bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Properties of Carbon Nanoparticles
Authors: Melnik Nikolay N.
Published: September 2011

Samples of carbon nanoparticles obtained by different technologies (carbon plasma deposition, irradiation, anodic etching etc.). by Raman scattering and photoluminescence were studied. It was shown that there are carbon nanoparticles which consist of a core containing sp2 bonds and a shell containing sp3 bonds. These particles have a rather intense photoluminescence. We propose the following photoluminescence mechanism of such nanoparticles: first the nanoparticle core absorbs light; further excitation is transmitted to the external cover or environment where photorecombination occurs. This effect occurs when the size of the particles becomes smaller than the size of the wave function excited state of the nanoparticle. The aim of this research is to check this mechanism.
Photocatalytic reforming of formic acid with simultaneous hydrogen production under visible light over CdS sensitized Na2Ti2O4(OH)2
Authors: Tang Wendong , Jing Dengwei , Guo Liejin
Published: September 2011

The present work reports the renewable hydrogen production by an anaerobic photocatalytic reforming of formic acid over CdS sensitized Na2Ti2O4(OH)2 nanotubes. the Na2Ti2O4(OH)2 nanotube was prepared and charactered by X-ray diffraction, UV-visible absorption, transmission electron microscopy, etc. The activity of the catalyst in formic acid was investigated. The greatest photocatalytic reforming activity of formic acid occurs as the formic acid initial concentration is 20 v.%. A probable mechanism for the photocatalytic reforming process was proposed and discussed.
Influence of Process Parameters on Resistive Switching in MOCVD NiO Films
Authors: Wang X.P. , Wouters D.J. , Toeller M. , Meersschaut J. , Goux L. , Chen Y.Y. , Govoreanu B. , Pantisano L. , Degraeve R. , Jurczak M. , Altimime L. , Kittl J.
Published: September 2011

The unipolar resisitive switching properties of MOCVD deposited NiO in Ni/NiO/TiN stacks is reported. The switching quality is defined as function of RESET current and Roff/Ron ratio, and the importance of the Forming current and voltage on these parameters is discussed. The effect of structural stack variations as NiO thickness, Ti doping, and TiN thickness on the switching behavior of NiO is explained by the effect on the forming current and voltage conditions, and on Joule heating dissipation. Thinner NiO films, Ti doping, as well as thicker top electrode improve the switching quality by decreasing the RESET current and increasing the Roff/Ron ratio.
Ion irradiation effects in silicon nanowires
Authors: Nordlund K. , Hoilijoki S. , Holmstr¨om E.
Published: September 2011

Ion irradiation effects in nanowires are of increasing interest due to potential applications of the wires as e.g. current-carrying elements in transistors or as efficient light emitters. Although several experiments have already demonstrated such functionalities, very few theoretical studies on the fundamental mechanisms of ion irradiation have been carried out. To shed light on the basic mechanisms of nanowire irradiation, we have simulated 0.03- 10 keV Ar ion irradiation of Si nanowires with a < 111 >-oriented axis and with all side facets being < 112 >. We compare the results with those for Si surfaces and bulk. The results show that the damage production in the nanowire is strongly influenced by surface effects.
Evaluation of Ultra-thin Layer Fabricated by Wet-process as a Pore-Seal for Porous Low-k Films
Authors: Ono Shoko Sugiyama , Kohmura Kazuo , Tanaka Hirofumi , Kayaba Yasuhisa , Kikkawa Takamaro
Published: September 2011

We focused on detailed evaluations of properties of the ultra-thin pore-seal layer (< 3 nm-thick), such as Cu diffusion barrier property and thermal stability. Cu diffusion into dense thermal silica and porous silica low-k which are covered with the pore seal layer was evaluated using metal-insulator-semiconductor (MIS) capacitors under bias thermal stress (BTS). Triangular voltage sweep (TVS) measurement shows that the ultra-thin layer on dense thermal silica suppresses the drift of Cu ions. The Time-Dependent Dielectric Breakdown (TDDB) lifetime of porous silica low-k covered with the ultra-thin pore seal layer results in a drastic increase of the capacitor lifetime with respect to the no-pore-seal control system (stable at 125 °C at least for 10000 s). Thermal decomposition of bulk material of the pore sealant was measured by thermal gravity (TG) test in nitrogen. Bulk material did not decompose through around 350 °C. The amount of ultra-thin pore seal layer fabricated on silicon wafer after thermal cycle stress in vacuum was measured by x-ray photoelectron spectroscopy (XPS). Amount of pore sealant did not decrease even after 2 cycles of 20 min, at 250 °C. Those results show that the ultra-thin layer, which we propose here, has a potential as a pore seal layer for porous low-k films.
Synthesis and characterization of hybrid CdS/MEH-PPV nanocomposites for photovoltaic applications
Authors: Laera Anna M. , Resta Vincenzo , Piscopiello Emanuela , Schioppa Monica , Tapfer Leander
Published: September 2011

Inorganic-organic nanocomposites, with II-VI or III-V semiconductor nanocrystals (NCs) embedded in semiconducting polymer matrix, are very promising materials for photovoltaic applications.

Here, we present an effective and easy synthesis procedure to obtain a hybrid nanocomposite with CdS NCs dispersed in poly[2-methoxy-5-(2-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) conjugated polymer. CdS NCs are synthesized directly within the matrix through the decomposition of a suitable unimolecular precursor dispersed homogeneously in the polymer.

We show that CdS NCs are formed at low annealing temperature avoiding structural damages and without affecting the functional properties of the MEH-PPV polymer. The NCs diameter ranges between 1.5nm and 4nm depending on the annealing temperature. In addition, no coalescence phenomena of CdS NCs were noticed in TEM observations even at very high particle density (40 wt %).
Photoluminescence X-ray Excitation Spectra in Eu-doped GaN Grown by Organometallic Vapor Phase Epitaxy
Authors: Emura S. , Higashi K. , Itadani A. , Torigoe H. , Kuroda Y. , Nishikawa A. , Fujiwara Y. , Asahi H.
Published: September 2011

X-ray-excited luminescence of GaN doped with Eu ions as a luminescent center was observed in the wavelength range from 350 nm to 650 nm. Three peaks at 375 nm, 550 nm and 622 nm were found. To survey the mechanism of the photoluminescence due to non-resonance excitation, photoluminescence X-ray excitation spectra are also measured. The mechanism of the luminescence occurrence was briefly discussed based on the model developed by Emura et al.
Zinc Oxide Nanorod Films for Electrochemical Urea Biosensor
Authors: Palomera Netzahualcóyotl , Balaguera Marcia , Arya Sunil K. , Hernández Samuel , Tomar Maharaj S. , Ramírez-Vick Jaime E. , Singh Surinder P.
Published: September 2011

Metal oxide nanostructures have shown significant promise for biosensors, gas sensors, photocatalyst and other biomedical applications. Among these, zinc oxide (ZnO) nanostructures, exhibiting interesting properties such as high catalytic activity, biocompatibility, high isoelectric point, large surface to volume ratio, make them a good candidate for biosensing applications. Here we report the synthesis of ZnO nanorods (ZnONR) on ITO films in aqueous phase and its application in Urea biosensor fabrication. ZnONR have been synthesized by a two-step method, first seed growth of ZnO by sputtering on ITO films followed by decomposition of zinc nitrate hexahydrate / hexamethylenetetramine (HMT) in aqueous phase. Exploiting the high isoelectric point of ZnO, a Urease/ZnONR/ITO bioelectrode has been fabricated by physical binding of Urease (Urs) onto ZnONRs. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), and cyclic voltammetry (CV) have been used to characterize ZnONR and the Urs/ZnONR/ITO bioelectrode. The FE-SEM and XRD measurements confirm the formation of ZnONR. The electrochemical data from the Urs/ZnONR/ITO biolectrode reveal linearity between 1-11 mM with sensitivity of 0.9 μA/mM and a relatively low Michaelis-Menten constant (Km) of 5.01 mM for urea sensing. The results indicate the potential of ZnONR films for fabrication of commercial biosensors.
Tailoring the Crystallographic Texture and Electrical Properties of Inkjet-printed Interconnects for Use in Microelectronics
Authors: Cauchois Romain , Saadaoui Mohamed , Inal Karim , Dubois-Bonvalot Beatrice , Fidalgo Jean-Christophe
Published: September 2011

In this paper, silver nanoparticles with a mean diameter of 40 nm are studied for future applications in microelectronic devices. The enhanced diffusivity of nanoparticles is exploited to fabricate electrical interconnects at low temperature. Sintering condition has been tuned to tailor the grain size so that electrical resistivity can be lowered down to 3.4 μOhm∙cm. In this study, a {111}-textured gold thin film has been used to increase diffusion routes. The combined effects of the substrate crystalline orientation and the sintering condition have been demonstrated to have a significant impact on microstructures. In particular, a {111} fiber texture is developed above 300°C in printed silver only if the underlying film exhibits a preferential orientation. This condition appeared as essential for the efficiency of the gold wire-bonding process step. Thus, inkjet-printed interconnects show a prospective potential compared to conventional subtractive technique and offers new opportunities for low cost metallization in electronics packaging.
Effects of Hydrogen Ion Implantation and Thermal Annealing on Structural and Optical Properties of Single-crystal Sapphire.
Authors: Spratt William T. , Huang Mengbing , Jia Chuanlei , Wang Lei , Kamineni Vimal K. , Diebold Alain C. , Matyi Richard , Xia Hua
Published: September 2011

Due to its outstanding thermal and chemical stability, single-crystal sapphire is a crucial material for high-temperature optical sensing applications. The potential for using hydrogen ion implantation to fabricate stable, high temperature optical waveguides in single crystal sapphire is investigated in this work. Hydrogen ions were implanted in c-plane sapphire with energies of 35 keV and 1 MeV and fluences 1016-1017/cm2. Subsequent annealing was carried out in air at temperatures ranging from 500˚C to 1200˚C. Complementary techniques were used to characterize the samples, including ellipsometry and prism coupling to examine optical properties, Rutherford backscattering/ion channeling for crystal defects, and nuclear reaction analysis for hydrogen profiling. Several guiding modes were observed in H-implanted (1 MeV) samples annealed above 800˚C through prism coupling, and a maximum index modification of 3% was observed in the 35 keV samples and 1% in the 1 MeV samples through ellipsometry, with the 1 MeV index variation being confirmed through prism coupling. The possible causes of the index modifications, such as H related defects, as well as implications for tailoring the refractive index of sapphire are discussed.
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

Undoped 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

A 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

In 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

One 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

Mg1-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

We 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

Using 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

Processing 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

We 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

It 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

In 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

The 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

Undoped 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

Rechargeable 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

Solar 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

Oxygen 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

Nanoparticle 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

Two-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

In 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

Ternary 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

An 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

The 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.
Effect of Shot Peening on Fatigue Properties of Zr-based Amorphous Matrix Composites
Authors: Jeon Changwoo , Kim Choongnyun Paul , Lee Sunghak
Published: September 2011

Effects of shot peening on fatigue properties of Zr-based amorphous matrix composite containing ductile crystalline particles were investigated, and fatigue processes were analyzed and compared with those of an as-cast composite. The microstructural analysis results of the shot-peened composite surface indicated that the deformation and surface flexion were observed as the shot-peening time or pressure increased. The compressive residual stress formed on the shot-peened surface was about the half of the ultimate tensile strength, and was not varied much with shot-peening time or pressure. The fatigue limit and fatigue ratio of the shot-peened composite were considerably higher than those of the as-cast composite. This was because the compressive residual stress formed by the shot peening induced the initiation of fatigue cracks at the specimen interior, instead of the specimen surface, thereby leading to the enhanced fatigue limit and fatigue life.
Broadband Coverage Optical Sensor with Liquid Crystalline Materials and Pyroelectrics
Authors: Zhang Jingwen W. , Sun Xiudong , Zhao Hua
Published: September 2011

By utilizing a thin layer of supertwisted liquid crystal and potassium sodium strontium barium noibate crystal material with excellent pyroelectric effect, a broadband coverage optical sensing concept was proposed. Coating the pyroelectric substrate with a carbon layer of excellent absorption in the frequency range of interest, the intensity of an incident mid- or far-IR radiation can be converted to a corresponding intensity variation of a reflected near-IR beam via optical modulation of the liquid crystal film. As the result, the spatial intensity distribution of an incident mid- or far-IR radiation can thus be perceived directly by a low-cost semiconductor sensor/ sensor array. With flexible design of wave collecting arrangement, the broadband coverage sensor is suitable for viewing IR-giving objects with a large field-of-view.
Excitation-Induced Low Temperature Epitaxial Growth of Ge on Si(100)
Authors: Er Ali Oguz , Elsayed-Ali Hani
Published: September 2011

The effect of laser-induced electronic excitations on the self-assembly of Ge quantum dots (QD) on Si(100)-(2x1) grown by pulsed laser deposition is studied. The experiment was conducted in ultrahigh vacuum. A Q-switched Nd:YAG laser (wavelength λ = 1064 nm, 10 Hz repetition rate) was split into two beams; one used to ablate a Ge target while the other to electronically excite the substrate. In situ reflection high-energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM) were used to study the morphology of the grown QDs. The dependence of the QD morphology on substrate temperature and ablation and excitation laser energy density was studied. Electronic excitation is shown to affect the surface morphology. For Ge coverage of 22 monolayer, it was observed that the excitation laser reduces the epitaxial growth temperature to 250 °C, a temperature at which no epitaxy is possible without excitation. Applying the excitation laser to the substrate during the growth changes the QD morphology and island density and improves the size uniformity of QDs at 390 °C. Surface diffusion measurement calculated from RHEED recovery curves show that the excitation-laser increases the surface diffusion of the Ge atoms. A purely electronic mechanism of enhanced surface diffusion of the Ge adatoms is involved.
Stability and Dynamics of Boron Nitride Nanoscrolls
Authors: Perim Eric , Galvao Douglas S.
Published: September 2011

We report here molecular dynamics results for boron nitride nanoscroll structures (BNNSs) with relation to their stability and formation mechanisms. We show that, similarly to carbon nanoscrolls, BNNSs are stable due to van der Waals interactions among overlapping layers. The energy balance between losses and gains (due to elastic deformations and van der Waals interactions, respectively) when the structure is rolled up leads to the existence of a critical value of the internal scroll diameter where stable or metastable structures can be formed. The mechanisms of scroll formation and stability as a function of their chirality were also investigated.
Gold in Flux-less Bonding: Noble or not Noble
Authors: Balucani Marco , Nenzi Paolo , Palma Fabrizio , Bandarenka Hanna , Dolgyi Leonid , Shapel Aliksandr
Published: September 2011

This work highlights the solder joints reliability issues emerged during the development of a novel compliant contacting technology. The peculiar process in this technology is a mechanical lifting procedure in which a pulling force is exerted onto 63Sn-37Pb (eutectic) solder joints (realized by a flux-less thermo compression process), releasing metal traces from the substrate, to form free standing vertical structures. Since joints mechanical characteristics are critical for the successful fabrication of contacts, different bonding conditions (inert or forming atmosphere, temperature rates) and surface finishing (electroplated gold and preformed solder) have been tested. SEM and EDX analyses have been performed on failing joints to investigate failure causes and classify defect typologies. A constantly higher failure rate (percent number of failing joints) has been observed on gold finished surfaces. Analyses proved that such unusual rate was due to contamination of gold surface left by additives in the plating bath and to the embrittlement caused by gold diffusion into molten solder. Plating additives contamination reduces the wettability of gold surfaces. Concentration values of 3 wt.% for gold, considered safe for surface mount applications, caused embrittlement in solder bumps of 20-40 μm diameters.
Investigation of Nanofibrillar Influence on Cell-Cell Interactions of Astrocytes by Epi-fluorescence and Atomic Force Microscopies
Authors: Tiryaki Volkan M. , Ayres Virginia M. , Khan Adeel A. , Flowers Dexter A. , Ahmed Ijaz , Delgado-Rivera Roberto , Meiners Sally
Published: September 2011

Long distance intercellular communication between astrocytes on nanofibrillar and planar surfaces was investigated by epi-fluorescence microscopy and atomic force microscopy. We found that astrocytes on nanofibrillar surfaces and astrocytes on planar surfaces diverged in apparent cell-cell contact structures. Astrocytes on nanofibrillar surfaces exhibited a “single cellular process” response, while astrocytes on planar surfaces exhibited a filopodial network response. The possibility that astrocytes can sense their geometrical environment and form different cell-to-cell contacts on nanofibrillar versus planar surfaces, with activation of different signaling pathways, is discussed.
Development and Fundamental Characteristics of a Prototype Magnetocaloric Heat Pump
Authors: Kawanami Tsuyoshi , Hirano Shigeki
Published: September 2011

The primary objective of this study is to discuss the optimum operating conditions of magnetocaloric heat pumps according to the fundamental heat transfer characteristics of an active magnetic regenerator (AMR) bed. The AMR cycle has four sequential processes: magnetization, heat exchange fluid flow, demagnetization, and heat exchange fluid blow. The fundamental heat transfer characteristics of each process of the AMR cycle is investigated minutely. Moreover, the cooling power and the overall system performance are evaluated when the system is running continuously.

In addition to the aforementioned investigation, we have developed a prototype rotational magnetocaloric heat pump having a compact component arrangement and an uncomplicated control system. A performance evaluation has been conducted to obtain the optimum conditions for practical operation. The operation parameters such as the heat transfer fluid flow rate, rotational frequency, and initial temperature of the heat transfer fluid are examined, and the variations of the maximum temperature span between the inlet and outlet for the heat transfer fluid are discussed. As a result, the values of the optimum rotational frequency and flow rate are obtained to obtain the maximum temperature span between the inlet and outlet of the present magnetocaloric heat pump.
Discovery of γ-B28, a Novel Boron Allotrope with Partially Ionic Bonding
Authors: Oganov Artem R.
Published: September 2011

γ-B28is a recently discovered high-pressure phase of boron, with the structure consisting f icosahedral B12clusters and B2pairs in a NaCl-type arrangement: (B2)δ+(B12)δ-, and displaying a significant charge transfer δ~0.48. Boron is the only light element, for which the phase diagram has become clear only a few years ago, with the discovery of γ-B28, and this phase diagram is discussed here among other recent findings. γ-B28was first experimentally obtained as a pure boron allotrope in early 2004 by J.H. Chen and V.L. Solozhenko (although a similar diffraction pattern was published in a 1965 by R.H. Wentorf, in a paper that until recently was believed to be wrong) and its unique structure was discovered by A.R. Oganov in 2006 with the use of theab initioevolutionary algorithm USPEX (Oganov & Glass, 2006) and later confirmed by other studies. This allotrope, thermodynamically stable at high pressures, is shown to be also quenchable and dynamically stable upon decompression to 1 atm, and we show its phonon dispersion curves. Present discussion includes also the relative stability of other boron allotropes as a function of pressure. We also discuss more recent publications on the putative isosymmetric phase transition in γ-B28and the nature of chemical bonding in it. We demonstrate that a qualitative difference in the evolution of the band gap of γ-B28and the related α-B12structure, which is due to the partial ionicity of γ-B28.
Nanostructured Telluride Films on Macroporous Silicon for High Efficiency Thermoelectric Devices
Authors: Robinson Hans D. , Sneh Ofer , Kochergin Vladimir
Published: September 2011

We propose using macroporous silicon as an ultra-high aspect ratio scaffolding for epitaxially grown thermoelectric materials, so that thin films can be shaped into materials thick enough for practical devices. The self-limiting nature of atomic layer deposition (ALD) makes it an ideal growth technique for this substrate, as uniform thickness can be obtained at all points inside the macroporous structure, and we demonstrate successful deposition of antimony telluride on pore walls using ALD. Extension of this work to telluride superlattices should enable fabrication of thermoelectric devices with figures of merit (ZT) in excess of 2. Characterization of the thermoelectric and other properties of ALD grown telluride on silicon is ongoing.
Effects of temperature dependent chemical potential on the Seebeck coefficient of TiS2 thermoelectric material
Authors: Takeuchi Tsunehiro , Yamamoto Akio , Ogawa Koto
Published: September 2011

The relation between chemical potential and Seebeck coefficient was investigated by using high-resolution angle resolved photoemission spectroscopy. The temperature dependence of chemical potential was experimentally determined for the n-type TiS2 thermoelectric material and compared with the measured Seebeck coefficient. We found that the temperature dependence of chemical potential of TiS2 is significantly large, and its effect on Seebeck coefficient is not negligible. This fact strongly indicates that the temperature dependence of chemical potential has to be properly understood to construct the guiding principle for developing new, practical thermoelectric materials.
Excited Multiplets of Eu in GaN
Authors: Hourahine Ben
Published: September 2011

A method to calculate the multiplet states of lanthanide impurities in solids is presented. This approach is based on a semi-empirical density functional method which includes corrections to account for the correlation and spin-orbit coupling of the 4f electrons. Specific multiplet states of the rare earth are produced by constraining the system. This approach is then used to investigate some of the properties of substitutional europium impurities in gallium nitride, reproducing the relative energy of two multiplets, and discussing a potential excitation mechanism for these centers.