Zinc Single Crystals Research Articles

Various colour electroluminescence of rare-earth-implanted ZnS diodes

Single-crystal zinc sulphide has been implanted with one or two rare-earth elements and used to fabricate light-emitting diodes. The dependence of electroluminescence brightness on current, temperature and implantation fluence has been studied, and cathodoluminescence and electroluminescence emission spectra have been measured. Different relative proportions of two implanted rare-earth elements in a double implantation have been used to obtain different colours of electroluminescence emission.

The electric field gradient at iodine impurities in zinc and cadmium

The electric quadrupole interaction at iodine implanted in zinc and cadmium single crystals is investigated, using the β-γ perturbed angular correlation technique. The results show that the implanted129Te and132Te isotopes occupy two well-defined sites, identified by the electric field gradient parameters. One fraction of the impurities is substitutionally implanted, witheqzz=−1.49(9)1018 and −1.58(15)1018V/cm2, in Zn and Cd respectively. The other fraction is identified as an impurity-divacancy configuration with |eqzz|=3.81(8)1018V/cm2; η=0.72(4) for Zn and |eqzz|=3.55(11)1018V/cm2; η=0.53(13) for Cd. The electronic enhancement in the electric fieldgradient at the substitutional site equalsK=−0.66 and −0.56 respectively and follows the empirical trend ofK versus the impurity valence for the s-p elements in Zinc.

The contribution of pyramidal forest dislocations to the hardening of zinc single crystals

Abstract The influence of a pyramidal dislocation forest on basal-glide critical stress of zinc single crystals has been studied at 77, 198 and 298 K. The experiments gave the usual relationship τ0 = aKebρf 1/2 , where Ke is an elastic constant function, b the basal Burgers vector, ρf the forest density and a is a coefficient. The coefficient values are, at the three temperatures respectively, 1.46, 1.35 and 1.23 when the dislocation reaction is a3 + (c-a3 ) and 1.13 at 298 K in the case al + (c + a3 ). A model has been developed which consists of the following. (i) Calculation of the stress needed to break a junction created by a tree and a basal dislocation, in the different geometric cases. The reduced breaking stress γM is introduced. (ii) Calculation of the mean breaking stress y M. It is shown that a cubic average of the γm values gives the best result. (iii) Deduction of the relationship between the macroscopic critical stress of the crystal τ0, the local stress y M and the forest density ρf. The calculated and measured a values are in good agreement.

Preparation of low dislocation density and dislocation-free zinc and copper single crystals

We discuss the effect of growth conditions of Zn and Cu single crystals on their dislocation structure. The perfection of single crystals of pure metals grown from the melt is greatly determined by thermal stresses. A reduction of thermal stresses below a certain critical level produces dislocation-free crystals of copper. In addition, the nonequilibrium vacancy concentration is shown to influence the development of dislocation structures in Zn single crystals. A lower perfection of Zn single crystals than that of Cu crystals grown under similar conditions can be attributed to higher thermal stresses caused by the lattice anisotropy and to a higher efficiency of vacancies for the development of the dislocation structure.

The effect of deformation and forest dislocations density on the activation volume in zinc single crystals

The obstacle density calculated from the experimental values of the activation volume is compared with the density of forest dislocations. The density of obstacles is about two or three order higher than that of the forest dislocations. It is assumed that nonconservative jog motion is the rate-controlling mechanisms in stage A, while in stage B the activation volume is more directly determined by interaction with the forest dislocations.

Experimental estimation of the interaction parameter eO for ZnN

The use of dislocation measurements in Zinc single crystals reveals the presence of a yield point or flow stress corresponding to a Stages I–II (elastic to elastic-plastic) transition. This is commonly attributed to the presence of interstitials such as N. The mathematical models of Seeger and Dorn and Rajnak are used to evaluate certain microstructural parameters. These correlate favourably with experimental values. The excess work done over that to overcome the Peierls and frictional forces is then calculated per pair of pinning interstitials and equated to the energy of formation of a molecule of Zn 3N 2 which is believed to form. The results show that this assumption does lead to the stochiometry Zn 3N 2, thus verifying mathematical parameters from different equations using work-energy concepts. Use of the mechanical equivalent J also seems to indicate a favourable correlation for the stochiometry of Zn 3N 2, and for e O as calculated calorimetrically.

“Physical” adsorption on single crystal zinc oxide

Weak “physical” adsorption of CO 2, CO, O 2, Xe and H 2 was studied on ZnO(101̄0) in a molecular flow system (UHV conditions, 95 ⩽ T ⩽ 241 K, 1.3 × 10 −6 ⩽ 1.3 × 10 −4 Pa). Freundlich type of adsorption isotherms is found. Surprisingly broad, distributions of adsorption energies are determined in a thermodynamic analysis of equilibrium coverages as function of pressure and temperature. From an additional peak shape analysis of thermal desorption spectra, distributions of activation energies of thermal desorption are also estimated.

“Physical” adsorption on single crystal zinc oxide

“Physical” adsorption on single crystal zinc oxide

X-ray topographic examination of the generation, glide and locking of basal dislocations during the microplastic deformation of zinc and cadmium crystals

Abstract Nearly perfect zinc and cadmium single crystals were subjected to increasing tensile stresses and simultaneously characterized by transmission X-ray topography. Fresh dislocations were emitted in basal slip planes at resolved shear stresses as small as a few 104 Pa; in some crystals, an emission mechanism could be identified as the elongation and/or the expansion of original dipolar loops; in most eases however, the nucleation took place mainly from stress-enhanced parts of the specimens. Once emitted, the dislocations were observed to interact with sub-grain boundaries, prismatic loops of Burgers vector c or c + a, and with the crystal surface. A model is developed for the latter case, based on the dragging force felt by a dislocation at its point of emergence while it develops a slip step on the surface. In the rather thin crystals (80 pm) used for transmission X-ray topography, this surface effect, could be proved to be responsible for the locking of some fresh dislocations in their glide plane.

The fracture stress of single-crystal zinc

The basal plane fracture stress of 99.999 pct pure single-crystal zinc tensile specimens was determined from 77 to 298 K as a function of strain rate. The fracture stress was found to be dependent on the size of existing flaws associated with surface preparation, when the thermal variation of surface energy was taken into account. The stress at fracture was independent of strain and strain rate and was inversely proportional to the square root of the corrected flaw size, suggesting that a Griffith-type equation was obeyed to high strains. When flaws do not exist or are negligibly small, fracture is believed to be nucleated by the splitting of subboundaries as a result of plastic flow. The strain at fracture for constant fracture stress decreases with an increase in strain rate and a decrease in temperature and depends on the values of the work-hardening coefficient and exponent.

Recovery of zinc single crystals after fast-neutron irradiation at 5 K

Recovery of the c-axis spacing and the electrical resistivity in pure zinc crystals after neutron irradiation at about 5 K was measured in the range from 5 to 300 K. Reverse recovery of the c-axis spacing was found around 100–130 K. The recovery of the first stage below 20 K in electrical resistivity was suppressed, compared with that of electron and α-particle irradiation. Recovery mechanisms of defects are discussed.

Investigation of electron-irradiated zinc by diffuse x-ray scattering. I. Self-interstitials in zinc

Single crystals of zinc were irradiated at 6 K with 3-MeV electrons producing electrical resistivity changes varying from 32 to 215 n\ensuremath{\Omega}cm. Diffuse x-ray scattering from the irradiated samples was measured near ($00.h$), ($h0.0$), and ($\mathrm{hh}.0$) reflections. From the distribution of the diffuse scattering intensity we conclude that the configuration of the self-interstitial in Zn is a dumbbell aligned along the $c$ axis. A combination of lattice parameter, electrical resistivity, and Huang scattering measurements yields a volume change per interstitial of 3.6 atomic volumes (assuming a vacancy relaxation of -0.6 atomic volumes) and a specific resistivity per Frenkel pair ${\ensuremath{\rho}}_{F}=15.3$ \ensuremath{\mu}\ensuremath{\Omega}cm/at.%.

Theory of transport properties of pure, single crystal zinc

Pseudopotential calculations have been performed by Tomlinson and Swihart to obtain phonon frequencies and polarization vectors, the Fermi surface, band velocities, and multi-orthogonalized-plane-wave electron-phonon matrix elements for pure zinc. These results are then used to determine the electrical and thermal resistivities which result from the scattering of electrons by thermal phonons. The same interaction also contributes to the attenuation of ultrasonic waves and the finite lifetimes of quasiparticle states near the Fermi surface, and these effects are also calculated. The Fermi surface and electron wave functions are based on the extremely accurate fit to de Haas-van Alphen data obtained by Stark and Falicov. Tomlinson and Swihart also make use of their resulting nonlocal pseudopotential for the matrix elements. The phonon model used is based on a pseudopotential calculation, and agrees well with neutron-diffraction data for frequencies at all high-symmetry points and for the polarization vectors where they have been determined. We solve the Boltzmann equation by the variational method, where we assume that the trial distribution function can be well represented as an expansion in up to six spherical harmonics. Solution in terms of different types of trial functions and in terms of anisotropic scattering times are presented for comparison.

Equilibrium vacancy concentration measurements on zinc single crystals

The formation parameters of vacancies in hexagonal zinc single crystals have been investigated by combined lattice parameter change and length change measurements. A maximum vacancy concentration at melting temperature of (Cv)max=(4.9+or-0.3)*10-4 was found. The energy of formation and the entropy of formation for a single vacancy were determined to be E=(0.53+or-0.07)eV and s=(1.1+or-1) kB respectively. The creation of vacancies leads to a highly anisotropic volume change in zinc crystals. The ratio obtained from measurements in the a and c directions is ((Delta L/L)c-Delta c/c)/((Delta L/L)a-Delta a/a)=5.7. Six times as many etch pits were found on a surface as on c surfaces. The authors concluded that in their zinc crystals, dislocations were preferentially oriented in the basal plane.

Determination of the Burgers vector of perfect dislocations observed by X-ray topography in hexagonal single crystals

Individual dislocations were observed in high-quality cadmium and zinc single crystals by means of transmission X-ray topography. The contrast of their images was characterized on the topographs as a function of the direction of the line, the Burgers vector and the diffraction vector. In addition, the theoretical contrast of perfect dislocations with all the possible Burgers vectors of the hexagonal lattice was computed by using a program which takes into account the crystal anisotropy. The comparison of experimental and theoretical results showed unambiguously that the long dislocation lines contained in the crystals have an a-type Burgers vector, while the loops and spiral dislocations have either a c- or c + a-type Burgers vector.

Temperature and Strain Rate Effects upon the Strength of Zinc Single Crystals

Temperature and Strain Rate Effects upon the Strength of Zinc Single Crystals

Stress relaxation in hydrostatically compressed zinc single crystals

physica status solidi (a)Volume 50, Issue 1 p. K33-K36 Short Note Stress relaxation in hydrostatically compressed zinc single crystals G. Ya. Akimov, G. Ya. Akimov Physico-Technical Institute, Academy of Sciences of the Ukrainian SSR, DonetskSearch for more papers by this authorV. I. Zaitsev, V. I. Zaitsev Physico-Technical Institute, Academy of Sciences of the Ukrainian SSR, DonetskSearch for more papers by this authorV. A. Streltsov, V. A. Streltsov Physico-Technical Institute, Academy of Sciences of the Ukrainian SSR, DonetskSearch for more papers by this author G. Ya. Akimov, G. Ya. Akimov Physico-Technical Institute, Academy of Sciences of the Ukrainian SSR, DonetskSearch for more papers by this authorV. I. Zaitsev, V. I. Zaitsev Physico-Technical Institute, Academy of Sciences of the Ukrainian SSR, DonetskSearch for more papers by this authorV. A. Streltsov, V. A. Streltsov Physico-Technical Institute, Academy of Sciences of the Ukrainian SSR, DonetskSearch for more papers by this author First published: 16 November 1978 https://doi.org/10.1002/pssa.2210500151AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Volume50, Issue116 November 1978Pages K33-K36 RelatedInformation

On the creep mechanism of metals at low temperatures

The temperature dependence of the jump in the creep rate in cadmium and zinc single crystals at the instant of a small increment ΔT in the temperature is studied in the 1.5–80° K range. It is shown that below some characteristic temperature Θ the behavior of this dependence sharply contradicts the thermally activated creep predicted by theory as well as that following from the hypothesis of thermal heating of a crystal because of plastic deformation. A deduction is made that at temperatures below Θ the thermally activated creep mechanism is replaced by a quantum mechanism.

The trapping of positrons by dislocations produced in single crystal bending

The deformation by bending of high purity copper and zinc single crystals was studied by detection and measurement of the Doppler-broadened gamma ray spectrum due to the annihilation of positrons in the crystals. The measurements were performed with a Ge(Li) spectrometer. The crystals were oriented and bent so as to introduce primarily edge dislocations into the material. The range of dislocation densities studied was from about 1.6 × 109 m-2 to 1.3 × 1012 m-2.

The peculiar effect of forest dislocations on single twin layer development in zinc and beryllium single crystals

This is an investigation of the effect of different types of forest dislocation on the rate of twin layer broadening, V n, in zinc and beryllium crystals, and on the velocity of the twinning dislocation movement, V t, in zinc crystals under the action of a constant external shear stress. Increasing the forest basal dislocation density, ϱ b, was found to result in increasing V n and reducing V t, while increasing the forest pyramidal dislocation density, ϱ p, causes V n to decrease. An analysis in terms of crystal geometry shows that the dualism of the influence of the basal dislocations stems from the fact that they behave as twinning dislocation sources whose density, increasing with ϱ b, leads to higher V n. The decrease in the effective stress, τ ∗, with increasing ϱ b is estimated. An analysis of the experimental data yielded the relation V t (τ ∗) and an estimate of the activation volume, which amounted to 6 × 10 −21 cm 3. The close coincidence of the activation volumes as obtained from V t (τ ∗) and V n (τ) suggests that the rate-controlling mechanism of the twin layer development in zinc crystals with large forest basal dislocation density is the twinning dislocation inhibition. In Be crystals, the increasing V n effect is observed during untwinning. In Be twinned crystals, electron microscopy revealed twinning dislocations with a density of about 10 5 cm −1 at the twin boundaries and a large forest basal dislocation density inside the twin ( ca. 10 8 cm −2).