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.

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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

We report the molecular beam epitaxy growth of α‐Sn films on argon sputter cleaned (001) CdTe substrates on which a buffer layer of CdTe has been deposited. Films thinner than 400 A are p‐type with carrier densities as high as 2×1019 cm−3 ;thicker films are n‐type with carrier densities of (4–10)×1017 . The best film had a mobility of 1.3×104 cm2 /V s at 77 K.

Growth of n-type heteroepitaxial films of gray tin on (001) CdTe by molecular beam epitaxy

The use of a stable glow discharge for the synthesis of carbon nanotubes is reported. Bundles of buckytubes are synthesized with remarkably large diameters (up to 200 μm). The bundles are evenly spaced, parallel, and occupy the entire central region of the deposited rod. High resolution electron microscopy (HREM) images of the deposited rod produced by the glow discharge revealed higher yield and improved quality buckytubes as compared to those produced by an arc discharge. The behavior of the two deposition modes (glow and arc) has been compared and their effects on the formation of buckytubes are discussed.

Stable glow discharge for synthesis of carbon nanotubes

A study has been made of the superconducting properties of Fe/V/Fe sandwiches with V thickness ranging from 153 AP (atomic planes) to 5048 AP. All 20 samples studied were prepared in a single run. At zero magnetic field, the suppression of the transition temperature follows an inverse square dependence on the thickness, implying a strong pair-breaking effect in the Fe layers. The upper critical field data cross over smoothly from the 2D regime to the 3D regime with increasing V thickness. A comparison with some thin-film theories is given.

Superconducting properties of Fe/V/Fe sandwiches

We have made measurements of the extremal cross-sectional areas of the open hole surface of the Fermi surface of platinum for the previously unobserved, heavy mass orbits centered on γ and X with the magnetic field along the [100] and [110] directions, respectively. When combined with previous measurements, the necessary data associated with all classes of orbits on all three sheets of the surface are now available. Using a relativistic non-muffin-tin, Korringa-Kohn-Rostoker formalism, data were fitted using the scattering phase shifts associated with the appropriate irreducible relativistic cubic representations as disposable parameters (through l = 2) to an accuracy of 0.3%. The resulting radii of all sheets of the Fermi surface are reported. A volume integration yields the necessary charge neutrality for this even-valent metal to within 1%. Next, available cyclotron mass data were fitted using the energy derivatives of the scattering phase shifts as disposable parameters (many-body effects being absorbed in the parameter set) to an accuracy of 3.4% ; here the measured total electronic density of states was used as a constraint. The resulting Fermi velocities are also reported.

John B Ketterson

Papers

Growth of n-type heteroepitaxial films of gray tin on (001) CdTe by molecular beam epitaxy

Stable glow discharge for synthesis of carbon nanotubes

Superconducting properties of Fe/V/Fe sandwiches

The Fermi surface of platinum

Inversion of Fermi-Surface Data Using Partial-Wave Phase Shifts and Their Derivatives: An Application to the Noble Metals