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

Susceptibility measurements on the Kondo alloy La:Ce show that X = cF(T,H) for 1.3 K ≤ T ≤ 300 K, c ≤ 15 at %, H ≤ 20 kG where F is independent of concentration c. At high temperatures (T > 30 K), F(T,O), like other Kondo systems, obeys a Curie‐Weiss law 1/(T + 27). At low temperatures (0.6 ≤ T ≤ 30 K), f (T,0) ∝ T−1/2. To test the sensitivity of this result to local environment and the effect of spin‐orbit scattering, measurements were made on Ce .01ThxLa.99−x (x ≤ 0.4) alloys. These measurements show that the Ce contribution to the susceptibility, cF(T,0), is unchanged by the addition of Th. The magnetic field dependence of X does not fit a Brillouin function. Generalizing Anderson's suggestion, a phenomenological model is developed which assumes that the density of states N(E) ∝ (e2 + Δ)−1/4 whwrw Δ−1 is a lifetime. The calculated numerical results from this model for F(T,H) are in good agreement with the experimental results. Qualitatively F ∝ (T2 + μ2H2 + Δ)−δ where δ = 1/4. The Hirschkoff et al. dat...

EQUATION OF STATE FOR THE KONDO SYSTEM La:Ce.

UPt/sub 3/ is a superconducting heavy fermion compound showing unconventional properties in the superconducting state. Longitudinal sound attenuation and velocity measurements in the normal state of UPt/sub 3/ from 2 K to 300 K are presented for frequencies ranging from 85 MHz to 850 MHz, in a magnetic field up to 8 T. Attention is focused on the attenuation absorption peak developing at temperatures below 40 K, which is accompanied by a rapid increase in velocity. The center of this peak is located at about 10.5 K and, within the experimental resolution, its position is frequency-independent. The amplitude of this peak is found to be proportional to the square of the sound frequency. With an increasing applied magnetic field, the center of the peak is found to move to lower temperatures while the amplitude of the peak increases. >

Ultrasonic attenuation and velocity measurements in the normal state of the heavy fermion superconductor UPt/sub 3/

The heavy fermion superconductor UPt 3 shows evidence of a complex phase diagram in the H-T plane.A variety of experiments reveal the existence of at least two and maybe more superconducting phases.The phase transition line(s) obtained from the different experiments is (are) in qualitative agreement.

Phase diagram of superconducting UPt3

The vertical and in-plane resistive transition in a series of Si Nb multilayers has been studied. An anisotropic percolation model is adequate to explain the observed transition behavior. The measured temperature dependence of the supercurrent is compared with the Ambagaokar-Baratoff theory. The tail structure in Ic(T) curves near Tc is interpreted as the short coherence length effect.

Vertical resistive transition in {Si}/{Nb} multilayers

Thin films of YBCO with a high degree of alignment both normal to and within the basal plane have been prepared by an electron beam multilayer deposition technique. The a-axis oriented film consists of an array of orthogonal, interconnecting, rectangular crystal bars. The zero field critical current density for the a-axis oriented film measured with the magnetic field perpendicular to the plane of film is 6.7×10 6A/cm 2 at 4.4K and 1.2×105A/cm2 at 77K. In order to study the orientation dependence of the in-plane critical currents, the film was positioned so that the magnetic field was at angles of 0°, 30°, and 45° to the in-plane axes of the substrate. The critical current density J,(θ=0°) is 1.6 times larger than Jc(θ=45°) and Jc(θ=30°). These results imply that the degree of alignment of the crystal grains is crucial for achieving high quality thin films. The superconducting critical current density can be rather high, not only in the c-axis oriented films but also in the epitaxial a-axis oriented films, which have high degree of texture and excellent intergrain contact.

John B Ketterson

Papers

EQUATION OF STATE FOR THE KONDO SYSTEM La:Ce.

Ultrasonic attenuation and velocity measurements in the normal state of the heavy fermion superconductor UPt/sub 3/

Phase diagram of superconducting UPt3

Vertical resistive transition in {Si}/{Nb} multilayers

Orientation Dependence of Critical Currents in a-Axis Oriented YBCO Thin Films