bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal Stability of Nanostructured TiN-TiB2 Thin Films
Authors: Mayrhofer Paul H. , Mitterer Christian 
Published: April 2011

ABSTRACTNanocrystalline hard films have attracted increasing interest for wear-resistant applications. Especially, films within the system Ti-B-N with its numerous different phases are ideal candidates for materials science based studies on the nanoscale. In physical vapor deposited Ti-B-N films the nanostructure arises during growth by segregation-driven renucleation resulting in 2–3 nm sized TiN and TiB2 crystals. These films exhibit a hardness of ∼ 42 GPa in the as-deposited state which increases to ∼ 52 GPa during thermal annealing in vacuum. Here we show, that as-deposited films have a remarkable fraction of disordered regions surrounding TiN and TiB2 nanocrystals. During thermal annealing, the structural rearrangement causes the formation of compact boundary areas, leading to a hardness increase. At temperatures higher than 900 °C, the occurring B-loss, grain-growth, and recrystallization cause the hardness to decrease.
Surface Instability of Microscale Multilayer Thin Film System
Authors: Wei Yueguang , Jiang Di , Cao Ajing , Zhao Haifeng 
Published: April 2011

ABSTRACTFundamental relations of surface instability for micro-scale multilayer thin film systems are derived based on the Hill and Hutchinson bifurcation theory and the volume average integral. In the present relations, a size effect is considered through generalizing the plastic hardening modulus to include the strain gradient hardening effects. By using the model, firstly, the parameter-controlled instability region is divided and analyzed, secondly, the surface instability of the multilayer thin films are analyzed. In the surface instability analysis, several kinds of failure band formations are obtained, such as the kink bands and the compressive buckling bands in vertical direction and in inclined direction. Moreover, the failure mechanism of the multilayer thin film system due to surface instability is used to interpret the microstructure features of the surface-nanocrystallization materials.
Thermal Grooving in Single versus Multilayer Thin Films
Authors: Anderson Peter M. , Wang Jue , Narayanaswamy Sridhar 
Published: April 2011

ABSTRACTA 2D analytic result is presented for the penetration distance P of grain boundary grooves as a function of time t during heating and straining of polycrystalline multilayer thin films with immiscible phases. These grooves can ultimately pinch off individual layers. The result shows that P ∼ t0.25 initially and P ∼ t at longer time. This new analysis contrasts single- versus multilayer thin film response.
The Residual Stress Effect on Microstructure and Optical Property of ZnO Films produced by RF Sputtering
Authors: Ryu Sang , Kim Youngman 
Published: April 2011

ABSTRACTZnO films were produced on the Si(100) and sapphire(0001) wafers by RF magnetron sputtering in terms of processing variables such as substrate temperature and RF power. The stress in films was obtained from the Stoney's formula using a laser scanning device. The stress levels in the films showed the range from ∼40MPa to ∼-1100MPa depending on processing variables.SEM was employed to characterize the microstructure of the films. As the substrate temperature increased, the film surface became rougher and the films showed coarser grains. The optical property of the films was studied by PL measurements. At the highest substrate temperature 800°C the film exhibited sharper UV peaks unlike other conditions.
Residual stress and microstructural evolution in thin film materials for a micro solid oxide fuel cell (SOFC).
Authors: Quinn David , Mark Spearing S. , Wardle Brian L. 
Published: April 2011

ABSTRACTThe stability of multilayered membrane structures is a major challenge in the development of microfabricated solid oxide fuel cells (SOFC). The work presented here explores residual stress in sputter-deposited yttria stabilized zirconia (YSZ) thin films (5nm – 1000nm thickness) as a function of deposition pressure and substrate temperature. The results indicate variations in intrinsic stress from ∼0.5GPa compressive to mildly tensile (∼50 MPa). Microstructure is characterized by x-ray diffraction (XRD). The evolution of intrinsic stress with temperature is investigated by thermally cycling YSZ films deposited on silicon wafers. Observed changes of 100s of MPa in the intrinsic stress component of the film serve as indicators of possible changes in microstructure. Such changes in microstructure are subsequently characterized using x-ray diffraction of as-deposited and annealed films. Correlations with relevant mechanisms and models of residual stress evolution are discussed. Finally, use of such residual stress data in the fabrication and design of mechanically stable multilayered membranes for micro SOFC devices is discussed.
Mode–I Fracture Toughness of Tetrahedral Amorphous Diamond-like Carbon (ta-C) MEMS
Authors: Jonnalagadda K. , Cho S.W. , Chasiotis I. , Friedmann T.A. , Sullivan J.P. 
Published: April 2011

ABSTRACTMode-I fracture toughness studies were conducted on hydrogen-free tetrahedral amorphous diamond-like carbon (ta-C) MEMS specimens of various thicknesses. Mathematically sharp edge pre-cracks were generated through micro indentation on the Silicon dioxide sacrificial layer. An atomic force microscope (AFM) was employed to measure the precise length and orientation of each pre-crack. Upon wet etching and release the freestanding uniform width and varying thickness MEMS-scale specimens were tested in Mode-I using a custom-made micro-tensile tester. Fracture toughness values were computed from the test data using linear elastic fracture mechanics (LEFM) for a finite width specimen with an edge crack in the fixed grip loading configuration. The average Mode-I fracture toughness for 0.5 micron thick specimens was found to be while the average mode-I fracture toughness for 1 micron specimens was .
Cast NiTi Shape-Memory Alloys
Authors: Ortega Alicia M. , Frick Carl P. , Tyber Jeffrey , Gall Ken , Maier Hans J. 
Published: April 2011

ABSTRACTThe purpose of this study is to investigate the structure and properties of polycrystalline NiTi in its cast form. Although it is commonly stated in the literature that cast NiTi has poor shape-memory behavior, this study demonstrates that with appropriate nano/micro structural design, cast NiTi possesses excellent shape-memory properties. Cast NiTi shape-memory alloys may give rise to a new palette of low-cost, complex-geometry components. Results from two different nominal compositions of cast NiTi are presented: 50.1 at.%Ni and 50.9 at.%Ni. The cast NiTi showed a spatial variance in grain size and a random grain orientation distribution throughout the cast material. However, small variances in the thermo-mechanical response of the cast material resulted. Transformation temperatures were slightly influenced by the radial location from which the material was extracted from the casting, showing a change in Differential Scanning Calorimetry peak diffuseness as well as a change in transformation sequence for the 50.9 at.%Ni material. Mildly aged 50.9 at.%Ni material was capable of full shape-memory strain recovery after being strained to 5% under compression, while the 50.1 at.%Ni demonstrated residual plastic strains of around 1.5%. The isotropic and symmetric response under tensile and compressive loading is a result of the measured random grain orientation distribution. The favorable recovery properties in the cast material are primarily attributed to the presence of nanometer scale precipitates, which inhibit dislocation motion and favor the martensitic transformation.
Micro-fluidic applications of telephone cord delamination blisters
Authors: Volinsky Alex A. , Waters Patrick , Wright Gregory 
Published: April 2011

ABSTRACTArgon pressure significantly affects the residual stress in sputter deposited thin films and coatings. In case of W thin films, high residual stresses on the order of 1–2 GPa are quite common. With the rest of sputtering parameters being equal, argon pressure determines the sign and the value of residual stress.When the amount of stored elastic energy in the film due to the residual stress exceeds the interfacial toughness, fracture normally occurs. Telephone cord buckling delamination blisters are commonly observed in compressed thin films. These mechanically active features form by a loss of adhesion between the film and the substrate due to residual stress relief, and exhibit directional growth under certain conditions. This paper considers telephone cord delamination channels for micro-fluidics applications, as this could to be a valuable, reliable, and inexpensive method of forming open channels.
Electrochemical Tuning of Single-Wall Carbon Nanotube Mat and Investigations on Actuator Mechanism
Authors: Gupta S. , Hughes M. , Robertson J. 
Published: April 2011

ABSTRACTElectrochemical tuning of single-wall carbon nanotubes has been investigated using in situ Raman spectroscopy. We built a linear actuator from single-wall carbon nanotube mat and studied in several alkali metal (Li, Na, and K) and alkaline earth (Ca) halide solutions. The variation of bonding with electrochemical biasing was monitored using in situ Raman. This is since Raman can detect changes in C-C bond length: the radial breathing mode (RBM) at ∼190 cm−1 varies inversely with the nanotube diameter and the G band at ∼1590 cm−1 varies with the axial bond length. In addition, the intensities of both the modes vary significantly in a nonmonotonic manner pointing at the emptying/depleting or filling of the bonding and anti-bonding states - electrochemical charge injection. We discuss the variation of spectroscopic observables (intensity/frequency) of these modes providing valuable information on the charge transfer dynamics on the single-wall carbon nanotubes mat surface. We found the in-plane compressive strain (∼ -0.25%) and the charge transfer per carbon atom (fc ∼ -0.005) as an upper bound for the electrolytes used i.e. CaCl2. These results can be quantitatively understood in terms of the changes in the energy gaps between the one-dimensional van Hove singularities in the electron density of states arising possibly due to the alterations in the overlap integral of π bonds between the p orbitals of the adjacent carbon atoms. Moreover, the extent of variation of the absolute potential of the Fermi level or alternatively modification of band gap is estimated from modeling Raman intensity to be around 0.1 eV as an upper bound for CaCl2.
Kinematic and Topological Models of Martensitic Interfaces
Authors: Pond Robert C. , Ma Xiao , Chai Yaw W. , Hirth John P. 
Published: April 2011

ABSTRACTThe Phenomenological Theory of Martensite Crystallography, developed fifty years ago, envisages martensitic interfaces to be invariant planes of the shape transformation. This theory has been very successful, but neither incorporates the notion of atomic relaxations at martensitic interfaces, nor explicitly demonstrates that such interfaces are glissile. A new model, called the Topological Model, is proposed that addresses these issues. Predictions of the habit plane and relative orientation of the crystals according to the two models are compared and contrasted.
A Unified Model for Hysteresis in Ferroic Materials
Authors: Seelecke Stefan , Smith Ralph C. 
Published: April 2011

ABSTRACTThis paper provides a unified modeling framework for ferroelectric, ferromagnetic and ferroelastic materials operating in hysteretic and nonlinear regimes. Whereas the physical mechanisms which produce hysteresis and constitutive nonlinearities in these materials differ at the microscopic level, shared energy relations can be derived at the lattice, or mesoscopic, scale. This yields a class of models which are appropriate for homogeneous, single crystal compounds. Stochastic homogenization techniques are then employed to construct macroscopic models suitable for nonhomogeneous, polycrystalline compounds with variable effective fields or stresses. This unified methodology for quantifying hysteresis and constitutive nonlinearities for a broad class of ferroic compounds facilitates both material characterization and subsequent model-based control design. Attributes of the models are illustrated through comparison with piezoceramic, magnetostrictive and thin film SMA data.
Anisotropic saturable absorption of single wall carbon nanotubes aligned in polyvinyl alcohol
Authors: Rozhin Aleksey G. , Sakakibara Youichi , Kataura Hiromichi , Matsuzaki Shun , Ishida Kohtaro , Achiba Yohji , Tokumoto Madoka 
Published: April 2011

ABSTRACTWe report anisotropic optical absorption and saturable absorption (SA) properties of aligned single wall carbon nanotubes (SWNT) embedded in the mechanically stretched polyvinyl alcohol (PVA) film. Polarized absorption spectra of the film showed a strong anisotropy for the near-infrared band gap transition of semiconductor SWNT with a dichroic ratio of 7.4, indicating the good alignment of the embedded SWNT. The SA property of the band gap transition measured using a polarized femtosecond fiber laser showed a strong polarization angle dependence for the stretched film. When the polarization of light is parallel to the stretching direction, the absorption saturation of the stretched film became more efficient than that of the unstretched film because of the apparently stronger transition moment.
Raman studies of suspensions and solutions of singlewall carbon nanotubes
Authors: Izard N. , Pénicaud A. , Anglaret E. 
Published: April 2011

ABSTRACTRaman spectroscopy is used to probe the structure and electronic properties of nanotubes dispersed in a liquid phase. We show that the radial breathing modes are upshifted in suspensions due to the molecular pressure of the solvent. On the other hand, we directly probe charge transfer in solutions of nanotube polyelectrolytes and its reversibility after oxydation in air.
Quantitative evaluation of bundling effect on single walled carbon nanotubes by resonance Raman spectra
Authors: Luo Zhengtang , Li Rongfu , Kim Sang Nyon , Papadimitrakopoulos Fotios 
Published: April 2011

ABSTRACTThe radial breathing mode (RBM) region of the resonance Raman spectra of HiPco single walled carbon nanotubes (SWNTs) was investigated as a function of aggregation. This was modeled using an energetic deviation term (ΔE), imparted to the optical transitions (Eii(n, m)) by bundling effect. Eii(n, m) values obtained from photoluminescence (PL) measurements were used to reconstruct these RBM profiles. The simulation revealed that the PL-determined Eii(n, m) set provided a good fit in terms of peak position. Providing an accurate set of Eii(n, m) values becomes available, the RBM profile reconstruction methodology discussed herein could greatly enhance our ability to model a range of physicochemical changes to the immediate environment of SWNTs.
Integration Of Carbon Nanotubes Into Device Structures
Authors: Lägel B. , Schumacher J. D. , Nguyen N. , Zivanovic B. , Schlaf R. 
Published: April 2011

ABSTRACTCarbon nanotubes have shown promising properties for applications in electronic circuits and other device structures. Several device structures have been demonstrated in recent years by manual manipulation of single nanotubes. The integration of large numbers of nanotubes on wafer size substrates, however, has been a challenge.Our approach addressing this issue utilizes nano-patterning methods in combination with plasma enhanced chemical vapor deposition to directly assemble carbon nanotubes on wafer structures. A secondary formation step is used to actually form device structures connecting the nanotubes to electrode structures. We present first results demonstrating the feasibility of our approach. Electrode structures were prepared using multi-step electron beam lithography processes. Carbon nanotubes were grown in pre-defined locations, and contact formation procedures were carried out to establish multi-terminal contact structures.
A New Carbon Nanotube-Based Field Enhanced Thermionic Cathode
Authors: Jin Feng , Day Christopher 
Published: April 2011

ABSTRACTThe electron emission properties and field enhancement effects of carbon nanotubes (CNTs) have been extensively studied. However, all of these studies focus only on the field emission aspect of the materials and its application in cold cathode electron emitters. So far, we have not seen any studies in the literature that link CNTs with thermionic cathodes, which are an equally important cathode type because of their many applications. We present a study of field enhanced electron emissions from a new type of cathode: the CNT-based field enhanced thermionic cathode. This new cathode consists of a metal substrate with CNTs grown on top of its surface. The CNTs are coated with thermionic emission materials (BaO, SrO, and CaO). This unique cathode structure takes advantage of both the field enhancement effect from CNTs and the high electron emission capability of thermionic materials. The electron emission properties of this new cathode, particularly the field enhancement factor and effective work function, are compared with the conventional thermionic cathodes that are made of same oxide coating.
Nanotube-based systems for broadband optical limiting: towards an operational system
Authors: Izard N. , Riehl D. , Anglaret E. 
Published: April 2011

ABSTRACTNanotube-based systems are good candidates for optical limiting against broadband laser pulses. We explore new routes to improve their limiting performances. We show that the diameter of the nanotubes is a key factor to control the performances. On the other hand, we demonstrate that chemically modified nanotubes can be mixed with organic chromophores, leading to high performance composite limiting systems which are particularly efficient in the nanosecond regime due to the cumulative effects of nonlinear scattering and multiphoton absorption.
Corrections to the Optical Transition Energies in Single-Wall Carbon Nanotubes of Smaller Diameters
Authors: Samsonidze Georgii G. , Saito Riichiro , Jiang Jie , Grüneis Alexander , Kobayashi Naoki , Jorio Ado , Chou Shin G. , Dresselhaus Gene , Dresselhaus Mildred S. 
Published: April 2011

ABSTRACTOptical spectroscopy characterization of carbon nanotube samples requires accurate determination of their band structure and exciton binding energies. In this paper, we present a non-orthogonal density-functional based tight-binding calculation for the electronic transition energies in single-wall carbon nanotubes. We show that the curvature-induced rehybridization of the electronic orbitals, long-range atomic interactions, and geometrical structure relaxation all have a significant impact on the electronic transition energies in the small diameter limit. After including quasiparticle corrections and exciton binding energies, the calculated electronic transition energies show good agreement with the experimental transition energies observed by photoluminescence and resonance Raman spectroscopy.
Carbon Nanotube Electron Sources for Electron Microscopes
Authors: Jonge Niels de , Oostveen Jim T. , Rooij Theo van , Allioux Myriam , Doytcheva Maya , Kaiser Monja , Teo Kenneth B. K. , Lacerda Rodrigo G. , Milne William I. 
Published: April 2011

ABSTRACTHigh-quality electron sources can be made from individual multi-walled carbon nanotubes. A process was developed allowing the control over 1) the length of the fraction of the nanotube protruding from the support tip, 2) the contact length of the nanotube with the support tip, 3) the diameter of the nanotube. In addition, the cap of the nanotube was closed and the nanotube was cleaned thoroughly. The field emission model successfully describes the electron emission process of these electron sources and the work function is 5.1 eV. The emitters show a highly stable emission, as expected on account of the extremely stable structure of the carbon nanotube.
Cluster Diffusion and Coalescence on Metal Surfaces: applications of a Self-learning Kinetic Monte-Carlo method
Authors: Rahman Talat S. , Kara Abdelkader , Karim Altaf , Trushin Oleg 
Published: April 2011

ABSTRACTThe Kinetic Monte Carlo (KMC) method has become an important tool for examination of phenomena like surface diffusion and thin film growth because of its ability to carry out simulations for time scales that are relevant to experiments. But the method generally has limited predictive power because of its reliance on predetermined atomic events and their energetics as input. We present a novel method, within the lattice gas model in which we combine standard KMC with automatic generation of a table of microscopic events, facilitated by a pattern recognition scheme. Each time the system encounters a new configuration, the algorithm initiates a procedure for saddle point search around a given energy minimum. Nontrivial paths are thus selected and the fully characterized transition path is permanently recorded in a database for future usage. The system thus automatically builds up all possible single and multiple atom processes that it needs for a sustained simulation. Application of the method to the examination of the diffusion of 2-dimensional adatom clusters on Cu(111) displays the key role played by specific diffusion processes and also reveals the presence of a number of multiple atom processes, whose importance is found to decrease with increasing cluster size and decreasing surface temperature. Similarly, the rate limiting steps in the coalescence of adatom islands are determined. Results are compared with those from experiments where available and with those from KMC simulations based on a fixed catalogue of diffusion processes.
Corrosion of archaeological model glasses after 32 years of burial at Ballidon
Authors: McLoughlin Sean D. , Hyatt Neil C. , Hand R. J. , Lee William E. 
Published: April 2011

ABSTRACTThe groundwater corrosion of three archaeological model glass compositions, a replica Roman glass (B1), a medieval glass (B2) and a 17th century glass (B3), recovered from the Ballidon burial site, were investigated by field emission scanning electron microscopy. Given the equivalent burial conditions for all three glasses, the different corrosion mechanisms of these glasses are dependent principally upon composition, and in particular the dominant alkali and network former content. Composition B1 was found to the most durable glass and showed progressive Na leaching coupled with dissolution of the silicate matrix in the outermost 5μm after 32 years of burial. The B2 and B3 compositions were found to be less durable and corroded via congruent dissolution of the silicate matrix and in situ condensation, resulting in the formation of a discrete 5-15μm thick layer after only 1 year of burial. The formation of a protective Ca-rich surface layer was observed for B2, hindering successive inward growth of the dissolution reaction and favouring localised pitting of the extant layer. The protective surface phenomenon was not observed for B3, and a large increase in layer thickness was observed after nine years of burial.