Experimental observation of vibrational modes on Ag(111) along ΓM and ΓK

We present an off-specular high-resolution electron energy-loss spectroscopy study of the vibrational modes along the ΓM and ΓK directions in the surface Brillouin zone of clean Ag(111). We show experimental data of vibrational modes at the K̄ edge, thereby extending the earlier He-scattering data on the S1 Rayleigh mode and pseudo-Rayleigh mode. In addition, we observed the S3 gap mode and three high-frequency modes along ΓK. According to our knowledge, this is the first experimental evidence for the existence of these high-frequency modes in the (111) surface Brillouin zone of fcc metals. Along ΓM the experimental dataset of the S2 gap mode is extended to smaller Q//, and for the first time the high-frequency vibrational mode close to the top of the projected bulk phonon band is observed. The EELS data is analyzed by comparison to theoretical studies previously reported in the literature. This paper presents new experimental data of the surface vibrational structure, which can stimulate theoreticians to refine their modeling and improve the understanding of the Ag(111) surface lattice dynamics.</p

Work function dependent neutralization of low-energy noble gas ions

The work function dependence of the neutralization of low-energy He+, Ne+, and Ar+ ions was studied by determining the neutralization probability of ions scattered from submonolayer coverages of Ba on W(110) and Re(0001) substrates. At high work functions (&gt;3.5 eV), it was found that the dominant neutralization mechanism for noble gas ions with initial energy between 2 and 5 keV scattering from Ba is collision-induced neutralization. The neutralization probability for this mechanism was found to be insensitive to work function changes. We argue that collision-induced neutralization is also the dominant charge transfer process for scattering from other earth-alkali and alkali elements in this energy range, although at lower energies it is expected that Auger neutralization will become important. At work functions below roughly 3.5 eV, resonant neutralization to the first excited level of the noble gas ions occurs in addition to the charge transfer processes operating at high work functions. We show that the additional neutralization at low work functions can be described using resonant charge exchange theory. Due to resonant neutralization, the neutralization probability for noble gas ions increases exponentially with decreasing work function

Ordening &amp; oriëntatie van 4T: een studie naar de ordening en oriëntatie van organische moleculen op verschillende substraten, Si(100) en SiOx/Si(100)

No abstrac

Work function dependent neutralization of low-energy noble gas ions

The work function dependence of the neutralization of low-energy He+, Ne+, and Ar+ ions was studied by determining the neutralization probability of ions scattered from submonolayer coverages of Ba on W(110) and Re(0001) substrates. At high work functions (&gt;3.5 eV), it was found that the dominant neutralization mechanism for noble gas ions with initial energy between 2 and 5 keV scattering from Ba is collision-induced neutralization. The neutralization probability for this mechanism was found to be insensitive to work function changes. We argue that collision-induced neutralization is also the dominant charge transfer process for scattering from other earth-alkali and alkali elements in this energy range, although at lower energies it is expected that Auger neutralization will become important. At work functions below roughly 3.5 eV, resonant neutralization to the first excited level of the noble gas ions occurs in addition to the charge transfer processes operating at high work functions. We show that the additional neutralization at low work functions can be described using resonant charge exchange theory. Due to resonant neutralization, the neutralization probability for noble gas ions increases exponentially with decreasing work function

Crystal-face dependence of surface melting

FWN – Publicaties zonder aanstelling Universiteit Leide

LEIS studies op dendrimeren

No abstract

Influence of a partially oxidized calcium cathode on the performance of polymeric light emitting diodes

We investigated the influence of the presence of oxygen during the deposition of the calcium cathode on the structure and on the performance of polymeric light emitting diodes (pLEDs). The oxygen background pressure during deposition of the calcium cathode of polymeric LEDs was varied. Subsequently, the oxygen depth distribution was measured and correlated with the performance of the pLEDs. The devices have been fabricated in a recently built ultraclean setup. The polymer layers of the pLEDs have been spincoated in a dry nitrogen atmosphere and transported directly into an ultrahigh vacuum chamber where the metal electrodes have been deposited by evaporation. We used indium–tin–oxide as anode, OC1C10 PPV as electroluminescent polymer, calcium as cathode, and aluminum as protecting layer. We achieved reproducibility of about 15% in current and brightness for devices fabricated in an oxygen atmosphere o

Adsorptiepositie bepaling : bepaling van de adsorptiepositie van kalium op Fe(100)

No abstract

Polymeeroppervlakken : structuur en dynamica van polymeeroppervlakken en -grenslagen

No abstract

Preroughening, Diffusion, and Growth of An FCC(111) Surface

Preroughening of close-packed fcc(111) surfaces, found in rare gas solids, is an interesting, but poorly characterized phase transition. We introduce a restricted solid-on-solid model, named FCSOS, which describes it. Using mostly Monte Carlo, we study both statics, including critical behavior and scattering properties, and dynamics, including surface diffusion and growth. In antiphase scattering, it is shown that preroughening will generally show up at most as a dip. Surface growth is predicted to be continuous at preroughening, where surface self-diffusion should also drop. The physical mechanism leading to preroughening on rare gas surfaces is analysed, and identified in the step-step elastic repulsion.Comment: Revtex + uuencoded figures, to appear in Physical Review Letter