The wetting of Sn3Ag-based alloys on Al2O3 has been studied using the sessile-drop configuration. Small additions of Ti decrease the contact angle of Sn3Ag alloys on alumina from 115° to 23°. Adsorption of Ti-species at the solid–liquid interface prior to reaction is the driving force for the observed decrease in contact angle, and the spreading kinetics is controlled by the kinetics of Ti dissolution into the molten alloy. The addition of Ti increases the transport rates at the solid–liquid interface, resulting in the formation of triple-line ridges that pin the liquid front and promote a wide variability in the final contact angles.

The interfacial reaction between eutectic Sn-9 wt% Zn solder and two different kinds of ball-grid-array substrates (Cu and Au/Ni electroplated Cu) during aging at 150 °C and the shear strength of the resulting joints were investigated. In the Sn-9Zn/Cu joints, only Cu5Zn8 intermetallic compound (IMC) was observed between the solder and Cu layer during the first 100 h of aging. After aging for 1000 h, the layer-type Cu5Zn8 IMC layer was disrupted at the interface, causing it to act as a channel for the diffusion of Sn. As a result, Cu6Sn5 and Cu3Sn IMCs were formed underneath the Cu5Zn8 IMC layer. This interfacial reaction significantly degraded the joint strength. In the case of the Au/Ni/Cu substrate, an AuZn3 IMC layer formed at the interface because of the fast reaction between Au and Zn. In addition, the AuZn3 IMC layer became detached from the interface during reflow. The detachment of the AuZn3 IMC layer is presumably from the mismatch in the coefficients of thermal expansion and weak adhesion between the AuZn3 IMC layer and Ni layer caused by the depletion of the Au layer. When the aging time was extended to 100 h, Ni5Zn21 IMC was observed on the Ni substrate. The shear strength of the aged Sn-9Zn/Au/Ni/Cu joint was significantly related to the detachment of the AuZn3 IMC layer. After aging at 150 °C, fracturing occurred on the detached AuZn3 IMC layer. To ensure the reliability of the Sn-Zn/Au/Ni/Cu joint, the detachment of the AuZn3 IMC needs to be prevented.

The hydration of controlled tricalcium and dicalcium silicate mixtures was investigated using inelastic neutron scattering. The amount of Ca(OH)2 produced by each mixture was quantified based on the vibrational mode at approximately 41 meV. The results of compressive strength testing correlate with the amount of Ca(OH)2 produced and with previous results from quasielastic neutron scattering. These results establish a link between hydration mechanics and the evolution of hydration products leading to desirable properties, such as strength.

We have demonstrated previously, using nanoindentation, that the film thickness and substrate plasticity, the important two external variables in the film layer, control the failure of the film in a mutually exclusive way. In this work, we used a non-iterative Hankel transform method to analyze the stresses in an elastic film bound to an elastic substrate by a no-slip boundary condition and subjected to a Hertzian traction. We vary the substrate compliance by two orders of magnitude to generate interfacial mismatch stresses, which mimic the corresponding changes found in a real-life elastic film on an elastic-plastic substrate when the hardness of the substrate is changed. The analysis is found to reproduce faithfully the experimental trends, which showed that normal load and interfacial stresses generated by strain mismatch drive different modes of fracture depending on the film thickness in a mutually exclusive way. This validation paves the way for this theoretical technique to be used to design multilayered film structures.

The mechanisms of nanoindentation on single-walled carbon nanotubes (SWCNTs) have been studied by using molecular dynamics simulation and continuum analysis during which a flat layer of diamond atoms is pressed down incrementally on a vertically aligned SWCNT. SWCNTs are divided into three distinct categories based on their aspect ratios, such that the nanotube behavior transits from a shell (short tube) to a beam (long tube). Molecular dynamics simulations are used to explore the diverse indentation characteristics in each domain, where the relationships between the strain energy and indentation depth during loading, unloading, and reloading are continuously recorded. The nanoindentation mechanisms are characterized by the critical indentation depth, maximum strain energy and force associated with buckling, as well as with the evolution of carbon bond length and morphology of the SWCNTs. Bifurcation behaviors are explored by investigating the loading-unloading-reloading behaviors of the nanotubes. Parallel finite element simulations are also used to study the pre- and post-buckling behaviors of SWCNT by incorporating the van der Waals interaction into the continuum code. It is found that, for the most part, continuum analysis can effectively capture the overall indentation characteristics, yet some details related to the atomic characteristics of nanoindentation may only be revealed by molecular dynamics simulation. Finally, an indentation mechanism map is derived by comparing behaviors of SWCNTs with different aspect and section ratios. Focusing on the effects of nanotube length, this paper is the first of a series of numerical studies on the indentation mechanisms of carbon nanotubes, which may be used to determine the intrinsic mechanical properties of SWCNTs by means of nanoindentation.

Computational models of the cell nucleus, along with experimental observations, can help in understanding the biomechanics of force-induced nuclear deformation and mechanisms of stress transition throughout the nucleus. Here, we develop a computational model for an isolated nucleus undergoing indentation, which includes separate components representing the nucleoplasm and the nuclear envelope. The nuclear envelope itself is composed of three separate layers: two thin elastic layers representing the inner and outer nuclear membranes and one thicker layer representing the nuclear lamina. The proposed model is capable of separating the structural role of major nuclear components in the force-induced biological response of the nucleus (and ultimately the cell). A systematic analysis is carried out to explore the role of major individual nuclear elements, namely inner and outer membranes, nuclear lamina, and nucleoplasm, as well as the loading and experimental factors such as indentation rate and probe angle, on the biomechanical response of an isolated nucleus in atomic force microscopy indentation experiment.

Studies of RE5(SixGe1-x)4 alloys, where RE equals rare earth, have revealed a second-phase having a thin-plate morphology in essentially every alloy examined, independent of exact composition and matrix crystal structure. Identified as having a composition approximating Gd5(SixGe1-x)3 and a hexagonal crystal structure in the Gd-based system, it has been suggested that the observed thin-plate second phases seen in this family of rare earth alloys are all most likely of the form RE5(SixGe1-x)3. A number of interesting observations suggest that the formation of these second-phase plates is somewhat unusual. The purpose of this article is to investigate the stability of this second phase in Gd- and Er-based compounds. The stability was investigated as a function of thermal cycling and large-scale composition fluctuations. The results of scanning and transmission electron microscopy (SEM, TEM) studies indicate that the RE5(SixGe1-x)3 phase is extremely stable once it forms in a RE5(SixGe1-x)4 matrix.

Iron-oxide nanowires were synthesized by a hydrothermal treatment of Fe(OH)3 dispersion in NaOH. The obtained materials were first structurally investigated by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, and thermogravimetric analysis techniques. Their magnetic properties were then examined by superconducting quantum interference device and electron paramagnetic resonance methods. A typical nanowire measured 10–15 nm in diameter and 600 nm in length. All the structural and magnetic investigations were consistent with the nanowire goethite structure. The nanowire Neél transition temperature occurred at 375 K; i.e., it was lowered by 25 K with respect to the corresponding goethite bulk value. The shift in the ordering temperature was suggested to be a consequence of a growing importance of strains and surface effects at the nanoscale. We were also able to irreversibly convert goethite nanowires into hematite, by warming the sample to temperatures exceeding 530 K.

The thermal recoverability of a nanoporous silica-based system modified by a cross-linked polyelectrolyte is investigated. At room temperature, as a nominally hydrostatic pressure is applied, the gel matrix can be partially dehydrated. The released water molecules will be forced into the initially energetically unfavorable nanopores and are “locked” there. At an elevated temperature, the infiltration pressure increases slightly, which is contradictory to the experimental data of the unmodified system. More importantly, the defiltration of the confined liquid is significantly promoted, leading to a much higher system recoverability.

Fluorocarbon polymer films in the poly(tetrafluoroethylene) (PTFE)-like structure are formed by a low-pressure chemical vapor deposition technique using the hot filament excitation of the gaseous C3F6O precursor. The filament and substrate temperatures were found to influence the structure of the deposited films. Infrared absorption and electron spectroscopy studies reveal that a PTFE-like (CF2)2n linear molecular chain structure evolves by an adsorption driven nucleation and CF2 polymerization process in the films deposited with low (450 °C) filament and high (70 °C) substrate temperatures. The films formed at a low substrate temperature (–165 °C) show a higher concentration of CF and C–CF bond defects and shorter (CF2)2n chains. A high (8–10 at.%) oxygen concentration in the films deposited at 600 °C filament temperature is attributed to the reaction of the (CF2)2n chains with COF and peroxyradicals arising from the dissociation of CF3C(O)F and affects the thermal stability of the films. Such reactions are not involved in the film growth at a low (450 °C) filament temperature. These films have much lower (<2 at.%) bonded oxygen content. The films having an ordered (CF2)2n chain structure formed at 70 °C are characterized by low leakage currents ∼7 × 10−11 A cm−2 at 0.1 MV cm−1 field. In comparison, high leakage currents ∼1 × 10−8 A cm−2 are observed for the films having a higher concentration of C–F and C–CF bonds.

An expanding cavity model (ECM) for determining indentation hardness of elastic–strain-hardening plastic materials is developed. The derivation is based on a strain gradient plasticity solution for an internally pressurized thick-walled spherical shell of an elastic linear-hardening material. Closed-form formulas are provided for both conical and spherical indentations. The formulas explicitly show that indentation hardness depends on Young's modulus, yield stress, strain-hardening index, and strain gradient coefficient of the indented material as well as on the geometry of the indenter. The newly formulated ECM can capture the indentation size effect, unlike classical plasticity based ECMs. The new model reduces to existing classical plasticity based ECMs (including Johnson's ECM for elastic-perfectly plastic materials) when the strain gradient effect is not considered. The presently developed ECM is validated by comparing with existing experimental hardness data. The numerical results obtained using the new model reveal that the hardness is indeed indentation size dependent when the indentation radius is very small: the smaller the indentation, the larger the hardness. Also, the indentation hardness is seen to increase with the Young's modulus and strain-hardening level of the indented material for both conical and spherical indentations. The strain-hardening effect on the hardness is observed to be significant for materials having strong strain-hardening characteristics. In addition, it is found that the indentation hardness increases with decreasing cone angle of the conical indenter or decreasing radius of the spherical indenter. These trends agree with existing experimental observations and model predictions.

We experimentally investigated the pressure-induced infiltration of a nanoporous silica-based energy absorption system modified by polyacrylic acid partial sodium salt (sodium polyacrylate). Under ambient conditions, sodium polyacrylate forms a soft matter with water. As the hydrostatic pressure increases, the dehydration of the soft matter occurs and the nanopores are filled by water molecules, accompanied by a significant energy dissipation. This result has fundamental scientific interest for understanding behaviors of confined liquids and great technological importance for developing advanced solid-like protective/damping materials.

Ultrasmooth nanostructured diamond (USND) films were synthesized on Ti–6Al–4V medical grade substrates by adding helium in H2/CH4/N2 plasma and changing the N2/CH4 gas flow from 0 to 0.6. We were able to deposit diamond films as smooth as 6 nm (root-mean-square), as measured by an atomic force microscopy (AFM) scan area of 2 μm2. Grain size was 4–5 nm at 71% He in (H2 + He) and N2/CH4 gas flow ratio of 0.4 without deteriorating the hardness (∼50–60 GPa). The characterization of the films was performed with AFM, scanning electron microscopy, x-ray diffraction (XRD), Raman spectroscopy, and nanoindentation techniques. XRD and Raman results showed the nanocrystalline nature of the diamond films. The plasma species during deposition were monitored by optical emission spectroscopy. With increasing N2/CH4 feedgas ratio (CH4 was fixed) in He/H2/CH4/N2 plasma, a substantial increase of CN radical (normalized by Balmer Hα line) was observed along with a drop in surface roughness up to a critical N2/CH4 ratio of 0.4. The CN radical concentration in the plasma was thus correlated to the formation of ultrasmooth nanostructured diamond films.

Cadmium-doped ZnO was prepared for the first time by combustion synthesis using CdCl2 as a dopant precursor, with zinc nitrate and urea as the combustion mixture. Unlike previous studies of combustion synthesis of ZnO in the presence of an indium nitrate precursor, which resulted in (ZnO)mIn2O3 (m = 3 or 4) compound formation, In-doped ZnO was prepared by combustion synthesis in this study using an InCl3 precursor. The doped samples were compared and contrasted with undoped ZnO using scanning electron microscopy, x-ray powder diffraction, energy-dispersive x-ray analyses, and x-ray photoelectron spectroscopy. Diffuse reflectance spectroscopy showed the optical band gap of ZnO to shrink from 3.14 to 3.07 eV and 3.02 eV on Cd and In doping, respectively. Finally, the doped samples showed an improved photoelectrochemical response relative to undoped ZnO over the wavelength range from ∼300 to ∼450 nm.

The metastable solid solubility extension of CoO in ZnO (wurtzite) was investigated in precursor-derived powders as well as in thin films grown on sapphire substrates by pulsed laser deposition. A maximum solubility of 30% Co2+ in ZnO was achieved in the powders. Transmission electron microscopy (TEM) of the films revealed them to have grown epitaxially and retained up to nearly 40% CoO in solid solution, but some Co2+ precipitated as rock-salt. The temperature dependence of the metastable solubility limit in the ZnO–CoO system was assessed and is discussed in terms of the relevant thermodynamic factors. The magnetic properties of n-type conductive Zn0.79Co0.2Al0.01Ofilms were studied, yielding evidence of a ferromagnetic phase with a TC of 25 K and a second, magnetically ordered, phase with positive exchange and arguably a TC of ∼250 K. Connections between the properties and microstructural observations in high resolution TEM are proposed.

A micromechanical model was developed to predict the elastic moduli of hydroxyapatite (HA) whisker reinforced polymer biocomposites based upon the elastic properties of each phase and the reinforcement volume fraction, morphology, and preferred orientation. The effects of the HA whisker volume fraction, morphology, and orientation distribution were investigated by comparing model predictions with experimentally measured elastic moduli for HA whisker reinforced high-density polyethylene composites. Predictions using experimental measurements of the HA whisker aspect ratio distribution and orientation distribution were also compared to common idealized assumptions. The best model predictions were obtained using the experimentally measured HA whisker aspect ratio distribution and orientation distribution.

Electronic (UV-vis) and vibrational absorption spectroscopies were used to examine the impact of incident photon energy and local atmospheric composition on the development of photo-induced structural changes in poly[(methyl)(phenyl)silylene] thin films. The relative impact of atmosphere on the magnitude and nature of photostructural modifications in this material is found to be enhanced under 3.68 eV photon exposure where the incident photon is resonant with the lowest energy absorption of the Si-Si-conjugated backbone structure. This is in contrast to a greater overall magnitude of photo-induced structural change, with limited atmospheric dependence, observed under 5.1 eV exposure, resonant with absorption transitions associated with the π-conjugated phenyl ring side group. These results provide insight into the underlying structural mechanisms contributing to the large refractive index changes typically observed in these materials.

The scaling of the piezoelectric and dielectric constants with film thickness in ultra-thin ferroelectric heterostructures is investigated. Epitaxial (001) PbZr0.2Ti0.8O3 films ranging in thickness from 5 nm to 30 nm with top and bottom SrRuO3 electrodes were grown onto (001) SrTiO3 substrates via pulsed laser deposition. Piezoelectric and dielectric measurements were performed using an atomic force microscope. The remnant value of the out of plane piezoresponse (d33) decreases from 60 pm/V for the 30 nm film to just 7 pm/V for the 5 nm film. This systematic decline in d33 is accompanied by a corresponding increase in the coercive field. The d33 loops show a systematic increase in tilt towards the applied field axis as function of reducing thickness coupled with a decrease in piezoelectric tunability. The small-signal relative dielectric response in the direction normal to the film-substrate interface decreases from 140 for a 50 nm film to just 60 for a 8 nm film. A similar drop is also observed in the dielectric tunability, from ∼17% to approximately −2% at an electric field of 750 kV/cm with the film thickness decreasing from 50 nm to 8 nm. We show that these observations cannot be explained using a straightforward application of a modified Landau-Devonshire thermodynamic model that incorporates the internal stresses due to the lattice and thermal expansion mismatch between the film and the substrate. We attribute this behavior to degradation in the polarization due to an intrinsic finite size effect.

Solid-state wetting experiments were carried out to derive the work of adhesion (adhesion energy) of pertinent Cu/liner interfaces via the Young–Dupré equation using contact-angle measurements of the Cu equilibrium crystal shape on Ta and TaNx liners. Four types of liner surfaces were examined: untreated sputtered Ta (uSp-Ta), untreated sputtered TaNx (uSp-TaN), untreated atomic layer deposited (ALD) TaNx (uALD-TaN), and indium surfactant-treated ALD TaNx (tALD-TaN). All Cu-liner stacks were subsequently annealed at 600 °C for 48 h in a forming gas (95% Ar/5% H2) ambient. For Cu/uSp-Ta, the work of adhesion was found to be 2170 mJ/m2, corresponding to an average contact angle of 74°, while for Cu/uSp-TaN, the work of adhesion amounted to 1850 mJ/m2 for an average contact angle of 85°. Alternatively, the work of adhesion for Cu/uALD-TaN was determined to be 1850 mJ/m2, corresponding to an average contact angle of 85°, while for Cu/tALD-TaN, the work of adhesion was 2280 mJ/m2, at an average contact angle of 70°. These findings indicate that the highest degree of surface wetting occurs for the indium surfactant-treated ALD TaNx. It is thus suggested that surfactant treatment causes a reduction in the energy barrier to Cu nucleation, resulting in an enhancement in Cu wetting characteristics and a more uniform concentration of Cu nucleation sites. A critical potential outcome is the formation of atomically smooth Cu-liner interfaces with enhanced adhesion characteristics.