bluuebunny/crossref_metadata_2025 huggingface dataset:
Photonic Crystals: Shaping the Flow of Thermal Radiation
Authors: Čelanović Ivan , Ghebrebrhan Michael , Yeng Yi Xiang , Kassakian John , Soljačić Marin , Joannopoulos John
Published: August 2010

In this paper we explore theory, design, and fabrication of photonic crystal (PhC) based selective thermal emitters. In particular, we focus on tailoring spectral and spatial properties by means of resonant enhancement in PhC's. Firstly, we explore narrow-band resonant thermal emission in photonic crystals exhibiting strong spectral and directional selectivity. We demonstrate two interesting designs based on resonant Q-matching: a vertical cavity enhanced resonant thermal emitter and 2D silicon PhC slab Fano-resonance based thermal emitter. Secondly, we examine the design of 2D tungsten PhC as a broad-band selective emitter. Indeed, based on the resonant cavity coupled resonant modes we demonstrate a highly selective, highly-spectrally efficient thermal emitter. We show that an emitter with a photonic cut-off anywhere from 1.8 μm to 2.5 μm can be designed.
High Temperature Plasmonic Photonic Crystal MEMS Emitter
Authors: Puscasu Irina , Johnson Edward , Taylor Andrew , Schell Brent , Schaich William , Biswas Rana
Published: August 2010

We describe a new class of plasmonic photonic crystal emitters integrated into a MEMS platform for high temperature-intensity, high speed, and high efficiency tuned emitting and sensing applications in the infrared. We exploit 2D organized metallo-dielectric surface structures for angular and spectral control of reflection, absorption and emission from surfaces in the infrared. We have built a FDTD model that incorporates complex frequency dependent properties and provides quantitative agreement with measured spectral data. High temperature materials and special fabrication techniques allow high temperature operation. This technology offers new solutions for spectral control with application in thermophotovoltaic (TPV) energy conversion. Built on a MEMS platform, for thermal isolation from the environment, these devices also modulate at high speed, opening new applications in spectroscopy, infrared imaging, and signaling. Demonstrated wafer-level vacuum sealing improves the wall plug efficiency dramatically. We describe device architecture and fabrication considerations for plasmonic photonic crystal structures which simultaneously act as emitters and sensors in a defined narrow waveband radiation. In particular, this combined capability opens new avenues for research for vital commercial applications such as environmental protection, household safety, bio-hazardous material identification, meteorology and industrial environments.
Radiation Heat Transfer in Porous Materials
Authors: Shklover Valery , Braginsky Leonid , Mishrikey Matthew , Hafner Christian
Published: August 2010

The effect of porosity on the radiation component of the thermal conductivity of the thermal barrier coatings is studied. Heat transfer in the disordered porous structures as well as the porous photonic band-gap structures is investigated. The pores, which size is comparable with the characteristic radiation wavelength λmax=2897.8/T μm, were found to be most efficient obstacles for the heat radiation.
Origins of Twinned Microstructures in B12As2 Epilayers Grown on (0001) 6H-SiC and Their Influence on Physical Properties
Authors: Zhang Yu , Chen Hui , Zhang Ning , Dudley Michael , Gong Yinyan , Kuball Martin , Xu Zhou , Zhang Yi , Edgar James , Zhang Lihua , Zhu Yimei
Published: August 2010

The defect structure in B12As2 epitaxial layers grown at two different temperatures on (0001) 6H-SiC by chemical vapor deposition (CVD) was studied using synchrotron white beam x-ray topography (SWBXT) and high resolution transmission electron microscopy (HRTEM). The observed differences in microstructures were correlated with the differences in nucleation at the two growth temperatures. The effect of the difference in microstructure on macroscopic properties of the B12As2 was illustrated using the example of thermal conductivity which was measured using the 3-ω technique. The relationship between the measured thermal conductivity and observed microstructures is discussed.
Accelerating Laboratory Thin Film Photovoltaic Innovation into Commercial Production
Authors: Seymour Fred H.
Published: August 2010

Alternative energy sources such as thin film photovoltaics can be accelerated by improving the rapid and successful transition from laboratory research innovation to commercial production. Most laboratory research and development is on a small scale and its production is in small volumes. It focuses on exploration, discovery, and understanding. When the successful innovation is commercialized, both the scale and the volume increase dramatically and the focus shifts to performance, reliability, yield and cost. This transformation can be accelerated by closely managing risk and by integrating the equipment design and the process development. Also, the cadmium telluride photovoltaic technology has properties that make it more amenable to rapid scale up to low cost and high volume manufacturing.
A CdTe Thin Film Module Factory with a Novel Process
Authors: Romeo Nicola , Bosio Alessio , Romeo Alessandro , Mazzamuto Samantha
Published: August 2010

The CdTe thin film module technology can be considered mature for large scale application.

First Solar is now capable of producing more than 400MW/year of CdTe modules and it is still increasing its production. First Solar also announced that they can get a production cost close to 1$/W. A further cost reduction will render this kind of energy production competitive with the energy obtained from fossil fuels.

In our laboratory we developed a novel dry process that could further reduce the production cost.

This process is now being used by a new company (Arendi Spa) in a line that will produce ∼15-18MW/year. Half of the line has been already built and the complete line should be ready in July 2009. The module production will start at the end of 2009.
The Influence of CuCl Treatment on the PL Spectra of CdTe Thin Film, Component of CdS/CdTe Heterojunctions
Authors: Vatavu Sergiu A , Zhao Hehong , Caraman Iuliana M , Gasin Petru A , Morel Don L , Ferekides Chris S
Published: August 2010

Technology variations involving Cu and Cl impurities are among the major performance influencing factors for CdS/CdTe thin film solar cells. CuCl and CdCl2 influence on the energetic diagram of impurity levels with respect to variation of deposition parameters has been investigated. A comparative analysis has been carried out by using low temperature photoluminescence (PL) studies (17-98K) of CdTe thin films in the device configuration (from CdS/CdTe inteface and CdTe sides). To study the effect of CuCl influence, as-deposited, annealed heterojunctions, with CuCl treatment of CdS have been investigated.
Growth Conditions Effect on the Structure and Optical Properties of ZnO Thin Films Synthesized by rf magnetron Sputtering
Authors: Angelats-Silva Luis , Tomar Maharaj S. , Perales-Perez Oscar , Singh S. P. , Jauregui-Rosas Segundo R.
Published: August 2010

We report a systematic study of the influence of the target-substrate distance and rf power on the structural and optical properties of ZnO thin films grown by rf magnetron sputtering in Ar atmosphere from ZnO sputtering target. Sharp (002) peak showed by XRD indicates a c-axis crystalline growth of ZnO films. Growth rate remained almost constant for short target-substrate distances. However, the grain size increases with the rf power decreasing the compressive stress in ZnO films. As-grown ZnO films have average transmittance more than 80% in the visible region. Optical bandgap (Eg) increases from 3.18 to 3.27 eV as increase the target-substrate distance probably due to low stress compression in ZnO films. In addition, when rf power is above 100 W, the optical band gap increases as increase of the stress compression.
The Promise of Nanocomposite Thermoelectric Materials
Authors: Dresselhaus Mildred , Chen Gang , Ren Zhifeng , McEnaney Kenneth , Dresselhaus G. , Fleurial Jean-Pierre
Published: August 2010

The concept of using nanocomposite thermoelectric materials in bulk form for practical applications is presented. Laboratory studies have shown the possibilities of nanostructures to yield large reductions in the thermal conductivity while at the same time increasing the power factor. Theoretical studies have suggested that structural ordering in nano-systems is not necessary for the enhancement of ZT, leading to the idea of using nanocomposites as a practical scale-up technology for making bulk thermoelectric materials with enhanced ZT values. Specific examples are presented of nanocomposite thermoelectric materials developed by our group based on the familiar silicon germanium system, showing enhanced thermoelectric performance through nano-structuring.
Electronic structure and transport properties of ternary skutterudite: CoX3/2Y3/2
Authors: Volja Dmitri , Fornari Marco , Kozinsky Boris , Marzari Nicola
Published: August 2010

Electronic properties of ternary skutterudites AX3/2Y3/2 (A=Co, X=Ge, Sn and Y=S, Te) are investigated using first principles calculations to clarify recent experimental results. Band derivatives are computed accurately within an approach based on Maximally Localized Wannier Functions (MLWFs). Band structures exhibit larger effective masses compared to parental binary CoSb3. Our results also indicate a more parabolic dispersion near the top of the valence band and a multivalley character in both conduction and valence band. Despite the improved thermopower these skutterudites has relatively low power factor due to increased resistivity. The fundamental cause of such large resistivity seems to be associated with the ionicity of the bonding.
Characterization and Fabrication of InGaN-based Blue LED with Underlying AlGaN/GaN SLS Cladding Layer Grown on Si(111) Substrate
Authors: Ahmad Shuhaimi Bin Abu Bakar , Pum Chian Khai , Suzue Takaaki , Nomura Yukiyasu , Egawa Takashi
Published: August 2010

This paper reports improved optical characteristics of InGaN-based light-emitting-diode (LED) grown on Si(111) substrate by the insertion of an Al0.06Ga0.94N/GaN strained-layer-superlattices (SLS) cladding layer after AlN/GaN multilayer (ML) growth, under the multi-quantum-well (MQW) active layer. The insertion of underlying Al0.06Ga0.94N/GaN SLS cladding layer has shown to improve epitaxial layer quality in x-ray diffraction (XRD) analysis, reduce wavelength peak fluctuations in photoluminescence (PL) surface mapping, and improve optical and electrical characteristics of the LED sample. A 34% increase of light intensity at 50 mA current injection and a narrower wavelength peak have been achieved by the insertion of Al0.06Ga0.94N/GaN SLS cladding layer. LED with underlying Al0.06Ga0.94N/GaN also shows superior current-voltage (I-V) characteristics with operation voltage of 3.2 V at 20 mA and series resistance of 16 Ω.
Diffusion Effect between Schottky Metals and AlGaN/GaN Heterostructure during High Temperature Annealing Process
Authors: Choi Young-Hwan , Lim Jiyong , Kim Young-Shil , Han Min-Koo
Published: August 2010

We have investigated the change of the Schottky contact surface and the interface between Schottky metals and AlGaN/GaN heterostructure after the annealing process for 35 min at 300 °C. The secondary ion mass spectroscopy (SIMS) and the scanning electron microscopy (SEM) show that the Schottky metals and AlGaN/GaN heterostructure interacted actively during the annealing process. The atoms in Schottky contact and AlGaN/GaN heterostructure diffused interactively and the surface roughness of Schottky contact was increased. After the annealing process for fabricated AlGaN/GaN High-Electron-Mobility Transistor (HEMT), the threshold voltage was shifted by +0.2 V and the leakage current was decreased by 40 %.
Surface Modification of Tungsten Oxide-Based Photoanodes for Solar-Powered Hydrogen Production
Authors: Gaillard Nicolas , Kaneshiro Jess , Miller Eric L. , Weinhardt Lothar , Bär Marcus , Heske Clemens , Ahn Kwang-Soon , Yan Yanfa , Al-Jassim Mowafak
Published: August 2010

We report on the development of tungsten-oxide-based photoelectrochemical (PEC) water-splitting electrodes using surface modification techniques. The effect of molybdenum incorporation into the WO3 bulk or the surface region of the film is discussed. Our data indicate that Mo incorporation in the entire film (WO3:Mo) results in poor PEC performances, most likely due to defects that trap photo-generated charge carriers. However, compared to a pure WO3 (WO3:Mo)-based PEC electrode, a 20% (100%) increase of the photocurrent density at 1.6 V vs. SCE is observed if the Mo incorporation is limited to the near-surface region of the WO3 film. The resulting WO3:Mo/WO3 bilayer structure is formed by epitaxial growth of the WO3:Mo top layer on the WO3 bottom layer, which allows an optimization of the electronic structure induced by Mo incorporation while maintaining good crystallographic properties.
Effect of Cationic or Anionic Dopants on Optical and Photocatalytic Properties of TiO2 Nanopowders made by Flame Spray Synthesis (FSS)
Authors: Michalow Katarzyna Anna , Heel Andre , Graule Thomas , Rekas Mieczyslaw
Published: August 2010

TiO2, TiO2-1at.% W and TiO2-1at.% Cr were produced from metal-organic precursors by flame spray synthesis (FSS). TiO2-0.5at.% N was obtained by ammonolysis of FSS made TiO2 nanopowder in a rotating tube furnace under NH3 atmosphere. According to the X-ray diffraction (XRD) analysis, anatase is the predominant phase in all samples. Diffusive reflectance and the resulting band gap energy (Eg) were determined by diffusive reflection spectroscopy (DRS).
Additional impurity bands at 2.43 and 2.57 eV for N- and Cr-doped TiO2, respectively have been observed. The impurity band formed in the band gap resulted in increase of the light absorption in the visible range. The photocatalytic performance of the nanopowders under ultraviolet (UV, 290-410 nm) and visible light irradiation (Vis, 400-500 nm) was studied by the degradation of methylene blue (MB) in aqueous suspensions. It was found that all types of dopants influence the structure, interaction with the visible light as well as photocatalytic activity. Among all nanopowders, TiO2-W exhibited the best photoactivity, much higher than the commercial TiO2-P25 nanopowder. The optimum of the photodecolourization was obtained for 0.7 and 1 at.% W.
Efficient Carbon Nanotube Field Emitter using Electrospun Carbon Nanofibers as a Flexible Electrode
Authors: Matsumoto Hidetoshi , Suzuki Kenichi , Tsuboi Kazuma , Minagawa Mie , Tanioka Akihiko , Hayashi Yasuhiko , Fukuzono Kazuyuki , Amaratunga Gehan A.J.
Published: August 2010

Thermal-stable, conductive, and flexible carbon fabric (CF), which is composed of thin carbon fibers prepared by electrospinning, was used for the substrate of carbon nanotube (CNT) field emitter arrays. The field emitter arrays were prepared by chemical vapor deposition (CVD). The current density-electric field characteristics revealed that the CNT field emitter arrays on CF produced a higher current density at a lower turn-on voltage compared to ones on a Si substrate. This emitter integrated with a gate electrode based on hierarchy-structured carbon materials, CNTs on CF, can be used for light sources, displays, and other electronic devices.
Semiconductor-metal Phase Transition in Doped Ion Beam Synthesized VO2 Nanoclusters
Authors: Karl Helmut , Dreher J. , Stritzker B.
Published: August 2010

We have synthesized W and Mo doped VO2 nanoclusters embedded in 200 nm thick thermally grown SiO2 on 4-inch silicon wafers by sequential ion implantation of the elements V, W, Mo and O. The implantation energies have been chosen to locate the mean projected range in the centre of the SiO2 thin film. A post implantation rapid thermal annealing step in flowing Ar at 1000°C for 10 min leads to the growth of doped VO2 nanoclusters. The optical properties of the nanoclusters were analyzed by temperature dependent spectral ellipsometry in the spectral range of 320 to 1700 nm. It will be shown, that the semiconductor-metal phase transition hysteresis width starting at 50K in the undoped case can be systematically closed by increasing dopand concentration.
A Facile Method for Patterning Substrates with Zinc Oxide Nanowires
Authors: Cho Jeong-Hyun , Cha Elizabeth W , Gracias David
Published: August 2010

Conventional growth of zinc oxide (ZnO) nanowires (NWs) is typically carried out using vapor liquid solid (VLS) and chemical vapor deposition (CVD) methods. While these methods are effective, they often involve the use of specialty gasses and equipment. We have discovered that ZnO NWs grow spontaneously from zinc (Zn) films (thermally evaporated on silicon (Si) substrates) when the films are merely heated on a hot-plate in air at ambient pressures for 10 minutes. This process does not involve any metal catalysts, seed layers, specialty gasses or surface treatments in forming patterned regions (on silicon substrates) of NWs with typical diameters in the range of 20-50 nm and lengths of 2-3 μm.
Polyanion Conduction Mechanism in Solid Scandium Tungstate
Authors: Zhou Yongkai , Adams Stefan , Neiman Arkady
Published: August 2010

Scandium tungstate is investigated as a model material for solid electrolytes in which polyatomic anions, here WO42–, are mobile in the solid state. Simulations using structures with artificially induced WO42–vacancy, Frenkel defect and Schottky defects produced lower activation energy compared to the initially defect-free model. Simulations with Frenkel defect structures show low activation energy but the interstitial WO42–has initially a strong preference to return to the vacant tungstate site. The vacancy defect model reproduces the activation energy to the experimental conductivity studies more closely. Qualitative considerations support the idea that vacancies formed during the sample preparation are the most abundant mobile defect among the investigated cases. Nonstoichiometric samples with varying initial Sc2O3:WO3ratios Sc2O3- x WO3, where x = 2.9, 3.0 and 3.1, are synthesized and characterized by XRD and impedance measurements, but a significant influence on the conductivity could not be confirmed experimentally.
Enhancing Superconducting Parameters by Array of External Magnetic Dots
Authors: Yeh Wei Jiang , Cheng Bo
Published: August 2010

Enhancing the pinning force in high-Tc superconductors can be achieved by externally introduced periodic magnetic dots. We use a novel nano-technique to deposit periodic sub-micon Ni dots on YBa2Cu3O7 thin films. The current versus voltage characteristics of an YBa2Cu3O7 thin film strip with uniform Ni dots are measured at various temperatures and magnetic fields. They are compared with the current versus voltage characteristics of a bare YBa2Cu3O7 thin film strip without magnetic dots. It is found the critical current value of the strip with Ni dots reduces with a much slower pace as the magnetic field strength increases in comparison with the value of the bare sample.
Real-Time Visualization Method of Surface Plasmon Resonance with Spectroscopic Attenuated Total Reflection
Authors: Murai Kensuke
Published: August 2010

We report the real-time visualization method of surface plasmon resonance with the spectroscopic attenuated total reflection. Recently, surface plasmon resonance (SPR) had been studied for plasmonics devices to construct faster processor in the electronic microprocessors. SPR is strong interaction between light and free electron near metal surface, which cause absorption of light due to its resonance. The behavior can be explained with Fresnel’s equation. As the wave number of light with a certain frequency is not matched with that of surface plasmon, a prism or a grating is used in order to compensate this mismatching. In the prism case, the wave number is changed by changing the incident angle to the metal surface inside the prism as ksp=n*k0sinθ, where ksp and k0 is the wave numbers of surface plasmon and incident light, respectively, n is the refractive index of the prism and θ is the incident angle to the metal surface inside the prism. Therefore, the SPR can be observed by absorption of light as functions of the wavelength and the incident angle. This resonance behavior as functions of the wavelength and the incident angle can be observed directly with a two-dimensional detector such as a CCD camera. As the two-dimensional SPR images for 50nm-thick silver films on the prism surface have been observed experimentally, they have good agreement with calculated ones. Kretchmann configuration using a glass prism and an approximately 50-nm-thick silver or gold film was often used in order to evaluate the optical constants of the film. Most of SPR signals had been measured with either angular or spectral dependence with this geometry. In the case of angular dependence, the monochromatic laser, e.g. He-Ne laser at 632.8nm, is often used for the incident light. One can measure reflection loss as a function of an incident angle in the total reflection region. Increase in the resonance angle of SPR is well known when the thin oxide film on the metal film. The two-dimensional image of SPR is called “surface plasmon spectral fingerprint”, because it can inform conditions of metal films whether they are reacted or oxidized. Many fingerprints are expected by changing the thickness of the coating layer on the silver surface. In our method, thin metal film on a prism was excited by focusing beam of white light. SPR was clearly visualized with a spectrometer equipped with a two-dimensional CCD detector in the coordination of the incident angle and the wavelength. Various metal films could be distinguished even in partially oxidized condition. This real-time SPR visualization method would be useful not only for monitoring of surface reaction but for fabricating plasmonic devices.
Electron Microscope Study of Strain in InGaN Quantum Wells in GaN Nanowires
Authors: Geiss Roy , Bertness Kris , Roshko Alexana , Read David
Published: August 2010

Strains in GaN nanowires with InGaN quantum wells (QW) were measured from transmission electron microscope (TEM) images. The nanowires, all from a single growth run, are single crystals of the wurtzite structure that grow along the <0001> direction, and are approximately 1000 nm long and 60 nm to 130 nm wide with hexagonal cross-sections. The In concentration in the QWs ranges from 12 to 15 at %, as determined by energy dispersive spectroscopy in both the transmission and scanning electron microscopes. Fourier transform (FT) analyses of <0002> and <1100> lattice images of the QW region show a 4 to 10 % increase of the c-axis lattice spacing, across the full specimen width, and essentially no change in the a-axis value. The magnitude of the changes in the c-axis lattice spacing far exceeds values that would be expected by using a linear Vegard's law for GaN – InN with the measured In concentration. Therefore the increases are considered to represent tensile strains in the <0001> direction. Visual representations of the location and extent of the strained regions were produced by constructing inverse FT (IFT) images from selected regions in the FT covering the range of c-axis lattice parameters in and near the QW. The present strain values for InGaN QW in nanowires are larger than any found in the literature to date for other forms of InxGa1-xN (QW)/GaN.
Backside Analysis of Ultra-Thin Film Stacks in Microelectronics Technology Using X-ray Photoelectron Spectroscopy
Authors: Hantschel Thomas , Demeulemeester Cindy , Suderie Arnaud , Lacave Thomas , Conard Thierry , Vandervorst Wilfried
Published: August 2010

X-ray photoelectron spectroscopy (XPS) has become increasingly important over the past few years for supporting the development of ultra-thin layers for high-k metal gates. As the analysis depth of XPS is however limited to about 5-7 nm, it would be extremely useful if the analysis could be carried out from the backside using standard silicon wafers. This approach puts extreme requirements on the sample preparation as hundreds of micrometers of bulk silicon have to be removed and one has to stop with nanometer precision when reaching the interface to the ultra-thin layer stack. Therefore, we have developed dedicated procedures for preparing and analyzing samples for backside XPS analysis. This paper presents the developed approach with a focus on sample preparation using plan-parallel polishing, endpoint detection by interference fringes, and selective wet etching. First angle-resolved XPS (ARXPS) analysis results of metal gate stacks demonstrate the power of such backside analysis.
Quantitative Characterization of the Interface Between a V2O3 Layer and Cu3Au (001) by Cs Corrected HREM
Authors: Calderon Hector Alfredo , Niehus Horst , Freitag B. , Wall D. , Stavale Fernando , Achete Carlos
Published: August 2010

Vanadium oxides are materials of interest due to their electronic, magnetic and catalytic properties. In the case of V2O3 and Cu3Au, the interfacial bonding is rather difficult to describe since the two component materials have strongly different electronic structures. Thus a local investigation of the interface becomes important. In this investigation, the incoherent interface between a V2O3 (0001, corundum structure) layer and a Cu3Au (001, L12 structure) substrate is characterized with the help of image corrected high resolution electron microscopy (HRTEM) and focal series reconstruction in order to investigated both the true position of atoms and the nature of the atomic species. Semi-quantitative results can be shown for the chemical composition of columns and strains at one side of the interface.
Hierarchical Design and Nanomechanics of the Calcified Byssus of Anomia simplex
Authors: Eltzholtz Jakob R , Krogsgaard Marie , Birkedal Henrik
Published: August 2010

Biology has evolved several strategies for attachment of sedentary animals. In the bivalves, byssi abound and the best known example being the protein-based byssus of the blue mussel and other Mytilidae. In contrast the bivalve Anomia sp. has a single calcified thread. The byssus is hierarchical in design and contains several different types of structures as revealed by scanning electron microscopy images. The mechanical properties of the byssus are probed by nanoindentation. It is found that the mineralized part of the byssus is very stiff with a reduced modulus of about 67 GPa and a hardness of ˜3.7 GPa. This corresponds to a modulus roughly 20% smaller than that of pure calcite and a hardness that is about 20% larger than pure calcite. The results reveal the importance of microstructure on mechanical performance.
Substrate effect on Dynamic Indentation Measurement of Biological Cell Properties
Authors: Cao Guoxin , Chandra Namas
Published: August 2010

Viscoelastic mechanical properties of biological cells are commonly measured using atomic force microscope (AFM) dynamic indentation method with spherical tips. Storage and loss modulii of cells are then computed from the indentation force-displacement response under dynamic loading conditions. It is shown in current numerical simulations that those modulii computed based on existing analysis can not reflect the true values due to the substrate effect. This effect can alter the indentation modulus by changing the geometric relations between the indentation displacement and the contact area. Typically, the cell modulii are significantly overestimated in the existing indentation analysis.
Stress Liner Proximity Technique to Enhance Carrier Mobility in High-κ Metal Gate MOSFETs
Authors: Guo Dechao , Schonenberg Kathryn , Chen Jie , Jaeger Daniel , Kulkarni Pranita , Kwon Unoh , Liang Yue , Liu Joyce , Song Liyang , Arnaud Franck , Bu Huiming , Chudzik Michael , Henson William K , Oldiges Philip J , Sherony Melanie , Steegen An , Thean Voon-Yew , Khare Mukesh
Published: August 2010

For the first time, we discuss the compatibility of stress proximity technique (SPT) with dual stress liner (DSL) in high-κ/metal gate (HK/MG) technology. The short-channel mobility enhancement and the drive current improvement brought by SPT have been demonstrated at 32nm technology node. With maintained short channel control and threshold voltage roll-off characteristics, SPT has achieved 7% drive current improvement for both nFET and pFET from the optimization of SPT with DSL.
Novel Zirconium Formamidinate Precursor for the ALD of ZrO2
Authors: Li Huazhi , Shenai Deo V , Lehn Jean-Sebastien
Published: August 2010

Zirconium tetrakis(N,N’-dimethylformamidinate), Zr-FAMD, was synthesized and evaluated as a precursor for the deposition of zirconium oxide (zirconia) thin films via Atomic Layer Deposition (ALD) technique. Zr-FAMD has a high vapor pressure and displays an exceptionally high thermal stability; it is thus well-suited to be used as a precursor for the deposition of zirconia thin films. Zr-FAMD is a more ideally-suited precursor than tetrakisethylmethylaminozirconium or TEMAZr, which has an equivalent vapor pressure, but is plagued with a rather low thermal stability, limiting its usefulness at high deposition temperatures. Zr-FAMD can be used to deposit zirconia thin films at temperatures as high as 375 °C without evidence of decomposition.
Effects of Mechanical Strain on the Electrical Performance of Amorphous Silicon Thin-Film Transistors with a New Gate Dielectric
Authors: Song Katherine Wei , Han Lin , Wagner Sigurd , Mandlik Prashant
Published: August 2010

The stiff SiNx gate dielectric in conventional amorphous silicon thin film transistors (TFTs) limits their flexibility by brittle fracture when in tension. We report the effect on the overall flexibility of TFTs of replacing the brittle SiNx gate dielectric with a new, resilient SiO2-silicone hybrid material, which is deposited by plasma enhanced chemical vapor deposition. Individual TFTs on a 50μm-thick polyimide foil were bent to known radii, and measurement of transfer characteristics were made both during strain and after re-flattening. Compared with conventional TFTs made with SiNx, TFTs made with the new hybrid material demonstrated similar flexibility when strained in compression and significantly increased flexibility when strained in tension. Under bending to compressive strain, all TFTs tested delaminated from the substrate for compressive strains greater than 2%. Conventional a-Si:H/SiNx TFTs have been previously found to delaminate at a similar compressive strain. Under bending to tensile strain, the most flexible TFTs made with the new hybrid material that were tested after re-flattening did not exhibit significant changes in transfer characteristics up to strains of ∼2.5%. Conventional a-Si:H/SiNx TFTs have been found to remain functional for strains of up to 0.5%, a value only one-fifth of that for TFTs made with the new hybrid material.
Optical Gain in Foerster Energy Transfer Based Organic Guest-Host-Systems
Authors: Rabe Torsten , Döring Sebastian , Hildebrandt Niko , Riedl Thomas , Kowalsky Wolfgang , Scherf Ullrich
Published: August 2010

We study the optical gain for various doping concentrations in a dye doped polymer (poly-[9,9-dioctylfluorene] with 6,6'-[2,2'-octyloxy-1,1'-binaphthyl] spacer groups (BN-PFO) doped by the stilbene dye 1,4-bis[2-[4-[N,N-di[p-tolyl]amino]phenyl]vinyl-benzene] (DPAVB)). In such a guest-host-system (GHS) the occupation of the upper laser level (dopant site) is due to Förster energy transfer (FET), which strongly depends on the donor acceptor distance and hence on the concentration of the laser dye. Therefore, the doping concentration is varied over a wide range and the gain coefficients are measured at various excitation densities to analyze the stimulated emission cross section.

For the investigated GHS maximum gain coefficients up to ∼340 1/cm were found at absorbed pump energy densities of around 50 μJ/cm2. It will be shown that the stimulated emission cross section (σ = 1.8 × 10−16 cm2) is concentration independent which is quite different to a recently investigated small molecule based GHS. These effects will be discussed considering the rate and exciton diffusion constants.
Fluorinated Poly(N-vinylcarbazole) Host for Triplet Energy Confinement on Phosphorescent Emitter in Organic Light-emitting Diodes
Authors: Mizuno Yukitami , Takasu Isao , Uchikoga Shuichi , Enomoto Shintaro , Sawabe Tomoaki , Amano Akio , Wada Atsushi , Yoshida Jiro , Ono Tomio
Published: August 2010

Fluorinated carbazoles as host materials have been investigated for highly efficient organic light emitting diodes (OLEDs). By molecular orbital calculations, we found that fluorinations at position 2, 4, 5 and 7 of carbazole ring were effective for widening HOMO-LUMO energy gap. The energy gaps of our synthesized 2,7-difluorocarbazole (F2-Cz) and 2,4,5,7-tetrafluorocarbazole (F4-Cz), were estimated to be 3.71 eV and 3.87 eV by the absorption spectra, respectively. These energy gaps were higher than that of the non-substituted carbazole (Cz, 3.59 eV). We synthesized poly(N-vinyl-2,7-difluorocarbazole) (F2-PVK) and poly(N-vinyl-2,4,5,7-tetrafluorocarbazole) (F4-PVK) as solution processable polymer host materials. However, the F4-PVK was found to be an unsolved polymer. The F2-PVK could be compared with non substituted poly(N-vinylcarbazole) (PVK) in OLEDs. The emission layer (EML) contained iridium(III) bis [(4,6-di-fluorophenyl)-pyridinato-N,C2′] picolinate (FIrpic) as a blue phosphorescent dopant, and iridium(III) bis [2-(9,9-dihexylfluorenyl)-1-pyridine] acetylacetonate as a yellow dopant. The white OLED with the F2-PVK showed 1.4 times higher luminous current efficiency (24 cd/A) than the PVK (17 cd/A). These data show that the excitation energy is confined on dopants by using fluorinated polymer host material with higher T1 corresponding to wider HOMO-LUMO energy gap.
Bright Inkjet Printed Macromolecular Organic Light emitting Diodes on Flexible Substrates
Authors: Singh Madhusudan , Chae Hyun Sik , Froehlich Jesse D. , Kondou Takashi , Li Sheng , Mochizuki Amane , Jabbour Ghassan
Published: August 2010

We present results of printing solution-processable organic light emitting diodes (OLEDs) based on electrophosphorescent Ir(III) stellate polyhedral oligomeric silsesquioxane (POSS) macromolecules. The macromolecules are doped into a polymer-based ink containing a hole transporting polymer, poly(9-vinylcarbazole) (PVK) and an electron transporting material, 2-4-biphenylyl-5-4-tertbutyl-phenyl-1,3,4-oxadiazole (PBD), and the resulting ink is printed on a layer of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) spin-coated on indium tin oxide (ITO). An exciton-blocking layer consisting of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) is thermally evaporated onto the printed ink layers, followed by a LiF/Al cathode. While the photoluminescence (PL) spectrum of printed ink on glass indicates a significant contribution from the PVK:PBD exciplex, electroluminescence measurements (EL) suggest a much smaller effect of these states, which implies significant charge trapping at dopant molecular sites. Our latest experiments with devices printed on PEDOT:PSS/ITO/glass indicate that the devices exhibit high luminances (∼ 13,000 cd/m2 at 70 mA/cm2) and a fairly consistent quantum efficiency (∼ 2.5%) across a wide range of luminances. The corresponding figures for spin-coated devices are expectedly higher, with efficiencies ∼ 4.5% at similar levels of brightness. We use white light interferometry as a non-contact technique to quantify surface roughness and thickness of printed layers. Our current results thus indicate that inkjet printing of macromolecular phosphor doped polymer inks is suitable for fabrication of OLEDs with high brightness, in spite of the low glass transition temperature of some of the species. Our initial work with these devices on flexible ITO-coated plastic substrates shows devices with moderately high luminance values (∼ 2,500 cd/m2 at 35 mA/cm2). Our more recent devices show higher brightnesses (∼ 9, 600 cd/m2). We are working on the development of inkjet printing materials and processes for pure macromolecular OLEDs that are not performance and reliability limited by the presence of the PVK:PBD matrix with low glass transition temperatures. This requires the development of macromolecules that subsume all the functions of the host matrix and have high enough Tg to be usable in high concentrations needed. In conjunction with the inkjet printing technology demonstrated in this work, this has the potential to yield low-cost manufacturing of these devices.
Phenyl and Halophenyl Substituted Poly(p-phenylene vinylene)s for Capacitor Dielectrics
Authors: Johnson Ross , Kholwadwala Fenil M. , Dirk Shawn M.
Published: August 2010

Conducting polymers have attracted attention in many areas of materials chemistry due to their tunability and wide range of applications. We are interested in utilizing the thermo-switchable properties of precursor PPV polymers to develop capacitor dielectrics that will fail at specific temperatures due to the material irreversibly converting from an insulating to a conducting state. Here, we report the synthesis and characterization of a new halophenyl substituted PPV polymer. We show that the precursor polymer has good dielectric properties over a range of temperatures, but will fail at high temperatures due to the polymer backbone conjugating. By utilizing thermo-switchable dielectrics in capacitors, the unintentional discharge of electricity in the event of a fire or overheating could be averted, providing a fundamental safety mechanism for high-voltage electronics.
Evaluation of Thermopower of Organic Materials Toward Flexible Thermoelectric Power Generators
Authors: Nakamura Masakazu , Hoshi Atsushi , Sakai Masatoshi , Kudo Kazuhiro
Published: August 2010

Organic conducting and semiconducting materials are promising as thermoelectric conversion materials in flexible and wearable electronics because they have large Seebeck coefficients and small thermal conductivities. Since there have been only a limited number of studies on the thermoelectricity of organic materials to date, precise evaluation of Seebeck coefficient and electrical conductivity of various organic conducting/semiconducting thin films is important to examine what kind of material is the most effectual. To carry out such experiments, a specially designed instrument for organic thin films has been developed. Its ability to measure Seebeck coefficients of highly resistive materials was confirmed and Seebeck coefficients and power factors of several typical organic functional materials were preliminary evaluated.
Structural Response of BaTiO3/CaTiO3 Superlattice to Applied Electric Fields
Authors: Jo Ji Young , Sichel Rebecca , Lee Ho Nyung , Dufresne Eric , Evans Paul
Published: August 2010

The structural response of a ferroelectric BaTiO3/dielectric CaTiO3 superlattice to the bipolar applied electric field was studied using time-resolved x-ray microdiffraction. Structural results were compared to the polarization-electric field hysteresis curve obtained from electrical measurements. The superlattice x-ray reflections were found to have a broad distribution of intensity in reciprocal space under applied electric fields exceeding the nominal coercive electric field. The broad distribution of the lattice constant at high electric fields is compared with a model in which the constituent layers of the superlattice have different coercive fields for the polarization switching.
Imaging of Hybrid-Multiferroic and Translation Domains in a Spin-Spiral Ferroelectric
Authors: Meier Dennis , Leo Naëmi , Lottermoser Thomas , Becker Petra , Bohatý Ladislav , Fiebig Manfred
Published: August 2010

Two fundamentally different types of domains were resolved in multiferroic MnWO4 by optical second harmonic generation (SHG). Hybrid-multiferroic (absolute) domains reflect the magnetic chirality coupled 1:1 to the spontaneous polarization because of the magnetic origin of the ferroelectric order. Magnetic translation (relative) domains reflect discontinuities in the progression of the magnetic spin spiral. SHG topography is the only experimental method so far allowing one to image both types of domains. The imaging procedure and the SHG contributions involved are therefore discussed in detail.
Leakage Current of PLD- and CSD-BiFeO3 Thin Films Observed by Current Sensitive AFM
Authors: Nakashima Seiji , Fujisawa Hironori , Park Jung Min , Kanashima Takeshi , Okuyama Masanori , Shimizu Masaru
Published: August 2010

We have investigated relationships between leakage current and microstructure or domain structure of BiFeO3 (BFO) thin films, and leakage current mappings of BFO thin films have been performed by current sensitive AFM. 350-nm-thick and 250-nm-thick BFO thin films were prepared on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition (PLD) and chemical solution deposition (CSD), respectively. Average grain size of PLD-BFO thin film is about 480 nm, which is the same as the film thickness. From the leakage current mapping at a bias voltage of -16 Vdc, leakage current of the BFO thin film flows through not only grain boundary but also the grain itself. On the other hand, CSD-BFO thin film shows rosette structure and small size grains. From the leakage current mapping at a bias voltage of -10 Vdc, leakage current flows along boundaries of the rosette structures. These results indicate that leakage current of BFO strongly depends on its microstructure.
Structural, Magnetic and Dielectric Properties of Magnetoelectric TbMn1-xCuxO3
Authors: Ray Shishir , Buroker Larry , Williamsen Mark S , Zou Ying , Sen Somaditya , Guptasarma Prasenjit
Published: August 2010

TbMnO3 is a multiferroic magnetoelectric material known to simultaneously exhibit antiferromagnetism below 40K and ferroelectricity below 28K in the same crystalline phase [1]. Following interesting results of Cu substitution in LaMn1-yCuyO3 [2, 3], we report a study of TbMn1-x CuxO3 (0 < x < 0.15). We describe here our results of crystal structure refinement, together with measurements of magnetic and dielectric properties in the temperature range 2 - 320 K, and magnetic field 0 - 9 T. We find no major changes in structure or symmetry upon substitution of Cu up to x = 0.15 in TbMn1-x CuxO3. Unlike LaMn1-yCuyO3, which exhibits ferromagnetism with very low values of y, we observe antiferromagnetism at x = 0.15. Our study of dielectric properties as a function of temperature suggests increased lossy behavior upon substitution of Cu at the Mn site. In our temperature dependent studies of tan δ at 1 kHz, we observe a well-defined step-like feature near 120K in both pure and substituted samples, possibly ascribable to a change in carrier mobility, or a dielectric-relaxation process mediated by ordered oxygen vacancies [4, 5], which we will continue to study.
First-principles Investigation of Edged Ferroelectric PbTiO3 Nanowires and the Role of Axial Strain
Authors: Shimada Takahiro , Tomoda Shogo , Kitamura Takayuki
Published: August 2010

Atomistic and electronic structures of PbTiO3 nanowires with atomically sharp edges consisting of (100)/(010) surfaces using first-principles calculations. Ferroelectricity is enhanced at the PbO-terminated edge in the nanowire because the Pb-O covalent bond that predominates the ferroelectric distortions is partially strengthened. On the other hand, a significant suppression is observed in the TiO2-terminated nanowire. Surprisingly, the smallest (one-unit-cell cross- section) PbO-terminated nanowire can keep ferroelectricity, while ferroelectricity disappears in the TiO2-terminated nanowires with a diameter of smaller than 17 Å. The ferroelectricity is recovered by axial tension, where the thinner nanowire requires the higher critical strain.
First-principles study of ferromagnetic Ni2CoGa(Zn) alloys in the Heusler and the inverse Heusler structure
Authors: Dannenberg Antje , Gruner Markus Ernst , Wuttig Manfred , Entel Peter
Published: August 2010

We performed an ab initio characterization of ferro- and nonmagnetic Ni2CoGa and Ni2CoZn compounds with respect to their potential application as new ferromagnetic shape memory alloys. The calculation of structural energy differences and mixing energies in the common
X2YZ Heusler structure and the inverse (XY)XZ structure revealed, that both alloys are stable in the tetragonal distorted Heusler structure with a c/a ratio of 1.38 and show ferromagnetic ordering. The Curie temperatures are of the order of ≃ 250 K. Exchanging Ga with Zn improves the magnetic properties of the alloy without qualitative modiﬁcation of the structural energy landscape, but at the expense of a reduced mixing energy.
Magnetocaloric Effect in Ni-Mn-Ga and Ni-Co-Mn-In Heusler Alloys
Authors: Buchelnikov Vasiliy , Taskaev Sergey , Drobosyuk Mikhail , Sokolovskiy Vladimir , Koledov Viktor , Khovaylo Vladimir , Shavrov Vladimir , Fediy Alexander
Published: August 2010

The positive magnetocaloric effect (MCE) in the vicinity of the Curie point in Ni2+xMn1-xGa (x=0.33, 0.36, 0.39) Heusler alloys and the negative and positive MCE near the metamagnetostructural (MMS) transition and the Curie point, respectively, in Ni45Co5Mn36.5In13.5 Heusler alloy has been measured by a direct method. For the magnetic field change ΔH = 2 T, the maximal adiabatic temperature change ΔTad at the Curie point in Ni2+xMn1-xGa alloys is larger than 0.6 K. For Ni45Co5Mn36.5In13.5 alloy, the maximal value of ΔTad = 1.68 K (for the same magnetic field change, ΔH = 2 T) is observed at the MMS phase transition temperature.
Ni-Mn-Ga films in the austenite and the martensite structures at room temperature: Uniaxial texturation and epitaxial growth
Authors: Tillier Jérémy , Einig Antinéa , Bourgault Daniel , Odier Philippe , Ortega Luc , Pairis Sébastien , Porcar Laureline , Chometon Paul , Caillault Nathalie , Carbone Laurent
Published: August 2010

Ni-Mn-Ga films in the austenite and the martensite structures at room temperature have been obtained using the DC magnetron sputtering technique. Two elaboration processes were studied. A first batch of samples was deposited using a resist sacrificial layer in order to release the film from the substrate before vacuum annealing. This process leads to polycrystalline films with a strong (022) fiber texture. The martensitic phase transformation of such polycrystalline freestanding films has been studied by optical and scanning electron microscopy. A second batch of samples was grown epitaxially on (100)MgO substrates using different deposition temperatures. The texture has been analyzed with four-circle X-ray diffraction. Epitaxial films crystallized both in the austenite and the martensite structures at room temperature have been studied.
Galfenol-based Sensor/Actuator Devices for Smart by-Wire Steering System for Automobile Technology
Authors: Furuya Yasubumi , Saito Chihiro , Okazaki Teiko , Okada Kazumi , Sado Yusuke , Chinen Takeo , Ogasawara Naoki , Shimada Muneaki
Published: August 2010

Polycrystalline Galfenol (Fe-Ga-X, X=Al, C, Zr etc.) alloys were fabricated as a bulk sample from ark-melted and annealing process method for enhancing various engineering applicability. (Fe-Ga0.15-Al0.05)99.0-Zr0.5-C0.5 [at.%] sample showed a maximum magnetostriction of 134 ppm as well as a tensile stress over σ=800MPa. This large magnetostriction is caused by A2 phases without the excessive precipitation of ordered phases such as fcc ordered L12 and bcc ordered D03 phases. Secondarily, we will introduce an application as a smart torque sensor by utilizing Galfenol-ring around the steering shaft for steering-by-wire system of automobile. In this system, a torque sensing system by using the magnetostrictive ring of FeGa (Galfenol) alloy was developed and magnetic flux leaked from the Galfenol ring attached on the rotating shaft was experimentally measured by using two differential Hall probe sensor. As a result, the sensitivity in (Fe0.80Ga0.15Al0.05)99Zr0.5C0.5 ring increased by 2.9 times in comparison with the (Fe0.80Ga0.15Al0.05)98.5C1.5 alloy at rotations speed 500 rpm.