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.