Zinc Single Crystals Research Articles

Effect of ozone cleaning on Pt/Au and W/Pt/Au Schottky contacts to n-type ZnO

The role of UV ozone cleaning on the characteristics of Pt contacts on n-type (n∼1017cm−3) bulk single-crystal zinc oxide (ZnO) is reported. The contacts are Ohmic for samples that were not exposed to ozone prior to Pt deposition, but exhibit excellent rectifying behavior with ozone cleaning. The barrier height of these contacts obtained from current–voltage measurements was 0.70±0.04eV at 25°C with an ideality factor of 1.49 and a saturation current density of 6.17×10−6Acm−2. There is a significant decrease in surface carbon concentration after the ozone cleaning (29.5at.% down to 5.8at.%, as determined from Auger electron spectroscopy). The measured barrier height for Pt on ZnO is similar to the value reported for both Au and Ag rectifying contacts on this material. By sharp contrast, sputter-deposited W contacts are Ohmic, independent of the use of ozone cleaning and become rectifying after 700°C annealing to repair sputter-induced damage. The barrier height is ∼0.45–0.49eV, with the ozone cleaning producing values at the high end of this range.

Green luminescence in diffusion-doped layers of zinc selenide

Diffusion-doped layers with a green emission band dominating in the room-temperature luminescence spectrum are obtained by annealing single-crystal zinc selenide substrates in tellurium and zinc vapors.

Surface roughness changes on a hot-dipped galvanized sheet steel during deformation at low strain levels

During a study on surface roughening as a function of deformation, an anomalous behavior of the surface roughening for hot-dipped galvanized sheet steel was observed during low levels of imposed strain. A mechanistic model, which explains this surface roughening behavior, is presented. Surface topography parameters, including surface roughness, and relative zinc crystal orientation data, were measured after different amounts of deformation were imposed on the sheet. The proposed model is consistent with both sets of data. The model indicates that the zinc crystals on the surface of the coated sheet steel will initially deform by twinning, which causes a slight increase in surface roughness. The twin regions of the zinc crystals are then favorably oriented for dislocation glide, and the roughness during further deformation will slightly decrease. Once the zinc crystal orientations have homogenized, standard surface roughening due to adjacent grain constraint occurs. Further evidence to support the model include: (1) Twinning in a single crystal of zinc causes a roughness increase of the same magnitude as that found in the zinc coated steel after low strain deformation, (2) twinning of zinc has been observed in other studies of zinc-coated sheet steels, and (3) discontinuous yielding of the steel and recrystallization of the zinc during the sheet deformation did not occur and are not the cause for both the surface roughness and crystal orientation results.

Room-temperature single nanoribbon lasers

Using a single nano-object measurement methodology that enables the correlation between size/morphology/structure and photoluminescence (PL) characteristics, we show that nanoribbons are an excellent model system to study single nano-objects. In particular, we measure the PL characteristics of optically pumped individual single-crystal zinc–sulfide nanoribbons. Small collection angle measurements show that nanoribbons form excellent optical cavities and gain medium with high (full width at half maximum<0.1 nm) lasing modes free of PL background even for a low pumping power density of 9 kW/cm2. Large collection angles add a broad PL component and obscure the correct high-quality lasing of the nanowires/nanoribbons.

Macrolocalization of plastic flow in zinc single crystals oriented for basal glide

The pattern of plastic flow macrolocalization in actively loaded zinc single crystals has been studied. The character of localization consistently varies in accordance with the stage of plastic flow. The results are compared to the analogous data for single crystals with an fcc lattice. The common features and individual peculiarities in evolution of the patterns of plastic flow localization in materials with different crystal structures are revealed.

Room-Temperature Lasing Characteristics of Zinc Sulfide Single Nanoribbons

AbstractWe present a study of the photoluminescence and lasing characteristics of individual single-crystal zinc sulfide nanoribbons. We show that ZnS presents optical gain at the near band gap emission of ∼338 nm. Optical gain together with the optical cavity defined by the perfect crystallographic structure with a rectangular cross section results in lasing activity at optical pumping power densities of ∼ 50 kW/cm2. Small collection angle measurements show that nanoribbons form excellent optical cavities and gain medium with record (FWHM<0.1nm) lasing modes free of PL background. Large collection angles (as previously employed for nanowire measurements) add a broad, non-resonant PL component and obscure the original high-quality lasing of the nanowires/nanoribbons.

Growth of single crystal ZnO nanowires using sputter deposition

Single crystal zinc oxide is a very promising material for light-emitting devices in blue, violet, and ultraviolet regions due to its wide direct band gap of 3.37 eV. Single crystal ZnO has been in a form of thin film or tetrapod-like whisker. Recently, the growth of highly oriented ZnO whiskers was also reported. Irrespective of the form and growth technique, successful growth of single crystal films or whiskers inevitably requires the use of a single-crystal substrate such as sapphire and diamond. In this paper, we report the growth of single crystal ZnO nanowires on a non-single-crystal substrate using a conventional sputter deposition technique. An r.f. magnetron sputter deposition system was used for the growth of ZnO nanowires in O 2/Ar mixtures. The substrate used was silicon wafers with copper metallization. After the ZnO deposition, specimens were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), and selected area diffraction (SAD).

Plastic instability and Lüders bands in the tensile test: the role of crystal orientation

Considère's plastic stability criterion in tensile testing is rewritten by separating the effects of intrinsic and geometrical hardening for single and polycrystals deforming by slip. The Taylor factor is employed to describe the effect of orientation change in the stability of plastic deformation for which a new instability parameter has been defined. Analytical results are presented for single slip in f.c.c. and h.c.p. crystals, while numerical simulations were done for the polycrystal case using the Taylor model. Localization may lead to the formation of Lüders bands if the strains are limited either by intrinsic hardening or by geometric hardening (discussed on the example of a zinc single crystal).

Growth of platelets under diffusion conditions. Growth kinetics of platelets obtained on the zinc single crystals and determination of the timing of their appearance (II)

The kinetics of growth of platelets on the pyramidal { 1 0 1 ̄ 1 } and prismatic { 1 0 1 ̄ 0 } faces of zinc single crystals and the alteration with time t of the edge length a of the {0 0 0 1} basal face of the same crystals in the presence of argon were investigated. The measurements of the edge a with time show that at the moment when the critical size a k is reached, the transition from kinetic to diffusion regimes starts. The comparison between the time when the visible platelets appeared on the zinc crystals and the a 2 vs t curves revealed that the first platelets grow exactly at the transition between the two regimes. It has been established that during the initial stage, when the size L is small, the platelets grow at a constant rate. During further growth, as the size L increases and reaches the critical dimension L k , a change in the L 2 vs t curves appears: the linear curve is transformed into a parabolic one. In conformity with the morphological theory of Chernov in the isotropic case, it is concluded that the platelets grow in a kinetic and a diffusion regime. This effect of transition from the kinetic to the diffusion regime during the growth of platelets, similar to the effect observed during the growth of zinc single crystals, is a common phenomenon, which results from the diffusion conditions under which platelets and single crystals grow.

Relationships Between Metal-Metal Bonding and Crystallographic Pitting in hcp Metals

The orientation dependence of pit propagation in single-crystal beryllium (Be) is compared to observations for single-crystal zinc (Zn). Pits formed on the prism planes of both Be and Zn were characterized by interiors which had crystallographically oriented, parallel plates of unattacked material. In Be, the orientation of the unattacked material had a 90° asymmetry with respect to those formed in Zn. To explain this difference, the electron density distribution for low index planes in Be and Zn was analyzed. A conceptual model for crystallographic pit propagation that considers the role of orientation dependent metal-metal bonding is introduced.

The effect of gamma-irradiation on the bandgap width of ZnSe

Exposure to gamma-radiation from a 60Co source affects the exciton photoluminescence (PL) spectra of single crystal zinc selenide measured at 4.2 K. As the radiation dose increases, the exciton PL maximum first shifts toward higher energies, but then returns to the initial position (in the range of sufficiently high doses). It is concluded that this behavior is due to variations of the semiconductor bandgap width related to the radiation-stimulated solid-state recrystallization and the accumulation of radiation-induced point defects during exposure.

Hexagonal Corrosion Pattern upon Cleavage of a Zinc Single Crystal under a Vertical High Magnetic Field

Abstract A two-dimensional hexagonal pattern was observed upon cleavage of a zinc single crystal after attack with sulfuric acid under a vertical high magnetic field. This phenomenon results from the formation of microscopic magnetohydrodynamic flow (micro-MHD flow) as microscopic vortexes, which interact with fluctuations of the reaction activity. The spatial pattern of the zinc surface is thought to be a result of the growth of fluctuation in the reaction activity about the zinc anodic dissolution, which was stabilized by the micro-MHD vortexes.

Some indentation and sliding experiments on single crystal and polycrystalline materials

Indentation and sliding experiments were conducted on some fcc, bcc, and hcp structured, single crystal (copper, aluminum, iron, zinc, and cadmium) and polycrystalline (iron, tin, aluminum oxide and magnesium meta-aluminate) materials. Hard indenters (steel, sapphire, and diamond) were used to investigate the anisotropic behavior of these materials in indentation and sliding. A conventional microhardness tester modified to enable sliding of the specimens past the indenter and to incorporate the means for the measurement of frictional force using strain gages was used in this investigation. Optical microscopy (including interference contrast) was used to characterize the specimens after indentation/sliding. An attempt was made to correlate the gross macroscopic behavior in terms of microscopic events. The results of this study show that indentation and sliding on a microscopic scale, such as with a hard indenter can reveal unique characteristics for both single crystal and polycrystalline materials.

The influence of structural features on the thermal conductivity of polycrystalline zinc sulfide

The thermal conductivity of single-crystal zinc sulfide and optically transparent zinc sulfide polycrystals differing in crystal grain size and density is experimentally investigated in the temperature range 80–400 K. It is shown that the thermal conductivity of polycrystalline samples substantially depends on the crystal grain size and the defect concentration in the grain-boundary layers. In zinc sulfide samples with a grain size of 1 µm, excess thermal resistance due to phonon scattering by grain boundaries is observed at temperatures T 210 K), the heat transfer is associated not only with transverse phonon modes but also with longitudinal phonon modes and the role of the latter modes increases with an increase in temperature.

PZN-PT Single-Crystal Thin Film Monomorph Actuator

We report on the use of single-crystal lead zinc niobate-lead titanate films in monomorph actuators. The article responds to the growing interest in solid-solution (1 m x )Pb(Zn 1/3 Nb 2/3 )O 3 - x PbTiO 3 relaxor ferroelectrics based on their large piezoelectric coefficients and their integration into microelectromechanical system. Freestanding films are fabricated by slicing a 7 w m-thick layer off the crystal bulk and assembled into a flexural actuator, thus circumventing polycrystalline deposition techniques. One-micron deflections are observed at 100 V for ∼1 mm-long films. The article discusses the non-uniform electric field distribution profile established in the films and its role in the actuation process.

Growth of ZnO Thin Films and Whiskers

Copper-metallized silicon wafers were used as substrates for the deposition of zinc oxide thin films using a radio frequency sputter deposition technique. Copper metallization on silicon wafer was performed using two different methods, a plating technique and a sputter deposition technique. Copper-metallized silicon substrates were then deposited with zinc oxide thin films under various sputter deposition conditions. The characteristics of zinc oxide thin films were found to not only depend on the deposition conditions, but also be strongly influenced by the type and characteristics of the copper layers. In addition to polycrystalline thin-film zinc oxide, single-crystal zinc oxide whiskers were also found on silicon substrates with plated copper.

Analysis of dispersion of long-wavelength optical phonons in zinc with the help of light scattering

The temperature dependences (5–300 K) of the Raman spectra of E2g phonons and optical constants in zinc single crystals are measured in the excitation energy range 1.4–2.54 eV. It is found that phonon damping decreases upon an increase in the wavelength of exciting radiation. The obtained results are compared with the dependence of the phonon width on the excitation energy (the probed wave vector of the excitations under investigation), which are presented for the first time for the transition metal osmium, as well as with the calculated electron-phonon renormalization of damping, taking into account the actual distribution of wave vectors.

Study of the initial stage of white rust formation on zinc single crystal by EIS, STM/AFM and SEM/EDS techniques

The kinetic consequences of morphological changes due to the zinc exchange process have been related to the corrosion performance and a further understanding of the initial stage of the white rust formation occurring preferentially in a thin layer of moisture in the absence of oxygen. Electrochemical impedance diagrams for a uniformly covered Zn corrosion product layer can be interpreted by a one-step dissolution mechanism, while on a non-uniform, partially active surface a consecutive dissolution occurs via adsorbed Zn(I) and Zn(II) species. The in situ EC-STM and EC-AFM observations revealed oriented Zn dissolution, deposition along the atomic steps and oriented oxide formation on the redeposited crystal planes in the early stages of each process.

Nanowires Produce Ultraviolet Laser Light At Room Temperature

A team of scientists at the University of California, Berkeley, and Lawrence i Berkeley National Laboratory (LBNL) has developed nanowires that can be used as ultraviolet lasers [ Science , 292 ,1897 (2001)]. Team leader Peidong Yang, an assistant professor at UC Berkeley and a faculty scientist at LBNL, says this is the first demonstration of using nanowires to make an active lasing device. He believes that such lasers could find use in applications such as information storage and microanalysis; for example, lab-on-a-chip devices. Yang and his coworkers grew single-crystal zinc oxide nanowires 20 to 150 nm wide and 2 to 10 μm long on gold-coated sapphire substrates. The wires grow—catalyzed by the gold—vertically from the substrate. The nanowires form a natural resonance cavity suitable for lasing—without the addition of fabricated mirrors. Instead, the wires provide their own mirrors, with the interface between the substrate and ZnO serving as one mirror and the perfectly cleaved hexagonal ...

Growth of platelets under diffusion conditions: Morphological stability investigation of platelets obtained on the zinc single crystals (I)

The growth of zinc platelets on zinc single crystals in the presence of hydrogen or argon is investigated. It is shown that by the growth of platelets on the pyramidal 1 0 1 ̄ 1 and prismatic 1 0 1 ̄ 0 faces, zinc single crystals lost their morphological stability. It is established that the smooth {0 0 0 1} faces of the platelets change their shape in skeletal, while new platelets start growing from the peaks of the primary ones. The results are discussed and are in conformance with Chernov's theory for the disturbance of the morphological stability of crystal forms. The alteration of the surface structure of zinc single crystals and the platelets growing on them demonstrate the crucial role played by bulk diffusion during crystal growth.