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 velocity of longitudinal ultrasound propagated along the a axis in URu2Si2 has been studied at temperatures down to 40 mK and in magnetic fields of up to 45 T applied along the c axis. The frequencies of the observed acoustic quantum oscillations (560 T and 1070 T), as well as calculated effective masses (14.5me and 22me), are in reasonable agreement with the known dHvA extremal cross sections of the Fermi surface in URu2Si2. It is shown that features observed previously at temperatures of about 0.5 K in magnetic fields between about 29 and 30 T in the magnetoresistance. Hall coefficient and ultrasound velocity are associated with quantum oscillations, which are clearly seen at lower temperatures. A hysteresis observed at 40 mK for all three steps of the metamagnetic transition confirms that they all are first order transitions.

Ultrasonic Study Of URu2Si2At Very Low Temperatures

The heavy fermion superconductor URu2Si2 has a superconducting transition at 1.4 K and an antiferromagnetic transition at 17.5K. We present measurements in the vicinity of the antiferromagnetic transition of both sound velocity and magnetization.

Sound velocity and magnetization measurements near the antiferronagnetic transition in the heavy fernion system URu2Si2

We have investigated the structural and thermoelectric properties of (Sb/sub 1-x/Bi/sub x/)/sub 2/Te/sub 3/ MBE grown thin films on CdTe(111). Analysis of X-ray diffraction patterns (/spl theta/-2/spl theta/ scans and rocking curves) of the films shows that they are of high quality and that they are well aligned with their (00.l) axis normal to the substrates. Measurements of the temperature-dependent thermoelectric power of the films were performed with respect to the binary composition of Sb and Bi, x. For the samples in the range 0.2<x<0.3, the room temperature thermopower values are in the range 184-159 159 /spl mu/V/K. Measurements of the temperature-dependent resistivity and Hall coefficient of the films were also performed. For the samples in the range 0.2<x<0.3, the room temperature carrier concentrations were 3.93-5.13/spl times/10/sup 19/ cm/sup -3/ and the mobilities were 24.6-64.0 cm/sup 2/ V/sup -1/ s/sup -1/.

Bi substitution effects on Sb/sub 2/Te/sub 3/ thin films

We have grown high quality Bi2 Te3 thin films on CdTe(111)B substrates using MBE. Structural properties have been investigated using in-situ reflection high-energy electron diffraction (RHEED) and θ-2θ X-ray diffraction analysis. They show that Bi2 Te3 films on CdTe(111) grow along the (00. l) in the hexagonal cell with a layer-by-layer growth mode, resulting in a smooth surface, and an X-ray Bragg peak FWHM of 0.2°. The thermopower and electrical conductivity of the stoichiometric Bi2 Te3 films were ∼200 μV/K and 103(Ωcm)−1, respectively, comparable to the single crystal bulk values. We have observed the antisite defect effect in Te-rich Bi2 Te3 films: excess Te occupies Bi lattice sites and behaves as an n-type dopant. Crystallinity and transport properties are strongly affected by non-stoichiometry.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400174718

Mbe Growth and Thermoelectric Properties OF Bi2Te3 Thin Films

Previous measurements1 of the positive ion mobility in liquid 3He below 1°K indicated the existence of a minimum with temperature; however, scatter and a hysteresis phenomena prevented a clear conclusion. A better measurement of this mobility is relevant as it should provide information on the structure of the positive ion in liquid He, a structure that is now under closer examination. Recent measurements by Johnson and Glaberson2 revealed the effect of various impurity ions on the mobility of these structures. According to the classical snowball model of Atkins,3 the minimum with temperature mentioned above is expected near 0.3°K as a consequence of the well-known minimum in the melting curve of 3He. In this work we suggest that the shape of the mobility minimum is related to the layered model proposed by Johnson and Glaberson.2

John B Ketterson

Papers

Ultrasonic Study Of URu2Si2At Very Low Temperatures

Sound velocity and magnetization measurements near the antiferronagnetic transition in the heavy fernion system URu2Si2

Bi substitution effects on Sb/sub 2/Te/sub 3/ thin films

Mbe Growth and Thermoelectric Properties OF Bi2Te3 Thin Films

Positive Ion Mobility in Liquid 3He