4,218 publications from this institution
Abstract Health, infrastructure, and environmental monitoring as well as networking and defense technologies are only some of the potential areas of application of micro‐/nanosystems (MNSs). It is highly desirable that these MNSs operate without an external electricity source and instead draw the energy they require from the environment in which they are used. This Review covers various approaches for energy harvesting to meet the future demand for self‐powered MNSs.
The integrated nanogenerator (NG) based on vertical nanowire (NW) arrays is one of the dominant designs developed to harvest mechanical energy using piezoelectric nanostructures. Finite element method (FEM) simulations of such a NG are developed using ZnO NWs in compression mode to evaluate its performances in term of piezoelectric potential generated, capacitance, induced mechanical energy, output electrical energy, and efficiency. This evaluation is essential to correctly understand NG operation. Three main issues are highlighted. The mechanical and electrical structures of the NG as an integrated system are optimized, and strategies for concentrating the mechanical strain field in the NWs and increasing the force sensitivity are developed. In addition, the influence of NWs length and diameter on NG performances is investigated. The optimization results in a piezoelectric nano composite material where global performances are improved by mean of long and thin NWs.
Characterizing the physical properties of individual nanostructures is challenging because of the difficulty in manipulating the objects of sizes from nanometers to micrometers. Most nanomeasurements have been carried using scanning probe microscopy. In this article, we demonstrate that transmission electron microscopy can be a powerful tool for quantitative measurements of the mechanical and electrical properties of a single nanostructure. Dual-mode resonance of an oxide nanobelt has been observed, and its bending modulus has been measured. An in situ technique was demonstrated for measuring the work function at the tip of a carbon nanotube. The ballistic quantum conductance of a multiwalled carbon nanotube was observed at room temperature using the setup in TEM. It is concluded that in situ measurement by directly linking structure with property is a future direction of electron microscopy.
A formal statistical dynamical theory is developed to calculate diffuse scattering produced by short-range order (SRO) in a distorted crystal structure with consideration of atomic thermal vibrations. Diffuse scattering not only produces fine details in diffraction patterns but also introduces a non-local imaginary potential function that reduces the intensities of the Bragg reflected beams. The distribution of the diffusely scattered electrons and the Fourier coefficients of the absorption potential are directly related to a dynamic form factor S(Q,Q′), which has been calculated with consideration of SRO in the distorted lattices. The statistical structure average on imperfections is performed analytically and the final result is correlated to Cowley's short-range-order parameters. The theory is formulated in the Bloch-wave scheme (Bethe theory) for the convenience of numerical calculation in transmission electron diffraction. A rigorous theoretical proof is given to show that the inclusion of a complex potential in the dynamical calculation automatically recovers the contributions made by the high-order diffuse scattering, although the calculation is done using the equation derived for single diffuse scattering. This simply expands the capability of conventional single diffuse scattering theories. Therefore, the complex potential has a much richer meaning than the conventional interpretation of absorption effect.
A theory is proposed to include the effects of valence excitations in electron image simulations for high-resolution electron microscopy (HREM) based on the single inelastic scattering model.Under the small thickness approximation, this general theory reduces to the simplified theory of perfectly delocalized inelastic scattering model, in which the image can be considered to be an incoherent sum of those incident electrons of different energies weighted by the intensity distribution in the electron energy-loss spectrum from the area where the pattern was taken.The main effect of valence-loss is to introduce a focus shift due to chromatic aberration, resulting in contrast variation (or reversal) of the image.The generalization of this theory for simulations of interface images with considering surface and interface plasmon excitations is given.Calculations for GaAs surface profile images are demonstrated to show the effect of inelastic localization.