Search

Employing a silver nano semi-ellipsoid nanoarray with high symmetry into applications in plasmonic color printing, we fulfill printing images with colors independent of observing angles. Also, by decreasing the period of a nano semi-ellipsoid array into deep-subwavelength scales, we obtain high reflectivity over 50%, promising high efficiency for imaging generations. A facile technique based on the transfer of anodized aluminum oxide template is developed to fabricate the silver nano semi-ellipsoid nanoarray, realizing plasmonic color printing with features of low cost, scalable, full color and high flexibility. Our approach provides a feasible way to address the angle-dependent issue in the previous practice of plasmonic color printing, and boosts this field on its way to real-world commercial applications.

We study the properties of the localized interface plasmon modes (IPMs) arising from coupling and splitting of the plasmon eigenstates in two semi-infinite superlattices containing complex defect structures. Two kinds of defect structure are considered: one is a single quantum well, i.e., a barrier–well–barrier structure; the other is a well–barrier–well structure. The influences of the constitution of the defect structures, as well as the physical and geometric parameters of the superlattices on the characteristics of the localized IPMs are investigated in detail. The numerical results show that the localized modes exhibit peculiar features; the complexity of the dispersion of IPMs is essentially associated with the coupling of the interwell regions in the defect structure, and the barrier and well layers play different roles in the features of the localized IPMs. We also present a comparison of the dispersions of the localized IPMs between these two types of defect structure and give a physical picture to explain these results.

We demonstrate the utility of optical second harmonic generation (SHG) polarimetry to perform structural characterization of self-assembled zinc-blende/wurtzite III-V nanowire heterostructures. By analyzing four anisotropic SHG polarimetric patterns, we distinguish between wurtzite (WZ), zinc-blende (ZB) and ZB/WZ mixing III-V semiconducting crystal structures in nanowire systems. By neglecting the surface contributions and treating the bulk crystal within the quasi-static approximation, we can well explain the optical SHG polarimetry from the NWs with diameter from 200-600 nm. We show that the optical in-coupling and out-coupling coefficients arising from depolarization field can determine the polarization of the SHG. We also demonstrate micro-photoluminescence of GaAs quantum dots in related ZB and ZB/WZ mixing sections of core-shell NW structure, in agreement with the SHG polarimetry results. The ability to perform in situ SHG-based crystallographic study of semiconducting single and multi-crystalline nanowire heterostructures will be useful in displaying structure-property relationships of nanodevices.

We investigate the effects of extension and overlap of wavefunctions on the dispersion relations of plasmon modes in symmetric double-quantum-well structures. We compare the approximate results in two-dimensional layer-gas (2DLG) model with the exact ones where the extension and overlap of the wavefunctions are included. Our numerical results show that the 2DLG model is a good approximation only in the wide barrier case in the long wavelength limit. When the barrier is thin, the extension and overlap of the wavefunctions cannot be neglected. We also show that the long wavelength gap of the inter-subband mode is proportional to the energy difference between the ground and the first excited energy levels.

We have given a detailed investigation of the energy spectrum and the electrical properties of a two-dimensional electron gas modulated by a general form of one-dimensional periodic magnetic field along the x direction, by generalizing the theory of Peeters and Vasilopoulos and that of Xue and Xiao on the magnetic modulation in the lowest order of approximation of Fourier transformation. The presence of the magnetic modulation lifts the degeneracy of the Landau levels, which are broadened into bands, and leads to Weiss-like oscillations in the magnetoresistance. The oscillations in (and the modulation correction ) and (and ) are out of phase, while oscillates in phase with . The amplitude of oscillation of the modulation correction is much larger than those of and . We also find the surprising result that, while the Hall resistance displays quantized plateaux, the transport across the magnetic barriers can be nearly dissipationless. The contribution of high-frequency components of Fourier transformation is obvious at high fields and is negligible at low fields.

In the present work we report the detailed study of the above-barrier electronic states in the multi-barrier structures by using the transfer matrix technique. The energy levels and the corresponding wavefunctions are calculated by solving the Schrodinger equation directly. Analytical analysis is presented confirming the formation of subband structure, similar to that determined by Kronig–Penney model. Each subband contains energy states with being the number of periods in the structure. Furthermore, our calculations demonstrate that in each subband there is one energy state whose wavefunction is always localized in the barrier regions, while others remain partly localized in general. These localized states satisfy the constructive condition in consistence with experiments, where is the wave vector in the barrier region, is the barrier width, and is an integer.

We study resonant magnetotunneling in the double-barrier heterostructure in the sequential tunneling picture. The effects arising from charge buildup in the well are considered by assuming that the quasibound energy in the well varies linearly with the applied bias. Under appropriate approximations, the tunneling current density and the corresponding differential conductance are derived analytically. The results for the peak positions in differential conductance and the threshold current position are consistent with experiments.

We study theoretically the magnetic coupling between a superconducting film and a 2DEG by generalizing the theory of Meincke and that of Rammer and Shelankov, correctly taking into account the Hall effect in the 2DEG. The induced voltages are discussed in the magnetic-field regime in which the magnetoresistance is dominated by the SdH oscillations. The results obtained are found to be in good agreement with the experiment of Kruithof et al. We find the modulation of the magnetic field in the 2DEG is larger than previously expected.

We study the resonant tunnelling in double-barrier heterostructures via Landau levels in the sequential tunnelling approach. The effects of the space-charge formation in the electrodes and in the well together with inelastic-scattering broadening are taken into account. Under appropriate approximations, the tunnelling current and differential conductance can be written as simpler forms which analytically reproduce the main features of experiments. Then the dependences on the temperature and magnetic field are studied numerically; these are also in accordance with experiments.

LiFeAs is one of the new class of iron superconductors with a bulk [Formula: see text] in the 15-17 K range. We report on the specific heat characterization of single crystal material prepared by self-flux growth techniques with significantly improved properties, including a much decreased residual gamma, γ(r) (≡C/T as T → 0), in the superconducting state. Thus, in contrast to previous explanations of a finite γ(r) in LiFeAs being due to intrinsic states in the superconducting gap, the present work shows that such a finite residual γ in LiFeAs is instead a function of sample quality. Further, since LiFeAs has been characterized as nodeless with multiple superconducting gaps, we report here on its specific heat properties in zero and applied magnetic fields, to compare to similar results on nodal iron superconductors. For comparison, we also investigate LiFe(0.98)Cu(0.02)As, which has the reduced T(c) of ≈9 K and an H(c2) of 15 T. Interestingly, although presumably both LiFeAs and LiFe(0.98)Cu(0.02)As are nodeless, they clearly show a non-linear dependence of the electronic density of states (is proportional to specific heat γ) at the Fermi energy in the mixed state with the applied field, similar to the Volovik effect for nodal superconductors. However, rather than indicating nodal behavior, the satisfactory comparison with a recent theory for γ(H) for a superconductor with two isotropic gaps in the presence of impurities argues for nodeless behavior. Thus, in terms of specific heat in a magnetic field, LiFeAs can serve as the prototypical multiband, nodeless iron superconductor.

This paper presents a novel in-plane photonic crystal channel drop filter. The device is composed of a resonant cavity sandwiched by two parallel waveguides. The cavity has two resonant modes with opposite symmetries. Tuning these two modes into degeneracy causes destructive interference in bus waveguide, which results in high forward drop efficiency at the resonant wavelength. From the result of numerical analysis by using two-dimensional finite-difference time-domain method, the channel drop filter has a drop efficiency of 96% and a Q value of over 3000, which can be used in dense wavelength division multiplexing systems.

This paper presents a cost-effective nanofabrication method for forming large area and high coverage two-dimensional metal nanostructures on flat and curved surfaces. This method starts with a periodic array of hemispherical dimples on polystyrene (PS) film prepared by colloidal lithography with a sacrificial layer of polyacrylic acid (PAA) underneath. After the removal of PAA in water solution, the PS layer is turned over and attached to the substrate to be patterned. An inverted hemispherical mask is formed after oxygen plasma etching. As the holes at the bottom are much larger than those on the surface, the mask is especially suitable for a standard lift-off process. Based on this mask, metal nano-disk and pair-disk arrays, as well as two-dimensional nanostructures on a curved surface, have been fabricated. Optical measurement shows that a surface plasmon resonance exists in a periodic disk array. This method is valuable for the fabrication of a magnifying metamaterial hyperlens in order to eliminate the limitation of optical diffraction.

In this paper, we propose a vertical structure of light emitting diodes (LEDs) grown on a substrate embedded with a photonic crystal reflector to avoid light absorption in the absorbed substrate. Photonic crystal (PC) patterns are embedded in the interface between the epitaxial layer and substrate. Numerical simulation results prove that for both polarizations, there exists a range of PC lattice period, within which 1D or 2D PC patterns can demonstrate high reflectivity and function as a resonance reflector. LEDs grown on such a high reflective patterned substrate can achieve great omnidirectional emission enhancement compared with the conventional LEDs. In addition, we found that the combining of PCs with the surface of such LEDs can further enhance the emission and redistribute the photon energy. Embedding such an interfacial PC reflector might prove to be a promising method for enhancing the extraction efficiency of high-brightness LEDs.