Polycrystalline Zn Research Articles

Growth of amorphous zinc phosphide films by reactive radio frequency sputtering

Thin zinc phosphide films were grown by reactive radio frequency sputtering of pure zinc in a phosphine containing argon atmosphere. The influence of the deposition parameters and the substrate on film composition and structure was investigated. A prominent change of the growth was noticed between deposition at room temperature and higher temperatures due to high vapor pressure of zinc. For substrate temperatures above 100°C a range of the r.f. power exists for which the system is self limiting. In this regime the phosphine mass flow is the rate limiting quantity, and the growth of non-crystalline and polycrystalline stoichiometric Zn 3P 2 films is possible over a large range of r.f. power.

Chemical properties of bimetallic surfaces: the reaction of oxygen and nitrogen dioxide with zinc on ruthenium (001)

The dissociation of O[sub 2] and NO[sub 2] on Zn/Ru(001) surfaces and the properties of the resulting ZnO[sub x] adlayers have been investigated using TDS, XPS, and XAES. For submonolayer coverages of O and Zn on Ru(001), there is no lateral bonding between the adatoms. In these cases, strong Ru [leftrightarrow] O and Ru [leftrightarrow] Zn interactions prevent the formation of Zn-O bonds. ZnO[sub x] films were observed after increasing the Zn and O coverage above 1 monolayer. Some of these films displayed the typical O(1s) XPS and Zn L[sub 3]M[sub 45]M[sub 45] Auger spectra of polycrystalline ZnO, decomposing at temperatures between 800 and 1,050 K. At 80 K, the initial dissociation probability of O[sub 2] on Zn[sub 1.0]/Ru(001) is almost 2 orders of magnitude smaller than that on polycrystalline Zn. This reduction in the rate of O[sub 2] dissociation is accompanied by a change in the type of oxygen formed: for the supported Zn monolayer, surface oxygen predominates; whereas for pure Zn, oxygen incorporated into the bulk of the film is the dominant species. The dissociation of NO[sub 2] is similar on Zn[sub 1.0]/Ru(001) and polycrystalline Zn. At 80 K, the initial NO[sub 2] adsorption is dissociative: NO[sub 2,g]more » [yields] NO[sub g] + O[sub a]. The oxygen adatoms passivate the surface, and the subsequent adsorption of NO[sub 2] is molecular. Chemisorbed NO[sub 2] decomposes at temperatures between 160 and 250 K to yield gaseous NO and oxygen atoms that remain on the surface (Zn[sub 1.0]/Ru(001) case) or migrate into the bulk (pure Zn case). At 300 K, the probability for dissociation of NO[sub 2] on Zn surfaces is 2 orders of magnitude larger than the probability for dissociation of O[sub 2]. 61 refs., 14 figs., 1 tab.« less

Ellipsometric characterization of surface oxidation in polycrystalline Zn 3P 2 thin films

Zn 3P 2 is II–V semiconductor that has been studied as a light-absorbing material in highly efficient photovoltaic heterojunctions and in photodetectors. The optical properties of the films, as measured by spectroscopic ellipsometry, indicate the existence of two absorption peaks at 2.7 eV and 4.0 eV, as in the case of monocrystalline material. These peaks have a soft shape because of the polycrystalline character, roughness and surface oxide of the film. The spectral ellipsometric analysis, after surface etching, revealed notable evolutions of the optical spectra. Real-time ellipsometric analysis of the surface evolution, at a fixed wavelength, was performed in air at room temperature after surface etching. The results indicate the formation of a very thin and porous native zinc oxide layer with an exponentially decreasing growth rate. The results are discussed in terms of surface changes, such as oxidation, loss of stoichiometry and porosity which are of great interest for discerning the kinetics of surface degradation, with a view to the applications of these films in optoelectronic devices.

Derivative spectra of polycrystalline Zn 3P 2 thin films

Polycrystalline Zn 3P 2 thin films prepared by e-beam evaporation technique on glass substrates kept at 300°C, have exhibited low resistivity value, nearly stoichiometry and good adherence which are very promising features for device applications. Optical studies namely, optical absorption and derivative spectra, have been made which helped to understand not only the nature of the optical band gap (1.55 eV) but also the details of the other transitions related to the band structure (tetragonal) of this compound semiconductor. The results indicated the direct optical transitions at energies greater than 1.70 eV and the energy values for spin-orbit and crystal field splitting are found to be 0.16 and 0.02 eV respectively.

Electroluminescence of (Zn, Cd) S:Mn:Sm powder and sintered film phosphors

Polycrystalline (Zn, Cd)S:Mn:Sm phosphors have been synthesized in argon atmosphere at 900°C. Sintered films of these phosphors are prepared in nitrogen atmosphere using CdCl 2 as sintering aid. The voltage dependence of EL-brightness has been studied and found to obey power law (B=AV n) in both powder phosphors and sintered films. The n-value in case of sintered films is found to be higher as compared to that in powder phosphors. The EL-emission spectra of powder phosphors are found to exhibit a prominent band around 585nm and is attributed to 4T 1→ 6A 1 transition of Mn 2+ whereas EL spectra of sintered films show two additional emission bands at about 525 nm and 625 nm. The origin of additional bands has been explained on the basis of transition of conduction band electrons to deep acceptor levels and donor-acceptor pair recombination respectively.

Highly conductive Ga-doped polycrystalline (Zn,Cd)S films

Highly conducting Ga-doped (Zn,Cd)S thin films with various Zn contents are used as collector/window layers in chalcopyritebased heterojunction solar cells. The films were prepared by means of thermal evaporation. In order to elucidate the effects of Ga doping on carrier transport and optical properties, Hall effect, thermoelectric power and optical transmission measurements have been carried out. Both Hall data and thermoelectric power data show a decrease of mobility and of carrier concentration with increasing Zn content. The comparison of n Hall and n thermo versus conductivity of the films indicates polar optical phonon scattering for lower concentration levels and scattering determined by charged impurities at carrier concentrations exceeding 3 X 10 19 cm 3. With increasing Ga doping, carrier concentration n Hall and mobility μ Hall show different maxima depending on Zn content. For Zn 0.2 Cd 0.8 S films, a maximum carrier concentration of about 10 20 cm -3 at 0.5 at % Ga and a maximum mobility of about 40 cm 2/ V· s at 1 at% Ga can be achieved. Above a specific Ga doping level, both carrier concentration and Hall mobility diminish. Optical data show a significant Moss-Burstein shift (up to 300 meV) for carrier concentrations exceeding 3 X 10 19 cm -3. The electrical and optical data are in agreement.

Photoluminesce properties of doped and unintentionally doped hot wall deposited polycrystalline Zn3P2 films

Zn 3 P 2 films were subjected to photoluminescence measurement. Polycrystalline Zn 3 P 2 thin films were grown under optimized conditions of substrate, source and wall temperatures using the hot wall deposition technique. Unintentionally doped, silver doped and air annealed thin films were individually excited using an HeNe laser and the emission spectra were recorded at various temperatures from 14 to 350 K. Sub-band gap luminescence peaks were found to be weak compared to the broad and intense emission peak lying between the direct band gap at nearly 1.5 eV (at room temperature) and the fundamental indirect transition at 1.39 eV. The broad emission band is believed to originate from the transition from the conduction bands at the Γ point to the nearly uniformly distributed grain boundary energy states in the forbidden gap. The emissions due to acceptor impurity levels were detected in the sub-band gap region.

Preparation and properties of diodes on low-resistivity zinc phosphide films

It has been shown that it is possible to produce low-resistivity (10 2 ω cm) device-grade films of polycrystalline Zn 3P 2 by the hot-wall technique and to produce low-leakage diodes (rectification ratio greater than 100) by evaporating magnesium or aluminium dots onto the resulting Zn 3P 2 films. I–V and C–V measurements have been shown to be in qualitative agreement with the metal/ insulator/semiconductor model of Chattopadhyay and A.N. Daw, Solid State Electron., 29 (1986) 555.) which involves a patchy oxide between the metal and semiconductor regions. If the difference between the Fermi level and the valence band edge for our polycrystalline Zn 3P 2 films is assumed to be the same as that found by Szatkowski and Sieranski for single-crystal Zn 3P 2 (J. Szatkowski and K. Sieranski, Solid State Electron., 31 (1988) 257.) it is shown that it is possible to determine values of C 2 and δ p/δ, parameters entering the model of Chattopadhyay and Daw. The C–V results on the Mg/Zn 3P 2 and Al/Zn 3P 2 diodes can be interpreted as giving values for the carrier concentration N A in the Zn 3P 2 that differ by a factor of 11, and some possible reasons for this are examined.

Raman spectroscopic study of chain complexes of bis(hydrazine) zine and manganese halides

AbstractThe Raman spectra of polycrystalline Zn (N2H4)2X2 (X  Cl or Br) and Mn(N2H4)2Cl2 were run over the range 90–3590 cm−1. The bands observed in the higher frequency region (400–3590 cm−1) were assigned to perturbed hydrazine vibrations and generally agree well with previously reported infrared studies. A normal coordinate analysis was performed on the core of the complexes, metal · N4X2, and used to assign the observed metalnitrogen and metal–halide bands in the lower frequency range (90–400 cm−1).

ＳＥＥＬＦＳ及びＥＡＰＦＳによる多結晶Ｚｎの表面構造解析

ＳＥＥＬＦＳ及びＥＡＰＦＳによる多結晶Ｚｎの表面構造解析

X-ray diffraction studies on polycrystalline Zn 3P 2 films deposited by hot-wall method

Zn 3P 2 thin films were prepared by the hot-wall-deposition method on glass substrates and studies were made using predominantly X-ray diffraction analyses. The results showed clearly that the preferential (004) orientation became dominant as the deposited film thickness became larger regardless of the deposition conditions. Specimens with strongly preferential orientation showed clear column-like structure perpendicular to the substrate. This was confirmed by the SEM observations, X-ray analyses and RHEED patterns.

Internal stress superplasticity in anisotropic polycrystalline zinc and uranium

Internal stress superplasticity is assessed in powder metallurgy and wrought polycrystalline Zn and in polycrystalline α-U. These materials are anisotropic in their thermal expansion coefficients, and, as a result, internal stresses are generated during thermal cycling. A creep model is developed based on the contribution of internal stress to the enhancement and inhibition of normal plastic flow. This creep model, which has no disposable parameters, is shown to describe quantitatively the flow behavior of anisotropic materials under thermal cycling conditions, and correctly predicts the attainment of Newtonian flow characteristics at low stresses. It is predicted that certain polycrystalline ceramics can be made superplastic in tension when thermally cycled under small applied stress.

Ion-induced secondary electron emission from copper and zinc

Ion-induced secondary electron yields for clean polycrystalline Cu and Zn bombarded at normal incidence with 5–20 keV, H +, H + 2, He +, Ne +, Ar +, Kr + and Xe + ions have been measured under ultra-high vacuum conditions ( P ≲ 1 × 10 −7 Pa). Targets were cleaned by sputtering and inspected by Auger electron spectroscopy. A rather simple total electron yield determination procedure was used, employing direct current measurement combined with a variable positive target bias voltage. Good overall agreement was found with existing experimental data. Both the light projectile (H +, He +) results and the particular combination of Cu and Zn targets allow for a test of a recent sophisticated theory. From this confrontation conclusions can be drawn on the direction of improvements needed in a theoretical description.

Morphological and structural properties of Zn 3P 2 single crystals grown by recrystallization in a closed system

Large single crystals of Zn 3P 2 (up to 1.5 g) with large facets have been grown reproducibly by crystallization within a closed tube. For that purpose, lumps of polycrystalline Zn 3P 2 material were exposed together with an excess of phosphorus to a temperature gradient of 0.5°C/cm slightly below 850°C. The interfacial angles of the crystal faces measured with an optical two-circle goniometer agreed with the data obtained from the lattice constants ( a = 8.0905 A ̊ , c = 11.4135 A ̊ ), which were determined by high resolution X-ray diffractometry. The as-grown shape of the Zn 3P 2 crystal was consistent with the pointgroup D4h. A scanning X-ray reflection topograph showed no titled subgrains on the crystal surface. In addition, the high structural quality of the crystal was proved by a γ-ray transmission rocking curve analysis which did not detect mosaic angles greater than 12 seconds of arc.

Structure transformation in mixed polycrystalline Zn1–xCd xS doped with Mn and Cu

Structure transformation in mixed polycrystalline Zn_1–<i>x</i>Cd _<i>x</i>S doped with Mn and Cu

Photoelectron spectroscopy of solids using gas-phase spectrometers

By using continuous deposition of metal surfaces or a continuous scrape technique the ultraviolet photoelectron spectra of clean polycrystalline Zn, Cd, Sn and Pb have been obtained using spectrometers originally designed for gas-phase work. Spectra are calibrated with respect to an internal gas-phase standard. A study of the oxidation of lead is presented to illustrate the applicability of these techniques to adsorption studies. A second oxide in addition to the established orthorhombic form of PbO is observed for low O 2 doses.

Asymmetric effects in the extended X-ray absorption fine structure analysis of solid and liquid zinc

Extended X-ray absorption fine structure (EXAFS) results are presented for solid and liquid Zn for the temperature range 273 to 782 K. At the higher temperatures the distribution of nearest neighbour atoms is asymmetric. Neglect of the asymmetry and use of EXAFS analysis methods developed for symmetric distribution functions gives an underestimate of the nearest neighbour distance R1 and the disorder parameter σ12. It is shown that a transform analysis can be useful in detecting asymmetric effects, and methods of analyzing the EXAFS of asymmetric distributions are presented. An anharmonic oscillator model is applied to the EXAFS data of polycrystalline Zn to correct the values of R1 and σ12. The corrected values of σ12 are found to be~20% higher than those predicted by a Debye model. An empirical, analytically simple asymmetric distribution function is fitted to the liquid data to obtain promising agreement with the nearest neighbour structure as deduced from X-ray diffraction studies. Finally it is shown by applying the Blip-function model of liquid metals that, in principle, the large k-range spanned by EXAFS data can be used to specify the repulsive portion of the ion–ion interaction potential of liquid metals.

Thermal rearrangement of the copper(II)-L-cystine complex

Polycrystalline Cu(II), Ni(II), Zn(II), Pb(II), and Co(II) chelates of L-cystine have been prepared and analyzed. The compounds may be characterized from their infrared and Raman spectra, in particular by their SS stretching vibrations. A Cu(II) compound precipitates at temperatures <40°C with ν(SS) at 497 cm −1, similar to ν(SS) in solid, uncomplexed L-cystine, but in the temperature range 50–65°C (pH 9.45) the complex forms with ν(SS) at 510 cm −1. The apparent activation energy of reaction is 17 ± 4 kcal mol −1. The behaviour is interpreted in terms of ligand conformations adopted in the formation of crystals.

Line shape measurements of atoms sputtered from polycrystalline Cu, Zn, and Al by 300 keV Ar + bombardment

The line shape of atomic transitions of excited Cu, Zn, and Al atoms sputtered from polycristalline metal and from surface-coated Zn and Al by the bombardment with 300 keV Ar + ions has been measured. The influence of radiationless de-excitation processes on the line shape has been studied. The experimental results are compared with a single collision model introduced by van der Weg and Bierman 7) for Ar + bombardment of Cu.

Noise and modulation experiments on saturated cathodoluminescence from Willemite

Measurements of the spectral noise density and a.c. modulation response of saturated cathodoluminescence from polycrystalline Zn 2SiO 4-Mn (Willemite), are compared with a theory developed by Fijnaut and Zijlstra for the case of characteristic luminescence involving one relaxation time. It was found that, with increasing degree of saturation, the crossover frequencies of the excess noise spectrum and a.c. modulation response are shifted towards higher values, while the plateau value of the excess noise spectrum decreased with increasing degree of saturation. This behaviour was in qualitative agreement with the theory. A quantitative comparison was not possible because of the occurrence of more than one relaxation time in the luminescence under study. The degree of saturation of the luminescence was varied by varying the focussing of the electron beam incident on the phosphor, while keeping the total beam current constant.