Zur Elektronennachemission an LiF-Kristallen

The exoelectron-emission from LiF-crystal surfaces after cleavage and excitation by electrons or X-rays is investigated in high vacuum and ultrahigh vacuum. As we show by measurements in ultrahigh vacuum, in contrast with metals the exoelectron-emission of LiF-crystals in high vacuum is not essentially influenced by surface layers. Traps of the LiF-crystal are responsible for the emission. We can distinguish between surface states and volume traps —M- andF-colour centres — responsible for the exoelectron-emission from LiF-crystals.     

Elektronenemissionen und Farbzentren bei Ionenkristallen

Zusammenfassung Es werden weitere Erkenntnisse über die Elektronenemission aus verschiedenartig gefärbten Ionenkristallen angeführt und die näheren Zusammenhänge zwischen den Farbzentren und einigen physikalischen Erscheinungen besprochen, wie z. B. dem äusseren Photoeffekt, der Thermolumineszenz und der aktivierten Adsorption.     

Zur Labyrinthstruktur bei Martensit

Ohne Zusammenfassung

---

     

Theorie vibronischer Spektren in Ionenkristallen

The electronic bands of some foreign ions in a crystal exhibit one or a few intermixed sequences of equidistant lines (vibronic spectra.) Examples are the divalent rare-earth ions in alkali-halide and alkaline-earth-halide crystals. It is shown that such sequences of lines are only possible if a) the disturbed lattice dynamics gives rise to localized or quasi-localized modes and b) the electronic functions of the defect ion (properly symmetrized in the static crystal field) do not overlap the nearest lattice ions. To calculate the single lines of a vibronic band a refined method of moments is developed. Its parameters (oscillator displacement and frequency change) follow from the dynamics of the disturbed lattice. The lattice vibrations are calculated by means of modern scattering theory. To describe the scattering resonance the advantageous concept of metastable (quasi-localized) vibrations is introduced. Then the projection of the cartesian coupling functions of first and second order onto the disturbed lattice eigenvectors can be determined. Their matrix elements <n|U _x |n> and <n|U _xx |n> define the change of the equilibrium positions and frequencies during the transition. Further on general symmetry-selection rules are derived for the electron-lattice coupling. Finally the important case of a pure electrostatic coupling is discussed in more detail. It is evident that the study of vibronic spectra gives important information about the dynamics of the disturbed lattice and the electron-lattice coupling. Especially they constitute a method to investigate localized and quasi-localized modes, even if their dipole moment is too small for direct optical excitation, or if their frequency lies in the absorbing region of the crystal.     

Elektronennachemission und Photoemission von Alummiumoberflächen

Zeitschrift für Physik A Hadrons and nuclei - The specific heats of Zr-Rh alloys have been measured between 0.9 and 12 °K, and at atomic percent Rh concentrations between 0 and 8. The...     

Zur Frage der Thermoemission bei Halbleitern

Ohne Zusammenfassung

---

     

Zur Berechnung von Geometriefaktoren bei der Kernstrahlungsmessung

Der Geometriefaktor von radioaktiven umschlossenen oder offenen Strahlenquellen hängt bei der Messung mittels einer Kernstrahlungsmeßsonde von der räumlichen Anordnung der Strahlenquelle zu der strahlenexponierten wirksamen Fläche des Detektors und von der Geometrie der Strahlenquelle selbst ab. Fūr punktförmige Strahler in verschiedenen Positionen, Geraden, Kreisflächen und Zylinder wurde in möglichst einheitlicher Vorgehensweise die Berechnung der Geometriefaktoren bezüglich kreisförmiger ebener Detektionsflächen vorgenommen und rechentechnisch in Form von BESM 6-Algolprogrammen realisiert. Die Berechnungsergebnisse sind untereinander konsistent und wurden möglichst durch unabhängige Verfahren oder experimentelle Werte kontrolliert. Die Rechengenauigkeit kann gemäß den vorliegenden Anforderungen frei gewählt werden.     

Zur Widerstandsanomalie von Legierungen bei tiefen Temperaturen

Dilute alloys of Cu-Fe, Au-Fe, Zn-Mn, and Ag with V, Cr, Mn, Fe, Co are produced by simultaneous evaporation of both components on a substrate at 77 °K. By this method one succeeds in solving all systems, especially Cu alloys with high Fe concentration, which alloys normally show precipitations after cooling from the molten state. For these alloys we observe resistance minima up to 150 °K. Besides this, Cu-Fe shows a resistance maximum which depends on concentration. For Au-Fe and Ag-Mn we measure resistance anomalies which are even bigger for quenched films than for annealed films and bulk material. Apparently the lattice defects have an influence on the resistance anomaly. The increase of the resistance with decreasing temperature can be described by the functionρ _s /ρ _s0 =f(T/T _k ) for all systems. The result does not agree with the theories basing on Kondo's model. Here is tried an explanation by means of spin-orbit interaction. This interaction results in a temperature dependent cross-section for a molecule consisting of a magnetic impurity and a lattice defect.     

Zur thermischen Wandbelastbarkeit bei toroidalem Plasmaeinschluß

In this paper a model theory is demonstrated by which it is possible to determine the load capacity of a wall including an electric arc. This theory bases on exact numerical computations of the temperature distribution inside the wall of a toroidal arc tube. It is shown and explained that the thermal load capacity increases with the radius of curvature at fixed tube radius and decreases with the tube radius at fixed radius of curvature.