This paper studies the effective properties of multi-phase thermoelastic composites. Based on the Helmholtz free energy and the Gibbs free energy of individual phases, the effective elastic tensor, thermal-expansion tensor, and specific heats of the multi-phase composites are derived by means of the volume average of free-energies of these phases. Particular emphasis is placed on the derivation of new analytical expressions of effective specific heats at constant-strain and constant-stress situations, in which a modified Eshelby's micromechanics theory is developed and the interaction between inclusions is considered. As an illustrative example, the analytical expression of the effective specific heat for a three-phase thermoelastic composite is presented.
By irradiating a flat Al target with femtosecond laser pulses at moderate intensities of ∼1017 W/cm2, we obtained stable collimated quasimonoenergetic electrons in the specular direction but deviated somewhat toward the target normal. An associated local minimum located on the other side of the specular direction seems to indicate that the peak actually results from the deflection of the collimated electrons from their initial ejection direction. We have proposed a two-step model in which some laser-accelerated electrons are able to leave the plasma in a narrow phase-locked window of the moving wave interference pattern, and are then steered toward the target normal by the ponderomotive force of the interference field. The periodic repetition of the electron emission leads to a pulse train of collimated quasimonoenergetic electrons with subcycle duration.
Electron emission from individual graphene nanoribbons (GNRs) driven by an internal electric field was studied for the first time Inside a high resolution transmission electron microscope equipped with a state-of-art scanning tunneling microscope sample holder with independent twin probes. Electrons were driven out from Individual GNRs under an internal driving voltage of less than 3 V with an emission current increasing exponentially with the driving voltage. The emission characteristics were analyzed by taking Into account monatomic thickness of GNRs. While deviating from the two-dimensional Richardson equation for thermionic emission, they were well described by the recently proposed by us phonon-assisted electron emission model. Different from widely studied field electron emission from graphene edges, electrons were found to be emitted perpendicularly to the atomic graphene surfaces with an emission density as high as 12.7 A/cm(2). The internally driven electron emission is expected to be less sensitive to the microstructures of an emitter as compared to field emission. The low driving voltage, high emission density, and internal field driving character make the regarded electron emission highly promising for electron source applications.
We explore the electronic and transport properties out of a biased multilayer hexagonal boron nitride (h-BN) by first-principles calculations. The band gaps of multilayer h-BN decrease almost linearly with increasing perpendicular electric field, irrespective of the layer number N and stacking manner. The critical electric filed (E0) required to close the band gap decreases with the increasing N and can be approximated by E0 = 3.2 / (N − 1) (eV). We provide a quantum transport simulation of a dual-gated 4-layer h-BN with graphene electrodes. The transmission gap in this device can be effectively reduced by double gates, and a high on-off ratio of 3000 is obtained with relatively low voltage. This renders biased MLh-BN a promising channel in field effect transistor fabrication.