Es wird uber zwei Herstellungsverfahren fur Wismutoxid-Aufdampfschichten berichtct. Die nach beiden Verfahren, dem Diffusionsverfahren und der Elektronenstrahlverdampfung, hergestellten Schichten sind in ihren physikalischen Eigenschaften weitgehcnd gleicli. Durch Rontgenstrukturuntersuchungen wird gezeigt., daB in den Schichten die cc-Modifikation des Bi,O, vorliegt. Aus der Messung der Temperaturabhangigkeit der elektrischen Leitfahigkeit sowie aus Reflexions-und Durchlassigkeitsmessungen erhalt man fur den direkten optischen Bandabstand einen Energiewert von 2.91 eV und fur indirekte Bandubergange (optische und thermische) Energiewerte von 2,60 und 2,15 eV. Da iiber die Bandstruktur des Wismutoxides nichts bekannt ist, konnen eindeutige Zuordnungen der Valenz-Leitungsband-Ubergiinge nicht gemacht werden.Two methods to produce Bi,O, layers by evaporation are described: the so-called diffusion method and the electron-beam evaporation method. Both kinds of layers have similar physical properties. X-ray diffraction shows the layers to consist of the a-modification of Bi,O,. Measurements of the dependence of electrical conductivity on temperature as well as transmission and reflection measurements indicate band gaps of 2.91 eV for direct optical transitions and of 2.60 and 2.15 eV (optical and thermal results, respectively) for indirect transitions. Definite correlations of these band gaps to transitions between valence and conduction bands could not be established since the band struct,ure of Bi,O, is still unknown.

High quality BizSe 3 crystals with 50 to 65 At % Se have been produced. As a consequence of a Se-doping, the carrier density varies between 3 9 1019 to 8 9 1017 cm -3. Based on optical reflection and transmission measurements in the near infrared the dispersion of the refractive index n(2) has been calculated. The plasma resonance frequency Vp1 lies within the energy region from 0.05 to about 0.1 eV. From n(2) and Vpl the effective mass of the electrons in Bi2Se 3 has been evaluated. Near the band edge a value of m~_e=0.02 m 0 has been found. It depends on the orientation of the crystals and on the carrier concentration. The results of the electrical and optical investigations give reason to assume an isotropic mean free time of the electrons. The "six-valley-model" of HASHIMOTO for the energy-surfaces in BizSe3, is confirmed.

The type of conductivity of pure Bi,Os layers is determined by the change of conductivity under the influence of chemisorbed oxygen. The spectral photoconductive sensitivity is measured on undoped and doped Bi,O, layers within the range of 0.8 to 3.5 eV. The time constant of the photoelectric effect of pure Bi,O, layers can be reduced b y photoadsorption of oxygen. A sulfur or selenium doping of the layers causes a shift of the wavelength limit towards the near infra-red. The time constant is greatly reduced.

Abstract. Helium atoms were excited by hydrogen-ion impact, and electric dipole transitions between Stark substates of the 1 s 4f multiplet of HeI were induced. Resonance signals were investigated at various frequencies 200 MHz < v < 800 MHz by scanning a static electric field F o < 1 kV/cm and observing the intensity of the impact radiation for the singlet or triplet I s 3 d--1 s 2p spectral line. From these measurements the following zerofield transition frequencies of the 1 s 4f fine structure were deduced: =490.6(O.4)MHz. Using calculated parameters of the magnetic fine-structure coupling, the exchange integral 2K= 158.0(0.6) MHz of the 1 s 4f configuration was evaluated.

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