bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Erosion of TiO2 subjected to Energetic Oxygen Bombardment
Authors: Smith Roger , Möller Wolfhard
Published: April 2011

The effect of energetic oxygen bombardment of the TiO2 rutile {110} surface is studied by means of molecular dynamics simulations using a variable charge potential. A random selection of O atoms and O2 molecules are incident successively and normally onto the surface. At an energy of 5 eV the surface becomes saturated with oxygen until covered with between 1 and 2 monolayers of adatoms. As the fluence further increases Ti atoms are pulled out from the bulk and become surrounded by the O atoms forming well-defined atomic clusters on the surface which then desorb. At bombardment energies of 400 eV, the O atoms penetrate into the bulk and voids form whose surfaces are decorated with oxygen atoms. As the O fluence further increases the surface is sputtered and the voids then intersect the surface forming a very rough topography.
COMPARISON OF DEMINERALIZED AND DEPROTEINIZED BONE
Authors: Castro-Ceseña Ana B. , Novitskaya Ekaterina , Chen Po-Yu , Sánchez-Saavedra M. del Pilar , Hirata Gustavo , McKittrick Joanna
Published: April 2011

Cortical and cancellous bones were demineralized and deproteinized using 1 N HCl and 6% NaOCl, respectively. Experiments were performed at 37°C. The rate constants were calculated and the structural features of untreated and completely demineralized and deproteinized samples were studied by scanning electron microscopy, showing that intact, contiguous structures were obtained. For both cases, the rate constant was higher for cancellous bone than the cortical bone.
Enhanced UV Photon-response of Tin Nano Cluster Loaded- laser Irradiated ZnO Thin film detector
Authors: Menon Rashmi , Sreenivas K. , Gupta Vinay
Published: April 2011

Zinc Oxide (ZnO), II-VI compound semiconductor, is a promising material for ultraviolet (UV) photon sensor applications due to its attractive properties such as good photoconductivity, ease processing at low temperatures and excellent radiation hardness. The rf magnetron sputtering is a suitable deposition technique due to better control over stoichiometry and deposition of uniform film. Studies have shown that the presence of surface defects in ZnO and subsequently their passivation are crucial for enhanced photo-response characteristics, and to obtain the fast response speed. Worldwide efforts are continuing to develop good quality ZnO thin films with novel design structures for realization of an efficient UV photon sensor. In the present work, UV photon sensor is fabricated using a ZnO thin films deposited by rf magnetron sputtering on the corning glass substrate. Photo-response, (Ion/Ioff) of as-grown ZnO film of thickness 100 nm is found to be 3×103 with response time of 90 ms for UV intensity of 140 μW/cm2 (λ = 365 nm). With irradiation on ZnO thin film by pulsed Nd:YAG laser (forth harmonics 266 nm), the sensitivity of the UV sensor is found to enhance. The photo-response increases after laser irradiation to 4x104 with a fast response speed of 35 ms and attributed to the change in surface states and the native defects in the ZnO thin film. Further, enhancement in the ultraviolet (UV) photo-response (8×104) of detector was observed after integrating the nano-scale islands of Sn metal on the surface of laser irradiated ZnO thin film.
Effect of Different High-K Dielectrics on the Pt Nanocrystal Formation Statistics (size, density and area coverage) for Flash Memory Application
Authors: Misra Abhishek , Sadana Sunny , Suresh Satya , Bhaisare Meenakshi , Srinivasan Senthil , Waikar Mayur , Gaur Amit , Kottantharayil Anil
Published: April 2011

We here present, metal nanocrystal (NC) formation statistics (size, density, occupancy or area coverage) on different high dielectric constant (high-K) materials which may be used as tunnel dielectric or intermetal dielectric in flash memory devices. Four important high-K materials viz. SiO2, Al2O3, HfO2 and Si3N4 are chosen for this purpose and the nanocrystal formation statistics has been found to be strongly dependent on dielectric. Among all the four dielectrics, smallest size nanocrystals with largest density are obtained on Al2O3 dielectric while on HfO2 bigger size nanocrystals are formed. This difference in nanocrystal size and density on different dielectrics is attributed to the different surface properties of these materials.
Electronic States and Magnetic Coupling in Fe/Fe3O4 Junctions
Authors: Inoue J. , Kida T. , Honda S. , Itoh H. , Yanagihara H. , Kita E. , Mibu K.
Published: April 2011

Exchange coupling observed recently in Fe/ Fe3O4 (001) junctions shows comparable intensity to that in Co/Ru/Co trilayers, and has potential applicability to spintronics devices. To clarify the mechanism of the exchange coupling, electronic and magnetic states of Fe/ Fe3O4 junctions are calculated in the first principles method by assuming four junction structures of bcc Fe and Fe3O4 layers. It is shown that the local moments of bcc Fe atoms at the interface increase, but those of Fe ions at the interface of Fe3O4 layer decrease. The total energy of the junctions is plotted as a function of distance between Fe and Fe3O4 layers. Calculated results of the coupling energy between Fe and Fe3O4 layers, however, are larger than experimental ones by two orders of magnitude, and they correspond to inter-atomic exchange interactions at the interface. In order to explain the experimental results, we propose a mechanism of exchange coupling mediated by impurity-like states of interfacial Fe atoms which possess reversed magnetic moments in bcc Fe layer. Frustration effects in exchange coupling between Fe and Fe3O4 layers are also discussed.
Thermoplastic Wire Drawing from Bulk Metallic Glass
Authors: Bossuyt Sven , Soinila Erno , Penttinen Henri , Pulkki Ville , Hänninen Hannu
Published: April 2011

The low loss coefficient and high elastic energy storage of amorphous metals may provide novel opportunities in the design of stringed musical instruments. To produce prototypes for metallic glass music wire, bulk metallic glass pre-forms were reheated into the supercooled liquid region and stretched into wires. Investigations of these wires’ geometrical, mechanical, and physical properties are reported. The process is relatively simple and could be practical for producing continuous wire. A theoretical analysis shows the importance of the interaction between heating power input, radiative and convective cooling, and area reduction in determining the wire’s final properties.
(CdSe) ZnS core shell quantum dots decorated zinc oxide nanowires for solar energy harvesting applications
Authors: Prasad Abhishek , Pandey Archana , Walczak Karl , Friedrich Craig , Yap Yoke Khin
Published: April 2011

ZnO nanostructures have proven to be versatile functional materials with promising electronic, piezoelectric and optical properties. Here, we report on the application of (CdSe) ZnS Core Shell quantum dots decorated ZnO Nanowires (ZnONWs) and Nanobelts (NBs) in solar energy harvesting. Results indicate that both as grown and decorated ZnO Nanostructures are photoactive, have a fast response time and generate photocurrent under excitation in a photoelectrochemical cell setup. An order of magnitude enhancement in the photocurrent response of (CdSe) ZnS Core Shell quantum dots decorated ZnONBs is seen as compared to response from as grown ZnONBs. Generated photocurrent decreases with time but stabilizes at higher value for (CdSe) ZnS Core Shell quantum dots coated ZnONBs. Detailed performances of these devices are discussed.
A Study of Point Defects and Cause of Nonstoichiometry in InSb Nanowires
Authors: Philipose U. , Sapkota Gopal , Gali Pradeep , Nukala Prathyusha
Published: April 2011

Synthesis of InSb nanowires using chemical vapor deposition (CVD) is technically challenging due to the tuning of III-V vapor pressures. Growth parameters such as the choice of the metal catalyst, growth temperature and vapor pressure of constituents affect the morphology and stoichiometry of InSb nanowires. By controlling the growth temperature, it was possible to grow either stoichiometric InSb nanowires or In nanowires that contained no Sb within detectable limits. We present a simple model to show that the occurrence of native point defects in InSb is influenced by the growth kinetics and by the thermodynamics of defect formation. Results from this model are in good agreement with our experimental findings of the evidence of point defects in these nanowires.
The effect of Oxygen partial pressure during deposition in the magnetic properties of ZnO thin film
Authors: Biswas Anis , Shirong Wang , Nagar Sandeep , Belova L. , Rao K. V.
Published: April 2011

We have studied the magnetic properties of 100 nm thick ZnO thin films prepared by magnetron sputtering in different oxygen partial pressures (ratio of oxygen pressure to total pressure in deposition chamber, POxy). Only the films fabricated at POxy below ~ 0.5 show room temperature ferromagnetism. The saturation magnetization at room temperature is initially found to increase as POxy increases and reaches maximum value of ~ 5 emu/gm at POxy ~ 0.3 and then starts to decrease and becomes diamagnetic for POxy > 0.5. From small angle XRD study of structural properties of the films, we find that the lattice stress developed in the film along c-axis also exhibits a similar behavior with the variation of POxy. Thus, both the room temperature ferromagnetism and lattice stress appear to originate from the intrinsic defects present in the sample.
Singlet Exciton Quenching by Radical Cations of Aromatic Diamines as an Electron Donor in Organic Electroluminescent Devices
Authors: Battulga Munkhbat , Bolormaa Gendensuren , Naranbileg Batjargal , Ganzorig Chimed
Published: April 2011

In this study, we report the luminescence quenching by radical cations of aromatic diamines used as a hole transport layer (HTL) in organic electroluminescent (EL) devices. The EL characteristics of green organic EL devices with an electron transport layer (ETL) as an emitter i.e. ITO/TPD HTL/Alq3ETL/Al is studied. Here, ITO, TPD, and Alq3are abbreviations for indium-tin-oxide, N,N’-diphenyl-N,N’-bis(3-methylphenyl)-1,1’-biphenyl-4,4’-diamine, and tris (8-hydroxyquinoline) aluminum, respectively. UV-visible absorption and electrochemical data indicate the formation of radical cations in thin film and solution of TPD after chemical oxidation. We find that the EL luminance increases less than linearly with an increase in current for the EL devices studied in this study. The luminance loss in the devices is attributed to quenching of singlet excited states by large excess radical cations of TPD are accumulated in the emission zone due to large overlap between a flourescence spectrum of Alq3and an absorption spectrum of radical cations of TPD.
Electroluminescence Characteristics of Inorganic
(p-GaN/MgO)-Organic (Alq3) Hybrid p-n Junction Light Emitting
Diodes
Authors: Kikuchi Akihiko , Tsuji Tomoyuki
Published: April 2011

Inorganic/organic hybrid light-emitting diodes (LEDs) (IO-HyLEDs) composed
of p-type GaN/n-type Tris-(8-hydoroxyquinoline) aluminum (Alq3)
were fabricated with and without thin MgO electron-blocking layer (EBL) at
the inorganic/organic interface. These LEDs showed clear and stable current
rectifying diode characteristics and electroluminescence (EL) peaked at UV
region at room temperature. For the sample with MgO-EBL, obvious enhancement
of green emission from Alq3 layer was observed. This result
suggests that due to effective suppression of electron transport from
Alq3 to p-GaN by MgO-EBL, radiative recombination of electrons
and holes in Alq3 layer was enhanced. It was indicated that the
band engineering technique can be applied to control the emission property
of inorganic/organic hybrid LED.
Stability of fast elaborated small CdS quantum
dots
Authors: Fregnaux M. , Dalmasso S. , Gaumet J.-J. , Laurenti J.-P.
Published: April 2011

Small size CdS QDs were synthesized by (i) the single source precursor
methodology and by (ii) the microwave synthetic route. The consequences of
CdS QD direct exposure to air for a period of 7 days were investigated by
following the evolution of the photoluminescence (PL) and absortion spectra.
For QDs obtained by (i), the excitonic emission band (3.0 ‑ 3.1 eV)
decreases in intensity, relatively to the low energy one (2.2 ‑ 2.5 eV)
tentatively associated to midgap surface states. This suggests arising of
new recombination path(s) associated to degradations during aging, possibly
an oxidative formation of a CdO surface layer. On the other hand, no
significant change is observed in the absorption spectra. For QDs obtained
by (ii), no degradation is revealed by the PL spectra which remain
unchanged. On the other hand, the absorption spectra are dominated by an
unexplained broad band around 3.6 eV which tends to hide the fundamental
excitonic transition one and increases in intensity with aging.
Evidence of Conjugation Enhancement in P3HT/SWNT Mixtures for
Organic Photovoltaics
Authors: Bernardi Marco , Giulianini Michele , Motta Nunzio , Grossman Jeffrey C.
Published: April 2011

Classical molecular dynamics (MD) simulations in conjunction with optical
absorption and AFM/nano-Raman experiments are employed to relate the
molecular-scale arrangement and conjugation of poly-3-hexylthiophene (P3HT)
adsorbed onto single-walled carbon nanotubes (SWNTs) and multi-walled carbon
nanotubes (MWNTs). Taken together our results demonstrate the templating
role of carbon nanotubes in increasing the π-conjugation length of the P3HT
at the P3HT/carbon nanotube interface. The MD simulations show that SWNTs
and MWNTs, due to their inherent 1-dimensional (1D) cylindrical shape and
π-conjugation, planarize the P3HT molecules adsorbed at their surface and
thus quench their torsional disorder, regardless of the P3HT conformation
and nanotube chirality. This effect is more significant for higher SWNT
weight fractions in the sample (since it is an interface effect). We
investigated this effect experimentally by acquiring nano-Raman spectra in
regions of high-MWNT/low-P3HT content in addition to optical absorption
spectra of P3HT-SWNT composites with different SWNT concentrations . The
increase in the P3HT conjugation is confirmed by a shift of a P3HT feature
in the Raman spectrum when going from P3HT-rich to SWNT-rich areas in the
mixture. The significance of this work for charge transfer at the P3HT-SWNT
interface in bulk-heterojunction solar cells is discussed.
Charge transport in ambipolar pentacene thin film
transistors
Authors: Rahimi Ronak , Korakakis D.
Published: April 2011

Ambipolar organic transistors are technologically interesting because of
their potential applications in light-emitting field-effect transistors [1]
and complementary-metal-oxide-semiconductor (CMOS) devices by providing ease
of design, low cost of fabrication, and flexibility [2]. Although common
organic semiconductors show either n- or p-type charge transport
characteristic, organic transistors with ambipolar characteristics have been
reported recently. In this work, we show that ambipolar transport can be
achieved within a single transistor channel using LiF gate dielectric in the
transistors with pentacene active layer. This ambipolar behavior can be
controlled by the applied source-drain and gate biases. It was found that at
low source-drain biases multistep hopping is the dominant conduction
mechanism, while in high voltage regimes I-V data fits in Fowler-Nordheim
(F-N) tunneling model. From the slope of the F-N plots, the dependency
between field enhancement factor and the transition point in conduction
mechanism upon gate bias has been extracted. The transition points show more
dependency on gate voltage for negative biases compared to the positive
biases. While sweeping negative gate voltages from -5 to -20 V, the
source-drain voltages change from about 27 to 17 V. On the other hand, for
positive gate voltages from 5 to 20 V, the value of the transition point
stays at approximately 36 V. In order to further understand the transport
mechanisms, new structures with an interface layer between dielectric and
active layer have been fabricated and characterized. As expected, a
significant decrease in the amount of the source-drain current has been
observed after introducing the interface layer.
Magnetization Effects in bulk YFeO3 and their dependency on electric field strength and temperature as a basis for thin film investigation of Multiferroic Technology
Authors: Hinckley A. , Gupta R.K. , Kahol P.K. , Ghosh K.
Published: April 2011

Multiferroics, the study of materials which possess ferromagnetic and ferroelectric ordering in a single phase, has become an area of prominent research. Moreover, this behavior has been extensively studied in materials which possess a perovskite crystal structure such as BiFeO3 and YMnO3. Due to their weak saturation magnetic moment, many rare-earth orthoferrites are currently of extreme interest. Utilizing a solid-state reaction between Y2O3 and Fe2O3 we have developed the rare-earth orthoferrite YFeO3 and conducted a bulk material study to determine this material’s availability for thin film multiferroic research. The absence of Y2O3 and Fe2O3 impurities was confirmed using Copper-Kα XRD. Examination of the dependence of the magnetization M on the temperature T was conducted to determine the reliability of multiferroic behavior across varying temperatures in conjunction with the investigation of the dependence of M on the electric field strength H. Results clearly display ferromagnetic behavior in our bulk material, providing ample evidence that our bulk material is an excellent candidate for thin film studies. Future studies on multiferroic YFeO3 thin films grown via pulsed laser deposition on Lanthanum Aluminate substrates will be conducted. Detailed data will be provided via XRD and SQUID to confirm magnetic properties while impurities are non-existent in our thin films.
Alloying Effect of Ta on Microstructure and Mechanical Properties of Ni3(Si,Ti) Intermetallic Alloy
Authors: Imajo Daiki , Kaneno Yasuyuki , Takasugi Takayuki
Published: April 2011

The refractory element Ta was added to L12-type Ni3(Si,Ti) intermetallic alloys in order to substitute for Ti. The microstructure and the mechanical properties of the alloys were investigated as a function of the Ta content. All the alloys were doped with 50 wt.ppm boron to suppress intergranular fracture. The alloys containing up to 5 at.% Ta showed an L12 single-phase microstructure, while the alloys containing more than 5 at.% Ta exhibited a two-phase microstructure consisting of Ni3Ta particles in the L12 matrix. At room-temperature (RT), the hardness of the alloys with the L12 single-phase microstructure increased with increasing Ta content due to solid solution hardening of Ta. RT yield stress (0.2% yield strength) and tensile ultimate strength of the alloys with the L12 single-phase microstructure increased with increasing Ta content keeping a high level of tensile elongation. At high-temperature (HT), the positive temperature dependence of hardness was observed in all the alloys, irrespective of Ta addition. HT hardness was also enhanced by the addition of Ta. It was consequently demonstrated that Ta is a remarkable solid solution hardening element in the Ni3(Si,Ti) alloys.
Indium Alloy as Cadmium Brush Plating Replacement
Authors: Berman Elizabeth , Brezovec Paul , Klingenberg Melissa , Naguy Thomas , Schmura Eileen , Voevodin Natasha
Published: April 2011

It is well-known that cadmium and its corrosion product (cadmium oxide) are carcinogenic and toxic. Consequently, efforts to eliminate cadmium from original equipment and repair processes have been on-going. One potential replacement is indium, which is a soft post-transition metal, whose primary use is in the form of indium tin oxide, e.g., in liquid crystal displays (LCDs). The semi-conductive properties of indium oxide alloys make it possible to use these for cadmium brush plating replacement in applications where contact resistance and impedance are critical parameters. Critical requirements of an alternative to cadmium brush plating in a corrosive industrial atmosphere are (1) be sacrificial to mild steel and (2) provide good electrical conductivity. Cadmium oxide remains semi-conductive, while most other pure metal oxides are electrical insulators, such as aluminum oxide, nickel oxide, and zinc oxide, and therefore, fail in meeting the requirement for bonding and grounding. Similar to cadmium oxide, indium oxide is semi-conductive, but indium exhibits other properties such as cold welding. This paper discusses indium- electroplating approaches to overcome the insulating limitation of pure metal plating and to replace cadmium brush plating. Test results are given for the brush-plated indium-tin alloy as compared to cadmium brush plating and conclusions on such replacement feasibility are provided.
The ductility of cast TiAl-based alloys
Authors: Loretto M H , Wu Z. , Chu M Q , Hu D
Published: April 2011

The factors which influence the ductility of cast samples of TiAl-based alloys are briefly reviewed with emphasis on alloys where microstructural refinement has been used in an attempt to improve ductility. The grain size in cast samples of different TiAl-based alloys can be refined either by high additions of about 1at% boron, or by lower additions of about 0.2at%. In addition it is possible to refine the microstructure by massively transforming samples and heat treating the transformed samples in the (alpha + gamma) phase field to precipitate alpha. Significantly different ductilities are found in different alloys with similar grain sizes or with similar microstructures and the origins of the improvements in ductility and of these differences are discussed in this paper. The role of alloying elements in influencing the degree of order in alpha 2 and in turn influencing slip in alpha 2 is discussed.
Low-damage Processing of Organic Materials with Size-controlled Gas Cluster Ion Beams
Authors: Nakagiri Motohiro , Toyoda Noriaki , Yamada Isao
Published: April 2011

Organic materials have been widely used in various fields of electronic applications. However, they are difficult to process without damage by using a conventional ion beam which use energetic ions. In this study, gas cluster ion beam (GCIB), which shows low-damage process, was used for organic materials, and irradiation effect of size selected GCIB was studied with Xray photoelectron spectroscopy (XPS). In the case of irradiation of 500 eV Ar ion (monomer ion) on polyimide, the intensities of both N-C=O and C-O bond decreased after irradiation. On the other hand, there was small change in the XPS spectra after 15 keV Ar-GCIB irradiation with the same ion dose. The etching rate of polyimide per one ion with 15 keV Ar-GCIB was almost 1.8×104 times higher than that with 500 eV Ar monomer ions. The damages in polyimide decreased with increasing the Ar cluster size owing to the reduction of energy per atom at acceleration voltage of 15 kV. After irradiation of size selected 5 kV Ar cluster ion, damage was almost negligible. Although, the surface became rough after irradiation of Ar-GCIB, surface roughness and the change of chemical bond were very small with N2-GCIB irradiation. Ar-GCIB irradiation on dye-sensitized solar cells (N719) showed that very low-damage process is possible with GCIB, and it indicated that GCIB is suitable for surface processing of organic materials used in electronic devices.
Creating Novel Transport Properties in Electric Double Layer Field Effect Transistors Based on Layered Materials
Authors: Ye J. T. , Craciun M. F. , Koshino M. , Russo S. , Kasahara Y. , Yuan H. T. , Shimotani H. , Morpurgo A. F. , Iwasa Y.
Published: April 2011

We present a study on the liquid/solid interface, which can be electrostatically doped to a high carrier density (n~1014 cm-2) by electric-double-layer gating. Using micro-cleavage technique on the layered materials: ZrNCl and graphene, atomically flat channel surfaces can be easily prepared. Intrinsic high carrier density transport regime is accessed at the channel interface of electric double-layer field effect transistor, where novel transport properties are unveiled as the field-induced superconductivity on the ZrNCl with high transition temperature at 15 K, and accessing a high carrier density up to 2×1014 cm-2 in graphene and its multi-layers.
Influence of Quenching Rates on the Transformation of Ternary Phases in Nb-rich γ-TiAl Alloys
Authors: Stark Andreas , Oehring Michael , Pyczak Florian
Published: April 2011

Intermetallic γ-TiAl based alloys with additional amounts of the ternary bcc β phase attracted increasing attention in recent years due to their improved workability at elevated temperatures. At lower temperatures the ductile high-temperature β phase can transform to several ordered phases. However, actually available phase diagrams of these multiphase alloys are quite uncertain and the precipitation kinetics of some metastable phases is far from understood.

In the present study various transformations of the third phase are observed in situ by means of high-energy x-ray diffraction using synchrotron radiation. A Ti-45Al-10Nb (at.%) specimen is subject to a temperature ramp of repeated heating cycles (700 °C - 1100 °C) with subsequent quenching at different rates. Depending on the quenching rate reversible transformations of the B2-ordered βophase to different ω related phases are observed in Ti-45Al-10Nb. At low quenching rates the hexagonal B82-ordered ωophase is formed while at high quenching rates the metastable intermediate trigonal ω’’ phase can be preserved. The results indicate that the complete transformation from βoto hexagonal B82-ordered ωoconsists of two steps which are both diffusion controlled.
Effect of Microstructure on Cold Workability of Ni3Si base Multi-Phase Intermetallic Alloys
Authors: Kaneno Yasuyuki , Matsuoka Yasuyuki , Takasugi Takayuki
Published: April 2011

The effect of microstructure on cold-rolling workability and tensile properties of Ni3Si (L12)−Ni3Ti (D024)−Ni3Nb (D0a) multi-phase intermetallic alloys was investigated. The cast alloys with different microstructures containing the D024 phase and/or the D0a phase particles in the L12 matrix were homogenized and then cold rolled. For the alloys with the microstructure consisting of coarse plate-like D024 particles in the L12 matrix, serious cracks initiated at the coarse D024 particles in the early stage of the cold rolling process and then propagated, resulting in failure of the rolled plate. On the contrary, for the alloys with the microstructure consisting of fine needle-like D024 precipitates and/or granular-shaped D0a particles, these second phase particles did not spoil the cold workability, leading to successful cold rolling to 90 % reduction. After 90 % cold rolling, the rolled sheets were fully recrystallized at 1173 K for 1 h, resulting in the formation of a fine-grained microstructure. The room-temperature tensile strength and the yield stress of the recrystallized sheet were remarkably enhanced compared with that of the unrolled alloys, possibly due to the fine-grained microstructure as well as the particle hardening. Also, the high-temperature tensile strength and the elongation were improved in the recrystallized sheets compared to an L12 single-phase Ni3(Si,Ti) alloy sheet. Consequently, it was found that the cold rolling and annealing process was beneficial to improve the tensile properties for the present multi-phase intermetallic alloys.
Thermal effects on the Raman spectra of nanodiamonds
Authors: Chaigneau Marc , Girard Hugues A. , Arnault Jean-Charles , Ossikovski Razvigor
Published: April 2011

We report on the influence of the laser heating effect, potentially present in a Raman scattering experiment, on the behaviour of carbon phonon lines in the spectra of nanodiamond particles. Aside from the laser power used in the experiment, the extent of the thermal effect in question depends also on the nanodiamonds origin (obtained through detonation and high pressure high temperature techniques) as well as on the nanoparticles size. Laser heating should be properly taken into account when discussing Raman spectra of carbonaceous species, in particular, prior to addressing peak assignment and possible quantum confinement effects.
Phase Equilibria and Phase Transformations in Molybdenum-Containing TiAl Alloys
Authors: Mayer Svea , Sailer Christian , Nakashima Hirotoyo , Schmoelzer Thomas , Lippmann Thomas , Staron Peter , Liss Klaus-Dieter , Clemens Helmut , Takeyama Masao
Published: April 2011

Molybdenum, being a strong β stabilizer, is an important alloying element in TiAl alloys, since a significant volume fraction of the disordered bcc β-phase at elevated temperatures improves the processing characteristics during hot-working. Unfortunately, the effect of Mo on the individual phases and their transition temperatures is not completely known but is necessary for designing engineering applications. In this paper, sections of the Ti-Al-Mo ternary phase diagram derived from thermodynamic calculations as well as experimental data are presented. Further, the phase transition temperatures given by the phase diagrams are compared with results from isothermal heat treatment studies, differential scanning calorimetry measurements and in-situ high-temperature diffraction experiments. Combining all of these results, a revised phase diagram is proposed.
Group theoretical analysis of nitrogen-vacancy center’s energy levels and selection rules
Authors: Maze J. R. , Gali A. , Togan E. , Chu Y. , Trifonov A. , Kaxiras E. , Lukin M. D.
Published: April 2011

We use a group theoretical approach to model the nitrogen-vacancy defect in diamond. In our analysis we clarify several properties of this defect that have been source of controversy such as the ordering of the singlets and the mechanism that leads to spin mixing in the excited state of this defect. In particular, we demonstrate that the ordering of the ground state configuration (e2) is {3A2, 1E, 1A1} and that the spin-spin interaction causes the mixing in the excited state. In addition, we analyze the angular momentum and spin properties of the excited state structure that enables a spin photon entanglement scheme that has been recently demonstrate experimentally. Our description is general and it can be easily applied to other defects in solid-state systems.
Optimization of a Boron Doped Nanocrystalline Diamond Temperature Regulator for Sensing Applications
Authors: Clukers Tim , Van Grinsven Bart , Vandenryt Thijs , Janssens Stoffel D. , Wagner Patrick , De Ceuninck Ward , Thoelen Ronald , Daenen Michaël , Haenen Ken
Published: April 2011

Recently, the concept of creating a boron doped nanocrystalline diamond (B-NCD) based temperature regulator for bio-sensing applications was proven. In this work, the next step is taken, i.e. one device working simultaneously as thermistor and heater. In combination with a PID-control., it is possible to create a temperature control, with possible set points going from room temperature till 70°C, with an accuracy exceeding a maximum temperature variation of 0.2 °C. Parallel with steering the temperature by varying the current through the B-NCD film, its resistance is measured with a 4-point measurement from which the temperature can be derived using a calibration curve. This value is the feedback for the PID-control to steer the current used for the regulation.
Structural, Transport, and Magnetic Characterization of NiZr Metallic Glasses with varied Ni/Zr composition
Authors: Isakovic A. F. , Sulejmanovic S. D. , Mihac T. P. , Evans-Lutterodt K.
Published: April 2011

Three families of NixZry (x = 28, 36, 38, x + y = 100%) metallic glasses were prepared and examined using X-ray, temperature dependent transport and magnetic field. X-ray characterization shows characteristic diffuse spectrum, except for narrow regions of control samples, where partial crystallization was induced in finite small volumes. Magnetic properties confirm spin-fluctuating paramagnetic-like behavior, which we asses from preliminary Hall coefficient measurements, which is quantitatively different in three sample families. Temperature dependent AC and DC transport measurements were conducted in a broad temperature range from 70 K to 700 K, finding both quantitative and semi-qualitative differences between samples with different Ni/Zr ratio.
Texture Formation of α2-Ti3Al during Hot Forming of γ-TiAl Based Alloys
Authors: Stark Andreas , Gosslar Daniel , Pashkov Nikolai
Published: April 2011

In the present study the α2and the γ texture in a Ti-45Al (at.%) alloy were analyzed by means of x-ray diffraction after hot deformation. The initial Ti-45Al powder compact exhibits a random texture and shows a relatively high amount of α2phase (about 34 vol.%). Various hot compression tests were performed at temperatures ranging from 700 °C to 1100 °C with strain rates of 5·10–4s–1and 5·10–2s–1up to a true deformation of ε = –1.

Depending on the deformation temperature the γ-TiAl deformation texture consists of pure deformation components (700 °C) or components completely related to dynamic recrystallization (1100 °C). In contrast to the γ phase the α2phase shows no remarkable changing of the deformation texture with increasing temperature. The α2deformation texture basically consists of a similar component as it is known from hexagonal α-Ti, namely a tilted basal fiber. However, a significant influence of the deformation rate on the α2texture formation is observed at temperatures above 800 °C. With increasing deformation temperature the α2texture strengthens by applying a high deformation rate, whereas it weakens for a low deformation rate. This contrary behavior is attributed to the interaction of the α2and γ phases during texture formation.
Label-free Electrochemical Biosensor Based on Graphene/Ionic Liquid Nanocomposite for the Detection of Organophosphate Pesticides
Authors: Park Tae Jung , Yang MinHo , Choi Bong Gill , Heo Nam Su , Lee Seok Jae , Hong Won Hi , Lee Sang Yup
Published: April 2011

The advanced electrodes for detecting organophosphate pesticides were prepared by modification of the gold (Au) electrode with the reduced graphene oxide/ionic liquid (RGO/IL) nanohybrids. Due to the cationic and anionic parts, the ILs on RGO sheets provide the amount of functional groups for dispersion of hybrids and immobilization of organophosphorus hydrolase (OPH) enzymes. After the immobilization of OPH on the RGO/IL-modified Au electrodes, the modified electrodes represent faster electron transfer than that of Au electrode, resulting in high performance of biosensor with response time (~ 10 s) and sensitivity (4.56 nA μM−1). In addition, the OPH/RGO/IL-modified Au electrode displayed good stability and reproducibility.
Magneto-optics in Diluted Magnetic Semiconductors and in Ferromagnetic-Metal/Semiconductor Hybrids
Authors: Zayets V. , Debnath M. C , Saito H. , Yuasa S. , Ando K.
Published: April 2011

The optical isolator made of diluted magnetic semiconductor and the isolator made of a ferromagnetic-metal/semiconductor hybrid have been developed aiming to integrate nonreciprocal optical devices, such as an optical isolator and optical circulator, into the semiconductor-made optoelectronic integrated circuits,. The Cd1-xMnxTe exhibits a huge Faraday effect and can be grown on a semiconductor substrate. For Cd1-xMnxTe waveguide with a Cd1-xZnxTe/ Cd1-xMnxTe quantum well grown on GaAs substrate we achieved a high Faraday rotation of 2000 deg/cm, a high isolation ratio of 27 dB, a low optical loss of 0.5 dB/cm, and a high magneto-optical figure-of-merit of 2000 deg/dB/kG in a wide 25-nm wavelength range. It was predicted theoretically and proved experimentally the effect of non-reciprocal loss in hybrid semiconductor/ferromagnetic metal waveguides. This effect can be use for new design of waveguide optical isolator. Because of its simplicity and technological compatibility, this design is attractive for the integration into optoelectronic integrated circuits. The magneto-optical figure-of merit of 7% was demonstrated for the AlGaAs passive optical waveguide covered by Co.
Mapping Residual-Stress Distributions in a Laser-Peened Vit-105 Bulk-Metallic Glass Using the Focused-Ion-Beam Micro-Slitting Method
Authors: Winiarski B. , Wang G. , Xie X. , Cao Y. , Shin Y. , Liaw P. K. , Withers P. J.
Published: April 2011

Measuring residual-stresses at the micron scale in glassy materials imposes experimental challenges, particularly when using diffraction, or other conventional laboratory methods, e.g., optical non-contact methods, grid methods, etc. In this short paper, a technique for mapping residual-stress profiles in amorphous materials with high spatial definition is used to measure residual-stresses in a laser-peened and fatigued bulk-metallic glass - Vit-105. The method involves local deposition of nano Pt dots patterns on the mapped region of the specimen and milling of a series of micro-slots of size 15 × 2 × 0.4 μm3 using the focused ion beam of a dual beam Field Emission Gun Scanning Electron Microscope / Focused Ion Gun (FEGSEM/FIB) instrument. The deformation fields in the vicinity of slots are reconstructed by the digital image correlation analyses (DICA) of FEGSEM images recorded during milling. The residual-stresses are inferred by fitting a reference displacement field obtained from finite-element analyses (FEA) with the recorded displacement field. In this way, residual-stress distributions have been characterized as a function of the distance from the laser-peened surface to a depth of 1,200 microns with a spatial resolution of 30 μm. The influence of fatigue loading on the compressive residual-stresses spatial distribution is studied and discussed. It was found that the fatigue loading significantly changes the compressive residual-stress spatial distribution in the laser-peened layer.
Effects of additives on the phase stability of Nb3Si intermetallic compound and mechanical properties of Nb-Si alloy
Authors: Tanahashi Tatsuichi , Miura Seiji , Mohri Tetsuo
Published: April 2011

Recently, Nb-Si alloys have attracted attentions as substitutional materials of Ni-based superalloys because of its low density and high melting point. For attaining good room temperature toughness of Nb-Si alloys, proposed is a microstructure-control technique by combining eutectic reaction (L->Nb+Nb3Si) and eutectoid reaction (Nb3Si->Nb+ Nb5Si3) for spheroidizing Nb5Si3 strengthening phase embedded in Nb matrix [1]. For the solid solution strengthening of Nb matrix phase W and Mo are very effective, but Nb3Si phase disappears by adding these elements of as small as 3 at%. In contrast, Ti and Ta stabilize Nb3Si phase. For a further alloy development, establishment of an alloy design based on the control of phase stability of Nb3Si is needed. In the previous study [2], it was revealed that the phase stability of Nb3Si can be controlled by selecting appropriate Ta/Mo ratio. In the present study, this approach is expanded to other combinations of stabilizing and destabilizing elements of Nb3Si, such as Ti and W, Ta and W, and Ti and Mo. Vickers hardness tests were conducted on the heat-treated samples to reveal effects of additives on mechanical properties of Nb-Si alloy.
Quasi-Phase Matching Magneto-Optical Waveguides
Authors: Hutchings David C. , Holmes Barry M.
Published: April 2011

Photonic integration has proved remarkably successful in combining multiple optical devices onto a single chip with the benefits of added functionality, and reduction in costs, arising from the replacement of manual assembly and alignment of individual components with lithographic techniques. However, the incorporation of optical isolators and related non-reciprocal devices within standard optoelectronic wafer platforms is exceptionally challenging. Preferred magneto-optic materials cannot be exploited as waveguide core layers on semiconductor wafers due to a lower refractive index. Another difficulty is the phase velocity mismatch as a consequence of the inherent structural birefringence associated with waveguide geometries.

Our approach to the integration of an optical isolator with a III-V semiconductor laser involves combining a nonreciprocal mode converter with a reciprocal mode converter, based on an asymmetric profiled rib waveguide, fabricated by Reactive Ion Etching. We demonstrate that suitably tapered waveguides can be employed to connect the mode converter to other sections thereby avoiding problems caused by mode-matching and reflections from the section interfaces.

The nonreciprocal mode converter is formed from a continuation of the III-V semiconductor waveguide core with a magneto-optic upper cladding so that Faraday rotation occurs through the interaction of the evanescent tail. The phase velocity mismatch due to the waveguide birefringence is overcome using a quasi-phase-matching approach. Lithography is used to pattern the top cladding so that the film immediately on top of the waveguide core alternates between magnetooptic and a non-magneto-optic dielectric of a similar refractive index. Our first demonstrations used a dielectric (silica or silicon nitride) patterned by etching, or lift-off, on top of a GaAs rib waveguide, over which was deposited a magneto-optic film. This film was deposited by sputtering from a Ce:YIG target and demonstrated magnetic hysteresis, but, as it was not annealed, it was believed to consist of Ce:YIG and/or gamma iron oxide microcrystallites embedded in an amorphous matrix. With quasi-phase-matching periods of 110–160 μm and a waveguide length of 8 mm, we were able to demonstrate up to 12% non-reciprocal TE- to TM-mode conversion around a wavelength of 1.3 μm using the remanent magnetisation.

In order to enhance the magneto-optic effect it is desirable to anneal such films. However the mismatch in thermal expansion coefficients results in a catastrophic failure of samples with large area film coverage. This problem has been shown to be alleviated by patterning the YIG film. Unfortunately wet-etching of YIG also etches (Al)GaAs and, therefore, the development of a lift-off process for YIG deposition has been undertaken. Initial results are promising with ∼100 μm×2.5 μm YIG sections deposited on a GaAs layer which remain intact after an anneal in an oxygen atmosphere.
Displacement cascade decomposition within the Binary Collision Approximation
Authors: Luneville Laurence , Simeone David , Baldinozzi Gianguido , Gosset Dominique
Published: April 2011

The mechanism of damage production in solids during irradiation is of great practical interest in nuclear technology. The need to increase the life time of current nuclear plants as well as extreme conditions (high temperature and high neutron flux) in new generations of nuclear plants leads to have a deep insight into radiation damage in solids. In fact, the slowing down of particles in solids leads to a non homogeneous distribution of defects in solids, giving rise to complex microstructures with unusual properties. Numerous experiments, Molecular Dynamics (MD) and Monte Carlo (MC) simulations have clearly shown that highly damaged areas called displacement cascades are produced by neutron or impinging ions in solids. It is now clearly established that the number and the distribution of these subcascades dictate the long term evolution of the microstructure under irradiation. In this work, we present a new model to calculate the mean number of displacement cascades produced in a mono-atomic solid by an incident particle within the Binary Collision Approximation framework (BCA) taking into account all information extracted from MD simulations. To reach such a goal, the notion of subcascade threshold energy is introduced and discussed on some examples. Within this formalism, we exhibit a new way to estimate the number of defects created in a displacement cascade integrating results of MD simulations of cascades.
Alternative Current Magnetic Permeability of Fe81Ga19 Alloy with Bias Magnetic Fields
Authors: Zhang Hongping , Wu Guangheng , Liu Zheng , Xu Lihong , Wang Lei , Du Zhaofu , Pei Yongmao , Zhao Dongliang
Published: April 2011

In this study, the AC magnetic permeability of polycrystalline Fe81Ga19 alloy (Galfenol), without crystal orientation under both the bias applied fields and frequencies, was investigated by the method of measuring inductance of ring specimens. The results showed that the AC permeability of the alloy can reach more than 160 Gs/Oe under the conditions of low frequencies or quasi-static state. The permeability decreased with the increase of frequency. When the frequency was higher than 6 kHz, the permeability decreased slowly, and gradually stabilized with the increase of frequency. When applying a little of parallel bias magnetic field, the permeability decreases obviously with the increase of frequency. But applying a perpendicular bias magnetic fields, the permeability of the only initial point of the measuring frequency decreases a little compared to the permeability without bias field.
Shark-skin inspired surface engineering on intermetallic titanium aluminides for high temperature applications using the fluorine effect
Authors: Pflumm Raluca , Schütze Michael
Published: April 2011

Increasing demands on technical components for high-temperature applications (e.g. tur-bine blades) promote new developments not only in the field of alloy design, but also in surface engineering. This paper shows that it is possible to structure the surface of intermetallic titanium aluminides in-situ by locally controlled oxidation of the material due to selective doping with fluorine. The aim is to reproduce a shark-skin pattern (parallel riblets with valleys in between) in order to improve the surface aerodynamics. Riblets with widths in the single digit μm range have been generated. The nucleation process, the aspect ratio and the stability of the generated micro-structures are discussed as a function of the substrate composition and the oxidation conditions.
Compression of Micropillars of TiAl Coexisting with Ti3Al
Authors: Fujimura Kazuki , Kishida Kyosuke , Tanaka Katsushi , Inui Haruyuki
Published: April 2011

Square-shaped micropillar of nearly stoichiometric TiAl single crystals with various loading axis orientations were prepared from TiAl PST crystals by focused ion beam (FIB) technique and deformed in compression using a micro hardness testing machine equipped with a flat diamond tip in order to investigate the values of CRSS for the three types of operative deformation modes, namely ${111}1/2< 1 \bar 10 >$ ordinary slip, ${111}< \bar 101 >$ superlattice slip and ${111}<11\bar 2 >$ twinning. The selective activation of the three types of deformation modes was confirmed to be achieved by compression tests of $[\bar 2 11]-, \bar 110- and [\bar 2 12]$-oriented single crystalline micropillars, respectively. The average CRSS values for ordinary slip, superlattice slip and deformation twinning obtained for micropillars with an initial side length between 3.8 and 7.9μm were estimated to be about 145, 284 and 113 MPa, respectively.
Substitution Behavior of Ni3X-type Compounds with D0a Structure
Authors: Sugimura H. , Kaneno Y. , Takasugi T.
Published: April 2011

The site preference of ternary additions in GCP (geometrically close-packed) Ni3X-type compounds with D0a structure was determined from the direction of the single-phase region of the D0a phase in the reported ternary phase diagrams. The thermodynamic model based on the Bragg-Williams approximation, which is based on the change in heat of formation of the host compound by a small addition of ternary solute, was applied to predict the site preference of ternary additions. The heat of formation used in the thermodynamic calculation was derived from Miedema’s formula. Good agreement was obtained between the thermodynamic model and the result of the literature search.