bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystal growth of photovoltaic polycrystalline Si1-xGex by die-casting growth
Authors: Hirahara H. , Iida T. , Sugiyama Y. , Baba T. , Takanashi Y. , Sakuragi S.
Published: April 2011

Coin-shaped multicrystalline Si1-xGex crystals were grown using a Brigdman method combined with die-casting growth. Si1-xGex alloy is known as a candidate material for producing Auger generation, which creates more than one electron/hole pair per absorbed photon. Since Si1-xGex alloy shows a complete series of solid solutions, precipitating crystals with a certain composition of silicon or germanium by conventional selective growth methods is burdensome. Using die-casting combined with Bridgman growth brought about Si1-xGex precipitation in a form completely different from that predicted by the Si-Ge phase diagram. By combining this growth with subsequent heat treatment of the precipitated Si1-xGex sample, Si1-xGex (x= 0.5 ± 3 %) could be obtained. Indirect band-gap energy was estimated by measuring room-temperature optical absorption coefficient of the grown samples.
Characterization of polycrystalline Si silicon sheet grown by die casting combined with the Bridgman technique
Authors: Saito K. , Iida T. , Akimoto D. , Nose A. , Takanashi Y. , Sakuragi S. , Nanba H. , Sakuragi G. , Shimazaki T.
Published: April 2011

Die-casting growth was used for manufacturing the multicrystalline silicon sheet with a size of 100 × 120 × 0.5 mm. During the growth, incorporation of contaminants such as iron, cobalt, nickel and chromium was well suppressed. The average etch-pit density values ranged from 1×104 cm-2 to 4x106 cm-2 for growth rates of 5 to 60 mm/h, respectively. Measurement of minority-carrier lifetime bye microwave-photoconductivity-decay (μ-PCD) method was 0.5 μs for as-grown specimens, suggesting that defects and residual strain exist in the grown sheet. Moreover, post heat treatment at 1473 K reduced the etch-pit density and improved carrier lifetime up to 2.2 μs.
Mid-10 cm−2 threading dislocation density in optimized high-Ge content relaxed graded SiGe on Si for III-V solar on Si
Authors: Isaacson David M. , Dohrman Carl L. , Pitera Arthur J. , Gupta Saurabh , Fitzgerald Eugene A.
Published: April 2011

We present a framework for obtaining high quality relaxed graded SiGe buffers on Si for III-V integration. By avoiding dislocation nucleation in Si1−xGex layers of x>0.96, we have achieved a relaxed Si0.04Ge0.96 platform on Si(001) offcut 2° that has a threading dislocation density of 7.4×105 cm−2. This 2° offcut orientation was determined to be the minimum necessary for APB-free growth of GaAs. Furthermore, we found that we could compositionally grade the Ge content in the high-Ge portion of the buffer at up to 17 %Ge μm−1 with no penalty to the dislocation density. The reduction in both threading dislocation density and buffer thickness exhibited by our method is an especially significant development for relatively thick minority-carrier devices which use III-V materials such as multi-junction solar cells.
Cabon Nanofibrous Materials Prepared from Electrospun Polyacrylonitrile Nanofibers for Hydrogen Storage
Authors: Park S. H. , Kim B. C. , Jo S. M. , Kim D. Y. , Lee W. S.
Published: April 2011

Electrospun PAN nanofibers were carbonized with or without iron(III) acetylacetonate to induce catalytic graphitization within the range of 900–1500°C, resulting in ultrafine carbon fibers with the diameter of about 90–300 nm. The structural properties and morphologies of the resulting carbon nanofibers were investigated using XRD, Raman IR, SEM, TEM, and surface area/pore analysis. The PAN-based carbon nanofibers carbonized without a catalyst had amorphous structures, with d002 = 0.37 nm, and smooth surfaces with very low surface areas of 22–31 m2/g. The carbonization of PAN-based nanofibers in the presence of the catalyst produced the graphite nanofibers (GNF) with d002 = 0.341 nm, indicating turbostrate structures. The graphite structures were grown by increasing the catalyst contents and the carbonization temperature. The hydrogen storage capacities of the aforementioned carbon nanofiber materials were evaluated through the gravimetric method using Magnetic Suspension Balance (MSB) at room temperature and at 100 bars. The storage data were obtained after the buoyancy correction. The CNFs showed hydrogen storage capacities of 0.16–0.50 wt.%, increasing with the increase of carbonization temperature, but that of the CNF at 1500°C was lowest. The hydrogen storage capacities of the GNFs with low surface areas of 100–250m2/g were 0.14–1.01 wt%.
The Role of Metal Catalyst in Near Ambient Hydrogen Adsorption on Multi-walled Carbon Nanotubes
Authors: Lee Yong-Won , Deshpande Rohit , Dillon Anne C. , Hebe Michael J. , Dai Hongjie , Clemens Bruce M.
Published: April 2011

Multiwalled carbon nanotubes (MWNTs) were continuously synthesized by hot wire chemical vapor deposition (HWCVD) using a methane source catalyzed by metal-organic ferrocene. The microstructure of the MWNTs and the catalyst particles were subsequently characterized with transmission electron microscopy which identified three different phases, i.e., bcc α-Fe, fcc γ-Fe and orthorhombic Fe3C. The hydrogen storage capacity of MWNTs was determined with temperature-programmed desorption (TPD) technique. Hydrogen adsorption at near ambient conditions was observed only in as-synthesized MWNTs containing iron particles and was dramatically increased after hydrogen reducing treatment. Possible adsorption mechanism was also discussed.
Dehydrogenation kinetics and long term cycling behavior of Titanium doped NaAlH4
Authors: Srinivasan Sesha S. , Jensen Craig M.
Published: April 2011

The development of light weight hydrogen storage systems with high volumetric and gravimetric hydrogen densities is indeed essential for the on-board fuel cell vehicular applications. Titanium doped NaAlH4 is right now considered as the potential hydrogen storage system, which satisfies the said criteria. The dehydrogenation of NaAlH4 consists of two consecutive steps of decomposition at 220 and 250° C with the total hydrogen release of 5.6 wt.%. However, doping a few mole concentrations of selected transition metal complexes to the host hydride reduces significantly the decomposition temperatures to 100 and 185° C (equilibrium H2 pressure ∼1 MPa) respectively. This breakthrough has been followed by a great deal of effort to develop NaAlH4 as a practical hydrogen storage material. For an ideal hydrogen storage material, the dehydrogenation kinetics and the cycling stability are important properties to be evaluated. Keeping these points to ponder, we have studied the dehydriding kinetics of the Ti-doped NaAlH4 over a number of dehydrogenation and rehydrogenation cycles. Besides, the Ti-doped NaAlH4 has been prepared from the hydrogenation of NaH and Al using the solvent mediated milling method. Comparing the initial and final cycling stages of Ti doped (NaH + Al), the synchrotron powder x-ray diffraction profiles exhibit, a growing resistance to the hydrogenation of Na3AlH6 to NaAlH4.
An in-situ X-ray Diffraction Study of the Desorption of TiCl3-doped Sodium Alanate
Authors: Speakman Scott A. , Schneibel Joachim H. , Easton Dewey S.
Published: April 2011

Sodium alanate was milled with and without TiCl3. The hydrogen release and uptake was measured during temperature-programmed absorption and desorption, as well as by isothermal charging and discharging, using a Sieverts' type apparatus. These data were supplemented by in-situ X-ray diffraction studies of hydrogen desorption. Rate constants derived from XRD were slower than those derived from volumetric H2 measurements. Al formation observed in XRD exceeded that expected from the observed decomposition of NaAlH4 and Na3AlH6.
Discovering the Mechanism of H2 Adsorption on Aromatic Carbon Nanostructures to Develop Adsorbents for Vehicular Applications
Authors: Dillon A. C. , Blackburn J. L. , Parilla P. A. , Zhao Y. , Kim Y-H. , Zhang S. B. , Mahan A. H. , Alleman J. L. , Jones K. M. , Gilbert K. E. H. , Heben M. J
Published: April 2011

Hydrogen adsorption has been observed with a binding energy of ∼ 50 kJ /mol on as-synthesized carbon multi-wall nanotubes (MWNTs). The MWNTs are virtually free of non-nanotube carbon impurities but contain residual iron catalyst particles. The MWNTs are also highly graphitic. No hydrogen adsorption is observed at near ambient temperatures for purified MWNTs that are free of iron particles. However, hydrogen adsorption is also not observed on bare iron particles even following reduction in the presence of hydrogen at 775 K. These results imply that a special synergy occurs when small iron particles or atoms are in intimate contact with sp2-hybridized aromatic carbon. Interestingly, reducing the as-synthesized MWNTs in H2 at 573 K results in an increased hydrogen capacity. Understanding this hydrogen storage mechanism could facilitate the economical engineering of a hydrogen storage material that meets the United States Department of Energy targets for vehicular fuel cell applications. Recent theoretical studies have shown that an iron ad atom forms a complex with a C36 fullerene and shares charge with four carbon atoms of a bent five-membered ring. Three H2 ligands then coordinate with the iron forming a stable 18-electron organometallic complex. Here the binding energy of the molecular hydrogen ligands is ∼43 kJ /mol. These theoretical results could possibly explain the unique hydrogen storage properties of MWNTs that are grown with an iron catalyst.
Force-Strain Curves Of Microcapsules With Atomic Force Microscopy
Authors: Lansey Eli , Zypman Fredy R.
Published: April 2011

We develop an algorithm to measure elastic properties of microcapsules with Atomic Force Microscopy (AFM). The AFM is used as an indenter and presses down on a spherical microcapsule. We study the system from an atomic point of view (considering interactions between the atoms in the system via Equivalent Crystal Theory) and calculate the force produced by the system to balance the external AFM force. We plot this force as a function of the indentation depth, and from that curve we extract the interatomic parameters of ECT that are related with elastic constants. Our calculations model measurements of force-strain curves including non-linear effects. This is relevant as classical elasticity theory breaks down in the AFM indentation regime, when atomic interactions must be considered explicitly.
Frequency Response of Microcantilevers in Viscous Fluids
Authors: Schilowitz A. M. , Yablon D. G. , Zypman F.
Published: April 2011

This paper presents a new, general reconstruction algorithm that enables modeling of the experimental resonance spectrum of a prismatic microcantilever in a viscous fluid. A closed-form solution is obtained for the microcantilever frequency response from the equation of motion with fluid damping and internal friction terms, which allows direct calculation of the fluid damping and internal friction damping constants. In principle, the fluid damping constant has a simple relationship to viscosity thus potentially simplifying the process of obtaining viscosity from experimental data. Finally, the model is compared to experimental data.
In Situ Monitoring of Dispersion Film Formation Using Tapping-Mode Atomic Force Microscopy
Authors: Li Jing , Liang Wenbin , Chum Steve
Published: April 2011

The coalescence process of poly (ethylene-co-vinyl acetate) (EVA) and poly (ethylene-co-octene) (EO) dispersion particles was monitored in situ using tapping-mode atomic force microscopy (TMAFM) equipped with a miniature hot stage. This work describes the effect of particle size on the film formation temperature based on direct experimental observation, clarifying further the debate about particle size effect on minimum film formation temperature (MFFT). The results suggest that semicrystalline polyolefin particles have similar deformation temperature dependence. Smaller particles tend to deform faster than larger particles, which is attributed to their smaller mass. Furthermore, morphology changes and mechanical property development associated with the film formation process are also discussed. The TMAFM technique is shown to be very useful in gaining insight into the film formation mechanism, which will provide guidance in future practical applications with polyolefin dispersions.
Novel Dynamic Scanning Microscope Probe and its Application to Local Electrical Measurement in an Ion Sensitive Field Effect Transistor
Authors: Akiyama T. , Suter K. , de Rooij N. F. , Staufer U.
Published: April 2011

A unique self-actuating and self-sensing probe, which is based on a quartz tuning fork and a microfabricated cantilever, is presented for dynamic scanning probe microscopy. The probing tip can be electrically connected to an external source or measure unit. The sensitivity of the drain-source current of an ion sensitive field effect transistor (ISFET) was investigated as a function of the probe position in order to assess the potential of the probe in device testing, where its non-optical read-out mechanism may proof to be a particular advantage.
Improve the Accuracy of Scanning Kelvin Probe Microscopy by Eliminating the Cantilever Effect
Authors: Yang Zhitao , Spencer Michael G.
Published: April 2011

Scanning Kelvin probe microscopy (SKPM) is widely used to measure surface work functions and electrostatic potentials on nanoscale circuits, devices and materials. However, the accuracy of scanning Kelvin probe microscopy is reduced by a cantilever effect, which is due to a large capacitance gradient associated with the cantilever. We introduce an aperture structure to quantitatively moderate the strength of the cantilever effect. In this approach, the cantilever effect is eliminated and the true surface potential can be extracted by solving a set of linear equations. Experimental results show that this approach yields very accurate surface potentials when there is only a single potential source within the aperture. In the case of multiple potential sources, this method significantly improves accuracy as well. A mobile aperture structure mounted on a micromanipulator can make this approach more versatile.
Theory of Scanning Probe Microscopy of Carbon Nanostructures
Authors: Meunier Vincent , Kalinin Sergei , Lambin Philippe
Published: April 2011

Experimental techniques for SPM imaging and spectroscopy of low-dimensional systems have significantly progressed in recent years. At the same time, new simulation methods and computational techniques have allowed the development of a theoretical basis to the interpretation and understanding of the measurements. In this contribution, we concisely review two state-of-the-art modeling methods for scanning probe microscopy, as applied to carbon nanostructures.
Raman and Rayleigh Smart Imaging of Nanophases and Nanosized Materials. Alternatives Techniques to SEM, TEM and AFM ?
Authors: Colomban Philippe , Havel Mickaël
Published: April 2011

The imaging of nanostructural and topological variations on mechanically or chemically aged SiC materials has been performed using non-destructive Raman and Rayleigh μ-spectrometries. The case of a Hi-Nicalonf/(SiC/BN/C)m composite, corroded under alkali and oxidizing environment (modelled using molten NaNO3), is discussed. It is shown for the first time that Rayleigh imaging offers a competitive alternative to AFM measurements for un-prepared, very corrugated surface of materials containing carbon as a second phase. A comparison is made to the analysis of μ-indented areas performed on a polished section of the Ø∼140 μm SCS-6™ Textron SiC fibre. The “smart” Raman images allowed determining the strain distribution within the whole indented area.
Effects of Surface Functionality and Humidity on the Adhesion Force And Chemical Contrast Measured with AFM
Authors: Nguyen Tinh , Gu Xiaohong , Chen Lijiang , Julthongpiput Duangrut , Fasolka Michael , Briggman Kimberly , Hwang Jeeseong , Martin Jon
Published: April 2011

The ability to probe chemical heterogeneity with nanometer scale resolution is essential for developing a molecular–level understanding of a variety of phenomena occurring at surfaces of materials. One area that could benefit greatly from nanoscale chemical measurement is an understanding of the degradation mechanisms of polymeric materials exposed to the environment. For example, the degradation (photo and hydrolytic) of polymers and polymeric materials has been observed to occur non-uniformly in which nanometer pits form locally, which deepen and enlarge with exposure (1, 2). The pitting has been postulated to initiate in the hydrophilic degradation-susceptible regions of the films (3). However, due to the lack of spatial resolution of the most current surface analytical techniques, the chemical nature of the degradation-initiated locations has not been identified. The use of a chemically-functionalized probe in an AFM (chemical force microscopy CFM) (4) has been shown to be capable of discriminating chemically-different domains of self-assembled monolayer (SAM) surfaces at the nanoscale spatial resolution. This study provides data to demonstrate that, by using proper RH at the tip-sample environment, the contrast between the hydrophilic and hydrophobic domains in SAM and polymer samples can be discerned, and presents results on the effects of RH on tipsample adhesion forces for different substrates.
The μ-TA (Scanning Thermal Mcroscopy) - a tool for quantitative surface analysis and surface treatment
Authors: Fischer Hartmut
Published: April 2011

The analytical technique micro-thermal analysis (μ-TA) will be introduced and evaluated. It combines the visualisation power of atomic force microscopy (AFM) and it's ability to image topography, phase shifts, friction, stiffness, and adhesion with the characterisation capabilities of thermal analysis (thermal conductivity, micro-differential thermal analysis and micro-thermo mechanical analysis) resulting in a characterisation of surfaces with respect to their thermal and thermo-mechanical properties. The scanning mode may be used for the inspection of surfaces with respect to their thermal properties using a scanner with an active thermal sensor (heater, height and thermal sensor) as probe (tip), simultaneously acquiring topography, thermal conductivity and thermal diffusivity images. A second mode gives the option to perform a ocal thermo-mechanical analysis of discrete areas of a few square microns (L-TMA and L-CA), and detects at the same time during heating in contact mode changes of the sensor position and the heat flow to the sample in a very short time. Any thermodynamic phase transition, connected with a change in mechanical properties (softening, expansion, melting) and thermal properties (heat of fusion, change of heat capacity) will thus be detected by both methods. Applications for the analysis of especialy soft materials are presented and critically discussed. Moreover, the use of the instrument for controlled surface treatment is demonstrated resulting in the creation of super smooth polymeric surfaces. Furthermore, attempts to determine thermal conductivity's on surfaces on a quantitative matter wil be presented and discussed.
Materials analysis by aberration-corrected STEM
Authors: Krivanek Ondrej L. , Bacon Neil J. , Corbin George C. , Dellby Niklas , McManama-Smith Andrew , Murfitt Matthew F. , Nellist Peter D. , Szilagyi Zoltan S.
Published: April 2011

Electron-optical aberration correction has recently progressed from a promising concept to a powerful research tool. 100–120 kV scanning transmission electron microscopes (STEMs) equipped with spherical aberration (Cs) correctors now achieve sub-Å resolution in high-angle annular dark field (HAADF) imaging, and a 300 kV Cs-corrected STEM has reached 0.6 Å HAADF resolution. Moreover, the current available in an atom-sized probe has grown by about 10x, allowing electron energy loss spectroscopy (EELS) to detect single atoms. We summarize the factors that have made this possible, and outline likely future progress.
Transmission electron microscopy study of domain structures in ferroelectric SrBi2Nb2O9 ceramics
Authors: Karthik C. , Ravishankar N. , Varma K.B.R.
Published: April 2011

A transmission electron microscopy study has been carried out on the domain structures of SrBi2Nb2O9 (SBN) ferroelectric ceramics which belong to the Aurivillius family of bismuth layered perovskite oxides. SBN is a potential candidate for Ferroelectric Random access memory (FeRAM) applications. The 90° ferroelectric domains and antiphase boundaries (APBs) were identified with dark field imaging techniques using different superlattice reflections which arise as a consequence of octahedral rotations and cationic shifts. The 90° domain walls are irregular in shape without any faceting. The antiphase boundaries are less dense compared to that of SrBi2Ta2O9(SBT). The electron microscopy observations are correlated with the polarization fatigue nature of the ceramic where the domain structures possibly play a key role in the fatigue- free behavior of the Aurivillius family of ferroelectric oxides.
Surface engineering of SrTiO3 (111) substrates for the epitaxial growth of BLT films
Authors: Suh Ju Hyung , Lee Yong Seok , Park Chan-Gyung
Published: April 2011

The optimized surface termination of SrTiO3 (111) substrates was investigated and the effects of the terminated SrTiO3 (111) substrate on the growth characteristics of epitaxial Bi4−xLaxTi3O12 (BLT) films were evaluated. It was found that etching in buffered HF (BOE) solution for 2min provides a stable etching condition for SrTiO3 (111) substrates and that etching is an important factor for the formation of terrace structures. The microstructure of BLT films grown on the terminated substrate revealed a flat surface morphology and well-defined interfacial structure in comparison with BLT films grown on non-terminated substrate. Therefore, surface termination is a crucial factor for determining the quality of film morphology and interfacial structure.
Effect of Simulated Body Fluid on the Microstructure of Ferrimagnetic Bioglass-Ceramics
Authors: Papanearchou N. I. , Leventouri Th. , Kis A. C. , Hotiu A. , Anderson I. M.
Published: April 2011

The effect of simulated body fluid (SBF) on the structure and microstructure of ferrimagnetic bioglass ceramics (FBC) was investigated in series of samples in the system of the oxides [0.45(CaO, P2O5) (0.52-x)SiO2 xFe2O3 0.03Na2O], with X = 0.05, 0.10, 0.15, 0.20. Physical properties of the materials were studied as a function of processing parameters and time of immersion in SBF by x-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS). The in vitro experiment showed that bioactivity of the FBC varies with the composition of the oxides, heat treatment, and time of exposure in SBF in a non-systematic way. A surface layer of Si, P, Ca partially covers the Fe, O dendrites, while formation and size of pores is determined by the specific processing parameters of the materials.
Pair Distribution Function Analyses of Structural Relaxation in a Zr-Based Bulk Metallic Glass
Authors: Morrison Mark L. , Dmowski Wojtek , Wilson Timothy W. , Liaw Peter K. , Liu Chain T. , Richardson James W. , Maxey Evan R. , Buchanan Raymond A. , Fan Cang , Choo Hahn , Egami Takeshi , Porter Wallace D.
Published: April 2011

Zr-based alloy ingots with nominal compositions of Zr52.5Cu17.9Ni14.6Al10.0Ti5.0 (at.%), Vitre-loy 105, were isothermally annealed below the glass-transition temperature at 630 K for 10, 20, 30, 40, and 60 minutes in vacuum to obtain samples with various states of structural relaxation and compared to the as-cast state. Structural studies were performed using time-of-flight neutron diffraction followed by pair distribution function (PDF) analyses. Differential scanning calo-rimetry (DSC) was conducted to examine changes in the specific heat, which were correlated to the amount of structural relaxation in the various samples. These samples exhibited increasing structural relaxation with longer annealing times, which was evidenced in the atomic PDF. Relaxation related to the exothermic peak results in changes in the PDF that are consistent with the elimination of short and long inter-atomic distances. Further annealing led to rearrangements in the second atomic shell that may be related to local phase separation.
Self-Diffusion in Chemically Homogeneous Multilayers Using Neutron and Nuclear Resonance Reflectivity
Authors: Gupta Mukul , Gupta Ajay , Chakravarty Sujoy , Gutberlet T. , Wille H.-C. , Leupold O. , Rüffer R.
Published: April 2011

Neutron reflectivity is a well-established technique for studying self-diffusion in chemically homogeneous system as neutron scattering lengths are different for isotopes of an element. For x-ray there is no contrast for a multilayer with isotopic abundance. However, placing Mössbauer active nuclei in a chemically homogeneous system, self-diffusion of the constituents can be probed using nuclear resonance scattering of Mössbauer active nuclei. In the present work, we have applied the neutron reflectivity technique for studying the self-diffusion of iron and nitrogen in nano crystalline multilayers of FeN/57FeN and FeN/Fe15N and nuclear resonance reflectivity techniques for studying iron self diffusion in FeNZr/57FeNZr. Both the techniques are complementary to each other and give a unique depth resolution of the order of 0.1 nm. As compared with conventional techniques used for probing self-diffusion, neutron and nuclear resonance reflectivity techniques can be applied at significantly lower temperatures. On the basis of the obtained results the diffusion mechanism in chemically homogeneous multilayers is discussed in the present work.
Dynamic Transition in Proteins and DNA: Role of the Solvent
Authors: Sokolov A. P.
Published: April 2011

Hydrated proteins and DNA demonstrate a dynamic transition at temperatures TD∼200–230K. Sharp slowing down of protein functions (rate of biochemical reactions) was observed at the same temperature range. These results suggest a direct relationship between the dynamic transition and onset of biochemical activities of proteins. However, the microscopic nature of the dynamic transition in biomolecules remains poorly understood. This contribution presents an overview of neutron scattering and simulations data analyzing dynamics of proteins and DNA. We show that the dynamic transition is related to a “slow” relaxation process that appears in the experimental frequency window at temperatures above TD. Moreover, we show that the dynamic crossover in the solvents controls the activation of the slow process in biological macromolecules. Microscopic details of the slow process and of the dynamic transition are discussed.
Large-Scale Morphology of Dispersed Layered Silicates
Authors: Schaefer Dale W. , Justice Ryan S. , Koerner Hilmar , Vaia Richard , Zhao Chungui , Yang Mingshu , Vale Jim
Published: April 2011

Ultra small angle x-ray scattering is used to probe the morphology of highly dispersed montmorillonite (MMT) in water and polyamide-66. In water the scattered intensity, I(q) shows a q-2 dependence for q > 0.01 Å-1, where q is the magnitude of the scattering vector. This is as expected for a two dimensional sheet-like object. On larger scales (smaller q) mass-fractal character is evident up to the radius-of-gyration of the individual scattering entities. The scattering profile is interpreted using a semi-flexible sheet model in which flat, disk-like entities of radius = 80 Å (an areal persistence length) are fractally distributed on large scales with a mass fractal dimension of 2.65. These size scales correspond to a scattering entity comprised of one or a few crumpled sheets. No evidence of inter-particle correlations is found at concentrations below the gel point. In polyamide-66 loaded with organically modified MMT long-range fractal behavior is also observed but with larger fractal dimension.
The phase-diagram of Ca2-xSrxRuO4: Relation between crystal distortions and physical properties
Authors: Braden M. , Friedt O. , Schumann O. , Baier J. , Steffens P. , Kriener M. , Lorenz T. , Bourée F. , André G. , Gukasov A. , Radaelli P. G. , Nakatsuji S. , Maeno Y.
Published: April 2011

The phase-diagram of Ca2-xSrxRuO4 has been studied by several diffraction techniques as function of concentration, temperature, pressure and magnetic field. The substitution of Sr through the smaller Ca induces a series of structural phase transitions with a strong impact on the physical properties. The spin triplet superconductor Sr2RuO4 exhibits an undistorted crystal structure, and the Mott-insulator Ca2RuO4 strong structural distortions. For intermediate structural distortions samples stay metallic but with outstanding properties. Throughout the phase diagram we find a close coupling between the crystal structure on one side and magnetic and electronic behavior on the other side.
RECIPROCAL-LATTICE SPACE IMAGING OF X-RAY INTENSITIES DIFFRACTED FROM NANOWIRES
Authors: Sakata Osami , Kitano Akiko , Yashiro Wataru , Sakamoto Kunihiro , Miki Kazushi , Matsuda Akifumi , Hara Wakana , Akiba Shusaku , Yoshimoto Mamoru
Published: April 2011

A nondestructive method has been developed for quickly characterizing a 1 D crystalline structure. It required brilliant synchrotron x-rays in grazing incidence and an x-ray 2 D detector. X-ray patterns recorded on the detector showed anisotropically sheet-shape diffraction from NiO nanowires epitaxially grown on an ultra-smooth sapphire (0 0 0 1). Other shots obtained from Bi atomic wires embedded in Si (0 0 1) showed that the wires have a 2 × n superstructure, which indicated that the Bi-dimer bonds were parallel to the wires.
USANS as a Probe of Large-Scale Structure in Attractive Colloidal Glasses of Block Copolymer Micelles
Authors: Crichton Mark A. , Forbes Neil S. , Bhatia Surita R.
Published: April 2011

We have used ultra-small-angle scattering (USANS) and fluorescence microscopy to show the existence of large-scale structure in attractive colloidal glasses composed of block polyelectrolyte micelles. Our systems display evidence of surface scattering, with the scattered intensity I at low scattering vector q scaling as I ∼ qx with x in the range –3 to –4. We believe this is due to surface scattering from large, highly polydisperse aggregates with rough interfaces. USANS may provide an ideal way to distinguish fractal colloidal gels and colloidal glasses.
Nanoindentation of Ion Implanted and Deposited Amorphous Silicon
Authors: Williams J. S. , Haberl B. , Bradby J. E.
Published: April 2011

The deformation behavior of both ion-implanted and deposited amorphous Si (a-Si) films has been studied using spherical nanoindentation, followed by analysis using Raman spectroscopy and cross-sectional transmission electron microscopy (XTEM). Indentation was carried out on both unannealed a-Si films (the so-called unrelaxed state) and in ion implanted films that were annealed to 450°C to fully relax the amorphous film. The dominant mode of deformation in unrelaxed films was via plastic flow of the amorphous phase rather than phase transformation, with measured hardness being typically 75–85% of that of crystalline Si. In contrast, deformation via phase transformation was clearly observed in the relaxed state of ion implanted a-Si, with the load-unload curves displaying characteristic discontinuities and Raman and XTEM indicating the presence of high-pressure crystalline phases Si-III and Si-XII following pressure release. In such cases the measured hardness was within 5% of that of the crystalline phase.
Cross-Sectional TEM Studies of Indentation-Induced Phase Transformations in Si: Indenter Angle Effects
Authors: Wen Songqing , Bentley James , Jang Jae-il , Pharr G. M.
Published: April 2011

Nanoindentations were made on a (100) single crystal Si wafer at room temperature with a series of triangular pyramidal indenters having centerline-to-face angles ranging from 35° to 85°. Indentations produced at high (80 mN) and low (10 mN) loads were examined in plan-view by scanning electron microscopy and in cross-section by transmission electron microscopy. Microstructural observations were correlated with the indentation load-displacement behavior. Cracking and extrusion are more prevalent for sharp indenters with small centerline-to-face angles, regardless of the load. At low loads, the transformed material is amorphous silicon for all indenter angles. For Berkovich indentations made at high-load, the transformed material is a nanocrystalline mix of Si-I and Si-III/Si-XII, as confirmed by selected area diffraction. Extrusion of material at high loads for the cube-corner indenter reduces the volume of transformed material remaining underneath the indenter, thereby eliminating the pop-out in the unloading curve.
An analytical approach for relating hardness and yield strength for materials with high ratio of yield strength to Young modulus
Authors: Vandeperre Luc J. , Giuliani Finn , Clegg William J.
Published: April 2011

For materials with a high ratio of Y to the elastic modulus, E, experimental data show that the ratio of the hardness to the flow stress decreases from 3 toward 1 as Y / E increases. This behaviour is predicted by finite element calculations but to date analytical expressions have not been able to correctly predict the relation between Y and H nor have they been able to show how the geometry of the indenter is important. Therefore, in this paper the correlation between H and Y for such materials is re-examined using an analytical approach to provide a physical interpretation, which explains the trends observed.
Microbridge Nanoindentation Testing of Plasma-Enhanced Chemical Vapor Deposited Silicon Oxide Films
Authors: Cao Zhiqiang , Zhang Tong-Yi , Zhang Xin
Published: April 2011

Plasma-enhanced chemical vapor deposited (PECVD) silane-based oxides (SiOx) have been widely used in both microelectronics and MEMS (MicroElectroMechanical Systems) to form electrical and/or mechanical components. In this paper, a novel nanoindentation-based microbridge testing method is developed to measure both the residual stresses and Young's modulus of PECVD SiOx films. Our theoretical model employed a closed formula of deflection vs. load, considering both substrate deformation and the residual stresses in the thin films. In particular, the non-negligible residual deflection caused by excessive compressive stresses was taken into account. Freestanding microbridges made of PECVD SiOx films were fabricated using bulk micromachining techniques. To simulate the thermal processing in device fabrication, these microbridges were subjected to rapid thermal annealing (RTA) up to 800°C. A microstructure-based mechanism was applied to explain the experimental results of the residual stress changes in PECVD SiOx films after thermal annealing.
INVESTIGATION OF INDENTATION METHODS FOR PROPERTIES DETERMINATION IN HARD FILM – SOFT SUBSTRATE SYSTEMS
Authors: Kennedy M. S. , Moody N. R. , Bahr D. F.
Published: April 2011

Elastic modulus values of the thin films utilized in three different hard film- soft substrate systems were measured using a combination of traditional and continuous stiffness indentation. These systems were chosen to represent typical systems currently utilized in MEMS and included Si/SU8/W, Si/SiO2/Ti/Pt/PZT, and Si/SiO2/Ti/Pt. The last system was coated with either a compressive or nonstressed Cr film. By taking into account ratio between the creep due to the polymer substrate, SU8, to the unloading rate, the modulus of W was measured to be 400 GPa. The modulus of the SU8 was also determined to be 6 GPa. Comparing both the CSM and traditional indentation for the Si/SiO2/Ti/Pt/PZT system showed that the dynamic motion of the indenter caused pile-up in the PZT and resulting in the overestimation of the PZT modulus. This pile-up is a function of the sinusoidal loading frequency. Instead, the modulus of the PZT was measured by shallow depths of traditional indentation that resulted in the PZT modulus of 100 GPa. The hard film-soft substrate systems were show to follow the same trend as stressed soft-film hard-substrate systems with residual stress. The modulus was over estimated for compressively stressed Cr films.
Nanoscale Characterisation of Salivary Pellicle
Authors: Dickinson Michelle E. , Mann Adrian B.
Published: April 2011

Salivary pellicle is an organic biofilm formed by the physisorption of proteins and carbohydrates onto the surface of dental enamel exposed to the oral environment. The pellicle has several key roles in oral physiology including lubrication and reduction of friction between teeth during mastication, as well as chemical protection of the enamel against acidic solutions. However, pellicle proteins are known to react with dietary compounds to cause extrinsic staining on the tooth surface.

In this study, nanoindentation and AFM have been used in vitro to examine the acquired salivary pellicle formed in vivo on dental enamel. The mechanical properties, growth, structure and morphology of pellicle grown in vivo on human enamel surfaces have been analysed. In addition, the effects of dietary agents such as polyphenols on the pellicle's morphology and properties have been studied.

It was found that initial adsorption of proteins on the enamel surface occurred within 30 seconds of exposure to the oral cavity, with full growth achieved within 2 hours. Differences in the properties of the pellicles such as surface adhesion, and time dependent effects due to polyphenol interaction were measured using nanoindentation. It was seen that the polyphenol interaction has a significant effect on these properties. These results suggest that the stained pellicle is mechanically stiffer, but also less viscous and more fluid like. This could explain why traditional tooth brushing techniques do not efficiently remove this layer.
Elastic modulus of dental enamel: effect of enamel prism orientation and mineral content
Authors: Ferguson V. L. , Boyde Alan , Bushby Andrew J.
Published: April 2011

Nanomechanical properties of mineralized tissues are determined by microstructural tissue organization and relative composition of organic, mineral, and water phases. We combine nanoindentation and quantitative backscattered electron (qBSE) imaging to understand how these factors influence material properties at the ultrastructural and tissue level. Developmental stages of equine tooth enamel provide a good situation for studying the effects of enamel prism orientation and mineralization. Equine cheek teeth continue to form new enamel whilst mature tissue is being worn away. Hence we can study graded mineral content that increases with enamel maturity. Hunter-Schreger bands (HSBs) containing enamel prisms of contrasting orientations allow investigation of the effect of orientation on modulus. An equine second mandibular molar (2-year-old) was embedded in poly-methylmethacrylate, sectioned longitudinally, polished, carbon coated, imaged in qBSE, and subjected to nanoindentation testing. Elastic modulus increases significantly during maturation as enamel protein matrix degradation makes space for increased mineral content with closer proximity of enamel crystals, finally reaching values exceeding 80 GPa for little further increase in mineral content. Indentations spanning HSBs in immature, poorly mineralized enamel yielded modulus values that varied with prism orientation in a sinusoidal pattern where modulus varies by as much as a factor of three. Nanoindentation helps to elucidate how the composition and ultrastructural organization of enamel contribute to mechanical properties.
Effects of Osteopontin Deficiency and Aging on Nanomechanics of Mouse Bone
Authors: Kavukcuoglu B. , West C. , Denhardt D. T. , Mann A. B.
Published: April 2011

Osteopontin (OPN), a phosphorylated glycoprotein, is among the most abundant non-collageneous bone matrix proteins produced by osteoblasts and osteoclasts. OPN has been implicated in bone formation, resorption and remodeling. However, previous studies have presented contradictory results regarding the effect of OPN on the mechanics and microstructure of bone. This study has used nanoindentation to identify local variations in elastic modulus and hardness of OPN deficient (OPN -/-) and wild-type control (OPN+/+) mouse bones. Specifically, the study has looked at changes in the mechanical properties of OPN-/- and OPN+/+ mouse bones with the mouse's age. Cortical sections of femurs from different age groups ranging from 3 weeks to 58 weeks were tested and compared. The results suggest that there are large, abrupt variations in mechanical properties across the femur's radial section for 3-week-old mouse bone. The hardness (H) drops significantly towards the inner and outer sections so the cortical bone has a mean H=3.66 GPa with a standard deviation of 2.44 GPa. In contrast, the hardness of the 58-week-old mouse bone had a standard deviation of 0.35 GPa and a mean H=1.45 GPa. The hardness across the radial axis of the 58-week-old bone was found to be quite uniform. The elastic modulus showed similar variations to the hardness with respect to age and position on the bone. We conclude that the mechanical properties of the mouse bones decrease substantially with maturity, and statistically the hardness and elastic modulus are more uniform in mature bones than young ones. Surprisingly we found a similar variation in both OPN-/- and OPN+/+ bones, with no statistically significant difference in the mechanical properties of the OPN -/- and OPN+/+ bones. The results for OPN-/- and OPN+/+ mouse bones are particularly important as control of OPN activity has been postulated as a potential treatment for bone pathologies that exhibit a change in the bone mineralization, such as osteoporosis, osteopetrosis and Paget's disease. Understanding the effects of OPN on bone mechanics is a vital step in the development of these new treatments.
High Temperature Deformation of AlN/CrN Multilayers using Nanoindentation
Authors: Giuliani F. , Goruppa A. , Lloyd S. J. , Teer D. , Clegg W. J.
Published: April 2011

The aim of this paper is to investigate the deformation behaviour of an AlN/CrN multilayer with wavelengths varying from 6–400 nm, deposited on M42 tool steel and how this varies as the temperature is increased to 500 °C. These measurements have been correlated with changes in deformation patterns using cross-sectional transmission electron microscopy, where sections have been prepared directly through the indents.
Mechanical Properties of Wear Tested LIGA Nickel
Authors: Moody N. R. , Jungk J. M. , Kennedy M. S. , Prasad S. V. , Bahr D. F. , Gerberich W. W.
Published: April 2011

Strength, friction, and wear are dominant factors in the performance and reliability of materials and devices fabricated using nickel based LIGA and silicon based MEMS technologies. However, the effects of frictional contacts and wear on the mechanical performance of microdevices are not well-defined. To address these effects on performance of LIGA nickel, we have begun a program employing nanoscratch and nanoindentation. Nanoscratch techniques were used to generate wear patterns using loads of 100, 200, 500, and 990 μN with each load applied for 1, 2, 5, and 10 passes. Nanoindentation was then used to measure properties in each wear pattern correcting for surface roughness. The results showed a systematic increase in hardness with applied load and number of nanoscratch passes. The results also showed that the work hardening coefficient determined from indentation tests within wear patterns follows the work hardening behavior established from tensile tests, supporting use of a nanomechanics-based approach for studying mechanical properties of wear tested material.
TEM Observation of Microstructural Change of Silicon Single Crystal Caused by Scratching Tests Using SPM
Authors: Takagi M. , Onodera K. , Iwata H. , Imura T. , Sasaki K. , Saka H.
Published: April 2011

In this study, the microstructural change of the surface of Si single crystal (Si(100)) after the scratching tests under very small loading forces was investigated. At first, line-scratching tests and scanning-scratching tests were carried out using an atomic force/friction force microscope (AFM/FFM). Next, cross-sectional TEM observations of the wear marks which were generated by the scratching tests were carried out. As a result of the TEM observations after the line-scratching tests, it was found that dislocations were observed in the area of less than 100nm thickness from the surface of the wear marks which were formed under the loading forces of more than 5μN. In the case of the loading forces of more than 20μN, an amorphous region was also observed just under the wear marks. As a result of the TEM observations after the scanning-scratching tests, it was found that the introduction of dislocations took place and no amorphous region appeared. It was also found that the several atomic layers at the top surface of the wear marks shifted in parallel to (100).
Fracture mechanisms of GaAs under nanoscratching
Authors: Solletti J.-M. , Parlinska-Wojtan M. , Tharian J. , Wasmer K. , Michler J. , Ballif C. , Schulz D. , Karimi A.
Published: April 2011

Nanoscratching on GaAs (001) by a pyramidal diamond tip (Berkovitch) indenter has been carried on under different loads, scratching velocities and directions. Plastic deformation and fractures induced by scratching have been investigated by atomic force microscopy (AFM), and by scanning and transmission electron microscopy (SEM and TEM, respectively). Surface images revealed radial and surface tensile cracks. Focused ion beam (FIB) milling of the contact area revealed median and shear fracture distribution in the volume. The different cracks were characterized for various scratching conditions in terms of their direction of propagation, extension and frequencies. Plastic deformations have been characterized by vertical displacement of material. No purely ductile zone was observed, GaAs deformation occurred by fractures and plastic strain. Their preponderances are discussed in terms of material properties.
Microstructures and Mechanical Properties of NiAl-Mo Composites
Authors: Bei H. , George E. P.
Published: April 2011

In-situ composites consisting of ∼14 vol.% continuous Mo fibers embedded in a NiAl matrix were produced by directional solidification in a xenon-arc-lamp, floating-zone furnace. The fiber spacing and size were controlled in the range 1–2 μm and 400–800 nm, respectively, by varying the growth rate between 80 and 20 mm/h. Electron back-scatter diffraction patterns from the constituent phases revealed that the growth directions and interface boundaries exhibited the following orientation relationships: 〈l00〉NiAl//〈100〉Mo and {011}NiAl//{011}Mo. The temperature dependence of the tensile strength and ductility were investigated and the NiAl-Mo composite was found to be both stronger and have a lower ductile-brittle transition temperature than the unreinforced NiAl matrix.
The Effects of Substitutional Additions on Tensile Behavior of Nb-Silicide Based Composites
Authors: Cretegny Laurent , Bewlay Bernard P. , Ritter Ann M. , Jackson Melvin R.
Published: April 2011

Nb-silicide based in-situ composites consist of a ductile Nb-based solid solution with high-strength silicides, and they show excellent promise for aircraft engine applications. The Nb-silicide controls the high-temperature tensile behavior of the composite, and the Nb solid solution controls the low and intermediate temperature capability. The aim of the present study was to understand the effects of substitutional elements on the room temperature tensile behavior and identify the principal microstructural features contributing to strengthening mechanisms.