We use instrumented indentation to characterize the mechanical and transport behavior of a pH-sensitive hydrogel in various aqueous buffer solutions. In the measurement, an indenter is pressed to a fixed depth into a hydrogel disk and the load on the indenter is recorded as a function of time. By analyzing the load–relaxation curve using the theory of poroelasticity, the elastic constants of the hydrogel and the diffusivity of water in the gel can be evaluated. We investigate how the pH and ionic strength of the buffer solution, the hydrogel cross-link density, and the density of functional groups on the polymer backbone affect the properties of the hydrogel. This work demonstrates the utility of indentation techniques in the characterization of pH-sensitive hydrogels.

Polyaniline nanofiber (PANF) was synthesized using interfacial polymerization and was mixed with aqueous solution of poly(vinyl alcohol) (PVA) to form PANF–PVA binaries. The PANF suspension in water could be stabilized by PVA for more than 3 months due to the hydrogen bonding interaction between PANF and PVA. The specific characteristics of PANF–PVA films was checked by scanning electron microscopy, conductivity measurement, thermogravimetric analysis, Fourier transform infrared spectroscopy, and cyclic voltammetry. The composite film contained 25 wt% PVA (PANF–PVA25) casting at 105 °C was found to have a porous structure and good conductivity. The presence of hydrogen bonding interaction between PANF and PVA improves the electroactivity and electroactive stability of PANF–PVA25 for electrochemical applications. However, an ether linkage between PANF and PVA polymer chain was also found as casting the PANF–PVA film at 200 °C, which is unfavorable for electrochemical applications.

We report the results of constant strain rate experiments on electroplated, single crystalline copper pillars with diameters between 75 and 525 nm. At slow strain rates, 10−3 s−1, pillar diameters with 150 nm and above show a size-dependent strength similar to previous reports. Below 150 nm, we find that the size effect vanishes as the strength transitions to a relatively size-independent regime. Strain rate sensitivity and activation volume are determined from uniaxial compression tests at different strain rates and corroborate a deformation mechanism change. These results are discussed in the framework of recent in situ transmission electron microscopy experiments observing two distinct deformation mechanisms in pillars and thin films on flexible substrates: partial dislocation nucleation from stress concentrations in smaller structures and single arm source operation in larger samples. Models attempting to explain these different size-dependent regimes are discussed in relation to these experiments and existing literature revealing further insights into the likely small-scale deformation mechanisms.

Nanoindentation-induced phase transformations in both crystalline silicon (c-Si) (100) and ion-implanted amorphous silicon have been studied at temperatures up to 200 °C. The region under the indenter undergoes rapid volume expansion at temperatures above 125 °C during unloading, which is indicated by “bowing” behavior in the load–displacement curve. Polycrystalline Si-I is the predominant end phase for indentation in crystalline silicon whereas high-pressure Si-III/Si-XII phases are the result of indentation in amorphous silicon. We suggest that the Si-II phase is unstable in a c-Si matrix at elevated temperatures and can directly transform to Si-I during the early stages of unloading.

The relationship between hardness and flow stress in glassy polymers is examined. Materials studied include poly(methylmethacrylate), polystyrene, and polycarbonate. Properties are strongly rate dependent, so broadband nanoindentation creep (BNC) is used to measure hardness across a broad range of indentation strain rates (10−4 to 10 s−1). Molybdenum (Mo) is also studied to serve as a “control” whose rate-dependent hardness properties have been measured previously and whose flow stress, unlike the polymers, is pressure insensitive. The BNC hardness data are converted to uniaxial flow stress using two methods based on the usual Tabor–Marsh–Johnson correlation. With both methods the resulting BNC-derived uniaxial flow stress data agree closely with literature compression uniaxial flow stress data for all materials. For the polymers, the BNC hardness data depend on initial rate of loading, indicating that the measured properties are path dependent. Path dependence is not detected in Mo.

Ternary electroless nickel, NiXP, films were produced by adding salts of Mo, Re, Tl, Cu, W, Co, Fe, Zn, and Mn to conventional electroless Ni baths and subsequently reacted with Sn-3.5Ag solder. From the full width at the half maximum (FWHM) data, as-plated NiXP films can be categorized into two groups: one is close to the FWHM value of nanocrystalline Ni5P film and the other is close to amorphous Ni9P film. Alloying elements in the electrolessly plated under-bump metallurgy that effectively suppressed intermetallic compound (IMC) spalling were Mn, Zn, Re, Fe, and W, whereas Tl exacerbated spalling. The roles of Cu, Mo, and Co were less clear due to a lack of data. Based on scanning electron microscopy observations, a spalling map was presented, which showed elemental demarcation lines of IMC spalling in the X-P coordinates.

The authors discuss the contact-area-based indentation contact mechanics instead of the conventional penetration-depth-based analysis. In time-independent elastoplastic regime, the indentation load P versus contact area A relationship for a cone indentation is linear both for the loading and the unloading paths. The slope of the loading path directly yields the Meyer hardness HM, and the slope of the unloading path, i.e., the unloading modulus M, is related to the elastic modulus E′ through the relation of M = E′tan β/2. The relation of the total contact area A to the purely elastic and the purely plastic contact areas of Ae and Ap are theoretically as well as numerically examined. The normalized relationship between Ap/A versus Ap/Ae is equivalent to the Johnson’s hardness plot of HM/Y versus E′tan β/Y. By extending the concept of Ae and Ap to time-dependent viscoelastic-plastic regime, a detailed discussion is made how to eliminate the plastic deformation/flow from the total contact area A(t) to yield the viscoelastic contact area Ave(t) prior to determining the linear-viscoelastic parameters and functions.

Crystalline pentagonal nano- and microrods (PRs) and pentagonal nano- and microparticles (PPs) with 5-fold symmetry are studied. Structure of PRs and PPs and their elastic distortions are characterized in the framework of the disclination approach. Relaxation of mechanical stresses due to disclinations causes structural transformations in PRs and PPs. Experimental evidence of such transformations, namely, the appearance of internal cavities and pores, and growth of whiskers in copper PRs and PPs grown in the process of electrodeposition is demonstrated. A brief review of existing models of stress relaxation in PRs and PPs is presented. We discuss a new model of nanowhisker growth based on the nucleation of two dislocation loops of opposite signs near the surface of the crystal with disclination. As a result, vacancy-type dislocation loop remains in the material and serves as a nucleus for cavity, while the interstitial loop comes to the free surface and contributes to whisker growth.

Thin films of GaNBi alloys with up to 12.5 at.% Bi were grown on sapphire using low-temperature molecular beam epitaxy. The low growth temperature and incorporation of Bi resulted in a morphology of nanocrystallites embedded in an amorphous matrix. The composition and optical absorption shift were found to depend strongly on the III:V ratio controlled by the Ga flux during growth. Increasing the incorporation of Bi resulted in an increase in conductivity of almost five orders of magnitude to 144 Ω-cm−1. Holes were determined to be the majority charge carriers indicating that the conductivity most likely results from a GaNBi-related phase. Soft x-ray emission and x-ray absorption spectroscopies were used to probe the modification of the nitrogen partial density of states due to Bi. The valence band edge was found to shift abruptly to the midgap position of GaN, whereas the conduction band edge shifted more gradually.

Depending on the Ni:Co molar ratio, composites of NiCo/carbon nanorods and NiCo/carbon nanotubes can be synthesized through catalytic decomposition of benzene at 500 °C over NiCo nanoparticles derived from sol–gel synthesis followed by hydrogen reduction. According to x-ray diffraction results, the average grain size of NiCo31 is 11.2 nm, whereas that of NiCo13 and NiCo22 is 24.9 nm. Field-emission scanning electron microscopic and high-resolution transmission electron microscopic images reveal that over NiCo13 and NiCo22, the carbon nanomaterials are mainly in the form of nanorods, whereas over NiCo31, they are in the form of nanotubes. The composites of carbon and NiCo alloy are highly stable in air and show soft magnetic property and almost equal coercivity. It is observed that the saturation magnetization is affected by the composition of NiCo alloy.

Pile-up or sink-in is always a concern in a nanoindentation test because it gives rise to errors in the estimation of the projected contact area when it is theoretically analyzed with the classic Oliver–Pharr method. In this study, a three-dimensional finite element model is developed to simulate nanoindentation with a perfect Berkovich tip. The variation of the contact profile with respect to the work-hardening rate n and the ratio of yield stress to elastic modulus σy/E has been studied for a wide range of elastoplastic materials. The numerical results show that a low σy/E not only facilitates the pile-up for materials with little or no work-hardening but also enhances the sink-in for materials with a high work-hardening rate. It is attributed to the lateral-flow dominated plastic deformation in low work-hardening materials and the normal-flow dominated plastic deformation in high work-hardening materials, respectively. Because of the large sink-in, for the materials with high n and low σy/E, significant errors in the calculation of the projected contact area can be generated by using the classic Oliver–Pharr method.

An oleylamine-assisted solvothermal approach has been developed for the synthesis of nickel hydroxide nanomaterials. α-Ni(OH)2 flower-like spheres and β-Ni(OH)2 hexagonal sheets were obtained by tuning the water volume in the synthesis system. The water-induced phase and morphology evolution from α-Ni(OH)2 spheres to β-Ni(OH)2 sheets were investigated in detail by controlled experiments based on their crystal structures. Moreover, NiO spheres and sheets were obtained by direct thermal decomposition of corresponding nickel hydroxides. N2 adsorption/desorption, temperature-programmed reduction with H2, and catalytic activity tests reveal that NiO spheres exhibit higher surface area, larger pore volume, higher reducibility, and better catalysis activities for CO oxidation than NiO sheets.

Nd3+/Yb3+ co-doped TiO2–La2O3 glasses modified by ZrO2 were fabricated by containerless method. Under the excitation of 980 nm lasers, three intense emissions centered at 521, 545, and 655 nm were observed, which are assigned to the Nd3+: 4G9/2→4I9/2, 4G7/2→4I9/2, and 4G7/2→4I13/2 transitions, respectively. Besides, two very weak emission bands at 496 and 603 nm were also found due to the Nd3+ transition of 2G9/2→4I9/2 and 4G5/2 (or 2G7/2)→4I9/2, respectively. Pumping powder dependence of emission intensity suggests a two-photon adsorption process responsible for the upconversion luminescence. A combined phonon-assisted and cooperative sensitization mechanism is presented to interpret the energy transfer from Yb3+ to Nd3+ ions. In addition, the highest intensity of luminescence was found for the glass with 1.2 mol% Nd3+, and the upconversion efficiency can be enhanced by increasing of ZrO2 content.

Anelastic recovery of pure magnesium was monitored quantitatively by means of acoustic emission (AE) in cyclic compression–quick unloading–recovery process. The influences of grain size, strain rate, and the strain-controlled cyclic process on anelastic recovery were analyzed in details. A detwinning model in anelastic recovery process was proposed, and the results showed good agreement with the experimental data. Three stages of anelastic recovery behavior as a function of strain were observed: stages I and III were considered to be dominated by various detwinning processes and stage II was dominated by thermal motion of dislocation. A quantitative relationship between anelastic recovery strain and AE signals was obtained, and from which the anelastic recovery strains from dislocation motion and detwinning were separated for the first time. In the strain-controlled cyclic process, both the amount of AE signals and the anelastic recovery strain were observed to decrease while the fraction of anelastic recovery strain from dislocation motions was observed to decrease more rapidly than that from detwinning with increasing cyclic number.

We report synthesis of nanosize LiFePO4 and C-LiFePO4 powders with a narrow particle size distribution (20–30 nm) by ethanol-based sol–gel method using lauric acid (LA) as a surfactant for high specific capacity lithium-ion battery cathode material. X-ray diffraction measurements demonstrated that the samples were single-phase materials without any impurity phases. The average crystallite size was found to decrease slightly from 29 nm to approximately 23 nm with carbon coating. The ratio of the Raman D-band (∼1350 cm−1) to G-band (∼1590 cm−1) intensities (ID/IG) and electronic conductivity of these materials show strong dependence on the amount of surfactant coverage. Remarkably, cell prepared with carbon-coated LiFePO4 synthesized using 0.25 M solution of LA showed a very large specific capacity approaching the theoretical limit of 170 mAh/g, in stark contrast to the specific capacity of cell consisting of pure of LiFePO4 (∼75 mAh/g) measured at the same C/2 discharge rate.

The hardness of the carbon nanotubes (CNTs)-doped diamond-like carbon (DLC) films is modeled by a nanoindentation finite element analysis. A three-dimensional (3D) formation where CNTs are modeled as transverse isotropy is compared with a two-dimensional (2D) analysis with isotropic CNTs. The results showed that for small CNTs volume fraction, the overall hardness of CNTs/DLC/Si composites is controlled by the elastic modulus along the indentation direction. For vertical CNTs-doped DLC films, the hardness in 3D analysis is close to that in 2D analysis if the isotropic elastic modulus is taken as the long-axis direction. However, for horizontal CNTs-doped DLC films, the hardness in 3D and in 2D is similar if the 2D isotropic elastic modulus is taken as the short-axis direction of the 3D elastic modulus. As a result, for small CNTs volume fraction, the hardness of CNTs/DLC/Si composites can be modeled by a 2D isotropic inclusion as long as the elastic modulus is chosen properly. The hardness in CNTs/DLC/Si composites depends on the orientation of CNTs and the volume fraction. The mechanisms in hardness enhancement for different CNT orientations are explained by shear stress and the effective projected area. The issues like interface strength and indentation size effect are also addressed in terms of CNT orientations.