bluuebunny/crossref_metadata_2025_split huggingface dataset:
Greatly Reduced Leakage Current in Ti- and La-doped Bi2FeCrO6 Prepared by High Pressure Synthesis
Authors: Bai Feiming , Dai Lihong , Shi Lei , Zhang Huaiwu 
Published: September 2011

ABSTRACTUndoped Bi2FeCrO6, 5%Ti- and 10%La-doped Bi2FeCrO6 were prepared by a high pressure solid-state sintering method. The phase structure, electrical, ferroelectric and magnetic properties have been investigated. It is shown that undoped Bi2FeCrO6 has a serious leakage current problem, and doping either Ti or La can enhance the resistivity by 2-3 orders of magnitude. Furthermore, both Ti- and La-doped Bi2FeCrO6 show an antiferromagnetic spin order due to disordered B-site cation alignment. Weak ferromagnetism was only observed in undoped Bi2FeCrO6 and the reason is tentatively explained.
Monitoring the growth of microcrystalline silicon deposited by plasma-enhanced chemical vapor deposition using in-situ Raman spectroscopy
Authors: Muthmann S. , Köhler F. , Hülsbeck M. , Meier M. , Mück A. , Schmitz R. , Appenzeller W. , Carius R. , Gordijn A. 
Published: September 2011

ABSTRACTA novel setup for Raman measurements under small angles of incidence during the parallel plate plasma enhanced chemical vapor deposition of μc-Si:H films is described. The possible influence of disturbances introduced by the setup on growing films is studied. The substrate heating by the probe beam is investigated and reduced as far as possible. It is shown that with optimized experimental parameters the influence of the in-situ measurements on a growing film can be neglected. With optimized settings, in-situ Raman measurements on the intrinsic layer of a microcrystalline silicon solar cell are carried out with a time resolution of about 40 s corresponding to 20 nm of deposited material during each measurement.
Photoluminescence Properties of Core/Shell CdSe/ZnS Quantum Dots Encapsulated with Transparent layers for Third Generation Photovoltaics
Authors: Sadeghimakki Bahareh , Sadeghi Jahed Navid Mohammad , Sivoththaman Siva 
Published: September 2011

ABSTRACTIn this work hydrophobicaly ligated cadmium selenide/zinc sulfide CdSe/ZnS quantum dots (QDs) were incorporated in transparent matrices by formation of CdSe/ZnS/SiO2 core/shell/shell structure using microemolsion synthesis method. The optical properties of the QDs encapsulated with a chemically grown oxide layers were studied. Intense luminescence properties of the QD/silica nanoparticles (NPs) were observed using steady state photoluminescence (PL) measurements. Confocal microscopy demonstrates fluorescence of the single core/shell/shell nanoparticles. The obtained results along with the Secondary Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) images provide information on the geometry of the QDs. The excitonic emission of nanoparticles was also mapped using a liquid nitrogen cryostat the 77K - 300K range. The temperature dependent PL spectra of the film demonstrate the temperature-dependent band gap shrinkage of the QDs. PL lifetime measurements were performed on the ensemble of NPs. Experimental data was fitted to the numerical model with lifetime constants in nanoseconds range. We demonstrate that the main nonradiative processes that limit the quantum yield (QY) of the QDs at room temperature are the carrier trapping at the interface of QD/silica and the exciton-phonon coupling. These studies give us insight to exploit the QD layers for photon down shifting and multiple exciton generation for application in photovoltaics.
Photovoltaic applications of micro- and nano-crystalline silicon carbide
Authors: Konopka A. , Greulich-Weber S. , Rauls E. , Schmidt W.G. , Gerstmann U. 
Published: September 2011

ABSTRACTOne of the challenges on the way to optimized solar cells is to make the thickness of the individual layers smaller than the diffusion length of the charge carriers. In this work, we propose 3C-SiC microcrystals grown by a sol-gel based process as a promising acceptor material for photovoltaic applications. The μc-SiC samples were characterized by optical spectroscopy and electron paramagnetic resonance (EPR). The experimental data is analyzed with the help of ab-inito calculations in the framework of density functional theory (DFT) resulting in electronic band structures and g-tensors. Based on this, a possible scenario for the observed acceptor process is discussed.
Optical Indices of Hydride of Mg-Ca Alloy Thin Films Evaluated by Spectroscopic Ellipsometry
Authors: Yamada Y. , Tajima K. , Okada M. , Tazawa M. , Roos A. , Yoshimura K. 
Published: September 2011

ABSTRACTMg1-zCaz (0.03 < z < 0.17) alloy thin films covered with thin Pd are hydrogenated using 4% H2 in Ar under atmospheric pressure at room temperature. The optical indices, which are refractive indices and extinction coefficients, in the wavelength between 250 and 1700 nm of these hydrides were evaluated with spectroscopic ellipsometry. The evaluated refractive indices were about 2.0 for all hydrides, while the extinction coefficients showed the values less than 0.06 in the visible range for hydride with Ca composition of z ≤ 0.08 and the coefficients increased sharply to more than 0.3 with Ca composition z > 0.08.
An Experimental and Theoretical Multi-Mbar Study of Ti-6Al-4V
Authors: Tegner Bengt E. , MacLeod Simon G. , Cynn Hyunchae , Proctor John , Evans William J. , McMahon Malcolm I. , Ackland Graeme J. 
Published: September 2011

ABSTRACTWe report results from an experimental and theoretical study of the room temperature (RT) compression of the ternary alloy Ti-6Al-4V. In this work, we have extended knowledge of the equation of state (EOS) from 40 GPa to 221 GPa, and observed a different sequence of phase transitions to that reported previously for pure Ti.
Synthesis of Graphene-CNT Hybrid Nanostructures
Authors: Ghazinejad Maziar , Guo Shirui , Paul Rajat K. , George Aaron S. , Penchev Miroslav , Ozkan Mihrimah , Ozkan Cengiz S. 
Published: September 2011

ABSTRACTUsing chemical vapor deposition technique, a novel 3D carbon nano-architecture called a pillared graphene nanostructure (PGN) is in situ synthesized. The fabricated novel carbon nanostructure consists of CNT pillars of variable length grown vertically from large-area graphene planes. The formation of CNTs and graphene occurs simultaneously in one CVD growth treatment. The detailed characterization of synthesized pillared graphene shows the cohesive structure and seamless contact between graphene and CNTs in the hybrid structure. The synthesized graphene-CNT hybrid has a tunable architecture and attractive material properties, as it is solely built from sp2 hybridized carbon atoms in form of graphene and CNT. Our methodology provides a pathway for fabricating novel 3D nanostructures which are envisioned for applications in hydrogen storage, nanoelectronics, and supercapacitors.
Self-aligned Graphene Sheets-Polyurethane Nanocomposites
Authors: Moazzami Gudarzi Mohsen , Aboutalebi Seyed Hamed , Yousefi Nariman , Zheng Qing Bin , Sharif Farhad , Cao Jie , Liu Yayun , Xiao Allison , Kim Jang-Kyo 
Published: September 2011

ABSTRACTProcessing graphene and graphene polymer nanocomposites in an aqueous medium has always been a big challenge due to the hydrophobic nature of graphene (or reduced graphene oxide) nanosheets. In this work, a waterborne latex of polyurethane has been used both as the matrix material for embedding the graphene nanosheets and as a unique stabilizer to help produce an up to 5 wt% graphene/PU nanocomposites. The graphene oxide/polyurethane latex aqueous suspension is reduced in-situ using hydrazine, without any trace of aggregation/agglomeration upon completion of the reduction process, which would otherwise have occurred severely were PU not present. A highly aligned nanostructure is produced when graphene content is increased beyond 2 wt%, resulting in a remarkable improvement in electrical and mechanical properties of the nanocomposite. The exceptionally low electrical percolation threshold of 0.078%, as well as 21-fold and 14 fold increases in tensile modulus and strength, respectively, have been attained thanks to the alignment of graphene nanosheets in the polymeric matrix.
Low-Frequency Noise in “Graphene-Like” Exfoliated Thin Films of Topological Insulators
Authors: Hossain M. Z. , Rumyantsev S. L. , Shahil K. M. F. , Teweldebrhan D. , Shur M. , Balandin A. A. 
Published: September 2011

ABSTRACTWe report results of the study of the low-frequency noise in thin films of bismuth selenide topological insulators, which were mechanically exfoliated from bulk crystals via “graphene-like” procedures. From the resistance dependence on the film thickness, it was established that the surface conduction contributions to electron transport were dominant. It was found that the current fluctuations have the noise spectral density SI ∞ 1/f (where f is the frequency) for the frequency range up to 10 kHz. The obtained noise data are important for transport experiments with topological insulators and for any proposed device applications of these materials.
Pseudo-Superlattices of Bi2Te3 Topological Insulator Films with Enhanced Thermoelectric Performance
Authors: Goyal V. , Teweldebrhan D , Balandin A.A. 
Published: September 2011

ABSTRACTIt was recently suggested theoretically that atomically thin films of Bi2Te3 topological insulators have strongly enhanced thermoelectric figure of merit. We used the “graphene-like” exfoliation process to obtain Bi2Te3 thin films. The films were stacked and subjected to thermal treatment to fabricate pseudo-superlattices of single crystal Bi2Te3 films. Thermal conductivity of these structures was measured by the “hot disk” and “laser flash” techniques. The room temperature in-plane and cross-plane thermal conductivity of the stacks decreased by a factor of ∼2.4 and 3.5 respectively as compared to that of bulk. The strong decrease of thermal conductivity with preserved electrical properties translates to ∼140-250% increase in the thermoelectric figure if merit. It is expected that the film thinning to few-quintuples, and tuning of the Fermi level can lead to the topological insulator surface transport regime with the theoretically predicted extraordinary thermoelectric efficiency.
Thermal Properties of Graphene and Carbon Based Materials: Prospects of Thermal Management Applications
Authors: Ghosh Suchismita , Balandin Alexander A. 
Published: September 2011

ABSTRACTIn recent years, there has been an increasing interest in thermal properties of materials. This arises mostly from the practical needs of heat removal and thermal management, which have now become critical issues for the continuing progress in electronic and optoelectronic industries. Another motivation for the study of thermal properties at nanoscale is from a fundamental science perspective. Thermal conductivity of different allotropes of carbon materials span a uniquely large range of values with the highest in graphene and carbon nanotube and the lowest in amorphous or disordered carbon. Here we describe the thermal properties of graphene and carbon-based materials and analyze the prospects of applications of carbon materials in thermal management.
Ag Nanoparticle Films for Color Applications
Authors: Hashimoto Satoru , Hirano Teruyoshi O. , Okitsu Osamu , Ebisawa Mizue , Suzuki Takayasu , Maeda Shuichi 
Published: September 2011

ABSTRACTThe focus of this present work is concerned with a novel and facile method for obtaining colored Ag nanoparticle films using a sulfide as a coloring agent. The Ag nanoparticle films change their colors depending on the dipping time in a solution of a sulfide and the dipping time is at most on the second time scale. The color of the films, initially sliver (shiny white), changes to shiny yellow, red, and blue. Our scanning electron microscopy studies indicate that the color of the Ag nanoparticle films depend on the particle size of the Ag nanoparticle films.
Systematic study of methanol addition to enhance the film development of APCVD tin oxide
Authors: van Deelen Joop , Volintiru Ioanna , Poodt Paul 
Published: September 2011

ABSTRACTUndoped tin oxide (SnO2) thin films have been deposited in a stagnant point flow chemical vapor deposition reactor. By adding methanol during the deposition process ten times more conductive SnO2 films are obtained, with remarkably high mobility values of up to 55 cm2/Vs. The investigations on the morphological and structural properties indicate that the main effect of methanol is the densification of the SnO2 films, which probably causes the improvement in the electrical properties. In all conditions the nucleation and coalescence phases take place very early in the growth. The films are already very conductive at a thickness below 10 nm, which is very beneficial to applications that have strict requirements in terms of film transparency. This high conductivity was attributed to a high carrier concentration, obtained without intentional doping.
High specific capacity and excellent stability of interface-controlled MWCNT based anodes in lithium ion battery
Authors: Lahiri Indranil , Oh Sung-Woo , Sun Yang-Kook , Choi Wonbong 
Published: September 2011

ABSTRACTRechargeable batteries are in high demand for future hybrid vehicles and electronic devices markets. Among various kinds of rechargeable batteries, Li-ion batteries are most popular for their obvious advantages of high energy and power density, ability to offer higher operating voltage, absence of memory effect, operation over a wider temperature range and showing a low self-discharge rate. Researchers have shown great deal of interest in developing new, improved electrode materials for Li-ion batteries leading to higher specific capacity, longer cycle life and extra safety. In the present study, we have shown that an anode prepared from interface-controlled multiwall carbon nanotubes (MWCNT), directly grown on copper current collectors, may be the best suitable anode for a Li-ion battery. The newly developed anode structure has shown very high specific capacity (almost 2.5 times as that of graphite), excellent rate capability, nil capacity degradation in long-cycle operation and introduced a higher level of safety by avoiding organic binders. Enhanced properties of the anode were well supported by the structural characterization and can be related to very high Li-ion intercalation on the walls of CNTs, as observed in HRTEM. This newly developed CNT-based anode structure is expected to offer appreciable advancement in performance of future Li-ion batteries.
Optimal Design of a CIGS Module Grid
Authors: Li Yiyang , Yang Shihang , Zhang Xieqiu , Xiao Xudong 
Published: September 2011

ABSTRACTSolar cells based on Cu(In, Ga)Se2 (CIGS) have made significant strides in the past decades with a record efficiency of over 20% [1]. A problem with CIGS modules is the high resistive losses along the transparent top contact. One solution is to deposit highly-conductive metal grids to collect the current. We use finite-element analysis to determine the effectiveness of the metal grid under a variety of parameters. We identify the resistance of the top contact and the width of the scribes as the most important factors in determining whether a metal grid would present a significant efficiency gain. Using the same model, we also investigate methods to optimize the design of the grid.
First-principles Study of Defect Migration in RE-doped Ceria (RE = Pr, Gd)
Authors: Dholabhai Pratik , Adams James , Crozier Peter , Sharma Renu 
Published: September 2011

ABSTRACTOxygen vacancy formation and migration in ceria is central to its performance as an ionic conductor. Ceria doped with suitable aliovalent dopants has enhanced oxygen ion conductivity – higher than that of yttria stabilized zirconia (YSZ), the most widely used electrolyte material in solid oxide fuel cells (SOFC). To gain insight into atomic defect migration in this class of promising electrolyte materials, we have performed total energy calculations within the framework of density functional theory (DFT+U) to study oxygen vacancy migration in ceria, Pr-doped ceria (PDC) and Gd-doped ceria (GDC). We report activation energies for various oxygen vacancy migration pathways in PDC and GDC. Results pertaining to the preferred oxygen vacancy formation sites and migration pathways in these materials will be discussed in detail. Overall, the presence of Pr and Gd ions significantly affects oxygen vacancy formation and migration, in a complex manner requiring the investigation of many different migration events. We propose a relationship that explains the role of additional dopants in lowering the activation energy for vacancy migration in PDC and GDC.
Improved Electrochemical Durability of PtRuAu/C Catalyst Synthesized by Radiolytic Process
Authors: Kageyama Satoru , Murakami Akio , Seino Satoshi , Nakagawa Takashi , Daimon Hideo , Yamamoto Takao A. 
Published: September 2011

ABSTRACTNanoparticle catalyst of PtRuAu/C for direct methanol fuel cell anodes was synthesized by a radiolytic process. Its methanol oxidation activity and the electrochemical durability were evaluated by using the linear sweep voltammetry and the cyclic voltammety. The Au addition significantly improved the durability in comparison with PtRu/C catalyst without losing its high activity. The atomic structure was characterized with techniques of the transmission electron microscopy, the X-ray diffraction, the X-ray fluorescence spectroscopy and the X-ray absorption fine structure. These results implied that the arrangement of Pt and Ru atoms in the PtRuAu/C has no significant difference from that without Au, possessing a structure of Pt rich core and PtRu alloy shell. We concluded that the improvement in durability could originate from these PtRu nanoparticles decorated with Au, but not from particles with high Au contents.
Plasmon-Enhanced Emission Rates from III-Nitride Quantum Wells Using Tunable Surface Plasmons
Authors: Henson J. , DiMaria J. , Dimakis E. , Li R. , Minissale S. , Dal Negro L. , Moustakas T. D. , Paiella R. 
Published: September 2011

ABSTRACTTwo-dimensional arrays of silver nanocylinders fabricated by electron-beam lithography are used to demonstrate plasmon-enhanced near-green light emission from nitride semiconductor quantum wells. Large enhancements in peak photoluminescence intensity (up to a factor of over 3) are obtained, accompanied by a substantial reduction in recombination lifetime indicative of increased internal quantum efficiency. The measured enhancement factors exhibit a strong dependence on the nanoparticle dimensions, underscoring the importance of geometrical tuning for this application.
Consequences of Crystal Structure Differences between C14, C15, and C36 Laves Phase Polytypes for their Coexistence in Transition-Metal-Based Systems
Authors: Stein F. 
Published: September 2011

ABSTRACTIn various binary and ternary transition-metal-based systems, two or even three different polytypes of Laves phases coexist as equilibrium phases. A comparison of different phase diagrams reveals that the coexistence is characterized by some common features. In binary systems with cubic and hexagonal Laves phases existing at the same temperature but different compositions, the cubic C15 polytype always crystallizes at and around the stoichiometric composition whereas the hexagonal C14 and C36 polytypes are observed on theA-rich (C14) andB-rich (C36) side of the stoichiometry, respectively. On replacing theBatoms of an AB2Laves phase by ternary additions, the highest solubility is always found in the C14 Laves phase. Ternary Laves phases A(B,C)2in systems where none of the binary boundary systems contains a Laves phase are always of the C14 type. It is discussed how these observations are related to crystallographic differences between the three polytypic structures C14, C15, and C36.
Thermoelectric Properties of Ge-doped Cu3SbSe4
Authors: Skoug Eric J. , Cain Jeffrey D. , Morelli Donald T. 
Published: September 2011

ABSTRACTTernary variations of the II-VI zincblende semiconductors have received little attention for thermoelectric applications. Here we present the first systematic doping study on Cu3SbSe4, a zincblende-like ternary semiconductor with a unit cell four times larger than the parent II-VI compounds. The large unit cell of Cu3SbSe4results in a low room temperature thermal conductivity (~3.0 W/m*K) and its large hole effective mass produces a Seebeck coefficient approaching 500 μV/K in the undoped compound. Our results show that Ge is an effective p-type dopant in Cu3SbSe4, and the power factor reaches nearly 16 μW/cm*K2at 630K when 3% Ge is added, rivaling that of state-of-the-art thermoelectric materials at this temperature.
Unique metallurgical microstructures and characteristics of nano-amorphous state bulk alloys formed under high gravity by very high speed centrifugal casting
Authors: Furuya Yasubumi , Miura Tsuyoshi , Okazaki Teiko , Yokoyama Masanori , Kimura Hisamichi , Takahashi Shuji , Honda Rikio 
Published: September 2011

ABSTRACTAn innovative “Rapid-Solidification Centrifugal Casting (RSCC) Process” was applied to manufacturing more high functional Fe-based magnetic alloys and some amorphous bulk metallic glassy alloys (BMGs) components. The molten alloys were poured into copper mold with rotation speed up to 6000rpm which can cause the maximum 4000 times as much centrifugal pressurization force as gravity. The bulk components of ring or very small three dimensional component samples of Fe and Zr alloy systems were successfully fabricated within only a few seconds at one process from melts with more cheap production cost. The molten raw BMG alloys (ZrAl system) and Fe-based soft-magnetic alloys(FeGaAl and FeSiB systems) by high frequency induction heating method were poured into copper mold. The fabricated BMG components of artificial tooth and ring of ZrAlNiCu alloy system are almost amorphous state by XRD profiles. Especially, the soft magnetic properties of two Fe-based alloys showed drastic change and were enhanced generally depending on the unique very fine, nano-scale columnar grains with strong texture toward radius direction for FeGaAl(Galfenol) alloy. The magnetization saturation Bs was enhanced up to1.97T in FeSiBPCu alloy. In consequence, according to synergistic effect of rapid solidification and high pressurization casting in this manufacturing process, RSCCP has the technical advantages of expansion of element composition, uniformity of the quality, reduction of internal defects and prevention of degradation at the time of secondary fabrication process of nano-crystalline-structured alloys and BMGs.
The Effects of Annealing on Fatigue Behavior in Zr-based Bulk Metallic Glasses
Authors: Tong Peng , Louca Despina , Yokoyama Yoshihiko , Llobet Anna , Wang Gongyao , Shi Yunfeng , Liaw Peter , King Graham , Spence Rick 
Published: September 2011

ABSTRACTThe effects of annealing and fatigue on the local structure of Zr50Cu40Al10 and Zr60Cu30Al10 bulk metallic glasses (BMG) were investigated using the pair density function (PDF) analysis of synchrotron X-ray and neutron diffraction data. Our results indicate that the two compositions respond differently to annealing. The first PDF peak becomes sharper after annealing in Zr50Cu40Al10 with its intensity increasing, indicating that short-range ordering may be induced after the heat treatment. On the other hand, in Zr60Cu30Al10, the effects due to the heat treatment on the local structure are more subtle. Separately, the as-quenched and annealed alloys with the composition Zr50Cu40Al10 were subjected to fatigue loading conditions with ~ 106 compression cycles. The room temperature measurements showed changes in the local structure with fatigue especially for the annealed sample, involving the Cu-Zr correlations. Our results suggest that the physical properties of BMGs upon fatigue loading conditions may become accentuated due to the structural relaxation brought upon by annealing, leading to observable structural changes at the atomic level from fatigue.