Photoemission measurements for N,N'-bis-(1-naphthyl)-N,N'-diphenyl-1, 1'-biphenyl-4, 4'-diamine (NPB) overlayer on Ag (111) are reported. The growth of NPB overlayer from submonolayer on the single-crystal surface of Ag (111), ultraviolet photoemission spectroscopy (UPS) and x-ray photoemission spectroscopy (XPS) measurements at each growth step allowed a better determination of band bending and interface dipole related change in work function. The XPS measurements show a weak interaction between NPB and Ag (111) and the C 1s core level shift provides a measurement of the band bending occurring with the NPB overlayer. UPS measurements show a decrease in work function with increasing thickness of NPB overlayer. The dipole contribution to the work function as a function of NPB thickness is deduced by subtracting the band bending from the change in work function. The dipole contribution has a minimum at a NPB thickness of about a monolayer. The decrease of work function is attributed to both the band bending occurring within NPB overlayer and dipole layer formed due to surface polarization. Additionally, the top of the highest occupied molecular orbital of NPB is located at about 1.7meV below Fermi level.

A densely packed 1×1-O overlayer with an oxygen coverage of 1.0 (relative to the number of substrate surface atoms) was prepared on Ru (0001) by sequential dissociation of O2 and NO2 and studied by means of high-resolution electron-energy-loss spectroscopy. Two dipole-active modes were observed at 81 and 7.3meV due to a v⊥(Ru-O) stretch mode and a new surface mode, respectively. The value of v⊥(Ru-O) is shifted to higher energy compared to that for the known 2×2-O and 2×1-O adlayers at smaller oxygen coverages. These measurements indicate that the O2 dissociation is kinetically hindered for oxygen coverages larger than 0.5.

We report a high-resolution electron-energy-loss spectroscopy study of the coverage dependence of the Cs-Ru stretch vibration at 300K. Surprisingly, the frequency of Cs-Ru stretch vibration shifts upward by about 30% with Cs coverage for 0≤θCs≤0.19. Only a quarter of this shift can be explained through lateral dipoledipole interaction. We discuss two further mechanisms that may cause the other part of the shift. A slight decrease of the stretch frequency for θCs>0.19 is associated with the metallization of the alkali-metal layer including a structural change.

The interaction of Cs and CO was studied for submonolayer coverages of Cs on Ru (0001) by means of high-resolution electron energy-loss spectroscopy (HREELS), thermal desorption spectroscopy (TDS), and low-energy electron diffraction (LEED). From the HREEL spectra and the 2×2 LEED pattern it is concluded that two-dimensional islands of Cs+2CO stoichiometry are formed first. For high CO doses CO adsorbs on the bare Ru surface between the islands as concluded from the v(C-O) stretch-mode frequency and the (√3×√3)R30℃ LEED pattern. Besides some local interaction between CO and Cs, there is strong evidence found for a long range, through substrate interaction. Our data can be understood in terms of a charge redistribution model; Cs donates a given amount of charge to the surface which is then backdonated to and shared between the adsorbed CO molecules within the (Cs+2CO)-islands and outside of them on the bare surface. The desorption temperature of CO with θCO→0 increases nearly linearly with θCs indicating CO desorption out of a two dimensional Cs gas in which the lateral interaction increases with θCs .

On a Ru (0001) surface Cs and CO form a very well ordered (Cs+CO)-(2×2) compound layer whose structure was analyzed recently (Cs on-top, CO in threefold sites). Here we present a vibrational analysis of the same system using high-resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy (TDS), and low-energy electron diffraction (LEED). The bonding of CO to Ru is both local and nonlocal. Two (C-O) stretch frequencies are observed depending on whether there are one or two CO molecules in the 2×2 cell. They change in energy between 155 and 204meV depending on CO coverage θCO. Setting θmax CO=1.0, the evolution of the C-O stretch intensities indicates that up to θCO=0.22 the 1-CO-(2×2) phase is formed exclusively implying some mobility of the Cs layer. For θCO.0.22 the 2-CO-(2×2) phase grows additionally until at θCO=1.0 only the 2-CO-(2×2) phase is found. Two Ru-CO stretch modes are observed for the first time and are assigned to adsorption in the hcp and fcc hollow sites within the 2×2 unit cell. They are very weak in intensity which is attributed to the threefold-hollow site and some screening in the 2D compound. With CO adsorption a change of the electronic structure of the Cs adlayer is observed; the adlayer loses metallicity and the Cs-Ru stretch becomes visible. Strong changes of the Cs-Ru stretch energies are observed with CO coverage.

High-resolution electron-energy-loss spectroscopy (HREELS) showed that the dominant feature in the HREELS spectrum of the 'as-received' ITO was the loss peaks associated with the CHx group. Oxygen-plasma treatment of ITO led to the disappearance of the CHx loss peaks, and a concomitant increase in the intensity of the phonon peaks at 71 and 134meV. The result indicates the removal of the CHx group and additional oxidation of the ITO surface by the oxygen-plasma treatment. Both processes are proposed to be responsible for the increase in work function of ITO by the oxygen-plasma treatment.

Thin film growth of tetracene on Ag (110) has been investigated by using scanning tunneling microscopy (STM). In the monolayer regime, the tetracene molecules formed islands of ordered structure, which is commensurate (4-fold periodicity) in the [110] direction, but incommensurate in the [001] azimuth, with the substrate. All the tetracene molecules align regularly with their longer axes parallel to the [001] direction, and with their molecular planes parallel to the surface. At multilayer coverages, the tetracene molecules form a crystalline film in a novel 3D orthorhombic structure, with their orientations remained unchanged. Growth of tetracene on Ag (110) is in the layer-by-layer growth mode.

Interface studies of tris-(8-hydroxyquinoline) aluminum (Alq3)/LiF/Al were carried out with high-resolution electron-energy-loss spectroscopy. With LiF on Alq3 or Al on LiF, no significant changes in intensity were observed for the loss peak related to the Li-F stretch mode. However, the deposition of less than one monolayer of Al on Alq3/LiF resulted in a strong attenuation of the LiF-loss peak, providing a direct evidence of LiF dissociation in the coexistence of Alq3 and Al with LiF. On the other hand, the LiF-loss peak remained almost unchanged when Al was deposited on poly (9,9-dioctyl-fluorene)/LiF.

High-resolution electron-energy-loss spectroscopy (HREELS) and ultraviolet photoemission (UPS) measurements of the interface of phenyl diamine (NPB) and indium tin oxide (ITO) were performed. The HREELS spectrum of the oxygen-plasma-treated ITO was characterized by dipolar-active-phonon modes at 71 and 134meV. Upon deposition of NPB on ITO, the HREELS loss peaks of ITO gradually diminished, while the NPB-derived loss peaks appeared. The negligible energy shifts of the NPB peaks with NPB thickness suggested a rather weak interaction between NPB and ITO. The remarkable intensity change of the loss band at 71-65meV gave evidence for a strong vibrational coupling between the ITO phonon mode at 71meV and the NPB-derived vibrational mode at 65meV. Annealing of the NPB/ITO interface with 20

The interaction between magnesium (Mg) and tris(8-hydroxy-quinoline) aluminum (Alq3) has been studied using high-resolution electron energy-loss spectroscopy (HREELS). It was found that deposition of magnesium on the Alq3 film gave rise to clear changes in the HREELS spectra. The changes are attributed to the weakly bounded Mg atoms on the Alq3 layer. Interestingly, for a given amount of magnesium (Mg to Al atoms ratio=3) on Alq3 film, remarkable changes were observed in the HREELS spectra when the sample was heated. A loss peak at 81meV, which was assigned to Mg-O stretch mode, appeared upon annealing and increased in intensity as the annealing temperature increased up to about 360K. This suggested that the diffusion of Mg atoms into the Alq3 layer and the reaction between Mg and Alq3 molecule occurred at the temperature range investigated. The present work has provided direct evidence for the strong interaction between magnesium and Alq3.