Simulations of metal nanoimprinting by a rigid template are performed with the aim of finding the optimal conditions to retain imprints in a thin film on a substrate. Specifically, attention is focussed on the interface conditions between film and substrate and on the template shape. Deeper imprints are obtained when the interface between film and substrate is penetrable to dislocation motion. When the protruding contacts of the rigid template are closely spaced the interaction between neighboring contacts gives rise to material piles up between imprints.

Control of residual stress in thin films is critical in obtaining high mechanical quality coatings without cracking, buckling, or delamination. In this work, we present a simple and effective method of residual stress reduction in sputter deposited thin films by stacking low and high material density layers of the same material. This multilayer density modulated film is formed by successively changing working gas pressure between high and low values, which results in columnar nanostructured and dense continuous layers, respectively. In order to investigate the evolution of residual stress in density modulated thin films, we deposited ruthenium (Ru) films using a DC magnetron sputtering system at alternating argon (Ar) pressures of 20 and 2 mTorr. Wafer’s radius of curvature was measured to calculate the intrinsic thin film stress of multilayer Ru coatings as a function of total film thickness by changing the number of high density and low density layers. By engineering the film density, we were able to reduce film stress more than one order of magnitude compared to the conventional dense films produced at low working gas pressures. Due to their low stress and enhanced mechanical stability, we were able to grow these density modulated films to much higher thicknesses without suffering from buckling. Morphology and crystal structure of the thin films were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). A previously proposed model for stress reduction by means of relatively rough and compliant sublayers was used to explain the unusually low stress in the specimens investigated.

Transition pathway sampling was carried out for homogeneous dislocation nucleation in perfect crystal Si. The sampling algorithm employed was Nudged Elastic Band method. Results obtained were compared with corresponding results for Cu. The stress and activation barrier ranges were found to be much higher for Si than those reported for Cu. The results also showed that while for lower values of resolved shear stress the dislocation embryo approaches that of a perfect dislocation, for higher resolved shear stress values the embryo is far from perfect. That is, the shear displacement of most particles is considerably less than the Burger’s vector. This investigation also demonstrated for the first time that Athermal shear stress for homogeneous dislocation nucleation in Si does not exist, as the crystal undergoes twinning at such high stresses.

The effect of alloying elements Ta, Mo, W, Cr, Re, Ru, Co, and Ir on the elastic properties of both γ-Ni and γ′-Ni3Al is studied by first-principles method. Results for lattice properties, elastic moduli and the ductile/brittle behaviors are all presented. Our calculated values agree well with the existing experimental observations. Results show all the additions decrease the lattice misfit between and γ′ phases. Different alloying elements are found to have different effect on the elastic moduli of γ-Ni. Whereas all the alloying elements slightly increase the moduli of γ′-Ni3Al expect Co. Both of the two phases are becoming more brittle with alloying elements, but Co is excepted. The electronic structures of γ′ phase alloyed with different elements are provided as example to elucidate the different strengthening mechanisms.

We used thickness gradients for high throughput optimization of adhesion in film stacks. The idea is based on the so-called superlayer test where a top layer under high compression exerts a load onto the lower interfaces and may cause delamination and buckling. Thus, on one hand, the thickness gradient of the superlayer results in the gradient of the load. On the other hand, the adhesion gradient can be realized by changing the thickness of an adhesion enhancer (or an adhesion reducer). When applied in two perpendicular directions (cross-gradient), the gradient of the superlayer in one direction and of the adhesion enhancer in the other, the plane of the sample represents a map where the line of delamination relates the interfacial toughness to the thickness of the enhancer. In our tests we used Mo superlayers under compressive stress of the order of ˜1.5 GPa on a Si wafer with a native oxide. The adhesion reduction was observed with this methodology when Ag layer up to 10 nm thick was deposited onto the substrate prior to Mo deposition. The delamination occurred at Ag thicknesses starting from ˜6 nm. This thickness of Ag corresponds to the islands coalescence and formation of a continuous film which immediately results in adhesion reduction. The other test was performed with a step gradient of Ti enhancer placed under a 10 nm thick Ag layer in otherwise the same arrangement. A single test showed that 2.8 Å of Ti was sufficient to improve the adhesion between Ag and SiOx by several times.

This work aims at a quantitative simulation of instrumented indentation test based on physics of crystal plasticity. Indentation loading is associated with a complex 3D deformation path: it can be viewed as an ideal benchmark to test various crystal plasticity assumptions. For large scale indentation (micron size), a 3D numerical simulation using finite element crystal plasticity (FEM) is setup and quantitatively compared to experimental results using critical constraints: the load/stiffness-displacement curves and the surface displacements. Various set of parameters obtained from Dislocation Dynamics (DD) are used. A comparison with experiments shows the dominant effect of initial dislocation density and slip system interactions. For smaller depth (maximum 100 nm), Dislocation Dynamics coupled simulations to FEM are setup. Since this approach does not provide defect nucleation rules, several strategies are implemented and tested: fitting to Molecular Dynamics (MD) load-depth curve for spherical tip, or automatic generation of deformation accommodating dislocation (GND) for conical tip geometry for example. In this framework, size effects show up in the modification of the dislocation structures with depth through critical expansion of dislocation loops and junction formation.

Nano-crystalline films of pure cubic ZrO2 have been produced by ion beam assisted deposition (IBAD) processes which combine physical vapor deposition with the concurrent ion beam bombardment in a high vacuum environment and exhibit superior properties and strong adhesion to the substrate. Oxygen and argon gases are used as source materials to generate energetic ions to produce these coatings with differential nanoscale (7 to 70 nm grain size) characteristics that affect the wettability, roughness, mechanical and optical properties of the coating. The nanostructurally stabilized chemically pure cubic phase has been shown to possess hardness as high as 16 GPa and a bulk modulus of 235 GPa. We examine the mechanical properties and the phase stability in zirconia nanoparticles using first principle electronic structure method. The elastic constants of the bulk systems were calculated for monoclinic, tetragonal and cubic phases. We find that calculated bulk modulus of cubic phase (237GPa) agrees well with the measured values, while that of monoclinic (189GPa) or tetragonal (155GPa) are considerably lower. We observe considerable relaxation of lattice in the monoclinic phase near the surface. This effect combined with surface tension and possibly vacancies in nanostructures are sources of stability of cubic zirconia at nanoscale.

Elasto-plastic response of bulk metallic glasses (BMGs) follows closely the response of granular materials through pressure dependent (or normal stress) yield locus and shear stress induced material dilatation. On a micro-structural level, material dilatation is responsible for stress softening and formation of localized shear band, however its influence on the macro-scale flow and deformation is largely unknown. In this work, we systematically analyze the effect of material dilatation on the gross indentation response of Zr-based BMG via finite element simulation. The strengthening/softening effect on the load-depth response and corresponding stress-strain profiles are presented in light of differences in elastic-plastic regimes under common indenters. Through comparison with existing experimental results, we draw conclusions regarding selection of suitable dilatation parameters for accurately predicting the gross response of BMGs

The structural and electronic properties of AlMgB14 are investigated using ab initio methods. The impact of vacancies and electron doping on the crystal’s atomic and electronic structure is investigated. It is found that removing metal atoms does not influence the density of states, except for changes to the Fermi energy. The density of states of the off-stoichiometric Al0.75Mg0.75B14 crystal and the AlMgB14 crystal with five electrons removed are nearly identical. The removal of six electrons results in an 11% contraction in the crystal’s volume. This is associate with the removal of electrons from the B atoms’ 2p-states.

Uniaxial μ-compression tests have been performed on single crystal Mg with a <11-20> compression direction, an orientation unfavorable for basal slip. Results show that the early stages of deformation proceed via both twinning and dislocation plasticity. Twinning leads to a reorientation of the crystal favorable for basal slip, typically with the <2-1-1-3> aligned with the compression direction. At a critical strain a large strain burst occurs, and is associated with both rapid propagation of the twin and the activation of basal slip within the twin. Such a mechanistic picture of the deformation behavior is revealed through SEM, EBSD and TEM characterization of the deformation structures.

This paper presents molecular dynamics simulations of shear-coupled migration of tilt boundaries pinned by triple junctions in a simple model structure of columnar grains of different sizes. Simulations are for copper at 300 K. The phenomenon is of interest as a possible explanation of the Hall-Petch relationship breakdown in nano-grained polycrystals deformed at high or moderate strain rate and low-temperature.

The thermal effect on the nanofluidic behaviors in a nanoporous silica gel is investigated experimentally. When a nanoporous silica gel is modified by silyl groups, its surface becomes hydrophobic. A sufficiently high external pressure must be applied to overcome the capillary effect; otherwise liquid infiltration could not occur. The formation and the disappearance of a solid–liquid interface are employed for energy storage or dissipation. When the hydrophobic surface of nanoporous silica gel is decomposed at various temperatures, the organic surface layers can be deactivated. As a result, the degree of hydrophobicity, which can be measured by the liquid infiltration pressure, is lowered. The infiltration and defiltration behaviors of liquid are dependent on the controlled by the decomposition-treatment temperature.

Three kinds of nanocrystalline Co-Cu alloys: a nanocrystalline Co-Cu alloy with nanoscale lamellar structure, a supersaturated solid solution Co-Cu alloy and a nanocrystalline two-phase Co-Cu alloy were processed by electrodeposition, and their mechanical properties were investigated at room temperature. These nanocrystalline Co-Cu alloys showed the high hardness and the low activation volume. The mechanical properties of the nanocrystalline Co-Cu alloys strongly depended on the grain boundary characteristics. Molecular dynamics simulations were performed in the two-phase nanocrystalline Co-Cu alloy to investigate the dislocation emission at the Co/Cu interface. The MD simulations showed that the stacking faults, which are generated by the intense geometrical strain at the Co/Cu interface, play an important role in the dislocation emission.

In-house synthesized copolymers Polystyrene-co-glycidyl methacrylate (PSt-co-GMA) are electrospun as mat of surface modified nanofibers with and without multi walled carbon nanotubes (MWCNTs). Composites are then formed by embedding layers of the nanofiber mats into epoxy resin. Interfacial bonding between polymer matrix and the nanofibers, and surface modification driven enhancement in mechanical response is assessed under flexural loads. Results indicate that at elevated temperture storage modulus of epoxy reinforced by PSt-co-GMA nanofibers and PSt-co-GMA/ MWCNTs composite nanofibers is about 10 and 20 times higher than the neat epoxy, respectively, despite weight fraction of the nanofibers being as low as 2%. Interfacial interaction is revealed by the storage modulus comparison of unmodified Polystyrene (PSt) and modified PSt-co-GMA nanofiber reinforced composite. To enhance further the resulting “crosslinked” structure, crosslinking agent ethylenediamine is also sprayed on the nanofibrous mats. Increased crosslinking density improves mechanical response of sprayed-over PSt-co-GMA nanofibers reinforced composites which is about 4 times higher than plain PSt-co-GMA nanofibers.

The study of indentation responses of rate-dependent (viscoplastic or creeping) solids has generally focused on the relationship between indentation hardness and an effective strain rate, which can be defined from a similarity transformation of the governing equations. The strain rate sensitivity exponent can be determined from the slope of a log-log plot of the hardness versus effective strain rate, while determining other constitutive parameters requires a knowledge of the relationship between contact size, shape, and indentation depth. In this work, finite element simulations have shown that the effects of non-axisymmetric contact and crystallography are generally negligible. Theoretical predictions agree well with real nanoindentation measurements on amorphous selenium when tested above glass transition temperature, but deviate quite significantly for experiments on high-purity indium, coarse-grained aluminum, and nanocrystalline nickel. Such a discrepancy is likely to result from the transient creep behavior.

We have developed on the DIFFABS-SOLEIL beamline a biaxial tensile machine with synchrotron standard for in-situ diffraction characterization of thin polycrystalline metallic film mechanical response. The machine has been designed to test cruciform substrates coated by the studied film under controlled applied strain field. Technological challenges comprise the fixation of the substrate, the generation of a uniform strain field in the studied (central) volume, the operations from the beamline pilot. Tests on W and W/Cu multilayers films deposited on polyimide substrates are presented.

Bulk metallic glasses exhibit confined low and high frequency vibrational properties resulting from the significant bon and topological disorder occuring at the atomic scale. The precise nature of the low frequency modes and how they are influenced by local atomic structure remains unclear. Using standard harmonic analysis, the current work investigates various aspects of the problem by diagonalizing the Hessian of atomistic samples derived from molecular dynamics simulations via a model binary Lennard Jones pair potential.

The objective of this study is to characterize the nanoparticle dispersion and to investigate its effect on the surface mechanical properties of nanoparticle-polymer systems. Two types of TiO2 nanoparticles were chosen to mix in two polymeric matrices: solvent-borne acrylic urethane (AU) and water-borne butyl-acrylic styrene latex (latex) coatings. Nanoparticle dispersion was characterized using laser scanning confocal microscopy. Overall, Particle A (PA, without surface treatment) dispersed better than Particle B (PB, organic treatment) in both systems. The AU-PA system exhibited the best dispersion of the four systems, however PB forms big clusters in both of the matrices. Surface mechanical properties, such as surface modulus at micron and sub-micron length scales were determined from depth sensing indentation equipped with a pyramidal tip or a conical tip. The surface mechanical properties were strongly affected by the dispersion of nanoparticle clusters, and a good correlation was found between dispersion of nanoparticle clusters near surface and the modulus-depth mapping using a pyramid tip.

Nb-Ti-Ni alloy is one of the candidates for hydrogen permeation membranes. The hydrogen permeability of a membrane depends on its thickness, and mechanical properties such as the fracture toughness of the membrane are important to ensure reliability and durability. In the present work, micro-mechanical tests have been carried out for melt-spun Nb-Ti-Ni thin films consisting of amorphous and nano-crystalline phases. The relationship between the mechanical properties of the melt-spun films and the microstructural changes occurring in the films due to heat treatment has been also discussed. The Nb-Ti-Ni alloy thin films were prepared by the melt-spun technique and then heat-treated at 873-1173 K. Micro-sized cantilever specimens with dimensions of 10 × 10 × 50 μm3 were prepared by focused ion beam (FIB) machining. Fracture tests were carried out using a mechanical testing machine for the micro-sized specimens; the testing machine was developed by us. In addition, microstructures were observed by transmission electron microscopy (TEM). The fracture toughness (KQ) value decreased up to 823 K, and it increased above 1173 K. The specimen heat-treated above 1173 K showed ductile fracture. The fracture morphology of the specimen heat-treated up to 1023 K showed grain boundary fracture characteristics, and that of the specimen heat-treated at 1173 K changed to transgranular fracture.

Boron carbide (B4C) is currently used in lightweight armors and high temperature materials, because it has high meting point, good hardness, low specific gravity and good mechanical properties. The sintering of boron carbide, however, is restricted by its high covalent bonding and B2O3 coatings on B4C particles surface which can cause a microstructural coarsening during sintering. Therefore, it is necessary to remove B2O3 film of By4C particles surface to restrict microstructural coarsening and densification of B4C. B4C ceramics were fabricated by a hot-press sintering and its sintering behavior, microstructure and mechanical properties were evaluated. The relative density of B4C ceramics were obtained by a hot-press sintering reached as high as 99% without any sintering additives. The mechanical properties of B4C ceramics was improved by a methanol washing which can remove B2O3 phase from a B4C powder surface. This improvement is resulted from the formation of homogeneous microstructure because the grain coarsening was suppressed by the elimination of B2O3 phase. Particularly, the mechanical properties of the sintered samples using a methanol washed powder improved compared with the samples using an as-received commercial powder.