High Purity Zn Research Articles

Reactive pulsed laser deposition of piezoelectric and ferroelectric thin films

Piezoelectric (ZnO) and ferroelectric (PZT) thin films were deposited on different substrates (Au coated Si, Al 2O 3 Corning glass etc.) by reactive pulsed laser deposition, by using a pulsed Nd-YAG laser. ZnO films were deposited starting from high purity Zn plates while the PZT films were obtained from sintered targets, in different deposition conditions. The influence of the process parameters on the physical and chemical properties of the deposited films was analyzed by SIMS, XPS, XRD, SEM and TEM. XRD analysis showed that the ZnO films were c-axis oriented, while SEM on cross-sections showed evidence of a columnar structure. On PZT thin films XRD showed evidence of a crystalline pseudo-perovskite structure with (111) orientation, while surface and cross-section SEM studies showed evidence of a compact round grain structure. Electrical measurements on both ZnO and PZT films found good piezoelectric coefficients. The ferroelectric properties of the PZT films have been characterized by a Sawyer-Tower circuit. Samples of ZnO and PZT were selected and employed in the construction of acceleration sensor and bulk acoustic wave (BAW) devices. Results on frequency response and sensitivity of constructed devices as well as electroacustical characteristics are presented and discussed.

Microwave synthesis, single crystal growth and characterization of ZnTe

ZnTe has been synthesized for the first time by microwave heating from high purity Zn and Te and the minimum reaction time determined to be 30 min. Single crystals were grown by modified vertical Bridgman technique from 4% rich Te melt, the growth direction being found to be 〈1 1 1〉. XRD showed formation of the zincblende phase with lattice constant 6.106 Å. Inductively coupled plasma (ICP) analysis showed Si, In, Cu, Au and Fe to be the main impurities present at ppm level. Crystals were p-type with resistivity 8.5 Ω cm, hole concentration 1.6×10 16 cm −3 and mobility 46 cm 2/V s at 300 K. Mobility was found to vary with temperature as μ p∝ T −2.7 in the range 120–300 K. Photoluminescence (PL) at 10 K showed emission peaks at 2.06, 1.47, 1.33 and 1.05 eV. Thermal quenching of the PL bands has been studied. The samples showed weak photoconductivity due to small minority carrier lifetime. From the temperature dependence of the photoconductive gain, the minority carrier lifetime ( τ n) has been determined in the temperature range of 80–300 K. τ n was thus found to go through a maximum of 4.5×10 −7 s at 220 K and its variation with temperature is also discussed.

Low-temperature rapid thermal low pressure metalorganic chemical vapor deposition of Zn-doped InP layers using tertiarybutylphosphine

High purity Zn doped InP layers were grown by rapid thermal low pressure metalorganic chemical vapor deposition technique, using tertiarybutylphosphine as the phosphorus source. The best quality layer, which was grown at P:In ratio of 75, temperature as low as 525 °C, pressure of 2 Torr and growth rate of 2 nm/s, exhibited electron mobility of 80 cm2 V−1 s−1 and Hall carrier concentration of 3.5×1018 cm−3 at room temperature. The stoichiometry of the InP Zn-doped layer was excellent, regardless of the Zn content in the reactive gas mixture. The crystallographic defect density and the surface morphological particle concentration, however, were found to be strongly dependent on the Zn concentration.

Strain-free, ultra-high purity ZnSe layers grown by molecular beam epitaxy

ZnSe layers have been grown by molecular beam epitaxy on high-purity, high-quality ZnSe wafers [(100) oriented] cut from ingots grown by the iodine vapor transport method. Photoluminescence (PL) analysis indicates the homoepitaxial ZnSe material to be of ultra-high purity as well as being strain-free relative to ZnSe/(100) GaAs layers which exhibit in-plane biaxial tension. The 10 K PL spectra recorded from homoepitaxial layers exhibit unsplit free- and donor-bound exciton transitions of comparable intensity together with a strong peak at 2.7768 eV believed to be the so-called Iv transition in relaxed ZnSc. The ultra-high purity nature of the homoepitaxial layers is attributed to the high purity of the substrate material in addition to the use of high purity Zn and Se source materials in this work.

VPE Growth of ZnSe Thin Films on GaAs ( 100 ) and ZnSe ( 110 ) Substrates

Epitaxial growth of thin films on and substrates has been studied using high purity Zn and Se as source materials. The experiments have been performed at 723 and 873 K. The grown films have been evaluated by photoluminescence (PL) measurements, SIMS analysis, ellipsometry, and optical microscopy. The best epitaxial films are grown for the condition of the transport ratio of Zn and Se close to unity. SIMS analysis on the heteroepitaxial films indicates that the dominant acceptor‐type impurities are Li and Na. It is found that the epitaxial films grown on the high purity substrate show improved PL properties compared with those measured on the films grown on substrate under the same growth conditions. It should be noted that the purity of the film grown on substrates is strongly affected by the purity of the substrate.

Superplastic deformation behavior in commercial and high purity Zn- 22 Pct Al

The superplastic deformation behavior of two grades of the Zn-22 pct Al alloy was studied in detail under identical conditions of grain size, temperature, and stress. While these two grades were prepared by the same procedure, they have different impurity levels; grade 1 is of commercial purity (180 ppm of impurities) and grade 2 is of very high purity (6 ppm of impurities). The experimental results on the commercial grade show that the relationship between the applied stress and steady-state strain rate is sigmoidal and is manifested by the presence of three deformation regions; in region I (low-stress region) the stress exponent,n, is 3.8 and the activation energy for creep,Q, is higher than that for grain boundary diffusion,Q gb; in region II (intermediate-stress region)n = 2.5 andQ ≃ Q gb; and in region III (high-stress region)n again increases. The results on the high purity grade, when compared with those on the commercial grade, reveal a significant difference: the high purity grade, unlike the commercial grade, does not exhibit region I at low stresses. The difference in creep behavior between the two grades of Zn-22 pct Al at low stresses leads to the implication that the origin of region I during superplastic flow is related to the presence of impurity atoms. It is suggested, on the basis of consideration of various impurity-controlled deformation processes, that the creep behavior in region I is most likely a consequence of the existence of a threshold stress which is caused by impurity atom segregation at boundaries.

Fermi-surface structure effects revealed by the observation of conduction-electron-spin resonance in Zn

The first observation of conduction-electron-spin resonance (CESR) in polycrystalline highpurity Zn in the temperature range between 4.8 and 35 K is reported. The observed $g$ value equals 2.0033 \ifmmode\pm\else\textpm\fi{} 0.0005, and the linewidth above 11 K increases with temperature, as expected from the normal electron-phonon interaction. The signal is explained as being due to the "lens" part of the Zn Fermi surface, advancing herewith a new type of interpretation of CESR data. The usual CESR signal coming from the main part of the Fermi surface is believed to be broadened beyond the detection limit due to magnetic breakdown effects interplaying with the complex Fermi surface. Similar features in Mg are discussed.

Preferred Orientation in Splat-Quenched Materials

ABSTRACTHigh purity, splat-quenched metal ribbons, produced by the melt spinning technique, were examined for preferred orientation using x-ray diffraction. Of the materials tested (Zn, Cd, Ag, Bi, Pb, Sb, Mg, Sn) all except Sn exhibited some degree of preferred orientation in the plane of the metal ribbon. the hcp metals Zn and Cd showed an extreme degree of preferred orientation with the 002 plane being closely parallel to the ribbon plane. The Zn ribbon was analysed more closely with a view to its use as a crystal monochromator for x-ray diffraction. The high purity Zn was found to have some instability of preferred orientation with increase in time and temperature. The orientation was found to be effectively stabilized by the intentional addition of impurities, or by the use of lower purity (99.99%) Zn. In this form, the Zn ribbon could be used as a crystal analyser for x-ray diffraction with both intensity and resolution comparable to that of the 1011 plane in Quartz.

Preparation, analysis and properties of high purity Zn(l−x)MgxTe alloys

Several metallurgical and analytical methods were combined to produce pure and homogeneous Zn(l-x)MgxTe alloys. High purity magnesium was prepared by a new distillation method. By studying the growth conditions, alloy crystals of good quality were produced. Neutron and photon activation analysis was used to improve the preparation methods and to control the produced materials purity. The purity improvement had a consequence on the luminescence spectra. For x < 0.3 the luminescence efficiencies are comparable to those of undoped ZnTe. The carrier concentration, the mobi lities and resistivities are also comparable to undoped ZnTe for x < 0.1.

Evidence for cavitation in superplastic Zn-22 pct Ai of very high purity

The cavity formation of very high purity Zn--22% Al was studied. Results confirm that cavities are nucleated in the Zn--22% Al eutectoid during superplastic deformation, and the extent of cavitation is essentially identical to an alloy of commercial purity (190 ppm impurities). (FS)

Effect of solute atoms on the motion of a low angle tilt boundary

Modes of boundary motion in crystals containing controlled amounts of Ag as an alloying element in high-purity Zn crystals were examined. A discontinuous motion found in the alloy crystals at room temperature could be attributed to the diffusivity of solute atoms since such behavior is not observed in the alloy crystals at liquid nitrogen temperature and in the pure crystals at room temperature. A situation similar to the dynamic strain aging seems to have been created around the moving boundary. A further study is necessary to determine the diffusion mechanism. The absence of such discontinuous motion in the pure crystal seems to be due to the lack of sufficient impurity atoms. It appears that the jerky motion observed in pure crystals at room temperature is due to a higher impurity content of approx.100 ppM compared with that of <10 ppM impurity content in specimens exhibiting smooth and continuous motion. (JRD)

On the role of grain-boundary migration during the creep of zinc

Constant engineering strain-rate tensile tests have been carried out in the temperature range 20 to 150‡C on high purity Zn, Zn-0.14 at. % Cu (alloy C) and Zn-0.16 at. % Al (alloy A) alloys. Measurements of angular distribution of orientations of grain boundaries have been used to study grain-boundary migration during deformation. Significant cavitation, with increasing propensity at higher test temperatures, occurred in the two alloys but not in pure Zn. A striking feature of the observations in pure Zn and alloy C, as the test temperature was raised, was the formation and subsequent decay of a diamond pattern of uncavitated grain boundaries, a majority of which were preferentially aligned at ∼ 45‡ to the stress axis. By comparison the changes in the angular distribution of grain boundaries was least marked in alloy A. Cavitation was observed in alloy C to maintain grain boundaries in the 45‡ orientation. At the test temperature of 150‡C alloy C, which was prone to the formation of diamond grain-boundary configuration, developed much larger volume fraction of cavities than alloy A. These results are discussed in terms of the different distribution coefficients of Cu and Al in Zn, the different rates of grain-boundary migration in pure Zn and the two alloys and the differences in the substructural features (cells) formed during high-temperature deformation.

Interpretation of Radiation at 1.485 eV in High-Purity Zn- and Se-Doped GaAs

Interpretation of Radiation at 1.485 eV in High-Purity Zn- and Se-Doped GaAs

Electromigration in Zinc Single Crystals

The electromigration of high-purity Zn single crystals resistively heated in an argon atmosphere has been measured by the marker-motion technique in the temperature range of 360 to 395\ifmmode^\circ\else\textdegree\fi{}C with current densities of \ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}${10}^{3}$ A/${\mathrm{cm}}^{2}$. The cylindrical specimens were selected with $c$ axes oriented within 25\ifmmode^\circ\else\textdegree\fi{} perpendicular or parallel to the direction of current flow. Accurate measurements of both longitudinal and transverse strain rates were used to calculate the anode-directed atom-drift velocity ${v}_{a}$, and hence the effective charge on the moving ion, ${Z}^{*}$. The effective charge is found to be anisotropic: $\frac{{{Z}_{\mathrm{II}}}^{*}}{f}=\ensuremath{-}2.55\ifmmode\pm\else\textpm\fi{}0.15$ and $\frac{{{Z}_{\ensuremath{\perp}}}^{*}}{f}=\ensuremath{-}5.6\ifmmode\pm\else\textpm\fi{}0.4$, where $f$ is the correlation factor, which has been shown to be approximately 0.78. The anisotropy of the ion velocities is in the opposite sense and is greater than the anisotropy of the diffusivities. This results from the large anisotropy of the effective charge due to the band structure. It appears that this is the first demonstration of the crystalline anisotropy of the electromigration driving force.

高純度亜鉛中の不純分の定量分光分析法

Since analysis of high purity Zn metal and ZnCl2 70% solution is in strong demand recently, spectrochemical analysis by solution DC-arc method was studied, as follows: (1) Zn concentration in the sample solution is heightened by HCl containing a small quantity of H3PO4 (H3PO4 prevents the evaporation of impurity Sn in the form of SnCl4). (2) The various factors and the condition levels which affect the sensitivity of this method are determined by (5×5) Graeco-Latin square experimental designation. (3) The sensitivity is expanded about to twice by duplicate exposure, and (4) the optimum analytical line pairs are selected by the variation coefficients calculated from 70 repeated analysis. This spectrochemical method can be applied to industrial routine analysis, in which the impurities Cd, Cu, Fe, Mn, Pb and Sn are present in the order of 10−4%, with the precesion of 7% in term of variation coefficient at above S (Opt.d.)=0.4 of impurity line.