The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

Every few years, a new material with unique properties emerges and fascinates the scientific community, typical recent examples being high-temperature superconductors and carbon nanotubes. Graphene is the latest sensation with unusual properties, such as half-integer quantum Hall effect and ballistic electron transport. This two-dimensional material which is the parent of all graphitic carbon forms is strictly expected to comprise a single layer, but there is considerable interest in investigating two-layer and few-layer graphenes as well. Synthesis and characterization of graphenes pose challenges, but there has been considerable progress in the last year or so. Herein, we present the status of graphene research which includes aspects related to synthesis, characterization, structure, and properties.

Graphene: The New Two-Dimensional Nanomaterial

Topological insulators are materials with a bulk excitation gap generated by the spin-orbit interaction that are different from conventional insulators. This distinction is characterized by ${Z}_{2}$ topological invariants, which characterize the ground state. In two dimensions, there is a single ${Z}_{2}$ invariant that distinguishes the ordinary insulator from the quantum spin-Hall phase. In three dimensions, there are four ${Z}_{2}$ invariants that distinguish the ordinary insulator from ``weak'' and ``strong'' topological insulators. These phases are characterized by the presence of gapless surface (or edge) states. In the two-dimensional quantum spin-Hall phase and the three-dimensional strong topological insulator, these states are robust and are insensitive to weak disorder and interactions. In this paper, we show that the presence of inversion symmetry greatly simplifies the problem of evaluating the ${Z}_{2}$ invariants. We show that the invariants can be determined from the knowledge of the parity of the occupied Bloch wave functions at the time-reversal invariant points in the Brillouin zone. Using this approach, we predict a number of specific materials that are strong topological insulators, including the semiconducting alloy ${\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}$ as well as $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Sn}$ and HgTe under uniaxial strain. This paper also includes an expanded discussion of our formulation of the topological insulators in both two and three dimensions, as well as implications for experiments.

/pdf/topological-insulators-with-inversion-symmetry-1vaykhe1u1.pdf

Topological insulators with inversion symmetry

We have used the pH-induced self-assembly of a peptide-amphiphile to make a nanostructured fibrous scaffold reminiscent of extracellular matrix. The design of this peptide-amphiphile allows the nanofibers to be reversibly cross-linked to enhance or decrease their structural integrity. After cross-linking, the fibers are able to direct mineralization of hydroxyapatite to form a composite material in which the crystallographic c axes of hydroxyapatite are aligned with the long axes of the fibers. This alignment is the same as that observed between collagen fibrils and hydroxyapatite crystals in bone.

http://science.sciencemag.org/content/sci/294/5547/1684.full.pdf

Self-assembly and mineralization of peptide-amphiphile nanofibers

Nano-optics of surface plasmon polaritons

The angular dependence of the upper critical fields, H c (θ) for a set of NbTi-Ge superlattices were studied at various temperatures. The behavior of H c (θ) at lower temperatures deviates from the Tinkham expression which is expected to be valid only in the Ginzberg-Landau regime close to T c . We examine a model for calculating H c (θ) involving the lowest eigenvalue of the gauge invariant diffusion equation (subject to boundary conditions appropriate to a slab) in the de Gennes expression for the upper critical field of a dirty superconductor at all temperatures. The disorder related localization and interaction effects as well, as the paramagnetic limiting effect, are also considered.

Angular Dependent Critical Fields in NbTi-Ge Superlattices in the Weakly Localized Regime

All-optical modulation of light using metallic nanostructures can potentially enable processing of information with speed in the terahertz range. This is because the optical nonlinearity of metals dictated by the electron-phonon coupling is intrinsically fast. Nobel metals have achieved great success to this end due to their superior plasmonic properties in the visible. However, each type of noble metals only works in a specific wavelength range and therefore broadband spectral response covering the wide visible spectrum can be a challenge. Here we introduce indium-tin-oxide nanorod arrays (ITO-NRAs) which exhibit broadband response covering the visible spectrum. We show that the static spectral response of ITO-NRAs does not depend on the incident polarization and is insensitive to whether the lattice is a square or a rectangle. We further demonstrate that the transmission spectrum can be slightly shifted by changing the sample temperature, as well as adjusting the doping concentration which can be achieved by annealing the sample in oxygen rich environments. When pumped by an optical pulse with photon energy above the bandgap, the transmission can be modified in the entire visible range. These preliminary results show that ITONRAs offer unique opportunities for all-optical modulation in optical frequencies.

Fine-tune the spectrum of indium-tin-oxide nanorod arrays in the visible range

We report experimental results on characteristics of SFIFS junctions and multi-terminal SFIFSIS devices (where S, I, and F denote a superconductor (Nb), an insulator (AlO x), and a ferromagnetic material (Ni), respectively). The SFIFS j unctions serve as injectors in the SFIFSIS devices which have transistor- like properties; for this reason we call them Superco nducting- Ferromagnetic Transistors (SFTs). We have found the F (Ni) thickness at which the SFIFS current-voltage character istic (CVC) becomes linear. Furthermore, we investigated the DC and AC characteristics of SFTs of two types: ordinary devices with a single acceptor (SIS) junction, and devices with a dou ble acceptor. In the first case, we focused on studying the influence of the injection current through the SFIFS junction on the maximum Josephson current of the SIS acceptor. For devices of the second type, we studied voltage amplification prope rties when the operating point was chosen in the sub-gap region of the acceptor CVC. By applying an AC signal (in the kHz range) while biasing the injector (SFIFS) junction with a con stant DC current, we observed a voltage gain above 25 on the doubl e acceptor. In the reverse transmission experiment, we ap plied DC current and an AC modulation to the acceptor junction and, within the accuracy of the experiment, observed no res ponse on the injector junction, which implies an excellent in put-output isolation in our SFIFSIS devices. The experiments in dicate that, after optimization of the device parameters, they can be used as input/output isolators and amplifiers for memory, di gital, and RF applications.

Electrical Characteristics of Superconducting- Ferromagnetic Transistors

The temperature dependence of the mobility of the electron bubble in superfluid helium has been calculated1 using a hydrodynamic approach for the phonon-bubble scattering cross section. This calculation explains the observed T −3 dependence of previous experimental data2 in the range 0.33–0.5°K as arising from a prominent s-wave resonance in the bubble cross section for thermal phonons. Furthermore, this calculation predicts that the mobility at lower temperatures should rise more sharply than T −3. At very low temperature (T < 80 m°K) the mobility should vary as T −8. This behavior is characteristic of Rayleigh scattering. We have extended the measured temperature range down to 0.15°K and have observed that the mobility indeed increases faster than T −3.

John B Ketterson

Papers

Angular Dependent Critical Fields in NbTi-Ge Superlattices in the Weakly Localized Regime

Fine-tune the spectrum of indium-tin-oxide nanorod arrays in the visible range

Electrical Characteristics of Superconducting- Ferromagnetic Transistors

Temperature Dependence of the Electron Bubble Mobility Below 0.3°K

Electrons' eyeview of buckytubes and friends