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Two-dimensional (2D) materials are promising candidates for atomic-scale piezotronics and piezophototronics. Quantum edge states show fascinating fundamental physics such as nontrivial topological behavior and hold promising practical applications for low-power electronic devices. Here, using the tight-binding approach and quantum transport simulations, we investigate the piezotronic effect on the spin polarization of edge states in a zigzag-terminated monolayer MoS2 nanoribbon. We find that the strain-induced piezoelectric potential induces a phase transition of edge states from metal to semiconductor. However, in the presence of exchange field, edge states become semi-metallic with significant spin splitting and polarization that can be tuned by external strain. We show that quantum transport conductance exhibits a 100% spin polarization over a wide range of strain magnitudes. This effect is used in a propose prototype of piezotronic spin transistor. Our results provide a fundamental understanding of the piezotronic effect on edge states in zigzag monolayer MoS2 nanoribbons and are relevant for designing high-performance piezotronic spin devices.

Utilizing the tight-binding method, we investigate the electronic and optical properties of the zigzag hexagonal silicene quantum dots (ZHSQDs) subjected to a perpendicular magnetic field. The edge states emerge in the energy gap as the size of ZHSQDs increases. In the presence of spin–orbit coupling (SOC), the corresponding energy levels of edge states oscillate with magnetic flux. The reason is that the energy levels of silicene quantum dots are splitted in the presence of SOC. In addition, the optical absorption peak undergoes blue shift as the strength of SOC increases, and the optical absorption mainly occurs between the Landau levels in the presence of magnetic field.

Raman phonon relaxation dynamics in carbon allotropes including graphene, carbon nanotube, C60, carbon nanobud, graphite, and diamond has been formulated in terms of the bond order–length–strength (BOLS) correlation. The length and energy responses of the representative bond to the change of coordination environment, pressure, and temperature determine intrinsically the Raman shifts. Reproduction of the measured results in quantitative information of the bond length, bond energy, mode cohesive energy, binding energy density, Debye temperature, and the compressibility of the C–C bond in each phase without needing involvement of the phonon scattering resonant processes or the mode Gruneisen constants. 2013 Elsevier B.V. All rights reserved.

In spite of many superior high-temperature properties of intermetallics, it has been difficult to understand their intrinsic brittleness. To eliminate or improve the embrittlement, the conventional alloying technique based on the trial-and-error method is still the most effective and practical. However, it remains a main challenge for both physicists and materials scientists to provide either an alloying principle or a deep insight into its toughening mechanism at an atomic or electronic level. This letter reports a simple experimental approach that uses work function (WF) as a sensitive indicator of the role of alloying in changing mechanical behavior. NiAl is chosen as a typical example. It is found that with the addition of Cr and Ce, the ductility of NiAl increases significantly. Such an increase in ductility corresponds to a concomitant decrease in the WF, which is attributed to a change in the nature of the atomic bonding or in the electronic structure induced by the alloying. This fundamental under...

In this work, the structural stabilities and electronic properties of Mg–Nd intermetallic compounds were investigated using first-principles calculations based on density functional theory. The present results showed that lattice constants for all intermetallics considered are very close to the corresponding experimental values. The calculation of cohesive energies and densities of states (DOS) indicated that the structural stability of Mg–Nd alloy shifts to higher levels with increase in Nd element independent of crystal structure type. The DOS of these intermetallic compounds also revealed that the bonding occurred mainly among the valence electrons of Mg(3s), Mg(2p) and Nd(5d) electrons, and the discrepancy in the stability of Mg–Nd intermetallic compounds could be attributed to the variation of bonding electron numbers at low-energy region of Fermi level.

In this paper, the valence electron structure and embrittlement of TiAl are studied theoretically based on the empirical electron theory (EET). From the viewpoint of the EET, a model for the space topographic distribution of valence electron structure is proposed. This model can be used to simply explain the embrittlement of TiAl and could be extended to other intermetallic compounds.

Development of intermetallics in Ti–Al alloys for high-temperature structural applications has long been impeded by embrittlement, partly because there has been a complete understanding at an electronic level on the Ti–Al phase transformation behavior. In this study, based on the Empirical Electron Theory of Solids and Molecules (EET), effects of interstitial impurities on valence electron structures and liquidus temperatures in Ti–Al phase diagram are analyzed. Based on the theoretical analysis, some unclear experimental results in Ti–Al phase diagram are further discussed. It is demonstrated that because of the effects of interstitial impurities, the valence electron structures become seriously anisotropic, leading to the lowest liquidus temperatures in Ti–Al phase diagram.

A new efficient physics-based method to calculate gate current using space-dependent Boltzmann transport equation for electrons has been developed. The solution provides smooth space-dependent distribution functions for gate current calculation. The method spends less than 1% of the CPU time that the similar Monte Carlo method requires.