Calculation and XPS measurements of the Ta4f CDW splitting in Cu, Cs and Li intercalation phases of 1T TaX2 X S, Se

Metallic quasi two dimensional transition metal dichalcogenides TMDCs 1T TaS2 and 1T TaSe2 show charge density wave CDW at room temperature. These show up as a superstructure in low energy electron diffraction LEED and as a distinct splitting of the Ta4f core level and a part of the Ta d z 2 derived valence band. The changes in this Ta4f CDW splitting are investigated for in situ Cu, Li and Cs intercalated crystals by photoelectron spectroscopy PES, XPS, SXPS and LEED. The intercalation effects a certain number of CDW phase transitions, where each CDW phase is related to a characteristic CDW related splitting of the Ta4f core level. We extend the simple electrostatic model of Hughes and Pollak [1] to calculate the form of the splitting for different CDW phases and find a good correlation to the XPS measurements. This agreement confirms that the Ta4f CDW splitting is brought about by an electrostatic interaction between the Ta atoms and the free metallic charge density. The comparison of the phase transition sequence for three different intercalants indicates that a three dimensional rather than a two dimensional Fermi surface nesting mechanism is responsible for the phase transitions, as originally proposed by Wooley and Wexler [2

Model experiments on growth modes and interface electronics of CuInS2 Ultrathin epitaxial films on GaAs 100 substrates

The heterojunction formation between GaAs 100 and CuInS2 is investigated using ultraviolet photoelectron spectroscopy UPS , X ray photoelectron spectroscopy XPS , and low energy electron diffraction LEED . Thin layers of CuInS2 films were deposited in a step by step process on wet chemically pretreated GaAs 100 surfaces by molecular beam epitaxy MBE with a total upper thickness limit of the films of 60 nm. The film growth starts from a sulfur rich GaAs 100 surface. XPS core level analysis of the substrate and film reveals initially a transitory growth regime with the formation of a Ga containing chalcopyrite phase. With increasing film thickness, a change in stoichiometry from Cu poor to Cu rich composition is observed. The evaluation of the LEED data shows the occurrence of a recrystallization process where the film orientation follows that of the substrate with the epitaxial relation GaAs 100 CuInS2 001 . On the completed junction with a CuInS2 film thickness of 60 nm, the band discontinuities of the GaAs 100 CuInS2 structure measured with XPS and UPS were determined as DEV 0.1 0.1 eV and DEC 0.0 0.1 eV, thus showing a type II band alignmen

Investigation of photomоdified semiconductor/ electrolyte interfaces : The n-lnSe/CulSe

An overlayer of CulSe3-Se° of i to 2 µm was photogenerated at the surface of n-InSe electrodes in a solution of copper polyiodide. The morphology, chemical composition, and crystal structure of these films were characterized by SEM, EDAX, X-ray diffraction under grazing incidence, ESCA and SIMS. The spectral properties were characterized by spectral photoresponse and photoreflectance and they were correlated with photoelectrochemicl1 and EBIC studies in order to determine the mechanism of charge transport across such layers

Entwicklung und Charakterisierung duenner photoaktiver Schichten neuartiger Verbindungshalbleiter Abschlussbericht

The final report covers the following subjects: Van der Waals epitaxy at semiconducting layer lattice crystals, UHV experiments with pyrite surfaces and thin layers, preparation of pyrite layers, preparation and characterization of CuInS layers, ZnO deposition by reactive magnetron sputtering, photoconductive ploymers (modification of polymethylphenylsilane). (MM)In diesem Abschlussbericht werden folgende Themen behandelt: Van der Waals Epitaxie an halbleitenden Schichtgitterkristallen, UHV Experimente zu Pyrit-Oberflaechen und Schichten; Praeparation von Pyrit-Schichten; Herstellung und Charakterisierung von CuInS_2-Schichten; ZnO-Abscheidung durch reaktives Magnetron-Sputtern; Photoleitfaehige Polymere (Modifizierung von Polymethylphenylsilan). (MM)SIGLEAvailable from TIB Hannover: F96B303+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman