Zinc Single Crystals Research Articles

Bonding of Bulk Piezoelectric Material to Silicon Using a Gold-Tin Eutectic Bond

AbstractA class of MEMS devices, which utilizes microfabrication technology and bulk piezoelectric material, is currently being developed to produce high power density transducers. A thin-film gold-tin eutectic solder bond has been developed to bond electrically and mechanically bulk piezoelectric elements to microfabricated silicon structures in these devices. A 4.3 [.proportional]m thick multilayer film structure, consisting of a titanium adhesion layer, a platinum diffusion barrier, a gold-tin (80 wt.% Au - 20 wt.% Sn) alloy layer, and a pure gold capping layer, was sputter deposited on the piezoelectric components to be bonded. Bonding was accomplished by mating the piezoelectric components with silicon components metallized with a titanium-platinum-gold multilayer film and heating to approximately 300°C in a reducing atmosphere. The bonding technology allows thin, electrically conductive bonds to be formed between dissimilar materials with minimal amounts of applied pressure during bonding. Successful bonding has been achieved between single crystal silicon and polycrystalline lead-zirconate-titanate (PZT-5H) as well as between silicon and single crystal lead zinc niobate-lead titanate (PZN-PT). The process was optimized to produce mechanically robust, void-free bonds. The absence of voids was verified through scanning electron microscope examinations of bond cross-sections. Tensile tests conducted on representative structures indicated that the strength of the bond was limited by the strength of the titanium – PZT-5H interface.

EPR Studies of Cu2+ Doped Zinc Saccharin, [Zn(sac)2·(H20)4 ]·2H20 Single Crystals

Abstract The EPR spectra of Cu2+ in zinc saccharin crystalline powder and single crystals have been recorded at room temperature. The angular variation of the spectra indicates the substitution of the host Zn2+ with Cu2+. Two magnetically inequivalent sites for Cu2+ have been observed. The spectra were fitted with a rhombic spin-Hamiltonian, and the ground state wave function of the complex has been constructed.

Zinc self-diffusion, electrical properties, and defect structure of undoped, single crystal zinc oxide

Zinc self-diffusion was measured in single crystal zinc oxide using nonradioactive Zn70 as the tracer isotope and secondary ion mass spectrometry for data collection. Crystal mass was closely monitored to measure ZnO evaporation. Diffusion coefficients were isotropic with an activation energy of 372 kJ/mol. Zinc self-diffusion is most likely controlled by a vacancy mechanism. Electrical property measurements exhibit a plateau in conductivity at intermediate pO2 with an increase in reducing atmospheres. An analysis of the defect structure is presented that indicates that oxygen vacancies are probably the intrinsic ionic defects responsible for n-type conductivity in reducing atmospheres.

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

A point-source representation for laser-generated ultrasound in an elastic, transversely isotropic half-space is developed. This representation is comprised of a set of boundary conditions that approximates a thermoelastic point source located on the bounding surface of the half-space. An analytical expression representing the displacements for wave propagation along the symmetry axis is given for zinc where the bounding surface is the plane of transverse isotropy. The displacements obtained from theory are compared to experimental wave forms generated in a sample of single crystal zinc.

Distinctive features of the change in structural state and internal stresses present in shear bands of single-crystal zinc

Transmission electron microscopy is used to study the dislocation structure of strained zinc crystals. It is shown that shear bands in this material consist of dipoles and individual dislocation loops. A connection is established between internal stresses and the corresponding dislocation structure of the shear band.

Nanotribology of single crystal ZnO surfaces: Restructuring at high temperature annealing

Atomic force microscopy is used to study low friction structures formed on single crystal zinc oxide because of annealing. Zinc oxide thin films deposited in this laboratory showed low friction (∼0.2) and long wear life (over one million cycles) in humid air at room temperature. Research into the mechanisms for this low friction behavior, far exceeding the life of typical solid lubricants (e.g., MoS2 and graphite) led to the present work, which focuses on the nanotribology of single crystal ZnO surfaces. Thermal annealing was used to cause surface reconstruction and defect formation. Etch pits were formed on the (101̄0) surface and roughening or reconstruction occurred on the (0001) surface. These pits and roughened areas showed low friction that could be originating from interactions of defects and restructured crystal faces due to adsorbates. Adhesion and relative contact stiffness were not significantly different between friction contrasting regions. The results of lateral force microscope analysis of the different single crystal surfaces are presented here.

Excitonic structure and absorption coefficient measurements of ZnO single crystal epitaxial films deposited by pulsed laser deposition

The optical properties of high quality single crystal epitaxial zinc oxide thin films grown by pulsed laser deposition on c-plane sapphire substrates were studied. It was found that annealing the films in oxygen dramatically improved the optical and electrical properties. The absorption coefficient, band gap, and exciton binding energies were determined by transmission measurements and photoluminescence. In both the annealed and the as-deposited films excitonic absorption features were observed at both room temperature and 77 K. In the annealed films the excitonic absorption peaks were substantially sharper and deep level photoluminescence was suppressed.

Electric-field-induced phase transition in single-crystal lead zinc niobate

The behavior of lead zinc niobate, a relaxor ferroelectric, in electric fields has been studied by dielectric, optical transmittance, and small-angle light scattering techniques. A field-induced transition from an averaged cubic to macrodomain ferroelectric phase has been found. A comparison is made with the properties of the phase induced in lead magnoniobate, a classical relaxor.

A New Approach to Growth of Bulk Zno Crystals for Wide Bandgap Applications

ABSTRACTA novel technique was used to melt zinc oxide powder. This techniques involves the pressurized RF induction heating of ZnO, contained in a water-cooled crucible. The ability to obtain a pool of molten ZnO enables the pulling of large diameter ZnO crystals using conventional melt growth processes. Centimeter-sized crystals were obtained in the preliminary experiments by cooling the ZnO melt. These crystals were analyzed for crystalline perfection and stoichiometry using x-ray diffiraction and photoluminescence. The semiconductor properties of these crystals were also measured. This technology can potentially provide large, low cost ZnO single crystal wafers for use in the fabrication of GaN blue diodes and blue lasers, high temperature / high power FETs, as well as homoepitaxy of ZnO wide band-gap devices. Single crystal zinc oxide also has potential application in the piezoelectric device market.

Growth of High Quality Single Crystal ZnO Films on Sapphire by Pulsed Laser Ablation

AbstractThe structural and optical characterizations of single crystal zinc oxide films on sapphire have been performed. The ZnO films were deposited by pulsed laser deposition in an oxygen environment. These films were annealed in oxygen for further improvement in the oxygen stoichiometry. Both as-deposited and oxygen annealed films were high quality single crystal as characterized by X-ray diffraction and transmission electron microscopy. The defect density, comprised mainly of dislocations and stacking faults, was low as compared to high quality films of III-nitrides deposited on sapphire. Under these growth conditions, the ZnO films grow two dimensionally on sapphire as opposed to GaN which grows three dimensionally. The band edge photoluminescence was found to be dominant, and an order of magnitude higher in the annealed films. Transmission measurements and the electrical resistivity of the annealed films also show the films were of high quality after annealing. It is envisaged that these improvements in the quality of the ZnO films occur as a result of reduction of oxygen vacancies and the density of point defects.

Surface structure analysis with LEIS: subsurface oxygen on oxidized Zn(0001)

The (0001) plane of a cleaved zinc single crystal was oxidized in a controlled way under a low pressure oxygen ambient at 100 °C. Low Energy Ion Scattering (LEIS) (500 eV He +) was used to investigate the short range atomic structure of this surface by studying the anisotropy in the scattered Zn and O intensities caused by shadowing phenomena. These shadowing effects were also characterised on both (0001) and (0001̄) polar surfaces of single-crystalline zinc oxide, which features the non-centrosymmetric Wurtzite structure. Direct comparison of the results for the oxidized zinc metal surface with those of the polar surfaces of zinc oxide as references, unambiguously proves that, in the early stages of the oxidation, the structure of Zn(0001) + O corresponds to that of ZnO(0001), the Zn termination of ZnO. It thus appears that, somewhat unexpectedly, the O-atoms are situated in a subsurface position.

Athermal dislocational anomalies in microcontact spectra of zinc single crystals

Regularities in the behavior of athermal dislocational anomalies of microcontact spectra of zinc single crystals are established. It is shown that they arise due to emission of terahertz waves by dislocations. In this case hexagons of basis dislocations surrounding the microcontact generate in most cases monochromatic high-frequency waves, which promote the appearance of a nondecaying current. A model is proposed according to which properties of dislocations are determined by regularities in interactions of atoms that keep moving at an arbitrarily low temperature.

Diffusion Control during Vapour Crystal Growth

AbstractThe crystal growth rate under diffusion control is considered. Together with nutrient diffusion, the physi‐sorption of an inert gas, which impedes the surface kinetics during vapour growth, is taken into consideration. In this way the size of the diffusion field surrounding vapour grown crystals was estimated. The relations obtained are checked with data for the growth of zinc single crystals in argon atmosphere. The appearance of shallow cavities on their basal faces is used as a morphological mark for growth under diffusion control. Besides, the microstructure of the inner edge of the macroscopically flat periphery, surrounding the shallow cavities is investigated experimentally, by means of SEM.

Raman spectra of oxide zinc powders and single crystals

Raman spectra of oxide zinc powders and single crystals

Luminescence quenching effect of single-crystal copper-doped zinc sulfide containing microcavities

Luminescence quenching effect of single-crystal copper-doped zinc sulfide containing microcavities

Growth and characterization of pseudomorphic single crystal zinc blende MnS

We report the growth and characterization of crystalline, single-phase zinc blende MnS (i.e., β-MnS). The material was grown on ZnSe buffer layers on (100) GaAs substrates, using solid-source molecular beam epitaxy and a novel valved S cracker with deposition at low (∼110 °C) substrate temperatures. Characterization by reflection high energy electron diffraction, high resolution transmission electron microscopy, and low temperature photoluminescence confirms the pseudomorphic nature of the growth. Beyond a certain critical thickness, the layers either become amorphous or convert into the equilibrium rock salt polymorph (α-MnS), depending on the growth temperature.

Spectrum of the electron-phonon interactions of zinc single crystals induced by a basal-dislocation network

A dislocation spectrum of the electron-phonon interactions (EPI) of zinc single crystals is obtained for the first time. It is shown that dislocations are a source of hypersonic waves. Possible mechanisms of energy dissipation in vibrations of the network of basal dislocations in the point-contact zone are considered. It is noted that a change in the effective transport function of EPI results from the inertial properties of dislocations.

Anisotropic gamma -ray resonance scattering from a zinc single crystal and the uncertainty principle.

The nuclear-resonance photon-scattering technique was used for studying the temperature dependence between 12 and 295 K of the anisotropy in the scattering cross section from the 7362-keV level in $^{68}\mathrm{Zn}$ using a single crystal of metallic zinc. The anisotropy ratio of the scattering intensities with the beam parallel and perpendicular to the hexagonal planes of Zn was found to increase strongly between 295 and 12 K. This was interpreted in terms of the anisotropic binding of the Zn atoms and was used for deducing the mean-square momenta 〈${\mathit{p}}^{2}$${\mathrm{〉}}_{\mathrm{\ensuremath{\perp}}}$ and 〈${\mathit{p}}^{2}$${\mathrm{〉}}_{\mathrm{\ensuremath{\parallel}}}$ of the Zn atoms at 0 K perpendicular and parallel to the hexagonal planes, and the corresponding Debye temperatures ${\mathit{FTHETA}}_{\mathrm{\ensuremath{\parallel}}}$ and ${\mathit{FTHETA}}_{\mathrm{\ensuremath{\perp}}}$. When these values were combined with the known values of the zero-point vibrational amplitudes 〈${\mathit{x}}^{2}$${\mathrm{〉}}_{\mathrm{\ensuremath{\perp}}}$ and 〈${\mathit{x}}^{2}$${\mathrm{〉}}_{\mathrm{\ensuremath{\parallel}}}$ obtained using the M\ossbauer effect, the theoretical lower limit of the uncertainty principle for a metallic solid was found to be reached almost accurately.

Amplitude-dependent internal friction and dislocation inelastic strain in zinc and aluminium single crystals

An experimental study of the amplitude-dependent internal friction, Young modulus defect and reversible inelastic strain in Al and Zn single crystals has been performed. The investigations were carried out in the low frequency (0.005-1 Hz) range. The amplitude—frequency spectra of the internal friction and Young modulus defect were analysed taking into account the quasi-static athermal component due to dislocation—dislocation interaction or internal stress field hysteresis and the thermally activated component due to dislocation interaction with point defects. The marked amplitude hysteresis and time dependence of the internal friction in Zn single crystals were attributed to point defect redistribution in the glide planes of mobile dislocations. The analysis of stress—inelastic strain hysteretic loops for Zn single crystals confirms the Kressel—Brown model of quasi-static internal stress field hysteresis.

Focusing of acoustic energy at the conical point in zinc.

This paper reports observations of the intense focusing of acoustic energy that occurs along the symmetry axis in a zinc single crystal. The focusing is associated with a conical point in the wave surface and thereby the phenomenon of external conical refraction. Our observations have been obtained with (i) pointlike piezoelectric transducers (PZT) as source and detector, (ii) a focused pulsed laser source and small PZT detector, and (iii) a breaking capillary source and capacitive detector at epicenter.