bluuebunny/crossref_metadata_2025_split huggingface dataset:
Amorphization of Nanolaminates during Severe Plastic Deformation: Molecular Simulations in the Cu-Zr System
Authors: Lund Alan C. , Schuh Christopher A. 
Published: June 2019

AbstractMechanical alloying techniques, which use plastic deformation to effect structural changes, are commonly used to prepare nanostructured metals with exemplary mechanical properties. When these nanostructured metals are subjected to further straining fully amorphous alloys can result, but there is little understanding of the atomic-scale mechanisms behind this amorphization. In the present work, we explore the final stages of such a mechanical alloying process via molecular simulations. Initial Cu-Zr nanolaminates are sequentially strained and consolidated, and the amorphization process is followed explicitly. The results are in qualitative agreement with existing experimental data, and provide insight into experimentally inaccessible features of the structural evolution.
Sulfonated Polystyrene Ionomers Neutralized with Mixtures of Various Cations Studied by Dynamic Mechanical and Small-Angle X-Ray Scattering Techniques
Authors: Jeon Ho Seung , Song Ju-Myung , Kim Joon-Seop 
Published: June 2019

AbstractThe effects of the addition of mixed cations, i.e. Na+/Cs+, Ba2+/Cs+, and Ba2+/Zn2+, to the acid form sulfonated styrene copolymers on their dynamic mechanical properties and morphology were investigated. It was found that the matrix glass transition temperatures did not change with the ratio of the one cation to the other. As expected, however, the ratio of one cation to the other in the mixed cations affected cluster glass transition temperatures significantly. It was also found that the activation energies for the glass transitions for the matrix phase remained constant, while those for the cluster phase changed with the ratio of the two cations. In addition, the position of the SAXS peak was found to be affected by the type of cations. From the results obtained above, the decrease in the cluster Tg with increasing the amount of cesium and zinc cations in Na/Cs, Ba/ Cs, and Ba/Zn mixtures, were explained on the basis of the considerations of the size, charge, and type of cations, which alter the degree of clustering as well as ion-hopping mechanism.
Grain Size Effects on the Adhesion of Thin Ductile Films
Authors: Cordill M.J. , Muppidi T. , Bahr D.F. 
Published: June 2019

AbstractGrain size can be controlled by varying the process conditions used to deposit the film and post growth processing. This study examines how the grain size will impact the mechanical properties, hardness and adhesion, of thin ductile films on brittle substrates. The grain structures of copper and tin films were examined using OIM and AFM. The interfacial fracture toughness of each film was calculated using a tungsten overlayer and mechanics based models. The hardnesses of the films were correlated to the measured interfacial fracture toughness, and demonstrate that increased hardness correlates to an increased sensitivity to the Mode II component of loading.
Anisotropy of Nanoindentation – a tool for the determination of nanocrystal orientation ?
Authors: Christopher David , Kenny Steven , Smith Roger , Richter Asta , Wolf Bodo , King Bruce 
Published: June 2019

AbstractThe pile up patterns arising in nanoindentation are shown to be indicative of the sample crystal symmetry. To explain and interpret these patterns, complementary molecular dynamics simulations and experiments have been performed to determine the atomistic mechanisms of the nanoindentation process in single crystal Fe{110}. The simulations show that dislocation loops start from the tip and end on the crystal surface propagating outwards along the four in-plane <111> directions. These loops carry material away from the indenter and form bumps on the surface along these directions separated from the piled-up material around the indenter hole. Atoms also move in the two out-of-plane <111> directions causing propagation of subsurface defects and pile-up around the hole. This finding is confirmed by scanning force microscopy mapping of the imprint, the piling-up pattern proving a suitable indicator of the surface crystallography. Experimental force-depth curves over the depth range of a few nanometers do not appear smooth and show distinct pop-ins. On the sub-nanometer scale these pop-ins are also visible in the simulation curves and occur as a result of the initiation of the dislocation loops from the tip.
Mechanisms of misfit strain relaxation in epitaxially grown BLT (Bi4-xLaxTi3O12, x = 0.75) thin films
Authors: Kim Hyung Seok , Oh Sang Ho , Suh Ju Hyung , Park Chan Gyung 
Published: June 2019

AbstractMechanisms of misfit strain relaxation in epitaxially grown Bi4-xLaxTi3O12 (BLT) thin films deposited on SrTiO3 (STO) and LaAlO3 (LAO) substrates have been investigated by means of transmission electron microscopy (TEM). The misfit strain of 20 nm thick BLT films grown on STO substrate was relaxed by forming misfit dislocations at the interface. However, cracks were observed in 100 nm thick BLT films grown on the same STO. It was confirmed that cracks were formed because of high misfit strain accumulated with increasing the thickness of BLT, that was not sufficiently relaxed by misfit dislocations. In the case of the BLT film grown on LAO substrate, the magnitude of lattice misfit between BLT and LAO was very small (~1/10) in comparison with the case of the BLT grown on STO. The relatively small misfit strain formed in layered structure of the BLT films on LAO, therefore, was easily relaxed by distorting the film, rather than forming misfit dislocations or cracks, resulting in misorientation regions in the BLT film.
Strain Relaxation by Dislocation Arrays in Thin Films
Authors: Pant Prita , Baker Shefford P. 
Published: June 2019

AbstractAn analytical model for strain relaxation by misfit dislocation arrays in thin films is presented that takes into account all components of the strain tensor, including shear strains. The model is developed for (001) films and applied to strain relaxation in (011) oriented FCC metal films. Our results show that shear strains strongly influence the total strain energy of the film. Since both the critical strain for dislocation formation, and the equilibrium spacing of dislocations in arrays depend on the minimum energy values, these quantities are found to be different from those predicted by previous models. This model is useful for understanding both critical strain data and strain relaxation in films.
A CombinedAb Initioand Bond-Order Potentials Study of Cohesion in Iridium
Authors: Cawkwell Marc J. , Nguyen-Manh Duc , Vitek Vaclav , Pettifor David G. 
Published: June 2019

AbstractThe extremely high melting point and excellent resistance to oxidation and corrosion offered by iridium suggest numerous applications of this transition metal in static components at high temperatures and in aggressive environments. However, the mechanical and physical properties of f.c.c. Ir exhibit numerous anomalies when compared to other metals that crystallize in the f.c.c. structure. Notable examples include a negative Cauchy pressure, 1/2 (C12 – C44), brittle transgranular cleavage after a period of plastic flow even in pure single crystals and anomalous [ΆΆ0] branches in the phonon spectra. Atomistic studies of extended defects are needed to elucidate the origin of anomalous mechanical properties, such as brittleness. For this purpose we developed a Bond-Order Potential (BOP), anO(N)tight-binding formalism, employing physically transparent parameterizations that use experimental andab initiodata, generated in this study using the Full Potential Augmented Plane Wave plus Local Orbitals (APW+lo) method. The constructed BOP reproduces then both equilibrium as well as a variety of nonequilibrium properties of Ir and represents an excellent description of cohesion in f.c.c. Ir. This description of interatomic interactions is imminently suitable for studies of defects, such as dislocations and grain boundaries, that control plastic deformation and fracture.
Statistical Dislocation Dynamics – Multiplication and Long Range Interactions
Authors: Zaiser Michael , El-Azab Anter 
Published: June 2019

AbstractWe discuss dislocation multiplication and long range interactions in the framework of threedimensional (3-D) statistical dislocation dynamics. It is found that the long range interactions render the conservation equation for the ensemble-averaged dislocation density nonlinear and nonlocal. It is also shown that the conservation equation for the dislocation density must be supplemented by a gauge constraint in order to account for dislocation multiplication.
Generalized Quasicontinuum Approach to Atomistic-Continuum Modeling of Complex Oxides
Authors: El-Azab Anter , Trease Harold 
Published: June 2019

AbstractA formalism of the quasicontinuum method suitable for atomistic-continuum modeling of oxide crystals is presented. Multiple interacting quasicontinua, one per sublattice, which overlap in the physical crystal space, are used to model the oxide crystals. The method is implemented with the shell model for atomic interactions in ionic crystals, along with the Wolf's method for treating the long-range forces. Results are presented for the structural relaxation of strained and unstrained Fe2O3 crystal under periodic boundary conditions.
Modeling of Corrosion Protection Provided by an Aluminum-Based Clad Exposed to Atmospheric Conditions
Authors: Presue Francisco J. , Kelly R.G. 
Published: June 2019

AbstractA computational mass transport framework for occluded region corrosion was extended to study alloys exposed to the thin electrolytes characteristic of atmospheric corrosion. Of interest were the interactions of an aluminum-clad layer with its Al-substrate in the vicinity of a scratch. The model focuses on open circuit conditions and local galvanic couples. Accurate electrochemical kinetics for metallic clad and bare AA2024-T3 are used, including the observed decrease in the pitting potential with increasing chloride concentration. The model has been applied to studies of the parameters that affect the throwing power of metallic claddings (e.g., scratch size, [Cl-], ipass, idl). Two geometries were investigated: a 1-D model and a square sample (two spatial dimensions) with a scribed cross, the latter simulating to what is usually done experimentally in exposure testing. A quantitative computation of the throwing power of metallic cladding on AA2024-T3 in thin electrolytes was achieved, including the effect of the criterion for scratch protection. For the base case of electrochemical behavior studied, a loss of protection ability was observed between a scratch size of 50 μm and 500 μm for the most conservative protection criterion (i.e., protection is achieved when the potential of all points in the scratch is at or below the pitting potential of the cladding). When a less conservative protection criterion is used, the size of the scratch that can be protected increased to between 500 μm and 3500 μm.The metallic cladding modeling also demonstrated the equivalence of reducing the ipass of the clad or increasing the idl for oxygen reduction on the AA2024-T3 on the size of the scratch that can be protected. A less than linear dependence was found between these parameters and the scratch size that can be protected. An order of magnitude reduction in ipass (or increase in idl) led to a decrease of anywhere from 40% to 90% in the scratch size that was protected. Two competing effects of increasing the chloride concentration in the thin electrolyte were observed. Higher chloride concentrations increased the throwing power (due to increased conductivity), but they also lowered the pitting potential of both the cladding and the base material. In our simulations, the former dominated the latter, indicating better protection of scratches at higher chloride concentrations, with the extent of the effect depending on the protection criterion used.
The Impact of Annealing on the Corrosion Mechanism of Copper Films
Authors: Ernur D. , Carbonell L. , Maex K. 
Published: June 2019

AbstractWe investigated the corrosion mechanism of copper films. Based on our results regarding the morphology of the Cu surface, examined by scanning electron microscopy (SEM) and focused ion beam (FIB), it is shown that with an inorganic acid-based model CMP solution corrosion is initiated at the grain boundaries. In contrast, for an organic acid-based solution, corrosion starts with no preferential location. Some of the samples received an additional anneal after the CMP process was completed to monitor the influence of annealing on the corrosion mechanism by the acid solutions. Presence of facets especially after treatment with the inorganic acid-based model CMP solution suggests that a different mechanism governs the initiation and the evolution of corrosion. Desorption of the impurities during annealing, which is monitored by Atmospheric Pressure Ionized Mass Spectrometry (APIMS) revealed desorbing species from the copper films that could originate from the additives used in the Cu plating bath.
Nanocrystalline Germanium and Germanium Carbide Films and Devices
Authors: Niu Xuejun , Booher Jeremy , Dalal Vikram L. 
Published: June 2019

AbstractNanocrystalline Ge and its alloys with C are potentially useful materials for solar cells, thin film transistors and image sensors. In this paper, we discuss the growth and properties of these materials using remote, low pressure ECR plasma deposition. The materials and devices were grown from mixtures of germane, methane and hydrogen. It was found that high hydrogen dilutions (>40:1) were needed to crystallize the films. Studies of x-ray spectra revealed that the grains were primarily <220> oriented. The grain size was a strong function of hydrogen dilution and growth temperature. Higher growth temperatures resulted in larger grain size. High hydrogen dilution tended to reduce grain size. These results can be explained by recognizing that excessive amounts of bonded H can inhibit the growth of <220> grain, which is the thermodynamically favorable direction for grain growth. Grain sizes as large as 80 nm were obtained in nc-Ge. Addition of C reduced the crystallinity. Mobility and carrier concentrations in nc-Ge were measured using Hall effect. Mobility values of ˜5cm2/V-sand carrier concentrations of ˜1x1016/cm3were obtained in larger grains. p+nn+ devices were fabricated on stainless steel substrates and compared with similar devices deposited in nc-Si:H. It was found that the voltage decreased and current increased in nc-Ge devices, in comparison with devices in nc-Si:H. Addition of C to Ge devices increased the open circuit voltage and shifted the quantum efficiency to larger photon energies, as expected.
Effect of Fermi Level Position in Intrinsic a-Si:H on the Evolution of Defect States under Light Exposure.
Authors: Zeman M. , Nádaždy V. , Durný R. , Metselaar J.W. 
Published: June 2019

AbstractThe evolution of the programmed defect-state distributions in intrinsic hydrogenated amorphous silicon (a-Si:H) due to light soaking was qualitatively determined from charge deep-level transient spectroscopy. The defect-state distribution in a-Si:H was programmed by applying a particular bias voltage on the metal-oxide-semiconductor structure while annealing the structure above the equilibration temperature. The programmed distributions simulate defect-state distributions in different parts of an actual a-Si:H solar cell, particularly in the intrinsic regions close to the p/i and i/n interfaces.The defect-state distribution in the bulk of the intrinsic layer is characterized by comparable contributions from the positively charged defect states above midgap, Dh, neutral states, Dz, and negatively charged states below midgap, De. In the programmedp-type (n-type) defect-state distribution there is an excess of the Dh (De) states. Light exposure modifies the p-type distribution that evolves to a broad distribution of states with a maximum around midgap. This distribution is dominated by Dz states with substantial contributions from Dh and De states. In case of n-type distribution light soaking only slightly influences the distribution by removing a part of the Dh states and by a small increase of Dz and De states.
Observation of a Hydrogen Doublet Site in High Defect Density As-Grown a-Si:H by 1H NMR
Authors: Bobela D. , Su T. , Taylor P. C. , Ganguly G. 
Published: June 2019

Abstract1H NMR studies of hydrogenated amorphous silicon (a-Si:H) with ˜1017 cm-3 defects grown by PECVD with a rate of 5 Å/s show the existence of a hydrogen doublet for both asgrown and light-soaked samples. We observe the doublet over the temperature range from 5 to 20 K in a sample where no light soaking has occurred. The doublet line shapes display no narrowing over this temperature range. Vibrational modes characteristic of SiH2 wagging and scissor modes are seen from infrared spectroscopy. These results suggest that the doublet is due to SiH2 that occurs at a density of approximately 1 at. % in this sample. From line shape analysis, we estimate a lower limit of 1.8 ˜ for the hydrogen-to-hydrogen separation.
Growth of “New Form” of Polycrystalline Silicon Thin Films Synthesized by Hot Wire Chemical Vapor Deposition
Authors: Middya A. R. , Liang J-J. , Ghosh K. 
Published: June 2019

AbstractIn this work, we report on next-generation hot wire chemical vapor deposition technique, we call it ceramics hot-wire CVD. Using a new concept of rectangular ceramics filament holder and “confinement of thermal radiation from the filament”, a “new form” of polycrystalline silicon thin films has been developed at low temperature (˜ 250°C). The grains are found to be symmetrically distributed in array along the parallel lines, in (111) direction. On the surface of individual grains, “five-fold” and “six-fold” symmetries have been observed and we suspect that we developed “buckyball” type “giant silicon molecular solids” with different crystalline silicon lattice other than standard single-crystal silicon structure. We observed rarely found “icosaderal” symmetry in silicon thin films. This hypothesis has been supported by multiple Raman active transverse optical modes and the crystallographic structure analyzed by X-ray diffraction.
Nanocrystalline-Si Thin Film Deposited by Inductively Coupled Plasma Chemical Vapor Deposition (ICP-CVD) at 150°C
Authors: Han Sang-Myeon , Park Joong-Hyun , Lee Hye-Jin , Shin Kwang-Sub , Han Min-Koo 
Published: June 2019

AbstractNanocrystalline silicon (nc-Si) films were deposited by inductively coupled plasma chemical vapor deposition (ICP-CVD) at 150°C. ICP power was 400W. The process gas was SiH4 diluted with He as well as H2. The flow rate of He, H2 and He/H2 mixture was varied from 20sccm to 60sccm and that of SiH4 was 3sccm. X-ray diffraction (XRD) patterns of the nc-Si films were measured. From the XRD results of nc-Si films deposited by ICP-CVD, the properties of Si film deposited under each condition were studied. As the dilution ratio increases and He/H2 mixture was used as a dilution gas, intensities of <111>and<220> peaks were increased and the incubation layer was thin. These results were explained in the point of role of H2 plasma and He plasma in the nc-Si deposition process. Our experimental results show that nc-Si film deposited by ICP-CVD may be suitable for an active layer of nc-Si TFTs.
Doping Dependence of Chlorine Incorporation in SiC14-based Microcrystalline Silicon Films
Authors: Beyer Wolfhard , Carius Reinhard , Zastrow Uwe 
Published: June 2019

AbstractFor SiCl4-based microcrystalline silicon films the doping dependence of chlorine and hydrogen incorporation was studied. The results reveal a Fermi level dependence with a maximum chlorine (and hydrogen) incorporation for a Fermi level somewhat above midgap. As an explanation, a Fermi level dependence of the chlorine release rate during film growth is considered, similar as valid for hydrogen diffusion and desorption.
Initial Stage Hydrogen Movement and IR Absorption Proportionality Constants In Hot-Wire Deposited SiN1.2:H During High-Temperature Annealing
Authors: Goldbach H.D. , Verlaan V. , Werf C.H.M. van der , Arnoldbik W.M. , Rieffe H.C. , Romijn I.G. , Weeber A.W. , Schropp R.E.I. 
Published: June 2019

AbstractSilicon nitride (SiNx:H) layers were deposited using a high deposition rate Hot-Wire CVD technique (up to 5 nm/s) and their application as passivating antireflection coating on multicrystalline silicon solar cells was investigated. An important aspect is the hydrogen release and diffusion during a short annealing treatment at temperatures well above the deposition temperature. Such annealing treatments (firing) are used during contact formation of multicrystalline solar cells.A series of SiNx:H layers with Si/N ratio in the range of 0.7-1.45 was first characterized using optical R/T measurements, Fourier Transformed Infrared Spectroscopy (FTIR) and Elastic Recoil Detection (ERD) to determine optical constants n and k, Si-H, N-H and Si-N bond densities, Si-H peak position and H content. To get more insight in the passivation process during firing, which takes place at roughly 800 °C, samples with a N/Si ratio of 1.2 were annealed at this temperature for different times (15 s – 10 min). The total bonded H content, measured with FTIR, using conventional proportionality constants as proposed by Lanford and Rand [1], seems to show an increase within the first 60 s. At longer annealing times, the bonded H content decreases, as expected. The behavior of the H content under annealing measured by FTIR and ERD can be explained by using different matrix elements for calculating the H content from the FTIR data. The matrix element for the N-H stretching mode (3343 cm-1) was determined to be (4.7±0.2)x1020 cm-2 while the Si-H stretching (2193 cm-1) was found to be (0.55±0.04)x1020 cm-2. Such high matrix elements for the N-H stretching mode have not been reported earlier. The value of the Si-H stretching mode matrix element is within the reported values for different back bonding scenarios, but low for a peak position of 2193 cm-1. The ratio between the matrix elements of 8.5 differs strongly from the ratio of 2 observed by Lanford [1] or Bohne [2].
Micro-crystalline silicon-germanium thin films prepared by the multi-target RF sputtering system
Authors: Ajiki Toru , Nakamura Isao , Isomura Masao 
Published: June 2019

AbstractMicro-crystalline silicon-germanium (μc-SiGe) films were prepared by the multi-target RF sputtering system using Ar and Ar-H2 mixture gases. The crystallization temperature of Si0.3Ge0.7 films is reduced from 600 °C to 400 °C by the introduction of H2 into the sputtering gases. The dark conductivity of 1.7x10-7 S/cm and one order of magnitude of photosensitivity are obtained with the H2/Ar flow ratio of 2. The activation energy of dark conductivity is 0.42 eV, which is a half of the energy gaps of Si0.3Ge0.7, and show that the films have intrinsic nature. Besides, the absorption coefficients are similar to those of single crystalline Si0.3Ge0.7. The results suggest that the H2 introduction is effective both to reduce the dangling bond defects and to decrease the crystallization temperature of the μc-SiGe films.