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 “KIn2” Zintl phase activates tellurium under solvothermal conditions and yields the compound {[In(en)3][In5Te9(en)2]·0.5en}n (en = ethylenediamine). The material has both a polar and chiral layered framework and exhibits type I phase-matchable strong second harmonic generation (SHG) response.

A Polar and Chiral Indium Telluride Featuring Supertetrahedral T2 Clusters and Nonlinear Optical Second Harmonic Generation

We have studied the structural and transport properties of Sb2Te3 thin films prepared by molecular beam epitaxy as a function of the Te/Sb flux ratio during deposition Both the crystallinity and the transport properties are found to be strongly affected by nonstoichiometry The most stoichiometric sample (prepared with a Te/Sb ratio of 36) had a high degree of crystallinity, high thermopower, and high carrier mobility However, Sb2Te3 films with excess Sb or Te had poorer crystallinity, reduced magnitude of the thermopower, and reduced mobility as a result of the formation of antisite defects These antisite defects were able to be reduced by controlling the relative flow rate ratio of Te to Sb during growth

Structural and thermoelectric transport properties of Sb2Te3 thin films grown by molecular beam epitaxy

Enhanced Magnetization Density of a Compositionally Modulated CuNi Thin Film

We report on the measurements of the ferromagnetic resonance spectra of arrays of submicron size periodic particle arrays of permalloy produced by electron-beam lithography. in contrast to plane ferromagnetic films, the spectra of the arrays show a number of additional resonance peaks, whose position depends strongly on the orientation of the external magnetic field and the interparticle interaction. Time-dependent micromagnetic simulations of the ac response show that these peaks are associated with coupled exchange and dipolar spin-wave modes.

https://arxiv.org/pdf/cond-mat/0109307.pdf

Ferromagnetic resonance in periodic particle arrays

Measurements have been made of the Young’s, flexural, and torsional moduli of compositionally modulated Cu‐Ni foils. The average composition of the foils was 50‐at. % Ni and the wavelength of the modulation ranged from 8 to 80 A. At a wavelength of 20 A, the flexural modulus exhibited a maximum and had a value two times greater than that measured at shorter or longer wavelengths or that calculated from the bulk single‐crystal elastic constants of a homogeneous alloy. The Young’s and torsion moduli exhibited two maxima at 12 and 28 A. These results are consistent with earlier measurements of the biaxial modulus using a bulge tester. It was also observed that at a wavelength of 20 A there was a threefold increase in the breaking stress of the foils as compared with homogeneous bulk alloys.

John B Ketterson

Papers

A Polar and Chiral Indium Telluride Featuring Supertetrahedral T2 Clusters and Nonlinear Optical Second Harmonic Generation

Structural and thermoelectric transport properties of Sb2Te3 thin films grown by molecular beam epitaxy

Enhanced Magnetization Density of a Compositionally Modulated CuNi Thin Film

Ferromagnetic resonance in periodic particle arrays

Mechanical properties of composition modulated Cu‐Ni foils