Zinc Single Crystals Research Articles

Hydrogen migration in single crystal and polycrystalline zinc oxide

Hydrogen diffusion in single crystal and polycrystalline zinc oxide was investigated by deuterium diffusion and hydrogen effusion experiments. Deuterium concentration depth profiles were measured as a function of the passivation temperature, while in H effusion experiments the molecular hydrogen flux was measured as a function of the heating rate. The diffusion coefficient exhibits thermally activated behavior and varies between ${E}_{A}=0.17$ and $0.37\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The change of ${E}_{A}$ is accompanied by a change of the diffusion prefactor by eight orders of magnitude. This indicates that ${E}_{A}$ is not related to the energetic position of H transport sites or the barrier height between such sites. Using the microscopic diffusion prefactor, the position of the hydrogen chemical potential, ${\ensuremath{\mu}}_{H}$, was estimated. With increasing temperature, ${\ensuremath{\mu}}_{H}$ decreases with a rate of $\ensuremath{\approx}0.0013\phantom{\rule{0.3em}{0ex}}\mathrm{eV}∕\mathrm{K}$. At H concentrations of less than ${10}^{17}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ ${\ensuremath{\mu}}_{H}$ is pinned. The hydrogen density of states was derived from H effusion data, which is consistent with a diffusion activation of about $1.0\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ as was originally reported by Mollwo [Z. Phys. 138, 478 (1954)] and Thomas and Lander [J. Chem. Phys. 25, 1136 (1956)]. Clear evidence for hydrogen deep traps was found in single crystal and polycrystalline $\mathrm{ZnO}$.

Electron Momentum Density of Hexagonal Magnesium Studied by Compton Scattering

Directional Compton profiles of single crystal of hcp magnesium have been measured with scattering vectors along the [10 10], [1120] and [0001] directions in reciprocal space (special directions ΓΜ, ΓΚ, ΓΑ) using high-energy (662 keV) gamma radiation from a 137Cs isotope source. The experimental data were compared with corresponding theoretical Korringa-Kohn-Rostoker (KKR) calculations. The directional difference profiles, both experimental (of medium resolution) and theoretical ones, show very small anisotropy of the electron momentum density in magnesium, 2-3 times lower than in zinc and cadmium single crystals, significantly lower than observed in cubic metals. This small directional effect is in good agreement with Compton 60-keV energy experiments and positron annihilation data presented by other authors.

Generation of terahertz radiation using zinc oxide as photoconductive material excited by ultraviolet pulses

Terahertz (THz) radiation generated from photoconductive antenna fabricated on a single crystal zinc oxide (ZnO) is presented. The THz-radiation power is saturated at bias voltages above 800V∕cm and the obtained spectrum extends up to 1 THz. Moreover, ZnO is found to be highly transparent in the visible, near-infrared, mid-infrared and THz frequency regions. The results depicted here will categorically unravel the prospects of using ZnO as a material for integrated active optics.

Poly[diaqua-μ4-acetylenedicarboxylato-zinc(II)

From a solution of [Zn(H2O)6](NO3)2 and acetyl­enedicarb­oxylic acid in deionized water, single crystals of zinc acetyl­ene­dicarboxyl­ate dihydrate, {[Zn(C4O4)(H2O)2]}n, were obtained by slow evaporation of the solvent. The asymmetric unit consits of one zinc cation which is located on a centre of symmetry, half of an acetyl­enedicarboxyl­ate anion, the anion lying on a twofold axis, and one water mol­ecule in a general position. Thus, zinc is octa­hedrally coordinated by four O atoms of acetyl­enedicarboxyl­ate anions and two water mol­ecules in trans positions. These octa­hedra are connected by dicarboxyl­ate ligands into a three-dimensional network.

Influence of excitation density on photoluminescence of zinc oxide with different morphologies and dimensions

Photoluminescence from zinc oxide (ZnO) nanoparticles, nanorods, microparticles, and single crystals was measured under various conditions of ultraviolet excitation. Near-band-gap and deep-level emissions were observed from all samples. The intensities of both emissions from each ZnO sample exhibited a different nonlinear dependence on the excitation density. These differences could be interpreted by the variation of the light scattering and the specific surface areas of the ZnO morphologies. The intensity ratio of the near-band-gap emission to the deep-level emission from the ZnO samples strongly depended on the density of the excitation light. Our results indicated that the intensity ratio of two emissions depends on the sample type (such as the dimension, specific surface area, etc.), as well as the experimental conditions (such as excitation density, radiation area, etc.). Therefore, this ratio could not be simply employed to unequivocally evaluate the quality of the ZnO.

ZnO single crystal and epitaxial thin film studied by second harmonic generation and photoluminescence

Zinc oxide thin nanostructured film and single crystal were studied by photoluminescence (PL) and optical second harmonic generation (SHG). The single crystal reveals a strong blue excitonic luminescence, while for thin films “yellow”-defect PL is dominant, pointing to a strong contribution from the surface of film nanograins. In SHG the bulk contribution is dominant for both film and single crystal, although SHG enhancement was found in the film. Nonlinear parameters were calculated from the model and preferable orientation of the film grains was found.

High pressure electrical resistivity study on nonlinear single crystal zinc thiourea sulphate (ZTS)

The Tris Zinc Thiourea Sulphate (ZTS) crystals have been crystallized by slow evaporation technique. The lattice parameters of the grown crystals have been determined by the Energy dispersive x-ray diffraction technique (EDXRD) and the structure has been confirmed. And, the high pressure electrical resistivity study have been carried out on this crystal and the results have been reported here. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Macroscopic localization of plastic flow in zinc single crystals oriented for basal slip

The patterns of plastic-flow localization in hcp Zn single crystals oriented for slip in the {0001} 〈2110〉 systems are investigated. The main spatial and temporal regularities of the flow localization are established for all portions of the three-stage curve of such crystals. The relationship between the type of localization patterns and the regularities of strain-hardening of single crystals is traced for each stage. The role of the kinking in the formation of the observed macroscopic-flow distributions is estimated.

Radical-Beam Gettering Epitaxy of ZnO Films under UV Irradiation

Single-crystal ZnO films are grown by radical-beam gettering epitaxy: annealing of single-crystal zinc chalcogenide (ZnS, ZnSe, or ZnTe) substrates in a flow of oxygen atoms (radicals) and gettering of zinc atoms from the substrate bulk. The effect of UV irradiation during film growth on the structure and quality of the resulting ZnO films and the effect of ion implantation into the substrate on the growth of ZnO/ZnSe heterostructures are studied. The conditions are established for the growth of p-type ZnO films.

Pressurized melt growth of ZnO boules

Single crystal zinc oxide is a wide band gap semiconductor with great potential for a variety of commercial applications including substrates, UV photodetectors, acoustic wave devices, light emitting diodes, laser diodes, and high frequency electronic devices. ZnO is unique in that it has a very high exciton binding energy (60 meV) enabling stability at higher device operating temperatures, and it is highly resistant to radiation damage compared even to GaN. Bulk growth of ZnO single crystals is being conducted using the following primary methods: hydrothermal solution growth, seeded sublimation growth, and pressurized melt growth. Cermet, Inc. has employed the pressurized melt growth approach with much success. ZnO dissociates upon heating into a defective ZnO1−x structure, which is addressed by providing an overpressure of oxygen in the growth environment. Single crystals nucleate and grow from the stoichiometric ZnO melt, which is contained in a thin layer of cooled, polycrystalline ZnO, eliminating crucible-introduced impurities. From these large ingots, high quality (∼104 defects cm−2, linewidths as low as 49 arcsec), high purity ZnO crystals have been crystallized, oriented, and shaped into round or square boules and eventually processed into epitaxial-ready substrates. The pressurized melt growth approach is highly scalable and can accommodate high growth rates (up to 1 cm h−1), which are two criteria that are appealing to industrial productioin of high quality substrates.

Two-dimensional zinc oxide nanostructure

Transparent two-dimensional ultralong and ultrabroad single crystal zinc oxide (ZnO) nanosheets were directly synthesized by a simple solid vapor deposition process under lead oxide (PbO) atmosphere. The nanosheets are well grown single crystals with thickness of about 50–70 nm, breadth of 50–100 μm and length of 4–6 mm. The growth mode of the ultrabroad nanosheets displays a unique aspect that (001) planes form the narrowest facets of the nanosheets, which is completely different from other belt-like nanostructures of ZnO. Control experiments show that PbO play an important role in the vapor–solid growth process of ZnO nanosheets.

On the Yield Strength of Single-Crystal Zinc under Uniaxial Compression in a Plane Shock Wave

The shock wave pattern in zinc single crystals compressed in the direction normal to the basal plane of the crystal is traced with a high time resolution. In this geometry of the experiment, plastic deformation of the zinc is found to begin at a shock compression pressure above 15 GPa and is not accompanied by splitting of the shock wave into an elastic precursor and a plastic compression wave.

A systems-based approach for generating quantitative models of microstructural evolution in silicon materials processing

A systematic approach based on multiple model regression to several distinct types of experimental data is used to create a robust modeling framework for defect and impurity evolution during crystalline silicon processing. The three experimental systems considered here are Czochralski single-crystal growth, zinc diffusion, and oxide precipitation during wafer thermal annealing. All three systems are intimately connected at the atomistic level by the thermodynamic and transport properties of single point defects. The present work demonstrates how this microscopic overlap in these macroscopically distinct systems can substantially reduce uncertainty in model regression to experimental data, leading to strict bounds on the transport, reaction, and thermodynamic properties of the various species present. The resulting parameters lead to a solid, quantitative basis for modeling a wide variety of technologically important defect-related phenomena in silicon processing. Several different stochastic global optimization methods are employed to perform the computationally expensive multi-objective function minimization, namely simulated annealing, genetic algorithms, Tabu search and particle swarm optimization. These methods are compared and contrasted as part of the investigation and it is shown that a hybrid genetic algorithm that periodically incorporates a local search is the most robust approach for the types of problems considered in this work.

Line source representation for laser-generated ultrasound in an elastic transversely isotropic half-space

Theoretical and experimental results are presented for a laser line source in an elastic, transversely isotropic half-space. The thermoelastic source (laser source) is represented as an appropriately weighted shear stress dipole applied at the sample surface. The plane of isotropy coincides with the half-space boundary. Analytical expressions representing the out-of-plane displacements for the surface wave and for the epicentral cases are given for all crystal classes that exhibit elastic transverse isotropy. In addition, quasianalytical results are given for observation points off the epicentral axis. Theoretical wave forms for all of the source/observation geometries considered are compared with experimental wave forms generated in single crystal zinc samples. The close comparison between experiment and theory confirms, for this particular line source orientation and crystal symmetry, that a laser line source is accurately modeled using an equivalent boundary stress.

Anodic behaviour of zinc in methanol solutions of lithium perchlorate

Anodic dissolution of poly- and single-crystals of zinc was performed in methanol solution of lithium perchlorate by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The mechanism of anodic dissolution of zinc in organic solvents occurs in two oxidation steps. It is the first step that Z n L + surface anodic product is created. Stability of the surface product is much better in anhydrous organic environments than in aqueous media; because the product is stable, a barrier layer composed of Z n L + is formed at low anodic overvoltage. The formation of the Z n L + layer is much stronger on the low index ( 1 1 2 ¯ 0 ) than on the high-index plane (0 0 0 1), where the adsorption of anodic product is more difficult.

Grain Boundary Dynamics in High Magnetic Fields. Fundamentals and Implications for Materials Processing

The latest research on dynamics of grain boundaries in non-magnetic materials in high magnetic fields is reviewed. A control of grain boundary migration means control of microstructure evolution, which is a key for the design of materials with desire properties. Grain boundary motion can be affected by a magnetic field, if the anisotropy of the magnetic susceptibility generates a gradient of the magnetic free energy. In contrast to curvature driven boundary motion, a magnetic driving force also acts on planar boundaries so that the motion of crystallographically well-defined boundaries can be investigated, and the true grain boundary mobility can be determined. The results of migration measurements obtained on bismuth and zinc bicrystals are addressed. Selective growth of new grains in locally deformed zinc single crystals driven by a magnetic force is reported as well. Implications for materials processing, in particular the effect of magnetic fields on texture development in hcp metals are finally discussed.

Application of ion implantation for synthesis of copper nanoparticles in a zinc oxide matrix for obtaining new nonlinear optical materials

We have obtained a layered composite material by implantation of single crystal zinc oxide (ZnO) substrates with 160-keV Cu+ ions to a dose of 1016 or 1017 cm−2. The composite was studied by linear optical absorption spectroscopy; the nonlinear optical characteristics were determined by means of Z-scanning at a laser radiation wavelength of 532 nm. The appearance of the optical plasmon resonance bands in the spectra indicated that ion implantation to the higher dose provides for the formation of copper nanoparticles in a subsurface layer of ZnO. The new nonlinear optical material comprising metal nanoparticles in a ZnO matrix exhibits the phenomenon of self-defocusing and possesses a high nonlinear absorption coefficient (β=2.07×10−3 cm/W).

EPR studies of Cu2+-doped bis(saccharinato)bis(pyridine)zinc(II) single crystals

The electron paramagnetic resonance spectra of Cu 2+ impurities in bis(saccharinato)bis(pyridine)zinc(II) single crystals have been studied at room temperature in three mutually perpendicular planes. The angular variation of the spectra indicates the substitution of the host Zn 2+ with Cu 2+ . Two magnetically inequivalent sites for Cu 2+ have been observed. The spectra were fitted to the rhombic spin Hamiltonian. The spin Hamiltonian parameters and the molecular orbital coefficients were evaluated for the two sites. The ground-state wave function of Cu 2+ ion in the lattice has been constructed.

Effect of atmosphere on growth of single crystal zinc oxide nanowires

Single crystal zinc oxide (ZnO) nanowires were prepared by using enhanced two-step vapor–liquid–solid (VLS) growth mechanism. The experimental results indicate that the growth rate and morphologies of the nanowires depends on the carrier gas ambient during the thermal reaction process. The ZnO nanowire grown with N2, not only has the smaller diameter of about ∼30 nm but also exhibits a higher growth rate and larger number of density of nanowires per unit area than those grown with Ar. The photoluminescence measurements show that the ZnO nanowires grown with N2 have a stronger ultraviolet emission than those grown with Ar.

Measurement of the Third-Order Nonlinear Optical Coefficientof ZnO Crystals by Using ICCD-Z-Scan

We present an image-intensified charge-coupled-device (ICCD) version ofZ-scan by employing an ICCD detector and fixing thesample at the beam waist, and a measurement of the third-ordernonlinear optical coefficient of single crystal zinc oxide (ZnO). Theχ(3) value of −9.1×10−15 cm2/W measured is inagreement with the published result. Our Z-scan configuration of placingsample at beam waist and collecting the whole wavefront by an ICCDdetector is simple and can be deployed in cryogenic research where thesample cannot be Z-scanned.