A combined study of scanning tunneling microscopy ͑STM͒ and density functional theory ͑DFT͒ reveals that 3,4,9,10-perylene-tetracarboxylic-dianhydride ͑PTCDA͒ adsorbs on Ag͑111͒ at bridge sites in two nonequivalent orientations, one nearly aligned with the ͓101͔ substrate axis and the other 18°misaligned. Site-specific spectroscopy reveals that molecules in the two configurations exhibit subtle differences in their electronic structure. DFT-based STM simulations trace these back to the influence of distinct local adsorption geometries on the chemical molecule-substrate and molecule-molecule interactions.

The structural, optical and electrical behaviour of MnS under high pressure was investigated. For X-ray investigations and optical observations a gasketed diamond anvil cell was used. Measurements of the electrical conductivity were performed in a Bridgmari opposed-anvil apparatus. A structural phase transition at 7.2 GPa from the cubic a-phase (NaC1-type) t o the B16-type structure (GeS-type) was detected by X-ray investigations and confirmed by optical observations. Measurements of the electrical conductivity showed a linear decreasing electrical gap energy in dependence on pressure.Es wurde das strukturelle, optische und elektrische Verhalten von MnS unter Druck untersucht. Fur die Rontgenuntersuchungen und die optische Beobachtung wurde eine gasketierte Diamantstempelkammer verwendet. Die Messung der elektrischen Leitfkhigkeit wurde in einer Bridgrnan-Flachstempelapparatur durchgefuhrt. Ein struktureller Phasenubergeng bei 7.2 GPa von der kubischen a-Phase (NaC1-Typ) in die B16-Struktur (GeS-Typ) wurde durch Rontgenuntersuchungen festgestellt und durch optische Beobachtungen bestiitigt. Die Messung der elektrischen Leitflihigkeit zeigte eine lineare Abnahme der elektrischen Gap-Energie in Abhiingigkeit vom Druck.

We studied TbTe 3 using scanning tunneling microscopy (STM) in the temperature range of 298 -355 K. As seen in previous STM measurements on RTe 3 compounds, our measurements detect a unidirectional charge density wave state (CDW) in the surface Te-layer with a wavevector consistent with that of the bulk, = 0.30 ± 0.01 * . However, unlike previous STM measurements, and differing from measurements probing the bulk, we detect two perpendicular orientations for the unidirectional CDWs with no directional preference for the inplane crystal axes (a-or c-axis) and no noticeable difference in wavevector magnitude. In addition, we find regions in which the bidirectional CDW states coexist. We propose that observation of two CDW states indicates a decoupling of the surface Te-layer from the rare-earth block layer below, and that strain variations in the Te surface layer drive the local CDW direction to the specific unidirectional or, in rare occurrences, bidirectional CDW orders observed. This indicates that similar driving mechanisms for CDW formation in the bulk, where anisotropic lattice strain energy is important, are at play at the surface. In our bias-dependent measurements, we find no contrast inversion for the CDW state between occupied and empty states. This finding differs from other quasi 2-dimensional materials containing a "hidden" 1dimensional character which leads to a favorable Fermi surface nesting scenario. Our temperature-dependent measurements provide evidence for localized CDW formation above the bulk transition temperature, T cdw . Introduction:Charge density wave (CDW) states are broken-symmetry states prevalent in condensed matter systems, where they are often found to coexist and/or compete with other orders. In particular, in the intensely-studied graphene-related systems [1], layered chalcogenides [2,3], organic compounds [4], cuprate high-temperature superconductors [5][6][7][8][9], and BiS 2

Röntgenuntersuchungen bei 300 K in Abhängigkeit vom Druck ergaben, daß CuGaSe2 bei 12,5 GPa und CuGaTe2 bei 8 GPa von der Chalcopyrit‐Struktur in die NaCl‐Struktur übergehen. Dabei tritt ein Volumensprung von 8,6 bzw. 3,8% auf. Diese Ergebnisse werden im Zusammenhang mit Hochdruckuntersuchungen an anderen tetraedrisch koordinierten Verbindungen diskutiert.

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