Carbon nanofibers (CNFs) with different microstructures were synthesized by thermal chemical vapor deposition using different growth temperatures and methane/nitrogen gas mixtures. High-resolution transmission electron microscopy images revealed that bamboolike structure could be formed both by increasing the growth temperature and by increasing the nitrogen content in the reaction atmosphere at a lower growth temperature. Elemental analysis results indicated that no significant change in the nitrogen concentration was found regardless of the increase of nitrogen flow in the feed gas. The formation of bamboolike structure of CNFs and the effect of nitrogen gas on the microstructure change of CNFs were discussed.

Piezoresponse force microscopy (PFM) is a powerful method widely used for nanoscale studies of the electromechanical coupling effect in various materials systems. Here, we review recent progress in this field that demonstrates great potential of PFM for the investigation of static and dynamic properties of ferroelectric domains, nanofabrication and lithography, local functional control, and structural imaging in a variety of inorganic and organic materials, including piezoelectrics, semiconductors, polymers, biomolecules, and biological systems. Future pathways for PFM application in high-density data storage, nanofabrication, and spectroscopy are discussed.

Coupling between mechanical and electrical phenomena is ubiquitous at the nano-and molecular scales, with examples ranging from piezoelectricity and flexoelectricity in perovskites to complex molecular transformations in redox active molecules and ion channels. This article delineates the field of nanoelectromechanics enabled by recent advances in scanning probe, indentation, and interferometric techniques and provides a unified outlook at a number of related topics, including membrane and surface flexoelectricity, local piezoelectricity in ferroelectrics and associated devices, and electromechanical molecular machines. It also summarizes experimental and theoretical challenges on the pathway to visualize, control, and manipulate electromechanical activity on the nanoscale and molecular levels.

Three solid solutions of pyrochlores in the series Nd2-yearsGdyZr2O7 (y = 0.8, 1.0, 1.2) were synthesized by the gel combustion method using citric acid as fuel. This results in a soft agglomerate powder as verified by dynamic light scattering. The single-phase nature of the products has been confirmed by x-ray diffraction. The increase in full width at half-maxima in the Raman spectra with an increase in Gd3+ content indicates that disorder increases with Gd3+ content. The morphology and particle size of the products were investigated by transmission electron microscopy. Scanning electron microscopy study reveals that the sintered pellets have a density higher than 92% of theoretical densities. The total ionic conductivity measurements in the temperature range 375–800 °C show that with the increase of disorder (Gd3+ content) in the system the activation energy of conduction increases from 0.98 to 1.06 eV and the preexponential factor, which is proportional to the number of mobile species, also follow the same trend of increase. The total conductivity measured in reducing atmosphere shows no change in electrical conductivity, which verifies a negligible contribution of electronic contribution in this system.

The structural characteristics of TiMn1.5Vx (x = 0.1–0.5) alloys and the hysteresis phenomenon in the TiMn1.5Vx-H2 system have been studied. The TiMn1.5Vx alloy consists mainly of the C14 Laves phase plus some of the BCC solid solution phase, depending on x. The lattice parameters of the C14 Laves phase increase slightly as x increases from 0.1 to 0.2 but are invariant with a further increase in x up to 0.3–0.5. The pressure-composition isotherms clearly show a pressure hysteresis in the TiMn1.5Vx-H2 system which decreases with an increase in the x value mainly due to the equilibrium pressure change for hydride formation. The free energy loss during hydride formation is related to not only the volume expansion, but also the elastic strain in the TiMn1.5Vx alloy itself, that is, prior to hydrogen absorption.

In situ devitrification and consolidation of gas atomized Al87Ni8La5 glassy powders into highly dense bulk specimens was carried out by spark plasma sintering. Room temperature compression tests of the consolidated bulk material reveal remarkable mechanical properties, namely, high compression strength of 930 MPa combined with plastic strain exceeding 25%. These findings demonstrate that the combined devitrification and consolidation of glassy precursors by spark plasma sintering is a suitable method for the production of Al-based materials characterized by high strength and considerable plastic deformation.

Piezoelectric microelectromechanical systems (MEMS) offer the opportunity for high-sensitivity sensors and large displacement, low-voltage actuators. In particular, recent advances in the deposition of perovskite thin films point to a generation of MEMS devices capable of large displacements at complementary metal oxide semiconductor-compatible voltage levels. Moreover, if the devices are mounted in mechanically noisy environments, they also can be used for energy harvesting. Key to all of these applications is the ability to obtain high piezoelectric coefficients and retain these coefficients throughout the microfabrication process. This article will review the impact of composition, orientation, and microstructure on the piezoelectric properties of perovskite thin films such as PbZr1−xTixO3 (PZT). Superior piezoelectric coefficients (e31, f of −18 C/m2) are achieved in {001}-oriented PbZr0.52Ti0.48O3 films with improved compositional homogeneity on Si substrates. The advent of such high piezoelectric responses in films opens up a wide variety of possible applications. A few examples of these, including low-voltage radio frequency MEMS switches and resonators, actuators for millimeter-scale robotics, droplet ejectors, energy scavengers for unattended sensors, and medical imaging transducers, will be discussed.

The effect of prestrain on microstructure and mechanical behavior of aged Ti–10V–2Fe–3Al alloy was investigated. The results showed that prestrain caused the tensile strength to decrease by 5%, but the elongation to fracture significantly improved by about 200%, in comparison with the unstrained samples, using a much shorter aging time. Transmission electron microscopy investigations showed that nano-sized alpha (α) particles homogeneously precipitated in the beta (β) matrix, and continuous α films formed along grain boundaries in the unstrained and aged samples. However, in the prestrained samples, the coarse stress induced martensite laths decomposed into α- and β-phases in the form of alternately arranged plates, which suppressed formation of the continuous grain boundary α films during aging. The hardness of the prestrained samples was lower than that of the unstrained samples after the same aging treatments. The enhancement of ductility can be mainly attributed to the suppression of grain boundary α films and the reduced hardness in prestrained samples.

Polycrystalline HoGaMnO5, ErGaMnO5, and TmGaMnO5 oxides have been first prepared by soft chemistry procedures followed by high oxygen pressure treatments, to stabilize Mn4+ cations. Their crystal structures and magnetic behavior have been studied at room temperature and 5 K by neutron powder diffraction (NPD) data in complement with magnetization measurements. RGaMnO5 are orthorhombic, Pbam space group, and their crystal structures contain infinite chains of edge-sharing Mn4+O6 octahedra, interconnected by pyramidal Ga3+O5 and RO8 units. For R = Ho, a = 7.2810(4), b = 8.4526(4), and c = 5.6668(3) Å; for R = Er, a = 7.2575(3), b = 8.4357(3), and c = 5.6613(2) Å; and for R = Tm, a = 7.2438(3), b = 8.4124(3), and c = 5.6509(2) Å, at room temperature. Above 300 K the reciprocal magnetic susceptibility follows a Curie-Weiss law. In the paramagnetic region, a positive Weiss constant suggests the presence of ferromagnetic interactions, which have been investigated by low-temperature NPD for R = Er, Tm. The 5 K patterns show a detectable long-range magnetic ordering over the Mn and R positions, ferromagnetically aligned along the x-direction.

In situ observation of tin whisker growth in NdSn3 compound was carried out by using an optical microscope (OM) and scanning electron microscopy (SEM). The growth rate of Sn-whisker from NdSn3 is shown to be rapid (approximately 8-15Å/s) during exposure to room ambience, and it is accompanied by formation of a new compound, Nd(OH)3, as was confirmed by x-ray diffraction. This reaction between the Sn-RE compound and trace water in room ambience has significant influence on whisker growth. There is an electron irradiation effect on whisker growth; that is, whiskers stopped growing after being observed in SEM. Therefore, it is suggested that OM be used rather than SEM to observe the continuous whisker growth. In discussion, the driving force per Sn atom for whisker growth is estimated as 1 × 1014 N in accordance with the whisker growth rate, and its apparent force originates from a chemical potential gradient between the released Sn atoms and the whisker.

The initiation and evolution of shear bands in Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass tensile samples has been investigated in situ by scanning electron microscopy. The initial shear band originates from the highest stressed area, and does not propagate during further tension, which is attributed to the weakening of the stress field in front of the shear band tip, possibly caused by atomic rearrangement and local temperature rise. As a result, multiple shear bands occur in sequence with gradually increased length and offset. This result is due to the fact that the stress in front of the tip of the initial shear band does not concentrate again during further tension above the shear yield strength. Numerical analysis was carried out to investigate the stress distribution under tension, suggesting that the maximum pressure-dependent shear stress criterion overestimates the yield strength, while the shear plane criterion describes the conditions for the formation of shear bands well.

Novel ultrafine eutectic composites containing structural and spatial heterogeneities have been systematically developed in an Mg–Cu–Zn ternary system. Microstructural investigations of the ultrafine eutectic composites revealed that the bimodal eutectic structure consists of a mixture of cellular-type fine (α-Mg + MgZn2) and anomalous-type coarse (α-Mg + MgZn2 + MgCuZn) eutectic structures. An Mg72Cu5Zn23 alloy composed of the bimodal eutectic structure without micron-scale α-Mg dendrites presents a strong improvement of yield strength up to 455 MPa with a decent plastic strain of 5%. The rotation of the bimodal eutectic colony along the interfaces is considered to be an effective way to dissipate the stress localization thus enhancing the macroscopic plasticity.

In the past two decades, the fact that “small is different” has been established for a wide variety of phenomena, including electrical, optical, magnetic, and mechanical behavior of materials. However, one largely untapped but potentially very important area of nanoscience involves the interplay of electricity and mechanics at the nanoscale. In this article, predicated on both phenomenological approaches and atomistic calculations, we summarize the state-of-the-art in understanding electromechanical coupling at the nanoscale. First, we address flexoelectricity—the coupling of strain gradient to polarization. Flexoelectricity exists in both piezoelectric and nonpiezoelectric dielectrics. As a high-order spatial-dispersion effect, the flexoelectricity becomes more and more important with the reduction of the spatial scale of the problem. Exploitation of this phenomenon and the associated nanoscale size effects can lead to tantalizing applications, such as “piezoelectric nanocomposites without using piezoelectric materials.” The second issue concerns electromechanical effects at the dielectric/metal interface. An interface in solids typically exhibits a lower symmetry compared to that of the associated adhering materials. This symmetry reduction can drastically affect the electromechanical and dielectric behavior of the material at the nanoscale.

The role of high current stressing during growth of the P-rich phase at the electroless Ni/Sn interface was examined by transmission electron microscopy. Prior to current stressing, two layers of Ni12P5, columnar Ni12P5 and noncolumnar Ni12P5, were formed after soldering. Upon electric stressing, the two layers of P-rich phase showed opposite growth patterns at the two opposing electrode interfaces. At the cathode, columnar growth of the P-rich phase was greatly enhanced while growth of the noncolumnar layer was inhibited. By contrast, the opposite was found at the anode where the current stressing promoted the noncolumnar growth but suppressed the growth of the columnar layer. Such a strong polarity effect resulted from directional electromigration of the key reaction species, nickel, to and from the interfacial reaction fronts. As a result of the difference in reaction mechanism, overall growth of the P-rich phase was much faster at the cathode during current stressing.

Cells are ion conductive gels surrounded by a ∼5-nm-thick insulating membrane, and molecular ionic pumps in the membrane establish an internal potential of approximately −90 mV. This electrical energy store is used for high-speed communication in nerve and muscle and other cells. Nature also has used this electric field for high-speed motor activity, most notably in the ear, where transduction and detection can function as high as 120 kHz. In the ear, there are two sets of sensory cells: the “inner hair cells” that generate an electrical output to the nervous system and the more numerous “outer hair cells” that use electromotility to counteract viscosity and thus sharpen resonance to improve frequency resolution. Nature, in a remarkable exhibition of nanomechanics, has made out of soft, aqueous materials a microphone and high-speed decoder capable of functioning at 120 kHz, limited only by thermal noise. Both physics and biology are only now becoming aware of the material properties of biomembranes and their ability to perform work and sense the environment. We anticipate new examples of this biopiezoelectricity will be forthcoming.