RESUMEN
The spin features of surface resonance bands in single layer Bi on Ge(1 1 1) are studied by means of spin- and angle-resolved photoemission spectroscopy and inverse photoemission spectroscopy. We characterize the occupied and empty surface states of Ge(1 1 1) and show that the deposition of one monolayer of Bi on Ge(1 1 1) leads to the appearance of spin-polarized surface resonance bands. In particular, the C 3v symmetry, which Bi adatoms adopt on Ge(1 1 1), allows for the presence of Rashba-like occupied and unoccupied electronic states around the [Formula: see text] point of the Bi surface Brillouin zone with a giant spin-orbit constant [Formula: see text] eV · Å.
RESUMEN
We investigated the room temperature oxidation of ultra-thin Ni and Cr films grown on Fe(0 0 1). In particular, we characterized the degree of crystallinity and the stoichiometry of the oxide layers and addressed the chemical stability of the interface with the highly reactive Fe substrate by means of low-energy electron diffraction and x-ray and UV photoemission spectroscopy. In the Ni case we detected, upon oxidation, the formation of a Fe(3)O(4) layer covering the Ni oxide, due to the diffusion of Fe cations towards the surface. At high temperature and in ultra-high vacuum conditions, the Ni oxide dissolved and the Fe oxide layer was reduced to FeO. In the Cr case, we observed the formation of a thin Cr(2)O(3) oxide layer, showing a diffraction pattern compatible with a defective γ-Cr(2)O(3) phase. A thicker Cr oxide layer could be produced by oxidizing the sample at 300 °C, at the expense of the incorporation of trace amounts of Fe cations.
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We present a versatile apparatus for the study of ferromagnetic surfaces, which combines spin-polarized photoemission and inverse photoemission spectroscopies. Samples can be grown by molecular beam epitaxy and analyzed in situ. Spin-resolved photoemission spectroscopy analysis is done with a hemispherical electron analyzer coupled to a 25 kV-Mott detector. Inverse photoemission spectroscopy experiments are performed with GaAs crystals as spin-polarized electron sources and a UV bandpass photon detector. As an example, measurements on the oxygen passivated Fe(100)-p(1×1)O surface are presented.
RESUMEN
In polymer-metal oxide hybrid solar cells, an extremely careful engineering of the interface is required to ensure good device performances. Recently, very promising results have been obtained by functionalizing titanium dioxide (TiO2) by means of 4-mercaptopyridine (4-MPy) molecules, showing the beneficial effect of these molecules on the interface morphology. This study investigates the nature of the interaction of 4-MPy molecules with the TiO2 surface by means of X-ray photoemission spectroscopy. In order to mimic the device processing conditions, our analysis is carried out on molecules adsorbed from solution on a nanocrystalline surface. According to our analysis, 4-MPy molecules (C5H5NS) are likely bound with the oxide through the nitrogen atom. The bonding precedes either via a covalent interaction with Lewis surface sites, or via hydrogen mediation, possibly in the form of hydrogen bonds. Interestingly, in the latter case, we also observe strong changes in the spectroscopic features attributed to the thiol group.
Asunto(s)
Piridinas/química , Titanio/química , Adsorción , Cristalización , Espectroscopía de Fotoelectrones , Propiedades de SuperficieRESUMEN
The potential of positron annihilation spectroscopy (PAS) for defect characterization at the atomic scale in semiconductors has been demonstrated in thin multilayer structures of SiGe (50 nm) grown on UTB (ultra-thin body) SOI (silicon-on-insulator). A slow positron beam was used to probe the defect profile. The SiO(2)/Si interface in the UTB-SOI was well characterized, and a good estimation of its depth has been obtained. The chemical analysis indicates that the interface does not contain defects, but only strongly localized charged centers. In order to promote the relaxation, the samples have been submitted to a post-growth annealing treatment in vacuum. After this treatment, it was possible to observe the modifications of the defect structure of the relaxed film. Chemical analysis of the SiGe layers suggests a prevalent trapping site surrounded by germanium atoms, presumably Si vacancies associated with misfit dislocations and threading dislocations in the SiGe films.
Asunto(s)
Guarderías Infantiles , Brotes de Enfermedades , Intoxicación Alimentaria por Salmonella/epidemiología , Intoxicación Alimentaria por Salmonella/microbiología , Salmonella enteritidis/clasificación , Población Urbana , Preescolar , Brotes de Enfermedades/estadística & datos numéricos , Femenino , Genotipo , Humanos , Lactante , Italia/epidemiología , Masculino , Fenotipo , Reacción en Cadena de la Polimerasa , ARN Bacteriano/clasificación , ARN Ribosómico/clasificación , Salmonella enteritidis/genética , Salmonella enteritidis/aislamiento & purificación , Serotipificación , Población Urbana/estadística & datos numéricosRESUMEN
Tissue transglutaminase is a calcium-dependent enzyme which may influence cell morphology, cytoskeletal processes and membrane functions. During rat brain carcinogenesis induced by transplacental administration of N-ethyl-N-nitrosourea to BD IX rats, cytosolic tissue transglutaminase activity was increased by about 140% at 30 days of extrauterine life and returned towards the control values at 3-5 months. In the particulate fraction, enzyme activity progressively increased, reaching values similar to those present in the developed gliomas. Tissue transglutaminase activity in gliomas had a behavior inverse to that observed in controls, with a decrease (about 50%) in the cytosol and a marked increase (380%) in the particulate fraction, indicating a redistribution of enzyme activity.