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.

In this work, the silk fibroin/sericin (SF/SS) blend aqueous solutions with different SF/SS mass ratios (100/0, 90/10, 85/15, 75/25, and 65/35) were prepared and electrospun to get regenerated fibers. It was found that the addition of SS in the SF solution could increase the apparent viscosity of the solution and improve its electrospinnability so that the fine uniform electrospun SF/SS fibers could be obtained. The quantitative analysis result of Raman spectroscopy showed that the presence of SS facilitated the conformational transition of SF from random coil/α-helix structure to β-sheet structure. Combined with the differential scanning calorimetry result, it was further hypothesized that SS could affect the structural change of SF by dehydrating SF and inducing the formation of hydrogen bonds between SF molecules. Consequently, SS also played an important and positive role in the thermal and mechanical properties of the resultant SF/SS fibers.

Peripherally and nonperipherally tetrakisoctylthio- and tetrakisoctyloxy-substituted lead(II) phthalocyanines (PbPcs) were synthesized and characterized using elemental analysis, nuclear magnetic resonance, ultra violet–visible (UV-Vis), infrared (IR), and mass spectroscopies. The mesogenic properties of PbPcs were studied by differential scanning calorimetry, polarized optical microscopy, and x-ray diffraction. The effects of the substitution position and nature of linkage heteroatom on the liquid-crystalline properties and the orientation of the molecules were also studied. Visible absorption spectroscopy yielded an evidence of a thermally induced molecular reorganization in the films. Reflection–absorption IR spectroscopy was used to study the preferential orientation of molecules relative to the substrate surface. The intense bands in the IR spectra of the PbPcs were assigned with the aid of quantum chemical (density functional theory) computations.

Nitrogen-doped multiwalled carbon nanotubes with poly(bisphenol A carbonate) composites were prepared through simple solution blending. The scaling law, which is based on the percolation theory, is used to describe the electrical conductivities of the composites. Both direct current and alternating current conductivities are in good agreement with the unprecedented high saturated conductivities of the pristine samples (σsat = ∼734 s·cm−1, pc = 0.19 wt%). We attributed the high conductivities to the binding of nanotubes into large but tight bundles, which enable the composites to carry more charges. This is notably different from the conventional method, which focuses on forming a well-dispersed three-dimensional network resulting in the conductivities having a lower order of magnitude.

Indentation methods have been widely used to study bone at the micro- and nanoscales. It has been shown that bone exhibits viscoelastic behavior with permanent deformation during indentation. At the same time, damage due to microcracks is induced due to the stresses beneath the indenter tip. In this work, a simplified viscoelastic-plastic damage model was developed to more closely simulate indentation creep data, and the effect of the model parameters on the indentation curve was investigated. Experimentally, baseline and 2-year postovariectomized (OVX-2) ovine (sheep) bone samples were prepared and indented. The damage model was then applied via finite element analysis to simulate the bone indentation data. The mechanical properties of yielding, viscosity, and damage parameter were obtained from the simulations. The results suggest that damage develops more quickly for OVX-2 samples under the same indentation load conditions as the baseline data.

Solid polymer electrolytes (SPEs) with poly(vinylidene fluoride-hexafluoropropylene) [P(VdF-HFP)] as polymer host, doped with lithium trifluoromethanesulfonate (LiTf) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIMTf) have been synthesized via solution casting method. This P(VdF-HFP)/LiTf/BMIMTf-based SPE achieves ∼2.4 × 10−3 and ∼1.1 × 10−2 S·cm−1 at 30 and 80 °C, respectively, with 100 part by weight of BMIMTf incorporated into the system. A very interesting trend of temperature-dependence ionic conductivity has been obtained. A rationalization of the trend is given and the morphological changes observed in scanning electron micrographs seem to be commensurate with it. Thermogravimetric and differential thermogravimetric analyses reveal some changes in thermal properties of the SPEs, including the possibility of phase separation happening in the sample.

In this work, the ultimate bending strengths of as-grown Si and fully oxidized Si nanowires (NWs) were investigated by using a new atomic force microscopy (AFM) bending method. NWs dispersed on Si substrates were bent into hook and loop configurations by AFM manipulation. The adhesion between NWs and the substrate provided sufficient restraint to retain NWs in imposed bent states and allowed subsequent AFM imaging. The stress and friction force distributions along the bent NWs were calculated based on the in-plane configurations of the NWs in the AFM images. As revealed from the last-achieved bending state, before fracture, fracture strengths close to the ideal strength of materials were attained in these measurements: 17.3 GPa for Si NWs and 6.2 GPa for fully oxidized Si NWs.

Transparent conducting oxide films are usually several 100-nm thick to achieve the required low sheet resistance. In this study, we show that the filtered cathodic arc technique produces high-quality low-cost ZnO:Al material for comparably smaller thicknesses than achieved by magnetron sputtering, making arc deposition a promising choice for applications requiring films less than 100-nm thick. A mean surface roughness less than 1 nm is observed for ZnO:Al films less than 100-nm thick, and 35-nm-thick ZnO:Al films exhibit Hall mobility of 28 cm2/Vs and a low resistivity of 6.5 × 10−4 Ωcm. Resistivity as low as 5.2 × 10−4 Ωcm and mobility as high as 43.5 cm2/Vs are obtained for 135-nm films.

TiN–indium composite films were deposited by simultaneous sputtering of titanium and indium in a mixed Argon/Nitrogen atmosphere and characterized for tribological applications. Film compositions showed a nonlinear behavior as a function of sputter gun power. For films deposited at −50 V bias, and containing less than 29 relative percent indium, the films had a face centered cubic structure, but at higher indium contents (63–82%) the structure was not consistent with either TiN or indium. At −150 V bias, the films had either the TiN structure, In-type structure, or a mixture of the two. Atomic force microscopy images showed the formation of semispherical drops on the surface of the samples deposited at −50 V bias voltage, whereas at −150 V bias voltage the samples exhibited a smooth coating surface with occasional ellipsoidal blisters. Nanoindentation test of the films shows low hardness (5–12 GPa), but tribological testing showed that frictional behavior can be improved by moderate heating before testing, suggesting indium segregation to the surface.

Organic plasma polymers are currently attracting significant interest for their potential in the areas of flexible optoelectronics and biotechnology. Thin films of plasma-polymerized polyterpenol fabricated under varied deposition conditions were studied using nanoindentation and nanoscratch analyses. Coatings fabricated at higher deposition power were characterized by improved hardness, from 0.33 GPa for 10 W to 0.51 GPa for 100 W at 500-μN load, and enhanced wear resistance. The elastic recovery was estimated to be between 0.1 and 0.14. Coatings deposited at higher RF powers also showed less mechanical deformation and improved quality of adhesion. The average (Ra) and root mean square (Rq) surface roughness parameters decreased, from 0.44 nm and 0.56 nm for 10 W to 0.33 nm and 0.42 nm for 100 W, respectively.

After some background discussion, this review will focus on some recent developments in the areas of theoretical studies of semiconductor electronic structure, photovoltaics, semiconducting boron nitride nanotubes, and the search for modified semiconductors and insulators with higher superconducting transition temperatures. The background discussion covers the evolution of studies of solids, which changed dramatically after the development of quantum theory. These conceptual changes resulted in methods for calculating properties of materials and theoretical frameworks for interpreting experimental measurements. In some cases, the theoretical approaches have been successful in predicting new materials and new properties. As stated above, a few examples will be given to illustrate the development of this field.

To understand the brittleness transition in low-toughness materials, the nucleation and kinetics of dislocations must be measured and modeled. One aspect overlooked is that the apparent activation energy for plasticity is modified at very high stresses. Coupled with state of stress and length scale effects on plasticity, the lowering of the brittle-to-ductile transition (BDT) in such materials can be partially understood. Experimental evidence in silicon single crystals in the length scale regime of 40 nm to 1 mm is presented. It is shown that high stress affects both length scale and temperature-dependent properties of activation volume and activation energy for dislocation nucleation and/or mobility. Nanoparticles and nanopillars of single-crystal silicon demonstrate unexpectedly high fracture toughness at low temperatures under compression. A thermal activation approach can model the three decades of size associated with the factor of three absolute temperature shift in the BDT.

Most biological materials are hierarchically structured composites that often possess exceptional mechanical properties. We show that nanoindentation can be a powerful tool for understanding the structure‑mechanical property relationship of biological materials and illustrate this for fish teeth and scales, not heretofore investigated at the nanoscale. Piranha and shark teeth consist of enameloid and dentin. Nanoindentation measurements show that the reduced modulus and hardness of enameloid are 4‑5 times higher than those of dentin. Arapaima scales are multilayered composites that consist of mineralized collagen fibers. The external layer is more highly mineralized, resulting in a higher modulus and hardness compared with the internal layer. Alligator gar scales are composed of a highly mineralized external ganoin layer and an internal bony layer. Similar design strategies, gradient structures, and a hard external layer backed by a more compliant inner layer are exhibited by fish teeth and scales and seem to fulfill their functional purposes.

Half-Heusler (HH) phases, a versatile class of alloys with promising functional properties, have recently gained attention as emerging thermoelectric materials. These materials are investigated from the perspective of thermal and electronic transport properties for enhancing the dimensionless figure of merit (ZT) at 800–1000 K. The electronic origin of thermopower enhancement is reviewed. Grain refinement and embedment of nanoparticles in HH alloy hosts were used to produce fine-grained as well as nanocomposites and monolithic nanostructured materials. Present experiments indicated that n-type Hf0.6Zr0.4NiSn0.995Sb0.005 HH alloys and p-type Hf0.3Zr0.7CoSn0.3Sb0.7/nano-ZrO2 composites can attain ZT = 1.05 and 0.8 near 900–1000 K, respectively. The observed ZT enhancements could be attributed to multiple origins; in particular, the electronic origin was identified. The prospect for higher ZT was investigated in light of a recently developed nanostructure model of lattice thermal conductivity. Tests performed on p–n couple devices from the newly developed HH materials showed good power generation efficiencies—achieving 8.7% efficiency for hot-side temperatures of about 700 °C.

Nanopillars and nanocoils fabricated by chemical vapor deposition using a focused ion beam were used to estimate bending and torsional rigidities under infinitesimal deformation and to investigate nonlinear large deformation behaviors. For the pillars, we performed bending tests using a unique double-cantilever specimen, which was made by joining two pillars together using focused electron beam deposition in a scanning electron microscope. The reproducible load–deflection curves, which were not severely disturbed by the ambiguous chuck condition of the specimens, indicated that the pillar deformation resistance decreased after the linear response (called softening), and it was dependent on the pillar diameter and the ratio of diameter to length. However, all pillars became extremely hardened at large deformation. At diameters of less than 300 nm, and at diameter/length ratios of over 10−2, this nanopillar size effect (characterized as softening) was consistently observed.

Nanomechanical testing of silicon is primarily motivated toward characterizing scale effects on the mechanical behavior. “Defect-free” nanoscale silicon additionally offers a road to large deformation permitting the investigation of transport characteristics and surface instabilities of a significantly perturbed atomic arrangement. The need for developing simple and generic characterization tools to deform free-standing silicon beams down to the nanometer scale, sufficiently equipped to investigate both the mechanical properties and the carrier transport under large strains, has been met in this research through the design of a versatile lab-on-chip. The original on-chip characterization technique has been applied to monocrystalline Si beams produced from Silicon-on-Insulator wafers. The Young’s modulus was observed to decrease from 160 GPa down to 108 GPa when varying the thickness from 200 down to 50 nm. The fracture strain increases when decreasing the volume of the test specimen to reach 5% in the smallest samples. Additionally, atomic force microscope-based characterizations reveal that the surface roughness decreases by a factor of 5 when deforming by 2% the Si specimen. Proof of concept transport measurements were also performed under deformation up till 3.5% on 40-nm-thick lightly p-doped silicon beams.

The influence of Co content on stacking fault energy (SFE) of the γ matrix in four Ni–Co base superalloys, including newly developed alloys, has been studied by utilizing high-resolution transmission electron microscopy. The results indicated the SFE was not linear with Co content of the γ matrix. The lowest SFE could be attained at around 34.0 at.% Co. This effect was attributed to variation of electron holes, saturated Co content in the matrix, and the effect of Co on the partition coefficient of other alloying elements. A high density of twins was related to low SFE and could improve the mechanical properties.

Friction forces for a nanowire (NW) elastically bent on flat substrate were investigated both theoretically and experimentally. Models based on elastic beam theory were proposed considering balance of external, frictional, and elastic forces along the NW. The distributed friction force was determined for two cases: (i) the NW was uniformly dragged at its midpoint and bent by kinetic friction forces and (ii) the NW was held in a bent state by static friction forces. The first case considers a uniform distribution of kinetic friction along the NW and enables the measurement of the friction force from the elastically deformed NW profile. The second case exploits the interplay between static friction and elastic forces inside the NW to find the distributed friction force. An original method for the measurement of frictional forces in both cases while maintaining total force and momentum equilibrium was introduced and demonstrated for ZnO NWs on a Si wafer. Averaged kinetic and static friction forces were compared for the same individual NW.