Polycrystalline Zn Research Articles

Electrochemical growth of ZnO nano-rods on polycrystalline Zn foil

ZnO nano-rods were grown on polycrystalline Zn foil by cathodic electrodeposition inan aqueous zinc chloride/calcium chloride solution at 80°C.Variations in the solution concentration and substrate surface preparation wereexplored to shed light on the nucleation of the nano-rods. It was found that thenano-rod diameter increased with increasing solution concentration. Rolling striationsand native ZnO on the surface of the Zn appeared to enhance nucleation andallowed more highly aligned, dense structures to be grown. By using lowsolution concentrations (5.0 × 10−4 M ZnCl2)and non-electropolished Zn substrates, well faceted, hexagonalnano-rod structures of dimension ∼80 nmdiameter and >1 µmlength were obtained. X-ray studies showed the samples to be highly aligned butcontaining a Zn-oxychloride impurity phase. Annealing caused the impurity phaseto disappear and resulted in the films having a sharp photoluminescence doublepeak at 380/396 nm.

Orientation domains and texture in hot-dipped galvanized coatings

The crystallographic orientation of galvanized coatings (Zn-0.2Al-0.15Sb in wt pct) has been characterized by Electron-Backscattered Diffraction (EBSD) and optical microscopy. While 80 pct of the nucleation spots in the coating give rise to single-crystal Zn grains, it has been found that about 20 pct of them give rise to two or more orientation domains, each having a specific crystallographic orientation. For such “polycrystalline Zn grains,” the orientations of the domains are crystallographically related: they have a dense crystallographic direction (〈1010〉, 〈1120〉, or 〈0001〉) in common. Moreover, the crystallographic relationships are similar to those observed in snowflakes and can be partially explained by the concept of a coincidence-site lattice (CSL). The EBSD measurements were also used in order to measure quantitatively the crystallographic texture. In particular, it has been evidenced that the (0001) texture of galvanized coatings is the result of two contributions: (1) the nuclei are preferentially oriented with the basal plane parallel to the coating plane (33 pct of the grains have an angle between the basal plane and the coating plane smaller than 22.5 deg), and (2) the grains having the basal plane parallel to the coating plane grow faster (these grains represent 43 pct of the coating surface). This reinforcement of the texture during growth is in agreement with that predicted by growth models, which take into account the effect of the interfaces.

Infrared absorption spectroscopic study of Nd3+ substituted Zn-Mg ferrites

Compositions of polycrystalline Zn x Mg1−x Fe2−y Nd y O4 (x = 0.00, 0.20, 0.40, 0.60, 0.80 and 1.00;y = 0.00, 0.05 and 0.10) ferrites were prepared by standard ceramic method and characterized by X-ray diffraction, scanning electron microscopy and infrared absorption spectroscopy. Far infrared absorption spectra show two significant absorption bands, first at about 600 cm−1 and second at about 425 cm−−1, which were respectively attributed to tetrahedral (A) and octahedral (B) sites of the spinel. The positions of bands are found to be composition dependent. The force constants,K T andK O, were calculated and plotted against zinc concentration. Compositional dependence of force constants is explained on the basis of cation-oxygen bond distances of respective sites and cation distribution.

Grain-dependent passivation of surfaces of polycrystalline zinc

Effects of texture on the electrochemical behaviors of single grains in polycrystalline zinc were investigated using a capillary-based micro-droplet cell. Pontiodynamic sweeps and capacity measurements were carried out in pH 9 borate buffer solution. The cyclic voltammograms and the capacity measurements on single grains with different crystallographic orientations in polycrystalline Zn showed a strong dependence of oxide growth on crystallographic grain orientation. The total charge consumed for oxide formation and the inverse capacity increased with an increase of surface packing density of grain, suggesting the oxide formation was greater on grains with higher surface packing density.

Origin of spin-glass behavior of Zn1-xMnxO

Alternating current susceptibility has been studied for polycrystalline Zn1 − x Mn x O. Stoichiometric samples demonstrate Curie–Weiss behavior, which indicates mostly antiferromagnetic interactions. Magnetic susceptibility can be described by a diluted Heisenberg magnet model developed for semimagnetic semiconductors. High-pressure oxygen annealing induces spin-glass like behavior in Zn1 − x Mn x O by precipitation of ZnMnO3 in the paramagnetic matrix.

Some dielectric parameters of Zn 3As 2

The Drude oscillator and a multi-oscillator model is utilized to determine some dielectric parameters of polycrystalline Zn 3As 2 in the infrared region 200–1000 cm −1 (50–10 μm).

Defect formation during Zn diffusion in GaP and GaSb

The defect structures induced by zinc diffusion in intrinsic GaP single crystals at temperatures between 1182K and 1358K and in an intrinsic GaSb single crystal at 883K are characterized for diffusion times t ≤ 90 min by analytical transmission electron microscopy. The results are compared with Zn concentration depth profiles obtained by secondary ion mass spectroscopy. In regions near the Zn diffusion front dislocation loops of interstitial type and Ga-rich precipitates are found. Closer to the surface a loose network of dislocations, dislocation loops and faceted voids with Ga-rich precipitates are observed. In addition, a surface layer of polycrystalline Zn 3 P 2 is formed at the surface of GaP at higher diffusion temperatures. The formation of diffusion-induced defects can be understood in a similar way as the defect formation during Zn diffusion in GaAs and InP.

Influence of the core polarization on the dielectric properties of polyvalent metals

We have measured the dispersion of plasmon excitations in polycrystalline Sn, Pb, Cd and Zn using electron energy-loss spectroscopy (EELS) in transmission. These metals show a remarkable deviation of their plasmon behaviour from standard theoretical expectations which can be attributed to the presence of shallow core levels in the energetic neighborhood of the plasmon energy. The position of the plasmon resonance in the long wavelength limit is in line with predictions from model assumptions taking into account the core level polarization effects. We show that not only the plasmon energy in the optical limit but also the plasmon dispersion is altered by the interaction of the charge carrier plasmon and the core level excitations.

Surface Chemistry of SO2 on Zn and ZnO: Photoemission and Molecular Orbital Studies

The reaction of SO2 with polycrystalline Zn and ZnO surfaces has been investigated using synchrotron-based high-resolution photoemission spectroscopy and ab initio self-consistent-field calculations. The chemistry of SO2 on Zn surfaces is quite complex and depends on both the temperature of adsorption and the SO2 exposure. At 300 K, SO2 dissociates on a clean Zn surface to form atomic sulfur and atomic oxygen (SO2,gas → Sa + 2Oa; SO2,gas → SOgas + Oa). The Zn ↔ SO2 bonding interactions induce a significant weakening of the S−O bonds. The theoretical calculations suggest the η2-O,O and η2-S,O bonding conformations of SO2 as the two possible precursors for the dissociation of the molecule. The dissociation reactions are much more exothermic than the formation of SO3 or SO4: SO2,gas + nOa → SOx, where x = 3 or 4. At high SO2 exposures (300 K), when most surface sites are blocked and dissociation of SO2 cannot occur, SO3 and SO4 are formed on the Zn surface. Adsorption at 100 K suppresses the SO2 dissociatio...

Structural, electrical and optical properties of zinc nitride thin films prepared by reactive rf magnetron sputtering

Polycrystalline zinc nitride (Zn 3N 2) thin films are prepared by reactive rf magnetron sputtering with different N 2 concentrations in sputtering gases (N 2–Ar mixtures). Structure and chemical bonding states are measured with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Single phase Zn 3N 2 film formation and texture strongly depend on N 2 concentration. Polycrystalline Zn 3N 2 films are formed at N 2 concentrations over 20% and show a 100 preferred orientation. The XPS N 1s peak (395.8 eV) for Zn 3N 2 indicates a large chemical shift of 3.0 eV from the N 1s peak for free amine (398.8 eV) indicative of the formation of N–Zn bonds. Moreover, the modified Auger parameter, which is a good measure of the chemical state, is determined to be 2012.3 eV for Zn 3N 2 from XPS measurements. This value is significantly different from the values for ZnO and metallic zinc. The polycrystalline Zn 3N 2 films show a high electron mobility of about 100 cm 2 V −1 s −1 at room temperature. Zn 3N 2 is determined to be an n-type semiconductor with direct gap of 1.23±0.02 eV.

Optical constants of polycrystalline ZnSeCdSe alloy films

Reflection and transmission spectra have been recorded at room temperature to determine the optical constants (refractive index, n, and extinction coefficient, k) for electron beam evaporated polycrystalline Zn 1− x Cd x Se (0 ≦ x ≦ 1) thin films on glass substrates as a function of composition ( x). The Newton-Raphson method is employed to determine n and k from the measured reflectance, transmittance and film thickness (∼ 1.00 μm). The n values are in the range from 2.42 to 2.92 depending upon the composition and wavelength (λ). The values of k are in the range from 0.02 to 0.15. The bandgap ( E g) variation with x is also obtained from absorption spectra analysis and a quadratic relation with x is obtained as E g = 2.63 − 1.39 x + 0.43 x 2.

Energy loss of H+ and He+ in Al, Zn, and Au in the very low- to intermediate-energy range.

The energy loss of ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{+}$ ions in polycrystalline Al, Zn, and Au films has been determined by the transmission method in the energy range between 1 and 200 keV. The velocity dependence of the different projectile-target pairs has been analyzed, as well as the ratio of the energy losses of helium ions and protons in the different materials. An increase of this ratio toward very low velocities has been observed and possible explanations are explored. The results are compared with the existing theoretical models and semiempirical approximations, and observed differences are discussed. \textcopyright{} 1996 The American Physical Society.

Derivative spectra of polycrystalline Zn 1− xCd xSe thin films

Derivative spectra have been recorded at room temperature to determine the energies at the lowest gap ( E 0) and spin-orbit splitting parameter ( Δ 0) for the electron beam deposited polycrystalline Zn 1− x Cd x Se (0 < x < 1) thin films on glass substrates as a function of composition ( x). The spectra clearly indicated the well resolved transitions due to E 0 and E 0 + Δ 0 gaps. A quadratic relation of E 0 and E 0 + Δ 0 with x is observed, giving respectively the bowing parameters as 0.46 and 0.52 eV. The variation of Δ 0 with x at Γ point is very small and found to be in the range from 0.38 to 0.43 eV.

Surface reaction of SO2 with machined (polycrystalline) Zn, Cd, Cu and Ag surfaces studied by He I/II photoelectron spectroscopy

Abstract SO 2 and NO 2 are two of the more reactive common atmospheric pollutants and their reactions with metal surfaces are very important in the study of corrosion. In a recent paper, we used ultraviolet photoelectron (UP) studies to discuss the possible interactions between NO 2 and clean polycrystalline surfaces of the group 1B and 2B metals, Zn, Cd, Cu and Ag, generated with a vacuum lathe. In this paper, we extend the treatment to the interaction of SO 2 with these metals. For Zn, the observed valence shell spectra and the chemical shift for the core-like metal 3d shell suggest the formation of a chemically bonded SO 3 or SO 4 species on the surface. For Cd, which is considerably less reactive than Zn, and SO n species is formed on the surface, but the absence of a chemically shifted Cd 4d shell suggests only weak bonding to the metal surface. For Cu and Ag, the observed valence shell structure strongly suggests that either a sulphide or a mixture of sulphide and oxide is formed.

Magnetic state of Fe at and near the interface between Fe–Al–Si magnetic thin films and Zn–ferrite

The magnetic state of Fe atoms at and near the interface between Fe74.3Al9.8Si15.9 sendust magnetic thin films and polycrystalline Zn–ferrite substrates has been examined using conversion electron Mössbauer spectroscopy. The thicknesses of sputtered films are 0.05, 0.08, 0.47, and 1.91 μm, and the annealing conditions are at 500 °C for 1 h. The sendust films/Zn–ferrite interface is very reactive, and the DO3-type ordered structure is not formed near the interface. This is the reason that excellent soft magnetic properties are not obtained for the films with a thickness of less than 0.47 μm. The presence of ferromagnetic Fe atoms with an internal magnetic field of 324 or 330 kOe is confirmed near the interface, indicating the formation of an Fe-rich phase such as Fe94Si6 and diffusions of Al and Si atoms from the sendust films to the interface. The thickness of the Fe-rich phase in the films has been estimated to be approximately 0.42 μm from the value (12.8 kG) of saturation magnetic-flux density for the film with 1.91 μm. It is found that a large part of Fe3+ ions in Zn–ferrite being at the interface is reduced to Fe2+ ions. The redox reaction at the interface has been proposed.

Photoconductivity in polycrystalline semiconductors: Grain boundary effects

Photoconductivity of polycrystalline Zn x Cd 1− x Se films (0< x<1.0)with direct band gap ( E g) is reported here. The experimental data were analyzed for h ̷ ω < E g in order to obtain the grain boundary parameters (e.g., barrier height Eb, density of trap states Q t and the capture cross-section σ 1 of the majority carriers). The variations of Eb with intensity Φ and energy ħω of the incident photon indicated an excellent agreement with the theoretical plot obtained on the basis of the existing models considering monovalent trapping states.

Energy loss of protons in Zn: Measurements between 2 and 200 keV.

The energy loss of ${\mathrm{H}}^{+}$ ions in polycrystalline Zn films has been determined by the transmission method in the energy range between 2 and 200 keV. Experiments in this energy range are of special interest for the study of the energy-loss mechanism in the region of the stopping-power maximum where important phase effects have been recently determined by other authors, as well as in the low-energy range where we have previously found deviations from the predicted velocity proportionality for other metallic elements. The data obtained here allow an experimental evaluation of the phase effect and provide a test of the velocity dependence for low energies at a very good level of accuracy. In addition, the experiment contributes to filling an important gap in the data due to the lack of low-energy measurements for Zn targets.

A comparative study on the passivation and localized corrosion of α- and β-brass in borate buffer solutions containing sodium chloride—II. X-ray photoelectron and Auger electron spectroscopy data

The composition of corrosion layers formed on α-, β- and (α + β)-brass anodized in the passive region in borate-boric acid buffer and 0.5 M NaCl + borate-boric acid buffer (pH 9) was studied comparatively by X-ray photo-electron and Auger electron spectroscopy. Passivation of brass in both solutions involves the formation of a complex passive layer consisting of ZnO and Cu 2O. In both solutions, the ZnO electroformation results in a dezincification so that a thin Cu rich layer is formed at the alloy/metal oxide interface. Passive layer composition and dezincification of the alloy surface explain the localized corrosion resistance of brass as compared to polycrystalline Cu and Zn.

A comparative study on the passivation and localized corrosion of α, β, and α + β brass in borate buffer solutions containing sodium chloride—I. Electrochemical data

The passivation and localized corrosion of α-, β-, and (α + β)-brass in borate-boric acid buffer solutions (pH 9) containing different NaCl concentrations ( c NaCl ) were studied comparatively using conventional electrochemical techniques at 25 °C. The passivation of brass in borate-boric acid buffer was due to the electroformation of a complex passive layer consisting of ZnO · xH 2O and Cu 2OCuO. In NaCl-containing borate-boric acid buffer the breakdown of the passive layer occurs leading to pitting corrosion when the applied potential exceeds a certain critical value, E b . For a given type of brass, the value of E b is shifted negatively as c NaCl is increased. At a constant c NaCl the localized corrosion resistance of brass increases in the following order (α + β)-brass ≅ β-brass < α-brass. For all brass the localized corrosion resistance was lower than that of polycrystalline Cu, but considerably greater than that of polycrystalline Zn. Passive film composition and de-alloying can account for the localized corrosion resistance of these alloys.

Electrical properties of electron-beam-evaporated Zn 3P 2Cd 3P 2 alloy films

Electrical conductivity, Hall mobility and spectral photoconductivity response measurements conducted on polycrystalline (Zn x Cd 1− x ) 3P 2 thin films, for various compositions ( x = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0), are reported in this paper. Zn 3P 2-rich films are found to be p-type, while Cd 3P 2-rich films are n-type. Compensation effects are observed for the films with composition x = 0.5 and 0.6, which exhibited comparatively very low conductivity. The photoconduction spectrum indicated broad maxima at the wavelengths corresponding to the optical band gap. The results are discussed taking into account the role of the native defects of these systems, namely, the P interstitials, P vacancies and their associated complexes.