Change In Scattering Mechanism Research Articles

Theoretical study of nonadiabatic hydrogen atom scattering dynamics on metal surfaces using the hierarchical equations of motion method.

Hydrogen atom scattering on metal surfaces is investigated based on a simplified Newns-Anderson model. Both the nuclear and electronic degrees of freedom are treated quantum mechanically. By partitioning all the surface electronic states as the bath, the hierarchical equations of motion method for the fermionic bath is employed to simulate the scattering dynamics. It is found that, with a reasonable set of parameters, the main features of the recent experimental studies of hydrogen atom scattering on metal surfaces can be reproduced. Vibrational states on the chemisorption state whose energies are close to the incident energy are found to play an important role, and the scattering process is dominated by a single-pass electronic transition forth and back between the diabatic physisorption and chemisorption states. Further study on the effects of the atom-surface coupling strength reveals that, upon increasing the atom-surface coupling strength, the scattering mechanism changes from typical nonadiabatic transitions to dynamics in the electronic friction regime.

Tuning the carrier scattering mechanism to improve the thermoelectric performance of p-type Mg3Sb1.5Bi0.5-based material by Ge doping

P-type Mg3Sb2-based Zintl compounds remain largely unexplored due to their inferior ZT values compared with n-type counterparts. The intrinsic p-type Mg3Sb1.5Bi0.5 manifests relatively poor thermoelectric performance because of its low electrical conductivity of about 3 × 102 S/m at room temperature. In this work, Ge is doped on the Bi site of Mg3Sb1.5Bi0.5, where the carrier scattering mechanism changes from ionized impurity scattering to mixed ionized impurity and acoustic phonon scattering. A significant improvement in Hall mobility from ∼1.8 to ∼24 cm2 V−1/s is obtained, thus leading to a notably enhanced electrical conductivity of 2.2 × 104 S/m from 2.9 × 102 S/m. A simultaneous reduction in lattice thermal conductivity is also achieved. Collectively, a maximum ZT value of 0.5 is obtained at 723 K in Mg3Sb1.5Bi0.47Ge0.03 with a carrier concentration of 5.02 × 1019/cm3.

Sentinel-1 Backscatter Analysis and Radiative Transfer Modeling of Dense Winter Wheat Time Series

This study evaluates a temporally dense VV-polarized Sentinel-1 C-band backscatter time series (revisit time of 1.5 days) for wheat fields near Munich (Germany). A dense time series consisting of images from different orbits (varying acquisition) is analyzed, and Radiative Transfer (RT)-based model combinations are adapted and evaluated with the use of radar backscatter. The model shortcomings are related to scattering mechanism changes throughout the growth period with the use of polarimetric decomposition. Furthermore, changes in the RT modeled backscatter results with spatial aggregation from the pixel to field scales are quantified and related to the sensitivity of the RT models, and their soil moisture output are quantified and related to changes in backscatter. Therefore, various (sub)sets of the dense Sentinel-1 time series are analyzed to relate and quantify the impact of the abovementioned points on the modeling results. The results indicate that the incidence angle is the main driver for backscatter differences between consecutive acquisitions with various recording scenarios. The influence of changing azimuth angles was found to be negligible. Further analyses of polarimetric entropy and scattering alpha angle using a dual polarimetric eigen-based decomposition show that scattering mechanisms change over time. The patterns analyzed in the entropy-alpha space indicate that scattering mechanism changes are mainly driven by the incidence angle and not by the azimuth angle. Besides the analysis of differences within the Sentinel-1 data, we analyze the capability of RT model approaches to capture the observed Sentinel-1 backscatter changes due to various acquisition geometries. For this, the surface models “Oh92” or “IEM_B” (Baghdadi’s version of the Integral Equation Method) are coupled with the canopy model “SSRT” (Single Scattering Radiative Transfer). To resolve the shortcomings of the RT model setup in handling varying incidence angles and therefore the backscatter changes observed between consecutive time steps of a dense winter wheat time series, an empirical calibration parameter (coef) influencing the transmissivity (T) is introduced. The results show that shortcomings of simplified RT model architectures caused by handling time series consisting of images with varied incidence angles can be at least partially compensated by including a calibration coefficient to parameterize the modeled transmissivity for the varying incidence angle scenarios individually.

Structure and thermoelectric properties of In<sub>1+</sub><i><sub>x</sub></i>Te compounds

The inharmonic lattice vibration induced by the lone pair electrons of In<sup>+</sup> in the InTe compound produces its intrinsically low thermal conductivity, thus InTe compound shows a great potential serving as an intermediate temperature thermoelectric material. However, its poor electrical transport properties result in an inferior thermoelectric performance. In this study, a series of single-phase In<sub>1+</sub><i><sub>x</sub></i>Te (<i>x</i> = 0, 0.001, 0.003, 0.005, 0.01) polycrystalline samples were prepared by a melting-annealing process combined with spark plasma sintering. The influence of In content on the electronic and thermal transport properties for In<sub>1+</sub><i><sub>x</sub></i>Te compounds was systematically studied. As the temperature rises, the predominant carrier scattering mechanism changes from grain boundary scattering to acoustic phonon scattering, leading to an unusual semiconductor-to-metal transition in In<sub>1+</sub><i><sub>x</sub></i>Te samples. Positron annihilation spectroscopy and electrical transport properties demonstrate that In vacancies are the main source for the charge carrier. Adding extra In effectively suppresses the concentration of In vacancies, reduces the carrier concentration and improves the Seebeck coefficient of In<sub>1+</sub><i><sub>x</sub></i>Te samples. The power factor of the In excess samples in the test temperature range is greatly improved in comparison with that of the pristine InTe sample. In<sub>1.005</sub>Te sample achieves a maximum power factor of 0.60 mW·m<sup>–1</sup>·K<sup>–2</sup> at 585 K, which is approximately 40% higher than the pristine InTe sample. In addition, the In excess sample maintains a thermal conductivity as intrinsically low as the thermal conductivity of pristine InTe, and the total thermal conductivity of the In<sub>1.01</sub>Te sample at 773 K is 0.46 W·m<sup>–1</sup>·K<sup>–1</sup>. Owing to the improvement of the power factor and the low thermal conductivity, the <i>ZT</i> value of the In excess sample is greatly improved in the entire measure temperature range. A maximum <i>ZT</i> value of 0.71 is attained at 750 K for In<sub>1.003</sub>Te sample, and a maximum <italic/><i>ZT</i><sub>ave</sub> of 0.39 is achieved for In<sub>1.005</sub>Te sample in a temperature range of 300–750 K, which is about 23% higher than that of pristine InTe sample.

Thermoelectric transport properties of naturally nanostructured Ga–ZnO ceramics: Effect of point defect and interfaces

Point defects and nanoscale interfaces have been found of significant influence on the phonon and electrical transport properties. In the preset work, we present the high temperature thermoelectric properties of naturally nanostructured Ga–ZnO ceramics synthesized by sparking plasma sintering process. By varying the GaO1.5 doping concentration, compositionally dependent structures were formed, from point defected solid solution to nanostructures with superlattices and nanotwins. The introduction of low GaO1.5 concentration increases both electron and point defect concentrations, leading to significantly increased electrical conductivity while reduced thermal conductivity. The nanostructure interfaces are found to increase scattering of both charge carriers and phonons, leading to drastically reduced electronic mobility and lattice thermal conductivity. A combined analysis of electrical conductivity and Seebeck coefficient with temperature was also developed, which revealed that the dominant electron scattering mechanism changes with defect concentration. We believe that this approach is also likely applicable to other thermoelectric material systems.

The backscattering characteristics of wetland vegetation and water-level changes detection using multi-mode SAR: A case study

A full understanding of the backscattering characteristics of wetlands is necessary for the analysis of the hydrological conditions. In this study, a temporal set of synthetic aperture radar (SAR) imagery, acquired at different frequencies, polarizations and incidence angles over the coastal wetlands of the Liaohe River Delta, China, were used to characterize seasonal variations in radar backscattering coefficient for reed marshes and rice fields. The combination of SAR backscattering intensity and an optical-based normalized difference vegetation index (NDVI) for long time series can provide additional insight into vegetation structural and its hydrological states. After identifying the factors that induce the backscattering and scattering mechanism changes, detailed analysis of L-band ALOS PALSAR interferometric SAR (InSAR) imagery was conducted to study water-level changes under different environmental conditions. In addition, ENVISAT altimetry was used to validate the accuracy of the water-level changes estimated using the InSAR technique—this is an effective tool instead of sparsely distributed gauge stations for the validation. Our study demonstrates that L-band SAR data with horizontal polarization is particularly suitable for the extraction of water-level changes in the study area; however, vertically-polarized C-band data may also be useful where the density of herbaceous vegetation is low at the initial stage. It is also shown that integrated analysis of the backscattering mechanism and interferometric characteristics using multi-mode SAR can considerably enhance the reliability of the water-level retrieval scheme and better capture the spatial distribution of hydrological patterns.

Tsunami Damage Investigation of Built-Up Areas Using Multitemporal Spaceborne Full Polarimetric SAR Images

This paper explores the use of full polarimetric synthetic aperture radar (PolSAR) images for tsunami damage investigation from the polarimetric viewpoint. The great tsunami induced by the earthquake of March 11th, 2011, which occurred beneath the Pacific off the northeastern coast of Japan, is adopted as the study case using the Advanced Land Observing Satellite/Phased Array type L-band Synthetic Aperture Radar multitemporal PolSAR images. The polarimetric scattering mechanism changes were quantitatively examined with model-based decomposition. It is clear that the observed reduction in the double-bounce scattering was due to a change into odd-bounce scattering, since a number of buildings were completely washed away, leaving relatively a rough surface. Polarization orientation (PO) angles in built-up areas are also investigated. After the tsunami, PO angle distributions from damaged areas spread to a wider range and fluctuated more strongly than those from the before-tsunami period. Two polarimetric indicators are proposed for damage level discrimination at the city block scale. One is the ratio of the dominant double-bounce scattering mechanism observed after-tsunami to that observed before-tsunami, which can directly reflect the amount of destroyed ground-wall structures in built-up areas. The second indicator is the standard deviation of the PO angle differences, which is used to interpret the homogeneity reduction of PO angles. Experimental results from after- and before-tsunami comparisons validate the efficiency of these indexes, since the built-up areas with different damage levels can be well discriminated. In addition, comparisons between before-tsunami pairs further confirm the stability of the two polarimetric indexes over a long temporal duration. These interesting results also demonstrate the importance of full polarimetric information for natural disaster assessment.

Polarimetric SAR Analysis of Tsunami Damage Following the March 11, 2011 East Japan Earthquake

The earthquake and tsunami of March 11, 2011 killed more than 15 000 people in Eastern Japan. The importance of remote sensing in understanding the damage caused by natural disasters is quite significant, and many data sets were acquired after the events. In this paper, we demonstrate the importance and the potential of full polarimetric synthetic aperture radar (SAR) images for damage assessment. Full polarimetric SAR images acquired by the spaceborne ALOS/PALSAR system from the Japan Aerospace Exploration Agency (JAXA) on November 21, 2010 and April 8, 2011 and acquired by the airborne Pi-SAR2 system from the National Institute of Information and Communications Technology (NICT) on March 12 and 18, 2011 are used for this analysis. Model-based decomposition is applied and clearly shows the scattering mechanism changes at the seriously damaged downtown of Ishinomaki city and the flooded areas near the main stream of the Kitakami River. Polarization orientation angle is estimated to provide additional information to understand the damage effect in the built-up areas. Eigenvalue-eigenvector-based decomposition analysis is also employed to further confirm the scattering mechanism changes of the flooded areas. ALOS/PALSAR does not have fine enough resolution; however, the difference of the scattering mechanisms is sufficient to identify the damaged and flooded areas. In addition, the Pi-SAR2 data sets are used to analyze the flooded paddy fields in Natori city. The relative backscattering values are compared with the multitemporal images and the cross-polarization component (HV) is observed to be more sensitive to the flooded boundary. The automatically detected flooding maps using the cross-polarization component were found to provide relatively accurate results.

Transparent Polycrystalline Alumina Ceramic with Sub-Micrometre Microstructure by Means of Electrophoretic Deposition

The optical quality attainable in coarse-grained polycrystalline alumina is severely limited by grain-boundary scattering, which is inherent to non-cubic materials. The optical properties of sub-micrometre polycrystalline alumina are of growing interest triggered by the fact that a decrease in the grain sizes of the final sintered material yields an improvement in the optical quality while the scattering mechanism changes as the grain size becomes comparable with the wavelength of light. To achieve transparent alumina ceramics with a fine-grained microstructure, however, porosity and other defects must be avoided. This necessitates the optimization of processing and sintering procedures. Electrophoretic deposition (EPD) is a colloidal process in which ceramic bodies are directly shaped from a stable suspension by application of an electric field. Electrophoretic deposition enables the formation of homogeneous, uniform green microstructures with high density, which can be sintered to transparency. It is a simple and precise technique to synthesize not only monoliths, but also composites with complex geometries [1]. Alumina green bodies were deposited from stabilized aqueous suspensions with and without doping. Green alumina compacts were evaluated based on their pore size distribution and density. Densification behaviour was characterized by dilatometric studies conducted at constant heating rate. Samples were sintered at different temperatures with subsequent post-densification by hot isostatic pressing. Transparency was evaluated by means of spectroscopic measurements. The measured in-line transmission of the samples at 645 nm was more than 50 % and that is 58 % of the value of sapphire. The influence of dopings on transparency was investigated. The mechanical properties of the samples were tested.

Energy-dependent in situ small-angle X-ray scattering study of nano-ceramics

Energy-dependent small-angle X-ray scattering (SAXS) measurements near the Zr–K absorption edge of a nano-scale alumina–zirconia–silicate ceramic are reported. The in situ experiments cover the temperature range from 250 to 725°C, during which the sol-gel prepared nano-particles consolidate and the glass matrix phase begins to soften, leading to a compaction of the ceramic. The dominant scattering mechanism changes from a surface-fractal type to a mass-fractal type linked to direct contact areas between nano-particles and matrix. The energy-dependent data identify the zirconium-bearing phase as dominant in the high-q range. The experimental data are placed in the context of recent advances in in situ anomalous small-angle X-ray scattering (ASAXS) and some experimental problems and solutions of near-edge scattering are discussed. Contents 1. Introduction 4 2. Anomalous small-angle scattering 4 3. Experimental 6 4. Results 7 5. Discussion 8 6. Conclusions and outlook 10 Acknowledgments 10 References 11 Subject Index 12

Synthetic aperture radar (SAR)-based mapping of volcanic flows: Manam Island, Papua New Guinea

Abstract. We present new radar-based techniques for efficient identification of surface changes generated by lava and pyroclastic flows, and apply these to the 1996 eruption of Manam Volcano, Papua New Guinea. Polarimetric L- and P-band airborne synthetic aperture radar (SAR) data, along with a C-band DEM, were acquired over the volcano on 17 November 1996 during a major eruption sequence. The L-band data are analyzed for dominant scattering mechanisms on a per pixel basis using radar target decomposition techniques. A classification method is presented, and when applied to the L-band polarimetry, it readily distinguishes bare surfaces from forest cover over Manam volcano. In particular, the classification scheme identifies a post-1992 lava flow in NE Valley of Manam Island as a mainly bare surface and the underlying 1992 flow units as mainly vegetated surfaces. The Smithsonian's Global Volcanism Network reports allow us to speculate whether the bare surface is a flow dating from October or November in the early part of the late-1996 eruption sequence. This work shows that fully polarimetric SAR is sensitive to scattering mechanism changes caused by volcanic resurfacing processes such as lava and pyroclastic flows. By extension, this technique should also prove useful in mapping debris flows, ash deposits and volcanic landslides associated with major eruptions.

Transport properties of boron-doped crystallized amorphous Si1−xGex films

Transport properties of crystallized amorphous Si1−xGex films, having different Ge content (x) and highly doped with boron were studied. The films were deposited by molecular beam at room temperature and subsequently annealed in vacuum at different temperatures between 500 and 900 °C for 1 h. The microstructure of the crystallized Si1−xGex films was characterized by means of transmission electron microscopy, x-ray diffraction, and scanning electron microscopy. Measured transport properties included Hall hole concentration (pH), Hall mobility (μH), electrical conductivity (σ), and the Seebeck coefficient (S), from which the “power factor” (S2σ) was evaluated. The results obtained for the Hall mobility of the Si1−xGex films are discussed on the basis of the carrier trapping model. The trapping state density at the grain boundaries increases with increasing B concentration, although it is not significantly dependent on Ge content. Consequently, the mobility energy barrier decreases with increasing B concentration and increasing Ge content. It was found that in all the studied Si1−xGex films, independent of x, the predominant scattering mechanism changes from acoustic phonon scattering to ionized impurity scattering with increasing the boron concentration from 5×1018 to 5×1020 cm−3. In addition, the Si1−xGex films demonstrate high electrical conductivity as well as a high Seebeck coefficient, after 1 h annealing at 600–800 °C, and thus exhibit a high “power factor” of the order of 6 μW/cm K2. Thus, these films have potential applications in thin-film thermoelectric devices.

C-band backscatter signatures of old sea ice in the central Arctic during freeze-up

Radar backscatter signatures of old sea ice in the central Arctic have been measured and analyzed. A ship-mounted scatterometer was used to acquire backscattering coefficients at 5.4 GHz in the four linear polarization states and at incidence angles between 20 degrees and 60 degrees . Detailed in situ characterizations of the snow and ice were also made to enable comparison with theoretical backscatter models. Freeze-up conditions were prevalent during the experiment. The average backscattering coefficient was found to increase when the temperature of the ice surface layer decreased. The semi-empirical backscatter model is used to evaluate the measurements and shows that the backscatter increase is due to an increasing penetration depth, causing the volume scattering to increase. Model predictions also show that both surface and volume scattering contribute significantly at incidence angles of 20 degrees to 26 degrees . At these incidence angles, the dominating scattering mechanism changes from surface to volume scattering as the ice surface temperature decreases.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Evolution of Light Scattering and Electrical Properties of Tungsten Oxide Gel

Evolution of the light scattering and electrical properties of the tungstic acid during the gelation process has been investigated. The scattered light becomes anisotropic and the depolarized scattering grows strong around 2 hours after the beginning of gelation. On the other hand, the resistance shows a steady increase. With the results obtained from the present study, we concluded that the light scattering mechanism changes from the Rayleigh scattering to the Mie scattering with the progress of gelation.