point defects of thorium monocarbide (ThC) have been studied by means of density functional theory based on the projector-augmented-wave method. The calculated electronic and elastic properties of ThC are in good agreement with experimental data and previous theoretical results. Five types of point defects have been considered in our study, including the vacancy defect, interstitial defect, antisite defect, schottky defect, and composition-conserving defect. Among these defects, the carbon vacancy defect has the lowest formation energy of 0.29 eV. The second most stable defect (0.49 eV) is one of composition-conserving defects in which one carbon is removed to another carbon site forming a C2 dimer. In addition, we also discuss several kinds of carbon interstitial defects, and predict that the carbon trimer configuration may be a transition state for a carbon dimer diffusion in ThC. Project supported by the International S&T Cooperation Program of China (Grant No. 2014DFG60230), the National Natural Science Foundation of China (Grant No. 91326105), the National Basic Research Program of China (Grant No. 2010CB934504), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA02040104).

Electron Scattering and Doping Mechanisms in Solid-Phase-Crystallized In2O3:H Prepared by Atomic Layer Deposition.

PubMed

Macco, Bart; Knoops, Harm C M; Kessels, Wilhelmus M M

2015-08-05

Hydrogen-doped indium oxide (In2O3:H) has recently emerged as an enabling transparent conductive oxide for solar cells, in particular for silicon heterojunction solar cells because its high electron mobility (>100 cm(2)/(V s)) allows for a simultaneously high electrical conductivity and optical transparency. Here, we report on high-quality In2O3:H prepared by a low-temperature atomic layer deposition (ALD) process and present insights into the doping mechanism and the electron scattering processes that limit the carrier mobility in such films. The process consists of ALD of amorphous In2O3:H at 100 °C and subsequent solid-phase crystallization at 150-200 °C to obtain large-grained polycrystalline In2O3:H films. The changes in optoelectronic properties upon crystallization have been monitored both electrically by Hall measurements and optically by analysis of the Drude response. After crystallization, an excellent carrier mobility of 128 ± 4 cm(2)/(V s) can be obtained at a carrier density of 1.8 × 10(20) cm(-3), irrespective of the annealing temperature. Temperature-dependent Hall measurements have revealed that electron scattering is dominated by unavoidable phonon and ionized impurity scattering from singly charged H-donors. Extrinsic defect scattering related to material quality such as grain boundary and neutral impurity scattering was found to be negligible in crystallized films indicating that the carrier mobility is maximized. Furthermore, by comparison of the absolute H-concentration and the carrier density in crystallized films, it is deduced that <4% of the incorporated H is an active dopant in crystallized films. Therefore, it can be concluded that inactive H atoms do not (significantly) contribute to defect scattering, which potentially explains why In2O3:H films are capable of achieving a much higher carrier mobility than conventional In2O3:Sn (ITO).

Physical Interpretation of Mixing Diagrams

NASA Astrophysics Data System (ADS)

Khain, Alexander; Pinsky, Mark; Magaritz-Ronen, L.

2018-01-01

Type of mixing at cloud edges is often determined by means of mixing diagrams showing the dependence of normalized cube of the mean volume radius on the dilution level. The mixing diagrams correspond to the final equilibrium state of mixing between two air volumes. While interpreting in situ measurements, scattering diagrams are plotted in which normalized droplet concentration is used instead of dilution level. Utilization of such scattering diagrams for interpretation of in situ observations faces significant difficulties and often leads to misinterpretation of the mixing process and to uncertain conclusions concerning the mixing type. In this study we analyze the scattering diagrams obtained by means of a Lagrangian-Eulerian model of a stratocumulus cloud. The model consists of 2,000 interacting Largangian parcels which mix with their neighbors during their motion in the atmospheric boundary layer. In the diagram, each parcel is denoted by a point. Changes of microphysical parameters of the parcel are represented by movements of the point in the scattering diagram. The method of plotting the scattering diagrams using the model is in many aspects similar to that used in in situ measurements. It is shown that a scattering diagram shows snapshots of a transient mixing process. The location of points in the scattering diagrams reflects largely the history and the origin of air parcels. Location of points on scattering diagram characterizes intensity of entrainment, and different parameters of droplet size distributions (DSDs) like concentration, mean volume (or effective) radius, and DSD width.

Pipe wall damage detection by electromagnetic acoustic transducer generated guided waves in absence of defect signals.

PubMed

Vasiljevic, Milos; Kundu, Tribikram; Grill, Wolfgang; Twerdowski, Evgeny

2008-05-01

Most investigators emphasize the importance of detecting the reflected signal from the defect to determine if the pipe wall has any damage and to predict the damage location. However, often the small signal from the defect is hidden behind the other arriving wave modes and signal noise. To overcome the difficulties associated with the identification of the small defect signal in the time history plots, in this paper the time history is analyzed well after the arrival of the first defect signal, and after different wave modes have propagated multiple times through the pipe. It is shown that the defective pipe can be clearly identified by analyzing these late arriving diffuse ultrasonic signals. Multiple reflections and scattering of the propagating wave modes by the defect and pipe ends do not hamper the defect detection capability; on the contrary, it apparently stabilizes the signal and makes it easier to distinguish the defective pipe from the defect-free pipe. This paper also highlights difficulties associated with the interpretation of the recorded time histories due to mode conversion by the defect. The design of electro-magnetic acoustic transducers used to generate and receive the guided waves in the pipe is briefly described in the paper.

Automated real-time detection of defects during machining of ceramics

DOEpatents

Ellingson, W.A.; Sun, J.

1997-11-18

Apparatus for the automated real-time detection and classification of defects during the machining of ceramic components employs an elastic optical scattering technique using polarized laser light. A ceramic specimen is continuously moved while being machined. Polarized laser light is directed onto the ceramic specimen surface at a fixed position just aft of the machining tool for examination of the newly machined surface. Any foreign material near the location of the laser light on the ceramic specimen is cleared by an air blast. As the specimen is moved, its surface is continuously scanned by the polarized laser light beam to provide a two-dimensional image presented in real-time on a video display unit, with the motion of the ceramic specimen synchronized with the data acquisition speed. By storing known ``feature masks`` representing various surface and sub-surface defects and comparing measured defects with the stored feature masks, detected defects may be automatically characterized. Using multiple detectors, various types of defects may be detected and classified. 14 figs.

Automated real-time detection of defects during machining of ceramics

DOEpatents

Ellingson, William A.; Sun, Jiangang

1997-01-01

Apparatus for the automated real-time detection and classification of defects during the machining of ceramic components employs an elastic optical scattering technique using polarized laser light. A ceramic specimen is continuously moved while being machined. Polarized laser light is directed onto the ceramic specimen surface at a fixed position just aft of the machining tool for examination of the newly machined surface. Any foreign material near the location of the laser light on the ceramic specimen is cleared by an air blast. As the specimen is moved, its surface is continuously scanned by the polarized laser light beam to provide a two-dimensional image presented in real-time on a video display unit, with the motion of the ceramic specimen synchronized with the data acquisition speed. By storing known "feature masks" representing various surface and sub-surface defects and comparing measured defects with the stored feature masks, detected defects may be automatically characterized. Using multiple detectors, various types of defects may be detected and classified.

Brillouin light scattering spectroscopy for tissue engineering application

NASA Astrophysics Data System (ADS)

Akilbekova, Dana; Yakupov, Talgat; Ogay, Vyacheslav; Umbayev, Bauyrzhan; Yakovlev, Vladislav V.; Utegulov, Zhandos N.

2018-02-01

Biomechanical properties of mammalian bones, such as strength, toughness and plasticity, are essential for understanding how microscopic scale mechanical features can link to macroscale bones' strength and fracture resistance. We employ Brillouin light scattering (BLS) micro-spectroscopy for local assessment of elastic properties of bones under compression and the efficacy of the tissue engineering approach based on heparin-conjugated fibrin (HCF) hydrogels, bone morphogenic proteins (BMPs) and osteogenic stem cells in the regeneration of the bone tissues. BLS is noninvasive and label-free imaging modality for probing mechanical properties of hard tissues that can give information on structure-function properties of normal and pathological tissues. Results showed that HCF gels containing combination of all factors had the best effect with complete defect regeneration at week 9 and that the bones with fully consolidated fractures have higher values of elastic moduli compared to the bones with defects.

First-principle calculation on mechanical and thermal properties of B2-NiSc with point defects

NASA Astrophysics Data System (ADS)

Yuan, Zhipeng; Cui, Hongbao; Guo, Xuefeng

2017-01-01

Using the first-principles plane-wave pseudo-potential method based on density functional theory, the effect of vacancy and anti-position defect on the mechanical and thermal properties of B2-NiSc intermetallics were discussed in detail. Several parameters, such as the shear modulus, bulk modulus, modulus of elasticity, C 11-C 11, the Debye temperature and Poisson's ratio, have been calculated to evaluate the effect of vacancy and anti-position defect on the hardness, ductility and thermal properties of B2-NiSc intermetallics. The results show that VNi, ScNi, VSc and NiSc the four point defects all make the crystal hardness decrease and improve plasticity of B2-NiSc intermetallics. The entropy, enthalpy and free energy of VNi, ScNi, VSc and NiSc are monotonously changed as temperature changes. From the perspective of free energy, NiSc is the most stable, while ScNi is the most unstable. Debye temperature of NiSc intermetallics with four different point defects shows VNi, ScNi, VSc and NiSc the four point defects all reduce the stability of B2-NiSc intermetallics. Project supported by the National Natural Science Foundation of China (Nos. 51301063, 51571086) and the Talent Introduction Foundation of Henan Polytechnic University (No. Y-2009).

Strong spin-orbit splitting and magnetism of point defect states in monolayer WS2

NASA Astrophysics Data System (ADS)

Li, Wun-Fan; Fang, Changming; van Huis, Marijn A.

2016-11-01

The spin-orbit coupling (SOC) effect has been known to be profound in monolayer pristine transition metal dichalcogenides (TMDs). Here we show that point defects, which are omnipresent in the TMD membranes, exhibit even stronger SOC effects and change the physics of the host materials drastically. In this article we chose the representative monolayer WS2 slabs from the TMD family together with seven typical types of point defects including monovacancies, interstitials, and antisites. We calculated the formation energies of these defects, and studied the effect of spin-orbit coupling (SOC) on the corresponding defect states. We found that the S monovacancy (VS) and S interstitial (adatom) have the lowest formation energies. In the case of VS and both of the WS and WS 2 antisites, the defect states exhibit strong splitting up to 296 meV when SOC is considered. Depending on the relative position of the defect state with respect to the conduction band minimum (CBM), the hybrid functional HSE will either increase the splitting by up to 60 meV (far from CBM), or decrease the splitting by up to 57 meV (close to CBM). Furthermore, we found that both the WS and WS 2 antisites possess a magnetic moment of 2 μB localized at the antisite W atom and the neighboring W atoms. The dependence of SOC on the orientation of the magnetic moment for the WS and WS 2 antisites is discussed. All these findings provide insights in the defect behavior under SOC and point to possibilities for spintronics applications for TMDs.

Epitaxial Growths of m-Plane AlGaN/GaN and AlInN/GaN Heterostructures Applicable for Normally-Off Mode High Power Field Effect Transistors on Freestanding GaN Substrates

DTIC Science & Technology

2011-08-17

cathodoluminescence (CL), and Hall effect measurement. We will disclose how structural and point defects affect the internal quantum efficiency. We have a complete...18. S. F. Chichibu, A. Uedono, T. Onuma, S. P. DenBaars, U. K. Mishra, J. S. Speck, and S. Nakamura, “Impact of Point Defects on the Luminescence...A. Uedono, “Major impacts of point defects and impurities on the carrier recombination dynamics in AlN,” Appl. Phys. Lett. 97(20), 201904 (2010

Scattering and the Point Spread Function of the New Generation Space Telescope

NASA Technical Reports Server (NTRS)

Schreur, Julian J.

1996-01-01

Preliminary design work on the New Generation Space Telescope (NGST) is currently under way. This telescope is envisioned as a lightweight, deployable Cassegrain reflector with an aperture of 8 meters, and an effective focal length of 80 meters. It is to be folded into a small-diameter package for launch by an Atlas booster, and unfolded in orbit. The primary is to consist of an octagon with a hole at the center, and with eight segments arranged in a flower petal configuration about the octagon. The comers of the petal-shaped segments are to be trimmed so that the package will fit atop the Atlas booster. This mirror, along with its secondary will focus the light from a point source into an image which is spread from a point by diffraction effects, figure errors, and scattering of light from the surface. The distribution of light in the image of a point source is called a point spread function (PSF). The obstruction of the incident light by the secondary mirror and its support structure, the trimmed corners of the petals, and the grooves between the segments all cause the diffraction pattern characterizing an ideal point spread function to be changed, with the trimmed comers causing the rings of the Airy pattern to become broken up, and the linear grooves causing diffraction spikes running radially away from the central spot, or Airy disk. Any figure errors the mirror segments may have, or any errors in aligning the petals with the central octagon will also spread the light out from the ideal point spread function. A point spread function for a mirror the size of the NGST and having an incident wavelength of 900 nm is considered. Most of the light is confined in a circle with a diameter of 0.05 arc seconds. The ring pattern ranges in intensity from 10(exp -2) near the center to 10(exp -6) near the edge of the plotted field, and can be clearly discerned in a log plot of the intensity. The total fraction of the light scattered from this point spread function is called the total integrated scattering (TIS), and the fraction remaining is called the Strehl ratio. The angular distribution of the scattered light is called the angle resolved scattering (ARS), and it shows a strong spike centered on a scattering angle of zero, and a broad , less intense distribution at larger angles. It is this scattered light, and its effect on the point spread function which is the focus of this study.

Tunneling of heat: Beyond linear response regime

NASA Astrophysics Data System (ADS)

Walczak, Kamil; Saroka, David

2018-02-01

We examine nanoscale processes of heat (energy) transfer as carried by electrons tunneling via potential barriers and molecular interconnects between two heat reservoirs (thermal baths). For that purpose, we use Landauer-type formulas to calculate thermal conductance and quadratic correction to heat flux flowing via quantum systems. As an input, we implement analytical expressions for transmission functions related to simple potential barriers and atomic bridges. Our results are discussed with respect to energy of tunneling electrons, temperature, the presence of resonant states, and specific parameters characterizing potential barriers as well as heat carriers. The simplicity of semi-analytical models developed by us allows to fit experimental data and extract crucial information about the values of model parameters. Further investigations are expected for more realistic transmission functions, while time-dependent aspects of nanoscale heat transfer may be addressed by using the concept of wave packets scattered on potential barriers and point-like defects within regular (periodic) nanostructures.

Wave bandgap formation and its evolution in two-dimensional phononic crystals composed of rubber matrix with periodic steel quarter-cylinders

NASA Astrophysics Data System (ADS)

Li, Peng; Wang, Guan; Luo, Dong; Cao, Xiaoshan

2018-02-01

The band structure of a two-dimensional phononic crystal, which is composed of four homogenous steel quarter-cylinders immersed in rubber matrix, is investigated and compared with the traditional steel/rubber crystal by the finite element method (FEM). It is revealed that the frequency can then be tuned by changing the distance between adjacent quarter-cylinders. When the distance is relatively small, the integrality of scatterers makes the inner region inside them almost motionless, so that they can be viewed as a whole at high-frequencies. In the case of relatively larger distance, the interaction between each quarter-cylinder and rubber will introduce some new bandgaps at relatively low-frequencies. Lastly, the point defect states induced by the four quarter-cylinders are revealed. These results will be helpful in fabricating devices, such as vibration insulators and acoustic/elastic filters, whose band frequencies can be manipulated artificially.

Large thermal conductivity reduction induced by La/O vacancies in the thermoelectric LaCoO3 system.

PubMed

Wang, Yang; Li, Fang; Xu, Luxiang; Sui, Yu; Wang, Xianjie; Su, Wenhui; Liu, Xiaoyang

2011-05-16

A series of compact La/O-vacant La(1-x)CoO(3-y) compounds were prepared by a cold high-pressure procedure, and their thermoelectric (TE) properties were investigated. Compared with the ion-substituted hole-type LaCoO(3) systems (e.g., La(1-x)Sr(x)CoO(3)), the thermal conduction of La(1-x)CoO(3-y) is noticeably reduced by the La/O vacancies, whereas the electric transport is less influenced, which results in an efficient ZT enhancement. We demonstrate that the large thermal conductivity reduction originates from the strong point-defect scattering, and La(1-x)CoO(3-y) can be rationalized as a partially filled solid solution: La(1-x)◻(x)CoO(3-y)◻(y), where ◻ denotes a vacancy. Such intrinsic thermal conductivity suppression provides an effective pathway for the design of better TE materials.

Controlling the ripple density and heights: a new way to improve the electrical performance of CVD-grown graphene.

PubMed

Park, Won-Hwa; Jo, Insu; Hong, Byung Hee; Cheong, Hyeonsik

2016-05-14

We report a new way to enhance the electrical performances of large area CVD-grown graphene through controlling the ripple density and heights after transfer onto SiO2/Si substrates by employing different cooling rates during fabrication. We find that graphene films prepared with a high cooling rate have reduced ripple density and heights and improved electrical characteristics such as higher electron/hole mobilities as well as reduced sheet resistance. The corresponding Raman analysis also shows a significant decrease of the defects when a higher cooling rate is employed. We suggest a model that explains the improved morphology of the graphene film obtained with higher cooling rates. From these points of view, we can suggest a new pathway toward a relatively lower density and heights of ripples in order to reduce the flexural phonon-electron scattering effect, leading to higher lateral carrier mobilities.

Electronegative Guests in CoSb 3

DOE PAGES

Duan, Bo; Yang, Jiong; Salvador, James R.; ...

2016-04-19

Introducing guests into a host framework to form a so called inclusion compound can be used to design materials with new and fascinating functionalities. The vast majority of inclusion compounds have electropositive guests with neutral or negatively charged frameworks. Here, we show a series of electronegative guest filled skutterudites with inverse polarity. The strong covalent guest-host interactions observed for the electronegative group VIA guests, i.e., S and Se, feature a unique localized cluster vibration which significantly influences the lattice dynamics, together with the point-defect scattering caused by element substitutions, resulting in very low lattice thermal conductivity values. The findings ofmore » electronegative guests provide a new perspective for guest-filling in skutterudites, and the covalent filler/lattice interactions lead to an unusual lattice dynamics phenomenon which can be used for designing high-efficiency thermoelectric materials and novel functional inclusion compounds with open structures.« less

THz Acoustic Spectroscopy by using Double Quantum Wells and Ultrafast Optical Spectroscopy.

PubMed

Wei, Fan Jun; Yeh, Yu-Hsiang; Sheu, Jinn-Kong; Lin, Kung-Hsuan

2016-06-27

GaN is a pivotal material for acoustic transducers and acoustic spectroscopy in the THz regime, but its THz phonon properties have not been experimentally and comprehensively studied. In this report, we demonstrate how to use double quantum wells as a THz acoustic transducer for measuring generated acoustic phonons and deriving a broadband acoustic spectrum with continuous frequencies. We experimentally investigated the sub-THz frequency dependence of acoustic attenuation (i.e., phonon mean-free paths) in GaN, in addition to its physical origins such as anharmonic scattering, defect scattering, and boundary scattering. A new upper limit of attenuation caused by anharmonic scattering, which is lower than previously reported values, was obtained. Our results should be noteworthy for THz acoustic spectroscopy and for gaining a fundamental understanding of heat conduction.

Native point defects in GaSb

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kujala, J.; Segercrantz, N.; Tuomisto, F.

2014-10-14

We have applied positron annihilation spectroscopy to study native point defects in Te-doped n-type and nominally undoped p-type GaSb single crystals. The results show that the dominant vacancy defect trapping positrons in bulk GaSb is the gallium monovacancy. The temperature dependence of the average positron lifetime in both p- and n-type GaSb indicates that negative ion type defects with no associated open volume compete with the Ga vacancies. Based on comparison with theoretical predictions, these negative ions are identified as Ga antisites. The concentrations of these negatively charged defects exceed the Ga vacancy concentrations nearly by an order of magnitude.more » We conclude that the Ga antisite is the native defect responsible for p-type conductivity in GaSb single crystals.« less

Generation and characterization of point defects in SrTiO3 and Y3Al5O12

NASA Astrophysics Data System (ADS)

Selim, F. A.; Winarski, D.; Varney, C. R.; Tarun, M. C.; Ji, Jianfeng; McCluskey, M. D.

Positron annihilation lifetime spectroscopy (PALS) was applied to characterize point defects in single crystals of Y3Al5O12 and SrTiO3 after populating different types of defects by relevant thermal treatments. In SrTiO3, PALS measurements identified Sr vacancy, Ti vacancy, vacancy complexes of Ti-O (vacancy) and hydrogen complex defects. In Y3Al5O12 single crystals the measurements showed the presence of Al-vacancy, (Al-O) vacancy and Al-vacancy passivated by hydrogen. These defects are shown to play the major role in defining the electronic and optical properties of these complex oxides.

A review of defects and disorder in multinary tetrahedrally bonded semiconductors [Defects and disorder in multinary tetrahedrally bonded semiconductors studied by experiment and theory

DOE PAGES

Baranowski, Lauryn L.; Zawadzki, Pawel; Lany, Stephan; ...

2016-11-10

Defects are critical to understanding the electronic properties of semiconducting compounds, for applications such as light-emitting diodes, transistors, photovoltaics, and thermoelectrics. In this review, we describe our work investigating defects in tetrahedrally bonded, multinary semiconductors, and discuss the place of our research within the context of publications by other groups. We applied experimental and theory techniques to understand point defects, structural disorder, and extended antisite defects in one semiconductor of interest for photovoltaic applications, Cu 2SnS 3. We contrast our findings on Cu 2SnS 3 with other chemically related Cu-Sn-S compounds, as well as structurally related compounds such as Cumore » 2ZnSnS 4 and Cu(In,Ga)Se 2. We find that evaluation of point defects alone is not sufficient to understand defect behavior in multinary tetrahedrally bonded semiconductors. In the case of Cu 2SnS 3 and Cu 2ZnSnS 4, structural disorder and entropy-driven cation clustering can result in nanoscale compositional inhomogeneities which detrimentally impact the electronic transport. Therefore, it is not sufficient to assess only the point defect behavior of new multinary tetrahedrally bonded compounds; effects such as structural disorder and extended antisite defects must also be considered. Altogether, this review provides a framework for evaluating tetrahedrally bonded semiconducting compounds with respect to their defect behavior for photovoltaic and other applications, and suggests new materials that may not be as prone to such imperfections.« less

A review of defects and disorder in multinary tetrahedrally bonded semiconductors [Defects and disorder in multinary tetrahedrally bonded semiconductors studied by experiment and theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baranowski, Lauryn L.; Zawadzki, Pawel; Lany, Stephan

Defects are critical to understanding the electronic properties of semiconducting compounds, for applications such as light-emitting diodes, transistors, photovoltaics, and thermoelectrics. In this review, we describe our work investigating defects in tetrahedrally bonded, multinary semiconductors, and discuss the place of our research within the context of publications by other groups. We applied experimental and theory techniques to understand point defects, structural disorder, and extended antisite defects in one semiconductor of interest for photovoltaic applications, Cu 2SnS 3. We contrast our findings on Cu 2SnS 3 with other chemically related Cu-Sn-S compounds, as well as structurally related compounds such as Cumore » 2ZnSnS 4 and Cu(In,Ga)Se 2. We find that evaluation of point defects alone is not sufficient to understand defect behavior in multinary tetrahedrally bonded semiconductors. In the case of Cu 2SnS 3 and Cu 2ZnSnS 4, structural disorder and entropy-driven cation clustering can result in nanoscale compositional inhomogeneities which detrimentally impact the electronic transport. Therefore, it is not sufficient to assess only the point defect behavior of new multinary tetrahedrally bonded compounds; effects such as structural disorder and extended antisite defects must also be considered. Altogether, this review provides a framework for evaluating tetrahedrally bonded semiconducting compounds with respect to their defect behavior for photovoltaic and other applications, and suggests new materials that may not be as prone to such imperfections.« less

Quark-mass dependence of the H dibaryon in Λ Λ scattering

NASA Astrophysics Data System (ADS)

Yamaguchi, Yasuhiro; Hyodo, Tetsuo

2016-12-01

We study the quark mass dependence of the H dibaryon in the strangeness S =-2 baryon-baryon scattering. A low-energy effective field theory is used to describe the coupled-channel scattering, in which the quark mass dependence is incorporated so as to reproduce the lattice QCD data by the HAL QCD collaboration in the SU(3) limit. We point out the existence of the Castillejo-Dalitz-Dyson pole in the Λ Λ scattering amplitude below the threshold in the SU(3) limit, which may cause the Ramsauer-Townsend effect near the N Ξ threshold at the physical point. The H dibaryon is unbound at the physical point, and a resonance appears just below the N Ξ threshold. As a consequence of the coupled-channel dynamics, the pole associated with the resonance is not continuously connected to the bound state in the SU(3) limit. Through the extrapolation in quark masses, we show that the unitary limit of the Λ Λ scattering is achieved between the physical point and the SU(3) limit. We discuss the possible realization of the "H matter" in the unphysical quark mass region.

Theoretical model of dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide

NASA Astrophysics Data System (ADS)

Ivády, Viktor; Szász, Krisztián; Falk, Abram L.; Klimov, Paul V.; Christle, David J.; Janzén, Erik; Abrikosov, Igor A.; Awschalom, David D.; Gali, Adam

2015-09-01

Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point defects in semiconductors is a key resource for both initializing nuclear quantum memories and producing nuclear hyperpolarization. DNP is therefore an important process in the field of quantum-information processing, sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based spintronics. DNP based on optical pumping of point defects has been demonstrated by using the electron spin of nitrogen-vacancy (NV) center in diamond, and more recently, by using divacancy and related defect spins in hexagonal silicon carbide (SiC). Here, we describe a general model for these optical DNP processes that allows the effects of many microscopic processes to be integrated. Applying this theory, we gain a deeper insight into dynamic nuclear spin polarization and the physics of diamond and SiC defects. Our results are in good agreement with experimental observations and provide a detailed and unified understanding. In particular, our findings show that the defect electron spin coherence times and excited state lifetimes are crucial factors in the entire DNP process.

Defect reduction of patterned media templates and disks

NASA Astrophysics Data System (ADS)

Luo, Kang; Ha, Steven; Fretwell, John; Ramos, Rick; Ye, Zhengmao; Schmid, Gerard; LaBrake, Dwayne; Resnick, Douglas J.; Sreenivasan, S. V.

2010-05-01

Imprint lithography has been shown to be an effective technique for the replication of nano-scale features. Acceptance of imprint lithography for manufacturing will require a demonstration of defect levels commensurate with cost-effective device production. This work summarizes the results of defect inspections of hard disks patterned using Jet and Flash Imprint Lithography (J-FILTM). Inspections were performed with optical based automated inspection tools. For the hard drive market, it is important to understand the defectivity of both the template and the imprinted disk. This work presents a methodology for automated pattern inspection and defect classification for imprint-patterned media. Candela CS20 and 6120 tools from KLA-Tencor map the optical properties of the disk surface, producing highresolution grayscale images of surface reflectivity and scattered light. Defects that have been identified in this manner are further characterized according to the morphology. The imprint process was tested after optimizing both the disk cleaning and adhesion layers processes that precede imprinting. An extended imprint run was performed and both the defect types and trends are reported.

Brillouin-scattering studies of a sodium silicate glass in solid and melt conditions at temperatures up to 1000 °C

NASA Astrophysics Data System (ADS)

Xu, Ji-An; Manghnani, Murli H.

1992-01-01

By using the sapphire-glass-sapphire sandwich-glass-assemblage Brillouin-scattering technique, the velocities of shear and longitudinal modes of a sodium silicate glass have been measured as a function of temperature up to 1000 °C. A turning point was found at the strain point (494 °C) but not at the softening point (720 °C). Combined with the results of the 90°- and 180°-scattering-geometry measurements, the refractive index (n) of the glass as a function of temperature was also determined. As a result, independent criteria for both the strain and softening points are suggested.

SU-F-J-144: Scatter and Leakage Survey of An Integrated MR-Linac System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, J; Bosco, G; Darenbourg, B

2016-06-15

Purpose: To assess the scatter and leakage radiation of an integrated 1.5T MRI-Linac system. Methods: A 150cc chamber (model 96020C, Inovision) was used in all the scatter and leakage measurements, after being recalibrated for MV energy by the Accredited Dosimetry Calibration Laboratory at MD Anderson. The scatter radiation was measured by placing a 25 cm stack of solid-water materials at iso-center on the patient couch to simulate patient scatter. Gantry angles were positioned at 0 degree (beam pointing downward) and 270 (beam pointing laterally). Scatter radiation was measured at selective locations inside the RF room. Beam stopper leakage was measuredmore » at the exterior panel of the gantry. The head leakage was measured at 1 meter away from the Linac head in the direction which was determined to be the area of maximum leakage by wrapped films test. All measurements were repeated with the 1.5T magnetic field turned off to study the effect of magnetic field. Results: When the magnet was on (B=1.5T), the maximum head leakage at 1 meter was 191.6mR/1000MU. The scatter radiation at 1 meter from the iso-center was 1.091R/1000MU when the radiation beam was pointing downward, 1.296R/1000MU when the beam pointed laterally. The beam stopper leakage was measured as 299.4 mR/1000MU at the exterior panel of the gantry. When magnet was off (B=0), the head leakage was measured as 198.6mR/1000MU. The scatter radiation at 1 meter was 1.153R/1000MU when beam pointed downward, 1.287R/1000MU when beam pointed laterally. The beam stopper leakage was measured as 309.4 mR/1000MU at the exterior panel of the gantry. Conclusion: The measurements indicate that the scatter and leakage radiation from the integrated MR-Linac system are in-line with the expected values. The beam stopper leakage is approximately 300 mR/1000MU. The leakage and scatter difference with the magnetic field ON and OFF was within 5%. The authors received a corporate sponsored grant from Elekta which is the vendor of the MR-Linac system studied in this work.« less

Molecular dynamical simulations of melting Al nanoparticles using a reaxff reactive force field

NASA Astrophysics Data System (ADS)

Liu, Junpeng; Wang, Mengjun; Liu, Pingan

2018-06-01

Molecular dynamics simulations were performed to study thermal properties and melting points of Al nanoparticles by using a reactive force field under canonical (NVT) ensembles. Al nanoparticles (particle size 2–4 nm) were considered in simulations. A combination of structural and thermodynamic parameters such as the Lindemann index, heat capacities, potential energy and radial-distribution functions was employed to decide melting points. We used annealing technique to obtain the initial Al nanoparticle model. Comparison was made between ReaxFF results and other simulation results. We found that ReaxFF force field is reasonable to describe Al cluster melting behavior. The linear relationship between particle size and melting points was found. After validating the ReaxFF force field, more attention was paid on thermal properties of Al nanoparticles with different defect concentrations. 4 nm Al nanoparticles with different defect concentrations (5%–20%) were considered in this paper. Our results revealed that: the melting points are irrelevant with defect concentration at a certain particle size. The extra storage energy of Al nanoparticles is proportional to nanoparticles’ defect concentration, when defect concentration is 5%–15%. While the particle with 20% defect concentration is similar to the cluster with 10% defect concentration. After melting, the extra energy of all nanoparticles decreases sharply, and the extra storage energy is nearly zero at 600 K. The centro-symmetry parameter analysis shows structure evolution of different models during melting processes.

Theoretical Study of Defect Signatures in III-V and II-VI Semiconductors

DTIC Science & Technology

2006-03-01

collaboration with experimentalists at Linköpin University (Sweden), we identified the recently observed EPR signals in diluted GaPN to be Gallium ...the results from USPP calculations to all electron calculations. o Study NO-Zni complexes and other point defects in ZnO using USPP calculations...parameters for point defects in semiconductors. o Results on stability of NO-Zni complexes in ZnO and preliminary results on their electronic

Local defect resonance for sensitive non-destructive testing

NASA Astrophysics Data System (ADS)

Adebahr, W.; Solodov, I.; Rahammer, M.; Gulnizkij, N.; Kreutzbruck, M.

2016-02-01

Ultrasonic wave-defect interaction is a background of ultrasound activated techniques for imaging and non-destructive testing (NDT) of materials and industrial components. The interaction, primarily, results in acoustic response of a defect which provides attenuation and scattering of ultrasound used as an indicator of defects in conventional ultrasonic NDT. The derivative ultrasonic-induced effects include e.g. nonlinear, thermal, acousto-optic, etc. responses also applied for NDT and defect imaging. These secondary effects are normally relatively inefficient so that the corresponding NDT techniques require an elevated acoustic power and stand out from conventional ultrasonic NDT counterparts for their specific instrumentation particularly adapted to high-power ultrasonic. In this paper, a consistent way to enhance ultrasonic, optical and thermal defect responses and thus to reduce an ultrasonic power required is suggested by using selective ultrasonic activation of defects based on the concept of local defect resonance (LDR). A strong increase in vibration amplitude at LDR enables to reliably detect and visualize the defect as soon as the driving ultrasonic frequency is matched to the LDR frequency. This also provides a high frequency selectivity of the LDR-based imaging, i.e. an opportunity of detecting a certain defect among a multitude of other defects in material. Some examples are shown how to use LDR in non-destructive testing techniques, like vibrometry, ultrasonic thermography and shearography in order to enhance the sensitivity of defect visualization.

Defects in Amorphous Semiconductors: The Case of Amorphous Indium Gallium Zinc Oxide

NASA Astrophysics Data System (ADS)

de Jamblinne de Meux, A.; Pourtois, G.; Genoe, J.; Heremans, P.

2018-05-01

Based on a rational classification of defects in amorphous materials, we propose a simplified model to describe intrinsic defects and hydrogen impurities in amorphous indium gallium zinc oxide (a -IGZO). The proposed approach consists of organizing defects into two categories: point defects, generating structural anomalies such as metal—metal or oxygen—oxygen bonds, and defects emerging from changes in the material stoichiometry, such as vacancies and interstitial atoms. Based on first-principles simulations, it is argued that the defects originating from the second group always act as perfect donors or perfect acceptors. This classification simplifies and rationalizes the nature of defects in amorphous phases. In a -IGZO, the most important point defects are metal—metal bonds (or small metal clusters) and peroxides (O - O single bonds). Electrons are captured by metal—metal bonds and released by the formation of peroxides. The presence of hydrogen can lead to two additional types of defects: metal-hydrogen defects, acting as acceptors, and oxygen-hydrogen defects, acting as donors. The impact of these defects is linked to different instabilities observed in a -IGZO. Specifically, the diffusion of hydrogen and oxygen is connected to positive- and negative-bias stresses, while negative-bias illumination stress originates from the formation of peroxides.

Basic Study on Term of Warranty Liability for Water Supply, Drainage, and Sanitation Arrangement Work Defect in Apartment Building

NASA Astrophysics Data System (ADS)

Park, Junmo; Seo, DeokSeok

2017-06-01

The defect lawsuit of the apartment which is the representative residential style of Korea continues and becomes a social problem. In the defect lawsuit, the term of warranty liability is a period that can demand the defect repair according to defect occurrence, and the exclusion period of the exercise of rights. However, the term of warranty liability stipulated in relevant laws such as Enforcement Decree of the Housing Act is being changed arbitrarily, without any established grounds. Therefore, a reasonable standard for establishing the term of warranty liability is required. In this study, the defects of water supply, drainage and sanitation arrangement work were studied. As a result of analyzing the number of defect occurrence in the apartment, it was shown that the defects in water supply, drainage and sanitation arrangement work occurred more than 80% in the 1st ∼ 2nd year after completion. However, the occurrence of defects from the 3rd year was extremely slight. On the other hand, it was confirmed that the defect occurrence continued until fairly late point of time as the end point of time of the defects was in the 7th to 9th years.

Enhanced thermoelectric performance of In2O3-based ceramics via Nanostructuring and Point Defect Engineering

PubMed Central

Lan, Jin-Le; Liu, Yaochun; Lin, Yuan-Hua; Nan, Ce-Wen; Cai, Qing; Yang, Xiaoping

2015-01-01

The issue of how to improve the thermoelectric figure of merit (ZT) in oxide semiconductors has been challenging for more than 20 years. In this work, we report an effective path to substantial reduction in thermal conductivity and increment in carrier concentration, and thus a remarkable enhancement in the ZT value is achieved. The ZT value of In2O3 system was enhanced 4-fold by nanostructuing (nano-grains and nano-inclusions) and point defect engineering. The introduction of point defects in In2O3 results in a glass-like thermal conductivity. The lattice thermal conductivity could be reduced by 60%, and extraordinary low lattice thermal conductivity (1.2 W m−1 K−1 @ 973 K) below the amorphous limit was achieved. Our work paves a path for enhancing the ZT in oxides by both the nanosturcturing and the point defect engineering for better phonon-glasses and electron-crystal (PGEC) materials. PMID:25586762

Measurement and Modeling of Ultrasonic Pitch/catch Grain Noise

NASA Astrophysics Data System (ADS)

Margetan, F. J.; Gray, T. A.; Thompson, R. B.

2008-02-01

Ultrasonic grain noise arises from the scattering of sound waves by microstructural boundaries, and can limit the detection of weakly-reflecting internal defects in metals. In some cases of practical interest, such as focused-transducer inspections of aircraft engine components, so-called "single scattering" or "independent scatterer" models have proven to be reasonably accurate in predicting grain noise characteristics. In pulse/echo inspections it is difficult to experimentally assess the relative contributions of single scattering and multiple scattering, because both can generally contribute to the backscattered noise seen at any given observation time. For pitch/catch inspections, however, it is relatively easy to construct inspection geometries for which single-scattered noise should be insignificant, and hence any observed noise is presumably due to multiple scattering. This concept is demonstrated using pitch/catch shear-wave measurements performed on a well-characterized stainless-steel specimen. The inspection geometry allows us to control the overlap volume of the intersecting radiation fields of the two transducers. As we proceed from maximally overlapping fields to zero overlap, the single-scattering contribution to the observed grain noise is expected to decrease. Measurements are compared to the predictions of a single-scatterer model, and the relative contributions of single and multiple scattering to the observed grain noise are estimated.

Many-Body Theory of Proton-Generated Point Defects for Losses of Electron Energy and Photons in Quantum Wells

NASA Astrophysics Data System (ADS)

Huang, Danhong; Iurov, Andrii; Gao, Fei; Gumbs, Godfrey; Cardimona, D. A.

2018-02-01

The effects of point defects on the loss of either energies of ballistic electron beams or incident photons are studied by using a many-body theory in a multi-quantum-well system. This theory includes the defect-induced vertex correction to a bare polarization function of electrons within the ladder approximation, and the intralayer and interlayer screening of defect-electron interactions is also taken into account in the random-phase approximation. The numerical results of defect effects on both energy-loss and optical-absorption spectra are presented and analyzed for various defect densities, numbers of quantum wells, and wave vectors. The diffusion-reaction equation is employed for calculating distributions of point defects in a layered structure. For completeness, the production rate for Frenkel-pair defects and their initial concentration are obtained based on atomic-level molecular-dynamics simulations. By combining the defect-effect, diffusion-reaction, and molecular-dynamics models with an available space-weather-forecast model, it will be possible in the future to enable specific designing for electronic and optoelectronic quantum devices that will be operated in space with radiation-hardening protection and, therefore, effectively extend the lifetime of these satellite onboard electronic and optoelectronic devices. Specifically, this theory can lead to a better characterization of quantum-well photodetectors not only for high quantum efficiency and low dark current density but also for radiation tolerance or mitigating the effects of the radiation.

Effect of molecular anisotropy on the intensity and degree of polarization of light scattered from model atmospheres

NASA Technical Reports Server (NTRS)

Bahethi, O. P.; Fraser, R. S.

1975-01-01

Computations of the intensity, flux, degree of polarization, and the positions of neutral points are presented for models of the terrestrial gaseous and hazy atmospheres by incorporating the molecular anisotropy due to air in the Rayleigh scattering optical thickness and phase matrix. Molecular anisotropy causes significant changes in the intensity, flux and the degree of polarization of the scattered light. The positions of neutral points do not change significantly. When the Rayleigh scattering optical thickness is kept constant and the molecular anisotropy factor is included only in the Rayleigh phase matrix, the flux does not change and the intensity and positions of neutron points change by a small amount. The changes in the degree of polarization are still significant.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozlovski, V. V.; Lebedev, A. A.; Bogdanova, E. V.

The model of conductivity compensation in SiC under irradiation with high-energy electrons is presented. The following processes are considered to cause a decrease in the free carrier concentration: (i) formation of deep traps by intrinsic point defects, Frenkel pairs produced by irradiation; (ii) 'deactivation' of the dopant via formation of neutral complexes including a dopant atom and a radiation-induced point defect; and (iii) formation of deep compensating traps via generation of charged complexes constituted by a dopant atom and a radiation-induced point defect. To determine the compensation mechanism, dose dependences of the deep compensation of moderately doped SiC (CVD) undermore » electron irradiation have been experimentally studied. It is demonstrated that, in contrast to n-FZ-Si, moderately doped SiC (CVD) exhibits linear dependences (with a strongly nonlinear dependence observed for Si). Therefore, the conductivity compensation in silicon carbide under electron irradiation occurs due to deep traps formed by primary radiation defects (vacancies and interstitial atoms) in the silicon and carbon sublattices. It is known that the compensation in silicon is due to the formation of secondary radiation defects that include a dopant atom. It is shown that, in contrast to n-SiC (CVD), primary defects in only the carbon sublattice of moderately doped p-SiC (CVD) cannot account for the compensation process. In p-SiC, either primary defects in the silicon sublattice or defects in both sublattices are responsible for the conductivity compensation.« less

Vacancy-type defects induced by grinding of Si wafers studied by monoenergetic positron beams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uedono, Akira; Yoshihara, Nakaaki; Mizushima, Yoriko

2014-10-07

Vacancy-type defects introduced by the grinding of Czochralski-grown Si wafers were studied using monoenergetic positron beams. Measurements of Doppler broadening spectra of the annihilation radiation and the lifetime spectra of positrons showed that vacancy-type defects were introduced in the surface region (<98 nm), and the major defect species were identified as (i) relatively small vacancies incorporated in dislocations and (ii) large vacancy clusters. Annealing experiments showed that the defect concentration decreased with increasing annealing temperature in the range between 100 and 500°C. After 600–700°C annealing, the defect-rich region expanded up to about 170 nm, which was attributed to rearrangements ofmore » dislocation networks, and a resultant emission of point defects toward the inside of the sample. Above 800°C, the stability limit of those vacancies was reached and they started to disappear. After the vacancies were annealed out (900°C), oxygen-related defects were the major point defects and they were located at <25 nm.« less

Detection and characterization of microdefects and microprecipitates in Si wafers by Brewster angle illumination using an optical fiber system

NASA Astrophysics Data System (ADS)

Taijing, Lu; Toyoda, Koichi; Nango, Nobuhito; Ogawa, Tomoya

1991-10-01

Microdefects and microprecipitates were non-destructively detected in bulk and near surface of a Si wafer by Brewster angle illumination using an optical fiber system, because the p-component of the illumination enters completely into the wafer and then makes scattering from the defects while the other s-component reflects on the wafer surface so as to deviate from an objective lens for the detection of the scattering. Some results of observations and discussions will be done here about the scatterers in epitaxially grown Si layers, denuded zones of Si wafers, annealed amorphous SiC films, SIMOX specimens and slip bands in Si crystals.

Silicon displacement threshold energy determined by electron paramagnetic resonance and positron annihilation spectroscopy in cubic and hexagonal polytypes of silicon carbide

NASA Astrophysics Data System (ADS)

Kerbiriou, X.; Barthe, M.-F.; Esnouf, S.; Desgardin, P.; Blondiaux, G.; Petite, G.

2007-05-01

Both for electronic and nuclear applications, it is of major interest to understand the properties of point defects into silicon carbide (SiC). Low energy electron irradiations are supposed to create primary defects into materials. SiC single crystals have been irradiated with electrons at two beam energies in order to investigate the silicon displacement threshold energy into SiC. This paper presents the characterization of the electron irradiation-induced point defects into both polytypes hexagonal (6H) and cubic (3C) SiC single crystals by using both positron annihilation spectroscopy (PAS) and electron paramagnetic resonance (EPR). The nature and the concentration of the generated point defects depend on the energy of the electron beam and the polytype. After an electron irradiation at an energy of 800 keV vSi mono-vacancies and vSi-vC di-vacancies are detected in both 3C and 6H-SiC polytypes. On the contrary, the nature of point defects detected after an electron irradiation at 190 keV strongly depends on the polytype. Into 6H-SiC crystals, silicon Frenkel pairs vSi-Si are detected whereas only carbon vacancy related defects are detected into 3C-SiC crystals. The difference observed in the distribution of defects detected into the two polytypes can be explained by the different values of the silicon displacement threshold energies for 3C and 6H-SiC. By comparing the calculated theoretical numbers of displaced atoms with the defects numbers measured using EPR, the silicon displacement threshold energy has been estimated to be slightly lower than 20 eV in the 6H polytype and close to 25 eV in the 3C polytype.

Local and transient nanoscale strain mapping during in situ deformation

DOE PAGES

Gammer, C.; Kacher, J.; Czarnik, C.; ...

2016-08-26

The mobility of defects such as dislocations controls the mechanical properties of metals. This mobility is determined both by the characteristics of the defect and the material, as well as the local stress and strain applied to the defect. Therefore, the knowledge of the stress and strain during deformation at the scale of defects is important for understanding fundamental deformation mechanisms. In this paper, we demonstrate a method of measuring local stresses and strains during continuous in situ deformation with a resolution of a few nanometers using nanodiffraction strain mapping. Finally, our results demonstrate how large multidimensional data sets capturedmore » with high speed electron detectors can be analyzed in multiple ways after an in situ TEM experiment, opening the door for true multimodal analysis from a single electron scattering experiment.« less

Computational modeling of properties

NASA Technical Reports Server (NTRS)

Franz, Judy R.

1994-01-01

A simple model was developed to calculate the electronic transport parameters in disordered semiconductors in strong scattered regime. The calculation is based on a Green function solution to Kubo equation for the energy-dependent conductivity. This solution together with a rigorous calculation of the temperature-dependent chemical potential allows the determination of the dc conductivity and the thermopower. For wise-gap semiconductors with single defect bands, these transport properties are investigated as a function of defect concentration, defect energy, Fermi level, and temperature. Under certain conditions the calculated conductivity is quite similar to the measured conductivity in liquid II-VI semiconductors in that two distinct temperature regimes are found. Under different conditions the conductivity is found to decrease with temperature; this result agrees with measurements in amorphous Si. Finally the calculated thermopower can be positive or negative and may change sign with temperature or defect concentration.

Computational modeling of properties

NASA Technical Reports Server (NTRS)

Franz, Judy R.

1994-01-01

A simple model was developed to calculate the electronic transport parameters in disordered semiconductors in strong scattered regime. The calculation is based on a Green function solution to Kubo equation for the energy-dependent conductivity. This solution together with a rigorous calculation of the temperature-dependent chemical potential allows the determination of the dc conductivity and the thermopower. For wide-gap semiconductors with single defect bands, these transport properties are investigated as a function of defect concentration, defect energy, Fermi level, and temperature. Under certain conditions the calculated conductivity is quite similar to the measured conductivity in liquid 2-6 semiconductors in that two distinct temperature regimes are found. Under different conditions the conductivity is found to decrease with temperature; this result agrees with measurements in amorphous Si. Finally the calculated thermopower can be positive or negative and may change sign with temperature or defect concentration.

Effect of proton irradiation on superconductivity in optimally doped BaFe 2 ( As 1 - x P x ) 2 single crystals

DOE PAGES

Smylie, M. P.; Leroux, M.; Mishra, V.; ...

2016-03-10

In this paper, irradiation with 4 MeV protons was used to systematically introduce defects in single crystals of the iron-arsenide superconductor BaFe 2(As 1-xP x) 2, x = 0.33. The effect of disorder on the low-temperature behavior of the London penetration depth λ(T) and transition temperature T c was investigated. In nearly optimally doped samples with T c ~ 29 K, signatures of a superconducting gap with nodes were observed. Contrary to previous reports on electron-irradiated crystals, we do not see a disorder-driven lifting of accidental nodes, and we observe that proton-induced defects are weaker pair breakers than electron-induced defects.more » Finally, we attribute our findings to anisotropic electron scattering caused by proton irradiation defects.« less

Fermi Level Control of Point Defects During Growth of Mg-Doped GaN

NASA Astrophysics Data System (ADS)

Bryan, Zachary; Hoffmann, Marc; Tweedie, James; Kirste, Ronny; Callsen, Gordon; Bryan, Isaac; Rice, Anthony; Bobea, Milena; Mita, Seiji; Xie, Jinqiao; Sitar, Zlatko; Collazo, Ramón

2013-05-01

In this study, Fermi level control of point defects during metalorganic chemical vapor deposition (MOCVD) of Mg-doped GaN has been demonstrated by above-bandgap illumination. Resistivity and photoluminescence (PL) measurements are used to investigate the Mg dopant activation of samples with Mg concentration of 2 × 1019 cm-3 grown with and without exposure to ultraviolet (UV) illumination. Samples grown under UV illumination have five orders of magnitude lower resistivity values compared with typical unannealed GaN:Mg samples. The PL spectra of samples grown with UV exposure are similar to the spectra of those grown without UV exposure that were subsequently annealed, indicating a different incorporation of compensating defects during growth. Based on PL and resistivity measurements we show that Fermi level control of point defects during growth of III-nitrides is feasible.

Modelling of thermal field and point defect dynamics during silicon single crystal growth using CZ technique

NASA Astrophysics Data System (ADS)

Sabanskis, A.; Virbulis, J.

2018-05-01

Mathematical modelling is employed to numerically analyse the dynamics of the Czochralski (CZ) silicon single crystal growth. The model is axisymmetric, its thermal part describes heat transfer by conduction and thermal radiation, and allows to predict the time-dependent shape of the crystal-melt interface. Besides the thermal field, the point defect dynamics is modelled using the finite element method. The considered process consists of cone growth and cylindrical phases, including a short period of a reduced crystal pull rate, and a power jump to avoid large diameter changes. The influence of the thermal stresses on the point defects is also investigated.

Probabilistic failure analysis of bone using a finite element model of mineral-collagen composites.

PubMed

Dong, X Neil; Guda, Teja; Millwater, Harry R; Wang, Xiaodu

2009-02-09

Microdamage accumulation is a major pathway for energy dissipation during the post-yield deformation of bone. In this study, a two-dimensional probabilistic finite element model of a mineral-collagen composite was developed to investigate the influence of the tissue and ultrastructural properties of bone on the evolution of microdamage from an initial defect in tension. The probabilistic failure analyses indicated that the microdamage progression would be along the plane of the initial defect when the debonding at mineral-collagen interfaces was either absent or limited in the vicinity of the defect. In this case, the formation of a linear microcrack would be facilitated. However, the microdamage progression would be scattered away from the initial defect plane if interfacial debonding takes place at a large scale. This would suggest the possible formation of diffuse damage. In addition to interfacial debonding, the sensitivity analyses indicated that the microdamage progression was also dependent on the other material and ultrastructural properties of bone. The intensity of stress concentration accompanied with microdamage progression was more sensitive to the elastic modulus of the mineral phase and the nonlinearity of the collagen phase, whereas the scattering of failure location was largely dependent on the mineral to collagen ratio and the nonlinearity of the collagen phase. The findings of this study may help understanding the post-yield behavior of bone at the ultrastructural level and shed light on the underlying mechanism of bone fractures.

Probabilistic Failure Analysis of Bone Using a Finite Element Model of Mineral-Collagen Composites

PubMed Central

Dong, X. Neil; Guda, Teja; Millwater, Harry R.; Wang, Xiaodu

2009-01-01

Microdamage accumulation is a major pathway for energy dissipation during the post-yield deformation of bone. In this study, a two-dimensional probabilistic finite element model of a mineral-collagen composite was developed to investigate the influence of the tissue and ultrastructural properties of bone on the evolution of microdamage from an initial defect in tension. The probabilistic failure analyses indicated that the microdamage progression would be along the plane of the initial defect when the debonding at mineral-collagen interfaces was either absent or limited in the vicinity of the defect. In this case, the formation of a linear microcrack would be facilitated. However, the microdamage progression would be scattered away from the initial defect plane if interfacial debonding takes place at a large scale. This would suggest the possible formation of diffuse damage. In addition to interfacial debonding, the sensitivity analyses indicated that the microdamage progression was also dependent on the other material and ultrastructural properties of bone. The intensity of stress concentration accompanied with microdamage progression was more sensitive to the elastic modulus of the mineral phase and the nonlinearity of the collagen phase, whereas the scattering of failure location was largely dependent on the mineral to collagen ratio and the nonlinearity of the collagen phase. The findings of this study may help understanding the post-yield behavior of bone at the ultrastructural level and shed light on the underlying mechanism of bone fractures. PMID:19058806

Tunable dielectric response, resistive switching, and unconventional transport in SrTiO3

NASA Astrophysics Data System (ADS)

Mikheev, Evgeny

The first section of this thesis discusses integration of SR TiO3 grown by molecular beam epitaxy (MBE) in vertical device structures. One target application is as a tunable dielectric. Parallel plate capacitors based on epitaxial Pt(001) bottom electrodes and (Ba,Sr)TiO 3 dielectric layers grown by MBE are demonstrated. Optimization of structural quality of the vertical stack is shown to produce very low dielectric loss combined with very high tunability of the dielectric constant by DC bias. This results in considerable improvement of common figures of merit for varactor performance in comparison to previous reports. Another target application for transition metals oxides is in resistive switching memories, which are based on the hysteretic current-voltage response observed in many oxide-based Schottky junctions and capacitors. A study on the role of metal/oxide interface quality is presented. In particular, the use of epitaxial Pt(001) as Schottky contacts to Nb:SRTiO 3 is shown to suppress resistive switching hysteresis by eliminating unintentional contributions to interface capacitance. Such uncontrolled factors are discussed as a probable root cause for poor reproducibility in resistive switching memories, currently a ubiquitous challenge in the field. Potential routes towards stabilizing reproducible switching through intentional control of defect densities in high-quality structures are discussed, including a proof of concept demonstration using Schottky junctions incorporating intentionally non-stoichiometric SRTiO3 interlayers grown by MBE. The second section of this thesis is concerned with unconventional electronic transport in SRTiO3. A systematic description of scattering mechanisms will be presented for three related material systems: uniformly-doped SRTiO3, two-dimensional electron liquids (2DEL) at SRTiO3/RTiO 3 interfaces (R = Gd, Sm) and confined 2DELs in RTiO3/SRTiO3/ RTiO3 quantum wells. In particular, the prevalence of a well-defined T2 scattering rate in doped SRTiO3 will be discussed as being incompatible with its traditional assignment as electron-electron scattering in a Fermi liquid. In the case of ultrathin SRTiO3 quantum wells bound by RTiO3, evidence will be presented for the existence of a quantum critical point. This refers to a quantum phase transition at zero temperature towards an ordered phase in SRTiO 3. This transition is driven by increasing confinement of the 2DEL, with a critical point located at the 5 SrO layer thickness of SRTiO 3. It is manifested in anomalous temperature exponents of the power law resistivity. Additionally, a well-defined trend for the separation of the Hall and longitudinal scattering rates will be presented, analogously to a similar effect observed in the normal state of high-Tc superconductors. In particular, a unique pattern of residual scattering separation was documented, consistent with a quantum critical correction to the Hall lifetime that is divergent at the quantum critical point.

Concentration of point defects in 4H-SiC characterized by a magnetic measurement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, B.; Jia, R. X., E-mail: rxjia@mail.xidian.edu.cn; Wang, Y. T.

A magnetic method is presented to characterize the concentration of point defects in silicon carbide. In this method, the concentration of common charged point defects, which is related to the density of paramagnetic centers, is determined by fitting the paramagnetic component of the specimen to the Brillouin function. Several parameters in the Brillouin function can be measured such as: the g-factor can be obtained from electron spin resonance spectroscopy, and the magnetic moment of paramagnetic centers can be obtained from positron lifetime spectroscopy combined with a first-principles calculation. To evaluate the characterization method, silicon carbide specimens with different concentrations ofmore » point defects are prepared with aluminum ion implantation. The fitting results of the densities of paramagnetic centers for the implanted doses of 1 × 10{sup 14} cm{sup −2}, 1 × 10{sup 15} cm{sup −2} and 1 × 10{sup 16} cm{sup −2} are 6.52 × 10{sup 14}/g, 1.14 × 10{sup 15}/g and 9.45 × 10{sup 14}/g, respectively. The same trends are also observed for the S-parameters in the Doppler broadening spectra. It is shown that this method is an accurate and convenient way to obtain the concentration of point defects in 4H-SiC.« less

Effect of substrate morphology slope distributions on light scattering, nc-Si:H film growth, and solar cell performance.

PubMed

Kim, Do Yun; Santbergen, Rudi; Jäger, Klaus; Sever, Martin; Krč, Janez; Topič, Marko; Hänni, Simon; Zhang, Chao; Heidt, Anna; Meier, Matthias; van Swaaij, René A C M M; Zeman, Miro

2014-12-24

Thin-film silicon solar cells are often deposited on textured ZnO substrates. The solar-cell performance is strongly correlated to the substrate morphology, as this morphology determines light scattering, defective-region formation, and crystalline growth of hydrogenated nanocrystalline silicon (nc-Si:H). Our objective is to gain deeper insight in these correlations using the slope distribution, rms roughness (σ(rms)) and correlation length (lc) of textured substrates. A wide range of surface morphologies was obtained by Ar plasma treatment and wet etching of textured and flat-as-deposited ZnO substrates. The σ(rms), lc and slope distribution were deduced from AFM scans. Especially, the slope distribution of substrates was represented in an efficient way that light scattering and film growth direction can be more directly estimated at the same time. We observed that besides a high σ(rms), a high slope angle is beneficial to obtain high haze and scattering of light at larger angles, resulting in higher short-circuit current density of nc-Si:H solar cells. However, a high slope angle can also promote the creation of defective regions in nc-Si:H films grown on the substrate. It is also found that the crystalline fraction of nc-Si:H solar cells has a stronger correlation with the slope distributions than with σ(rms) of substrates. In this study, we successfully correlate all these observations with the solar-cell performance by using the slope distribution of substrates.

Diffuse x-ray scattering and transmission electron microscopy study of defects in antimony-implanted silicon

NASA Astrophysics Data System (ADS)

Takamura, Y.; Marshall, A. F.; Mehta, A.; Arthur, J.; Griffin, P. B.; Plummer, J. D.; Patel, J. R.

2004-04-01

Ion implantation followed by laser annealing has been used to create supersaturated and electrically active concentrations of antimony in silicon. Upon subsequent thermal annealing, however, these metastable dopants deactivate towards the equilibrium solubility limit. In this work, the formation of inactive antimony structures has been studied with grazing incidence diffuse x-ray scattering, and transmission electron microscopy, and the results are correlated to previous high-resolution x-ray diffraction data. We find that at a concentration of 6.0×1020 cm-3, small, incoherent clusters of radius 3-4 Å form during annealing at 900 °C. At a higher concentration of 2.2×1021 cm-3, deactivation at 600 °C occurs through the formation of small, antimony aggregates and antimony precipitates. The size of these precipitates from diffuse x-ray scattering is roughly 15 Å in radius for anneal times from 15 to 180 seconds. This value is consistent with the features observed in high-resolution and mass contrast transmission electron microscopy images. The coherent nature of the aggregates and precipitates causes the expansion of the surrounding silicon matrix as the deactivation progresses. In addition, the sensitivity of the diffuse x-ray scattering technique has allowed us to detect the presence of small clusters of radius ˜2 Å in unprocessed Czochralski silicon wafers. These defects are not observed in floating zone silicon wafers, and are tentatively attributed to thermal donors.

A Compton scattering technique to determine wood density and locating defects in it

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tondon, Akash, E-mail: akashtondonnsl@gmail.com; Sandhu, B. S.; Singh, Bhajan

A Compton scattering technique is presented to determine density and void location in the given wooden samples. The technique uses a well collimated gamma ray beam from {sup 137}Cs along with the NaI(Tl) scintillation detector. First, a linear relationship is established between Compton scattered intensity and known density of chemical compounds, and then density of the wood is determined from this linear relation. In another experiment, the ability of penetration of gamma rays is explored to detect voids in wooden (low Z) sample. The sudden reduction in the Compton scattered intensities agrees well with the position and size of voidsmore » in the wooden sample. It is concluded that wood density and the voids of size ∼ 4 mm and more can be detected easily by this method.« less

The challenges encountered in the integration of an early test wafer surface scanning inspection system into a 450mm manufacturing line

NASA Astrophysics Data System (ADS)

Lee, Jeffrey; McGarvey, Steve

2013-04-01

The introduction of early test wafer (ETW) 450mm Surface Scanning Inspection Systems (SSIS) into Si manufacturing has brought with it numerous technical, commercial, and logistical challenges on the path to rapid recipe development and subsequent qualification of other 450mm wafer processing equipment. This paper will explore the feasibility of eliminating the Polystyrene Latex Sphere deposition process step and the subsequent creation of SSIS recipes based upon the theoretical optical properties of both the SSIS and the process film stack(s). The process of Polystyrene Latex Sphere deposition for SSIS recipe generation and development is generally accepted on the previous technology nodes for 150/200/300mm wafers. PSL is deposited with a commercially available deposition system onto a non-patterned bare Si or non-patterned filmed Si wafer. After deposition of multiple PSL spots, located in different positions on a wafer, the wafer is inspected on a SSIS and a response curve is generated. The response curve is based on the the light scattering intensity of the NIST certified PSL that was deposited on the wafer. As the initial 450mm Si wafer manufacturing began, there were no inspection systems with sub-90nm sensitivities available for defect and haze level verification. The introduction of a 450mm sub-30nm inspection system into the manufacturing line generated instant challenges. Whereas the 450mm wafers were relatively defect free at 90nm, at 40nm the wafers contained several hundred thousand defects. When PSL was deposited onto wafers with these kinds of defect levels, PSL with signals less than the sub-90nm defects were difficult to extract. As the defectivity level of the wafers from the Si suppliers rapidly improves the challenges of SSIS recipe creation with high defectivity decreases while at the same time the cost of PSL deposition increases. The current cost per wafer is fifteen thousand dollars for a 450mm PSL deposition service. When viewed from the standpoint of the generations of hundreds of SSIS recipes for the global member companies of ISMI, it is simply not economically viable to create all recipes based on PSL based light scattering response curves. This paper will explore the challenges/end results encountered with the PSL based SSIS recipe generation and compare those against the challenges/end results of SSIS recipes generated based strictly upon theoretical Bidirectional reflectance distribution function (BRDF) light scattering modeling. The BRDF modeling will allow for the creation of SSIS recipes without PSL deposition, which is greatly appealing for a multitude of both technical and commercial considerations. This paper will also explore the technical challenges of SSIS recipe generation based strictly upon BRDF modeling.

The verification of printability about marginal defects and the detectability at the inspection tool in sub 50nm node

NASA Astrophysics Data System (ADS)

Lee, Hyemi; Jeong, Goomin; Seo, Kangjun; Kim, Sangchul; kim, changreol

2008-05-01

Since mask design rule is smaller and smaller, Defects become one of the issues dropping the mask yield. Furthermore controlled defect size become smaller while masks are manufactured. According to ITRS roadmap on 2007, controlled defect size is 46nm in 57nm node and 36nm in 45nm node on a mask. However the machine development is delayed in contrast with the speed of the photolithography development. Generally mask manufacturing process is divided into 3 parts. First part is patterning on a mask and second part is inspecting the pattern and repairing the defect on the mask. At that time, inspection tools of transmitted light type are normally used and are the most trustful as progressive type in the developed inspection tools until now. Final part is shipping the mask after the qualifying the issue points and weak points. Issue points on a mask are qualified by using the AIMS (Aerial image measurement system). But this system is including the inherent error possibility, which is AIMS measures the issue points based on the inspection results. It means defects printed on a wafer are over the specific size detected by inspection tools and the inspection tool detects the almost defects. Even though there are no tools to detect the 46nm and 36nm defects suggested by ITRS roadmap, this assumption is applied to manufacturing the 57nm and 45nm device. So we make the programmed defect mask consisted with various defect type such as spot, clear extension, dark extension and CD variation on L/S(line and space), C/H(contact hole) and Active pattern in 55nm and 45nm node. And the programmed defect mask was inspected by using the inspection tool of transmitted light type and was measured by using AIMS 45-193i. Then the marginal defects were compared between the inspection tool and AIMS. Accordingly we could verify whether defect size is proper or not, which was suggested to be controlled on a mask by ITRS roadmap. Also this result could suggest appropriate inspection tools for next generation device among the inspection tools of transmitted light type, reflected light type and aerial image type.

Summary report on UO 2 thermal conductivity model refinement and assessment studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xiang-Yang; Cooper, Michael William Donald; Mcclellan, Kenneth James

Uranium dioxide (UO 2) is the most commonly used fuel in light water nuclear reactors and thermal conductivity controls the removal of heat produced by fission, therefore, governing fuel temperature during normal and accident conditions. The use of fuel performance codes by the industry to predict operational behavior is widespread. A primary source of uncertainty in these codes is thermal conductivity, and optimized fuel utilization may be possible if existing empirical models were replaced with models that incorporate explicit thermal conductivity degradation mechanisms during fuel burn-up. This approach is able to represent the degradation of thermal conductivity due to eachmore » individual defect type, rather than the overall burn-up measure typically used which is not an accurate representation of the chemical or microstructure state of the fuel that actually governs thermal conductivity and other properties. To generate a mechanistic thermal conductivity model, molecular dynamics (MD) simulations of UO 2 thermal conductivity including representative uranium and oxygen defects and fission products are carried out. These calculations employ a standard Buckingham type interatomic potential and a potential that combines the many-body embedded atom method potential with Morse-Buckingham pair potentials. Potential parameters for UO 2+x and ZrO 2 are developed for the latter potential. Physical insights from the resonant phonon-spin scattering mechanism due to spins on the magnetic uranium ions have been introduced into the treatment of the MD results, with the corresponding relaxation time derived from existing experimental data. High defect scattering is predicted for Xe atoms compared to that of La and Zr ions. Uranium defects reduce the thermal conductivity more than oxygen defects. For each defect and fission product, scattering parameters are derived for application in both a Callaway model and the corresponding high-temperature model typically used in fuel performance codes. The model is validated by comparison to low-temperature experimental measurements on single crystal hyper-stoichiometric UO 2+x samples and high-temperature literature data. Ongoing works include investigation of the effect of phase separation to UO 2+U 4O 9 on the low temperature thermal conductivity of UO 2+x, and modeling of thermal conductivity using the Green-Kubo method. Ultimately, this work will enable more accurate fuel performance simulations as well as extension to new fuel types and operating conditions, all of which improve the fuel economics of nuclear energy and maintain high fuel reliability and safety.« less

Neutron and x-ray scattering study of phonon dispersion and diffuse scattering in ( Na , Bi ) Ti O 3 - x BaTi O 3 single crystals near the morphotropic phase boundary

DOE PAGES

Luo, Chengtao; Bansal, Dipanshu; Li, Jiefang; ...

2017-11-10

Neutron and x-ray scattering measurements were performed on (Na 1/2Bi 1/2)TiO 3-x at % BaTiO 3 (NBT-xBT) single crystals (x = 4, 5, 6.5, and 7.5) across the morphotropic phase boundary (MPB), as a function of both composition and temperature, and probing both structural and dynamical aspects. In addition to the known diffuse scattering pattern near the gamma points, our measurements revealed new, faint superlattice peaks, as well as an extensive diffuse scattering network, revealing a short-range ordering of polar nanoregions (PNR) with a static stacking morphology. Furthermore, in samples with compositions closest to the MPB, our inelastic neutron scatteringmore » investigations of the phonon dynamics showed two unusual features in the acoustic phonon branches, between the superlattice points, and between the superlattice points and gamma points, respectively. Finally, these critical elements are not present in the other compositions away from the MPB, which suggests that these features may be related to the tilt modes coupling behavior near the MPB.« less

Neutron and x-ray scattering study of phonon dispersion and diffuse scattering in ( Na , Bi ) Ti O 3 - x BaTi O 3 single crystals near the morphotropic phase boundary

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Chengtao; Bansal, Dipanshu; Li, Jiefang

Neutron and x-ray scattering measurements were performed on (Na 1/2Bi 1/2)TiO 3-x at % BaTiO 3 (NBT-xBT) single crystals (x = 4, 5, 6.5, and 7.5) across the morphotropic phase boundary (MPB), as a function of both composition and temperature, and probing both structural and dynamical aspects. In addition to the known diffuse scattering pattern near the gamma points, our measurements revealed new, faint superlattice peaks, as well as an extensive diffuse scattering network, revealing a short-range ordering of polar nanoregions (PNR) with a static stacking morphology. Furthermore, in samples with compositions closest to the MPB, our inelastic neutron scatteringmore » investigations of the phonon dynamics showed two unusual features in the acoustic phonon branches, between the superlattice points, and between the superlattice points and gamma points, respectively. Finally, these critical elements are not present in the other compositions away from the MPB, which suggests that these features may be related to the tilt modes coupling behavior near the MPB.« less

Analysis of an optimization-based atomistic-to-continuum coupling method for point defects

DOE PAGES

Olson, Derek; Shapeev, Alexander V.; Bochev, Pavel B.; ...

2015-11-16

Here, we formulate and analyze an optimization-based Atomistic-to-Continuum (AtC) coupling method for problems with point defects. Application of a potential-based atomistic model near the defect core enables accurate simulation of the defect. Away from the core, where site energies become nearly independent of the lattice position, the method switches to a more efficient continuum model. The two models are merged by minimizing the mismatch of their states on an overlap region, subject to the atomistic and continuum force balance equations acting independently in their domains. We prove that the optimization problem is well-posed and establish error estimates.

Effective response theory for zero-energy Majorana bound states in three spatial dimensions

NASA Astrophysics Data System (ADS)

Lopes, Pedro L. e. S.; Teo, Jeffrey C. Y.; Ryu, Shinsei

2015-05-01

We propose a gravitational response theory for point defects (hedgehogs) binding Majorana zero modes in (3 + 1)-dimensional superconductors. Starting in 4 + 1 dimensions, where the point defect is extended into a line, a coupling of the bulk defect texture with the gravitational field is introduced. Diffeomorphism invariance then leads to an S U (2) 2 Kac-Moody current running along the defect line. The S U (2) 2 Kac-Moody algebra accounts for the non-Abelian nature of the zero modes in 3 + 1 dimensions. It is then shown to also encode the angular momentum density which permeates throughout the bulk between hedgehog-antihedgehog pairs.

Self-regulation mechanism for charged point defects in hybrid halide perovskites

DOE PAGES

Walsh, Aron; Scanlon, David O.; Chen, Shiyou; ...

2014-12-11

Hybrid halide perovskites such as methylammonium lead iodide (CH 3NH 3PbI 3) exhibit unusually low free-carrier concentrations despite being processed at low-temperatures from solution. We demonstrate, through quantum mechanical calculations, that an origin of this phenomenon is a prevalence of ionic over electronic disorder in stoichiometric materials. Schottky defect formation provides a mechanism to self-regulate the concentration of charge carriers through ionic compensation of charged point defects. The equilibrium charged vacancy concentration is predicted to exceed 0.4 % at room temperature. Furthermore, this behavior, which goes against established defect conventions for inorganic semiconductors, has implications for photovoltaic performance.

Precision pointing and tracking through random media by exploitation of the enhanced backscatter phenomenon.

PubMed

Harvey, J E; Reddy, S P; Phillips, R L

1996-07-20

The active illumination of a target through a turbulent medium with a monostatic transmitter-receiver results in a naturally occurring conjugate wave caused by reciprocal scattering paths that experience identical phase variations. This reciprocal path-scattering phenomenon produces an enhanced backscatter in the retroverse direction (precisely along the boresight of the pointing telescope). A dual aperture causes this intensity enhancement to take the form of Young's interference fringes. Interference fringes produced by the reciprocal path-scattering phenomenon are temporally stable even in the presence of time-varying turbulence. Choosing the width-to-separation ratio of the dual apertures appropriately and utilizing orthogonal polarizations to suppress the time-varying common-path scattered radiation allow one to achieve interferometric sensitivity in pointing accuracy through a random medium or turbulent atmosphere. Computer simulations are compared with laboratory experimental data. This new precision pointing and tracking technique has potential applications in ground-to-space laser communications, laser power beaming to satellites, and theater missile defense scenarios.

A sharp interface model for void growth in irradiated materials

NASA Astrophysics Data System (ADS)

Hochrainer, Thomas; El-Azab, Anter

2015-03-01

A thermodynamic formalism for the interaction of point defects with free surfaces in single-component solids has been developed and applied to the problem of void growth by absorption of point defects in irradiated metals. This formalism consists of two parts, a detailed description of the dynamics of defects within the non-equilibrium thermodynamic frame, and the application of the second law of thermodynamics to provide closure relations for all kinetic equations. Enforcing the principle of non-negative entropy production showed that the description of the problem of void evolution under irradiation must include a relationship between the normal fluxes of defects into the void surface and the driving thermodynamic forces for the void surface motion; these thermodynamic forces are identified for both vacancies and interstitials and the relationships between these forces and the normal point defect fluxes are established using the concepts of transition state theory. The latter theory implies that the defect accommodation into the surface is a thermally activated process. Numerical examples are given to illustrate void growth dynamics in this new formalism and to investigate the effect of the surface energy barriers on void growth. Consequences for phase field models of void growth are discussed.

Characterization of Point Defects in Lithium Aluminate (LiAlO2) Single Crystals

DTIC Science & Technology

2015-09-17

high-quality neutron detectors since 235U and 239Pu, the two isotopes used to fuel nuclear weapons , both emit neu- trons through spontaneous fission of...dissertation has iden- tified and characterized the major point defects created and induced through x ray and neutron radiation using electron paramagnetic... neutron irradiation is an F+ center; an oxygen vacancy with one trapped electron. This defect has two states, a stable state that survives up to 500 ◦C and

On the similarity of theories of anelastic and scattering attenuation

USGS Publications Warehouse

Wennerberg, Leif; Frankel, Arthur D.

1989-01-01

We point out basic parallels between theories of anelastic and scattering attenuation. We consider approximations to scattering effects presented by O'Doherty and Anstey (1971), Sato (1982), and Wu (1982). We use the linear theory of anelasticity. We note that the frequency dependence of Q can be related to a distribution of scales of physical properties of the medium. The frequency dependence of anelastic Q is related to the distribution of relaxation times in exactly the same manner as the frequency dependence of scattering Q is related to the distribution of scatterer sizes. Thus, the well-known difficulty of separating scattering from intrinsic attenuation is seen from this point of view as a consequence of the fact that certain observables can be interpreted by identical equations resulting from either of two credible physical theories describing fundamentally different processes. -from Authors

Finite Element Creep Damage Analyses and Life Prediction of P91 Pipe Containing Local Wall Thinning Defect

NASA Astrophysics Data System (ADS)

Xue, Jilin; Zhou, Changyu

2016-03-01

Creep continuum damage finite element (FE) analyses were performed for P91 steel pipe containing local wall thinning (LWT) defect subjected to monotonic internal pressure, monotonic bending moment and combined internal pressure and bending moment by orthogonal experimental design method. The creep damage lives of pipe containing LWT defect under different load conditions were obtained. Then, the creep damage life formulas were regressed based on the creep damage life results from FE method. At the same time a skeletal point rupture stress was found and used for life prediction which was compared with creep damage lives obtained by continuum damage analyses. From the results, the failure lives of pipe containing LWT defect can be obtained accurately by using skeletal point rupture stress method. Finally, the influence of LWT defect geometry was analysed, which indicated that relative defect depth was the most significant factor for creep damage lives of pipe containing LWT defect.

Probing Photoexcited Carriers in a Few-Layer MoS2 Laminate by Time-Resolved Optical Pump-Terahertz Probe Spectroscopy.

PubMed

Kar, Srabani; Su, Y; Nair, R R; Sood, A K

2015-12-22

We report the dynamics of photoinduced carriers in a free-standing MoS2 laminate consisting of a few layers (1-6 layers) using time-resolved optical pump-terahertz probe spectroscopy. Upon photoexcitation with the 800 nm pump pulse, the terahertz conductivity increases due to absorption by the photoinduced charge carriers. The relaxation of the non-equilibrium carriers shows fast as well as slow decay channels, analyzed using a rate equation model incorporating defect-assisted Auger scattering of photoexcited electrons, holes, and excitons. The fast relaxation time occurs due to the capture of electrons and holes by defects via Auger processes, resulting in nonradiative recombination. The slower relaxation arises since the excitons are bound to the defects, preventing the defect-assisted Auger recombination of the electrons and the holes. Our results provide a comprehensive understanding of the non-equilibrium carrier kinetics in a system of unscreened Coulomb interactions, where defect-assisted Auger processes dominate and should be applicable to other 2D systems.

Study on off-axis detection of pulsed laser in atmosphere

NASA Astrophysics Data System (ADS)

Liang, Weiwei

2018-02-01

Laser communication, designation, and ranging are point to point and have a high degree of specificity, current laser detection, such as laser warning receiver system, could detect the scattering laser from the off-axis distance by scattering track on natural aerosols, which is helpful to locate the laser source. However, the intensity of the scattering laser is extremely weak and affected by many factors, in order to evaluate the detection characteristic, a simplified model of off-axis detection for scattering laser in the lower atmosphere based on the Mie scattering theory is presented in this paper, the performances of the off-axis laser detection in different conditions such as off-axis distance, visibility, incidence angle, and delay time are investigated.

Box 6: Nanoscale Defects

NASA Astrophysics Data System (ADS)

Alves, Eduardo; Breese, Mark

Defects affect virtually all properties of crystalline materials, and their role is magnified in nanoscale structures. In this box we describe the different type of defects with particular emphasis on point and linear defects. Above zero Kelvin all real materials have a defect population within their structure, which affects either their crystalline, electronic or optical properties. It is common to attribute a negative connotation to the presence of defects. However, a perfect silicon crystal or any other defect-free semiconductor would have a limited functionality and might even be useless.

Public Data Set: Control and Automation of the Pegasus Multi-point Thomson Scattering System

DOE Data Explorer

Bodner, Grant M. [University of Wisconsin-Madison] (ORCID:0000000324979172); Bongard, Michael W. [University of Wisconsin-Madison] (ORCID:0000000231609746); Fonck, Raymond J. [University of Wisconsin-Madison] (ORCID:0000000294386762); Reusch, Joshua A. [University of Wisconsin-Madison] (ORCID:0000000284249422); Rodriguez Sanchez, Cuauhtemoc [University of Wisconsin-Madison] (ORCID:0000000334712586); Schlossberg, David J. [University of Wisconsin-Madison] (ORCID:0000000287139448)

2016-08-12

This public data set contains openly-documented, machine readable digital research data corresponding to figures published in G.M. Bodner et al., 'Control and Automation of the Pegasus Multi-point Thomson Scattering System,' Rev. Sci. Instrum. 87, 11E523 (2016).

Research on stratified evolution of composite materials under four-point bending loading

NASA Astrophysics Data System (ADS)

Hao, M. J.; You, Q. J.; Zheng, J. C.; Yue, Z.; Xie, Z. P.

2017-12-01

In order to explore the effect of stratified evolution and delamination on the load capacity and service life of the composite materials under the four-point bending loading, the artificial tectonic defects of the different positions were set up. The four-point bending test was carried out, and the whole process was recorded by acoustic emission, and the damage degree of the composite layer was judged by the impact accumulation of the specimen - time-amplitude history chart, load-time-relative energy history chart, acoustic emission impact signal positioning map. The results show that the stratified defects near the surface of the specimen accelerate the process of material failure and expansion. The location of the delamination defects changes the bending performance of the composites to a great extent. The closer the stratification defects are to the surface of the specimen, the greater the damage, the worse the service capacity of the specimen.

Point Defects and p -Type Doping in ScN from First Principles

NASA Astrophysics Data System (ADS)

Kumagai, Yu; Tsunoda, Naoki; Oba, Fumiyasu

2018-03-01

Scandium nitride (ScN) has been intensively researched as a prototype of rocksalt nitrides and a potential counterpart of the wurtzite group IIIa nitrides. It also holds great promise for applications in various fields, including optoelectronics, thermoelectrics, spintronics, and piezoelectrics. We theoretically investigate the bulk properties, band-edge positions, chemical stability, and point defects, i.e., native defects, unintentionally doped impurities, and p -type dopants of ScN using the Heyd-Scuseria-Ernzerhof hybrid functional. We find several fascinating behaviors: (i) a high level for the valence-band maximum, (ii) the lowest formation energy among binary nitrides, (iii) high formation energies of native point defects, (iv) low formation energies of donor-type impurities, and (v) a p -type conversion by Mg doping. Furthermore, we uncover the origins of the Burstein-Moss shift commonly observed in ScN. Our work sheds light on a fundamental understanding of ScN in regard to its technological applications.

Role of the charge state of interface defects in electronic inhomogeneity evolution with gate voltage in graphene

NASA Astrophysics Data System (ADS)

Singh, Anil Kumar; Gupta, Anjan K.

2018-05-01

Evolution of electronic inhomogeneities with back-gate voltage in graphene on SiO2 was studied using room temperature scanning tunneling microscopy and spectroscopy. Reversal of contrast in some places in the conductance maps and sharp changes in cross correlations between topographic and conductance maps, when graphene Fermi energy approaches its Dirac point, are attributed to the change in charge state of interface defects. The spatial correlations in the conductance maps, described by two length scales, and their growth during approach to Dirac point, show a qualitative agreement with the predictions of the screening theory of graphene. Thus a sharp change in the two length scales close to the Dirac point, seen in our experiments, is interpreted in terms of the change in charge state of some of the interface defects. A systematic understanding and control of the charge state of defects can help in memory applications of graphene.

The interaction between atomic displacement cascades and tilt symmetrical grain boundaries in α-zirconium

NASA Astrophysics Data System (ADS)

Kapustin, P.; Svetukhin, V.; Tikhonchev, M.

2017-06-01

The atomic displacement cascade simulations near symmetric tilt grain boundaries (GBs) in hexagonal close packed-Zirconium were considered in this paper. Further defect structure analysis was conducted. Four symmetrical tilt GBs -∑14?, ∑14? with the axis of rotation [0 0 0 1] and ∑32?, ∑32? with the axis of rotation ? - were considered. The molecular dynamics method was used for atomic displacement cascades' simulation. A tendency of the point defects produced in the cascade to accumulate near the GB plane, which was an obstacle to the spread of the cascade, was discovered. The results of the point defects' clustering produced in the cascade were obtained. The clusters of both types were represented mainly by single point defects. At the same time, vacancies formed clusters of a large size (more than 20 vacancies per cluster), while self-interstitial atom clusters were small-sized.

Hidden topological constellations and polyvalent charges in chiral nematic droplets

NASA Astrophysics Data System (ADS)

Posnjak, Gregor; Čopar, Simon; Muševič, Igor

2017-02-01

Topology has an increasingly important role in the physics of condensed matter, quantum systems, material science, photonics and biology, with spectacular realizations of topological concepts in liquid crystals. Here we report on long-lived hidden topological states in thermally quenched, chiral nematic droplets, formed from string-like, triangular and polyhedral constellations of monovalent and polyvalent singular point defects. These topological defects are regularly packed into a spherical liquid volume and stabilized by the elastic energy barrier due to the helical structure and confinement of the liquid crystal in the micro-sphere. We observe, for the first time, topological three-dimensional point defects of the quantized hedgehog charge q=-2, -3. These higher-charge defects act as ideal polyvalent artificial atoms, binding the defects into polyhedral constellations representing topological molecules.

Hidden topological constellations and polyvalent charges in chiral nematic droplets

PubMed Central

Posnjak, Gregor; Čopar, Simon; Muševič, Igor

2017-01-01

Topology has an increasingly important role in the physics of condensed matter, quantum systems, material science, photonics and biology, with spectacular realizations of topological concepts in liquid crystals. Here we report on long-lived hidden topological states in thermally quenched, chiral nematic droplets, formed from string-like, triangular and polyhedral constellations of monovalent and polyvalent singular point defects. These topological defects are regularly packed into a spherical liquid volume and stabilized by the elastic energy barrier due to the helical structure and confinement of the liquid crystal in the micro-sphere. We observe, for the first time, topological three-dimensional point defects of the quantized hedgehog charge q=−2, −3. These higher-charge defects act as ideal polyvalent artificial atoms, binding the defects into polyhedral constellations representing topological molecules. PMID:28220770

Development of high sensitivity and high speed large size blank inspection system LBIS

NASA Astrophysics Data System (ADS)

Ohara, Shinobu; Yoshida, Akinori; Hirai, Mitsuo; Kato, Takenori; Moriizumi, Koichi; Kusunose, Haruhiko

2017-07-01

The production of high-resolution flat panel displays (FPDs) for mobile phones today requires the use of high-quality large-size photomasks (LSPMs). Organic light emitting diode (OLED) displays use several transistors on each pixel for precise current control and, as such, the mask patterns for OLED displays are denser and finer than the patterns for the previous generation displays throughout the entire mask surface. It is therefore strongly demanded that mask patterns be produced with high fidelity and free of defect. To enable the production of a high quality LSPM in a short lead time, the manufacturers need a high-sensitivity high-speed mask blank inspection system that meets the requirement of advanced LSPMs. Lasertec has developed a large-size blank inspection system called LBIS, which achieves high sensitivity based on a laser-scattering technique. LBIS employs a high power laser as its inspection light source. LBIS's delivery optics, including a scanner and F-Theta scan lens, focus the light from the source linearly on the surface of the blank. Its specially-designed optics collect the light scattered by particles and defects generated during the manufacturing process, such as scratches, on the surface and guide it to photo multiplier tubes (PMTs) with high efficiency. Multiple PMTs are used on LBIS for the stable detection of scattered light, which may be distributed at various angles due to irregular shapes of defects. LBIS captures 0.3mμ PSL at a detection rate of over 99.5% with uniform sensitivity. Its inspection time is 20 minutes for a G8 blank and 35 minutes for G10. The differential interference contrast (DIC) microscope on the inspection head of LBIS captures high-contrast review images after inspection. The images are classified automatically.

Algorithms and applications of aberration correction and American standard-based digital evaluation in surface defects evaluating system

NASA Astrophysics Data System (ADS)

Wu, Fan; Cao, Pin; Yang, Yongying; Li, Chen; Chai, Huiting; Zhang, Yihui; Xiong, Haoliang; Xu, Wenlin; Yan, Kai; Zhou, Lin; Liu, Dong; Bai, Jian; Shen, Yibing

2016-11-01

The inspection of surface defects is one of significant sections of optical surface quality evaluation. Based on microscopic scattering dark-field imaging, sub-aperture scanning and stitching, the Surface Defects Evaluating System (SDES) can acquire full-aperture image of defects on optical elements surface and then extract geometric size and position information of defects with image processing such as feature recognization. However, optical distortion existing in the SDES badly affects the inspection precision of surface defects. In this paper, a distortion correction algorithm based on standard lattice pattern is proposed. Feature extraction, polynomial fitting and bilinear interpolation techniques in combination with adjacent sub-aperture stitching are employed to correct the optical distortion of the SDES automatically in high accuracy. Subsequently, in order to digitally evaluate surface defects with American standard by using American military standards MIL-PRF-13830B to judge the surface defects information obtained from the SDES, an American standard-based digital evaluation algorithm is proposed, which mainly includes a judgment method of surface defects concentration. The judgment method establishes weight region for each defect and adopts the method of overlap of weight region to calculate defects concentration. This algorithm takes full advantage of convenience of matrix operations and has merits of low complexity and fast in running, which makes itself suitable very well for highefficiency inspection of surface defects. Finally, various experiments are conducted and the correctness of these algorithms are verified. At present, these algorithms have been used in SDES.

Remote monitoring of bond line defects between a composite panel and a stiffener using distributed piezoelectric sensors

NASA Astrophysics Data System (ADS)

Yu, Xudong; Fan, Zheng; Puliyakote, Sreedhar; Castaings, Michel

2018-03-01

Structural health monitoring (SHM) using ultrasonic guided waves has proven to be attractive for the identification of damage in composite plate-like structures, due to its realization of both significant propagation distances and reasonable sensitivity to defects. However, topographical features such as bends, lap joints, and bonded stiffeners are often encountered in these structures, and they are susceptible to various types of defects as a consequence of stress concentration and cyclic loading during the service life. Therefore, the health condition of such features has to be assessed effectively to ensure the safe operation of the entire structure. This paper proposes a novel feature guided wave (FGW) based SHM strategy, in which proper FGWs are exploited as a screening tool to rapidly interrogate the representative stiffener-adhesive bond-composite skin assembly. An array of sensors permanently attached to the vicinity of the feature is used to capture scattered waves from the localized damage occurring in the bond line. This technique is combined with an imaging approach, and the damage reconstruction is achieved by the synthetic focusing algorithm using these scattered signals. The proposed SHM scheme is implemented in both the 3D finite element simulation and the experiment, and the results are in good agreement, demonstrating the feasibility of such SHM strategy.

Application of the Boundary Element Method to Elastic Wave Scattering Problems in Ultrasonic Nondestructive Evaluation.

NASA Astrophysics Data System (ADS)

Schafbuch, Paul Jay

The boundary element method (BEM) is used to numerically simulate the interaction of ultrasonic waves with material defects such as voids, inclusions, and open cracks. The time harmonic formulation is in 3D and therefore allows flaws of arbitrary shape to be modeled. The BEM makes such problems feasible because the underlying boundary integral equation only requires a surface (2D) integration and difficulties associated with the seemingly infinite extent of the host domain are not encountered. The computer code utilized in this work is built upon recent advances in elastodynamic boundary element theory such as a scheme for self adjusting integration order and singular integration regularization. Incident fields may be taken as compressional or shear plane waves or predicted by an approximate Gauss -Hermite beam model. The code is highly optimized for voids and has been coupled with computer aided engineering packages for automated flaw shape definition and mesh generation. Subsequent graphical display of intermediate results supports model refinement and physical interpretation. Final results are typically cast in a nondestructive evaluation (NDE) context as either scattering amplitudes or flaw signals (via a measurement model based on a reciprocity integral). The near field is also predicted which allows for improved physical insight into the scattering process and the evaluation of certain modeling approximations. The accuracy of the BEM approach is first examined by comparing its predictions to those of other models for single, isolated scatterers. The comparisons are with the predictions of analytical solutions for spherical defects and with MOOT and T-matrix calculations for axisymmetric flaws. Experimental comparisons are also made for volumetric shapes with different characteristic dimensions in all three directions, since no other numerical approach has yet produced results of this type. Theoretical findings regarding the fictitious eigenfrequency difficulty are substantiated through the analytical solution of a fundamental elastodynamics problem and corresponding BEM studies. Given the confidence in the BEM technique engendered by these comparisons, it is then used to investigate the modeling of "open", cracklike defects amenable to a volumetric formulation. The limits of applicability of approximate theories (e.g., quasistatic, Kirchhoff, and geometric theory of diffraction) are explored for elliptical cracks, from this basis. The problem of two interacting scatterers is then considered. Results from a fully implicit approach and from a more efficient hybrid scheme are compared with generalized Born and farfield approximate interaction theories.

Application of the boundary element method to elastic wave scattering problems in ultrasonic nondestructive evaluation

NASA Astrophysics Data System (ADS)

Schafbuch, Paul Jay

1991-02-01

The boundary element method (BEM) is used to numerically simulate the interaction of ultrasonic waves with material defects such as voids, inclusions, and open cracks. The time harmonic formulation is in 3D and therefore allows flaws of arbitrary shape to be modeled. The BEM makes such problems feasible because the underlying boundary integral equation only requires a surface (2D) integration and difficulties associated with the seemingly infinite extent of the host domain are not encountered. The computer code utilized in this work is built upon recent advances in elastodynamic boundary element theory such as a scheme for self adjusting integration order and singular integration regularization. Incident fields may be taken as compressional or shear plane waves or predicted by an approximate Gauss-Hermite beam model. The code is highly optimized for voids and has been coupled with computer aided engineering packages for automated flaw shape definition and mesh generation. Subsequent graphical display of intermediate results supports model refinement and physical interpretation. Final results are typically cast in a nondestructive evaluation (NDE) context as either scattering amplitudes or flaw signals (via a measurement model based on a reciprocity integral). The near field is also predicted which allows for improved physical insight into the scattering process and the evaluation of certain modeling approximations. The accuracy of the BEM approach is first examined by comparing its predictions to those of other models for single, isolated scatters. The comparisons are with the predictions of analytical solutions for spherical defects and with MOOT and T-matrix calculations for axisymmetric flaws. Experimental comparisons are also made for volumetric shapes with different characteristic dimensions in all three directions, since no other numerical approach has yet produced results of this type. Theoretical findings regarding the fictitious eigenfrequency difficulty are substantiated through the analytical solution of a fundamental elastodynamics problem and corresponding BEM studies. Given the confidence in the BEM technique engendered by these comparisons, it is then used to investigate the modeling of 'open', cracklike defects amenable to a volumetric formulation. The limits of applicability of approximate theories (e.g., quasistatic, Kirchhoff, and geometric theory of diffraction) are explored for elliptical cracks, from this basis. The problem of two interacting scatterers is then considered. Results from a fully implicit approach and from a more efficient hybrid scheme are compared with generalized Born and farfield approximate interaction theories.

The statistical kinematical theory of X-ray diffraction as applied to reciprocal-space mapping

PubMed

Nesterets; Punegov

2000-11-01

The statistical kinematical X-ray diffraction theory is developed to describe reciprocal-space maps (RSMs) from deformed crystals with defects of the structure. The general solutions for coherent and diffuse components of the scattered intensity in reciprocal space are derived. As an example, the explicit expressions for intensity distributions in the case of spherical defects and of a mosaic crystal were obtained. The theory takes into account the instrumental function of the triple-crystal diffractometer and can therefore be used for experimental data analysis.

Fundamentals of microcrack nucleation mechanics

NASA Technical Reports Server (NTRS)

Fu, L. S.; Sheu, Y. C.; Co, C. M.; Zhong, W. F.; Shen, H. D.

1985-01-01

A foundation for ultrasonic evaluation of microcrack nucleation mechanics is identified in order to establish a basis for correlations between plane strain fracture toughness and ultrasonic factors through the interaction of elastic waves with material microstructures. Since microcracking is the origin of (brittle) fracture, it is appropriate to consider the role of stress waves in the dynamics of microcracking. Therefore, the following topics are discussed: (1) microstress distributions with typical microstructural defects located in the stress field; (2) elastic wave scattering from various idealized defects; and (3) dynamic effective-properties of media with randomly distributed inhomogeneities.

Modification of the crystal structure of gadolinium gallium garnet by helium ion irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ostafiychuk, B. K.; Yaremiy, I. P., E-mail: yaremiy@rambler.ru; Yaremiy, S. I.

2013-12-15

The structure of gadolinium gallium garnet (GGG) single crystals before and after implantation by He{sup +} ions has been investigated using high-resolution X-ray diffraction methods and the generalized dynamic theory of X-ray scattering. The main types of growth defects in GGG single crystals and radiation-induced defects in the ion-implanted layer have been determined. It is established that the concentration of dislocation loops in the GGG surface layer modified by ion implantation increases and their radius decreases with an increase in the implantation dose.

Near-infrared imaging of developmental defects in dental enamel.

PubMed

Hirasuna, Krista; Fried, Daniel; Darling, Cynthia L

2008-01-01

Polarization-sensitive optical coherence tomography (PS-OCT) and near-infrared (NIR) imaging are promising new technologies under development for monitoring early carious lesions. Fluorosis is a growing problem in the United States, and the more prevalent mild fluorosis can be visually mistaken for early enamel demineralization. Unfortunately, there is little quantitative information available regarding the differences in optical properties of sound enamel, enamel developmental defects, and caries. Thirty extracted human teeth with various degrees of suspected fluorosis were imaged using PS-OCT and NIR. An InGaAs camera and a NIR diode laser were used to measure the optical attenuation through transverse tooth sections (approximately 200 microm). A digital microradiography system was used to quantify the enamel defect severity by measurement of the relative mineral loss for comparison with optical scattering measurements. Developmental defects were clearly visible in the polarization-resolved OCT images, demonstrating that PS-OCT can be used to nondestructively measure the depth and possible severity of the defects. Enamel defects on whole teeth that could be imaged with high contrast with visible light were transparent in the NIR. This study suggests that PS-OCT and NIR methods may potentially be used as tools to assess the severity and extent of enamel defects.

A cascade method for TFT-LCD defect detection

NASA Astrophysics Data System (ADS)

Yi, Songsong; Wu, Xiaojun; Yu, Zhiyang; Mo, Zhuoya

2017-07-01

In this paper, we propose a novel cascade detection algorithm which focuses on point and line defects on TFT-LCD. At the first step of the algorithm, we use the gray level difference of su-bimage to segment the abnormal area. The second step is based on phase only transform (POT) which corresponds to the Discrete Fourier Transform (DFT), normalized by the magnitude. It can remove regularities like texture and noise. After that, we improve the method of setting regions of interest (ROI) with the method of edge segmentation and polar transformation. The algorithm has outstanding performance in both computation speed and accuracy. It can solve most of the defect detections including dark point, light point, dark line, etc.

Polaronic and ionic conduction in NaMnO2: influence of native point defects

NASA Astrophysics Data System (ADS)

Zhu, Zhen; Peelaers, Hartwin; van de Walle, Chris G.

Layered NaMnO2 has promising applications as a cathode material for sodium ion batteries. We will discuss strategies to improve the electrical performance of NaMnO2, including how to optimize the conditions of synthesis and how impurity doping affects the performance. Using hybrid density functional theory, we explored the structural, electronic, and defect properties of bulk NaMnO2. It is antiferromagnetic in the ground state with a band gap of 3.75 eV. Small hole and electron polarons can form in the bulk either through self-trapping or adjacent to point defects. We find that both Na and Mn vacancies are shallow acceptors with the induced holes trapped as small polarons, while O vacancies are deep defect centers. Cation antisites, especially MnNa, are found to have low formation energies. As a result, we expect that MnNa exists in as-grown NaMnO2 in moderate concentrations, rather than forming only at a later stage of the charging process, at which point it causes undesirable structural phase transitions. Both electronic conduction, via polaron hopping, and ionic conduction, through VNa migration, are significantly affected by the presence of point defects. This work was supported by DOE.

N vacancy, self-interstitial diffusion, and Frenkel-pair formation/dissociation in TiN studied by ab-initio and classical molecular dynamics

NASA Astrophysics Data System (ADS)

Sangiovanni, Davide G.; Alling, Björn; Hultman, Lars; Abrikosov, Igor A.

2015-03-01

We use ab-initio and classical molecular dynamics (AIMD, CMD) to simulate diffusion of N vacancy and N self-interstitial point-defects in B1 TiN. The physical properties of TiN, important material system for thin film and coatings applications, are largely dictated by concentration and mobility of point defects. We determine N dilute-point-defect diffusion pathways, activation energies, attempt frequencies, and diffusion coefficients as a function of temperature. In addition, MD simulations reveal an unanticipated atomistic process, which controls the spontaneous formation of N-self-interstitial/N-vacancy pairs (Frenkel pairs) in defect-free TiN. This entails that a N lattice atom leaves its bulk position and bonds to a neighboring N lattice atom. In most cases, Frenkel-pair NI and NV recombine within a fraction of ns; 50% of these processes result in the exchange of two nitrogen lattice atoms. Occasionally, however, Frenkel-pair N-interstitial atoms permanently escape from the anion vacancy site, thus producing unpaired NI and NV point defects. The Knut and Alice Wallenberg foundation (Isotope Project, 2011.0094), the Swedish Research Council (VR) Linköping Linnaeus Initiative LiLi-NFM (Grant 2008-6572), and the Swedish Government Strategic Research (Grant MatLiU 2009-00971).

Nitrogen vacancy, self-interstitial diffusion, and Frenkel-pair formation/dissociation in B 1 TiN studied by ab initio and classical molecular dynamics with optimized potentials

NASA Astrophysics Data System (ADS)

Sangiovanni, D. G.; Alling, B.; Steneteg, P.; Hultman, L.; Abrikosov, I. A.

2015-02-01

We use ab initio and classical molecular dynamics (AIMD and CMD) based on the modified embedded-atom method (MEAM) potential to simulate diffusion of N vacancy and N self-interstitial point defects in B 1 TiN. TiN MEAM parameters are optimized to obtain CMD nitrogen point-defect jump rates in agreement with AIMD predictions, as well as an excellent description of Ti Nx(˜0.7

A molecular dynamics simulation study of irradiation induced defects in gold nanowire

NASA Astrophysics Data System (ADS)

Liu, Wenqiang; Chen, Piheng; Qiu, Ruizhi; Khan, Maaz; Liu, Jie; Hou, Mingdong; Duan, Jinglai

2017-08-01

Displacement cascade in gold nanowires was studied using molecular dynamics computer simulations. Primary knock-on atoms (PKAs) with different kinetic energies were initiated either at the surface or at the center of the nanowires. We found three kinds of defects that were induced by the cascade, including point defects, stacking faults and crater at the surface. The starting points of PKAs influence the number of residual point defects, and this consequently affect the boundary of anti-radiation window which was proposed by calculation of diffusion of point defects to the free surface of nanowires. Formation of stacking faults that expanded the whole cross-section of gold nanowires was observed when the PKA's kinetic energy was higher than 5 keV. Increasing the PKA's kinetic energy up to more than 10 keV may lead to the formation of crater at the surface of nanowires due to microexplosion of hot atoms. At this energy, PKAs started from the center of nanowires can also result in the creation of crater because length of cascade region is comparable to diameter of nanowires. Both the two factors, namely initial positions of PKAs as well as the craters induced by higher energy irradiation, would influence the ability of radiation resistance of metal nanowires.

Modification of electronic structure, magnetic structure, and topological phase of bismuthene by point defects

NASA Astrophysics Data System (ADS)

Kadioglu, Yelda; Kilic, Sevket Berkay; Demirci, Salih; Aktürk, O. Üzengi; Aktürk, Ethem; Ciraci, Salim

2017-12-01

This paper reveals how the electronic structure, magnetic structure, and topological phase of two-dimensional (2D), single-layer structures of bismuth are modified by point defects. We first showed that a free-standing, single-layer, hexagonal structure of bismuth, named h-bismuthene, exhibits nontrivial band topology. We then investigated interactions between single foreign adatoms and bismuthene structures, which comprise stability, bonding, electronic structure, and magnetic structures. Localized states in diverse locations of the band gap and resonant states in band continua of bismuthene are induced upon the adsorption of different adatoms, which modify electronic and magnetic properties. Specific adatoms result in reconstruction around the adsorption site. Single vacancies and divacancies can form readily in bismuthene structures and remain stable at high temperatures. Through rebondings, Stone-Whales-type defects are constructed by divacancies, which transform into a large hole at high temperature. Like adsorbed adatoms, vacancies induce also localized gap states, which can be eliminated through rebondings in divacancies. We also showed that not only the optical and magnetic properties, but also the topological features of pristine h-bismuthene can be modified by point defects. The modification of the topological features depends on the energies of localized states and also on the strength of coupling between point defects.

Joint Processing of Envelope Alignment and Phase Compensation for Isar Imaging

NASA Astrophysics Data System (ADS)

Chen, Tao; Jin, Guanghu; Dong, Zhen

2018-04-01

Range envelope alignment and phase compensation are spilt into two isolated parts in the classical methods of translational motion compensation in Inverse Synthetic Aperture Radar (ISAR) imaging. In classic method of the rotating object imaging, the two reference points of the envelope alignment and the Phase Difference (PD) estimation are probably not the same point, making it difficult to uncouple the coupling term by conducting the correction of Migration Through Resolution Cell (MTRC). In this paper, an improved approach of joint processing which chooses certain scattering point as the sole reference point is proposed to perform with utilizing the Prominent Point Processing (PPP) method. With this end in view, we firstly get the initial image using classical methods from which a certain scattering point can be chose. The envelope alignment and phase compensation using the selected scattering point as the same reference point are subsequently conducted. The keystone transform is thus smoothly applied to further improve imaging quality. Both simulation experiments and real data processing are provided to demonstrate the performance of the proposed method compared with classical method.

Beyond spatial correlation effect in micro-Raman light scattering: An example of zinc-blende GaN/GaAs hetero-interface

NASA Astrophysics Data System (ADS)

Ning, J. Q.; Zheng, C. C.; Zheng, L. X.; Xu, S. J.

2015-08-01

Spatially resolved Raman light scattering experiments were performed on a zinc-blende GaN/GaAs heterostructure with confocal micro-Raman scattering technique under the backscattering geometric configuration. By varying the illumination spot locations across the heterostructure interface, we found that the Raman light scattering spectral features change remarkably. The interface effect on the GaAs substrate manifested as a much broader lineshape of the transverse optical (TO) phonon mode. Two kinds of broadening mechanisms, namely, spatial correlation induced wave-vector relaxation effect and lattice-mismatch strain + compositional intermixing effect, have been identified. The former leads to the broadening of the TO mode at the low-energy side, whereas the latter accounts for the broadening at the high-energy side. The diffuse light scattering from the highly defective nucleation layer of GaN was found to produce a broad scattering background of the GaN TO mode. The methodology and conclusions of the present work could be applicable to Raman spectroscopic studies on other material interfaces.

Correlation between quarter-point angle and nuclear radius

NASA Astrophysics Data System (ADS)

Ma, Wei-Hu; Wang, Jian-Song; Mukherjee, S.; Wang, Qi; Patel, D.; Yang, Yan-Yun; Ma, Jun-Bing; Ma, Peng; Jin, Shi-Lun; Bai, Zhen; Liu, Xing-Quan

2017-04-01

The correlation between quarter-point angle of elastic scattering and nuclear matter radius is studied systematically. Various phenomenological formulae with parameters for nuclear radius are adopted and compared by fitting the experimental data of quarter point angle extracted from nuclear elastic scattering reaction systems. A parameterized formula related to binding energy is recommended, which gives a good reproduction of nuclear matter radii of halo nuclei. It indicates that the quarter-point angle of elastic scattering is quite sensitive to the nuclear matter radius and can be used to extract the nuclear matter radius. Supported by National Natural Science Foundation of China (U1432247, 11575256), National Basic Research Program of China (973 Program)(2014CB845405 and 2013CB83440x) and (SM) Chinese Academy of Sciences President’s International Fellowship Initiative (2015-FX-04)

Anderson localization of graphene by helium ion irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Naitou, Y., E-mail: yu-naitou@aist.go.jp; Ogawa, S.

Irradiation of a single-layer graphene (SLG) with accelerated helium ions (He{sup +}) controllably generates defect distributions, which create a charge carrier scattering source within the SLG. We report direct experimental observation of metal-insulator transition in SLG on SiO{sub 2}/Si substrates induced by Anderson localization. This transition was investigated using scanning capacitance microscopy by monitoring the He{sup +} dose conditions on the SLG. The experimental data show that a defect density of more than ∼1.2% induced Anderson localization. We also investigated the localization length by determining patterned placement of the defects and estimated the length to be several dozen nanometers. Thesemore » findings provide valuable insight for patterning and designing graphene-based nanostructures using helium ion microscopy.« less

Development of an optical inspection platform for surface defect detection in touch panel glass

NASA Astrophysics Data System (ADS)

Chang, Ming; Chen, Bo-Cheng; Gabayno, Jacque Lynn; Chen, Ming-Fu

2016-04-01

An optical inspection platform combining parallel image processing with high resolution opto-mechanical module was developed for defect inspection of touch panel glass. Dark field images were acquired using a 12288-pixel line CCD camera with 3.5 µm per pixel resolution and 12 kHz line rate. Key features of the glass surface were analyzed by parallel image processing on combined CPU and GPU platforms. Defect inspection of touch panel glass, which provided 386 megapixel image data per sample, was completed in roughly 5 seconds. High detection rate of surface scratches on the touch panel glass was realized with minimum defects size of about 10 µm after inspection. The implementation of a custom illumination source significantly improved the scattering efficiency on the surface, therefore enhancing the contrast in the acquired images and overall performance of the inspection system.

Amorphization due to electronic energy deposition in defective strontium titanate

DOE PAGES

Xue, Haizhou; Zarkadoula, Eva; Liu, Peng; ...

2017-01-27

The synergistic interaction of electronic energy loss by ions with ion-induced defects created by elastic nuclear scattering processes has been investigated for single crystal SrTiO 3. An initial pre-damaged defect state corresponding to a relative disorder level of 0.10–0.15 sensitizes the SrTiO 3 to amorphous track formation along the ion path of 12 and 20 MeV Ti, 21 MeV Cl and 21 MeV Ni ions, where Ti, Cl and Ni ions otherwise do not produce amorphous or damage tracks in pristine SrTiO 3. The electronic stopping power threshold for amorphous ion track formation is found to be 6.7 keV/nm formore » the pre-damaged defect state studied in this work. Lastly, these results suggest the possibility of selectively producing nanometer scale, amorphous ion tracks in thin films of epitaxial SrTiO 3.« less

Effect of point defects on the amorphization of metallic alloys during ion implantation. [NiTi

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pedraza, D.F.; Mansur, L.K.

1985-01-01

A theoretical model of radiation-induced amorphization of ordered intermetallic compounds is developed. The mechanism is proposed to be the buildup of lattice defects to very high concentrations, which destabilizes the crystalline structure. Because simple point defects do not normally reach such levels during irradiation, a new defect complex containing a vacancy and an interstitial is hypothesized. Crucial properties of the complex are that the interstitial sees a local chemical environment similar to that of an atom in the ordered lattice, that the formation of the complex prevents mutual recombination and that the complex is immobile. The evolution of a disordermore » based on complexes is not accompanied by like point defect aggregation. The latter leads to the development of a sink microstructure in alloys that do not become amorphous. For electron irradiation, the complexes form by diffusional encounters. For ion irradiation, complexes are also formed directly in cascades. The possibility of direct amorphization in cascades is also included. Calculations for the compound NiTi show reasonable agreement with measured amorphization kinetics.« less

Anticorrelation between Surface and Subsurface Point Defects and the Impact on the Redox Chemistry of TiO2(110)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoon, Yeohoon; Du, Yingge; Garcia, Juan C.

2015-02-02

Using combination of STM, DFT and SIMS, we explored the interplay and relative impact of surface vs. subsurface defects on the surface chemistry of rutile TiO2. STM results show that surface O vacancies (VO’s) are virtually absent in the vicinity of positively-charged subsurface point-defects. This observation is consistent with DFT calculations of impact of subsurface defect proximity on VO formation energy. To monitor the influence of such lateral anticorrelation on surface redox chemistry, a test reaction of the dissociative adsorption of O2 is employed, which is observed to be suppressed around them. DFT results attribute this to a perceived absencemore » of the intrinsic (Ti) (and likely extrinsic) interstitials in the nearest subsurface layer beneath “inhibited” areas. We also postulate that the entire nearest subsurface region could be voided of any charged point-defects, whereas prevalent VO’s are largely responsible for mediation of the redox chemistry at reduced TiO2(110) surface.« less

Study of Te Inclusion and Related Point Defects in THM-Growth CdMnTe Crystal

NASA Astrophysics Data System (ADS)

Mao, Yifei; Zhang, Jijun; Min, Jiahua; Liang, Xiaoyan; Huang, Jian; Tang, Ke; Ling, Liwen; Li, Ming; Zhang, Ying; Wang, Linjun

2018-02-01

This study establishes a model for describing the interaction between Te inclusions, dislocations and point defects in CdMnTe crystals. The role of the complex environment surrounding the formation of Te inclusions was analyzed. Images of Te inclusions captured by scanning electron microscope and infrared microscope were used to observe the morphology of Te inclusions. The morphology of Te inclusions is discussed in light of crystallography, from the crystal growth temperature at 900°C to the melting temperature of Te inclusions using the traveling heater method. The dislocation nets around Te inclusions were calculated by counting lattice mismatches between the Te inclusions and the bulk CdMnTe at 470°C. The point defects of Te antisites were found to be gathered around Te inclusions, with dislocation climb during the cooling phase of crystal growth from 470°C to room temperature. The Te inclusions, dislocation nets and surrounding point defects are considered to be an entirety for evaluating the effect of Te inclusions on CdMnTe detector performance, and an effective mobility-lifetime product (μτ) was obtained.

Interface roughness induced asymmetric magnetic property in sputter-deposited Co/CoO/Co exchange coupled trilayers

NASA Astrophysics Data System (ADS)

Wang, J.; Sannomiya, T.; Shi, J.; Nakamura, Y.

2012-04-01

The effect of interface roughness on magnetic properties of exchange coupled polycrystalline Co/CoO(tAF)/Co trilayers has been investigated by varying antiferromagnetic layer (CoO) thickness. It has been found that the upper CoO/Co interface becomes rougher with increasing CoO layer thickness, resulting in stronger exchange bias of the upper interface than the lower one. The interfacial exchange coupling is strengthened by the increase of defect-generated uncompensated antiferromagnetic spins; such spins form coupling with spins in the Co layer at the interface. As a result, the CoO layer thickness dependence of exchange bias is much enhanced for the upper Co layer. The transition from anisotropic magnetoresistance to isotropic magnetoresistance for the top Co layer has also been found. This could be attributed to the defects, probably partial thin oxide layers, between Co grains in the top Co layer that leads a switch from spin-orbit scattering related magnetoresistance to spin-dependent electron scattering dominated magnetoresistance.

Investigation of point and extended defects in electron irradiated silicon—Dependence on the particle energy

NASA Astrophysics Data System (ADS)

Radu, R.; Pintilie, I.; Nistor, L. C.; Fretwurst, E.; Lindstroem, G.; Makarenko, L. F.

2015-04-01

This work is focusing on generation, time evolution, and impact on the electrical performance of silicon diodes impaired by radiation induced active defects. n-type silicon diodes had been irradiated with electrons ranging from 1.5 MeV to 27 MeV. It is shown that the formation of small clusters starts already after irradiation with high fluence of 1.5 MeV electrons. An increase of the introduction rates of both point defects and small clusters with increasing energy is seen, showing saturation for electron energies above ˜15 MeV. The changes in the leakage current at low irradiation fluence-values proved to be determined by the change in the configuration of the tri-vacancy (V3). Similar to V3, other cluster related defects are showing bistability indicating that they might be associated with larger vacancy clusters. The change of the space charge density with irradiation and with annealing time after irradiation is fully described by accounting for the radiation induced trapping centers. High resolution electron microscopy investigations correlated with the annealing experiments revealed changes in the spatial structure of the defects. Furthermore, it is shown that while the generation of point defects is well described by the classical Non Ionizing Energy Loss (NIEL), the formation of small defect clusters is better described by the "effective NIEL" using results from molecular dynamics simulations.

Defect classification in sparsity-based structural health monitoring

NASA Astrophysics Data System (ADS)

Golato, Andrew; Ahmad, Fauzia; Santhanam, Sridhar; Amin, Moeness G.

2017-05-01

Guided waves have gained popularity in structural health monitoring (SHM) due to their ability to inspect large areas with little attenuation, while providing rich interactions with defects. For thin-walled structures, the propagating waves are Lamb waves, which are a complex but well understood type of guided waves. Recent works have cast the defect localization problem of Lamb wave based SHM within the sparse reconstruction framework. These methods make use of a linear model relating the measurements with the scene reflectivity under the assumption of point-like defects. However, most structural defects are not perfect points but tend to assume specific forms, such as surface cracks or internal cracks. Knowledge of the "type" of defects is useful in the assessment phase of SHM. In this paper, we present a dual purpose sparsity-based imaging scheme which, in addition to accurately localizing defects, properly classifies the defects present simultaneously. The proposed approach takes advantage of the bias exhibited by certain types of defects toward a specific Lamb wave mode. For example, some defects strongly interact with the anti-symmetric modes, while others strongly interact with the symmetric modes. We build model based dictionaries for the fundamental symmetric and anti-symmetric wave modes, which are then utilized in unison to properly localize and classify the defects present. Simulated data of surface and internal defects in a thin Aluminum plate are used to validate the proposed scheme.

Detecting Submicron Pattern Defects On Optical Photomasks Using An Enhanced El-3 Electron-Beam Lithography Tool

NASA Astrophysics Data System (ADS)

Simpson, R. A.; Davis, D. E.

1982-09-01

This paper describes techniques to detect submicron pattern defects on optical photomasks with an enhanced direct-write, electron-beam lithographic tool. EL-3 is a third generation, shaped spot, electron-beam lithography tool developed by IBM to fabricate semiconductor devices and masks. This tool is being upgraded to provide 100% inspection of optical photomasks for submicron pattern defects, which are subsequently repaired. Fixed-size overlapped spots are stepped over the mask patterns while a signal derived from the back-scattered electrons is monitored to detect pattern defects. Inspection does not require pattern recognition because the inspection scan patterns are derived from the original design data. The inspection spot is square and larger than the minimum defect to be detected, to improve throughput. A new registration technique provides the beam-to-pattern overlay required to locate submicron defects. The 'guard banding" of inspection shapes prevents mask and system tolerances from producing false alarms that would occur should the spots be mispositioned such that they only partially covered a shape being inspected. A rescanning technique eliminates noise-related false alarms and significantly improves throughput. Data is accumulated during inspection and processed offline, as required for defect repair. EL-3 will detect 0.5 um pattern defects at throughputs compatible with mask manufacturing.

Optical signatures of deep level defects in Ga2O3

NASA Astrophysics Data System (ADS)

Gao, Hantian; Muralidharan, Shreyas; Pronin, Nicholas; Karim, Md Rezaul; White, Susan M.; Asel, Thaddeus; Foster, Geoffrey; Krishnamoorthy, Sriram; Rajan, Siddharth; Cao, Lei R.; Higashiwaki, Masataka; von Wenckstern, Holger; Grundmann, Marius; Zhao, Hongping; Look, David C.; Brillson, Leonard J.

2018-06-01

We used depth-resolved cathodoluminescence spectroscopy and surface photovoltage spectroscopy to measure the effects of near-surface plasma processing and neutron irradiation on native point defects in β-Ga2O3. The near-surface sensitivity and depth resolution of these optical techniques enabled us to identify spectral changes associated with removing or creating these defects, leading to identification of one oxygen vacancy-related and two gallium vacancy-related energy levels in the β-Ga2O3 bandgap. The combined near-surface detection and processing of Ga2O3 suggests an avenue for identifying the physical nature and reducing the density of native point defects in this and other semiconductors.

Visualizing One-Dimensional Electronic States and their Scattering in Semi-conducting Nanowires

NASA Astrophysics Data System (ADS)

Beidenkopf, Haim; Reiner, Jonathan; Norris, Andrew; Nayak, Abhay Kumar; Avraham, Nurit; Shtrikman, Hadas

One-dimensional electronic systems constitute a fascinating playground for the emergence of exotic electronic effects and phases, within and beyond the Tomonaga-Luttinger liquid paradigm. More recently topological superconductivity and Majorana modes were added to that long list of phenomena. We report scanning tunneling microscopy and spectroscopy measurements conducted on pristine, epitaxialy grown InAs nanowires. We resolve the 1D electronic band structure manifested both via Van-Hove singularities in the local density-of-states, as well as by the quasi-particle interference patterns, induced by scattering from surface impurities. By studying the scattering of the one-dimensional electronic states off various scatterers, including crystallographic defects and the nanowire end, we identify new one-dimensional relaxation regimes and yet unexplored effects of interactions. Some of these may bear implications on the topological superconducting state and Majorana modes therein. The authors acknowledge support from the Israeli Science Foundation (ISF).

Inspection of imprint lithography patterns for semiconductor and patterned media

NASA Astrophysics Data System (ADS)

Resnick, Douglas J.; Haase, Gaddi; Singh, Lovejeet; Curran, David; Schmid, Gerard M.; Luo, Kang; Brooks, Cindy; Selinidis, Kosta; Fretwell, John; Sreenivasan, S. V.

2010-03-01

Imprint lithography has been shown to be an effective technique for replication of nano-scale features. Acceptance of imprint lithography for manufacturing will require demonstration that it can attain defect levels commensurate with the requirements of cost-effective device production. This work summarizes the results of defect inspections of semiconductor masks, wafers and hard disks patterned using Jet and Flash Imprint Lithography (J-FILTM). Inspections were performed with optical and e-beam based automated inspection tools. For the semiconductor market, a test mask was designed which included dense features (with half pitches ranging between 32 nm and 48 nm) containing an extensive array of programmed defects. For this work, both e-beam inspection and optical inspection were used to detect both random defects and the programmed defects. Analytical SEMs were then used to review the defects detected by the inspection. Defect trends over the course of many wafers were observed with another test mask using a KLA-T 2132 optical inspection tool. The primary source of defects over 2000 imprints were particle related. For the hard drive market, it is important to understand the defectivity of both the template and the imprinted disk. This work presents a methodology for automated pattern inspection and defect classification for imprint-patterned media. Candela CS20 and 6120 tools from KLA-Tencor map the optical properties of the disk surface, producing highresolution grayscale images of surface reflectivity, scattered light, phase shift, etc. Defects that have been identified in this manner are further characterized according to the morphology

Analytical close-to-source investigation for an isotropic point source in an unbounded, anisotropically scattering medium

NASA Astrophysics Data System (ADS)

Rinzema, Kees; ten Bosch, Jaap J.; Ferwerda, Hedzer A.; Hoenders, Bernhard J.

1995-01-01

The diffusion approximation, which is often used to describe the propagation of light in biological tissues, is only good at a sufficient distance from sources and boundaries. Light- tissue interaction is however most intense in the region close to the source. It would therefore be interesting to study this region more closely. Although scattering in biological tissues is predominantly forward peaked, explicit solutions to the transport equation have only been obtained in the case of isotropic scattering. Particularly, for the case of an isotropic point source in an unbounded, isotropically scattering medium the solution is well known. We show that this problem can also be solved analytically if the scattering is no longer isotropic, while everything else remains the same.

Multiwalled carbon nanotubes and dispersed nanodiamond novel hybrids: Microscopic structure evolution, physical properties, and radiation resilience

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, S.; Farmer, J.

2011-01-01

We report the structure and physical properties of novel hybrids of multiwalled carbon nanotubes (MWCNTs) and ultradispersed diamond (UDD) forming nanocomposite ensemble that were subjected to 50, 100, and 10{sup 3} kGy gamma ray doses and characterized using various analytical tools to investigate hierarchical defects evolution. This work is prompted by recent work on single-walled CNTs and UDD ensemble [Gupta et al., J. Appl. Phys. 107, 104308 (2010)] where radiation-induced microscopic defects seem to be stabilized by UDD. The present experiments show similar effects where these hybrids display only a minimal structural modification under the maximum dose. Quantitative analyses ofmore » multiwavelength Raman spectra revealed lattice defects induced by irradiation assessed through the variation in prominent D, G, and 2D bands. A minimal change in the position of D, G, and 2D bands and a marginal increase in intensity of the defect-induced double resonant Raman scattered D and 2D bands are some of the implications suggesting the radiation coupling. The in-plane correlation length (L{sub a}) was also determined following Tunistra-Koenig relation from the ratio of D to G band (I{sub D}/I{sub G}) besides microscopic stress. However, we also suggest the following taking into account of intrinsic defects of the constituents: (a) charge transfer arising at the interface due to the difference in electronegativity of MWCNT C sp{sup 2} and UDD core (C sp{sup 3}) leading to phonon and electron energy renormalization; (b) misorientation of C sp{sup 2} at the interface of MWCNT and UDD shell (C sp{sup 2}) resulting in structural disorder; (c) softening or violation of the q{approx}0 selection rule leading to D band broadening and a minimal change in G band intensity; and (d) normalized intensity of D and G bands with 2D band help to distinguish defect-induced double resonance phenomena. The MWCNT when combined with nanodiamond showed a slight decrease in their conductance further affected by irradiation pointing at relatively good interfacial contact. Furthermore, owing to high thermal and electrical conductivity properties, they can facilitate potentially efficient heat-transfer applications and some results deduced using Nielsen's model is provided.« less

Cementoblast Delivery for Periodontal Tissue Engineering

PubMed Central

Zhao, Ming; Jin, Qiming; Berry, Janice E.; Nociti, Francisco H.; Giannobile, William V.; Somerman, Martha J.

2008-01-01

Background Predictable periodontal regeneration following periodontal disease is a major goal of therapy. The objective of this proof of concept investigation was to evaluate the ability of cementoblasts and dental follicle cells to promote periodontal regeneration in a rodent periodontal fenestration model. Methods The buccal aspect of the distal root of the first mandibular molar was denuded of its periodontal ligament (PDL), cementum, and superficial dentin through a bony window created bilaterally in 12 athymic rats. Treated defects were divided into three groups: 1) carrier alone (PLGA polymer sponges), 2) carrier + follicle cells, and 3) carrier + cementoblasts. Cultured murine primary follicle cells and immortalized cementoblasts were delivered to the defects via biodegradable PLGA polymer sponges, and mandibulae were retrieved 3 weeks and 6 weeks post-surgery for histological evaluation. In situ hybridization, for gene expression of bone sialoprotein (BSP) and osteocalcin (OCN), and histomorphometric analysis were further done on 3-week specimens. Results Three weeks after surgery, histology of defects treated with carrier alone indicated PLGA particles, fibrous tissue, and newly formed bone scattered within the defect area. Defects treated with carrier + follicle cells had a similar appearance, but with less formation of bone. In contrast, in defects treated with carrier + cementoblasts, mineralized tissues were noted at the healing site with extension toward the root surface, PDL region, and laterally beyond the buccal plate envelope of bone. No PDL-bone fibrous attachment was observed in any of the groups at this point. In situ hybridization showed that the mineralized tissue formed by cementoblasts gave strong signals for both BSP and OCN genes, confirming its nature as cementum or bone. The changes noted at 3 weeks were also observed at 6 weeks. Cementoblast-treated and carrier alone-treated defects exhibited complete bone bridging and PDL formation, whereas follicle cell-treated defects showed minimal evidence of osteogenesis. No new cementum was formed along the root surface in the above two groups. Cementoblast-treated defects were filled with trabeculated mineralized tissue similar to, but more mature, than that seen at 3 weeks. Furthermore, the PDL region was maintained with well-organized collagen fibers connecting the adjacent bone to a thin layer of cementum-like tissue observed on the root surface. Neoplastic changes were observed at the superficial portions of the implants in two of the 6-week cementoblast-treated specimens, possibly due in part to the SV40-transformed nature of the implanted cell line. Conclusions This pilot study demonstrates that cementoblasts have a marked ability to induce mineralization in periodontal wounds when delivered via polymer sponges, while implanted dental follicle cells seem to inhibit periodontal healing. These results confirm the selective behaviors of different cell types in vivo and support the role of cementoblasts as a tool to better understand periodontal regeneration and cementogenesis. PMID:15025227

Detection of small surface defects using DCT based enhancement approach in machine vision systems

NASA Astrophysics Data System (ADS)

He, Fuqiang; Wang, Wen; Chen, Zichen

2005-12-01

Utilizing DCT based enhancement approach, an improved small defect detection algorithm for real-time leather surface inspection was developed. A two-stage decomposition procedure was proposed to extract an odd-odd frequency matrix after a digital image has been transformed to DCT domain. Then, the reverse cumulative sum algorithm was proposed to detect the transition points of the gentle curves plotted from the odd-odd frequency matrix. The best radius of the cutting sector was computed in terms of the transition points and the high-pass filtering operation was implemented. The filtered image was then inversed and transformed back to the spatial domain. Finally, the restored image was segmented by an entropy method and some defect features are calculated. Experimental results show the proposed small defect detection method can reach the small defect detection rate by 94%.

Characterisation of large scale structures in starch granules via small-angle neutron and X-ray scattering.

PubMed

Doutch, James; Gilbert, Elliot P

2013-01-02

Small angle scattering (SAS) techniques have a distinguished track record in illuminating the semi-crystalline lamellar structure of the starch granule. To date, there have been few attempts to use SAS techniques to characterise larger-scale structures reported from imaging techniques such as growth rings, blocklets or pores, nor how these structures would modulate the well-known scattering arising from the semi-crystalline lamellar structure. In this study, SAS data collected over an extended q range were gathered from dry and hydrated starch powders from varied botanical sources. The use of neutrons and X-rays, as well as comparing dry and hydrated granules, allowed different levels of contrast in scattering length density to be probed and therefore selected structural regions to be highlighted. The lowest q range, 0.002-0.04 Å(-1), was found to be dominated by scattering from the starch granules themselves, especially in the dry powders; however an inflection point from a low contrast structure was observed at 0.035 Å(-1). The associated scattering was interpreted within a unified scattering framework with the inflexion point correlating with a structure with radius of gyration ~90 Å - a size comparable to small blocklets or superhelices. In hydrated starches, it is observed that there is an inflection point between lamellar and q(-4) power-law scattering regions at approximately 0.004 Å(-1) which may correlate with growth rings and large blocklets. The implications of these findings on existing models of starch lamellar scattering are discussed. Crown Copyright © 2012. Published by Elsevier Ltd. All rights reserved.

Ab initio theory of point defects in oxide materials: structure, properties, chemical reactivity

NASA Astrophysics Data System (ADS)

Pacchioni, Gianfranco

2000-05-01

Point defects play a fundamental role in determining the physical and chemical properties of inorganic materials. This holds not only for the bulk properties but also for the surface of oxides where several kinds of point defects exist and exhibit a rich and complex chemistry. A particularly important defect in oxides is the oxygen vacancy. Depending on the electronic structure of the material the nature of oxygen vacancies changes dramatically. In this article we provide a rationalization of the very different electronic structure of neutral and charged oxygen vacancies in SiO 2 and MgO, two oxide materials with completely different electronic structure (from very ionic, MgO, to largely covalent, SiO 2). We used methods of ab initio quantum chemistry, from density functional theory (DFT) to configuration interaction (CI), to determine the ground and excited state properties of these defects. The theoretical results are combined with recent spectroscopic measurements. A series of observable properties has been determined in this way: defect formation energies, hyperfine interactions in electron paramagnetic resonance (EPR) spectra of paramagnetic centers, optical spectra, surface chemical reactivity. The interplay between experimental and theoretical information allows one to unambiguously identify the structure of oxygen vacancies in these binary oxides and on their surfaces.

X-ray scattering signatures of β-thalassemia

NASA Astrophysics Data System (ADS)

Desouky, Omar S.; Elshemey, Wael M.; Selim, Nabila S.

2009-08-01

X-ray scattering from lyophilized proteins or protein-rich samples is characterized by the presence of two characteristic broad peaks at scattering angles equivalent to momentum transfer values of 0.27 and 0.6 nm -1, respectively. These peaks arise from the interference of coherently scattered photons. Once the conformation of a protein is changed, these two peaks reflect such change with considerable sensitivity. The present work examines the possibility of characterizing the most common cause of hemolytic anaemia in Egypt and many Mediterranean countries; β-thalassemia, from its X-ray scattering profile. This disease emerges from a genetic defect causing reduced rate in the synthesis of one of the globin chains that make up hemoglobin. As a result, structurally abnormal hemoglobin molecules are formed. In order to detect such molecular disorder, hemoglobin samples of β-thalassemia patients are collected, lyophilized and measured using a conventional X-ray diffractometer. Results show significant differences in the X-ray scattering profiles of most of the diseased samples compared to control. The shape of the first scattering peak at 0.27 nm -1, in addition to the relative intensity of the first to the second scattering peaks, provides the most reliable signs of abnormality in diseased samples. The results are interpreted and confirmed with the aid of Fourier Transform Infrared (FTIR) spectroscopy of normal and thalassemia samples.

Microwave and Millimeter Wave Imaging Using Synthetic Aperture Focusing and Holographical Techniques

NASA Technical Reports Server (NTRS)

Case, Joseph Tobias

2005-01-01

Microwave and millimeter wave nondestructive testing and evaluation (NDT&E) methods have shown great potential for determining material composition in composite structures, determining material thickness or debond thickness between two layers, and determining the location and size of flaws, defects, and anomalies. The same testing methods have also shown great potential to produce relatively high-resolution images of voids inside Spray On Foam Insulation (SOFI) test panels using real focused methods employing lens antennas. An alternative to real focusing methods are synthetic focusing methods. The essence of synthetic focusing is to match the phase of the scattered signal to measured points spaced regularly on a plane. Many variations of synthetic focusing methods have already been developed for radars, ultrasonic testing applications, and microwave concealed weapon detection. Two synthetic focusing methods were investigated; namely, a) frequency-domain synthetic aperture focusing technique (FDSAFT), and b) wide-band microwave holography. These methods were applied towards materials whose defects were of low dielectric contrast like air void in SOFI. It is important to note that this investigation used relatively low frequencies from 8.2 GHz to 26.5 GHz that are not conducive for direct imaging of the SOFI. The ultimate goal of this work has been to demonstrate the capability of these methods before they are applied to much higher frequencies such as the millimeter wave frequency spectrum (e.g., 30-300 GHz).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Amekura, Hiro, E-mail: amekura.hiroshi@nims.go.jp; Akhmadaliev, Shavkat; Zhou, Shengqiang

When ion irradiation introduces point-defects in semiconductors/insulators, discrete energy levels can be introduced in the bandgap, and then optical transitions whose energies are lower than the bandgap become possible. The electronic transitions between the discrete level and the continuous host band are observed as a continuous tail starting from the fundamental edge. This is the well-known mechanism of the absorption tail close to the band-edge observed in many semiconductors/insulators. In this paper, we propose another mechanism for the absorption tail, which is probably active in Nd-doped yttrium aluminum garnet (Nd:YAG) after ion irradiation and annealing. A Nd:YAG bulk crystal wasmore » irradiated with 15 MeV Au{sup 5+} ions to a fluence of 8 × 10{sup 14} ions/cm{sup 2}. The irradiation generates an amorphous layer of ∼3 μm thick with refractive index reduction of Δn = −0.03. Thermal annealing at 1000 °C induces recrystallization to randomly aligned small crystalline grains. Simultaneously, an extraordinarily long absorption tail appeared in the optical spectrum covering from 0.24 to ∼2 μm without fringes. The origin of the tail is discussed based on two models: (i) conventional electronic transitions between defect levels and YAG host band and (ii) enhanced light scattering by randomly aligned small grains.« less

Influence of RF excitation during pulsed laser deposition in oxygen atmosphere on the structural properties and luminescence of nanocrystalline ZnO:Al thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meljanac, Daniel, E-mail: dmeljan@irb.hr; Plodinec, Milivoj; Siketić, Zdravko

2016-03-15

Thin ZnO:Al layers were deposited by pulsed laser deposition in vacuum and in oxygen atmosphere at gas pressures between 10 and 70 Pa and by applying radio-frequency (RF) plasma. Grazing incidence small angle x-ray scattering and grazing incidence x-ray diffraction (GIXRD) data showed that an increase in the oxygen pressure leads to an increase in the roughness, a decrease in the sample density, and changes in the size distribution of nanovoids. The nanocrystal sizes estimated from GIXRD were around 20 nm, while the sizes of the nanovoids increased from 1 to 2 nm with the oxygen pressure. The RF plasma mainly influenced themore » nanostructural properties and point defects dynamics. The photoluminescence consisted of three contributions, ultraviolet (UV), blue emission due to Zn vacancies, and red emission, which are related to an excess of oxygen. The RF excitation lowered the defect level related to blue emission and narrowed the UV luminescence peak, which indicates an improvement of the structural ordering. The observed influence of the deposition conditions on the film properties is discussed as a consequence of two main effects: the variation of the energy transfer from the laser plume to the growing film and changes in the growth chemistry.« less

Computational techniques in gamma-ray skyshine analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

George, D.L.

1988-12-01

Two computer codes were developed to analyze gamma-ray skyshine, the scattering of gamma photons by air molecules. A review of previous gamma-ray skyshine studies discusses several Monte Carlo codes, programs using a single-scatter model, and the MicroSkyshine program for microcomputers. A benchmark gamma-ray skyshine experiment performed at Kansas State University is also described. A single-scatter numerical model was presented which traces photons from the source to their first scatter, then applies a buildup factor along a direct path from the scattering point to a detector. The FORTRAN code SKY, developed with this model before the present study, was modified tomore » use Gauss quadrature, recent photon attenuation data and a more accurate buildup approximation. The resulting code, SILOGP, computes response from a point photon source on the axis of a silo, with and without concrete shielding over the opening. Another program, WALLGP, was developed using the same model to compute response from a point gamma source behind a perfectly absorbing wall, with and without shielding overhead. 29 refs., 48 figs., 13 tabs.« less

Public Data Set: A Novel, Cost-Effective, Multi-Point Thomson Scattering System on the Pegasus Toroidal Experiment

DOE Data Explorer

Schlossberg, David J. [University of Wisconsin-Madison] (ORCID:0000000287139448); Bodner, Grant M. [University of Wisconsin-Madison] (ORCID:0000000324979172); Reusch, Joshua A. [University of Wisconsin-Madison] (ORCID:0000000284249422); Bongard, Michael W. [University of Wisconsin-Madison] (ORCID:0000000231609746); Fonck, Raymond J. [University of Wisconsin-Madison] (ORCID:0000000294386762); Rodriguez Sanchez, Cuauhtemoc [University of Wisconsin-Madison] (ORCID:0000000334712586)

2016-09-16

This public data set contains openly-documented, machine readable digital research data corresponding to figures published in D.J. Schlossberg et. al., 'A Novel, Cost-Effective, Multi-Point Thomson Scattering System on the Pegasus Toroidal Experiment,' Rev. Sci. Instrum. 87, 11E403 (2016).

[Forensic medical evaluation of stab-incised wounds caused by knives with point defects].

PubMed

Krupin, K N; Leonov, S V

2011-01-01

The present experimental study allowed to characterize specific signs of stab-incised wounds caused by knives with operational point defects. Diagnostic coefficients calculated for these macro- and microscopic features facilitate differential diagnostics of the injuries and make it possible to identify a concrete stabbing/cutting weapon with which the wound was inflicted..

First-principles study on oxidation effects in uranium oxides and high-pressure high-temperature behavior of point defects in uranium dioxide

NASA Astrophysics Data System (ADS)

Geng, Hua Y.; Song, Hong X.; Jin, K.; Xiang, S. K.; Wu, Q.

2011-11-01

Formation Gibbs free energy of point defects and oxygen clusters in uranium dioxide at high-pressure high-temperature conditions are calculated from first principles, using the LSDA+U approach for the electronic structure and the Debye model for the lattice vibrations. The phonon contribution on Frenkel pairs is found to be notable, whereas it is negligible for the Schottky defect. Hydrostatic compression changes the formation energies drastically, making defect concentrations depend more sensitively on pressure. Calculations show that, if no oxygen clusters are considered, uranium vacancy becomes predominant in overstoichiometric UO2 with the aid of the contribution from lattice vibrations, while compression favors oxygen defects and suppresses uranium vacancy greatly. At ambient pressure, however, the experimental observation of predominant oxygen defects in this regime can be reproduced only in a form of cuboctahedral clusters, underlining the importance of defect clustering in UO2+x. Making use of the point defect model, an equation of state for nonstoichiometric oxides is established, which is then applied to describe the shock Hugoniot of UO2+x. Furthermore, the oxidization and compression behavior of uranium monoxide, triuranium octoxide, uranium trioxide, and a series of defective UO2 at 0 K are investigated. The evolution of mechanical properties and electronic structures with an increase of the oxidation degree are analyzed, revealing the transition of the ground state of uranium oxides from metallic to Mott insulator and then to charge-transfer insulator due to the interplay of strongly correlated effects of 5f orbitals and the shift of electrons from uranium to oxygen atoms.

MicroCT and optical coherence tomography imagistic assessment of the dental roots adhesive

NASA Astrophysics Data System (ADS)

Sinescu, Cosmin; Negrutiu, Meda Lavinia; Nica, Luminita; Manescu, Adrian; Duma, Virgil-Florin; Podoleanu, Adrian G.

2015-03-01

Several obturation methods are available today to study the 3D filling of the root canal. There are also several methods capable to evaluate the ability to seal apically the root canals. However, the common methods of investigation are invasive; they also lead to the destruction of the samples. If the sectioning differs slightly from the desired area, the investigation is non-conclusive regarding the micro-leakages. Also, although the use of Cone-Beam Micro Computer Tomography (CBCT) appears to be most promising for endodontic purposes, its effective radiation doses are higher than with conventional intra-oral and panoramic imaging. In contrast, enface (ef) Optical Coherence Tomography (OCT) proves to be efficient for the investigation of material defects of dental restorations, dental materials, and micro-leakage at the interfaces, where the penetration depth depends on the material. Therefore, ef OCT has been proposed in our studies as a potential tool for in vivo endodontic imaging. Twenty five recently extracted human maxillary molars were selected for the study for caries or periodontal reasons. The pulp chambers were completely opened, the dental pulp was removed, and the root canals were shaped. Silver nanoparticles were used in half of the samples in order to increase the scattering of the adhesive material in comparison with the dental roots walls. The sample teeth were then probed using Time Domain (TD) OCT working at 1300 nm. A synchrotron radiation X-Ray microCT experiment was also performed. The imagistic results pointed out the efficiency of the silver nanoparticle layer used in order to increase the scattering of the root canal adhesive scattering for the OCT non-invasive investigation. MicroCT allowed for obtaining qualitative data related to the depth penetration of the root canal adhesive into the dentin walls.

R-on-1 automatic mapping: A new tool for laser damage testing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hue, J.; Garrec, P.; Dijon, J.

1996-12-31

Laser damage threshold measurement is statistical in nature. For a commercial qualification or for a user, the threshold determined by the weakest point is a satisfactory characterization. When a new coating is designed, threshold mapping is very useful. It enables the technology to be improved and followed more accurately. Different statistical parameters such as the minimum, maximum, average, and standard deviation of the damage threshold as well as spatial parameters such as the threshold uniformity of the coating can be determined. Therefore, in order to achieve a mapping, all the tested sites should give data. This is the major interestmore » of the R-on-1 test in spite of the fact that the laser damage threshold obtained by this method may be different from the 1-on-1 test (smaller or greater). Moreover, on the damage laser test facility, the beam size is smaller (diameters of a few hundred micrometers) than the characteristic sizes of the components in use (diameters of several centimeters up to one meter). Hence, a laser damage threshold mapping appears very interesting, especially for applications linked to large optical components like the Megajoule project or the National Ignition Facility (N.I.F). On the test bench used, damage detection with a Nomarski microscope and scattered light measurement are almost equivalent. Therefore, it becomes possible to automatically detect on line the first defects induced by YAG irradiation. Scattered light mappings and laser damage threshold mappings can therefore be achieved using a X-Y automatic stage (where the test sample is located). The major difficulties due to the automatic capabilities are shown. These characterizations are illustrated at 355 nm. The numerous experiments performed show different kinds of scattering curves, which are discussed in relation with the damage mechanisms.« less

Anomalous Dirac point transport due to extended defects in bilayer graphene.

PubMed

Shallcross, Sam; Sharma, Sangeeta; Weber, Heiko B

2017-08-24

Charge transport at the Dirac point in bilayer graphene exhibits two dramatically different transport states, insulating and metallic, that occur in apparently otherwise indistinguishable experimental samples. We demonstrate that the existence of these two transport states has its origin in an interplay between evanescent modes, that dominate charge transport near the Dirac point, and disordered configurations of extended defects in the form of partial dislocations. In a large ensemble of bilayer systems with randomly positioned partial dislocations, the distribution of conductivities is found to be strongly peaked at both the insulating and metallic limits. We argue that this distribution form, that occurs only at the Dirac point, lies at the heart of the observation of both metallic and insulating states in bilayer graphene.In seemingly indistinguishable bilayer graphene samples, two distinct transport regimes, insulating and metallic, have been identified experimentally. Here, the authors demonstrate that these two states originate from the interplay between extended defects and evanescent modes at the Dirac point.

Experimental investigation on the microscopic structure of intrinsic paramagnetic point defects in amorphous silicon dioxide

NASA Astrophysics Data System (ADS)

Buscarino, G.

2007-11-01

In the present Ph.D. Thesis we report an experimental investigation on the effects of gamma- and beta-ray irradiation and of subsequent thermal treatment on many types of a-SiO2 materials, differing in the production methods, OH- and Al-content, and oxygen deficiencies. Our main objective is to gain further insight on the microscopic structures of the E'_gamma, E'_delta, E'_alpha and triplet paramagnetic centers, which are among the most important and studied class of radiation induced intrinsic point defects in a-SiO2. To pursue this objective, we use prevalently the EPR spectroscopy. In particular, our work is focused on the properties of the unpaired electrons wave functions involved in the defects, and this aspect is mainly investigated through the study of the EPR signals originating from the interaction of the unpaired electrons with 29Si magnetic nuclei (with nuclear spin I=1/2 and natural abundance 4.7 %). In addition, in some cases of interest, OA measurements are also performed with the aim to further characterize the electronic properties of the defects. Furthermore, due to its relevance for electronics application, the charge state of the defects is investigated by looking at the processes responsible for the generation of the defects of interest. Once these information were gained, the possible sites that can serve as precursors for defects formation are deduced, with the definitive purpose to obtain in the future more radiation resistant a-SiO2 materials in which the deleterious effects connected with the point defects are significantly reduced.

First-principles investigation of point defect and atomic diffusion in Al2Ca

NASA Astrophysics Data System (ADS)

Tian, Xiao; Wang, Jia-Ning; Wang, Ya-Ping; Shi, Xue-Feng; Tang, Bi-Yu

2017-04-01

Point defects and atomic diffusion in Al2Ca have been studied from first-principles calculations within density functional framework. After formation energy and relative stability of point defects are investigated, several predominant diffusion processes in Al2Ca are studied, including sublattice one-step mechanism, 3-jump vacancy cycles and antistructure sublattice mechanism. The associated energy profiles are calculated with climbing image nudged elastic band (CI-NEB) method, then the saddle points and activation barriers during atomic diffusion are further determined. The resulted activation barriers show that both Al and Ca can diffuse mainly mediated by neighbor vacancy on their own sublattice. 3-jump cycle mechanism mediated by VCa may make some contribution to the overall Al diffusion. And antistructure (AS) sublattice mechanism can also play an important role in Ca atomic diffusion owing to the moderate activation barrier.

Defect production in nonlinear quench across a quantum critical point.

PubMed

Sen, Diptiman; Sengupta, K; Mondal, Shreyoshi

2008-07-04

We show that the defect density n, for a slow nonlinear power-law quench with a rate tau(-1) and an exponent alpha>0, which takes the system through a critical point characterized by correlation length and dynamical critical exponents nu and z, scales as n approximately tau(-alphanud/(alphaznu+1)) [n approximately (alphag((alpha-1)/alpha)/tau)(nud/(znu+1))] if the quench takes the system across the critical point at time t=0 [t=t(0) not = 0], where g is a nonuniversal constant and d is the system dimension. These scaling laws constitute the first theoretical results for defect production in nonlinear quenches across quantum critical points and reproduce their well-known counterpart for a linear quench (alpha=1) as a special case. We supplement our results with numerical studies of well-known models and suggest experiments to test our theory.

Stitching h-BN by atomic layer deposition of LiF as a stable interface for lithium metal anode

PubMed Central

Xie, Jin; Liao, Lei; Gong, Yongji; Li, Yanbin; Shi, Feifei; Pei, Allen; Sun, Jie; Zhang, Rufan; Kong, Biao; Subbaraman, Ram; Christensen, Jake; Cui, Yi

2017-01-01

Defects are important features in two-dimensional (2D) materials that have a strong influence on their chemical and physical properties. Through the enhanced chemical reactivity at defect sites (point defects, line defects, etc.), one can selectively functionalize 2D materials via chemical reactions and thereby tune their physical properties. We demonstrate the selective atomic layer deposition of LiF on defect sites of h-BN prepared by chemical vapor deposition. The LiF deposits primarily on the line and point defects of h-BN, thereby creating seams that hold the h-BN crystallites together. The chemically and mechanically stable hybrid LiF/h-BN film successfully suppresses lithium dendrite formation during both the initial electrochemical deposition onto a copper foil and the subsequent cycling. The protected lithium electrodes exhibit good cycling behavior with more than 300 cycles at relatively high coulombic efficiency (>95%) in an additive-free carbonate electrolyte. PMID:29202031

Stitching h-BN by atomic layer deposition of LiF as a stable interface for lithium metal anode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Jin; Liao, Lei; Gong, Yongji

Defects are important features in two-dimensional (2D) materials that have a strong influence on their chemical and physical properties. Through the enhanced chemical reactivity at defect sites (point defects, line defects, etc.), one can selectively functionalize 2D materials via chemical reactions and thereby tune their physical properties. We demonstrate the selective atomic layer deposition of LiF on defect sites of h-BN prepared by chemical vapor deposition. The LiF deposits primarily on the line and point defects of h-BN, thereby creating seams that hold the h-BN crystallites together. The chemically and mechanically stable hybrid LiF/h-BN film successfully suppresses lithium dendrite formationmore » during both the initial electrochemical deposition onto a copper foil and the subsequent cycling. In conclusion, the protected lithium electrodes exhibit good cycling behavior with more than 300 cycles at relatively high coulombic efficiency (>95%) in an additive-free carbonate electrolyte.« less

Stitching h-BN by atomic layer deposition of LiF as a stable interface for lithium metal anode

DOE PAGES

Xie, Jin; Liao, Lei; Gong, Yongji; ...

2017-11-29

Defects are important features in two-dimensional (2D) materials that have a strong influence on their chemical and physical properties. Through the enhanced chemical reactivity at defect sites (point defects, line defects, etc.), one can selectively functionalize 2D materials via chemical reactions and thereby tune their physical properties. We demonstrate the selective atomic layer deposition of LiF on defect sites of h-BN prepared by chemical vapor deposition. The LiF deposits primarily on the line and point defects of h-BN, thereby creating seams that hold the h-BN crystallites together. The chemically and mechanically stable hybrid LiF/h-BN film successfully suppresses lithium dendrite formationmore » during both the initial electrochemical deposition onto a copper foil and the subsequent cycling. In conclusion, the protected lithium electrodes exhibit good cycling behavior with more than 300 cycles at relatively high coulombic efficiency (>95%) in an additive-free carbonate electrolyte.« less

Point-spread imaging for measurement of skin translucency and scattering.

PubMed

Jiang, Zhi-xing; Kaplan, Peter D

2008-08-01

The translucency of skin has long been identified as an important cue for healthy and youthful looking skin. There is currently no universal definition for skin translucency let alone a measurement method. We propose that skin translucency is the light scattering beneath skin surface. We demonstrate the use of polarization gated point spreading imaging for non-invasive, in vivo measurement of the translucency and the reduced scattering coefficient m's of skin. We developed a polarization-gated point-spread imaging system to measure the spread of the incident pencil-thin laser beam on the skin. Skin translucency was calculated as the spread of the laser beam. From the measurement of the shift of the light diffuse center from the light injection point, the reduced scattering coefficient m's of the skin was calculated. We validated the measurement technique with milk as an in vitro model for skin. The measured m's of milk solution was found to be linearly proportional to the milk concentration, in agreement with Beer's law. The calculated translucency decreased as the milk concentration increased or as the reduced scattering coefficient m's increased. It was also found that the translucency decreased as the absorption coefficient of the milk solution increased. The measured translucency of a set of custom made clay tiles correlated well with the consumer perception of the incremental ranking of the translucency. In vivo measurement of skin translucency and the reduced scattering coefficient m's were carried out on several volunteers. The measured reduced scattering coefficient m's was in agreement with those in the literature. The measured skin translucency for different skin ethnicities of Caucasian, North Asian, South Asian and African American were in line with the expectation that skin translucency decreases as the skin color gets darker.

Point defects in thorium nitride: A first-principles study

NASA Astrophysics Data System (ADS)

Pérez Daroca, D.; Llois, A. M.; Mosca, H. O.

2016-11-01

Thorium and its compounds (carbides and nitrides) are being investigated as possible materials to be used as nuclear fuels for Generation-IV reactors. As a first step in the research of these materials under irradiation, we study the formation energies and stability of point defects in thorium nitride by means of first-principles calculations within the framework of density functional theory. We focus on vacancies, interstitials, Frenkel pairs and Schottky defects. We found that N and Th vacancies have almost the same formation energy and that the most energetically favorable defects of all studied in this work are N interstitials. These kind of results for ThN, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically.

Estimates of point defect production in α-quartz using molecular dynamics simulations

NASA Astrophysics Data System (ADS)

Cowen, Benjamin J.; El-Genk, Mohamed S.

2017-07-01

Molecular dynamics (MD) simulations are performed to investigate the production of point defects in α-quartz by oxygen and silicon primary knock-on atoms (PKAs) of 0.25-2 keV. The Wigner-Seitz (WS) defect analysis is used to identify the produced vacancies, interstitials, and antisites, and the coordination defect analysis is used to identify the under and over-coordinated oxygen and silicon atoms. The defects at the end of the ballistic phase and the residual defects, after annealing, increase with increased PKA energy, and are statistically the same for the oxygen and silicon PKAs. The WS defect analysis results show that the numbers of the oxygen vacancies and interstitials (VO, Oi) at the end of the ballistic phase is the highest, followed closely by those of the silicon vacancies and interstitials (VSi, Sii). The number of the residual oxygen and silicon vacancies and interstitials are statistically the same. In addition, the under-coordinated OI and SiIII, which are the primary defects during the ballistic phase, have high annealing efficiencies (>89%). The over-coordinated defects of OIII and SiV, which are not nearly as abundant in the ballistic phase, have much lower annealing efficiencies (<63%) that decrease with increased PKA energy.

X-Ray Diffraction and Imaging Study of Imperfections of Crystallized Lysozyme with Coherent X-Rays

NASA Technical Reports Server (NTRS)

Hu, Zheng-Wei; Chu, Y. S.; Lai, B.; Cai, Z.; Thomas, B. R.; Chernov, A. A.

2003-01-01

Phase-sensitive x-ray diffraction imaging and high angular-resolution diffraction combined with phase contrast radiographic imaging are employed to characterize defects and perfection of a uniformly grown tetragonal lysozyme crystal in symmetric Laue case. The fill width at half-maximum (FWHM) of a 4 4 0 rocking curve measured from the original crystal is approximately 16.7 arcseconds, and defects, which include point defects, line defects, and microscopic domains, have been clearly observed in the diffraction images of the crystal. The observed line defects carry distinct dislocation features running approximately along the <110> growth front, and they have been found to originate mostly at a central growth area and occasionally at outer growth regions. Individual point defects trapped at a crystal nucleus are resolved in the images of high sensitivity to defects. Slow dehydration has led to the broadening of the 4 4 0 rocking curve by a factor of approximately 2.4. A significant change of the defect structure and configuration with drying has been revealed, which suggests the dehydration induced migration and evolution of dislocations and lattice rearrangements to reduce overall strain energy. The sufficient details of the observed defects shed light upon perfection, nucleation and growth, and properties of protein crystals.

Field-Theoretical Studies of a doped Mott Insulator

NASA Astrophysics Data System (ADS)

Juricic, Vladimir

2006-06-01

In this thesis, the magnetic and the transport properties of La(2-x)Sr(x)CuO(4) in the undoped and lightly doped regime are investigated. In Chapter 2, we consider the role of the Dzyaloshinskii-Moriya (DM) and the pseudodipolar (XY) interactions in determining the magnetic properties of the undoped material, La(2)CuO(4), motivated by recent experiments, which show a complete anisotropy in the magnetic susceptibility response. We start with the microscopic spin model, which, besides the Heisenberg superexchange interaction, contains the anisotropic DM and the XY interactions. We map this microscopic model into a corresponding field theory, which turns out to be a generalized nonlinear sigma model. The effect of the anisotropies is to introduce gaps for the spin excitations, which are responsible for the ground-state properties of the material. When a magnetic field is applied, the DM anisotropy leads to an unexpected linear coupling of the staggered magnetization to the magnetic field, which is responsible for a completely anisotropic magnetic susceptibility, in agreement with experiments. In Chapter 3, we investigate the effect of the DM and the XY anisotropies on the magnetism when Sr doping is introduced in La(2)CuO(4). Our starting point is the nonlinear sigma model, which includes these anisotropies, and also the dopant holes, represented via an effective dipole field which couples to the background magnetization current. In the antiferromagnetic phase, x<2%, the dipole-magnetization current coupling leads to a decrease of the spin gaps, in good agreement with recent experiments. The DM gap gives rise to the stability of the antiferromagnetic state up to the doping level x=2%, at which the dipole field acquires a nonzero expectation value, causing a change in the magnetic ground state of the system. Beyond this doping concentration, the spins rearrange to form an incommensurate helicoidal state, which gives rise to two incommensurate peaks in the spin-glass phase of La(2-x)Sr(x)CuO(4), as observed by neutron scattering experiments. The incommensurability is related to the doping and the XY gap in a way that allows us to explain the linear doping dependence of the incommensurability at higher doping, as well as the deviation from the linear behavior at the onset of the spin-glass phase. We propose a measurement of the doping dependence of the incommensurability in the magnetic field as a smoking-gun experiment that would discriminate between the helicoidal and the stripe scenarios in the spin-glass phase of La(2-x)Sr(x)CuO(4). In Chapter 4, we study the dynamics of topological defects of a frustrated spin system displaying helicoidal order. As a starting point we consider the SO(3) nonlinear sigma model to describe long-wavelength fluctuations around the noncollinear spin state. This model allows for vortex-like topological defects, associated with the change of chirality of the noncollinear state. We consider single vortices and vortex-antivortex pairs, and quantize them using the collective coordinate method, which allows us to represent the defect as a particle coupled to a bath of harmonic oscillators. As a result, the defect motion is damped due to the scattering by the magnons. Finally, motivated by recent experiments, we consider an application of the model for describing the transport in lightly doped La(2-x)Sr(x)CuO(4).

Non-destructive evaluation techniques, high temperature ceramic component parts for gas turbines

NASA Technical Reports Server (NTRS)

Reiter, H.; Hirsekorn, S.; Lottermoser, J.; Goebbels, K.

1984-01-01

This report concerns studies conducted on various tests undertaken on material without destroying the material. Tests included: microradiographic techniques, vibration analysis, high-frequency ultrasonic tests with the addition of evaluation of defects and structure through analysis of ultrasonic scattering data, microwave tests and analysis of sound emission.

Fast Estimation of Defect Profiles from the Magnetic Flux Leakage Signal Based on a Multi-Power Affine Projection Algorithm

PubMed Central

Han, Wenhua; Shen, Xiaohui; Xu, Jun; Wang, Ping; Tian, Guiyun; Wu, Zhengyang

2014-01-01

Magnetic flux leakage (MFL) inspection is one of the most important and sensitive nondestructive testing approaches. For online MFL inspection of a long-range railway track or oil pipeline, a fast and effective defect profile estimating method based on a multi-power affine projection algorithm (MAPA) is proposed, where the depth of a sampling point is related with not only the MFL signals before it, but also the ones after it, and all of the sampling points related to one point appear as serials or multi-power. Defect profile estimation has two steps: regulating a weight vector in an MAPA filter and estimating a defect profile with the MAPA filter. Both simulation and experimental data are used to test the performance of the proposed method. The results demonstrate that the proposed method exhibits high speed while maintaining the estimated profiles clearly close to the desired ones in a noisy environment, thereby meeting the demand of accurate online inspection. PMID:25192314

Fast estimation of defect profiles from the magnetic flux leakage signal based on a multi-power affine projection algorithm.

PubMed

Han, Wenhua; Shen, Xiaohui; Xu, Jun; Wang, Ping; Tian, Guiyun; Wu, Zhengyang

2014-09-04

Magnetic flux leakage (MFL) inspection is one of the most important and sensitive nondestructive testing approaches. For online MFL inspection of a long-range railway track or oil pipeline, a fast and effective defect profile estimating method based on a multi-power affine projection algorithm (MAPA) is proposed, where the depth of a sampling point is related with not only the MFL signals before it, but also the ones after it, and all of the sampling points related to one point appear as serials or multi-power. Defect profile estimation has two steps: regulating a weight vector in an MAPA filter and estimating a defect profile with the MAPA filter. Both simulation and experimental data are used to test the performance of the proposed method. The results demonstrate that the proposed method exhibits high speed while maintaining the estimated profiles clearly close to the desired ones in a noisy environment, thereby meeting the demand of accurate online inspection.

On the Enthalpy and Entropy of Point Defect Formation in Crystals

NASA Astrophysics Data System (ADS)

Kobelev, N. P.; Khonik, V. A.

2018-03-01

A standard way to determine the formation enthalpy H and entropy S of point defect formation in crystals consists in the application of the Arrhenius equation for the defect concentration. In this work, we show that a formal use of this method actually gives the effective (apparent) values of these quantities, which appear to be significantly overestimated. The underlying physical reason lies in temperature-dependent formation enthalpy of the defects, which is controlled by temperature dependence of the elastic moduli. We present an evaluation of the "true" H- and S-values for aluminum, which are derived on the basis of experimental data by taking into account temperature dependence of the formation enthalpy related to temperature dependence of the elastic moduli. The knowledge of the "true" activation parameters is needed for a correct calculation of the defect concentration constituting thus an issue of major importance for different fundamental and application issues of condensed matter physics and chemistry.

Electrically active point defects in Mg implanted n-type GaN grown by metal-organic chemical vapor deposition

NASA Astrophysics Data System (ADS)

Alfieri, G.; Sundaramoorthy, V. K.; Micheletto, R.

2018-05-01

Magnesium (Mg) is the p-type doping of choice for GaN, and selective area doping by ion implantation is a routine technique employed during device processing. While electrically active defects have been thoroughly studied in as-grown GaN, not much is known about defects generated by ion implantation. This is especially true for the case of Mg. In this study, we carried out an electrical characterization investigation of point defects generated by Mg implantation in GaN. We have found at least nine electrically active levels in the 0.2-1.2 eV energy range, below the conduction band. The isochronal annealing behavior of these levels showed that most of them are thermally stable up to 1000 °C. The nature of the detected defects is then discussed in the light of the results found in the literature.

Point defects in hexagonal germanium carbide monolayer: A first-principles calculation

NASA Astrophysics Data System (ADS)

Ersan, Fatih; Gökçe, Aytaç Gürhan; Aktürk, Ethem

2016-12-01

On the basis of first-principles plane-wave calculations, we investigated the electronic and magnetic properties of various point defects including single Ge and C vacancies, Ge + C divacancy, Ge↔C antisites and the Stone-Wales (SW) defects in a GeC monolayer. We found that various periodic vacancy defects in GeC single layer give rise to crucial effects on the electronic and magnetic properties. The band gaps of GeC monolayer vary significantly from 0.308 eV to 1.738 eV due to the presence of antisites and Stone-Wales defects. While nonmagnetic ground state of semiconducting GeC turns into metal by introducing a carbon vacancy, it becomes half-metal by a single Ge vacancy with high magnetization (4 μB) value per supercell. All the vacancy types have zero net magnetic moments, except single Ge vacancy.

Identification of bearing faults using time domain zero-crossings

NASA Astrophysics Data System (ADS)

William, P. E.; Hoffman, M. W.

2011-11-01

In this paper, zero-crossing characteristic features are employed for early detection and identification of single point bearing defects in rotating machinery. As a result of bearing defects, characteristic defect frequencies appear in the machine vibration signal, normally requiring spectral analysis or envelope analysis to identify the defect type. Zero-crossing features are extracted directly from the time domain vibration signal using only the duration between successive zero-crossing intervals and do not require estimation of the rotational frequency. The features are a time domain representation of the composite vibration signature in the spectral domain. Features are normalized by the length of the observation window and classification is performed using a multilayer feedforward neural network. The model was evaluated on vibration data recorded using an accelerometer mounted on an induction motor housing subjected to a number of single point defects with different severity levels.

Dimensional control of defect dynamics in perovskite oxide superlattices

NASA Astrophysics Data System (ADS)

Bredeson, Isaac; Zhang, Lipeng; Kent, P. R. C.; Cooper, Valentino R.; Xu, Haixuan

2018-03-01

Point defects play a critical role in the structural, physical, and interfacial properties of perovskite oxide superlattices. However, understanding of the fundamental properties of point defects in superlattices, especially their transport properties, is rather limited. Here, we report predictions of the stability and dynamics of oxygen vacancies in SrTi O3/PbTi O3 oxide superlattices using first-principles calculations in combination with the kinetic Monte Carlo method. By varying the stacking period, i.e., changing of n in n STO /n PTO , we discover a crossover from three-dimensional diffusion to primarily two-dimensional planar diffusion. Such planar diffusion may lead to novel designs of ionic conductors. We show that the dominant vacancy position may vary in the superlattices, depending on the superlattice structure and stacking period, contradicting the common assumption that point defects reside at interfaces. Moreover, we predict a significant increase in room-temperature ionic conductivity for 3STO/3PTO relative to the bulk phases. Considering the variety of cations that can be accommodated in perovskite superlattices and the potential mismatch of spin, charge, and orbitals at the interfaces, this paper identifies a pathway to control defect dynamics for technological applications.

High Temperature Electronic and Thermal Transport Properties of EuGa2- x In x Sb2

NASA Astrophysics Data System (ADS)

Chanakian, Sevan; Weber, Rochelle; Aydemir, Umut; Ormeci, Alim; Fleurial, Jean-Pierre; Bux, Sabah; Snyder, G. Jeffrey

2017-08-01

The Zintl phase EuGa2Sb2 was synthesized via ball milling followed by hot pressing. The crystal structure of EuGa2Sb2 is comprised of a 3-D network of polyanionic [Ga2Sb2]2- tunnels filled with Eu cations that provide charge balance (Eu2+[Ga2Sb2]2-). Here we report the temperature-dependent resistivity, Hall Effect, Seebeck coefficient and thermal conductivity for EuGa2- x In x Sb2 ( x = 0, 0.05, 0.1) from 300 K to 775 K. Experimental results demonstrate that the material is a p-type semiconductor. However, a small band gap (˜0.1 eV) prevents EuGa2Sb2 from having high zT at higher temperatures. Isoelectronic substitution of In on the Ga site leads to point defect scattering of holes and phonons, thus reducing thermal conductivity and resulting in a slight improvement in zT.

Realizing high figure of merit in heavy-band p-type half-Heusler thermoelectric materials

PubMed Central

Fu, Chenguang; Bai, Shengqiang; Liu, Yintu; Tang, Yunshan; Chen, Lidong; Zhao, Xinbing; Zhu, Tiejun

2015-01-01

Solid-state thermoelectric technology offers a promising solution for converting waste heat to useful electrical power. Both high operating temperature and high figure of merit zT are desirable for high-efficiency thermoelectric power generation. Here we report a high zT of ∼1.5 at 1,200 K for the p-type FeNbSb heavy-band half-Heusler alloys. High content of heavier Hf dopant simultaneously optimizes the electrical power factor and suppresses thermal conductivity. Both the enhanced point-defect and electron–phonon scatterings contribute to a significant reduction in the lattice thermal conductivity. An eight couple prototype thermoelectric module exhibits a high conversion efficiency of 6.2% and a high power density of 2.2 W cm−2 at a temperature difference of 655 K. These findings highlight the optimization strategy for heavy-band thermoelectric materials and demonstrate a realistic prospect of high-temperature thermoelectric modules based on half-Heusler alloys with low cost, excellent mechanical robustness and stability. PMID:26330371

Realizing high figure of merit in heavy-band p-type half-Heusler thermoelectric materials.

PubMed

Fu, Chenguang; Bai, Shengqiang; Liu, Yintu; Tang, Yunshan; Chen, Lidong; Zhao, Xinbing; Zhu, Tiejun

2015-09-02

Solid-state thermoelectric technology offers a promising solution for converting waste heat to useful electrical power. Both high operating temperature and high figure of merit zT are desirable for high-efficiency thermoelectric power generation. Here we report a high zT of ∼1.5 at 1,200 K for the p-type FeNbSb heavy-band half-Heusler alloys. High content of heavier Hf dopant simultaneously optimizes the electrical power factor and suppresses thermal conductivity. Both the enhanced point-defect and electron-phonon scatterings contribute to a significant reduction in the lattice thermal conductivity. An eight couple prototype thermoelectric module exhibits a high conversion efficiency of 6.2% and a high power density of 2.2 W cm(-2) at a temperature difference of 655 K. These findings highlight the optimization strategy for heavy-band thermoelectric materials and demonstrate a realistic prospect of high-temperature thermoelectric modules based on half-Heusler alloys with low cost, excellent mechanical robustness and stability.

IR-LTS a powerful non-invasive tool to observe crystal defects in as-grown silicon, after device processing, and in heteroepitaxial layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kissinger, G.; Richter, H.; Vanhellemont, J.

1996-12-01

One of the main advantages of infrared light scattering tomography (IR-LST) is the wide range of defect densities that can be studied using this technique. As-grown defects of low density and very small size as well as oxygen precipitation related defects that appear in densities up to some 1010 cm{sup -3} can be observed. As-grown wafers with a {open_quotes}stacking fault ring{close_quotes} were investigated in order to correlate the defects observed by IR-LST with the results of Secco etching and alcaline cleaning solution (SC1) treatment revealing flow pattern defects (FPDs) and crystal originated particles (COPs), respectively. These wafers were studied aftermore » a wet oxidation at 1100{degrees}C for 100 min. In processed CZ silicon wafers it was possible to identify stacking faults and prismatic punching systems directly from the IR-LST image. Brewster angle illumination is a special mode to reveal defects in epitaxial layers in a non-destructive way. Misfit dislocations in the interface between a Ge{sub 0.92}Si{sub 0.08} layer and a silicon substrate were studied using this mode that allows to observe very low dislocation densities.« less

Magnetotransport of proton-irradiated BaFe 2As 2 and BaFe 1.985Co 0.015As 2 single crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moseley, D. A.; Yates, K. A.; Peng, N.

2015-02-17

In this paper, we study the magnetotransport properties of the ferropnictide crystals BaFe 2As 2 and BaFe 1.985Co 0.015As 2. These materials exhibit a high field linear magnetoresistance that has been attributed to the quantum linear magnetoresistance model. In this model, the linear magnetoresistance is dependent on the concentration of scattering centers in the material. By using proton-beam irradiation to change the defect scattering density, we find that the dependence of the magnitude of the linear magnetoresistance on scattering quite clearly contravenes this prediction. Finally, a number of other scaling trends in the magnetoresistance and high field Hall data aremore » observed and discussed.« less

Impurity distribution and microstructure of Ga-doped ZnO films grown by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Kvit, A. V.; Yankovich, A. B.; Avrutin, V.; Liu, H.; Izyumskaya, N.; Özgür, Ü.; Morkoç, H.; Voyles, P. M.

2012-12-01

We report microstructural characterization of heavily Ga-doped ZnO (GZO) thin films on GaN and sapphire by aberration-corrected scanning transmission electron microscopy. Growth under oxygen-rich and metal-rich growth conditions leads to changes in the GZO polarity and different extended defects. For GZO layers on sapphire, the primary extended defects are voids, inversion domain boundaries, and low-angle grain boundaries. Ga doping of ZnO grown under metal-rich conditions causes a switch from pure oxygen polarity to mixed oxygen and zinc polarity in small domains. Electron energy loss spectroscopy and energy dispersive spectroscopy spectrum imaging show that Ga is homogeneous, but other residual impurities tend to accumulate at the GZO surface and at extended defects. GZO grown on GaN on c-plane sapphire has Zn polarity and no voids. There are misfit dislocations at the interfaces between GZO and an undoped ZnO buffer layer and at the buffer/GaN interface. Low-angle grain boundaries are the only threading microstructural defects. The potential effects of different extended defects and impurity distributions on free carrier scattering are discussed.

A comparative study of Conroy and Monte Carlo methods applied to multiple quadratures and multiple scattering

NASA Technical Reports Server (NTRS)

Deepak, A.; Fluellen, A.

1978-01-01

An efficient numerical method of multiple quadratures, the Conroy method, is applied to the problem of computing multiple scattering contributions in the radiative transfer through realistic planetary atmospheres. A brief error analysis of the method is given and comparisons are drawn with the more familiar Monte Carlo method. Both methods are stochastic problem-solving models of a physical or mathematical process and utilize the sampling scheme for points distributed over a definite region. In the Monte Carlo scheme the sample points are distributed randomly over the integration region. In the Conroy method, the sample points are distributed systematically, such that the point distribution forms a unique, closed, symmetrical pattern which effectively fills the region of the multidimensional integration. The methods are illustrated by two simple examples: one, of multidimensional integration involving two independent variables, and the other, of computing the second order scattering contribution to the sky radiance.

Combining the 3D model generated from point clouds and thermography to identify the defects presented on the facades of a building

NASA Astrophysics Data System (ADS)

Huang, Yishuo; Chiang, Chih-Hung; Hsu, Keng-Tsang

2018-03-01

Defects presented on the facades of a building do have profound impacts on extending the life cycle of the building. How to identify the defects is a crucial issue; destructive and non-destructive methods are usually employed to identify the defects presented on a building. Destructive methods always cause the permanent damages for the examined objects; on the other hand, non-destructive testing (NDT) methods have been widely applied to detect those defects presented on exterior layers of a building. However, NDT methods cannot provide efficient and reliable information for identifying the defects because of the huge examination areas. Infrared thermography is often applied to quantitative energy performance measurements for building envelopes. Defects on the exterior layer of buildings may be caused by several factors: ventilation losses, conduction losses, thermal bridging, defective services, moisture condensation, moisture ingress, and structure defects. Analyzing the collected thermal images can be quite difficult when the spatial variations of surface temperature are small. In this paper the authors employ image segmentation to cluster those pixels with similar surface temperatures such that the processed thermal images can be composed of limited groups. The surface temperature distribution in each segmented group is homogenous. In doing so, the regional boundaries of the segmented regions can be identified and extracted. A terrestrial laser scanner (TLS) is widely used to collect the point clouds of a building, and those point clouds are applied to reconstruct the 3D model of the building. A mapping model is constructed such that the segmented thermal images can be projected onto the 2D image of the specified 3D building. In this paper, the administrative building in Chaoyang University campus is used as an example. The experimental results not only provide the defect information but also offer their corresponding spatial locations in the 3D model.

Effect of interstitial low level laser therapy on tibial defect

NASA Astrophysics Data System (ADS)

Lee, Sangyeob; Ha, Myungjin; Hwang, Donghyun; Yu, Sungkon; Jang, Seulki; Park, Jihoon; Radfar, Edalat; Kim, Hansung; Jung, Byungjo

2016-03-01

Tibial defect is very common musculoskeletal disorder which makes patient painful and uncomfortable. Many studies about bone regeneration tried to figure out fast bone healing on early phase. It is already known that low level laser therapy (LLLT) is very convenient and good for beginning of bone disorder. However, light scattering and absorption obstruct musculoskeletal therapy which need optimal photon energy delivery. This study has used an interstitial laser probe (ILP) to overcome the limitations of light penetration depth and scattering. Animals (mouse, C57BL/6) were divided into three groups: laser treated test group 1 (660 nm; power 10 mW; total energy 5 J) and test group 2 (660 nm; power 20 mW; total energy 10 J); and untreated control group. All animals were taken surgical operation to make tibial defect on right crest of tibia. The test groups were treated every 48 hours with ILP. Bone volume and X-ray attenuation coefficient were measured on 0, 14th and 28th day with u-CT after treatment and were used to evaluate effect of LLLT. Results show that bone volume of test groups has been improved more than control group. X-ray attenuation coefficients of each groups have slightly different. The results suggest that LLLT combined with ILP may affect on early phase of bone regeneration and may be used in various musculoskeletal disease in deep tissue layer.

Photon migration in non-scattering tissue and the effects on image reconstruction

NASA Astrophysics Data System (ADS)

Dehghani, H.; Delpy, D. T.; Arridge, S. R.

1999-12-01

Photon propagation in tissue can be calculated using the relationship described by the transport equation. For scattering tissue this relationship is often simplified and expressed in terms of the diffusion approximation. This approximation, however, is not valid for non-scattering regions, for example cerebrospinal fluid (CSF) below the skull. This study looks at the effects of a thin clear layer in a simple model representing the head and examines its effect on image reconstruction. Specifically, boundary photon intensities (total number of photons exiting at a point on the boundary due to a source input at another point on the boundary) are calculated using the transport equation and compared with data calculated using the diffusion approximation for both non-scattering and scattering regions. The effect of non-scattering regions on the calculated boundary photon intensities is presented together with the advantages and restrictions of the transport code used. Reconstructed images are then presented where the forward problem is solved using the transport equation for a simple two-dimensional system containing a non-scattering ring and the inverse problem is solved using the diffusion approximation to the transport equation.

Quantification of Valleys of Randomly Textured Substrates as a Function of Opening Angle: Correlation to the Defect Density in Intrinsic nc-Si:H.

PubMed

Kim, Do Yun; Hänni, Simon; Schüttauf, Jan-Willem; van Swaaij, René A C M M; Zeman, Miro

2016-08-17

Optical and electrical properties of hydrogenated nanocrystalline silicon (nc-Si:H) solar cells are strongly influenced by the morphology of underlying substrates. By texturing the substrates, the photogenerated current of nc-Si:H solar cells can increase due to enhanced light scattering. These textured substrates are, however, often incompatible with defect-less nc-Si:H growth resulting in lower Voc and FF. In this study we investigate the correlation between the substrate morphology, the nc-Si:H solar-cell performance, and the defect density in the intrinsic layer of the solar cells (i-nc-Si:H). Statistical surface parameters representing the substrate morphology do not show a strong correlation with the solar-cell parameters. Thus, we first quantify the line density of potentially defective valleys of randomly textured ZnO substrates where the opening angle is smaller than 130° (ρ<130). This ρ<130 is subsequently compared with the solar-cell performance and the defect density of i-nc-Si:H (ρdefect), which is obtained by fitting external photovoltaic parameters from experimental results and simulations. We confirm that when ρ<130 increases the Voc and FF significantly drops. It is also observed that ρdefect increases following a power law dependence of ρ<130. This result is attributed to more frequently formed defective regions for substrates having higher ρ<130.

Data mining graphene: Correlative analysis of structure and electronic degrees of freedom in graphenic monolayers with defects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ziatdinov, Maxim A.; Fujii, Shintaro; Kiguchi, Manabu

The link between changes in the material crystal structure and its mechanical, electronic, magnetic, and optical functionalities known as the structure-property relationship is the cornerstone of the contemporary materials science research. The recent advances in scanning transmission electron and scanning probe microscopies (STEM and SPM) have opened an unprecedented path towards examining the materials structure property relationships on the single-impurity and atomic-configuration levels. Lacking, however, are the statistics-based approaches for cross-correlation of structure and property variables obtained in different information channels of the STEM and SPM experiments. Here we have designed an approach based on a combination of sliding windowmore » Fast Fourier Transform, Pearson correlation matrix, linear and kernel canonical correlation, to study a relationship between lattice distortions and electron scattering from the SPM data on graphene with defects. Our analysis revealed that the strength of coupling to strain is altered between different scattering channels which can explain coexistence of several quasiparticle interference patterns in the nanoscale regions of interest. In addition, the application of the kernel functions allowed us extracting a non-linear component of the relationship between the lattice strain and scattering intensity in graphene. Lastly, the outlined approach can be further utilized to analyzing correlations in various multi-modal imaging techniques where the information of interest is spatially distributed and has usually a complex multidimensional nature.« less

Data mining graphene: Correlative analysis of structure and electronic degrees of freedom in graphenic monolayers with defects

DOE PAGES

Ziatdinov, Maxim A.; Fujii, Shintaro; Kiguchi, Manabu; ...

2016-11-09

The link between changes in the material crystal structure and its mechanical, electronic, magnetic, and optical functionalities known as the structure-property relationship is the cornerstone of the contemporary materials science research. The recent advances in scanning transmission electron and scanning probe microscopies (STEM and SPM) have opened an unprecedented path towards examining the materials structure property relationships on the single-impurity and atomic-configuration levels. Lacking, however, are the statistics-based approaches for cross-correlation of structure and property variables obtained in different information channels of the STEM and SPM experiments. Here we have designed an approach based on a combination of sliding windowmore » Fast Fourier Transform, Pearson correlation matrix, linear and kernel canonical correlation, to study a relationship between lattice distortions and electron scattering from the SPM data on graphene with defects. Our analysis revealed that the strength of coupling to strain is altered between different scattering channels which can explain coexistence of several quasiparticle interference patterns in the nanoscale regions of interest. In addition, the application of the kernel functions allowed us extracting a non-linear component of the relationship between the lattice strain and scattering intensity in graphene. Lastly, the outlined approach can be further utilized to analyzing correlations in various multi-modal imaging techniques where the information of interest is spatially distributed and has usually a complex multidimensional nature.« less

Gamma-rays and heat-treatment conversions of point defects in massive rose quartz from the Borborema Pegmatite Province, Northeast Brazil

NASA Astrophysics Data System (ADS)

Guzzo, Pedro L.; Barreto, Sandra B.; Miranda, Milena R.; Gonzaga, Raysa S. G.; Casals, Sandra A.

2017-11-01

An extensive characterization of trace elements and point defects in rose quartz from the Borborema Pegmatite Province (BPP) in the northeast of Brazil was carried out by complementary spectroscopic methods. The aim here was to document the change in the configuration of point defects into the quartz lattice induced by heat-treatment and ionizing radiation. The samples were extracted from the core of two granitic rare element (REL) pegmatites, Taboa (Carnaúba dos Dantas, RN) and Alto do Feio (Pedra Lavrada, PB). The contents of Al, P, Ti, Ni, Fe, Ge, Li, Be, B and K were measured by laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Polished plates were heat-treated at 500 and 1000 °C and then irradiated with 50 kGy of γ rays. Point defects were characterized by optical (UV-Vis), infrared (IR), and electron paramagnetic resonance (EPR) spectroscopies. In the as-received condition, [AlO4/H]0 centers, Li- and B-dependent OH defects were observed. Point defects related to Al and Li species were significantly affected by heat-treatment at 1000 °C and/or γ radiation. Paramagnetic centers such as [AlO4]0, [GeO4/Li]0, [TiO4/Li]0 and [O2 3-/Li]0 were created by the diffusion of Li+ ions from their original diamagnetic centers related to substitutional Al3+ and OH-species. The smoky color developed after irradiation and the signal intensities of the paramagnetic centers were independent from the original rose color grade. The samples from the Taboa (TB) pegmatite showed the highest concentration of Al, Ti, Fe and Li elements as well as the highest signal intensities for [AlO4]0, [AlO4/H]0, [GeO4/Li]0 and [TiO4/Li]0 centers. Although TB also showed the higher concentration of B element, the intensity of the 3597 cm-1 IR band related to [BO4/H]0 centers was higher for Alto do Feio (AF) samples. This result suggests that the uptake of B into the quartz core of each pegmatite took place through different mechanisms. It was concluded that the change in the point defect configuration was essentially governed by the motion of Li species whose incorporation into the quartz lattice is closely related to Al concentration.

Chondral defect repair after the microfracture procedure: a nonhuman primate model.

PubMed

Gill, Thomas J; McCulloch, Patrick C; Glasson, Sonya S; Blanchet, Tracey; Morris, Elizabeth A

2005-05-01

The extent and time course of chondral defect healing after microfracture in humans are not well described. Although most physicians recommend a period of activity and weightbearing restriction to protect the healing cartilage, there are limited data on which to base decisions regarding the duration of such restrictions. Evaluation of the status of chondral defect repair at different time points after microfracture in a primate model may provide a rationale for postoperative activity recommendations. Descriptive laboratory study. Full-thickness chondral defects created on the femoral condyles and trochlea of 12 cynomolgus macaques were treated with microfracture and evaluated by gross and histologic examination at 6 and 12 weeks. At 6 weeks, there was limited chondral repair and ongoing resorption of subchondral bone. By 12 weeks, the defects were completely filled and showed more mature cartilage and bone repair. In the primate animal model, significant improvements in the extent and quality of cartilage repair were observed from the 6- to 12-week time points after microfracture. The poor status of the defect repair at 6 weeks and the ongoing healing observed from the 6- to 12-week time points may indicate that the repair is vulnerable during this initial postoperative period. Assuming the goal of postoperative weightbearing and activity restriction in patients after microfracture is to protect immature repair tissue, this study lends support to extending such recommendations longer than 6 weeks.

Quasiparticle interference in ZrSiS: Strongly band-selective scattering depending on impurity lattice site

NASA Astrophysics Data System (ADS)

Butler, Christopher J.; Wu, Yu-Mi; Hsing, Cheng-Rong; Tseng, Yi; Sankar, Raman; Wei, Ching-Ming; Chou, Fang-Cheng; Lin, Minn-Tsong

2017-11-01

Scanning tunneling microscopy visualizations of quasiparticle interference (QPI) enable powerful insights into the k -space properties of superconducting, topological, Rashba, and other exotic electronic phases, but their reliance on impurities acting as scattering centers is rarely scrutinized. Here, we investigate QPI at the vacuum-cleaved (001) surface of the Dirac semimetal ZrSiS. We find that interference patterns around impurities located on the Zr and S lattice sites appear very different, and can be ascribed to selective scattering of different subsets of the predominantly Zr 4 d -derived band structure, namely, the m =0 and ±1 components. We show that the selectivity of scattering channels requires an explanation beyond the different bands' orbital characteristics and their respective charge density distributions over Zr and S lattice sites. Importantly, this result shows that the usual assumption of generic scattering centers allowing observations of quasiparticle interference to shed light indiscriminately and isotropically upon the q space of scattering events does not hold, and that the scope and interpretation of QPI observations can therefore be be strongly contingent on the material defect chemistry. This finding promises to spur new investigations into the quasiparticle scattering process itself, to inform future interpretations of quasiparticle interference observations, and ultimately to aid the understanding and engineering of quantum electronic transport properties.

Holographic corrections to meson scattering amplitudes

NASA Astrophysics Data System (ADS)

Armoni, Adi; Ireson, Edwin

2017-06-01

We compute meson scattering amplitudes using the holographic duality between confining gauge theories and string theory, in order to consider holographic corrections to the Veneziano amplitude and associated higher-point functions. The generic nature of such computations is explained, thanks to the well-understood nature of confining string backgrounds, and two different examples of the calculation in given backgrounds are used to illustrate the details. The effect we discover, whilst only qualitative, is re-obtainable in many such examples, in four-point but also higher point amplitudes.

Structures and interactions among globular proteins above the isoelectric point in the presence of divalent ions: A small angle neutron scattering and dynamic light scattering study

NASA Astrophysics Data System (ADS)

Kundu, Sarathi; Pandit, Subhankar; Abbas, Sohrab; Aswal, V. K.; Kohlbrecher, J.

2018-02-01

Small angle neutron scattering study reveals that at pD ≈ 7.0, above the isoelectric point of the globular protein Bovine Serum Albumin (BSA), in the presence of different divalent ions (Mg2+, Ca2+, Sr2+ and Ba2+), the short-range attractive interaction remains nearly constant and the intermediate-range repulsive interaction decreases with increasing salt concentration up to a certain concentration value but after that remains unchanged. However, for the monovalent ion (Na+), repulsive interaction decreases gradually up to 1 M salt concentration. Dynamic light scattering study shows that for all ions, diffusion coefficient of BSA decreases with increasing salt concentration and then nearly saturates.

Photoluminescence as a tool for characterizing point defects in semiconductors

NASA Astrophysics Data System (ADS)

Reshchikov, Michael

2012-02-01

Photoluminescence is one of the most powerful tools used to study optically-active point defects in semiconductors, especially in wide-bandgap materials. Gallium nitride (GaN) and zinc oxide (ZnO) have attracted considerable attention in the last two decades due to their prospects in optoelectronics applications, including blue and ultraviolet light-emitting devices. However, in spite of many years of extensive studies and a great number of publications on photoluminescence from GaN and ZnO, only a few defect-related luminescence bands are reliably identified. Among them are the Zn-related blue band in GaN, Cu-related green band and Li-related orange band in ZnO. Numerous suggestions for the identification of other luminescence bands, such as the yellow band in GaN, or green and yellow bands in ZnO, do not stand up under scrutiny. In these conditions, it is important to classify the defect-related luminescence bands and find their unique characteristics. In this presentation, we will review the origin of the major luminescence bands in GaN and ZnO. Through simulations of the temperature and excitation intensity dependences of photoluminescence and by employing phenomenological models we are able to obtain important characteristics of point defects such as carrier capture cross-sections for defects, concentrations of defects, and their charge states. These models are also used to find the absolute internal quantum efficiency of photoluminescence and obtain information about nonradiative defects. Results from photoluminescence measurements will be compared with results of the first-principle calculations, as well as with the experimental data obtained by other techniques such as positron annihilation spectroscopy, deep-level transient spectroscopy, and secondary ion mass spectrometry.

The evolution of interaction between grain boundary and irradiation-induced point defects: Symmetric tilt GB in tungsten

NASA Astrophysics Data System (ADS)

Li, Hong; Qin, Yuan; Yang, Yingying; Yao, Man; Wang, Xudong; Xu, Haixuan; Phillpot, Simon R.

2018-03-01

Molecular dynamics method is used and scheme of calculational tests is designed. The atomic evolution view of the interaction between grain boundary (GB) and irradiation-induced point defects is given in six symmetric tilt GB structures of bcc tungsten with the energy of the primary knock-on atom (PKA) EPKA of 3 and 5 keV and the simulated temperature of 300 K. During the collision cascade with GB structure there are synergistic mechanisms to reduce the number of point defects: one is vacancies recombine with interstitials, and another is interstitials diffuse towards the GB with vacancies almost not move. The larger the ratio of the peak defect zone of the cascades overlaps with the GB region, the statistically relative smaller the number of surviving point defects in the grain interior (GI); and when the two almost do not overlap, vacancy-intensive area generally exists nearby GBs, and has a tendency to move toward GB with the increase of EPKA. In contrast, the distribution of interstitials is relatively uniform nearby GBs and is affected by the EPKA far less than the vacancy. The GB has a bias-absorption effect on the interstitials compared with vacancies. It shows that the number of surviving vacancies statistically has increasing trend with the increase of the distance between PKA and GB. While the number of surviving interstitials does not change much, and is less than the number of interstitials in the single crystal at the same conditions. The number of surviving vacancies in the GI is always larger than that of interstitials. The GB local extension after irradiation is observed for which the interstitials absorbed by the GB may be responsible. The designed scheme of calculational tests in the paper is completely applicable to the investigation of the interaction between other types of GBs and irradiation-induced point defects.

Core-level photoabsorption study of defects and metastable bonding configurations in boron nitride

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jimenez, I.; Jankowski, A.F.; Terminello, L.J.

1997-04-01

Boron nitride is an interesting material for technological applications and for fundamental solid state physics investigations. It is a compound isoelectronic with carbon and, like carbon can possess sp{sup 2} and sp{sup 3} bonded phases resembling graphite and diamond. BN crystallizes in the sp{sup 2}-bonded hexagonal (h-BN), rhombohedral (r-BN) and turbostratic phases, and in the sp{sup 3}-bonded cubic (c-BN) and wurtzite (w-BN) phases. A new family of materials is obtained when replacing C-C pairs in graphite with isoelectronic B-N pairs, resulting in C{sub 2}BN compounds. Regarding other boron compounds, BN is exceptional in the sense that it has standard two-centermore » bonds with conventional coordination numbers, while other boron compounds (e.g. B{sub 4}C) are based on the boron icosahedron unit with three-center bonds and high coordination numbers. The existence of several allotropic forms and fullerene-like structures for BN suggests a rich variety of local bonding and poses the questions of how this affects the local electronic structure and how the material accommodates the stress induced in the transition regions between different phases. One would expect point defects to play a crucial role in stress accommodation, but these must also have a strong influence in the electronic structure, since the B-N bond is polar and a point defect will thus be a charged structure. The study of point defects in relationship to the electronic structure is of fundamental interest in these materials. Recently, the authors have shown that Near-Edge X-ray Absorption Fine Structure (NEXAFS) is sensitive to point defects in h-BN, and to the formation of metastable phases even in amorphous materials. This is significant since other phase identification techniques like vibrational spectroscopies or x-ray diffraction yield ambiguous results for nanocrystalline and amorphous samples. Serendipitously, NEXAFS also combines chemical selectivity with point defect sensitivity.« less

Study of coherent reflectometer for imaging internal structures of highly scattering media

NASA Astrophysics Data System (ADS)

Poupardin, Mathieu; Dolfi, Agnes

1996-01-01

Optical reflectometers are potentially useful tools for imaging internal structures of turbid media, particularly of biological media. To get a point by point image, an active imaging system has to distinguish light scattered from a sample volume and light scattered by other locations in the media. Operating this discrimination of light with reflectometers based on coherence can be realized in two ways: assuring a geometric selection or a temporal selection. In this paper we present both methods, showing in each case the influence of the different parameters on the size of the sample volume under the assumption of single scattering. We also study the influence on the detection efficiency of the coherence loss of the incident light resulting from multiple scattering. We adapt a model, first developed for atmospheric lidar in turbulent atmosphere, to get an analytical expression of this detection efficiency in the function of the optical coefficients of the media.

Elastic scattering and soft diffraction with ALFA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Puzo, P.

The ALFA detector in ATLAS aims at measuring the absolute luminosity and the total cross-section with 2-3% accuracy. Its uses elastically scattered protons whose impact position on a fiber detector, located 240 m away from the interaction point, allow a measurement of the scattering angle.

Point Defects in Oxides: Tailoring Materials Through Defect Engineering

NASA Astrophysics Data System (ADS)

Tuller, Harry L.; Bishop, Sean R.

2011-08-01

Optimization of electrical, optical, mechanical, and other properties of many advanced, functional materials today relies on precise control of point defects. This article illustrates the progress that has been made in elucidating the often complex equilibria exhibited by many materials by examining two recently well-characterized model systems, TlBr for radiation detection and PrxCe1-xO2-δ, of potential interest in solid-oxide fuel cells. The interplay between material composition, electrical conductivity, and mechanical properties (electrochemomechanics) is discussed, and implications in these relations, for example, enhancing electrical properties through large mechanical strains, are described. The impact of space charge and strain fields at interfaces, particularly important in nanostructure materials, is also emphasized. Key experimental techniques useful in characterizing bulk and surface defects are summarized and reviewed.

Scattering of Lamb waves by cracks in a composite graphite fiber-reinforced epoxy plate

NASA Technical Reports Server (NTRS)

Bratton, Robert; Datta, Subhendu K.; Shah, Arvind

1990-01-01

Recent investigations of space construction techniques have explored the used of composite materials in the construction of space stations and platforms. These composites offer superior strength to weight ratio and are thermally stable. For example, a composite material being considered is laminates of graphite fibers in an epoxy matrix. The overall effective elastic constants of such a medium can be calculated from fiber and matrix properties by using an effective modulus theory as shown in Datta, el. al. The investigation of propagation and scattering of elastic waves in composite materials is necessary in order to develop an ability to characterize cracks and predict the reliability of composite structures. The objective of this investigation is the characterization of a surface breaking crack by ultrasonic techniques. In particular, the use of Lamb waves for this purpose is studied here. The Lamb waves travel through the plate, encountering a crack, and scatter. Of interest is the modeling of the scattered wave in terms of the Lamb wave modes. The direct problem of propagation and scattering of Lamb waves by a surface breaking crack has been analyzed. This would permit an experimentalist to characterize the crack by comparing the measured response to the analytical model. The plate is assumed to be infinite in the x and y directions with a constant thickness in the z direction. The top and bottom surfaces are traction free. Solving the governing wave equations and using the stress-free boundary conditions results in the dispersion equation. This equation yields the guided modes in the homogeneous plate. The theoretical model is a hybrid method that combines analytical and finite elements techniques to describe the scattered displacements. A finite region containing the defects is discretized by finite elements. Outside the local region, the far field solution is expressed as a Fourier summation of the guided modes obtained from the dispersion equation. Continuity of tractions and displacements at the boundaries of the two regions provides the necessary equations to determine the expansion coefficients and the nodal displacements. In the hybrid method used here these defects can be of arbitrary shapes as well as inclusions of different materials.

Point defects in ZnO: an approach from first principles

PubMed Central

Oba, Fumiyasu; Choi, Minseok; Togo, Atsushi; Tanaka, Isao

2011-01-01

Recent first-principles studies of point defects in ZnO are reviewed with a focus on native defects. Key properties of defects, such as formation energies, donor and acceptor levels, optical transition energies, migration energies and atomic and electronic structure, have been evaluated using various approaches including the local density approximation (LDA) and generalized gradient approximation (GGA) to DFT, LDA+U/GGA+U, hybrid Hartree–Fock density functionals, sX and GW approximation. Results significantly depend on the approximation to exchange correlation, the simulation models for defects and the post-processes to correct shortcomings of the approximation and models. The choice of a proper approach is, therefore, crucial for reliable theoretical predictions. First-principles studies have provided an insight into the energetics and atomic and electronic structures of native point defects and impurities and defect-induced properties of ZnO. Native defects that are relevant to the n-type conductivity and the non-stoichiometry toward the O-deficient side in reduced ZnO have been debated. It is suggested that the O vacancy is responsible for the non-stoichiometry because of its low formation energy under O-poor chemical potential conditions. However, the O vacancy is a very deep donor and cannot be a major source of carrier electrons. The Zn interstitial and anti-site are shallow donors, but these defects are unlikely to form at a high concentration in n-type ZnO under thermal equilibrium. Therefore, the n-type conductivity is attributed to other sources such as residual impurities including H impurities with several atomic configurations, a metastable shallow donor state of the O vacancy, and defect complexes involving the Zn interstitial. Among the native acceptor-type defects, the Zn vacancy is dominant. It is a deep acceptor and cannot produce a high concentration of holes. The O interstitial and anti-site are high in formation energy and/or are electrically inactive and, hence, are unlikely to play essential roles in electrical properties. Overall defect energetics suggests a preference for the native donor-type defects over acceptor-type defects in ZnO. The O vacancy, Zn interstitial and Zn anti-site have very low formation energies when the Fermi level is low. Therefore, these defects are expected to be sources of a strong hole compensation in p-type ZnO. For the n-type doping, the compensation of carrier electrons by the native acceptor-type defects can be mostly suppressed when O-poor chemical potential conditions, i.e. low O partial pressure conditions, are chosen during crystal growth and/or doping. PMID:27877390

Elastic constant and Brillouin oscillations in sputtered vitreous SiO2 thin films

NASA Astrophysics Data System (ADS)

Ogi, H.; Shagawa, T.; Nakamura, N.; Hirao, M.; Odaka, H.; Kihara, N.

2008-10-01

We studied the relationship between elastic constants and microstructure in sputtered vitreous SiO2 thin films using pump-probe picosecond laser ultrasound. The delayed probe light pulse is diffracted by the acoustic wave excited by the pump light pulse, inducing Brillouin oscillations, seen as reflectivity change in the probe pulse, whose frequency can be used to extract the sound velocity and elastic moduli. Theoretical calculations were made to explain the asymmetric response of Brillouin oscillations and to predict the possible error limit of the determined elastic constants. The thin films containing defects exhibited lower elastic constant. A micromechanics modeling was developed to evaluate defect porosity and attenuation caused by scattering was able to predict the defect size. Elastic moduli of the defect-free specimens increased with increasing sputtering power, eventually exceeding the bulk value, and correlated with phonon frequencies, indicating that the decrease in the Si-O-Si bond angle of the tetrahedral structure increased the stiffness.

Monte Carlo Computational Modeling of the Energy Dependence of Atomic Oxygen Undercutting of Protected Polymers

NASA Technical Reports Server (NTRS)

Banks, Bruce A.; Stueber, Thomas J.; Norris, Mary Jo

1998-01-01

A Monte Carlo computational model has been developed which simulates atomic oxygen attack of protected polymers at defect sites in the protective coatings. The parameters defining how atomic oxygen interacts with polymers and protective coatings as well as the scattering processes which occur have been optimized to replicate experimental results observed from protected polyimide Kapton on the Long Duration Exposure Facility (LDEF) mission. Computational prediction of atomic oxygen undercutting at defect sites in protective coatings for various arrival energies was investigated. The atomic oxygen undercutting energy dependence predictions enable one to predict mass loss that would occur in low Earth orbit, based on lower energy ground laboratory atomic oxygen beam systems. Results of computational model prediction of undercut cavity size as a function of energy and defect size will be presented to provide insight into expected in-space mass loss of protected polymers with protective coating defects based on lower energy ground laboratory testing.

Thermoelectric phonon-glass electron-crystal via ion beam patterning of silicon

NASA Astrophysics Data System (ADS)

Zhu, Taishan; Swaminathan-Gopalan, Krishnan; Stephani, Kelly; Ertekin, Elif

2018-05-01

Ion beam irradiation has recently emerged as a versatile approach to functional materials design. We show in this work that patterned defective regions generated by ion beam irradiation of silicon can create a phonon-glass electron-crystal (PGEC), a long-standing goal of thermoelectrics. By controlling the effective diameter of and spacing between the defective regions, molecular dynamics simulations suggest a reduction of the thermal conductivity by a factor of ˜20 is achievable. Boltzmann theory shows that the thermoelectric power factor remains largely intact in the damaged material. To facilitate the Boltzmann theory, we derive an analytical model for electron scattering with cylindrical defective regions based on partial-wave analysis. Together we predict a figure of merit of Z T ≈0.5 or more at room temperature for optimally patterned geometries of these silicon metamaterials. These findings indicate that nanostructuring of patterned defective regions in crystalline materials is a viable approach to realize a PGEC, and ion beam irradiation could be a promising fabrication strategy.

Defect interactions with stepped CeO₂/SrTiO₃ interfaces: implications for radiation damage evolution and fast ion conduction.

PubMed

Dholabhai, Pratik P; Aguiar, Jeffery A; Misra, Amit; Uberuaga, Blas P

2014-05-21

Due to reduced dimensions and increased interfacial content, nanocomposite oxides offer improved functionalities in a wide variety of advanced technological applications, including their potential use as radiation tolerant materials. To better understand the role of interface structures in influencing the radiation damage tolerance of oxides, we have conducted atomistic calculations to elucidate the behavior of radiation-induced point defects (vacancies and interstitials) at interface steps in a model CeO2/SrTiO3 system. We find that atomic-scale steps at the interface have substantial influence on the defect behavior, which ultimately dictate the material performance in hostile irradiation environments. Distinctive steps react dissimilarly to cation and anion defects, effectively becoming biased sinks for different types of defects. Steps also attract cation interstitials, leaving behind an excess of immobile vacancies. Further, defects introduce significant structural and chemical distortions primarily at the steps. These two factors are plausible origins for the enhanced amorphization at steps seen in our recent experiments. The present work indicates that comprehensive examination of the interaction of radiation-induced point defects with the atomic-scale topology and defect structure of heterointerfaces is essential to evaluate the radiation tolerance of nanocomposites. Finally, our results have implications for other applications, such as fast ion conduction.

Point-Defect Nature of the Ultraviolet Absorption Band in AlN

NASA Astrophysics Data System (ADS)

Alden, D.; Harris, J. S.; Bryan, Z.; Baker, J. N.; Reddy, P.; Mita, S.; Callsen, G.; Hoffmann, A.; Irving, D. L.; Collazo, R.; Sitar, Z.

2018-05-01

We present an approach where point defects and defect complexes are identified using power-dependent photoluminescence excitation spectroscopy, impurity data from SIMS, and density-functional-theory (DFT)-based calculations accounting for the total charge balance in the crystal. Employing the capabilities of such an experimental computational approach, in this work, the ultraviolet-C absorption band at 4.7 eV, as well as the 2.7- and 3.9-eV luminescence bands in AlN single crystals grown via physical vapor transport (PVT) are studied in detail. Photoluminescence excitation spectroscopy measurements demonstrate the relationship between the defect luminescent bands centered at 3.9 and 2.7 eV to the commonly observed absorption band centered at 4.7 eV. Accordingly, the thermodynamic transition energy for the absorption band at 4.7 eV and the luminescence band at 3.9 eV is estimated at 4.2 eV, in agreement with the thermodynamic transition energy for the CN- point defect. Finally, the 2.7-eV PL band is the result of a donor-acceptor pair transition between the VN and CN point defects since nitrogen vacancies are predicted to be present in the crystal in concentrations similar to carbon-employing charge-balance-constrained DFT calculations. Power-dependent photoluminescence measurements reveal the presence of the deep donor state with a thermodynamic transition energy of 5.0 eV, which we hypothesize to be nitrogen vacancies in agreement with predictions based on theory. The charge state, concentration, and type of impurities in the crystal are calculated considering a fixed amount of impurities and using a DFT-based defect solver, which considers their respective formation energies and the total charge balance in the crystal. The presented results show that nitrogen vacancies are the most likely candidate for the deep donor state involved in the donor-acceptor pair transition with peak emission at 2.7 eV for the conditions relevant to PVT growth.

Evolution of displacement cascades in Fe-Cr structures with different [001] tilt grain boundaries

NASA Astrophysics Data System (ADS)

Abu-Shams, M.; Haider, W.; Shabib, I.

2017-06-01

Reduced-activation ferritic/martensitic steels of Cr concentration between 2.25 and 12 wt% are candidate structural materials for next-generation nuclear reactors. In this study, molecular dynamics (MD) simulation is used to generate the displacement cascades in Fe-Cr structures with different Cr concentrations by using different primary knock-on atom (PKA) energies between 2 and 10 keV. A concentration-dependent model potential has been used to describe the interactions between Fe and Cr. Single crystals (SCs) of three different coordinate bases (e.g. [310], [510], and [530]) and bi-crystal (BC) structures with three different [001] tilt grain boundaries (GBs) (e.g. Σ5, Σ13, and Σ17) have been simulated. The Wigner-Seitz cell criterion has been used to identify the produced Frenkel pairs. The results show a marked difference between collisions observed in SCs and those in BC structures. The numbers of vacancies and interstitials are found to be significantly higher in BC structures than those found in SCs. The number of point defects exhibits a power relationship with the PKA energies; however, the Cr concentration does not seem to have any influence on the number of survived point defects. In BC models, a large fraction of the total survived point defects (between 59% and 93%) tends accumulate at the GBs, which seem to trap the generated point defects. The BC structure with Σ17 GB is found to trap more defects than Σ5 and Σ13 GBs. The defect trapping is found to be dictated by the crystallographic parameters of the GBs. For all studied GBs, self-interstitial atoms (SIAs) are easily trapped within the GB region than vacancies. An analysis of defect composition reveals an enrichment of Cr in SIAs, and in BC cases, more than half of the Cr-SIAs are found to be located within the GB region.

Energy-loss spectrum for inelastic scattering of charged particles in disordered systems near the critical point

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerasimov, O. I.; Adamian, V. M.

The behavior of the theoretically predicted correlational ''fine''energy-loss spectrum of inelastic electron scattering in disordered systemsclose to single resonance is investigated near the critical point. In extendingour earlier work, it is shown that the relation of the statistical expressionof the cross section of energy loss to the function which describes the lineshape in an ideal gas asymptotically increases near the critical point as apower law. ''Fracton'' interpretation of display of the localization of asingle excitation in disordered systems in the resonance-line shape of theenergy-loss spectrum is suggested. The possibility of direct determination ofthe pair distribution function (without Fourier transformation ofmore » the structurefactor) using the method of charged-particle scattering is discussed.« less

Brillouin-scattering studies of K2Si4O9 glass and melt up to 1000 °C

NASA Astrophysics Data System (ADS)

Xu, Ji-An; Manghnani, Murli H.; Richet, Pascal

1992-10-01

The Brillouin-scattering technique has been used with glass plate samples and with glass sandwich assemblies to measure the acoustic velocities of K2Si4O9 glass as a function of temperature up to 1000 °C. Results differ from those of the sodium silicate glass reported earlier in that the turning points of the velocity versus temperature curves for the potassium silicate glass are found not only at the strain point (466 °C) but also at the softening point (720 °C). Combined with the results of the 90° platelet- and 180° back-scattering geometry measurements, the refractive index n and equation of state of the glass and melt as a function of temperature were also determined.

Point Defects and Grain Boundaries in Rotationally Commensurate MoS 2 on Epitaxial Graphene

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Xiaolong; Balla, Itamar; Bergeron, Hadallia

2016-03-28

With reduced degrees of freedom, structural defects are expected to play a greater role in two-dimensional materials in comparison to their bulk counterparts. In particular, mechanical strength, electronic properties, and chemical reactivity are strongly affected by crystal imperfections in the atomically thin limit. Here, ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) and spectroscopy (STS) are employed to interrogate point and line defects in monolayer MoS2 grown on epitaxial graphene (EG) at the atomic scale. Five types of point defects are observed with the majority species showing apparent structures that are consistent with vacancy and interstitial models. The total defect densitymore » is observed to be lower than MoS2 grown on other substrates and is likely attributed to the van der Waals epitaxy of MoS2 on EG. Grain boundaries (GBs) with 30° and 60° tilt angles resulting from the rotational commensurability of MoS2 on EG are more easily resolved by STM than atomic force microscopy at similar scales due to the enhanced contrast from their distinct electronic states. For example, band gap reduction to ~0.8 and ~0.5 eV is observed with STS for 30° and 60° GBs, respectively. In addition, atomic resolution STM images of these GBs are found to agree well with proposed structure models. This work offers quantitative insight into the structure and properties of common defects in MoS2 and suggests pathways for tailoring the performance of MoS2/graphene heterostructures via defect engineering.« less

High-energy photon-hadron scattering in holographic QCD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishio, Ryoichi; Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwano-ha 5-1-5, 277-8583; Watari, Taizan

2011-10-01

This article provides an in-depth look at hadron high-energy scattering by using gravity dual descriptions of strongly coupled gauge theories. Just like deeply inelastic scattering (DIS) and deeply virtual Compton scattering (DVCS) serve as clean experimental probes into nonperturbative internal structure of hadrons, elastic scattering amplitude of a hadron and a (virtual) photon in gravity dual can be exploited as a theoretical probe. Since the scattering amplitude at sufficiently high energy (small Bjorken x) is dominated by parton contributions (=Pomeron contributions) even in strong coupling regime, there is a chance to learn a lesson for generalized parton distribution (GPD) bymore » using gravity dual models. We begin with refining derivation of the Brower-Polchinski-Strassler-Tan (BPST) Pomeron kernel in gravity dual, paying particular attention to the role played by the complex spin variable j. The BPST Pomeron on warped spacetime consists of a Kaluza-Klein tower of 4D Pomerons with nonlinear trajectories, and we clarify the relation between Pomeron couplings and the Pomeron form factor. We emphasize that the saddle-point value j* of the scattering amplitude in the complex j-plane representation is a very important concept in understanding qualitative behavior of the scattering amplitude. The total Pomeron contribution to the scattering is decomposed into the saddle-point contribution and at most a finite number of pole contributions, and when the pole contributions are absent (which we call saddle-point phase), kinematical variable (q,x,t)-dependence of ln(1/q) evolution and ln(1/x) evolution parameters {gamma}{sub eff} and {lambda}{sub eff} in DIS and t-slope parameter B of DVCS in HERA experiment are all reproduced qualitatively in gravity dual. All of these observations shed a new light on modeling of GPD. Straightforward application of those results to other hadron high-energy scattering is also discussed.« less

Effect of time-of-flight and point spread function modeling on detectability of myocardial defects in PET

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schaefferkoetter, Joshua, E-mail: dnrjds@nus.edu.sg; Ouyang, Jinsong; Rakvongthai, Yothin

2014-06-15

Purpose: A study was designed to investigate the impact of time-of-flight (TOF) and point spread function (PSF) modeling on the detectability of myocardial defects. Methods: Clinical FDG-PET data were used to generate populations of defect-present and defect-absent images. Defects were incorporated at three contrast levels, and images were reconstructed by ordered subset expectation maximization (OSEM) iterative methods including ordinary Poisson, alone and with PSF, TOF, and PSF+TOF. Channelized Hotelling observer signal-to-noise ratio (SNR) was the surrogate for human observer performance. Results: For three iterations, 12 subsets, and no postreconstruction smoothing, TOF improved overall defect detection SNR by 8.6% as comparedmore » to its non-TOF counterpart for all the defect contrasts. Due to the slow convergence of PSF reconstruction, PSF yielded 4.4% less SNR than non-PSF. For reconstruction parameters (iteration number and postreconstruction smoothing kernel size) optimizing observer SNR, PSF showed larger improvement for faint defects. The combination of TOF and PSF improved mean detection SNR as compared to non-TOF and non-PSF counterparts by 3.0% and 3.2%, respectively. Conclusions: For typical reconstruction protocol used in clinical practice, i.e., less than five iterations, TOF improved defect detectability. In contrast, PSF generally yielded less detectability. For large number of iterations, TOF+PSF yields the best observer performance.« less

Transmission/Scanning Transmission Electron Microscopy | Materials Science

Science.gov Websites

imaging such as high resolution TEM. Transmission electron diffraction patterns help to determine the microstructure of a material and its defects. Phase-contrast imaging or high-resolution (HR) TEM imaging gives high scattering angle can be collected to form high-resolution, chemically sensitive, atomic number (Z

Precision calculation of the lowest 1S resonance in e-H scattering. [electron-hydrogen scattering

NASA Technical Reports Server (NTRS)

Ho, Y. K.; Bhatia, A. K.; Temkin, A.

1977-01-01

The position and width of the lowest resonance in electron-hydrogen scattering have been calculated using a Hylleraas correlation function with up to 95 terms in the optical potential formalism. The results should be useful as calibration points for experimental electron scattering purposes. A formula relating the conventional (Breit-Wigner) width with the Feschbach formalism is derived.