An amorphous polymer was contacted by a Berkovich indenter using the same loading history but with four different unloading rates following a wide range of load-hold time periods. The strain-rate sensitivity index of the creeping solid was determined at each load-hold period based on two readily determinable parameters, which are the effective contact stiffness and strain rate at the onset of unloading. The measured strain-rate sensitivity index was found to increase with decreasing load-hold period, suggesting that the elastic moduli of the amorphous polymers determined by nanoindentation (together with the true contact area) depends significantly on the selection of the load-hold period. The rheological condition of the creeping solid under constant load changes substantially with time to affect the subsequent unloading recovery process. It is therefore advisable to control not only the unloading strain rate but also the load-hold period when testing time-dependent materials.

Flowerlike manganese oxide microspheres and cryptomelane-type manganese oxide nanobelts were selectively synthesized by a simple decomposition of KMnO4 under mild hydrothermal conditions without using template or cross-linking reagents. The effect of varying the hydrothermal times and temperatures on the nanostructure, morphology, compositional, and electrochemical properties of the obtained manganese oxides was investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies showed that the flowerlike manganese oxide microspheres could be obtained at relatively low hydrothermal temperatures, while high hydrothermal temperatures were favorable for the formation of cryptomelane-type manganese oxide nanobelts. A morphology and crystalline evolution of the nanostructures was observed as the hydrothermal temperature was increased from 180 to 240 °C. On the basis of changing the temperatures and hydrothermal reaction times, the formation mechanism of cryptomelane-type manganese oxide nanobelts is discussed. Cyclic voltammetry (CV) was used to evaluate the electrochemical properties of the obtained manganese oxide nanostructures, and the results show that the electrochemical properties depend on their shape and crystalline structure. This easily controllable, template-free, and environmentally friendly method has the potential for being used in syntheses of manganese oxide nanomaterials with uniform morphologies and crystal structures.

Small-scale depth-sensing indentation (nanoindentation) is a popular technique for measuring the mechanical properties of a wide range of materials. Contact mechanics solutions used in data analysis are based on the indentation of a homogeneous half-space, but the experiments are frequently conducted on mineralized biological tissues—biocomposite materials with nanometer-scale features—such as bone and dentin. The current study examines the experimental indentation response of bone across orders of magnitude in contact dimension length-scale, from nanometers to micrometers. Scaling arguments are used to establish the need for nanoscale simulations of mineralized tissue indentation. A finite element model of an inhomogeneous contact problem is developed and used to interpret experimental indentation data on bone and dentin. Both experimental data and modeling results demonstrate a convergence in apparent elastic modulus at increasing contact length-scales. Models results are used to estimate a feature size associated with inhomogeneity of the indentation response; for experiments conducted here the characteristic feature size is found to be substantially larger for bone than for dentin, and in both cases larger than for individual nanometer-scale mineral platelets.

Hydrogenated nanocrystalline Si (nc-Si:H) thin films were prepared by plasma- enhanced chemical vapor deposition (PECVD). The films were deposited with a radio-frequency power of 100 W, while substrates were exposed to direct current (dc) biases in the range from 0 to −400 V. The effects of dc bias on the formation of nanoscale Si crystallites in the films and on their optical characteristics were investigated. The size of the Si crystallites in the films ranges from ∼1.9 to ∼4.1 nm. The relative fraction of the crystallites in the films reached up to ∼56.5% when a dc bias of −400 V was applied. Based on the variation in the structural, chemical, and optical features of the films with dc bias voltages, a model for the formation of nanostructures of the nc-Si:H films prepared by PECVD was suggested. This model can be utilized to understand the evolution in the size and relative fraction of the nanocrystallites as well as the amorphous matrix in the nc-Si:H films.

We propose a parallel resistance model (PRM) in which total resistance (Rtotal) is given by the parallel connection of resistance of a filament (Rfila) and that of a film excluding the filament (Rexcl)—that is, 1/Rtotal = 1/Rfila + 1/Rexcl—to understand direct current (dc) electric properties of resistive random-access memory (ReRAM). To prove the validity of this model, the dependence of the resistance on temperature, R(T), and the relative standard deviation (RSD) of RHRS of Pt/NiO/Pt on the area of a top electrode, S, are investigated. It is clarified that both the R(T) and RSD depended on S, and all such dependencies can be explained by the PRM. The fact that Rtotal is decided by the magnitude relation between Rfila and Rexcl makes transport properties S-dependent and hinders the correct understanding of ReRAM. Smaller S is essential to observe the intrinsic transport properties of ReRAM filaments.

A combustion-synthesized AlN powder was investigated for use as a starting material in obtaining a high thermal conductivity AlN by microwave sintering followed by microwave reheating under a reducing atmosphere. Microwave sintering was found to proceed very quickly so that a density of 99.5% of theoretical with a thermal conductivity of 165 W/mK was achieved after sintering at 1900 °C for 5 min. The thermal conductivity could be improved by prolonging the soaking time, which is attributed to decreases in both oxygen content and secondary phases by evaporation and sublimation of the secondary phases. The reducing atmosphere was created by adding carbon particles to the AlN packing powder surrounding the specimen. The thermal conductivity could be significantly improved by microwave reheating of the sintered specimen under the reducing atmosphere. This is considered to be due to enhanced removal of the secondary phases by the reducing atmosphere. Sintering under the reducing atmosphere was found to retard densification because of the earlier removal of the secondary phases, thus resulting in a poor densification and a low thermal conductivity.

The present study shows that the as-melt-spun Zr28Y28Al22Co22 amorphous ribbon undergoes solid-state phase separation into Zr- and Y-rich regions when heated below the glass transition temperature (Tg). Dynamic mechanical measurements show that two types of low-temperature relaxation occur below Tg, and transmission electron microscopy observation confirms the solid-state phase-separated microstructure. The diffusion coefficient of solid-state phase separation is calculated by the measured separation distance.

Two important analytical means—theoretical bounds and homogenization techniques—have gained increasing attention and led to substantial progress in material research. Nevertheless, there is a lack of relating material microstructures to an entire theoretical bound and exploring the possibility of generating multiple microstructures for each property value. This paper aims to provide a microstructure diagram in relation to “bound B” constructed by translation and Weiner bounds. The inverse homogenization technique is used to seek for the optimal phase distribution within a base cell model to make the effective conductivity approach the “bound B” in two- or three-phase material cases. The design shows that the “bound B” is exactly attainable for two-phase composites even with single-length-scale microstructures. Although the multiphase translations bounds are well known to be asymptotically attainable on some parts, they still appear too roomy to be attained by single-length-scale composites. Our results showed a certain improvement in the attainability of single-length-scale structural composites when compared with new bounds established by [V. Nesi: Proc. R. Soc. Edinburgh Sect. A125, 1219 (1995)], [V. Cherkaev: Variational Methods for Structural Optimization (Springer Verlag, New York, 2000)], and (N. Albin et al.: Proc. R. Soc. London Ser. A463, 2031 (2007)]. Applicability of the translation bounds to the composites with high-contrast conductivities of phase compositions is also studied in this paper. Finally, we explore the multiple solutions to the optimal microstructures and categorize them into three classes in line with their topological resemblance, namely, spatially identical, unidirectionally identical, and bidirectionally different solutions.

Field-activated electroactive polymers (FEAPs) are a class of electroactive polymers that are insulating and exhibit coulombic interaction with and dipole formation in response to external electric signals. There are many polarization mechanisms in insulating polymers, from the molecular to the mesoscopic and even the macroscopic level, which couple strongly with mechanical deformation and can be used to create polymer actuators and sensors. FEAPs feature fast response speed limited by the polymer dielectric and elastic relaxation time, a very large strain level (to more than 100% strain), high electromechanical efficiency, the ability to operate down to micro/nanoelectromechanical devices, and a highly reproducible strain response under electric fields. One challenge in FEAP actuators and electromechanical devices is reducing the operation voltage to below 100 V or even 10 V while achieving an electromechanical conversion efficiency comparable with that of inorganic electroactive materials.

A new amphiphile: octyl-β-D-glucopyranoside along with a single-source precursor, barium titanium methoxyethoxide, were used to develop a facile route for synthesis of BaTiO3, via either a hydrolytic or a nonhydrolytic method. The average particle size for the samples was on the order of 20 to 30 nm, while that for the control samples (without the amphiphile) ranged from 100 nm to several microns. The high-resolution transmission electron microscopy (HRTEM) images and selected-area electron- diffraction patterns revealed that these nanoparticles were single crystalline; the Raman active longitudinal optical modes observed in calcined (650 °C) samples at 718 and 304 cm−1 directly indicated the presence of tetragonal domains in an overall cubic lattice structure. Moreover, the one-step nonhydrolytic approach developed for the synthesis of BaTiO3 is fast, and it eliminates tedious steps such as prolonged refluxing and aging. Thermogravimetric and Fourier transform infrared (FTIR) analysis were performed to investigate the role of octyl-β-D-glucopyranoside in the evolution of the perovskite phase, grain size, and morphology. These techniques suggested that van der Waals type of interactions were present between the amphiphile and barium titanium methoxyethoxide oligomers, and in turn they led to the controlled growth of nanoparticles.

A new grain-growth mode is observed in thick sputtered copper films. This new grain-growth mode, also referred to in this work as super secondary grain growth (SSGG) leads to highly concentric grain growth with grain diameters of many tens of micrometers, and drives the system toward a {100} texture. The appearance, growth dynamics, final grain size, and self-annealing time of this new grain-growth mode strongly depends on the applied bias voltage during deposition of these sputtered films, the film thickness, the post-deposition annealing temperature, and the properties of the copper diffusion barrier layers used in this work. Moreover, a clear rivalry between this new growth mode and the regularly observed secondary grain-growth mode in sputtered copper films was found. The microstructure and texture evolution in these films is explained in terms of surface/interface energy and strain-energy density minimizing driving forces, where the latter seems to be an important driving force for the observed new growth mode. By combining these sputtered copper films with electrochemically deposited (ECD) copper films of different thickness, the SSGG growth mode could also be introduced in ECD copper, but this led to a reduced final SSGG grain size for thicker ECD films. The knowledge about the thin-film level is used to also implement this new growth mode in small copper features by slightly modifying the standard deposition process. It is shown that the SSGG growth mode can be introduced in narrow structures, but optimizations are still necessary to further increase the mean grain size in features.

Transmission electron microscopy (TEM) and fast Fourier transformation (FFT) analysis were used to examine the microstructures of amorphous carbon (a-C) films deposited on Si(100) by radio-frequency (rf) sputtering without magnetron. TEM analysis revealed that a-C films synthesized under certain deposition conditions contained randomly dispersed nanocrystallites ∼35 Å in size. FFT results indicated that the nanocrystallites possessed diamondlike cubic structures with their close-packed {111} planes parallel to the film surface. The formation of diamondlike nanocrystallites is attributed to metastable carbon atom clusters of trigonal carbon hybridization that were sputtered off from the graphite target under certain process conditions. Cluster distortion upon deposition onto the growing film surface by the bombarding Ar+ ions promoted tetrahedral carbon atom hybridization and, possibly, epitaxial growth of diamondlike nanocrystallites for a short duration.

Nanoparticles of antimony-doped tin oxide (ATO) were characterized for 0–33.3% Sb doping, both in aqueous dispersion and as dried powder. Antimony is incorporated in the cassiterite SnO2 structure of the ATO nanoparticles (d ≈ 7 nm) up to the highest doping levels, mainly as SbV, but with increasing Sb doping the SbIII content increases. We found adsorption of NH3 at the particle surface and evidence for the incorporation of nitrogen in the crystal lattice of the particles. The total nitrogen content increases with increasing Sb doping of the particles. Compact powder conductivity measurements show an increase in conductivity of ATO powder up to 13% Sb and a small decrease for higher Sb contents. Furthermore, we show that these particles can be used to prepare highly transparent conductive cross-linked ATO/acrylate nanocomposites with a continuous fractal particle network through the polymer matrix and a very low percolation threshold (ϕc ≈ 0.3 vol%).

Gels, soft polymeric or composite materials that have a high fraction of water, are often found as structural materials and actuators in nature but have so far not found many uses when fabricated synthetically. We first examine some natural systems such as jellyfish, sea anemones, starfish, legumes, and human tissue, all having interesting ways of moving or otherwise reacting to the surrounding environment. Then we discuss swelling and cross-linking of hydrogels, followed by a look at actuation by electrically, thermally, and chemically stimulated gels, noting that electrical stimulation needs a chemical intermediary to show substantial actuation (comparable to human muscle, for instance). Electroactive gels have great potential as sensors and actuators but their actual uses are mainly restricted to passive drug delivery and matrices for sensors. For most applications as artificial muscles, electrically driven actuators are too weak, but chemically driven actuators look very promising. Better ways of coupling electrical energy to chemically driven gels are needed.