Einfluß der Transportkinetik auf die Kristallisation von AIIBIVC-Verbindungen beim Gasphasentransport

The reported investigation intended to find tendencies in the influence of thermal and chemical conditions of chemical transport reactions on the growth of ZnSiP₂ and ZnSiAs₂ crystals. A more favourable crystallisation with less intergrowth is proved, if transport gases of the same system — as e.g. ZnCl₂ or SiCl₄ — is used instead of PbCl₂ and TeCl₄. — Depending on the concentration of the transporting medium the largest amount of crystals with lengths of more than 5 mm coincides with the point of lowest transport rate. The number of crystal defects increases with the dimensions of the crystals. — From the experimental results a hypothesis for explaining the locally different growth of crystals of ternary compounds is presented.     

Die Berechnung von Kriterien für die Abscheidung reiner Phasen binärer Systeme beim chemischen Transport und der Transport im System Cu-O

A thermodynamical analysing method is described of the deposition of binary solids AB_x, which specially takes into account the influence of the coexistence equilibria in the A—B-system. This analysis is applicated to the Cu—O system. It permits to calculate the conditions, under which Cu₂O is deposited without deposition of any other phases. The deposition of cuprous oxide by CTR-techniques is investigated using hydrogen halides as transport media. The experiments result in the growth of Cu₂O-monocrystals (2 × 2 × 2 mm) only if HCl is used as transport medium. Using HI the simultaneous deposition of Cu₂O and Cu is observed.     

Homogenitätsuntersuchungen und Bestimmung der molaren Konzentration x an CdxHg1–xTe mit Hilfe der Elektronenstrahlmikrosonde

The semiconductor Cd_xHg_1–xTe serves as a starting material for the production of infrared detectors with a high detectivity and a small time constant. Cd_xHg_1–xTe single crystals are necessary to manufacture detectors efficiently. The single crystals should not contain segregations and have to include a homogeneous molar concentration x. An electron microprobe X-ray analyzer meets all requirements expected from the measuring method for checking the homogeneity of Cd_xHg_1–xTe crystals. — Results of qualitative and quantitative studies in the microscopical and macroscopical range are presented. Typical defects of the crystals were detected by using the qualitative electron microprobe X-ray analysis. The quantitative analysis was carried out with standard samples. The method for determination of the molar concentration x of the standard samples is described.     

Über die Züchtung von ZnS-, ZnSe- und ZnTe-Einkristallen unter Anwendung der chemischen Transportreaktion

In connection with investigations on the synthesis of ZnS, ZnSe and ZnTe single crystals by chemical transport using iodine as transport agent in sealed tubes the mechanism of mass-transport and the relationship between material-transport and growth process were studied. In this way the optimum conditions for growing single crystals were found. The dependence of the transport rate on the undercooling ΔT, on the diameter of the ampoule and on the pressure in the system is described. Relative large crystals in good quality could be propared by influencing the nucleation and the growth process by help of well defined transport rates. In all cases crystals with sphalerite structure only were obtained. The habit with the most common faces (110), (111) and (211) was found to be predominant. The dominant habit is responsive to variations in the experimental parameters. The crystal perfection have been determined by etch patterns and by X-ray topography.     

Untersuchung der Volumenstruktur dünner Bi1–xSbx-Schichten

The cross-sectional structure of evaporated Bi_1–xSb_x film has been investigated using electron microscopy and a replica technique. The conditions of film formation were varied by using different hydrocarbon partial pressures. After formation the films were annealed at 150°C. The cross-sectional structure is supposed to be columnary. This is in good agreement with the 〈00.1〉 texture. Grain coarsing during annealing is mainly influenced by the hydrocarbon concentration of the film. The upper part of the film shares most of the hydrocarbons. The correlation between surface- and cross-sectional structure disappeares by formation of an oxid layer.     

Beitrag zur Kristallisation von ZnSiP2 aus der Gasphase

The influence of thermal conditions on the synthesis and crystallinity of ZnSiP₂ is investigated. Extensive measurements lead to statements on the axial and radial distribution of temperature in the apparatus and in the reaction vessel. The axial temperature gradient in the crystallization room equals some 3 deg/cm, whereas in the ampoule a radial gradient of 4 to 5 deg/cm is ruling. — At different temperature differences the thermal conditions of deposition of ZnSiP₂ are discussed, and it is found that ΔT should not fall below a minimum value of 15 deg, if ZnSiP₂ is to be produced by means of gas phase transport in a finite period of time. — In a full discussion the characteristic transport effects are explained. — Condensation of ZnP₂ at the end of the ampoule and by secondary transport caused by local temperature and concentration gradients in the crystallization room are stated to be responsible for different concentration profiles, for the phases present and for the crystallinity depending on the place of crystallization. — Hints for favourable variants of growing are given.     

Preparation and structure of CdGeP2

The production of CdGeP₂ through vapour transport was studied. Proceeding from thermodynamic observations on the possibility of Ge-transport in the form of chloride an optimisation of the parameters in volved in the process was achieved through systematic variation of the transport conditions. The produced crystals were characterized through main component chemical analysis, microhardness measurements, microprobe analysis and X-ray phase analysis.     

Predicting the rate of chemical transport using the flux function method

A systematic approach to the selection of independent variables for a theoretical analysis of the rate of chemical transport is discussed. The methodology is based on the use of the transport flux function, which enables optimum conditions to be found on the basis of a minimum number of the variables most likely to have the greatest effect on the transport rate. A more precise quantitative comparison between experimental and theoretical results can be made by taking into account the effects of convection, uncertainties in thermochemical data, and differences in the diffusion properties of vapour species. The latter effect can lead to a redistribution of components in the vapour, and this may have important consequences in certain CVT processes. The theoretical methodology is exemplified by consideration of transport of CoP₃ in the Co-P-Br system, FeP in the Fe-P-I system, and YIG in the Y-Fe-O-Cl and Y-Fe-O-HCl systems. The complex behaviour revealed would probably have been difficult to rationalize on the basis of experimental studies alone.     

Zu dem Transportsystem V-O-Te-Cl und dem Transportverhalten der Vanadinoxide mit TeCl4(II). Der chemische Transport der Magnéliphasen VnO2n–1, des V6O13 und des V2O5

It was reported on the transport system V O Te Cl and on the transport behaviour of VO₂ in a previous paper. This paper deals with the chemical transport of Magnéli phases V_nO_2n–1, and of V₆O₁₃, and of V₂O₅. Resulting from the composition of the gas phase over the solid phases in the presence of TeCl₄ the chronological sequence of the transported phases as well as the direction and rate of transport are calculated. These results are compared with experiments. All of the oxides are obtained without deposition of any other phases. Their phase boundaries are determined. The dependence on temperature is investigated for the upper phase boundary of V₂O₃.     

Formation of oxygen deficient BaPbO3‐x by oxalate decomposition

BaPbO₃ is assumed to be oxygen deficient but the exact determination has never been reported. The aim of this study is to investigate the correlation between synthetic conditions and the resulting oxygen deficiency of BaPbO_3‐x. The formation of BaPbO_3‐x by decomposition of barium‐ and lead oxalate up to 850 °C is significantly faster compared to conventional high temperature solid state reactions of oxide compounds. The discrete reaction steps were studied by simultaneous thermal analysis and X‐ray powder diffraction. The oxygen content was determined by temperature‐programmed reduction analysis. It is shown that the formation process is very sensitive to the chosen starting materials leading to different oxygen deficits caused by partial oxidation from Pb²⁺ to Pb⁴⁺. The resulting perovskites show chemical compositions of BaPbO_2.74 and BaPbO_2.82. The varying oxygen deficits should have an effect on structural properties. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and transport rates of GeSe and GeTe in micro-gravity environment

Six vapor transport experiments on the systems GeSe-GeI₄ and GeTe-GeI₄ were performed on Skylab to determine the effects of micro-gravity on crystal growth and transport rates. Based on a direct comparison of crystals and transport data obtained on earth and in space, employing X-ray diffraction, microscopic and etching techniques, the results demonstrate a considerable improvement of the space grown crystals in terms of growth morphology and bulk perfection. The observation of greater mass transport rates than expected in micro-gravity for diffusion-controlled transport could indicate the existence of other transport modes in a reactive solid-gas phase system. The combined results show that the interference of gravity-driven convection with the transport process causes negative effects on crystal growth as observed on earth for otherwise identical conditions. This points to the unique environment of weightlessness for the observation of basic transport phenomena.     

Untersuchung der Kinetik der Kristallisation unterkühlter Schmelzen

Experimental arrangement and a method are given to investigate the kinetics of solidification of supercooled liquids in thin layers. The kinetics of isothermal phase transformation of supercooled melts of betol are investigated between 0° and 85°C. Kinetic curves present the course of phase transformation in this range. It is stated that the process of isothermal solidification can sufficiently be described by the equation S_π = S₀ [1 − exp (− a τ^b)], b lying between 2 and 3. Compared with the theoretical value the experimental one is lowered, this being explained by the presence of active impurities and their exhaustion during the process of solidification.     

Quantitative Elektronenstrahlmikroanalyse und Zyklotronresonanzmessungen an Wismut-Antimon (Bi1−xSbx)

For the investigation of the electronic properties of bismuth-antimony single crystals the analysis of their chemical composition is important. For this te Electron Microprobe Analysis is a suitable method. In general the quantitative Elektron Microprobe Analysis requires to take into account various influences. This is possible by correcting calculations on the basis of theoretical models. For the reproducibility and the comparability of analytical results information is necessary on conditions of measurement and on theoretical corrections. In this paper an investigation is made, under which conditions in the analysis of bismuth-rich bismuth-antimony alloys the correction can be neglected. The successful utilization of the Electron Microprobe Analysis for the investigation of the dependence of the band structure of Bi_1−xSb_x on the antimony concentration x is shown by the example of the measurements of cyclotron resonance.     

Zum Einfluß des Primärionenstrahlprofils bei der Monolagenanalyse mittels der Methode SIMS

The influence of the primary ion beam profile on the secondary ion currents has been investigated by the SIMS method. The results obtained by Benninghoven concerning the destruction of monolayers could be generalized for the conditions existing in some SIMS devices, namely that the primary ion beam profile is not rectangular, that means, the current density of the irradiation disc is not constant. Moreover, an analytical formula has been given in order to eliminate numerically the so-called „crater effect”︁ existing at the estimation of depth profiles by means of such a stationary primary ion beam of not rectangular profile. Using experimental curves obtained by investigations of the oxidation of (100) CrNi steel surface by means of the SIMS method, it was demonstrated how to carry out a quantitative analysis.     

Spektrochemische Bestimmung von Silizium in AlxGa1–xAs und physikalische Eigenschaften der Kristalle

A direct spectrochemical method for the quantitative determination of silicon in Al_xGa_1–xAs (x ≈ 0,8) crystals was elaborated. The results of the analysis of highly doped samples (10¹⁹ … 10²⁰ cm⁻³) were discussed in connection with photoluminescence spectra and electrical measurements.     

Study of the ZnO crystal growth by vapour transport methods

The crystal growth of ZnO by vapour transport is classically made with the assistance of additional species that produce a gaseous mixture, the role of which remains often uncertain in the transport and growth process. Initially, in order to study the mass transport process, a numerical simulation is made to analyse which are the requirements to have an effective transport. As the pressure of each gaseous species is generally unknown, the numerical study has been performed for different total pressures. It is found that, if congruent and equilibrium conditions are assumed at the sublimation and crystallisation interfaces, effective growth conditions can only be attained for a narrow range of total pressures. Nevertheless, it is well known that ZnO growth by vapour transport is possible for a wide range of pressures of gaseous species. As a consequence, partial pressures higher than the equilibrium ones must be present in order to justify the experimental results. We suggest that the thermal decomposition of ZnO is given by an activated process. The analysis of different mechanisms that could justify the activated decomposition, in accord with a systematic set of growth experiments, suggests that some additional species in the growth of ZnO by vapour transport promote the generation of an additional Zn pressure. This zinc pressure would act autocatalytically inducing O₂ and Zn partial pressures higher than the equilibrium ones and promoting thermal decomposition. The above-cited set of experimental growth experiences, that include the presence of C, Zn, Fe, Cu and H₂, will be analysed and interpreted according to this approach.     

Zur Errechnung der Intensitäten von Auger-Übergängen für die quantitative Analyse von Festkörperoberflächen mit der Augerelektronenspektroskopie (AES)

According to an empirical equation for the Auger electron intensity arising from primary electron bombardment of solid surfaces, the parameters such as ionization cross section, relative Auger transition probability, backscattering factor and mean escape depth were evaluated for the L₃M₄₅M₄₅ Auger transition of elements with atomic number Z = 22 to 33. A comparison of the calculated relative intensities with experimental values from Palmberg et al. indicates a good agreement of both curves representing the intensity in dependence of atomic number. The mean relative deviation of calculated intensities from measured ones amounts to 20%. This is nearly the same value, as it has been estimated so far for the accuracy of quantitative AES without standard. Examining the influence of individual intensity parameters we were able to show that above all the ionization cross section and in the present case also the relative Auger transition probability determine the value of intensity.     

Abscheidung von Cu2O aus der Gasphase im strömenden Medium

CVD-experiments in the system Cu O H Cl N result in the growth of Cu₂O single crystals. The characteristic faces of the various forms are the {100} ones. A thermodynamic analysis permits to predict such conditions under which Cu₂O is deposited without deposition of any other phases.