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High resolution low-energy electron diffraction, scanning tunneling microscopy (STM), and transmission electron microscopy (TEM) have been used to study the temperature dependence of a vicinal (stepped) Si(111) surface with a polar angle of 6° from (111) along an azimuth rotated about 10° away from the high symmetry [112] direction. At the (1×1) to (7×7) reconstructive transition, the kinks at the step edges precipitate into a phase with high step density and increased rotation from the [112] direction, leaving behind a [112] oriented phase with triple-layer height steps and (7×7) reconstruction. The inclination and azimuth of the orientation of the kinked phase change continuously with temperature. When the surface is cooled to room temperature, STM images confirm a coexistence between the [112] oriented step-tripling phase and the kinked phase. In the step-tripling phase, the steps are very straight (kinks are rare) and oriented in the [112] direction. There is a small fraction of single-layer height steps between the predominant triple-layer height steps. All the terraces in this phase are (7×7) reconstructed. In the kinked phase, steps with a high density of kinks are bunched together and rotated to a direction about 45° away from [112]. TEM images of the surface topography also confirm the phase coexistence on a macroscopic scale. This phase separation (azimuthal faceting) is reversible, and can be understood thermodynamically by analogy with phase separation in a two-component fluid. [ABSTRACT FROM AUTHOR]

We present a low-temperature scanning tunneling microscopy investigation revealing the formation of a long range ordered α-sexithiophene (6T) monolayer nanostripe array on highly ordered pyrolytic graphite, with thiophene ring units oriented parallel to the surface. The 6T monolayer nanostripe is an effective molecular nanotemplate for the assembly of an ordered “zigzag” C60 chain array, accompanied by a slight structural modification of the underlying 6T nanostripes due to donor-acceptor intermolecular interactions between 6T and C60 molecules. [ABSTRACT FROM AUTHOR]