P.A. Thiry

Electron spectroscopic characterization of oxygen adsorption on gold surfaces: II. Production of gold oxide in oxygen DC reactive sputtering

Abstract Gold oxide is produced by oxygen DC reactive sputtering in a UHV compatible chamber. It is subsequently characterized by High Resolution Electron Energy Loss, Auger and X-ray Photoelectron Spectroscopies. It is demonstrated that the oxide is of the Au 2 O 3 type (auric oxide) and that it decomposes under thermal treatment. Au 2 O (aurous oxide) is a possible intermediate of this reduction.

STM study of a grain boundary in graphite

Abstract A grain boundary in highly oriented pyrolitic graphite has been investigated by scanning tunneling microscopy (STM). Along the boundary, a periodic structure has been observed. Crystallographic models have been constructed in order to explain the bonding between the two grains and STM theoretical simulations have been carried out. They conclude to the probable presence of pentagon–heptagon chains at the boundary.

Electron spectroscopic characterization of oxygen adsorption on gold surfaces

Tentative adsorption on clean gold (110) and (111) crystals of molecular oxygen in the pressure range 10 −10 to 10 −5 Torr, at a temperature varying between 100 and 800 K is reported together with the subsequent characterization of the surfaces by High Resolution Electron Energy Loss, Auger and X-ray Photoelectron Spectroscopies. It is found that oxygen does not adsorb in these UHV conditions, except when a contaminant is present on the surface. Such an interaction with a low level silicon impurity is described.

The aluminum–polyimide interface: An electron‐induced vibrational spectroscopy approach

Clean polyimide films spin‐coated onto gold substrate have been fully characterized by high resolution electron energy loss spectroscopy (HREELS): 19 electron‐induced vibrational bands could be resolved and assigned by comparison with IR spectroscopy. The attribution of these peaks constitutes a firm and necessary basis for the detailed study of the incipient interface formation with aluminum at room temperature. The metal being evaporated at a low rate from a Knudsen effusion cell, its equivalent coverage on the polymer could be monitored very efficiently and allowed a clear distinction between three reaction steps: (i) at an Al coverage below 4×1014 Al atom/cm2, the aluminum atoms interact only with the C–O carbonyl in the polymer to form a C–O–metal complex; (ii) between 4 and 10×1014 atom/cm2, no further Al ‘‘reaction’’ occurs, but the appearance of new CH and OH stretching bands is attributed to bond breaking in the polymer and diffusion of the residues towards the surface; (iii) after further metal ...

High resolution electron energy loss spectroscopy of an anisotropic insulator surface: A test for the dielectric theory

Electron energy loss measurements were performed on the α‐Al2O3(0001) surface at temperatures between 120 and 350 K. Spectra of the Fuchs–Kliewer phonons were recorded with high energy resolution (26 cm−1). Numerical fits revealed that the spectra are quantitatively described by the macroscopic dielectric theory for anisotropic crystals. Comparisons are made with infrared data.

Pumping picosecond optical parametric oscillators by a pulsed Nd:YAG laser mode locked using a nonlinear mirror

We report on the performances of the mode locking of a flash-lamp-pumped Nd:YAG laser using a frequency-doubling nonlinear mirror combined with a two-photon absorber. Pulse lengths from 12 to 8 ps are generated. We show that the flat shape of the pulse-train envelope generated by the oscillator is adapted for the synchronous pumping of optical parametric oscillators and we demonstrate the efficient generation of an infrared beam tunable from 3800 to 1100 cm−1 with bandwidth of 2 cm−1 in one single conversion stage in LiNbO3 or AgGaS2. The “all-solid-state” laser system enables surface sum-frequency generation spectroscopy to be performed with high sensitivity and high resolution.

Electron interaction mechanisms in high resolution electron energy loss spectroscopy

Three aspects of the interaction of a low energy electron beam with surface excitations are described. The long range dipolar scattering concentrates the inelastic electrons in a narrow lobe close to the specular reflection. The resulting spectra are quantitatively interpreted by the macroscopic dielectric theory in order to retrieve the infrared dielectric response of the target. Dipolar HREEL spectra of adsorbates obey the metal surface selection rule. Short range impact scattering disperses the inelastic electrons in a broad isotropic distribution. It allows the observation of short wavelength excitations and cancels the dipolar selection rule. Resonance scattering is a particular scattering mechanism which is observed for certain conditions of electron beam energy.

Study of the water/poly(ethylene glycol) interface by IR-visible sum-frequency generation spectroscopy

We used infrared-visible sum-frequency generation spectroscopy to investigate the vibrational properties of the water/poly(ethylene glycol) interface in the 2800–3800 cm−1 spectral range. The vibrational fingerprint of the interface differs significantly from the one associated with the air/poly(ethylene glycol) interface. It is shown that the poly(ethylene glycol) molecular arrangement, originally relatively well-ordered, becomes disorganised in the presence of water. Moreover, a new OH band is identified demonstrating the strong interaction of water with the polymer.

High resolution electron energy loss spectroscopy of epitaxial films of C60 grown on GaSe

Abstract The growth of thin C 60 films on GaSe(0001) has been studied by infrared High Resolution Electron Energy Loss Spectroscopy (HREELS) in specular reflection geometry. In contrast to previously studied disordered films on Si(100), it was found that deposition on a GaSe substrate heated to 120°C leads to well-ordered, epitaxial C 60 films. The structural order, manifested by a sharp LEED pattern, was confirmed by the clear detection in the specular beam of all four T lu dipole-active vibrations of the C 60 molecule. Several other infrared inactive modes, which were prominent in the C 60 /Si HREELS spectrum, are still seen in C 60 /GaSe but with reduced intensities. Application of the dielectric theory of reflection EELS allows a quantitative determination of the contribution of the dipole-active modes to the total spectrum. Although the relative oscillator strengths of the four infrared modes are in good agreement with optical absorption measurements, their absolute values, as determined by theoretical simulation, are found to be three times larger than the optical results.

C60 growth on Si(100), GaSe(0001) and GeS(001)

C60 films have been grown in ultra high vacuum on various crystalline substrates and the structure of the films has been investigated by low energy electron diffraction (LEED) and high resolution electron energy loss spectroscopy (HREELS). The C60 films form randomly oriented nanocrystals on Si(100), mesoscopic polycrystals on GaSe(0001) and microscopic single crystals on GeS(001). The vibrational structure of the C60/substrate interfaces is analyzed in detail by HREELS carried out in the dipole and impact scattering regimes. It is shown that the epitaxy of C60 on GeS(001) is induced by the weak van der Waals bonding and the peculiar corrugation of the substrate surface.