bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative Scanning Transmission Electron Microscopy for the Measurement of Thicknesses and Volumes of Individual Nanoparticles
Authors: Heinrich Helge , Yuan Biao , Nukala Haritha , Yao Bo
Published: August 2010

In Scanning Transmission Electron Microscopy (STEM) the High-Angle Annular Dark-Field (HAADF) signal increases with atomic number and sample thickness, while dynamic scattering effects and sample orientation have little influence on the contrast. The sensitivity of the HAADF detector for a FEI F30 transmission electron microscope has been calibrated. Additionally, a nearly linear relationship of the HAADF signal with the incident electron current is confirmed. Cross sections of multilayered samples for contrast calibration were obtained by focused ion-beam (FIB) preparation. These cross sections contained several layers with known composition. A database with several pure elements and compounds has been compiled, containing experimental data on the fraction of electrons scattered onto the HAADF detector for each nanometer of sample thickness. Contrast simulations are based on the multi-slice formalism and confirm the differences in HAADF-scattering contrast for the elements and compounds. TEM offers high lateral resolution, but contains little or no information on the thickness of samples. Thickness maps in energy-filtered transmission electron microscopy, convergent-beam electron diffraction and tilt series are so far the only methods to determine thicknesses of particles in a transmission electron microscope. We show that the calibrated HAADF contrast can be used to determine the thicknesses of individual nanoparticles deposited on carbon films. With this information the volumes of nanoparticles with known composition were determined.
Size, Stability and Chemistry of Nanomaterials and their Precursors by Mass Spectrometry Techniques
Authors: Gaumet Jean Jacques , Arl Didier , Dalmasso Stéphane , Aubriet Frédéric , Laurenti Jean-Pierre
Published: August 2010

Soft ionization mass spectrometry (MS) methods [Electro-Spray Ionisation - Fourier Transform Ion Cyclotronic Resonance MS (ESI-FTICRMS) and Matrix Assisted Laser Desorption Ionization coupled with Time of Flight MS (MALDI-TOFMS)] and associated fragmentation techniques appear to be an alternative way providing data on the size, stability and exact chemical composition of nanoparticles and their precursors, and potentially on interactions between particles. We report the application of both mass spectrometry techniques to analyze II-VI semiconductor nanomaterials (CdX with X = S or Se) and their organometallic precursors.
Composition Quantification of Microelectronics Multilayer Thin Films by EDX: Toward Small Scale Analysis
Authors: Conard Thierry , Arstila Kai , Hantschel Thomas , Franquet Alexis , Vandervorst Wilfried , Vecchio Emma , Burgess Simon , Bauer Frank
Published: August 2010

In order to continuously improve the performances of microelectronics devices through scaling, SiO2 is being replaced by high-k materials as gate dielectric; metal gates are replacing poly-Si. This leads to increasingly more complex stacks. For future generations, the replacement of Si as a substrate by Ge and/or III/V material is also considered. This also increases the demand on the metrology tools as a thorough characterization, including composition and thickness is thus needed. Many different techniques exist for composition analysis. They usually require however large area for the analysis, complex instrumentation and can be time consuming. EDS (Energy Dispersive Spectroscopy) when coupled to Scanning Electron Microscopy (SEM) has the potential to allow fast analysis on small scale areas.

In this work, we evaluate the possibilities of EDS for thin film analysis based on an intercomparison of composition analysis with different techniques. We show that using proper modeling, high quality quantitative composition and thickness of multilayers can be achieved.
Methods to Measure Mechanical Properties of NEMS and MEMS: Challenges and Pitfalls
Authors: De Wolf Ingrid , Kalicinski Stanislaw , De Coster Jeroen , Oprins Herman
Published: August 2010

This paper focuses on the measurement of material properties of micro and nano-electromechanical systems. Two different methods are discussed: electrical or optical measurements of the resonance frequency, and measurements of the Raman frequency shift. The main focus of this paper is on challenges and pitfalls related to the use of these techniques for the study of MEMS and NEMS.
On the effects of dislocation density on micropillar strength
Authors: Benzerga Amine
Published: August 2010

There is an increasing amount of experimental evidence that the plastic behavior of crystals changes at micro- and nano-scales in a way that is not necessarily captured by state-of-the-art plasticity models. In this paper, length scale effects in the plasticity of crystals are analyzed by means of direct numerical simulations that resolve the scale of the carriers of plasticity, i.e., the dislocations. A computationally efficient, atomistically informed dislocation dynamics framework which has the capability of reaching high dislocation densities and large strains at moderately low strain rates in finite volumes is recalled. Using this theoretical framework, a new type of size effect in the hardening of crystals subject to nominally uniform compression is discovered. In light of such findings, behavior transitions in the space of meaningful structural parameters, from forest-hardening dominated regime to an exhaustion hardening dominated regime are discussed. Various scalings of the flow stress with crystal size emerge in the simulations, which are compared with recent experimental data on micro- and nano-pillars.
Stress-strain behavior of individual electrospun polymer fibers using combination AFM and SEM
Authors: Hang Fei , Lu Dun , Li Shuang Wu , Barber Asa H
Published: August 2010

Tensile deformation of individual electrospun polyvinyl alcohol (PVA) nanofibres was performed using a novel combination atomic force microscope (AFM)- scanning electron microscope (SEM) technique. The AFM was used to provide manipulation and mechanical testing of individual PVA nanofibers while the SEM was used to observe the deformation process. Resultant stress-strain curves show how the elastic modulus shows comparable, or even slightly increased, values to isotropic films. In addition, the electrospun fibers were tested to failure to measure their tensile strength.
Iron oxide crystal formation on a substrate modified with the Mms6 protein from magnetotactic bacteria
Authors: Arakaki Atsushi , Masuda Fukashi , Matsunaga Tadashi
Published: August 2010

Mms6 is a small acidic protein which is tightly bound to magnetite in the bacterium Magnetospirillum magneticum AMB-1. Mms6 has been previously shown to promote iron-binding capacity as well as modulate the size and morphology of magnetic iron oxide crystals in vitro. In this study, we synthesized iron oxide crystals by using a monolayer-modified substrate. A self-assembled monolayer of octadecyltrimethoxysilane was modified on a silicon substrate. Recombinant Mms6 protein was attached to the substrate through the hydrophobic interactions between the protein molecules and the monolayer. The immobilization of protein molecules on the substrate surface was confirmed by fluorescent labeling of these molecules and subsequent fluorescence microscopy. This protein-modified substrate was then used as a template for iron oxide crystal formation in a ferrous solution. Scanning electron microscopy revealed site-specific formation of iron oxide crystals in substrate regions with immobilized proteins. This use of proteins might provide an alternative method for the bottom-up fabrication of nano-sized magnetic particles.
Nanosilica Formation at Lipid Membranes Induced by Silaffin Peptides
Authors: Kent Michael , Murton Jaclyn K. , Satija Sushil , Kuzmenko Ivan , Simmons Blake
Published: August 2010

Diatoms are unicellular eukaryotic algae found in fresh and marine water. Each cell is surrounded by an outer shell called a frustule that is composed of highly structured amorphous silica. Diatoms are able to transform silicic acid into these sturdy intricate structures at ambient temperatures and pressures, whereas the chemical synthesis of silica-based materials typically requires extremes of temperature and pH. Cationic polypeptides, termed silica affinity proteins (or silaffins) recently identified from dissolved frustules of specific species of diatoms are clearly involved and have been shown to initiate the formation of silica in solution. The relationship between the local environment of catalytic sites on these peptides, which can be influenced by the amino acid sequence and the extent of aggregation, and the observed structure of the silica is not understood. Moreover, the activity of these peptides in promoting silicification at lipid membranes has not yet been clarified. In this work we developed a model system to address some of these questions. We studied peptide adsorption to Langmuir monolayers and subsequent silicification using X-ray reflectivity and grazing incidence X-ray diffraction. The results demonstrate the lipid affinity of the parent sequences of several silaffin peptides. Further, the results show that the membrane-bound peptides promote the formation of interfacial nanoscale layers of amorphous silica at the lipid-water interface that vary in structure according to the peptide sequence.
Structural and Electrical Characterization of Diatom Pinnularia sp. Biosilica Coated with CdS Thin Film
Authors: Gutu Timothy , Jeffryes Clayton , Wang Wei , Chang Chih-hung , Rorrer Gregory , Jiao Jun
Published: August 2010

Diatoms are unicellular, photosynthetic microalgae that live in marine and freshwater environments. The cell walls of diatoms are composed of biosilica and have exceedingly hierarchical ornate nanostructures. Consequently, these nanostructures have long been regarded as the paradigm for future silica nanotechnology. We have coated diatom Pinnularia sp. biosilica with a thin film of CdS using a chemical bath deposition technique. Possible uses for these CdS coated diatoms include the development of new nanodevice fabrication techniques and optoelectronic applications. Electron microscopy techniques were utilized to study their morphologies. Their electrical characteristics were investigated using an Agilent 4156C precision semiconductor parameter analyzer and a Cascade probe station. The CdS coating was found to be dense, adherent and nanostructured. The diatoms coated with CdS exhibited both metallic and semiconductor diode behavior.
Dynamic Fiber Bundle Model of Biopolymer Deformation
Authors: Jhon Mark Hyunpong , Chrzan Daryl
Published: August 2010

A statistical model is developed to study the loading-rate dependent mechanical response of biopolymer arrays. Using the kinetic Monte Carlo method, bundles of fibers are studied under load-controlled and displacement-controlled conditions.
Catalytic Forming Gas Anneal on III-V/Ge MOS Systems
Authors: Wang Wei-E , Lin Han-Chung , Brammertz Guy , Delabie Annelies , simoen eddy , Caymax Matty , Meuris Marc , Heyns Marc
Published: August 2010

Catalytic-FGA, a combination of the standard forming gas anneal with a catalytic metal gate, has been applied to study the hydrogen passivation of III-V/Ge MOS systems. Pd (or Pt) metal gate catalytically dissociates molecular hydrogen into atomic hydrogen atoms, which then diffuse through the dielectric layer and neutralize certain semiconductor/dielectric interfacial defects. MOS systems with various interfacial qualities, including lattice-matched (n/p) In0.53Ga0.47As/10nm ALD-Al2O3 (or ZrO2)/Pd capacitors, an undoped Ge/˜1nm GeO2/4nm ALD-Al2O3/Pt capacitor, and an nGe/8nm ALD-Al2O3/Pt capacitor are fabricated to evaluate the effectiveness of C-FGA.
Ultrafast Self-Assembly of Microscale Particles by Open-Channel Flow
Authors: Choi Sun , Pisano Albert P. , Zohdi Tarek I.
Published: August 2010

We developed an ultrafast microfluidic approach to self-assemble microparticles in threedimensions by taking advantage of simple photolithography and capillary action of microparticle-dispersed suspensions. The experimental verifications of the assembly of various sizes of silica microspheres and silica gel microspheres within thin and long open microchannels by using this approach have been demonstrated. We anticipate that the presented technique will be widely used in semiconductor and Bio-MEMS (microelectromechanical Systems) fields because it offers a fast way to control 3D, microscale particle assemblies and also has superb compatibility with photolithography, which can lead to an easy integration of particle assembly with existing CMOS (complementary metal-oxide-semiconductor) and MEMS fabrication processes.
Organic Thin Film Transistors based on Pentacene and PTCDI as the Active Layer and LiF as the Insulating Layer
Authors: Rahimi Ronak , Korakakis D.
Published: August 2010

Due to the advantages of low production cost, flexibility and low temperature fabrication, much effort has been devoted to the development of organic electronic devices such as light emitting diodes, photovoltaics and transistors. Organic thin film transistors have several important applications such as switching devices for active-matrix OLED displays, smart cards, identification tags and sensors [1-3]. However, the low carrier mobility in organic materials and the difficulty of integrating organic devices into inorganic processing procedures have hindered the development of organic transistors that are comparable to traditional transistors [4]. Much effort has been devoted to develop new organic materials with higher carrier mobility, while retaining the same conventional inorganic metal-oxide-semiconductor structures.

Lithium fluoride (LiF) has the largest band gap and the largest negative electron affinity of any solid, [5] making it a superb candidate for use in the insulating layer of transistors. Using LiF as the gate dielectric layer can facilitate the organic transistor fabrication. In this work, thin film transistors based on pentacene and PTCDI-C8 (N,N′-Dioctyl-3,4,9,10-perylenedicarboximide) as organic semiconductor layers and LiF as gate dielectrics are studied. The electrical properties of these devices have been investigated in atmospheric conditions and under variable light exposure. Output and transfer characteristics of several photo-responsive thin film transistors using different organic materials but with the same insulating layer will be presented and the increase of drain-source current upon illumination will be discussed based on the photoconduction properties of the transistor active layer.
The Salt and Paper Battery; Ultrafast and All-polymer Based
Authors: Nyström Gustav , Razaq Aamir , Mihranyan Albert , Nyholm Leif , Strømme Maria
Published: August 2010

We have recently developed a flexible battery using two common, inexpensive ingredients: cellulose and salt. This lightweight, rechargeable battery uses thin pieces of paper—originating from cellulose fibers from the environmentally polluting Cladophora sp.algae—as electrodes, while a solution of sodium chloride acts as the electrolyte. Conducting polymers for battery applications have been subject to numerous investigations during the last decades. However, the functional charging rates and the cycling stabilities have so far been found to be insufficient for practical applications. These shortcomings can, at least partially, be explained by the fact that thick layers of the conducting polymers have been used to obtain sufficient capacities of the batteries. We now introduce a novel nanostructured high-surface area electrode material for energy storage applications composed of cellulose fibers of algal origin individually coated with a 50 nm thin layer of polypyrrole. Our results show the hitherto highest reported charge capacities and charging rates for an all polymer paper-based battery. The composite conductive paper material is shown to have a specific surface area of 80 m2/g and batteries based on this material can be charged with currents as high as 600 mA/cm2. The aqueous-based batteries, which are entirely based on cellulose and polypyrrole and exhibit charge capacities between 25 and 33 mAh/g or 38-50 mAh/g per weight of the active material, open up new possibilities for the production of environmentally friendly, cost efficient, up-scalable and lightweight energy storage systems.
A Theoretical Study and Realization of New Spin Quantum Cross Structure Devices using Organic Materials
Authors: Kondo Kenji , Kaiju Hideo , Ishibashi Akira
Published: August 2010

We have proposed a spin quantum cross structure (SQCS) device as a candidate beyond CMOS. The SQCS device consists of two ferromagnetic metal thin films with their edges crossed, and sandwiches a few atoms or molecules. In this work, the spin dependent transport formula has been derived for SQCS devices with collinear ferromagnetic electrodes within the framework of the Anderson Hamiltonian. Also, the calculation of the magnetoresistance (MR) ratio has been done as a function of renormalized transfer matrices including magnetostriction effects and the other effects phenomenologically. It is shown that the MR ratio can be controlled by changing the renormalized coupling constants. The MR ratio is represented by a new formula. Also, we have realized an SQCS device with Ni magnetic thin-film electrodes, sandwiching poly (3-hexylthiophene) (P3HT): 6, 6-phenyl-C61-butyric acid methyl ester (PCBM) organic molecules between both the electrodes. The current-voltage characteristics of SQCS devices were measured by a four-terminal method and agree well with the theoretical results, quantitatively.
Development of PLZT Film-on-Foil Capacitors with High Dielectric Strength
Authors: Ma Beihai , Narayanan Manoj , Balachandran U.
Published: August 2010

Ferroelectric film-on-foil capacitors hold special promise to replace discrete passive components in the development of electronic devices that require greater performance and smaller size. We have grown ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3(PLZT) films on nickel substrates by chemical solution deposition. The dielectric properties were determined for samples of ≈1.15-μm-thick PLZT film grown on LaNiO3-buffered nickel substrates. Measurements on these samples yielded a dielectric constant of ≈1300, dielectric loss (tan δ) of ≈0.05, and leakage current density of ≈7 × 10-9A/cm2. An energy density of ≈74 J/cm3was measured at room temperature with 250-μm-diameter capacitors. Highly accelerated lifetime tests were conducted at 100°C to determine the reliability of the ≈1.15-μm-thick film-on-foil capacitors under field stress conditions (with applied electric field from 8.7 × 105V/cm to 1.3 × 106V/cm). The breakdown behavior of the PLZT film-on-foil capacitors was evaluated by Weibull analysis. A voltage acceleration factor of ≈-6.3 was obtained. From the test results, a mean time to failure of >3000 hr was projected for capacitors operated at 100°C with ≈2.6 × 105V/cm dc electric field.
Fabrication and Characterization of Artificially Designed PZT/LSMO Multiferroics Heterostructure
Authors: Dussan Sandra , Kumar Ashok , Katiyar Ram S.
Published: August 2010

Highly oriented and epitaxial bilayers of PbZr0.52Ti0.48O3/La0.67Sr0.33MnO3 (PZT/LSMO) thin films have been grown by pulsed laser deposition on two different substrates (100) - MgO and -LaAlO3 (LAO) respectively. The structural analysis using X-ray diffraction (XRD) evidenced that layered structure was formed without any secondary phase. Atomic force microscopy (AFM) images shown change in the grain size and surface roughness with change of the substrate. Room temperature magnetization-field (M-H) exhibited well-shaped magnetization hysteresis loops, good saturation and low coercivity. The electrical properties of hetrostructure exhibited high remnant polarization (30-54 μC/cm2) and dielectric constant (400-1700) depending upon the different substrate and temperature deposition of FM layer. Frequency dependent change in dielectric constant and loss were observed above metallic ferromagnet to insulator paramagnet transition temperature. It is important to note that the frequency dependent dielectric anomalies are attributed to the change in metallic nature of LSMO bottom electrode and also the bilayer.
One-axis Oriented CaBi4Ti4O15 and SrBi4Ti4O15 Films Prepared on Silicon Wafer by Chemical Solution Deposition Technique
Authors: Mizutani Yuki , Uchida Hiroshi , Funakubo Hiroshi , Koda Seiichiro
Published: August 2010

One-axis oriented bismuth layer-structured dielectric (BLSD) films were designed using perovskite buffer layers for assembling the crystal orientation and the dielectric properties of the BLSD crystals on silicon wafer. The BLSD crystals with the general formula of (Bi2O2)2+-(Am-1BmO3m+1)2- possess excellent dielectric permittivity with lower size effect and temperature coefficient of capacitance (TCC), as well as high electrical resistivity along to the c-axis direction. These phenomena would contribute for constructing high performance dielectric devices driven under harsh environment, e.g., at high-temperature condition above 100°C. In this study, thin films of CaBi4Ti4O15 and SrBi4Ti4O15, kinds of BLSD compounds with the number of BO6 octahedra in pseudo-perovskite blocks, m, = 4, were prepared by chemical solution deposition (CSD) technique on (100)LaNiO3/(111)Pt/TiO2/(100)Si and (100)SrRuO3// (100)LaNiO3/(111)Pt/TiO2/(100)Si substrates. These films consisted of crystalline phase of BLSD crystal with preferential crystal orientation of (001) plane normal to the substrate surface. Anisotropic crystal growth of BLSD occurred by the lattice matching between pseudo-perovskite blocks in BLSD crystal and (100)LaNiO3 or (100)SrRuO3 plane with perovskite structure. The dielectric constants (εr) of (001)-plane oriented CaBi4Ti4O15 and SrBi4Ti4O15 films were approximately 250-350 at room temperature. The r values of the CaBi4Ti4O15 and SrBi4Ti4O15 films increased slightly with ambient temperature. The TCCs at a temperature range from 25 to 200°C were approximately +103 - +514 ppm/K respectively, which were significantly different from those of (Ba,Sr)TiO3 thin films and would satisfy the performance requirement for driving at high-temperature condition.
Process-dependent Coercive Fields in Undoped and Mn-doped BiFeO3 Films Formed on SrRuO3/Pt(111) Electrodes by rf Sputtering
Authors: Kim Jeong Hwan , Funakubo Hiroshi , Sugiyama Yoshihiro , Ishiwara Hiroshi
Published: August 2010

We deposited BiFeO3 (BFO) thin films on SrRuO3 (SRO)/Pt bottom electrodes by radio-frequency (RF) sputtering. Some samples were formed at the substrate temperature of 550 °C, and others were foremed at 450 °C and post-annealed at 650°C for crystallization. The coercive field in the post-annealed BFO film was smaller than that in the 550°C-deposited BFO film. The coercive field in Mn-doped BiFeO3 (BFMO) films which were deposited at 550 ˚C on SRO/Pt(111) was lower than that in undoped BFO films. Degradation of the remanent polarization was less significant in the post-annealed BFO film.
Geometric Phase Analysis of Nano-Scale Strain Fields Around 90° Domains in PbTiO3/SrTiO3 Epitaxial Thin Film
Authors: Kiguchi Takanori , Aoyagi Kenta , Konno Toyohiko J. , Utsugi Satoru , Yamada Tomoaki , Funakubo Hiroshi
Published: August 2010

The nano-scale strain fields analysis around 90° domains and misfit dislocations in PbTiO3/SrTiO3 001 epitaxial thin film has been conducted using the geometric phase analysis (GPA) combined with high angle annular dark field - scanning transmission electron microscopy (HAADF-STEM). The films typically possess a-c mixed domain configuration with misfit dislocations. The PbTiO3 layer was formed from the two layer: the upper 200 nm layer shows the typical a- and c- mixed domain configuration where the a-domains are several tens nm in width; the bottom 100 nm layer shows the different domain configuration that the width is several nm. In the latter case, a-domains are terminated within the film and are short in length. On the other hand, the bottom of a-domains does not contact the film/substrate interface. It keeps away from the interface, and there is completely c-domain layer under a-domains. The HAADF-STEM-GPA shows that the strain fields around an a-domain and a misfit dislocation interact each other: the tensile strain field and lattice plane bending fit together. This result indicates that the a-domain originates from the misfit dislocation.
Magnetocaloric Properties of Rapidly Solidified Ni51.1Mn31.2In17.7 Heusler Alloy Ribbons
Authors: Sánchez Llamazares Jose , Hernando Blanca , Prida Víctor , García Carlos , Ross Caroline
Published: August 2010

Magnetic entropy change and refrigerant capacity have been determined for a field change of 20 kOe around the second-order magnetic transition of austenite in as-quenched Ni51.1Mn31.2In17.7 alloy ribbons produced by melt spinning technique. Samples crystallize in a single-phase austenite with the highly ordered L21-type crystal structure and a Curie temperature of 275 K. The material shows a maximum magnetic entropy change of ΔSMmax= - 1.7 Jkg-1K-1, an useful working temperature range of 78 K (δTFWHM) and a refrigerant capacity of RC=132 Jkg-1 (RC= │ΔSMmax│ x δTFWHM). The considerable RC value obtained together with the fabrication via a single-step process make austenitic Ni-Mn-In ribbons of potential interest as magnetic refrigerants for room temperature magnetic refrigeration.
Structural Characterization of PLD-grown Nanometer Size Ferromagnetic NiFeMo Films
Authors: Banerjee Mitali , Majumdar Alak Kumar , Choudhary R J , Phase D M , Rai S , Tiwari Pragya , Lodha G S
Published: August 2010

Thin films of 3 different thicknesses each of Ni83.2Fe3.3Mo13.5 and Ni83.1Fe6.0Mo10.9alloys have been grown using Pulsed Laser Deposition (PLD) technique. Our motivation is to investigate the magnetic properties of a few nm thick Ni alloys with mostly Mo (4d element) addition since the corresponding soft ferromagnetic bulk alloys have shown very small coercivity of ˜ 0.1 Oe. Detailed structural characterization has been undertaken before probing the magnetic properties. Arc melted alloy buttons after homogenization are used directly as targets for the deposition. Films were deposited on single crystal Sapphire (0001) substrates using excimer laser. The structural characterization has been done by X-ray diffraction (XRD), X-ray reflectivity (XRR), Energy dispersive x-ray spectroscopy (EDS), and Atomic force microscopy (AFM). The X-ray diffraction pattern shows that the films are highly textured and grown along [111] direction of the alloys. They have high lattice strain which makes the films highly resistive and the resistance decreases with increasing thickness. The EDS measurements, using Scanning electron microscope (SEM), indicate that the compositions of the films are almost the same as those of the targets. Thickness, roughness, and density gradients are estimated using XRR measurements. The thinner films have higher roughness compared to the thicker ones for both the compositions. The films have density gradient across their thickness. The bottommost low density layer has high roughness which is supposed to be the result of initial non uniform coverage of the substrate. The density of the middle layer, having the lowest roughness, is approximately near the bulk value and it increases with increasing film thickness. The change in density is not due to the variation of composition; instead it is due to the variation of void densities in the layers. The topmost layer, having the lowest density and the highest roughness, is interpreted as a porous layer which is also evident from the AFM images.
Study of Magnetocaloric Properties of Ni-Mn-X (X = Ga, In) Heusler Alloys by Monte Carlo Technique
Authors: Buchelnikov Vasiliy , Sokolovskiy Vladimir , Taskaev Sergey , Entel Peter
Published: August 2010

Two theoretical Monte Carlo models have been presented for description of the positive and negative magnetocaloric effects of Heusler Ni-Mn-X (X = Ga, In) alloys undergoing first order coupled magnetostructural phase transition. For both models all quantities such as temperature dependence of the magnetic contribution to the total specific heat, magnetization and isothermal magnetic entropy change are in qualitative agreement with the available experimental data.
Electronic Impact of Inclusions in Diamond
Authors: Muller Erik M. , Smedley John , Raghothamachar Balaji , Gaowei Mengjia , Keister Jeffrey W. , Ben-Zvi Ilan , Dudley Michael , Wu Qiong
Published: August 2010

X-ray topography data are compared with photodiode responsivity maps to identify potential candidates for electron trapping in high purity, single crystal diamond. X-ray topography data reveal the defects that exist in the diamond material, which are dominated by non-electrically active linear dislocations. However, many diamonds also contain defects configurations (groups of threading dislocations originating from a secondary phase region or inclusion) in the bulk of the wafer which map well to regions of photoconductive gain, indicating that these inclusions are a source of electron trapping which affect the performance of diamond X-ray detectors. It was determined that photoconductive gain is only possible with the combination of an injecting contact and charge trapping in the near surface region. Typical photoconductive gain regions are 0.2 mm across; away from these near-surface inclusions the device yields the expected diode responsivity.
Synthesis of Ca Decorated Carbon Nanostructures for Hydrogen Storage
Authors: Mirabile Gattia Daniele , Vittori Antisari Marco , Marazzi Renzo , Montone Amelia , Piscopiello Emanuela , Mingazzini Claudio
Published: August 2010

The AC powered electric arc has been used to synthesize single wall carbon nanohorns aggregates with Ca dispersed inside. To this purpose the electric arc has been ignited between two electrodes, one of which was constituted by a mixture of graphite and CaCO3. The experimental evidence on the microstructure and on the chemical composition has been obtained by observation with a transmission electron microscope equipped with X-ray microanalysis. X-ray diffraction revealed the presence of residual CaCO3 indicating that the process has still to be optimized. The experiment represents a first attempt to decorate carbon nanostructures with alkaline earth metals, in particular Ca, by this relatively simple method. These composites are theorized to adsorb relevant amounts of hydrogen. Further work will be focused to optimize the dispersion of Ca atoms in the carbon nanostructure.
Contactless Measurement of Carrier Lifetime on Silicon Ingots and Bricks
Authors: Swirhun James S , Forsyth M Keith , Mankad Tanaya , Sinton Ronald Alan
Published: August 2010

High efficiency silicon solar cells demand the use of high lifetime silicon wafers. Characterization of boules and bricks before wafering allows poor quality material to be rejected before expensive processing steps. This paper extends simulation techniques previously used in quasi-steady-state-photoconductance to transient photoconductance decay measurements of high lifetime bulk samples. Simulated photogenerated carrier density profiles allow estimation of the bulk lifetime of a thick silicon sample with high surface recombination velocity.
Optimizing sulfurisation conditions in the fabrication of Cu2ZnSnS4absorber layers from electroplated precursors
Authors: Scragg Jonathan James , Wolverson Daniel , Zoppi Guillaume , Peter Laurence M
Published: August 2010

Using direct photoelectrochemical measurement of the photocurrent obtained from Cu2ZnSnS4(CZTS) absorber layers made by a two-stage electroplating-sulfurisation process, the influence of processing conditions (temperature, time, and pressure) on material quality was investigated with a view to understanding the long sulfurisation times usually found in the literature. The improvement in photocurrent due to KCN etching was also studied, and seems to be due both to removal of surface phases and also slower etching of the bulk material. The optimum sulfurisation time was found to be around 50 minutes, despite evidence that sulfur incorporation and phase formation are complete within 5 minutes. Slow grain growth was suggested as a rate-limiting factor, and a rate constant was derived based on a simple model.
Optimization of gettering processes of metallurgical-grade silicon for solar cell applications
Authors: Iskandarova Inna M. , Zvyagin Igor P. , Knizhnik Andrey , Konovalov Andrey V. , Potapkin Boris , Arutyunyan Natalya , Zaitsev Alexander I. , McNulty Thomas , Sommerer Timothy , Rahmane Mohamed , Lou Victor , Soloviev Stanislav , Vert Alexei , Selezneva Svetlana
Published: August 2010

Conversion efficiency of a solar energy in the electric is substantially determined not only by the total impurity concentration in solar cell element, but also by impurity chemical and physical state. Gettering processes, which are included in the technology of solar cell manufacturing, are usually used for such impurity redistribution. In order to optimize gettering processes we developed a program tool based on the fundamental physical and chemical laws. The description of physical and chemical behaviour of impurities in silicon is based both on known experimental data, and on calculations of necessary parameters by means of present-day thermodynamic and quantum-chemical methods. Developed tool helps to choose a gettering regime (a temperature profile, time, getter layer thickness) for optimization of these processes for the given initial chemical composition of the silicon wafer. Possibility of analysis of recombination activity of various types of defects in silicon on the basis of carrier lifetime criterion allows to obtain an estimation of efficiency of the gettering processes. Using this program tool we demonstrated that solar cell efficiency can be significantly increased by optimal choice of gettering conditions.
White Organic Light-Emitting Diodes with Fluorescent Tube Efficiency
Authors: Reineke Sebastian , Lindner Frank , Schwartz Gregor , Seidler Nico , Walzer Karsten , Lüssem Björn , Leo Karl
Published: August 2010

White organic LEDs are seen as one of the next generation light-sources, with their potential to reach internal efficiencies of unity and their unique appearance as large-area and ultrathin devices. However, to replace existing lighting technologies, they have to be at least on par with the state-of-the-art. In terms of efficiency, the fluorescent tube with 60-70 lumen per Watt (lm W-1) in a fixture is the current benchmark. In the scientific literature, so far only values of 44 lm W-1 have been published for white OLEDs.

Here, we present results (Reineke et al., Nature 459, 234 (2009)) of white OLEDs with 90 lm W-1 at an illumination relevant brightness of 1,000 candela per square meter (cd m-2). Extracting all light from the glass substrate using a 3D light extraction system, we even obtain 124 lm W-1. In order to achieve such high efficacy values, we reduced the energetic losses prior to photon emission that include ohmic and thermal relaxation losses, leading to very low operating voltages. This is accomplished by the use of doped transport layers and a novel, very energy efficient emission layer concept. Equally important, we addressed the optics of the OLED architecture, because about 80% of the generated light remains trapped in conventional devices. Therefore, we used high refractive index substrates to couple out more light and placed the emission to the second field antinode to avoid plasmonic losses. Our devices are also characterized by an outstandingly high efficiency at high brightness, reaching 74 lm W-1 at 5,000 cd m-2.
Hybrid P3HT/CdSe Photovoltaic Cells: Effects of Nanocrystal Size and Device Aging
Authors: Yang Jihua , Zhou Renjia , Tang Aiwei , Xue Jiangeng
Published: August 2010

Hybrid solar cells based on conjugated polymers and colloidally synthesized inorganic nanoparticles have been recognized as an alternative to all-organic solar cells due to the intrinsically higher charge transport property in inorganic component. In this work, CdSe nanoparticles with different sizes, served as the electron acceptor, have been used together with poly(3-hexylthiophene) (P3HT) as the active layer for the hybrid solar cells. The power-conversion efficiency (ηp) of these devices strongly depends on the size of the CdSe nanoparticles, increasing from ηp ˜0.5% for 4.0 nm size nanoparticles to ηp ˜2.4% for 6.8 nm size nanoparticles under AM 1.5 G solar illumination. Furthermore, the devices also exhibit an unusual initial aging period when exposed to the air, which results in a significant enhancement in the short-circuit current, open-circuit voltage and power conversion efficiency.
HRTEM Study of Oxide Nanoparticles in 16Cr-4Al-2W-0.3Ti-0.3Y2O3 ODS Steel
Authors: Hsiung Luke , Fluss Mike , Wall Mark , Kimura Akihiko
Published: August 2010

Crystal and interfacial structures of oxide nanoparticles in 16Cr-4Al-2W-0.3Ti-0.3Y2O3 ODS ferritic steel have been examined using high-resolution transmission electron microscopy (HRTEM) techniques. Oxide nanoparticles with a complex-oxide core and an amorphous shell were frequently observed. The crystal structure of complex-oxide core is identified to be mainly monoclinic Y4Al2O9 (YAM) oxide compound. Orientation relationships between the oxide and matrix are found to be dependent on the particle size. Large particles (> 20 nm) tend to be incoherent and have a spherical shape, whereas small particles (< 10 nm) tend to be coherent or semi-coherent and have a faceted interface. The observations of partially amorphous nanoparticles lead us to propose three-stage mechanisms in order to rationalize the formation of oxide nanoparticles containing core/shell structures in as-fabricated ODS steels.
Radiation Response of a 12YWT Nanostructured Ferritic Steel
Authors: Miller Michael , Hoelzer David , Russell Kaye F.
Published: August 2010

In order to evaluate the radiation response of 12YWT nanostructured ferritic steel to high dose neutron irradiation, the solute distribution, and size, number density, and compositions of nanoclusters in the unirradiated condition and after neutron irradiation to a dose of 3 dpa at a controlled temperature of 600 °C were estimated by atom probe tomography. No statistical difference in the average size or size distribution of the nanoclusters was found between the unirradiated and irradiated conditions. Therefore, these nanostructured ferritic steels are promising candidate materials for use under extreme conditions in future generations of advanced reactors.
Densification of Inert Matrix Fuels Using Naturally-occurring Material as a Sintering Additive
Authors: Miwa Shuhei , Osaka Masahiko , Usuki Toshiyuki , Yano Toyohiko
Published: August 2010

We proposed a new concept for densification of inert matrix fuels containing minor actinides. In this concept, magnesium silicates which are both a naturally-occurring material and asbestos waste were used as a sintering additive which protects public health by safely disposing of the asbestos waste. In this study, the effects of magnesium silicate additives on the densification behaviors of MgO, Mo and CeO2 were experimentally investigated. The densities of MgO and CeO2 pellets increased with only 1 wt.% additives of MgSiO3 and Mg2SiO4. The densities of Mo pellets showed little change with additives.
Effect of Americium and Simulated Fission Products Addition on Oxygen Potential of Uranium-Plutonium Mixed Oxide Fuels
Authors: Tanaka Kosuke , Osaka Masahiko , Kurosaki Ken , Muta Hiroaki , Uno Masayoshi , Yamanaka Shinsuke
Published: August 2010

The oxygen potentials at 1273 K of mixed oxide (MOX) fuels with Am and 26 kinds of fission product elements (FPs), simulating low-decontaminated MOX fuel and high burn-up of up to 250 GWd/t, have been measured by using thermogravimetric analysis (TGA). The oxygen potentials for simulated low-decontaminated MOX fuels were higher than the fuels without FPs and increased with increasing simulated burn-up.
Are Slit Pores in Carbonaceus Materials Real?
Authors: Romero Cristina , Valladares Ariel A. , Valladares R. M. , Valladares Alexander
Published: August 2010

Nanoporous carbon is a widely studied material due to its potential applications in hydrogen storage or for filtering undesirable products. Most of the developments have been experimental although some simulation work has been carried out based on the use of graphene sheets and/or carbon chains and classical molecular dynamics. The slit pore model is one of the oldest models proposed to describe porous carbon. Developed by Emmet in 1948 [1] it has been recurrently used and in its most basic form consists of two parallel graphene layers separated by a distance that is taken as the width of the pore. Its simplicity limits its applicability since experimental evidence suggests that the walls of the carbon pores have widths of a few graphene layers [2], but it still is appealing for computational simulations due to its low computational cost. Using a previously developed ab initio approach to generate porous semiconductors [3] we have obtained porous carbonaceous materials with walls made up of a few graphene layers (four layers), in agreement with experimental results; these walls are separated by distances comparable to those used in the slit pore model [4]. This validates the idea of a modified slit pore model obtained without the use of ad hoc suppositions. Structures will be presented, analyzed and compared to available experimental results.
Twining and Slip Activity in Magnesium <11-20> Single Crystal
Authors: Kim Gyu Seok , Yi Sangbong , Huang Yuanding , Lilleodden Erica
Published: August 2010

Uniaxial μ-compression tests have been performed on single crystal Mg with a <11-20> compression direction, an orientation unfavorable for basal slip. Results show that the early stages of deformation proceed via both twinning and dislocation plasticity. Twinning leads to a reorientation of the crystal favorable for basal slip, typically with the <2-1-1-3> aligned with the compression direction. At a critical strain a large strain burst occurs, and is associated with both rapid propagation of the twin and the activation of basal slip within the twin. Such a mechanistic picture of the deformation behavior is revealed through SEM, EBSD and TEM characterization of the deformation structures.
Variable Elastic-Plastic Properties of the Grain Boundaries and Their Effect on the Macroscopic Flow Stress of Nano-Crystalline Metals
Authors: Lewandowska Malgorzata , Dobosz Romuald , Kurzydlowski Krzysztof J
Published: August 2010

The paper reports new experimental results describing properties and microstructure of nanocrystalline metals. Nano- and sub-micron aluminium has been produced by hydrostatic extrusion at ambient tempearture. The structures have been quantified in terms of size of grains and misorientation of the grain boundaries. Different average size of grains, variable normalized width of grain size distribution and changing grain boundary misorientation distribution functions have been revealed depending on processing parameters. The results of the tensile tests showed that the average grain size, grain size distribution and the distribution function of misorientation angles influence the flow stress of obtained nano-metals. In order to explain the observed difference in the properties of nano- and micro-sized aluminium alloys, a Finite Element Method models have been developed, which assumes that both grain boundaries and grain interiors may accommodated elastic and non-linear plastic deformation. These models assumed true geometry of grains (which differed in size and shape). Also, variable mechanical properties of grain boundaries have been taken into account (elastic modulus, yield strength and work hardening rate). The results of modelling explain in a semi-quantitative way macroscopic deformation of nano-crystalline aggregates. In particular, they illustrate the importance of the interplay between properties of grain boundaries and grain interiors in elastic and plastic regime.
Nanoporous Polymeric Periodic Structures Fabricated by Emulsion-assisted Holographic Patterning
Authors: Hsiao Vincent K.S , Chang Wei-Ting
Published: August 2010

We report a new technique of creating a nanoporous polymeric nanostructure by photo-patterning emulsions generated from a formamide (polar phase) and an acrylate-monomer (nonpolar phase). Formamide is a highly polar solvent that forms well dispersed, non-aqueous emulsion droplets within the monomer-containing nonpolar phase before holographic patterning. Photochemically initiated polymerization of the nonpolar phase (acrylate monomer) forces the formation of ordered formamide emulsions defined by the holographic interference. Evaporation of the formamide from the ordered structure yields a periodic structure with high optical reflectivity and a wide reflection bandwidth. The average size and the size distribution of formamide droplets in the photopolymer fluid must be controlled to fabricate a periodic structure with high reflectivity. Furthermore, we found that the addition of sodium dioctyl sulfosuccinate (AOT) surfactant helps to stabilize the formamide emulsion which further facilitates the formation of the ordered nanopores with uniform size.
Collinear Generation of Ultrashort UV and XUV Pulses for Pump/probe Spectroscopy
Authors: Bothschafter Elisabeth , Schiffrin Agustin , Krausz Ferenc , Ernstorfer Ralph , Kienberger Reinhard
Published: August 2010

The collinear generation of sub-4 fs ultraviolet (UV) and attosecond extreme ultraviolet (XUV) pulses via subsequent third-harmonic and high harmonic generation in noble gases is demonstrated. The ultrashort coherent light bursts are produced by focusing a sub-1.5 cycle near-infrared/visible (NIR) laser pulse in two subsequent quasi-static noble gas targets. With this simple approach, inherently synchronized UV pulsed radiation with a photon energy of ˜5 eV and a pulse energy of ˜1 μJ, and XUV pulses with a cut-off photon energy of more than 120 eV and up to ˜107 XUV photons can be generated. This source represents a novel tool for future UV pump/XUV probe experiments with unprecedented time-resolution.
Ultrafast Mid-Infrared Intra-Excitonic Response of Individualized Single-Walled Carbon Nanotubes
Authors: Wang Jigang , Graham Matt W. , Ma Yingzhong , Fleming Graham R. , Kaindl Robert A
Published: August 2010

We present femtosecond mid-infrared (mid-IR) studies of the broadband low-energy response of individualized (6,5) and (7,5) single-walled carbon nanotubes. Strong photoinduced absorption is observed in these semiconducting tubes around 200 meV photon energy. The transition energy and broadly sloping spectral shape are characteristic of quasi 1D intra-excitonic transitions between different relative-momentum states. Our result yields a value of the intra-excitonic absorption cross section of σ∥MIR≈4×10-5.
Ultrafast Dynamics of Highly Excited Dirac Fermions in Few-Layer Graphene: Evidence for Three-Particle Auger Scattering
Authors: Li T , Luo L , Hupalo M. , Tringides M C , Wang Jigang
Published: August 2010

We present femtosecond differential reflectivity studies of few-layer graphene from weak to strong excitation regime. Temporal profiles of the differential reflectivity exhibit strong non-exponential decay. A nonlinear, cubic root dependence of their peak amplitudes on the pump fluence is clearly observed under relatively high intensity excitation, which indicates three-particle decay of transient carrier population via Auger scattering. Our results identify the critical role of such three-particle scattering in the initial electronic relaxation in photo-excited graphene with increasing phase-space filling of the correlated Dirac Fermions.