XPS DOS Studies of Oxygen-Plasma Treated YBa\u3csub\u3e2\u3c/sub\u3eCu\u3csub\u3e3\u3c/sub\u3eO\u3csub\u3e7-δ\u3c/sub\u3e Surfaces as a Function of Temperature

Monochromatized Alkα XPS has been used to monitor changes in the electronic structure of 123 sintered pellets as a function of temperature (90-650K). Since 123 surfaces are known to lose oxygen and react with water, a novel procedure was used to prepare the material surface that would be representative of the bulk material. In contrast with published results, we observed drastic DOS modification (i.e. the appearance of a new peak close to the Fermi level at low temperature)

Electron-Induced Vibrational Spectroscopy. A New and Unique Tool To Unravel the Molecular Structure of Polymer Surfaces

Among the surface-sensitive spectroscopies used to characterize clean and surface-modified polymers, one technique has rather recently emerged as a very promising complementary tool. High-resolution electron energy loss spectroscopy, or electron-induced vibrational spectroscopy, has potentially all the attributes of the well-known optical (infrared and Raman) spectroscopies; it clearly adds to X-ray photoelectron spectroscopy the possibility to go beyond surface elemental and chemical analysis and to unravel the molecular structure of an extremely thin surface layer of a polymer. This ultrahigh vacuum spectroscopy is shown here to gather information from the last 25 angstrom or so of the polymer surface, as deduced from the analysis of sandwich layers of normal and perdeuterated PMMA Langmuir-Blodgett films. Four case studies of molecular-type information are presented, illustrating (1) the preferential surface segregation of CH3 chain ends on a crystalline polyethylene, (2) selective surface segregation and dynamics of deuterated material in mixtures of normal and deuterated polystyrenes, (3) tacticity induced molecular orientation of PMMA's and polystyrene, and (4) metalization induced molecular reorientation on the surface of polyimide films.</p

Croissance et caractérisation d'interfaces de fullerènes sur substrats métalliques et semiconducteurs

This paper gives an overview of the changes in the structural, electronic and vibrational properties of C60 brought upon by its interaction with a semiconductor or a metal surface. The focus is on ordered monolayers for which general trends in adsorption geometry are illustrated. Direct and inverse photoemission results show that the molecule is polarised when it is physisorbed on the lamellar semiconductor GeS and demonstrate an important hybridisation of both the occupied and the unoccupied molecular orbitals with substrate electronic states for C60 chemisoption on metals, with or without charge transfer to the C60. Vibrational spectroscopy data reveal the consequences of the symmetry breaking at the interfaceas well as mode specific shifts and intensity variations when charge is transferred to the fullerene, which are discussed in association with electron-phonon coupling effects.

Croissance et caractérisation d'interfaces de fullerènes sur substrats métalliques et semiconducteurs

Cet article présente les changements des propriétés structurelles, électroniques et vibrationnelles du C60 induits par son interaction avec un substrat semiconducteur ou métallique. La structure de la première couche de fullerène dépend essentiellement de l'accord entre les paramètres réticulaires du C60 et du substrat, ainsi que de la réactivité du substrat et de sa tendance à la reconstruction. L'influence de chacun de ses facteurs sur la géométrie d'interface est illustrée. Les mesures de photoémission directe et inverse montrent une polarisation de la molécule de C60 lorsqu'elle est physisorbée sur un semiconducteur lamellaire, le GeS. Pour le C60 chimisorbé sur des substrats métalliques, avec ou sans transfert de charge, ces mesures révèlent, par contre, une hybridation importante des orbitales moléculaires occupées et inoccupées avec les états du métal. La spectroscopie vibrationnelle de ces interfaces met en évidence les conséquences de la rupture de symétrie à l'interface, ainsi que des effets de couplage électron-phonon quand existe un transfert de charge du substrat vers la molécule.This paper gives an overview of the changes in the structural, electronic and vibrational properties of C60 brought upon by its interaction with a semiconductor or a metal surface. The focus is on ordered monolayers for which general trends in adsorption geometry are illustrated. Direct and inverse photoemission results show that the molecule is polarised when it is physisorbed on the lamellar semiconductor GeS and demonstrate an important hybridisation of both the occupied and the unoccupied molecular orbitals with substrate electronic states for C60 chemisoption on metals, with or without charge transfer to the C60. Vibrational spectroscopy data reveal the consequences of the symmetry breaking at the interface as well as mode specific shifts and intensity variations when charge is transferred to the fullerene, which are discussed in association with electron-phonon coupling effects