Results 1 - 10 of 4591
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[en] TaNiSe is the strongest candidate for the long conjectured excitonic insulator state. It is a direct zero gap semiconductor at high temperature, and undergoes at T = 326 K a semiconductor-insulator transition simultaneous with an orthorhombic-monoclinic q = 0 structure transition. Our low temperature STM evidences its layered structure with rippling atomic chains. The local spectroscopy reveals the opening of the excitonic insulator gap and the spectral weight shift with decreasing temperature. High resolution STM topography shows a local distortion associated with the structure transition. This distortion may play an important role in the formation of the excitonic state, as also supported by our band structure calculations.
[en] We report on the 5.5√3x5.5√3- R30"0 overlayers superstructure observed by the scanning tunneling microscopy on the Ge(111) surface. It shows pronounced effects of the local density of states leading to the strong dependence of STM images on the bias voltage and some dynamic changes of images at 300 K. This overlayer is tentatively interpreted as graphene formed in small submonolayer amounts due to the pyrolysis of hydrocarbon constituents of the residual atmosphere of the vacuum chamber during the annealing of a Ge(111) sample at 900 K. We suggest a model of the graphene/Ge(111)- 5.5 √3x5.5√3-R30"0. Heteroepitaxial interface, featuring the reconstructed Ge(111) substrate with no long-range order under the graphene layer, the latter being corrugated due to spatial variations of the interatomic geometry of the Ge(111) and graphene(0001) atomic lattices with extremely large mismatch
[en] Electrochemical scanning tunneling microscopy (Ec-STM) is a powerful technique that can provide molecular-level information regarding electrode surface processes in-situ in electrolyte solvent under ambient conditions. In this study, the adsorption and electro polymerization of an industrially important conducting polymer precursor, 3,4-ethylenedioxy thiophene (EDOT), on Au (100) single crystal was probed using Ec-STM. The Au (100) single crystal electrode substrate used for this study was fabricated using the well-known Clavilier's flame melting procedure. Cyclic voltammetry (CV) was used along with Ec-STM to characterize the bare, EDOT-modified, and poly(EDOT)-modified Au (100) single crystal electrode. Time-dependent Ec-STM imaging at 0.550 V showed the formation of an EDOT self-assembled monolayer through 2-D surface dillusion. The resulting EDOT molecular assembly on Au (100) single crystal electrode was found to fit in a 4√2χ3√2 unit cell. Difference in apparent corrugation between molecular rows was attributed to different angular orientation with respect to the substrate. The electro polymerization of EDOT on Au (100) single crystal electrode was done by potentiostatic and potentiodynamic methods. Both methods suggested a solution-process mechanism for EDOT electro polymerization. (author)