bluuebunny/crossref_metadata_2025_split huggingface dataset:
Harvesting Betavoltaic and Photovoltaic Energy with Three Dimensional Porous Silicon Diodes
Authors: Sun Wei , Kherani Nazir P. , Hirschman Karl D. , Gadeken Larry L. , Fauchet Philippe M. 
Published: April 2011

ABSTRACTConventional two-dimensional p-n diodes can be used for betavoltaic and photovoltaic energy conversion, but the device efficiency is limited by the planar geometry. We propose and demonstrate a novel three-dimensional diode geometry based on porous silicon. The 3D pore array provides two very important features: (1) the storage of the radioisotope energy source and (2) its extreme proximity to the p-n junction on each pore wall. The particle energy losses are thereby minimized prior to entering the conversion layer. In betavoltaics, our 3D betavoltaic device efficiency is 10 times that of a similar planar device. In photovoltaics, photons play the role of beta particles and photon trapping inside the pores enhances the conversion efficiency. Further fabrication and geometry optimization can result in practical, high performance devices.
Density of States in Tritiated Amorphous Silicon Measured Using CPM
Authors: Pisana Simone , Costea Stefan , Kosteski Tome , Kherani Nazir P. , Zukotynski Stefan , Shmayda Walter T. 
Published: April 2011

ABSTRACTThe constant photocurrent method has been used to obtain the density of occupied electronic states of tritiated amorphous silicon thin films. The analyses showed a peak of defects located 1.24 eV below the conduction band edge, suggesting that the main type of defect present in the films was a doubly occupied dangling bond. The concentration of defect states increases as a result of tritium decay by about two orders of magnitude over a period of 500 hours. The defect density in the tritiated amorphous silicon samples could be reduced by thermal annealing, after which it increased once more.
Structure and stability of complex metal hydrides – theoretical approach
Authors: Łodziana Zbigniew , Vegge Tejs 
Published: April 2011

AbstractIn this paper systematic approach to study the structural stability of the complex hydride, LiBH4 is presented. The ground state energies of various symmetry structures are determined by means of Density Functional Theory. Simulated annealing method is used to confirm if ground state structures represent real energy minima. The vibrational spectrum and temperature dependence of the free energy of the structures with the lowest energies is determined. Calculated Raman active modes for three symmetries are presented. We show that at high temperatures LiBH4 possesses monoclinic symmetry and some of the low energy structures are unstable with respect to atomic vibrations. Our studies point to the necessity of calculation of the phonon spectra for complex metal hydrides that contain covalently bounded hydrogen.
In situX-ray and neutron powder diffraction study of LaNi5-xSnx–H systems
Authors: Nakamura Yumiko , Bowman Robert C. , Akiba Etsuo 
Published: April 2011

ABSTRACTWe have studied structural change and lattice strain formation during absorption and desorption of hydrogen (deuterium) by high purity LaNi5-xSnxalloys (x= 0.22, 0.25) usingin situX-ray and neutron diffraction along with simultaneously measuring theP-Cisotherms. From profile analysis of the X-ray diffraction data, lattice parameter and lattice strain in each hydriding state are evaluated.In situneutron diffraction data provided hydrogen occupation changing with hydrogen content. Significant lattice contract and strain formation were observed in the hydride phase in desorption. This behavior was related with decrease in hydrogen occupation in the hydride phase revealed from the neutron diffraction data.
Electronic Structure and Hydrogen Desorption in NaAlH4
Authors: Li S. , Jena P. , Araujo C. M. , Ahuja R. 
Published: April 2011

ABSTRACTFirst principles calculations based on gradient corrected density functional theory are carried out to understand the electronic structure and mechanisms responsible for desorption of hydrogen from Ti doped and vacancy containing sodium-alanate (NaAlH4). The energy necessary to remove a hydrogen atom from Ti doped NaAlH4 is significantly smaller than that from pristine NaAlH4 irrespective of whether Ti substitutes the Na or the Al site. However, the presence of Na and Al vacancies is shown to play an even more important role: The removal of hydrogen associated with both Na and Al vacancies is found to be exothermic. It is suggested that this role of vacancies can be exploited in the design and synthesis of complex light metal hydrides suitable for hydrogen storage.
Photoelectrochemical Properties of Highly-ordered Titania Nanotube-arrays
Authors: Paulose Maggie , Varghese Oomman K. , Shankar Karthik , Mor Gopal K. , Grimes Craig A. 
Published: April 2011

ABSTRACTWe report on non-particulate titania photoelectrodes with a unique highly-ordered nanotube-array architecture prepared by an anodization process that enables precise control over array dimensions. Under 320–400 nm illumination titania nanotube-array photoanodes, pore size 110 nm, wall thickness 20 nm, and 6 μm length, generate hydrogen by water photoelectrolysis at a normalized rate of 80 mL/W•hr, to date the most efficient titania-based photoelectrochemical device, with a conversion efficiency of 12.25%. The highly-ordered nanotubular architecture allows for superior charge separation and charge transport, with a calculated quantum efficiency of nearly 100% for incident photons with energies larger than the titania bandgap.
STM Image Simulation: Effect of the Number of Tunneling States and the Isosurface Value
Authors: Radilla Juan , Galván Marcelo , Trinidad-Reyes Yolanda , Batina Nikola 
Published: April 2011

ABSTRACTIn this work, Scanning Tunneling Microscopy (STM) images were simulated for the organic molecule 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA) to study the effect of the number of tunneling states and the integrated Local Density of States (LDOS) isosurface value. Local Density Approximation of Density Functional Theory (DFT-LDA) calculations were performed to achieve the simulated images under the Tersoff and Hamann approximation. The number of tunneling states has a strong effect on the image appearance of the patterns. Intermediate isosurface values for the integrated LDOS produce good resolution and matching in relation to the experimental STM image. Both parameters seem to be of significant importance for STM image simulation.
Ballistic Electron Emission Luminescence of InAs Quantum Dots Embedded in a GaAs/AlxGa1−xAs Heterostructure
Authors: Yi Wei , Appelbaum Ian , Russell Kasey J. , Narayanamurti Venkatesh , Hanson Micah P. , Gossard Arthur C. 
Published: April 2011

ABSTRACTBallistic electron emission luminescence (BEEL) is a further development of ballistic electron emission microscopy (BEEM) combining three-terminal hot electron injection and interband radiative recombination in direct-gap semiconductor materials. By using a planar tunnel-junction emitter rather than a STM tip, a spectrographic analysis of the induced electroluminescence can be performed with the help of much higher current injection level. We demonstrate the operational principle of BEEL in a GaAs/AlxGa1−xAs heterostructure with a layer of InAs quantum dots (QDs) as the optical active layer. The wavelength-resolved BEEL spectra from planar tunnel-junction devices disclose the QD luminescence as a peak near 1.34 eV accompanied with a linear quantum-confined Stark shift. At higher collector voltage, luminescence from bulk states of GaAs peaked at 1.48 eV is observed. The spectrally integrated BEEL intensity as a function of collector voltage fits well with the results from STM tip injection, which is measured in a single-photon-counting mode. Measurement of ballistic electron current spectroscopy is made possible by freezing out the thermionic leakage current at low temperatures. Our results indicate that it is feasible to simultaneously acquire topographic, electronic and photonic information of buried light-emitting semiconductor heterostructures.
Scanning Probe Recognition Microscopy Investigation of the Elastic Properties of Tissue Scaffolding
Authors: Chen Q. , Fan Y. , Ayres V. M. , Udpa L. , Schindler M. S. , Rice A. F. 
Published: April 2011

ABSTRACTScanning Probe Recognition Microscopy is a new scanning probe capability under development within our group to reliably return to and directly interact with a specific nanoscale feature of interest, without the use of a zoom box with its thermal drift and local origin difficulties. It is a recognition-driven and learning approach, made possible through combining SPM piezoelectric implementation with on-line image processing and dynamically adaptive learning algorithms. Segmentation plus a recognized pattern is implemented within a scan plan and used to guide the tip in a recognition-driven return to a specific site.The specific application focus of our group is on the development of Scanning Probe Recognition Microscopy for nanobiological investigations. In the present work, Scanning Probe Recognition Microscopy is used in a direct investigation of the surface and elastic properties along individual tubules within a tissue scaffolding matrix. Elastic properties are indicated as important influences on actin polymerization and consequent cell pseudopodia extension and contraction.
Direct observation of polar nanostructures in PLZT ceramics for electrooptic applications
Authors: Shvartsman V. V. , Orlova A. , Kiselev D. , Sternberg A. , Kholkin A. L. 
Published: April 2011

ABSTRACTTransparent Pb1-yLay(Zr1-xTix)1-y/4O3(PLZT, y=0.0975, x=0.35) ceramics prepared via hot pressing techniques were studied via piezoelectric force microscopy (PFM). Clear piezoelectric contrast is observed in a cubic relaxor phase indicating spatial distribution of polarization with an average cluster size of about 50 nm. The irregular polarization pattern is associated with the formation of a glassy state, where random electric and stress fields are responsible for the disruption of the long-range ferroelectric order. Local poling of the ceramics resulted in the formation of a stable micron-size domain that could be continuously switched under varying dc bias (local hysteresis loop). The applied voltage of 10–12 Volts was enough to switch relaxor into the ferroelectric state. Fractal and correlation analysis of the observed images is presented. The fractal dimension close to 1.55 is consistent with the random distribution of charge defects in this material. The nature of the observed phenomena is discussed based on the current understanding of relaxor state in PLZT and possible effect of PFM instrumentation.
Radiation Induced Subsurface Charging in the Buried Oxide Layer in SIMOX
Authors: Stevens-Kalceff M. A. , Mickle S. 
Published: April 2011

ABSTRACTKelvin Probe Microscopy has been used to characterize the magnitude and spatial distribution of reproducible characteristic residual potential in electron beam irradiated silicon on insulator specimens (SIMOX). Focussed electron beam irradiation produces trapped charge within the insulating buried oxide layer which produces highly localized electric fields. The charging processes are dynamic, localized, and dependent on pre-existing and irradiation induced defect concentrations. The characteristic experimental surface potential distributions are compared with calculated model surface potential distributions. This work demonstrates that proximal probe methods which are usually considered to be surface analysis techniques, can be used to investigate subsurface properties and give insight into subsurface charging processes.
Scanning Conductance Microscopy and High Frequency Scanning Gate Microscopy of Carbon Nanotubes and Polyethylene based Nanofibers
Authors: Staii Cristian , Shao Rui , Pinto Nicholas J. , Bonnell Dawn A. , Johnson Alan T. 
Published: April 2011

ABSTRACTWe present two new approaches that significantly enhance the analytic power of Scanning Conductance Microscopy (SCM) and Scanning Gate Microscopy (SGM). First, we present a quantitative model that explains the phase shifts observed in SCM, by considering the change in the total capacitance of the tip-sample-substrate system. We show excellent agreement with data on samples of (conducting) single wall nanotubes and insulating polyethylene oxide (PEO) nanofibers. This model is also used to determine the dielectric constant of PEO nanofibers, a general approach that can be extended to other dielectric nanowires. Second, we extend the SGM to frequencies up to 15MHz, and use it to image changes in the impedance of carbon nanotube field effect transistor (CNFET) circuits induced by the SGM-tip gate. We show that these measurements are consistent with a simple RC parallel circuit model of the CNFET, with a time constant of 0.3 μs.
In Situ Quantitative Plasmon Spectroscopic Determination and Imaging of Multiple SolidState Properties at the Nanoscale: a New Capability for Material Research
Authors: Oleshko Vladimir P. , Howe James M. 
Published: April 2011

ABSTRACTMeasuring material properties is critical to understanding the behavior of contemporary nanostructured materials. In this paper, we show that as a consequence of the universal binding energy relation (UBER), universal features and strong scaling correlations exist between the volume plasmon energy and cohesive energy, valence electron density, elastic constants and hardness of various materials with metallic and covalent bonding. Based on these relations, we propose novel techniques that allow direct measurement and imaging of material properties in situ using valence electron energy-loss spectroscopy combined with energy-filtering transmission electron microscopy. This is illustrated by evaluation of elastic and cohesive properties of individual metastable nanoprecipitates in structural alloys and hardness of diesel-engine soot particles. The results demonstrate that new plasmon spectro-microscopic techniques have the potential to determine quantitatively and image multiple solid-state properties at the nanoscale, establishing a new capability for material research.
Surface Chemistry of Combustion-Synthesized Iron Oxide Nanoparticles Determined by Electron Energy-Loss Spectroscopy
Authors: Leppert V.J. , Pinkerton K. E. , Jasinski J. 
Published: April 2011

ABSTRACTParticulate matter (PM) that is composed of a complex mixture of organic compounds, soot, transition metals, sulfates, nitrates, and other trace elements has been associated with a range of adverse health effects. The effect of the separate components of PM and their interaction with each other is important in order to understand the origins of toxicity in these materials. Iron and soot are common environmental contaminants occurring in ultrafine particulate matter in the air, and have been experimentally generated, in a manner simulating high-temperature, industrial processes, through the combustion of iron pentacarbonyl in a mixture of acetylene and ethylene. Nanoprobe electron energy-loss spectroscopy (EELS) in the transmission electron microscope was used to collect Fe L3:L2 white line-intensity ratios from the interiors and surfaces of iron oxide nanoparticles present in samples generated under low and high soot conditions. This ratio is sensitive to any change in the iron oxidation state, and indicated that iron oxide nanoparticles co-generated with large quantities of soot during combustion processes show a subsurface layer (of thickness 2–3 nm) of decreased iron oxidation state. A quantitative analysis of the iron L32 EELS ionization edge measured in nanoprobe mode indicated that in these particles, the oxidation state of iron at the surface is decreased from Fe3+ to Fe2+, possibly explaining the toxicity of these materials in the respiratory tract. The application of EELS to understanding the nanoscale distribution of the various components and their chemical interactions in these samples, and correlation of these results with acute respiratory toxicity studies of the laboratory-generated particulate matter, are discussed.
On the Effect of Local Grain-Boundary Chemistry on the Macroscopic Mechanical Properties of a High Purity Y2O3-Al2O3-Containing Silicon Nitride Ceramic
Authors: Ziegler A. , McNaney J.M. , Hoffmann M. J. , Ritchie R. O. 
Published: April 2011

ABSTRACTThe effects of grain-boundary chemistry on the mechanical properties of a high-purity silicon nitride ceramics were investigated, with specific emphasis on the role of oxygen. Variations in the grain-boundary oxygen content, through control of oxidizing heat treatments and sintering additives, was found to result in a transition in fracture mechanism from transgranular to intergranular fracture, with an associated increase in fracture toughness. This phenomenon is correlated to an oxygen-induced change in grain-boundary chemistry that appears to affect fracture by “weakening” the interface, facilitating debonding and crack advance along the boundaries, thereby enhancing the toughness by grain bridging. It is concluded that if the oxygen content in the thin grain-boundary films exceeds a lower limit, which is ∼0.87 equiv% oxygen content, then the interfacial structure and bonding characteristics favor intergranular debonding during crack propagation; otherwise, transgranular fracture ensues, with consequent low toughness.
Electron Holographic Characterization of Nano-Hetero Interface Effect in Gold Catalysts
Authors: Ichikawa S. , Akita T. , Okazaki K. , Tanaka K. , Kohyama M. 
Published: April 2011

ABSTRACTWe investigated the atomic structure near the interface and the size dependence of the mean inner potential of gold in Au/TiO2 catalysts prepared by the deposition precipitation (DP) method and the vacuum evaporation (VE) method using high resolution electron microscopy (HREM) and electron holography. The TiO2 supports prepared by DP method and VE method are considered to have oxygen-rich surfaces and titanium-rich surfaces respectively. In case of the Au/TiO2 catalyst prepared by DP method, the mean inner potential of gold increased depending on the size of the particle. When the size of the gold particle is over 5nm, the mean inner potential of gold was the same as that of bulk Au. When the size is below 5nm, the mean inner potential became to increase. It increases suddenly over 40V, particularly in case of below 2nm. It indicates that the electronic state of gold on TiO2 changes from that of bulk state as the size decreases. On the other hand, the mean inner potential of gold in Au/TiO2 catalysts prepared by VE method also increased as the size decreased, but the behavior of the size dependence is different from that of DP method. The critical size of the mean inner potential change is around 3nm. The size of the gold particle was below 3nm, the mean inner potential of gold increased gradually. The mean inner potential of VE method is less than that of DP method with the same particle size in spite of the size below 3nm. The stoichiometry at the interface between Au and TiO2 should be one of the dominant reasons for the behavior difference of the size dependence of the mean inner potential between the preparations.
Discrete Tomography of Ga and InGa Particles from HREM Image Simulation and Exit Wave Reconstruction
Authors: Jinschek J. R. , Calderon H. A. , Batenburg K. J. , Radmilovic V. , Kisielowski Ch. 
Published: April 2011

ABSTRACTLow-resolution tomography requires recording images every few degrees. As a consequence, the sample is often degraded after such a procedure. However the required input can be reduced drastically by using knowledge about the position and the number of atoms in each atomic column. This concept has been tested in the present investigation where HREM image simulation (MacTempas) together with exit wave reconstruction (FEI Trueimage) have been performed. A cubeoctahedral nanoparticle is used for the simulation with different compositions i.e., pure solid Ga and In-Ga particles. Six different zone axes ([111], [111], [001], [110], [110], [011]) have been used and the parameters of an aberration corrected microscope (200kV, Cs = 0 mm, resolution = 0.5Å). The discrete grid data were determined by constructing a channeling map from the reconstructed exit wave images. In this special case only three projections [001], [110], [110] were sufficient to find a unique volumetric reconstruction, illustrating the potential of the method. The other projections were used for checking the solution. The comparison between the projected potentials (simulated input) and the final result shows that discrete tomography reconstructs the exact position of all 309 atoms and the three-dimensional shape of the nanocrystal.
Electron Microscopy Analysis of the Central Dark Line Defect of the Human Tooth Enamel
Authors: Rodríguez-Hernández A. G. , Fernández M.E. , Carbajal-De-La-Torre G. , García-García R. , Reyes-Gasga J. 
Published: April 2011

ABSTRACTAfter some experimental results that indicated that HA is able to growth in an epitaxial way on the surface of OCP, it has been suggested that the central dark line (CDL) observed in the nanometric-sized grains of human tooth enamel corresponds to a one-unit-cell-thick layer of octacalcium phosphate (OCP). Based on this consideration, in this work we propose a model for CDL and we carried out the chemistry and structural analysis of the CDL with high resolution microscopy techniques such as Electron Energy Loss Spectroscopy (EELS) and Z-contrast (HAADF) with the aim of find the agreements and/or differences between the human tooth enamel HA and its CDL.
Mapping the Structure of a Hydrated Polymer Blend Using Energy-Loss Spectroscopy in the Cryo-STEM
Authors: Sousa Alioscka , Aitouchen Abdelaziz , Libera Matthew 
Published: April 2011

ABSTRACTWe use electron energy-loss spectroscopy (EELS) in the cryo-STEM to determine the spatial distribution of water in a model frozen-hydrated two-phase polymer blend composed of hydrophilic poly(vinylpyrrolidone) (PVP) and hydrophobic poly(styrene) (PS). We demonstrate that it is possible to directly correlate the water spatial distribution with variations in the underlying polymer morphology. HAADF-STEM imaging of both dry and frozen-hydrated specimens shows weak contrast between the polymer phases but gives no information regarding the composition of these phases and no indication of where water might be localized. Spatially-resolved EELS spectra collected at 100 nm pixel size show that this system is composed of discrete PVP-rich domains dispersed in a continuous PS-rich matrix. The PVP-rich domains were found to be hydrated up to a level of ∼ 23 wt%. We have made our compositional maps fully quantitative, given as mass-fraction maps, by measuring the total inelastic scattering cross-sections per unit mass of water, PVP and PS. This is an important quantity which we have determined for an incident beam energy of 200 keV. Hydrated PVP gives rise to hydrogen evolution when irradiated above an electron dose of 1500 e/nm2 as evidenced from changes in the 13 eV region, and this effect gives rise to dose-limited resolution in these experiments.