bluuebunny/crossref_metadata_2025 huggingface dataset:
The Stress Driven Rearrangement Instabilities in Electronic Materials and in Helium Crystals
Authors: Grinfeld Michael , Grinfeld Pavel , Kojima Haruo , Little John , Masutomi Ryuichi , Persson Per-Olof. , Zheleva Tsvetanka
Published: April 2011

At present, there is a consensus that various Stress Driven Rearrangement Instabilities (SDRI) are the implications of the mathematically rigorous theoretical Gibbs thermodynamics. Many applied researchers and practitioners believe that SDRI are also universal physical phenomena occurring over a large range of length scales and applied topics. There is a multitude of publications claiming experimental observation of the SDRI based phenomena. This opinion is challenged by other highly respected scholars claiming theoretical inconsistencies and multiple experimental counterexamples. Such an uncertainty is too costly for further progress on the SDRI topic. The ultimate goal of our project is to resolve this controversy.

The project includes experimental, theoretical, and numerical studies. Among various plausible manifestations of SDRI, the authors focused only on two most promising for which the validity of the SDRI has already been claimed by other researchers: a) stress driven corrugations of the solid-melt phase interface in macroscopic quantum 4He and b) the dislocation-free Stranski-Krastanov pattern of growth of semiconductor quantum dots. We devised a program and experimental set-ups for testing applicability of the SDRI mechanisms using the same physical systems as before but using implications of the SDRI theory for 2D patterning which have never been tested in the past.
Mechanisms of Cu<111> Columns Growth
Authors: Wang Jian , Huang Hanchen
Published: April 2011

The Cu <111> columns, which are formed during magnetron sputtering deposition, are faceted on the top and zigzag on sides. Our numerical results of large facet-facet diffusion barriers offer an explanation of the facet dimension. Based on the stacking fault formation energies of various face-centered-cubic metals, we suggest that the zigzag shape of Cu <111> columns is a result of deposition twins. Our molecular dynamics simulations indeed confirm this suggestion. Further, the dynamics simulations reveal the transient role of {100} facets, which facilitate the formation of {111} facets and disappear afterwards.
Multiscale Phenomena in Bruggeman Composites
Authors: Skomski Ralph , Li Jiangyu , Zhou Jian , Sellmyer David J.
Published: April 2011

Mechanical, magnetic, and transport properties of arbitrary inhomogeneous composites are investigated by a Bruggeman-type mean-field approach. The theory yields materials parameters as functions of the volume fractions, geometries, and materials constants of the phases. Each system is described by a single response parameter g, which is equal to the percolation threshold of the composite. For macroscopic systems, the approach yields very simple expressions, but nanoscale and multiferroic effects yield relatively complicated corrections to g. In the respective cases, the parametergdepends on the length scale of the composite and has the character of a combination of magnetic, electric, and mechanical degrees of freedom.
Processing and Development of a New High Strength Metal Foam
Authors: Rabiei A. , O'Neill Adrian T. , Neville Brian P.
Published: April 2011

The research sited in this paper involves the development of new closed cell metal foam composite materials using powder metallurgy (PM) and gravity casting techniques. The foam is comprised of steel hollow spheres packed into a random dense arrangement, with the interstitial space between spheres occupied with a solid metal matrix. Using a casting technique, an aluminum alloy infiltrates the interstitial spaces between steel spheres. In a powder metallurgy method, steel spheres and iron powder are sintered to form a solid, closed cell structure. The measured densities of the Al-Fe composite foam and iron foam are 2.4 g/cm3 and 3.2 g/cm3, with relative densities of 42% and 41% respectively.

The hollow sphere metal foam composite materials developed in this study displayed superior compressive strength as compared to hollow sphere foams currently being produced. The compressive strength of the cast Al-Fe foam averaged 67 MPa over a region of 10 to 50% strain, while the steel PM foam averaged 45 MPa over the same strain region. Densification began at approximately 50% for the cast foam and 55% for the PM foam.
Formation of boron carbonitride nanotubes from in situ grown carbon nanotubes for space applications
Authors: Piazza F. , Nocua J. E. , Hidalgo A. , De Jesús J. , Velázquez R. , Morell G.
Published: April 2011

Boron carbonitride nanotubes (BCNNTs) were grown with high yield by arc discharge without catalyst particles or pre-grown template nanostructures. Two types of nanotubes (NTs) were formed: thin NTs with diameters of 10–15 nm and thick NTs with diameters of 25–50 nm, all multiwall. Transmission electron microscopy, electron energy loss spectroscopy, and Raman spectroscopy analyses indicate that the thin NTs are carbon NTs (CNTs) while the thick NTs are BCNNTs wrapped around CNTs. The growth kinetic appears to be faster for CNTs than for BCNNTs. Through the concerted substitution of B and N for C in the in situ grown CNTs, template growth of BCNNTs follows the CNTs growth without causing topological changes.
Moscow State University Activities on Research of Space Environment Effect on Materials
Authors: Novikov Lev S.
Published: April 2011

Main areas of Skobeltsyn Institute of Nuclear Physics Moscow State University activities in study of space environment effect on materials are following: effect of space radiation on spacecraft materials and equipment elements, spacecraft charging in space plasma in various orbits, influence of atomic oxygen flux on materials in LEO, surface erosion and destruction under impact of micrometeoroids and small particles of space debris.

The methods of computer and laboratory modeling used are described. Results of the researches are presented, as far as some experiments onboard the MIR station and ISS are described. Principle problems for contemporary and future research are proposed for discussion. Principle problems for contemporary and future research are proposed for discussion.
Nanodosimetry: Present and perspectives
Authors: Chipara Mircea
Published: April 2011

The reasons to develop a nanodosimetry theory are critically reviewed. The necessity of such an approach is proved. The main features of nanodosimetry are analyzed. The predicted enhanced sensitivity of nanomaterials to ionizing radiation is demonstrated. It is concluded that the lifetime of nanomaterials in the harsh conditions of the space environment has to be accurately estimated.
Multifunctional Single-Walled Carbon Nanotube Polycarbonate Composites
Authors: Chen Jian , Ramasubramaniam Rajagopal , Liu Haiying
Published: April 2011

Uniform single-walled carbon nanotube (SWNT) polycarbonate composites were fabricated using noncovalently functionalized, soluble SWNTs. These composites showed dramatic improvements in the electrical conductivity and mechanical tensile strength at low SWNT loading. We also observed a stress-induced SWNT alignment in polycarbonate film, which is very difficult to achieve with pristine SWNTs.
Whisker Formation in Sn Coatings on Cu
Authors: Chason Eric , Reinbold Lucine , Kumar Sharvan
Published: April 2011

In the microelectronics industry, Sn is often electroplated as a protective layer on Cu conductors. Pure Sn layers on Cu develop whiskers that can cause component failures and have even been implicated in the loss of several satellites. Alloying Sn with Pb suppresses whisker formation, but the push towards Pb-free processing will make this unacceptable in the future. To understand the driving forces and mechanisms of whisker formation on pure Sn, we are measuring the kinetics of stress evolution and intermetallic formation in Sn/Cu layers. By using thin films of Sn and Cu, we can monitor the stress evolution in real time using wafer-curvature based techniques. Preliminary results of stress evolution in vapor-deposited films are presented showing the evolution of tensile stress in the Cu layers and compressive stress in the Sn layers.
Nanocrystalline Soft Magnetic Alloys for Space Applications
Authors: Willard Matthew A. , Francavilla Thomas , Goswami Ramasis , Harris Vincent G.
Published: April 2011

This study focuses on a Co-based nanocrystalline alloy (Co84.55Fe4.45Zr7B4) with potential for long-term high temperature use. As an indication of their performance, core losses were measured on toroidal samples using a Walker AC permeameter over a frequency range of 0.1 to 500 kHz, at induction amplitudes of 100, 300, and 500 mT, and temperatures from 22 to 300°C. For a given frequency and maximum induction amplitude, the losses were invariant as a function of measurement temperature. Vibrating sample magnetometry provided the magnetization and hysteretic losses as a function of temperature. As the temperature of the alloy was raised to 300°C from room temperature, the saturation magnetization (120 emu/g)was reduced by less than 15%. A toroid was aged at 300°C for up to 300 hours and core loss measured as a function of aging time at the previously mentioned frequencies and induction amplitudes. The losses were invariant over the aging time.
Investigation upon Mechanical Properties of Thin Film Silicon Under Cryogenic Temperature
Authors: Zhao Yi , Zhang Xin
Published: April 2011

Thin film silicon material has an extensive application in cooling satellite instrumentation under cryogenic environment. The performance and reliability of the cooling system heavily depends on mechanical behavior of the thin films. In this paper, we built an experimental setup and used compressive gas to actuate a silicon thin film under both room temperature and cryogenic temperature. The elastic modulus was derived from the film's deflection using laser Michelson interferometer. Stress distribution was obtained using Micro Raman spectroscopy. It was found that Young's modulus derived from the deflection increases with decreasing temperature. Compressive stress concentrated at edge centers of the film and tensile stress occurred at the center. There is a good match between the theoretical predications and experimental observations.
Simulation of InAsSb/InGaAs Quantum Dots for Optical Device Applications
Authors: Allmen Paul von , Lee Seungwon , Oyafuso Fabiano
Published: April 2011

Self-assembled InAsSb/InGaAs quantum dots are candidates for optical detectors and emitters in the 2–5 micron band with a wide range of applications for atmospheric chemistry studies. It is known that while the energy band gap of unstrained bulk InAs1−xSbx is smallest for x=0.62, the biaxial strain for bulk InAs1−xSbx grown on In0.53Ga0.47As shifts the energy gap to higher energies and the smallest band gap is reached for x=0.51. The aim of the present study is to examine how the electronic confinement in the quantum dots modifies these simple considerations. We have calculated the electronic structure of lens shaped InAs1−xSbx quantum dots with diameter 37 nm and height 4 nm embedded in a In0.53Ga0.47As matrix of thickness 7 nm and lattice matched to an InP buffer. The relaxed atomic positions were determined by minimizing the elastic energy obtained from a valence force field description of the inter-atomic interaction. The electronic structure was calculated with an empirical tight binding approach. For Sb concentrations larger than x=0.5, it is found that the InSb/ In0.53Ga0.47As heterostructure becomes type II leading to no electron confined in the dot. It is also found that the energy gap decreases with increasing Sb content in contradiction with previous experimental results. A possible explanation is a significant variation is quantum dot size with Sb content.
Correlation of Optical Luminescence with Radiation Hardness in Doped LiNbO3 Crystals
Authors: Thomes William J. , Simmons-Potter Kelly , Potter Barrett G. , Weichman Louis S.
Published: April 2011

Transient ionizing radiation fields have been observed to cause substantial optical loss in undoped LiNbO3 crystals operating at 1.06 microns. This loss is slow to recover and makes the selection of this material for Q-switch applications in radiation environments unfeasible. We have studied the effects of Mg doping on the radiation response of LiNbO3 crystals and have investigated the optical luminescence of doped and undoped samples. Our results indicate a strong correlation between crystal defects, formed primarily during crystal growth, and the radiation-induced optical loss exhibited by these materials. These findings have enabled us to produce radiation-hard LiNbO3 crystals for use in high gamma-field environments.
Low-Temperature Grain Boundary Diffusion Data Measured from Historical Artifacts
Authors: Kremer R.J. , Dayananda M.A. , King A.H.
Published: April 2011

Diffusion processes in typical metals are slow at room temperature but there are many applications for which very long-term use is envisaged and stability needs to be assured over a timescale of 10, 000 years, where even slow processes can be important. It is common to perform accelerated tests at higher temperatures and extrapolate the necessary information from the measurements so obtained. We have tested the validity of this type of extrapolation for room-temperature, grain boundary diffusion in the copper-silver system, by measuring low-temperature diffusion profiles in antique samples of Sheffield plate.
Electrochemical Techniques Applied to Metals Conservation
Authors: Costa Virginia
Published: April 2011

A review of the applications of electrochemical methods to the conservation of metal artifacts is presented with regards to their use in treatment and research. As treatment techniques electrochemical methods have been used for cleaning, stabilization and consolidation for many years. Presently electrochemical methods are increasingly being used as a research tool, allowing the identification and quantification of products present at the surface of the artifacts as well as evaluation of the compatibility between materials. Examples of application to silver-copper alloys and stainless steels are presented.
Atomic Oxygen Treatment and Its Effect on a Variety of Artist's Media
Authors: Miller Sharon K.R. , Banks Bruce A. , Waters Deborah L.
Published: April 2011

Atomic oxygen treatment has been investigated as an unconventional option for art restoration where conventional methods have not been effective. Exposure of surfaces to atomic oxygen was first performed to investigate the durability of materials in the low Earth orbit environment of space. The use of the ground based environmental simulation chambers, developed for atomic oxygen exposure testing, has been investigated in collaboration with conservators at a variety of institutions, as a method to clean the surfaces of works of art. The atomic oxygen treatment technique has been evaluated as a method to remove soot and char from the surface of oil paint (both varnished and unvarnished), watercolors, acrylic paint, and fabric as well as the removal of graffiti and other marks from surfaces which are too porous to lend themselves to conventional solvent removal techniques. This paper will discuss the treatment of these surfaces giving an example of each and a discussion of the treatment results.
Effects of Water Exposure on the Mechanical Properties of Early Artists' Acrylic Paints
Authors: Hagan Eric , Murray Alison
Published: April 2011

The mechanical properties of early artist's acrylic paints were investigated under controlled aqueous additive leaching for the purpose of identifying changes caused by cleaning paintings with water. Strength and stiffness values were obtained using a tensiometer to collect stress-strain curves of paint films. The results were compared to those from similar experiments in which paint films were tested under various age, temperature, and relative humidity (RH) values. Strength and stiffness both increased with decreased temperature, decreased RH, increased age, and increased additive removal. The most significant impact on mechanical properties was caused by lowering temperature to the Tg region around 5°C. Dramatic changes in properties were caused by RH fluctuations; however, the magnitudes were negligible in comparison to those induced by low temperature. Removal of water-soluble additives produced a uniform increase in tensile strength and secant modulus at all RH values. The films were equally responsive to fluctuations in RH before and after additive leaching. In comparing the material properties across a wide range of conditions it is evident that the acrylic paints in this study were not significantly altered by the amount of water exposure involved in cleaning paintings.
The Changing Mechanical Properties of Aging Oil Paints
Authors: Mecklenburg Marion F. , Tumosa Charles S. , Erhardt David
Published: April 2011

The stiffening and embrittlement of oil paints over time has been a real concern for those responsible for the long term care and preservation of paintings. This paper examines the effects of time, pigments, relative humidity (RH), temperature and solvents on the mechanical properties of traditional oil paints. In this way it is possible to determine the role of each factor in causing the paints to become brittle. Even after 14 years the oil paints show little evidence that the long term “maturing” processes have begun to slow down. It is shown that there seems to be little correlation between the time paint requires to “dry-to-the-touch” and the longer term mechanical properties. Both low and high temperature levels can increase the stiffness of the paints though the mechanisms are quite different. Considerable hydrolysis of the paints occurs early in their history and the ones that hydrolyze most quickly are the ones that remain the most flexible.
Investigations of the Decorative Techniques and Conservation Condition of a Majolica Altar by Andrea della Robbia
Authors: Ombelli Michela , Miliani Costanza , Morresi Assunta
Published: April 2011

A multi-disciplinary approach that involved chemical and microstructural characterization was used to aid technological interpretation and conservation condition evaluation and treatment of a della Robbia ceramic masterpiece. The majolica altar was manufactured by Andrea della Robbia in 1490 and has been preserved at St. Mary of the Angels in Assisi, Perugia, Italy. This study characterized the glaze and pigments used by the artist, and furthermore, presents information used to establish guidelines for restoration.
RECENT CASE STUDIES IN THE RAMAN ANALYSIS OF ANCIENT CERAMICS: Glaze Opacification in Abbasid Pottery, Medici and 18th century French Porcelains, Iznik and Kûtayha Ottoman Fritwares and an Unexpected Lapis Lazuli Pigment in Lajvardina Wares
Authors: Colomban Ph.
Published: April 2011

We demonstrate the potential of Raman spectroscopy as an on-site technique for the characterization of ancient ceramics. This non-destructive analysis offers a way to get information on the process and even sometimes on the date of ancient artifacts. Much information remains written in the microstructure of ceramics bodies and in the nanostructure of glasses, glaze and enamels. Raman signatures are specific to the technology that was applied to a given starting batch and to the process of manufacture. Recent studies that demonstrate: i) the use of cassiterite for opacification and its role in Islamic three-color wares and polychrome lustred pottery from the Abbasid to Fatimid period, ii) the invention of the “hybrid-paste porcelain” by the Duke of Medici, known as Medici porcelain and of the “soft-paste” porcelain by the French Manufactures in the eighteen century (Chantilly, Mennecy, Saint-Cloud), iii) the development of the underglaze pigment technology by Iznik and then Kütayha Ottoman potters; iii) the use of lapis lazuli gem as an unexpected pigment in the Iran Lajvardina wares. Finally we explore the relationship between glass makers and potters.
Morphological and Chemical Analyses of Manganese Dioxide Accretions on Mexican Ceramics
Authors: O'Grady Caitlin R.
Published: April 2011

Microscopic analysis of West Mexican ceramics (dating between in the collection of the Department of the Arts of Africa, Oceania and the Americas at the Metropolitan Museum of Art has established five different morphological types of manganese dioxide (MnO2) accretions. The accretions result mostly from a combination of bacterial and weathering activity in post-depositional contexts. Optical microscopy, scanning electron microscopy with energy dispersive x-ray analysis (SEM-EDS) and x-ray fluorescence (XRF) were successful; whereas microchemical spot tests, x-ray diffraction (XRD) and Raman spectroscopy proved inconclusive in the identification and differentiation of the five morphologies. Accretion morphology and substrate characteristics, together, suggest scenarios for the mechanism of formation and offer a qualitative tool for authentication. Accretions were documented using photomicrography, categorized based on empirical observations; sampled and analyzed using SEM-EDS and ND-XRF.
Spontaneous Formation of Ridges on Patterned Mesas and Their Role in the Evolution of
Authors: Arrays Step , Chang Kee-Chul , Blakely Jack M.
Published: April 2011

Mesa structures fabricated on Si(111) surfaces have been found experimentally to develop step arrays with large spacing of the order of a micron or more after annealing at temperatures where sublimation becomes important. Ridges around the edges initially develop during annealing and form barriers to step motion before eventually breaking down. This produces an array of steps of the same sign with a few wide terraces. Computer simulations using one dimensional Burton, Cabrera and Frank (BCF) theory including attachment-detachment rates and step-step repulsion for this configuration show that the terraces evolve under different dynamics depending on the terrace widths. For large terrace widths, sublimation dominates the step dynamics and the Ehrlich-Schwoebel effect is negligible. Sinusoidal terrace width distributions result in this case. The experimentally measured step distribution has such a sinusoidal shape suggesting that the step dynamics is sublimation dominated on the mesas after ridge breakdown.
Electronic excitations of stable fullerene-like GaP clusters
Authors: Malloci Giuliano , Cappellini Giancarlo , Mulas Giacomo , Satta Guido
Published: April 2011

We present quasi-particle (QP) corrections to the electronic energies for small GaP fullerenes, a new class of nanoscaled materials predicted to be stable and to show spontaneous formation. Using Time-Dependent Density Functional Theory we also computed the optical absorption spectra. The comparison between single-particle and optical absorption spectra yields strong excitonic effects with bonding energy up to 3.5 eV. The QP corrected HOMO-LUMO energy gaps confirm the high stability predicted for such molecules using ground-state computational schemes. The present results can be useful to identify the successful synthesis of these systems via optical absorption and QP spectra.
Simulation of the Organization of Heteroepitaxial Monolayer Islands Under Anisotropic Conditions
Authors: Pandey Gajendra , Kukta Robert V.
Published: April 2011

This paper addresses the effect of anisotropy on the organization of epitaxial islands deposited on a substrate. Focus is on in-plane anisotropies in surface stress and lattice mismatch between the film and substrate materials. Starting from a configuration where island sizes and position are random, evolution towards equilibrium through mass transport via condensation/evaporation is simulated. The effect of the degree of anisotropy is investigated. An efficient numerical method is obtained by reducing a model of square monolayer islands of finite size to point defects that interact through their elastic fields. Models for both the kinetics and energetics of the system are obtained by this reduction. It is found that the point source model is accurate for island separations larger than about 3 times the width of an island. Under isotropic conditions islands tend to form into hexagonal arrays, and as there is no preferred orientation of these arrays, defects analogous to grain boundaries in a crystalline material tend to arise. With anisotropy islands tend to align in particular directions. This is found to enhance organization in cases of modest anisotropy and cause islands to form into zigzagged lines in cases of high anisotropy.
Integration of nanocrystal quantum dots with crystalline semiconductor substrates: Structure, Stability, and Optical response
Authors: Konkar Atul , Lu Siyuan , Madhukar Anupam , Hughes Steven. M. , Paul Alivisatos A.
Published: April 2011

Integration of epitaxical and colloidal semiconductor nanostructures into hybrid structures can potentially open unprecedented functionalities and applications. We present here some results of a study of the structural and optical nature of adsorbed InAs nanocrystal quantum dots (NCQDs) on GaAs(001) substrates containing buried nanostructures, providing the first evidence of excitation transfer from NCQDs to the substrate. Results are also presented for the overgrowth of GaAs on the InAs NCQDs, addressing the all important issue of approach to removal of the chemical contamination left behind by the solvent during adsorption of the NCQDS. It is shown that high structural and optical quality buried integrated structures are feasible, thus opening a new field of investigation.
Enhanced Solubility of Cu in Ag Nanoparticles Synthesized by Inert Gas Condensation
Authors: Ceylan Abdullah , Ni C. , Ismat Shah S.
Published: April 2011

Ag-Cu alloy nanoparticles were prepared by rapid condensation of metal flux obtained by the simultaneous evaporation of high purity Cu and Ag wires on a tungsten boat in the presence of circulating He gas. Structural properties of the samples prepared at different conditions were investigated by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area diffraction (SAD) patterns. X-ray diffraction patterns showed that particles were phase separated. The particle size obtained either from Scherer's formula or the TEM images show no systematic change on the size of either Cu or Ag particles in the evaporation temperature range between 800 and 1400 °C. By using lattice constant values and Vegard's law, the composition of the particles was calculated to be 6.6 vol% Cu in Ag. Electron diffraction images revealed that particles were softly agglomerated; these electron diffraction results were also consistent with XRD results regarding phase separation. Individual diffraction rings of the Cu and Ag were observed in the SAD patterns.
Atmospheric Stability of E-Beam Deposited Optical Thin Film Stacks
Authors: Hou Ping , Sun Lianchao , Luo Fei
Published: April 2011

Optical thin films with SiO2-TiO2 stack were prepared by the technology of electron beam (e-beam) evaporation with ion beam assistant deposition (IBAD). The mechanical (stress) and optical properties of as-deposited thin films were studied as a function of exposure time in the atmospheric environment. Exposing to the air at the ambient temperature causes incremental compressive stress and spectrum profile changes, which is related to the absorption of water moisture into the films. Making a dense film is, therefore, a practical approach to improve structural stability of thin films and then the performance of optical devices.
Failure of brittle functional layers in flexible electronic devices
Authors: Goede Judith de , Bouten Piet , Médico Léonard , Leterrier Yves , Månson Jan-Anders , Nisato Giovanni
Published: April 2011

In the present study, 90 nm thick conducting tin-doped indium oxide (ITO) layers on polymer substrates are used to study the failure behaviour of brittle layers. In a two-point bending test the resistance of uniform ITO-layers and narrow ITO-lines (10 to 300 μm width) are determined as a function of the applied tensile strain. At a certain strain, the thin layer will crack and the resistance will strongly increase. This characteristic strain is analysed using a large number of samples. Early stages of crack development are studied in the fragmentation test. This paper presents the results of different failure mechanisms of thin brittle layers on the electrical conductivity of ITO-layers. When the strain in the ITO-layer increases, stable cracks of a limited length are initiated at defects in the layer (crack initiation). At the critical strain εpthe crack is no longer stable and it will propagate over the whole width of the layer (crack propagation). The experiments show a wide failure strain distribution for narrow ITO-lines. The wide distribution of defects, determining the crack initiation strain, controls the failure of narrow lines. The uniform layers show a narrow failure strain distribution. This is determined by the well-defined crack propagation strain εp.
Magnetic properties of submicron Ni-Mn-Ga martensitic thin films1
Authors: Kohl M. , Chernenko V.A. , Ohtsuka M. , Reuter H. , Takagi T.
Published: April 2011

Two series of Ni-Mn-Ga thin films with two different compositions and various thicknesses in the submicron range are investigated with respect to their structural and magnetic properties. The films are fabricated by sputter deposition on alumina substrates and subsequent heat treatment. The martensitic transformation occurs well above room temperature showing a small thermal hysteresis width of about 6 K. The magnetic properties turn out to be thickness-dependent in the submicron range. In particular, in-plane magnetic susceptibilities increase and critical field strengths for onset of saturation decrease for decreasing thickness down to 0.1 μm by factors of 3–5 depending on the chemical composition. The Curie temperature TC decreases by about 25 K for samples with TC higher than the martensitic transformation.
Electric Dipole Model and Computer Simulation of the Fracture Behavior of a Conductive Crack in a Dielectric Material
Authors: Wang Tianhong , Gao Xiaosheng
Published: April 2011

Fracture tests on poled and depoled lead zirconate titanate (PZT) ceramics indicate that purely electric fields are able to propagate the conductive cracks (notches) and fracture the samples. To understand the fracture behavior of conducting cracks in ferroelectric ceramics, an electric dipole model is proposed, in which a discrete electric dipole is used to represent the local spontaneous polarization and the force couples are used to represent the local strains. The electric dipole model provides basic solutions for microstructural modeling. The microstructural modeling is based on a domain switching mechanism. The domain structure is simulated with a grid of points where polarizations and strains vary with the applied loads. As a first step study, the microstructural modeling is conducted for a dielectric material with a conductive crack. The simulation result explains why the electric fracture toughness is much higher than the mechanical fracture toughness.
Optimizing the Thermomechanics of Shape-Memory Polymers for Biomedical Applications
Authors: Yakacki Christopher M. , Gall Ken , Shandas Robin , Ortega Alicia M. , Willett Nick , Greenberg Alan R.
Published: April 2011

We examine the shape-memory effect in polymer networks intended for biomedical applications. The polymers were photopolymerized from tert-butyl acrylate (tBA) with polyethyleneglycol dimethacrylate (PEGDMA) acting as a crosslinker. Three-point flexural tests were used to systematically investigate the thermomechanics of shape-storage deformation and shape recovery. The glass transition temperature (Tg) of the polymers varied over a range of 100°C and is dependent on the molecular weight and concentration of the crosslinker. The polymers show 100% strain recovery up to maximum strains of approximately 80% at low and high deformation temperatures (Td). Free strain recovery was determined to depend on the temperature during deformation; lower deformation temperatures (Td < Tg) decreased the temperature required for free strain recovery. Constrained stress recovery shows a complex evolution as a function of temperature and also depends on Td. The thermomechanical results are discussed in light of potential biomedical applications and a prototype stent that can be activated at body temperature is presented.
Parametric Study of Single-Walled Carbon Nanotubes Using Alcohol Catalytic Chemical Vapor Deposition
Authors: Emrah Unalan H. , Chhowalla Manish
Published: April 2011

Single-walled carbon nanotubes (SWNTs) were synthesized both in powder form and on substrates using alcohol catalytic chemical vapor deposition method (ACCVD). A detailed parametric study was conducted. As-grown SWNTs were analyzed using transmission electron microscopy (HRTEM), field-emission scanning electron microscopy (FE-SEM) and Raman spectroscopy. Nucleation and growth of SWNTs occurred within seconds after introduction of the alcohol vapor. The results show that high quality SWNTs with a narrow diameter distribution without amorphous carbon can be grown using Co acetate catalyst doped with Fe acetate above 750°C. Defective nanotubes were observed at low (450°C) and high (950°C) temperatures with the optimum temperature being 850°C. In brief, our work has taken a step towards optimizing SWNTs growth conditions using ACCVD.
Resonance Raman Spectroscopy to Study and Characterize Defects on Carbon Nanotubes and other Nano-Graphite Systems
Authors: Jorio Ado , Cançado Luiz Gustavo , Neves Bernardo R. A. , Souza Mauricio de , Fantini Cristiano , Pimenta Marcos A. , Medeiros-Ribeiro G. , Samsonidze Georgii G. , Chou Shin Grace , Dresselhaus Gene , Dresselhaus Mildred S. , Rao A. M. , Grüneis Alexander , Saito Riichiro
Published: April 2011

The use of resonance Raman spectroscopy (RRS) to study and characterize single wall carbon nanotubes (SWNTs) is discussed, focusing on preliminary efforts for the development of the RRS to characterize defects in SWNTs. The disorder-induced D-band, disorder-induced peaks just above the first-order allowed graphite G-band, as well as the intermediate frequency modes (IFMs) appearing between the RBM and the D/G spectral region are addressed. RRS on nanographite ribbons and on a step-like defect in highly ordered pyrolytic graphite (HOPG) sheds light into the problem of characterizing specific defects in nano-related carbons.
Self-Organization of Semiconductor Quantum Nanocrystals on Carbon Single-Wall Nanotubes into Close-Packed Linear Arrays
Authors: Engtrakul C. , Nedeljkovic J. M. , Kim Y.-H. , Ahrenkiel S. P. , Gilbert K. E. H. , Alleman J. L. , Zhang S. B. , Micic O. I. , Nozik A. J. , Heben M. J.
Published: April 2011

We report the synthesis of organized colloidal semiconductor nanocrystal / carbon singlewalled nanotube hybrid nanostructures. The synthetic protocol described here avoids the need for covalent chemical modification of carbon nanotube (CNT) surfaces. Specifically, InP quantum dots (QDs) and CdSe QDs were found to strongly adsorb onto the surfaces of carbon single-walled nanotubes (SWNTs) by gentle heating in organic solvents. Transmission electron microscopy (TEM) was used to characterize the semiconductor nanocrystal (NC) / SWNT assemblies, and revealed that the surfaces of the SWNT bundles template the adsorption of the NCs from solution. Small QDs were found to randomly absorb onto SWNTs, while larger QDs self-assembled into long linear chains. The nature of binding and ordering was investigated by simply considering van der Waals (vdW) forces for both NC-SWNT and NC-NC interactions. Quantum rods (QRs) were also found to adsorb along the nanotube surfaces. These findings have important implications for the synthesis of NC / SWNT hybrid nanostructures.
Probing the Phonon-Assisted Relaxation Processes in DNA-wrapped Carbon Nanotubes Using Photoluminescence Spectroscopy
Authors: Chou S. G. , Plentz F. , Jiang J. , Saito R. , Nezich D. , Ribeiro H. B. , Jorio A. , Pimenta M. A. , Samsonidze Ge. G. , Santos A. P. , Zheng M. , Onoa G. B. , Semke E. D. , Dresselhaus G. , Dresselhaus M. S.
Published: April 2011

We present a detailed photoluminescence study of a (6, 5) enriched DNA-wrapped single wall carbon nanotube (DNA-CNT) solid sample and an as-produced DNA-CNT solution. Multiple strong PL peaks were observed at excitation energies that do not correspond to the interband electronic transitions that are strongly enhanced by electronic van Hove singularities. These strong PL peaks are assigned to different mechanisms of excitation and relaxation, including one phonon, two phonon, hot luminescence processes, as well as radiative and non-radiative energy transferring mechanisms between neighboring nanotubes. These processes are assigned to different channels of phonon-assisted electron relaxation. The study shows that the electronic relaxation processes observed in PL can be used as a means to probe different physical interactions between photons, electrons, and phonons that are not separately identified in bulk semiconducting materials.
Solubility and Electrical Response of Single Walled Carbon Nanotubes with Thiolate Mediated Gold Nanoparticle Attachment
Authors: Cui Jingbiao , Daghlian Charles P. , Gibson Ursula J.
Published: April 2011

Dodecanethiol-stabilized-Au nanoparticles are successfully attached to the sidewall of as-grown single walled carbon nanotubes (SWCNTs) via a simple approach. This provides a straightforward method to functionalize and dissolve SWCNTs of full length in organic solvents. The modified nanotubes exhibit dramatic increase in tube resistance and strong gate dependence with a memory effect, which is explained in terms of nanotube structure deformation induced by surface thiolation. The mechanism for Au particle attachment is shown to be via dodecanethiol groups.
Electrophoretic Deposition of Carbon Nanotubes into Device Structures: An Approach to Integrate Nanostructures into Micro devices
Authors: Guduru Madhuri , Francis Anand , Dobbins Tabbetha A.
Published: April 2011

Charged particles in suspension tend to move when an electric field is applied. This simple phenomenon of migration of charged particles in a liquid medium and their subsequent deposition onto an oppositely charged electrode is called electrophoretic deposition (EPD), and is used in assembly of nanoparticles into microfabricated devices. This work reports the application of the EPD process for deposition of commercially available purified single-walled carbon nanotubes (CNT) onto microfabricated device structures. A direct current EPD in aqueous medium was used to position CNTs into two different microfabricated device structures: gold electrodes of 100nm thickness and gold microcantilevers. Control of the mass of CNTs deposited using EPD process is addressed in this work.
Matchstick Nanotubes: Structure Control and Properties
Authors: Jourdain Vincent , Paillet Matthieu , Poncharal Philippe , Zahab Ahmed , Loiseau Annick , Bernier Patrick , Robertson John
Published: April 2011

We report here on the catalyst features found critical in order to induce the growth of matchstick nanotubes by a sequential catalytic growth mechanism. The presence of phosphorus is required to form metal phosphide particles active for the formation of carbon nanotubes with a matchstick morphology. The metal composition does not influence the nanofilament type but strongly affect the nanotube yield. Original properties of these new periodic nanostructures are also highlighted, such as the preferential breaking at the thin nanomatch interjunctions, giving rise to individual nanomatches in suspension after ultrasonic treatment. The possibility to use this mechanism to insert carbon nanotubes with ferromagnetic nanoparticles is also reported.
On the Flexural Characteristics of Multi-walled Carbon Nanotubes
Authors: Bai Rong , Molenaur Justin , Byron Pipes R.
Published: April 2011

We use an analytical solution for bending of coaxial orthotropic cylinders to model the flexural deformation of multi-walled nanotubes with any number of layers. The simulation results show that the bending stiffness of the MWNT increases with the number of nanotube layers. For fixed number of layers, MWNT with larger inner radius has greater bending stiffness. The bending stiffness also increases with out layer radius. For certain outer radius, smaller inner radius results in a larger stiffness. The effective elastic modulus of the MWNT also increases with the number of layers and the outer radius. For the same value of the outer radius, the MWNT with smaller inner radius has a larger effective elastic modulus. As the number of layers increases, the effective modulus approaches the in-plane elastic modulus of graphene. In this work we find that the interface conditions, i.e., perfect bonding or no friction, do not affect the bending stiffness and effective elastic modulus of the MWNT. Furthermore, the cross-section of MWNT does not show any warping under bending, which suggest the classic beam theory is applicable in determining the flexural response of MWNT.
Magnetic Alignment of Carbon Nanofibers in Polymer Composites
Authors: Shi Donglu , He Peng , Lian Jie , Chaud Xavier , Beaugnon Eric , Wang Lumin , Ewing Rodney C. , Tournier Robert
Published: April 2011

Carbon nanofibers were well aligned in polymer composite magnetically at moderate fields up to 3 T. Due to the NiO-coating, carbon nanofibers exhibited strong magnetic moments that lead to alignment. Both TEM and SEM results showed the well-aligned nano-fibers in a polymer matrix. Mechanical testing showed a pronounced anisotropy in tensile strength in directions normal (12.1MPa) and parallel (22MPa) to the applied field, resulting from the well-aligned nanofibers in the polymer matrix. The mechanism of magnetic alignment due to coating of NiO on the nano fiber surface is discussed.
Band Engineering of Partially Exposed Carbon Nanotube Field-Effect Transistors
Authors: Liu Xiaolei , Luo Zhicheng , Han Song , Tang Tao , Zhang Daihua , Zhou Chongwu
Published: April 2011

We present a new approach to engineer the band structure of carbon nanotube field-effect transistors via selected area chemical gating. By exposing the center part or the contacts of the nanotube devices to oxidizing or reducing gases, a good control over the threshold voltage and subthreshold swing has been achieved. Our experiments reveal that NO2 shifts the threshold voltage higher while NH3 shifts it lower for both center-exposed and contact-exposed devices. However, modulations to the subthreshold swing are in opposite directions for center-exposed and contact-exposed devices: NO2 lowers the subthreshold swing of the contact-exposed devices, but increases that of the center-exposed devices; In contrast, NH3 reduces the subthreshold swing of the center-exposed devices, but increases that of the contact-exposed devices. A model has been developed based on Langmuir isotherm, and the experimental results can be well explained.
Competitive Etching and Oxidation of Vicinal Si(100) Surfaces
Authors: Albao Marvin A. , Liu Da-Jiang , Choi Cheol H. , Gordon Mark S. , Evans J. W.
Published: April 2011

Exposure of a vicinal Si(100) surface to oxygen at around 550 C produces etching-mediated step recession. In addition, some oxide islands are formed which locally pin receding steps. We develop an atomistic lattice-gas model for this process which accounts for the interplay between oxygen surface chemistry (adsorption, diffusion, oxide formation, and etching via SiO desorption) and the silicon surface and step dynamics (anisotropic diffusion and aggregation of di-vacancies formed by etching, and ad-dimer attachment-detachment dynamics at steps incorporating anisotropic energetics). Kinetic Monte Carlo simulation of this model produces step morphologies retaining some qualitative but not quantitative features of their equilibrium structure (alternating rough SB steps and smooth SA steps), except for pinning which produces protruding “fingers”. These features are seen in Scanning Tunneling Microscopy studies.
Droplet Behaviour in Inkjet Printing
Authors: Stringer Jonathan E , Smith Patrick J , Derby Brian
Published: April 2011

The interaction of an inkjet printed droplet with a substrate is of importance when determining the final size and shape of deposits. A simple model is proposed that relates droplet diameter, printed dot pitch and equilibrium contact angle to as-printed track width. Reasonable agreement was found between the model and final track width, with slight over-prediction accounted for by removal of the organic component of the ink during heat treatment. Immediately after droplet impact, the drop may spread to a considerably greater extent than predicted by equilibrium because of the kinetic energy of the droplet in flight. Simulations of droplet impact showed that the maximum droplet spread decreased linearly with equilibrium contact angle. Recoil of these droplets towards their equilibrium shape occurred above a threshold contact angle. This threshold was greater than expected, suggesting an energy barrier preventing recoil or the kinetics of recoil being too slow for recoil to occur within the timeframe of this study.
Repository performance assessment and advanced fuel cycle models for input to decision making of options for nuclear waste and resource management
Authors: Small J.S. , Zimmerman C.H. , Parker D.R. , Robbins C. , Bond A.E. , Stevens G.A.
Published: April 2011

A methodology and computer software is described which can be used to track the inventory of radionuclides as they are affected by various nuclear, physical and chemical processes during reactor, storage, effluent and disposal phases of the nuclear fuel cycle. Such a model is required to provide an assessment of economic, environmental and societal performance indicators which underpin decisions regarding options for the use and management and nuclear materials. An example generic deep repository model is described which can be used to provide an indicator of environmental performance of vitrified high level waste and UO2 and mixed oxide (MOX) spent fuels. The assessment models highlight the significance of the I-129 fission product which necessitates the use of appropriate dose assessment models to be considered for each process step of the nuclear fuel cycle in order that a complete environmental assessment of process options can be determined.
Sorption of Molybdenum(VI) on Synthetic Magnetite
Authors: Rovira Miquel , de Pablo Joan , Ignasi Casas I. , Giménez Javier , Clarens Frederic , Martinez-Lladó Xavier
Published: April 2011

In this study we experimentally investigated the interaction of Mo(VI) with magnetite, which is a corrosion product of steel. The work was conducted with commercial magnetite, and we studied the influence of pH, pe and solid/liquid ratio on Mo sorption. A Surface Complexation Model (SCM) has been applied tothe experimental data, allowing to explain the results using the Diffuse Layer Model (DLM) and by considering the formation of the monodentate complex: >FeOMo(OH)5. At pH 2, experimental data were satisfactorily fitted to a a Langmuir isotherm.
Field Test of Ethanol/Bentonite Slurry Grouting into Rock Fracture
Authors: Asada Motoyuki , Nakashima Hitoshi , Ishii Takashi , Horiuchi Sumio
Published: April 2011

Crystalline rocks have fractures which may cause unexpected routes of groundwater seepage. Cement grouting is one of the most effective methods to minimize seepage; however, cement materials may not be suitable for the purpose of extra-long durability, because cement is neutralized or degraded by chemical and physical influence of chemical reaction.

Natural clay like bentonite is one of the most promising materials for seepage barrier; however, water/bentonite grout is so viscous that enough amount of bentonite can not be grouted into rock fractures. To increase bentonite content in grout with low viscosity, the utilization of ethanol as a mixing liquid was studied. Ethanol suppresses bentonite swelling, and more bentonite can be injected more than that of water/bentonite slurry. In this paper, grouting into in-situ rock mass fracture from the ground surface was tested to investigate the barrier performance and workability of ethanol/bentonite slurry as a grouting material.