Emissionsmikroskopische Untersuchungen zur Änderung der Sekundärelektronenemission bei der plastischen Verformung

Both the electron optical image contrast and the electron current density of all crystal grains decrease by plastic deformation of polycrystalline samples in a secondary electron emission microscope with conventional high vacuum. As a presumption both the sample temperature and the vacuum must be so high that the secondary electron yield does not change during the variation of these parameters. After recrystallisation the electron current densities of the crystallites with preserved orientation return to those of the initial stage. From these results it follows that a connection exists between secondary electron yield and crystal lattice perfection. A qualitative explanation of this connection is tried.     

Grundlagen der Theorie des Parakristalls und ihre Anwendungsmöglichkeiten bei der Untersuchung der Realstruktur kristalliner Stoffe

A brief review is given concerning the basic ideas of the theory of paracrystals and its practical application in X-ray structure analysis. Moreover, the relationships are discussed which exist between the the ory of paracrystals and the theories of liquids as proposed by ORNSTEIN , ZERNIKE and ZERNIKE , PRINS , and between the theory of paracrystals and the treatment of imperfect crystals as introduced by KRIVOGLAZ .     

Gleitbanduntersuchungen während und nach Verformung der intermetallischen Verbindung MgZn2

Measurements of densities, lengths, offsets and velocities of slip bands have been performed by optical microscopy of surfaces of the single crystalline intermetallic compound MgZn₂ plastically deformed at temperatures from 245 to 427°C. From their shear strain dependence conclusions have been drawn concerning the behaviour of dislocations during deformation of this compound completely brittle at room temperature.     

Über die Zerfallsstruktur des Ni-Katalysators und die Ni(C)-Phase des Diamanten bei der Diamantsynthese

The nature of intermediate phases in the Ni C system is discussed and the concentration dependence of the specific atomic volume is determined. Decomposition structures of Ni C samples exposed to high pressures and temperatures are studied metallographically and by X-ray diffraction. The specific atomic volume of Ni(C) decomposition phase and of Ni(C) satellite phase of Diamond is measured by the asymmetric powder method and from this the concentration of carbon is ascertained. It is stated that the Ni(C_y) satellite phase of diamond — the terminal solid solution of carbon in nickel approximately contains 3 at.% of carbon. It is concluded from this that this phase is the result of the last stage of decomposition of carbon supersaturated catalyst. Thus, the intermediate phase is playing no important role in diamond nucleation.     

Die Änderung der Molekül- und Kristallstruktur des N-Methyl-piperidinum-acet-meta-chlor-anilid-jodid durch Einlagerung von Wasser

N-Methyl-piperidinium-acet-meta-chloro-anilide-iodide crystallizes from water in the space group Pna2₁ with 4 formula units C₁₄H₂₀N₂OClJ and 4 H₂O molecules in the unit cell. The lattice constants are a = 12.413 Å, b = 19.798 Å and c = 6.919 Å. The change of the molecular conformation caused by water molecules was investigated by X-ray structure analysis.     

Kinetik des Transportprozesses und der Kristallisation von InAs aus der Gasphase

Transport processes of InAs in a closed iodine system are investigated. Their rates depend on the temperature in the solution and crystallisation volumes respectively and on the cross-sectional area of the reactor. The transport is diffusion controlled. The deposition rates of InAs are calculated from the quasi-equilibrium diffusion theory and compared with experimental values of the rates of transport. Neglecting of the convective part of gas transport leads to considerable deviations from the values predicted by the theory. In the temperature range from 800 to 900°C - with iodine concentrations < 3 mg/cm³ - the transport of InAs is controlled by concentration conditional diffusion, with iodine concentrations >3 mg/cm³ the rate of transport is given by the equation of convective diffusion.     

Zum Einfluß der Diffusion auf Keimbildung und Wachstum bei der Kristallzüchtung aus der Gasphase

The crystal growth in the vapour phase is governed by the diffusion of the nutrient to the surface of the growing crystal. The diffusion fields are calculated for two idealized limiting cases. The conditions of the real growth process are discussed.     

Kristalle der Halogenide des einwertigen Quecksilbers und ihre optischen Grundeigenschaften

Single crystals of bromide and iodide of univalent mercury were prepared be means of a method developed before for mercury(I)chloride crystals. On crystals of all three halogenides refractive indices for the ordinary and extraordinary ray were measured. On the basis of these values splitting angles of both rays were computed for a vertical incidence of light and for different angles of crystallographical orientation of the crystal and for different wave lengths of light.     

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.     

Verteilungskoeffizienten und Konzentrationsanreicherungen an der Phasengrenzfläche bei ebenem und zellularem Erstarren von Zinn-Zink-Legierungen

The experimental results of KRUMNACKER on the effective distribution coefficient k_eff and the concentration-profil at the solidification interface were examined. On the basis of this examination and some new calculations the depencence of the segregation coefficient on the solidification rate R and on the concentration C₀ is studied in the cases of planar and cellular solidification. — In the case of planar interface the dependence of k_eff on the solidification rate is that of the Burton-Prim-Slichter-theorie. The interface distribution coefficient is not a function of R, or C₀. Thus, the result od BRICE , basing on the same experiments, is not correct. It is impossible, to improve the model of BRICE by these values. — In the case of cellular growth the distribution depends on the diffusion in the diffusion layer at the interface and on the segregation in the grooves of the cells. Under the applied experimental conditions of a large diffusion-boundary-layer the diffusion determines the dependence of k_eff on the solidification rate also under the condition of cellular growth.     

Zur Frage der seitlichen Ionenstreuung bei der Implantation in amorphen und polykristallinen Festkörpern

The regularities of lateral scattering of ions in amorphous and polycrystal targets were derived. In contrary to well known LSS' method the proposed theoretical procedure enables to calculate root-mean-square deviations of ranges and lateral ranges for arbitrary ratios of target atom to ion masses within a wide range of energies from several MeV to energies near the binding energy of the atoms in solids. The theoretical estimates of root-mean square lateral deflection of ions are in good agreement with experimental results of different authors.     

Darstellung von VO2-einkristallen der oberen und unteren phasengrenze durch chemischen transport

The chemical transport of VO₂ with TeCl₄ was investigated in the temperature range of about 1000°C and 600°C. In the first case there is TeO₂ existing in the gaseous phase, in the second case the TeO₂ has no noticeable vapour pressure. The transport takes place from the hot to the cool zone. In both cases we obtained high transport rates of 10 to 20 mg h^-1. The composition of the gaseous phase is calculated and the transport mechanisms are discussed. It is possible to obtain VO₂ with the upper and lower phase boundary by variation of the initial compositions. Starting with compositions lower than VO_1.99 we obtained near 1000°C in the deposition zone V₈O₁₅ first and after a time VO₂ with the lower phase boundary. Compositions higher than VO_2.00 give vanadium dioxide with the upper phase boundary. In the temperature range of about 600°C however we obtained the phase with the higher oxygen content first. The results are compared with those, which have been obtained by the transport of VO₂ with HCl and Cl₂ — which takes place from the cool to the hot zone.     

Bestimmung der relativen Stabilität der Zinkblende- und Wurtzitstruktur mit Hilfe des piezoelektrischen Effektes

A phenomenological model of the piezoelectric effect is used to determine the relative stability of zineblende and wurtzite structure in A_II B_VI-semiconductors. It is shown that compounds with a normalized longitudinal piezoelectric constant e_pol* > 0,15 ± 0,02 are stable in wurtzite but compounds with e*_pol < 0,15 ± 0,02 are stable in zineblende structure.