bluuebunny/crossref_metadata_2025 huggingface dataset:
Expanded experimental space for luminescence studies of thin film CdS/CdTe solar cells
Authors: Feldman Scott , Ohno Tim , Kaydanov Victor , Collins Reuben
Published: April 2011

We have explored a large range of experimental space for photoluminescence (PL) and electroluminescence (EL) measurements of CdS/CdTe solar cells. This space includes changes in temperature, injection intensity (laser power for PL, current for EL), electrical bias for PL, and laser energy for PL. Measurements were resolved both spectrally and spatially (2D for EL, 1D for PL). Combination of EL and PL measurements revealed that most spatial inhomogeneity was the result of non-uniform current transport rather than local variations in recombination rate. The greatest spectral resolution was obtained with low temperature EL at low injection rates. High injection EL as well as high forward biased PL suppressed band-edge emission at low temperatures. Spectral structure was found to be greater in EL than in PL. These effects likely originated from preferential current transport along grain boundaries and/or certain grains.
Improved Efficiency in Hydrogenated Amorphous Silicon Solar Cells Irradiated by Excimer Laser
Authors: Damitha A. A. , Adikaari T. , Ravi S. , Silva P. , Kearney Michael J. , Shannon John M.
Published: April 2011

Excimer laser crystallisation is used to fabricate nanocrystalline thin film silicon Schottky barrier solar cells, in a superstrate configuration with indium tin oxide as the front contact and chromium as the back contact. 150 nm thick intrinsic absorber layers are used for the solar cells, and was crystallised using an excimer laser with different laser energy densities. These layers were characterised using Raman spectroscopy and optical absorption before device fabrication. External quantum efficiencies of the devices were calculated from the spectral response data of the devices. A maximum efficiency of 70 % is observed for low energy irradiation, which is significant for very thin absorber layers. Device operation is discussed with proposed band structures for the devices and supplementary measurements.
Electrospun Poly(vinylidene fluoride)-based Carbon Nanofibers for Hydrogen Storage
Authors: Chung H. J. , Lee D. W. , Jo S. M. , Kim D. Y. , Lee W. S.
Published: April 2011

Poly(vinylidene fluoride) (PVdF) fine fiber of 200–300 nm in diameter was prepared through the electrospinning process. Dehydrofluorination of PVdF-based fibers for making infusible fiber was carried out using DBU, and the infusible PVdF-based nanofibers were then carbonized at 900–1800°C. The structural properties and morphologies of the resulting carbon nanofibers were investigated using XRD, Raman IR, SEM, TEM, and surface area & pore analysis. The PVdF-based carbon nanofibers had rough surfaces composed of 20-to 30-nm granular carbons, indicating their high surface area in the range of 400–970 m2/g. They showed amorphous structures. In the case of the highly ehydrofluorinated PVdF fiber, the resulting carbon fiber had a smoother surface, with d002 = 0.34–0.36 nm, and a very low surface area of 16–33 m2/g. The hydrogen storage capacities of the above carbon nano-fibers were measured, using the gravimetric method, by magnetic suspension balance (MSB), at room temperature and at 100 bars. The storage data were obtained after the buoyancy correction. The PVdF-based microporous carbon nanofibers showed a hydrogen storage capacity of 0.04–0.4 wt%. The hydrogen storage capacity depended on the dehydrofluorination of the PVdF nanofiber precursor, and on the carbonization temperatures.
Decomposition Kinetics of Lithium Amide and Its Implications for Hydrogen Storage
Authors: Pinkerton Frederick E.
Published: April 2011

Kinetics of the lithium amide (LiNH2) decomposition reaction 2 LiNH2 → Li2NH + NH3 were determined using thermogravimetric analysis (TGA). LiNH2 is a primary component of the hydrided state of Li3N- and Li2NH-based storage materials. Its decomposition by ammonia release, and the resulting degradation of hydrogen storage capacity, has important implications for the durability of Li-N-H storage systems. Fine powders of LiNH2 were prepared by ball milling for 20 min. Kinetic parameters were extracted from a set of TGA weight loss curves taken at different heating rates between 1 and 20°C/min, and the activation energy Ea was determined to be 124 kJ/mole. Although decomposition occurs slowly below 300°C, isothermal TGA measurements on Li3N demonstrate that its cumulative effect is large in real Li-N-H systems, where LiNH2-containing hydrided material is held at elevated temperature under dynamic gas flow.
Biaxial strain induced electrical inhomogenities and phase separation in the ferromagnetic metallic phase in thin films of La0.7Ca0.3MnO3: A scanning tunneling potentiometry/spectroscopy study.
Authors: Paranjape Mandar , Mitra J. , Raychaudhuri A. K. , Mathur N. D. , Blamire M. G.
Published: April 2011

We have investigated the effect of biaxial strain on local electrical/electronic properties in thin films of La0.7Ca0.3MnO3 with varying degrees of biaxial strain in them. The local electrical properties were investigated as a function of temperature by scanning tunneling spectroscopy (STS) and scanning tunneling potentiometry (STP), along with the bulk probe like conductance fluctuations.

The results indicate a positive correlation between the lattice mismatch biaxial strain and the local electrical/electronic inhomogenities observed in the strained sample. This is plausible since the crystal structure of the manganites interfere rather strongly with the magnetic/electronic degrees of freedom. Thus even a small imbalance (biaxial strain) can induce significant changes in the electrical properties of the system.
Linear measurements of nanomechanical phenomena using small-amplitude AFM
Authors: Hoffmann Peter M. , Patil Shivprasad , Matei George , Tanulku Atay , Grimble Ralph , Özer Özgur , Jeffery Steve , Oral Ahmet , Pethica John
Published: April 2011

Dynamic Atomic Force Microscopy (AFM) is typically performed at amplitudes that are quite large compared to the measured interaction range. This complicates the data interpretation as measurements become highly non-linear. A new dynamic AFM technique in which ultra-small amplitudes are used (as low as 0.15 Angstrom) is able to linearize measurements of nanomechanical phenomena in ultra-high vacuum (UHV) and in liquids. Using this new technique we have measured single atom bonding, atomic-scale dissipation and molecular ordering in liquid layers, including water.
Atomically Resolved Imaging of Epitaxial CaF2 on Si(111) using Noncontact Atomic Force Microscope
Authors: Seino Yoshihide , Abe Masayuki , Morita Seizo
Published: April 2011

Epitaxial calcium fluoride (CaF2) film surfaces grown on Si(111) were imaged with the atomic force microscopy operated in the noncontact mode in ultrahigh vacuum. Our experimental results reproducibly reveal two kind of topographic patterns with the atomic scale contrast. The line profiles obtained from the topographic image exhibit that the change of tip-polarity plays the important role for obtaining two atomic corrugation patterns by considering the interaction between the tip and the two topmost surface atoms. It is similar to the results from the literature obtained on the cleaved CaF2 surface with both positively and negatively terminated tip.
Electrical characterization using Scanning Capacitance Microscopy of the local electronics properties of Ge semiconductor nanostructures.
Authors: Brémond G. , Marchand J. J. , Descamps A. , Budau P. , Bassani F. , Ronda A. , Berbezier I. , Stoïca T. , Vescan L.
Published: April 2011

Ge nanocrystals embedded in SiO2 via a low temperature thermal oxidation of a Si/Ge/Si stack structure grown by low pressure chemical vapour deposition or by molecular beam epitaxy in localized focalized ion beam nanopatterns are characterized by scanning capacitance microscopy. Local electrical spectroscopy on the Ge structure shows hole or electron charging by the Ge nanocrystal, thanks to the complete electrical isolation induced by the oxidation process. The scanning capacitance microscope allows measuring the discharging kinetics of the electron, giving an order of the retention time value of several hours.
Mapping of local electronic properties in nanostructured CMR thin films by Scanning Tunneling Microscopy (STM) and Local Conductance Map (LCMAP)
Authors: Kar Sohini , Ghosh Barnali , Brar L. K. , Paranjape M A. , Raychaudhuri A. K.
Published: April 2011

We have investigated the local electronic properties and the spatially resolved magnetoresistance of a nanostructured film of a colossal magnetoresistive (CMR) material by local conductance mapping (LCMAP) using a variable temperature Scanning Tunneling Microscope (STM) operating in a magnetic field. The nanostructured thin films (thickness ≈500nm) of the CMR material La0.67Sr0.33MnO3(LSMO) on quartz substrates were prepared using chemical solution deposition (CSD) process. The CSD grown films were imaged by both STM and atomic force microscopy (AFM). Due to the presence of a large number of grain boundaries (GB's), these films show low field magnetoresistance (LFMR) which increases at lower temperatures.

The measurement of spatially resolved electronic properties reveal the extent of variation of the density of states (DOS) at and close to the Fermi level (EF) across the grain boundaries and its role in the electrical resistance of the GB. Measurement of the local conductance maps (LCMAP) as a function of magnetic field as well as temperature reveals that the LFMR occurs at the GB. While it was known that LFMR in CMR films originates from the GB, this is the first investigation that maps the local electronic properties at a GB in a magnetic field and traces the origin of LFMR at the GB.
Electrical AFM Measurements for Evaluation of Nitride Erosion in Shallow Trench Isolation Chemical Mechanical Planarization
Authors: Stefanov Yordan , Ruland Tino , Schwalke Udo
Published: April 2011

This article proposes a new application of tunneling current measurements Atomic Force Microscopy (AFM) for evaluation of silicon nitride stop-layer erosion in Shallow Trench Isolation (STI) Chemical Mechanical Planarization (CMP). Simultaneous topographical and electrical AFM measurements allow a clear identification of ‘open’ silicon surfaces on nanometer scale by enhanced tunneling currents in those areas. The measurement technique is non-destructive and can be successfully implemented for process control.
Near-Field Scanning Optical Microscopy of Phase Separation Effects in Dilute Nitride Alloys.
Authors: Mintairov Alexander , Kosel Thomas , Sun Kai , Ustinov Victor , Merz James
Published: April 2011

The effect of nitrogen composition on structural parameters of intrinsic quantum dots (QDs) has been studied in GaAs1-yNy and InxGa1-xAs1-yNy alloys (y∼0. 015–0.03) using low-temperature near-field scanning optical microscopy (NSOM) combined with magneto-photoluminescence spectroscopy. We used measurements of the diamagnetic shift (magnetic field strength 0–10T), temperature dependent spectra (temperature range 5–300K) and near-field monochromatic images for the estimation of the size, nitrogen excess and density of QDs. The obtained values (size ∼10–30 nm, nitrogen excess ∼0.005 and density ∼100 /μm-3) suggest spontaneous formation (phase separation) of QDs. Strong lateral inhomogeniety of the QD distribution on a micron length scale was observed.
Local electromechanical properties of ferroelectric materials for piezoelectric applications
Authors: Kholkin A. L. , Bdikin I. K. , Shvartsman V. V. , Orlova A. , Kiselev D. , Bogomolov A. A. , Kim S.-H.
Published: April 2011

Local electromechanical characterization is becoming prerequisite for the development of ferroelectric-based piezoelectric devices including multilayer actuators, micromotors, piezoelectric filters and, especially, microelectromechanical systems (MEMS), which combine piezoelectric elements and control electronics on the same chip. In this work, we present the results of local electromechanical characterization of several important ferroelectric materials including Pb(Zr, Ti)O3 (PZT) and (Pb, La)(Zr, Ti)O3 (PLZT) in both thin film and ceramic form. Local piezoelectric hysteresis measurements are performed by the piezoelectric force microscopy (PFM) that detects small electric field-induced deformation on the nanoscale e. g., within the single grain of a polycrystalline material. A number of novel phenomena is observed with increasing dc bias voltage including the jump of ferroelectric domain wall to the grain boundary, the “fingerlike” instability of domain wall, and the local phase transition into ferroelectric phase.
Semiconductor Dopant Profile and Dielectric Characterization with Scanning Capacitance Microscopy
Authors: Kopanski J. J.
Published: April 2011

Scanning capacitance microscopy (SCM) has been commonly used to image dopant gradients in silicon and other semiconductors. As a mobile, high-resolution (to 10 nm) metal-oxide-semiconductor (MOS) probe, SCM also is a non-destructive, contactless tool with which to examine local variations in dielectric thin film quality and local variations in semiconductor substrate properties. Virtually any measurement that can be made with fabricated metal electrodes can also be made with SCM. Two particular applications being pursued are characterization of high-κ dielectric films on silicon for next generation integrated circuits and characterization of native and deposited insulators on wide bandgap semiconductors.

Local differential capacitance (ΔC) versus tip bias (Vdc) measurements can be made with SCM using an ac voltage to generate the differential capacitance signal. These measurements differ from conventional C-V measurements due to the 3-D nature of the scanning capacitance microscope tip and the method used to generate the differential capacitance signal. Theoretical predictions and experimental measurements are made of SCM differential capacitance versus dc bias voltage (ΔC-V) curves for MOS capacitors with various levels of fixed and interface traps. The goal of this work is to determine if quantitative interface trap distributions can be made using SCM and if variations in interface density can be observed near defects or device structures. The response of the SCM MOS capacitance measurement to a local electric field stress and optical pumping from the atomic force microscope (AFM) laser will also be discussed.
The electron microscopy and XRD investigation of structure processes in CMR crystals LaMnO3+δ
Authors: Shekhtman V.Sh. , Sedykh V. , Afonikova N.S. , Dubovitskii A.V. , Kulakov V.I.
Published: April 2011

The specific features of structural transformations in lanthanum manganite are analyzed in terms of the macrosymmetry conservation principle. The possible mechanisms of phase transformations are proposed reasoning from a sequence of structural transitions, including the restoration of a virtual configuration of cubic perovskite with double the lattice parameter. It has been synthesized and investigated three phases Pnma I, Pnma II, R3c. It has been shown by X-ray diffraction analysis and Mössbauer spectroscopy that the transition from the Pnma I to Pnma II phase in LaMnO3+d compound occurs through the intermediate phase Pnma II* virtually by “jump”. The HEED investigations of the synthesized phases have shown that the Pnma I and R3c phases have the expected simple pattern whereas the electron-diffraction pattern of the Pnma II phase strongly differs.
Interactions of Hydrating Tricalcium and Dicalcium Silicate using Time-Resolved Quasielastic Neutron Scattering
Authors: Peterson Vanessa K. , Neumann Dan A. , Livingston Richard A.
Published: April 2011

Hydrating tricalcium and dicalcium silicate mixtures were studied using time-resolved quasielastic neutron scattering. Application of a hydration model allowed the extraction of several parameters describing the hydration mechanics. The hydration rate during the nucleation and growth period, diffusivity during the diffusion limited regime, and the maximum amount of product able to be formed were not related linearly to the mixture combinations. Addition of dicalcium silicate at approximately 20 wt. % caused a sharp alteration to these parameters, including reduced hydration rate and reaction layer permeability. These two factors lead to the prediction that more reaction products would be ultimately manufactured during the reactions at this composition.
Real-Time XRD Characterization of Growth of Sputtered Tantalum Films
Authors: Lee S. L. , Mueller J. , Windover D.
Published: April 2011

An in-situ DC magnetron sputter deposition system was constructed on the goniometer of an X-ray diffractometer for investigation of thin film nucleation and growth in real time. Tantalum films were deposited on silicon and A723 steel substrates under various deposition conditions. This paper showed: 1) Ta films evolved in single or mixed α-Ta and β-Ta phase on Si and Fe with very different growth characteristics. 2) Crystalline phase was sensitive to deposition mechanics, Ta film changed phase spontaneously without external parameter changes. 3) In pressure range 0.65–13 Pa at 100 watts, phase was not sensitive to pressure variations, but deposition rate and degree of texture decreased at high gas pressure. 4) Depositions using heavier gas showed higher a-Ta concentrations. 5) Reverse sputter cleaning of target and substrate surfaces improved Ta film adhesion.
X-Ray Nanoplasma Instruments and Tools
Authors: Bloom Scott , Rieger Harry , Alwan Jim
Published: April 2011

Soft x-rays have wavelengths in the range of 1–15 nm and therefore the diffraction limited spot size of focused x-rays can be as small as 1.22 × the radiation wavelength, or less than 20 nm spot size. Using our pulsed x-ray source and focusing a small collected solid angle of this x-ray radiation to a sample provides enough power to form a very hot plasma that emits a range of radiation from UV through IR that can be collected and analyzed on a conventional optical spectrometer. In addition to diagnostic capabilities the instrument can be also used as a tool to form structures at nanometer scale resolution. Since the plasma is formed by ablating the target material with x-rays the target can be patterned or nanomachined using the plasma itself. It should be possible to pattern nanoscale devices by rastering the material under the nanoplasma. Finally in analogy to plasma assisted CVD processes, organometallic vapors could introduced into the sample chamber such that the nanoplasma locally plates out specific species of metals of other materials on the target at nanoscale sizes for forming devices, circuits, wires, etc. This paper presents a design for a nanoplasma instrument, predicted performance parameters will be presented, and development issues identified and discussed.
CoPt3 nanoparticles adsorbed on SiO2: a GISAXS and SEM study
Authors: Flege Jan I. , Schmidt Thomas , Alexe Gabriela , Clausen Torben , Bernstorff Sigrid , Randjelovic Igor , Aleksandrovic Vesna , Kornowski Andreas , Weller Horst , Falta Jens
Published: April 2011

Ultra-thin CoPt3 nanoparticle films have been prepared on SiO2 surfaces using a Langmuir-Blodgett (LB) deposition technique. The structural properties of the overlayers have been investigated by grazing-incidence small-angle x-ray scattering (GISAXS) and high-resolution scanning electron microscopy (SEM) for the first time. Self-assembly of the nanoparticles is found and with GISAXS an average particle-particle distance of (8.23 ± 0.06) nm is determined, in good agreement with the SEM results. A particle correlation length of (22.3 ± 1.2) nm was derived which is shown to be independent of the surface coverage. The latter quantity may be controlled by choice of a suitable retraction speed during the LB step.
Internal Strain Measurements and X-ray Imaging in Interpenetrating-Phase Al2O3/Al Composites
Authors: Young Marcus L. , Almer Jon D. , Lienert Ulrich , Fezzaa Kamel , Lee Wah-Keat , Haeffner Dean R. , Dunand David C.
Published: April 2011

Interpenetrating Al2O3/Al composites were created by liquid-metal infiltration of alumina preforms with three-dimensional periodicity produced by a robotic deposition method. Volume-averaged lattice strains in the alumina phase were measured by synchrotron x-ray diffraction at various uniaxial compression stresses up to 350 MPa. Load transfer, which is experimentally found to occur between the aluminum and the alumina phase, is in agreement with simple rule of mixtures models. Spatially resolved measurements showed variations in load transfer at different positions within the composite for the elastic-, plastic-, and damage-deformation regimes. Using phase-enhanced imaging, the extent of damage within the composites was observed.
X-ray Microdiffraction Characterization of Deformation Heterogeneities in BCC Crystals
Authors: Magid K. R. , Lilleodden E. T. , Tamura N. , Florando J. N. , Lassila D. H. , LeBlanc M. M. , Barabash R. I. , Morris J. W.
Published: April 2011

The deformation behavior of BCC metals is being investigated by x-ray microdiffraction measurements (μXRD) for the purpose of characterizing the dislocation structure that results from uniaxial compression experiments. The high brilliance synchrotron source at the Advanced Light Source (Lawrence Berkeley National Lab) and the micron resolution of the focusing optics allow for the mapping of Laue diffraction patterns across a sample. These measurements are then analyzed in order to map the distribution of residual stresses in the crystal. An important finding is the observation of Laue spot “streaking”, which indicates localized rotations in the lattice. These may represent an accumulation of same-sign dislocations. Theoretical modeling of the diffraction response for various slip systems is presented, and compared to experimental data. Preliminary results include orientation maps from a highly strained Ta bicrystal and a less highly strained Mo single crystal. The orientation maps of the bicrystal indicate a cell-like structure of dense dislocation walls. This deformation structure is consistent with previous OIM studies of the same crystal. The results suggest that μXRD may be a particularly useful tool for microscale studies of deformation patterns in a multi-scale investigation of the mechanisms of deformation that ranges from macroscopic deformation tests to high resolution TEM studies of dislocation structures.
Measurement of Residual Strains with High Depth Resolution by Energy-Variable Diffraction on Synchrotron Beam Lines
Authors: Zolotoyabko E. , Pokroy B. , Quintana J. P.
Published: April 2011

An energy-variable synchrotron diffraction technique is established as a novel method for depth-resolved measurements of d-spacings and residual strains in polycrystalline structures. The depth sensitivity is achieved by the controlled changing the x-ray energy and, hence, the x-ray penetration into the sample. Quasi-parallel synchrotron radiation being diffracted at different depths deviates differently from the detector axis. As a result, the maximum diffraction intensity recorded in the detector is coming from a certain depth, which is energy dependent. This finding opens a way for strain measurements with high depth resolution by changing the x-ray energy in small enough steps. The developed technique is applied to characterize the electrodeposited Cu/Ni multilayers.
Measurement of Crystal Lattice Rotations under Nanoindents in Copper
Authors: McLaughlin Kirsten K. , Stelmashenko Nadia A. , Lloyd Stephen J. , Vandeperre Luc J. , Clegg William J.
Published: April 2011

A technique is described to measure the rotations of the crystal lattice in the deformed region around a nanoindent from volumes smaller than 3 × 10−5 μm3. To demonstrate this method, a copper crystal has been indented on its (001) face to depths of 500 and 1300 nm. Cross-sections of nanoindents were prepared for transmission electron microscopy by focused ion beam milling, and rotations were measured about the [001], [010] and [100] axes using convergent beam electron diffraction.
The Mechanics of Nanoimprint Forming
Authors: Cross Graham L. W. , Langford Richard M. , O'Connell Barry S. , Pethica John B.
Published: April 2011

Nanoimprint and a number of other related techniques are a collection of surface patterning technologies that involve direct contact of a master template with the target surface. As such, they are governed by the laws of contacting bodies, and the mechanics involved can readily be investigated by existing indentation methods or close variants thereof. Among the many demonstrated applications of nanoimprint, lithographic resist processing has generated considerable interest due to its combination of high resolution with rapid throughput over wide areas. Pattern transfer can be achieved by the application of heat and pressure to the stamp (hot embossing), or solely by the generation of shear stress at the contact (cold forming.) In both cases we have found that elastic and viscoplastic strains are present during the forming process, the former of which can considerably alter the characteristics of the pattern transfer. The use of depth sensing instrumented indentation in conjunction with specially designed stamps and a variety of microscopy techniques has allowed us to isolate, control, and measure many of the stresses and strains directly during the imprint process. Further, in a more standard role, the indenter can be used to characterize the mechanical properties of imprinted structures. In this paper we summarize our experimental findings and conclusions on the role of important factors influencing the fidelity of the imprint process including elastic stresses, plastic deformation mechanisms, complexities in the confined deformation rheology, and choices in the form of applied stress. These are illustrated by a series of idealized experiments ranging from the squeeze flow of prepared coupons to the flat punch indentation of thin films and back extrusion into isolated cavities. A connection between these more localized experiments and the established findings and requirements of applications such as wide area lithography and functional polymer patterning will be made to establish the concept of “instrumented imprint”.
A Nanoindentation Study of Thermally-Grown-Oxide Films on Silicon
Authors: Helvaci Fatih , Cho Junghyun
Published: April 2011

We explore the effect of the substrate on mechanical behavior of thin films using a depth-sensing indentation. For this purpose, nanoindentation has been performed on thermally grown silicon oxide films on the silicon substrate. One primary goal of this study is to extract ‘film-only’ mechanical properties from the nanoindentation data by subtracting the substrate effect. It is also shown that elastic modulus of the film is more influenced by the substrate than hardness due to a larger elastic extension beyond a plastically deformed region, as well as a larger elastic mismatch between the SiO2 film and the Si substrate. Further, an inverse analysis of indentation data is proposed to estimate a thickness of thin films. Consequently, this study provides a fundamental understanding in mechanical phenomena of thin films occurring at nanoscales.
Nanoindentation of Bone in a Physiological Environment
Authors: Akhtar R. , Morse S. , Mummery P. M.
Published: April 2011

Nanoindentation has been established as an effective method to measure the mechanical properties of bone tissue at the micron and sub-micron length scale. Although it is well-documented that the mechanical properties of macroscopic bone specimens vary depending on whether the samples are tested dry or wet, nanoindentation is generally conducted on dehydrated bone tissue at room temperature, primarily because nanoindentation systems are extremely sensitive to changes in environmental conditions such as humidity and temperature. In this study, these problems were overcome by using a specially constructed liquid cell with an extension piece that allowed the indenter tip to be submerged under 5 mm of liquid. The custom setup was used to test cortical bovine bone and cancellous human bone specimens in three distinct conditions – dehydrated, rehydrated in simulated body fluid (SBF) at 20°C, and rehydrated in SBF at 37.5°C. A heating element with a temperature control unit was used to test at 37.5°C. The hardness and elastic modulus of the bone samples were found to decrease when dry specimens were rehydrated and tested in physiological conditions. It is suggested that nanoindentation in physiological conditions gives a better estimate of the mechanical properties of the microstructural components of bone in vivo rather than nanoindentation under conventional conditions.
Multiple-Frequency Nanoindentation Testing
Authors: Fischer-Cripps A. C.
Published: April 2011

This paper describes a new method of dynamic nanoindentation testing whereby, instead of the imposition of a single sinusoidal modulation onto the driving force signal, a multiple-frequency modulation is applied and a Fourier analysis used to extract frequency-dependent mechanical properties. The instrument response is cancelled by the use of a reference transfer function using an equalization process. The present work gives details of the method and presents some example measurements.
Molecular Mobility and Confined Plasticity in NEMS Applications
Authors: Overney René M. , Sills Scott
Published: April 2011

Many modern and future technological applications involve ultrathin polymer films with a thickness below the 100-nanometer scale, where statistical bulk averaging is jeopardized and interfacial constraints dictate transport properties. In such confined polymeric systems, transport properties strongly depend on molecular relaxation and structural phases that deviate from the bulk. This is particularly relevant in applications involving nano-electromechanical systems (NEMS). In this paper, we address the correspondence between bulk deviating local glass transition values with the non-monotonic plastic deformation properties in ultrathin polystyrene films. Polystyrene serves as a model material in a NEMS application designed to circumvent the superparamagnetic limit associated with magnetic data storage. The application involves data bit writing via an ultrahigh density thermomechanical indentation process. An elaborate friction-velocity analysis is introduced as a material characterization tool. It provides fundamental insight into the glass forming process, and consequently, the glass transition value in ultrathin spin coated polymer films. The glass transition value is thereby discussed as a phenomenological limit, not unlike an asymptote, to a diverging size of cooperative rearranging regions upon cooling. Unexpected large cooperative clusters up to 40 nm were observed – a dimension that is noticeable at the 100-nanometer length scale. In the light of MD simulations and their good correspondence with the presented intrinsic friction analysis, the importance of angular and torsional intramolecular motions are particularly emphasized for nanotechnological applications.
Indentation Creep and Relaxation Measurements of Polymers
Authors: VanLandingham Mark R. , Drzal Peter L. , White Christopher C.
Published: April 2011

Instrumented indentation was used to characterize the mechanical response of polymeric materials. A model based on contact between a rigid probe and a linear viscoelastic material was used to calculate values for creep compliance and stress relaxation modulus for epoxy, poly(methyl methacrylate) (PMMA), and two poly(dimethyl siloxane) (PDMS) elastomers. Results from bulk rheometry studies were used for comparison to the indentation creep and stress relaxation results. For the two glassy polymers, the use of sharp pyramidal tips produced responses that were considerably more compliant (less stiff) than rheometry values. Additional study of the deformation remaining in epoxy after creep testing revealed that a large portion of the creep displacement measured was due to post-yield flow. Indentation creep measurements of the epoxy using a rounded conical tip also produced nonlinear responses, but the creep compliance values appeared to approach linear viscoelastic values with decreasing creep force. Responses measured for the PDMS were mainly linear elastic, but the filled PDMS exhibited some time-dependence and nonlinearity in both rheometry and indentation measurements.
Spherical Load Indentation in Submicron NiTiCu Shape Memory Thin Films
Authors: Hassdorf R. , Feydt J. , Thienhaus S. , Buforn L. , Conté N. , Pykhteev O. , Kružík M. , Botkin N. , Moske M.
Published: April 2011

Nanoindentation with spherical tipped indenters provides a powerful technique to explore surface and thin film mechanical properties through the application of Hertzian contact mechanics. The full range of mechanical response can be obtained from elastic, through the yield point, to permanent deformation. In this study spherical indentation has been used for probing MBE-grown NiTiCu alloy thin films into superelasticity or stress-induced martensitic transformation. By this way, obstacles typically occurring related to the fabrication of freestanding films (film thickness < 1 μm) are avoided. The indentation measurements were performed starting from the parent austenite state. Notably, for loads as small as 0.5 mN, deformation appears to be completely reversible. As loading is increased (up to 5 mN) the indent becomes irreversible following local plastic deformation within the tip-specimen contact area. Using finite-element simulations the indentation data were converted into a stress-strain diagram aimed at simulating uniaxial tension load. Therefrom, the superelastic strain is estimated to be around 3%.
Effect of Alloying Elements (Ga, Ge, Si) on Pseudoelasticity in Fe3Al Single Crystals
Authors: Yasuda Hiroyuki Y. , Kase Takashi , Umakoshi Yukichi
Published: April 2011

Pseudoelasticity in Fe3Al single crystals doped with a small amount of Ga, Ge and Si was investigated focusing on the antiphase boundary (APB) energy and the ordered domain structure. Single crystals of Fe-23at%Al and Fe-21at%Al-2at%X (X=Ga, Ge, Si) were grown by a floating zone method. In Fe-23at%Al single crystals, superpartial dislocations with Burgers vector (b) of 1/4<111> moved dragging APB during loading, while APB pulled back the superpartials during unloading. This resulted in giant pseudoelasticity regardless of martensitic transformation and the recoverable strain was about 5%. Ga addition was found to be effective in increasing the recovery strain compared with Fe-23at%Al crystals. In contrast, both Ge and Si additions decreased the amount of shape recovery. Stress at which the shape recovery started, was increased by Ga, Ge and Si additions. This means the APB energy increased by the additions, since the surface tension of APB pulling back the superpartials increases with increasing the energy. On the other hand, the frictional stress of the superpartials with b=1/4<111> increased significantly by Ge or Si doping due to solid solution hardening, though the stress of Ga-doped crystals was almost the same as that of the binary crystals. Higher frictional stress of Ge- and Si-doped crystals made the reversible motion of the superpartials difficult, resulting in the small recovery ratio. Ordered domains with displacement vector (R) of 1/4<111> in Fe-23at%Al and Fe-Al-Ga alloys were observed to be small, less than 100nm. In contrast, Ge and Si additions increased the domain size to more than 500nm. Since the domain boundaries with R=1/4<111> played an important role in the individual motion of the superpartials with b=1/4<111>, the fine domain structure was found to be favorable for giant pseudoelasticity in Fe3Al single crystals. Ga addition increased the APB energy following the superpartials and kept the domain size small, resulting in the increase in recovery strain.
First-Principles Study of Structural and Defect Properties in FeCo Intermetallics
Authors: Krcmar M. , Fu C. L. , Morris J. R.
Published: April 2011

Employing ab-initio calculations and statistical thermodynamic modeling, we investigated the structural stability, defect energies, and ordering of B2 FeCo intermetallics. We find that FeCo in the B2 structure is a marginally stable and weakly ordered system, with a high density of antisite defects on both sublattices and low APB energies for the <111> slip on both {110} and {112} planes. The structural stability of B2 FeCo is very sensitive to the change in local atomic environment, as the system transforms to a lower-symmetry L10 phase under the effects of reduced dimensionality or applied shear stress. We suggest that internal stresses near dislocation cores might be closely connected with the intrinsic brittleness of ordered FeCo, as it is likely to induce a local structural transformation from the B2 structure to the L10 structure.
Development of high temperature creep resistance in Fe-Al alloys
Authors: Morris D. G. , Muñoz-Morris M. A. , Baudin C.
Published: April 2011

Most of the studies aimed at the development of creep-resisting Fe-Al intermetallics have been oriented at application temperatures of the order of 500–650°C, where these materials may compete with conventional stainless steels. The Fe-Al intermetallics are, however, particularly excellent in their oxidation and corrosion resistances at temperatures of the order of 1000°C, where Chromium-Nickel steels are no longer able to withstand the aggressive environments. This presentation is part of a study aimed at the development of good creep resistance at such high temperatures.

Studies of a variety of cast Fe3Al-base alloys, strengthened by solution or precipitate/dispersoid-forming alloying additions, are reported. The alloys show good strength from room temperature to about 500°C, but thereafter strength falls rapidly as thermally-activated deformation processes become operative. Solution additions are capable of producing good low temperature strength, but do not contribute significantly to creep strength at very high temperatures (above 700°C). Precipitation hardening has been examined in Nb-containing alloys, where Fe2Nb Laves precipitates form at intermediate temperatures. These materials show good strength up to about 700°C, but at higher temperatures the fine precipitates coarsen excessively. Strengthening in the intermediate temperature range varies depending on whether the solute is precipitated prior to high temperature testing or concurrent with this.
Microstructures and Mechanical Properties in Ni3Si-Ni3Ti-Ni3Nb-Based Multi-Intermetallic Alloys
Authors: Takasugi T. , Ohira K. , Kaneno Y.
Published: April 2011

Microstructure, high-temperature tensile deformation and oxidation property of Ni3Si-Ni3Ti-Ni3Nb multi-phase intermetallic alloys with a microstructure consisting of L12, D024 and D0a phases were investigated. The tensile stress as well as the tensile elongation of these multi-phase alloys increased with increasing Si content, i.e. the volume fraction of L12 phase in the wide range of test temperatures. 50-ppm boron addition to these multi-phase intermetallic alloys resulted in increased tensile stress and tensile elongation. The multi-phase intermetallic alloy with a high Si content had good oxidation resistance, and also the boron addition to this alloy resulted in enhanced oxidation resistance. From an overall evaluation of the properties examined, it was shown that the multi-phase intermetallic alloy, which has a high Si content and is composed of L12 matrix dispersed by D024 and D0a phases, had the most favorable properties as high-temperature mechanical and chemical materials.
A Bond-Order Potential Incorporating Analytic Screening Functions for the Molybdenum Silicides
Authors: Cawkwell Marc J. , Mrovec Matous , Nguyen-Manh Duc , Pettifor David G. , Vitek Vaclav
Published: April 2011

The intermetallic compound MoSi2, which adopts the C11b crystal structure, and related alloys exhibit an excellent corrosion resistance at high temperatures but tend to be brittle at room and even relatively high temperatures. The limited ductility of MoSi2 in ambient conditions along with the anomalous temperature dependence of the critical resolved shear stress (CRSS) of the {110)<111], {011)<100] and {010)<100] slip systems and departure from Schmid law behavior of the {013)<331] slip system can all be attributed to complex dislocation core structures. We have therefore developed a Bond-Order Potential (BOP) for MoSi2 for use in the atomistic simulation of dislocations and other extended defects. BOPs are a real-space, O(N), two-center orthogonal tight-binding formalism that are naturally able to describe systems with mixed metallic and covalent bonding. In this development novel analytic screening functions have been adopted to properly describe the environmental dependence of bond integrals in the open, bcc-based C11b crystal structure. A many-body repulsive term is included in the model that allows us to fit the elastic constants and negative Cauchy pressures of MoSi2. Due to the internal degree of freedom in the position of the Si atoms in the C11b structure which is a function of volume, it was necessary to adopt a self-consistent procedure in the fitting of the BOP. The constructed BOP is found to be an excellent description of cohesion in C11b MoSi2 and we have carefully assessed its transferability to other crystal structures and stoichiometries, notably C 40, C 49 and C 54 MoSi2, A15 and D03 Mo3Si and D8m Mo5Si3 by comparing with ab initio structural optimizations.
Coarsening Behavior and Coercivity in L10-Ordered Intermetallic Fe-Pd Ferromagnets with Equiaxed Grain Morphology
Authors: Wiezorek Jörg M.K. , Deshpande Anirudha R.
Published: April 2011

Thermo mechanical processing of equiatomic FePd has been used to establish a nearly equiaxed microstructure that consists of mono-variant L10 ordered grains. The technically important hard magnetic properties, e.g. coercivity, of the uniaxial ferromagnetic L10-FePd with equiaxed microstructure depend on the grain size. Thus, here, the evolution of grain size during the later stages of annealing has been studied using SEM and computer assisted image analysis with the goal to determine the activation parameters for the relevant coarsening processes. Using a classical grain growth analysis the activation parameter for coarsening of the 5% largest grains in the populations of L10-ordered grains in FePd has been determined as approximately 30kcal/mol.
Magnetic Properties of E21-base Co3AlC and the Correlation with the Ordering of Carbon Atoms and Vacancies
Authors: Kimura Yoshisato , Wei Fu-Gao , Ohtsuka Hideyuki , Mishima Yoshinao
Published: April 2011

Targeting to develop E21 Co3AlC based heat resistant alloys, phase stability of E21 Co3AlC and (Co, Ni)3AlC has been investigated together with the magnetic properties of E21’ Co3AlC0.5 which is formed by the extra ordering of carbon atoms accompanying anti-phase boundary (APB). The correlation of ferromagnetism with APB in E21’ Co3AlC0.5 was evaluated using single crystals by high-resolution transmission electron microscopy (HRTEM) and vibrating sample magnetometer. Anti-phase domain (APD) size affects the ferromagnetism: for instance, the saturation magnetization becomes larger as the APD size is smaller. Local atomic configuration at APB was clearly observed by HRTEM image.
Thermal Analysis of Relaxation Processes of Supersaturated Vacancies in B2-Type Aluminides
Authors: Nakamura Ryusuke , Yoshimi Kyosuke , Yamauchi Akira , Hanada Shuji
Published: April 2011

Relaxation behavior of supersaturated vacancies in water-quenched and rapidly solidified B2 type CoAl and NiAl with the stoichiometric composition was studied by differential scanning calorimetry (DSC). In both CoAl and NiAl quenched from 1773 K, a single exothermic peak due mainly to the recovery of supersaturated vacancies appeared near 950 K. On the other hand, the exothermic peak was also observed in as-spun rapidly solidified CoAl and NiAl ribbons, and the temperature range of the peak was much broader than that of quenched-in bulks, suggesting that the peak in the rapidly solidified ribbons results from not only a single recovery process of vacancies but also those of some other lattice defects. TEM observation showed that a large amount of dislocations were introduced in the NiAl ribbon and that comparatively many voids as well as an amount of dislocations were introduced in the CoAl ribbon.
Parameters of Dislocation Structure and Work Hardening of Ni3Ge
Authors: Koneva N. A. , Solov'eva Yu.V. , Starenchenko V. A. , Kozlov E. V.
Published: April 2011

Orientation dependence of the yield stress temperature anomaly in Ni3Ge single crystals with the L12 structure was investigated during compression tests. The measurements were carried out in the 4.2 K-1000 K temperature interval for two orientations of single crystals, [001] and [234]. The dislocation structure was studied by TEM. Quantitative measurements of different parameters of dislocation structure were carried out. The values of the scalar dislocation density, ρ, were determined for different temperatures in the deformation interval from the yield stress up to fracture. Temperature dependence of the friction stress τF (T) and the interdislocation interaction parameter α(T) were also obtained. The change in the fraction of straight dislocations as a function of temperature was analyzed.
High Temperature Oxidation Behavior of Al Added Mo / Mo5SiB2in-situ Composites
Authors: Yamauchi Akira , Yoshimi Kyousuke , Hanada Shuji
Published: April 2011

Isothermal oxidation behavior of Mo/Mo5SiB2in-situ composites containing small amounts of Al was investigated under an Ar-20%O2 atmosphere in the temperature range of 1073–1673 K. The Mo/Mo5SiB2in-situ composites, (Mo-8.7mol%Si-17.4mol%B)100-xAlx (x=0, 1, 3, and 5mol%), were prepared by Ar arc-melting, and then homogenized at 2073 K for 24 h in an Ar-flow atmosphere. Without addition of Al, Mo/Mo5SiB2in-situ composite exhibits a rapid mass loss at the initial oxidation stage, followed by passive oxidation after the substrate is sealed with borosilicate glass in the temperature range of 1173–1473 K, whereas it exhibits a rapid mass gain around 1073 K. On the other hand, small Al additions, especially of 1 mol%, significantly improve the oxidation resistance of Mo/Mo5SiB2in-situ composites at temperatures from 1073–1573 K. The excellent oxidation resistance is considered to be due to the rapid formation of a continuous, dense scale of Al-Si-O complex oxides. The protective oxide scales contain crystalline oxides, and the amounts of the crystalline oxides obviously increase with Al concentration.
Nucleation of (Mo) Precipitates on Dislocations During Annealing of a Mo-rich Mo5SiB2 Phase
Authors: Sekido Nobuaki , Sakidja Ridwan , Perepezko John H.
Published: April 2011

Upon annealing an as-cast Mo-10Si-20B alloy at high temperatures, a Mo solid solution phase precipitates within a supersaturated Mo5SiB2 phase. The precipitation behavior of the Mo solid solution was investigated by means of transmission electron microscopy and X-ray diffractometry. It is found that the Mo5SiB2 phase in a Mo-10Si-20B alloy contains a significant amount of structural vacancies in the as-cast state. The excess vacancies are removed to form dislocations during annealing, which provides the heterogeneous nucleation sites for the (Mo) precipitates.
Structural Properties and Magnetic Behavior in the Pseudobinary Alloys CoFe-CoAl
Authors: Tadachi Nobutoshi , Ishibashi Hiroki , Kogachi Mineo
Published: April 2011

Structural properties and magnetic behavior in pseudobinary alloys CoFe1−x Alx are studied. The B2-phase exists stably over wide ranges of composition and temperature and the Heusler-phase appears around the stoichiometric composition (0.4< x< 0.6 ) below about 973K. The mean magnetic moment in the B2-phase region decreases nearly linearly with increase in x in x > 0.2. Further, it decreases with increase in quenching temperature in x < 0.4, while it remains almost constant in x > 0.4. The mean magnetic moment of Heusler alloy Co2FeAl (x = 0.5) has the value of 1.30μB/atom, nearly the same as in the B2-phase, and shows no remarkable quenching temperature dependence.