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ExperimentalMaterials: High-purity para-sexiphenyl (PSP) powder was purchased from TCI-GR Co., Japan. Further purification was performed by threefold sublimation at 280 C under a dynamical vacuum of 1´10 ±6 mbar. The substrate used was freshly cleaved (001)-oriented Muskovite mica.Growth of PSP: Thin films were grown in a HWE system, which has been used previously for the successful deposition of high-quality crystalline films of C 60 and Ba 6 C 60 [11,12]. In the growth chamber of the system a HWE reactor and a preheating/annealing oven were installed. The reactor consisted of two separately heated ovens for the wall and source zone, which could be kept at different suitable temperatures during growth. The quartz tube with the source material at the bottom was mounted inside the oven. The substrate was placed close to the tube end and could be heated separately. The hot wall zone between the substrate and the source guaranteed a nearly uniform and isotropic flux intensity and high kinetic energy of the molecules. The sample holder could be moved from the preheating oven to the HWE reactor and back using a computer-controlled step-motor. The vacuum during growth was about 6´10 ±6 mbar. All films were grown at a constant substrate and source temperature of 90 C and 240 C, respectively. The wall temperature was in the range of 240±260 C. These growth parameters resulted in a low deposition rate of about 2 nm/min, which gave nominally »120 nm thick films within the typical deposition time of one hour.AFM Measurements: The film morphology was investigated by AFM with a NanoScope IIIa (Digital Instruments, Santa Barbara, CA) operated in contact mode in air.XRD Measurements: The crystalline quality of the PSP films was investigated using a conventional X-ray diffractometer in coupled y/2y reflection mode using Cu Ka radiation.Optical Characterization: All measurements were performed at room temperature. Polarized absorption spectra were recorded with an UV-vis HP spectrophotometer at normal incidence. Polarized photoluminescence spectra were measured on a Hitachi F-4010 fluorescence spectrometer at normal incidence. Infrared reflection measurements were performed using a Bruker IFS-66 FTIR spectrometer.

We report on the experimental observation of STM-induced photon emission in ultrahigh vacuum on a network of 4-nm silver spheres. The spheres are covered by a dielectric, electrically insulating, organic layer and deposited on Au(111). The bias-dependent spatial distribution of the photon emission rates reveals the electric-field distribution of the different coupled plasmon modes in this model.

We have investigated the correlation between the change of the surface electronic properties ͑surface recombination velocity, surface barrier͒ and the change of the surface chemical bonds under annealing in ultrahigh vacuum of sulfide-passivated ͑001͒GaAs. The electronic properties of a ͑NH 4 ͒ 2 S-passivated surface were monitored using room-temperature photoreflectance, which gave the value of the surface barrier, and photoluminescence. The surface chemical bonds were probed by ͑i͒ reflectance anisotropy spectroscopy, which essentially monitors the optical transitions due to surface dimers, and ͑ii͒ core-level spectroscopy results on the same sample ͑companion paper in the same issue͒. We find that breaking of arsenic-related chemical bonds, which induces arsenic dimers on the surface, produces an increase of photoluminescence intensity ͑PLI͒. Conversely, a clear correlation is found between the desorption of sulfur due to breaking of Ga-S chemical bonds, the appearance of the gallium dimer line, and the decrease of PLI. Based on these results, we outline the dominant features of sulfide passivations: ͑i͒ The improvement of electronic properties of ͑001͒ GaAs arises due to formation of S-Ga bonds on the gallium-terminated part of the surface, ͑ii͒ electronic properties of the astreated surface are deteriorated by excess arsenic, which produces midgap levels, and ͑iii͒ the passivation efficiency can also be reduced by formation of additional surface defects due to etching of the surface in sulfide solutions.