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Multilayered oriented composites constituted from two materials of different thermal conductivities are shown to have the ability to direct thermal energy. The composites behave as effective media with anisotropic thermal conductivity. The guiding of the heat flux is shown experimentally with bending angle ranging from ~25° to the maximum possible value of ~45° (for the considered prototypical composites) with respect to a horizontal temperature gradient--in excellent accord with theoretical estimates and computational simulations. Such thermal metamaterials lay the basis for efficient manipulation of heat and for thermal elements, such as thermal concentrators and cloaks. [ABSTRACT FROM AUTHOR]

In a recent paper [J. Chem. Phys. 97, 4616 (1992)] that examines the relationship between experimental and computed intensities for bending modes of linear molecules, So\rensen and Jo\rgensen state that ‘‘most recent quantum mechanical computations predict band intensities of the bending modes in linear molecules that are approximately a factor of 2 bigger than observed intensities, and it is shown that the problem relates to the ab initio treatment.’’ It is further stated that ‘‘the disturbingly big discrepancies...are real, and the cause of the discrepancies has to be sought in the ab initio computation of the dipole moment.’’ This apparent failing of theory is addressed here by demonstrating that coupled-cluster calculations provide intensities for the bending modes of acetylene, carbon dioxide and nitrous oxide, of 177, 55, and 8 km/mol which compare favorably with the experimental values of 177, 55, and 7; while that for HCN is 70 compared to an experimental value of 58. The discrepancy in the latter might recommend some reconsideration of the experimental value, including the role of electrical and mechanical anharmonicity. [ABSTRACT FROM AUTHOR]

Simultaneous measurements of work function ([lowercase_phi_synonym]) and C 1s core level shift were employed to determine the change in electron affinity (χ) and band bending as a function of hole sheet density on H-terminated diamond for atmospheric and fullerene (C60F48) induced surface conductivity. Contrary to earlier investigations, it is shown that changes in work function do not reflect variations in the position of the surface Fermi level in response to surface transfer doping. Instead, with a transition from -0.96 to -0.33 eV, χ accounts for a significant amount of the change in [lowercase_phi_synonym] for hole densities between 5×108 and 4×1013 cm-2. [ABSTRACT FROM AUTHOR]

Utilizing high-resolution electron microscopy and image simulation, it is demonstrated that some of the crystal lattices of Fe-doped CaCu3Ti4O12 are intrinsically bent at the nanometer scale. A comparison between experimentally obtained and simulated images indicates that the bending angle is of a few milliradians, which is remarkable in a brittle oxide. Despite such lattice distortion, much of the lattice strain induced by the distortion appears to be released at the domain walls where a number of misfit dislocations are present. [ABSTRACT FROM AUTHOR]

A method of stress control in microelectromechanical systems (MEMS) devices is presented that consists of creating counterbalancing structures to position stressed layers at the neutral plane of the device, eliminating the bending momentum acting on the device. Upon metallization, many MEMS elements such as silicon membranes show substantial bow under the stress developed as a result of the difference in the thermal expansion coefficients of a metal and silicon. The proposed membranes with the counterbalancing structures remain flat in the entire test temperature range (25–150 °C). The method gives material-independent solution to stress-induced curvature problems in a variety of ultrathin devices. [ABSTRACT FROM AUTHOR]

We describe photothermal operation of nanoelectromechanical systems (NEMS) in ambient atmosphere. Using a tightly focused modulated laser source, we have actuated the out-of-plane flexural resonances of bilayered doubly clamped beams. The optically detected displacement profiles in these beams are consistent with a model where the absorbed laser power results in a local temperature rise and a subsequent thermally induced bending moment. The described technique allows probing and actuation of NEMS with exquisite spatial and temporal resolution. From a device perspective, the technique offers immense frequency tunability and may enable future NEMS that can be remotely accessed without electronic coupling. [ABSTRACT FROM AUTHOR]

The torsional dependence of the CH[sub 3] stretching and bending modes of methanol has been explored in terms of a local mode internal coordinate picture [X. Wang and D. S. Perry, J. Chem. Phys. 109, 10795 (1998)]. First, the torsional variations of the small-amplitude vibrational frequencies along the mass weighted intrinsic reaction coordinate from the top to the bottom of the torsional potential barrier were calculated by means of ab initio frequency projection utilizing GAUSSIAN 98. The resulting curves for the three C-H stretch ab initio frequencies as functions of the torsional angle cannot be reproduced by the original 3x3 local mode model incorporating stretch-torsion and stretch-stretch couplings at lowest-order only, but are well-fitted if the model is extended to include higher-order coupling terms. For the CH-bending modes, with internal coordinates chosen to give a high degree of localization, bend-torsion and bend-bend coupling parameters were determined from the ab initio projected frequencies, and were then used to predict torsional tunneling splittings. Just as observed for the C-H stretch modes, the two higher-frequency asymmetric CH-bend modes are predicted to have inverted tunneling splittings with reduced amplitudes, while the splitting pattern for the lower frequency symmetric-bend mode is predicted to be normal. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Determines bend strain characteristics of bismuth-lead-strontium-calcium- copper-oxygen/silver composite tapes. Preparation of monofilament and multifilament tapes; Increase in the irreversible strain limit for the onset of bend strain damage; Observation of irreversible damage in the form of microcracks and fracture of the superconductor filaments.

Photo-origami uses the dynamic control of the molecular architecture of a polymer by a combination of mechanical and non-contact optical stimuli to design and program spatially and temporally variable mechanical and optical fields into a material. The fields are essentially actuators, embedded in the material at molecular resolution, designed to enable controllable, sequenced, macroscopic bending and folding to create three-dimensional material structures. Here, we demonstrate, through a combination of theory, simulation-based design, synthesis, and experiment, the operative phenomena and capabilities of photo-origami that highlight its potential as a powerful, and potentially manufacturable, approach to create three-dimensional material structures. [ABSTRACT FROM AUTHOR]

Precipitation of nanocrystals in a Ni–P amorphous alloy film during application of a stress field has been investigated. Microsized cantilever-beam-type specimens were prepared from the film by focused-ion-beam machining and bending stress was applied to the specimen using a mechanical testing machine for microsized specimens. Transmission electron microscopy observation in the plane strain deformed region has revealed that the deformation induces the precipitation of nanocrystalline Ni particles, and a (111) plane of all crystalline particles is aligned parallel to the side surface of the specimen. This suggests that control of the nanocrystalline orientation in amorphous alloys would be possible using the application of a stress field. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

New insight into the mechanical behavior of thin metallic films on substrates can be obtained by a novel experimental technique. It comprises stress measurements by the wafer curvature technique in combination with a four-point bending of beam-shaped samples. A dedicated apparatus was constructed which allows such experiments in high vacuum between room temperature and 500 °C to be carried out. It has a stress measurement sensitivity better than 0.1 MPa and a long-term stability better than ±0.2 MPa over 24 h in the case of a 1 μm thick film. Strains up to 0.8% could be imposed by a four-point bending on films grown on 380 μm thick Si substrates before cracking of the substrates. Both the thermal cycling and the four-point bending technique were used to investigate the plastic behavior of 1 μm thick Cu films on oxidized Si substrates. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]