Wurtzite has the space-group symmetry P6 3 mc. The absence of inversion symmetry allows linear-k terms in the electronic band structure when the spin-orbit interaction is included. Their existence has been confirmed in a number of experiments, but no microscopic calculations have been published. In the present paper, we discuss the origin of these linear-k terms using group theory and k•p arguments. The various contributions to these terms are identified through band-structure models. We present an ab initio calculation, performed with the linear-muffin-tin-orbital method, of these spin splittings in CdS, CdSe, and ZnO. A renormalization of the valence-band spin-splitting coefficients obtained in the linear-muffin-tin-orbital calculations was found necessary to correct for errors in the relative energies of the uppermost valence bands as compared with the experimental values. We point out that a similar procedure should be used when evaluating masses and other band parameters from calculated local-density-approximation band structures.

We demonstrate that a pair of perpendicular electrical dipolar scatterers resonating at different frequencies can be used as a metamaterial unit cell to construct a nanometer-thin retarder in reflection, designing nanocross and nanobrick plasmonic configurations to function as reflecting quarter-wave plates at ~1520 and 770 nm, respectively. The design is corroborated experimentally with a monolayer of gold nanobricks, transforming linearly polarized incident radiation into circularly polarized radiation at ~780 nm.

No abstract

No abstract

We demonstrate that a pair of electrical dipolar scatterers resonating at different frequencies, i.e., detuned electrical dipoles, can be advantageously employed for plasmonic sensing of the environment, both as an individual subwavelength-sized sensor and as a unit cell of a periodic array. It is shown that the usage of the ratio between the powers of light scattered into opposite directions (or into different diffraction orders), which peaks at the intermediate frequency, allows one to reach a sensitivity of ≈ 400 nm/RIU with record high levels of figure of merit exceeding 200. Qualitative considerations are supported with detailed simulations and proof-of-principle experiments using lithographically fabricated gold nanorods with resonances at 800 nm.

Triboelectric nanogenerators (TENGs), using Maxwell's displacement current as the driving force, can effectively convert mechanical energy into electricity. In this work, an extensive review of theoretical models of TENGs is presented. Based on Maxwell's equations, a formal physical model is established referred to as the quasi-electrostatic model of a TENG. Since a TENG is electrically neutral at any time owing to the low operation frequency, it is conveniently regarded as a lumped circuit element. Then, using the lumped parameter equivalent circuit theory, the conventional capacitive model and Norton's equivalent circuit model are derived. Optimal conditions for power, voltage, and total energy conversion efficiency can be calculated. The presented TENG models provide an effective theoretical foundation for understanding and predicting the performance of TENGs for practical applications.

The influence of wetting-layer states on quantum-dot states and vice versa is analysed numerically for electrons in the conduction band in the general case with arbitrary kinetic energy in the plane of the quantum-well wetting layer. Since the analysed quantum dot is embedded in a barrier material with different properties, the effective mass approximation methodology leads to a Schrödinger model with discontinuous coefficients. This complicates the analysis and, in addition, requires a special attention to the formulation of boundary conditions for the entire structure, consisting of the quantum dot with wetting layer embedded in a barrier material. In the present paper, the complete model is formulated and solved numerically via a variational approach based on finite element approximations and Arnoldi iterations. By analysing different geometrical configurations, we demonstrate that the ground eigenstate of the entire structure can be considerably affected by the presence of the wetting layer. The dependency demonstrated between eigenstates of the 'pure' quantum dots and the quantum-well wetting layers indicates that a conventional analysis of quantum-dot structures without accounting for wetting layers may not be sufficient for an adequate characterization of quantum dots as active regions in future electronic and optical devices.

No abstract