M. Sancrotti

Ultraviolet inverse photoemission spectrograph with parallel multichannel isochromat acquisition

A simple and cost effective inverse photoemission spectrograph based on a spherical grating with very large optical acceptance ( f/2.8) is described. The system works in the 10–25 eV photon energy range. The dispersed photons are detected by a detector assembly based on a microchannelplate and consisting of twelve independent channels. Measurements are taken in the isochromat mode by sweeping the impinging electron energy, and the acquisition of the twelve channels is done in parallel. As an example of the apparatus performances data on polycrystalline Pt are presented.

The localisation of 3d hole states in Fe and FeAl studied by Auger vacancy satellite spectroscopy

Abstract For Ni, Cu and Zn the occurrence of the L2L3M4,5 Coster-Kronig transitions give rise to L3M4,5-M4,5M4,5 Auger vacancy satellite transitions to low kinetic energy of the main L3M4,5M4,5 transitions. In pure Fe the intensity of the Auger vacancy satellites are negligibly small even though L2L3M4,5 Coster-Kronig occur, a fact which has been attributed to the delocalisation of the M4,5 (3d) hole state within the lifetime of the L3 hole. In this work we present Auger spectra for Fe and FeAl excited using radiation obtained on station 5U.1 of the Daresbury synchrotron. Our spectra support earlier work regarding the relative lifetime of the L3 and M4,5 hole state in Fe though our spectra are different in detail. We also show that the Fe 3d hole is significantly more localised in FeAl than in Fe.

Time-dependent evolution of thin TiN films prepared by ion beam assisted deposition

Thin titanium nitride (TiN) films have been prepared by simultaneous Ti evaporation and 30 keV N2+ implantation onto Si(100) wafers, in the presence of a N2 partial atmosphere. A systematic chemical and compositional evaluation of the films has been performed by Auger electron spectroscopy and x-ray photoemission spectroscopy checking the homogeneity level, the degree of gaseous contamination, the different compounds formed by titanium and nitrogen, and their depth distribution. The Rayleigh velocity at various angles of incidence has been determined via Brillouin scattering measurements. The evidence of a Sezawa mode confined in the overlayer was also found. The films, which consist of a homogeneous outer layer above a relatively wide interface region with the substrate, show aging effects. On a mesoscopic scale, the film structure appears porous.

Photoemission and photoabsorption study of the high-temperature phases of the Ge(111) surface

Abstract The Ge(111) surface has been studied by photoemission and photoabsorption spectroscopies as a function of temperature up to 1200 K. Up to 1020 K the data indicate the presence of an adatom-restatom reconstruction, with a gradual weak metallization of the surface between 600 and 1020 K. Evidence for a high-temperature phase transition is found between 1020 and 1085 K from core-level spectroscopy. Valence-band photoemission spectra and photoabsorption data indicate a metallic surface layer above this phase transition. About 0.7–1 atomic bilayer is estimated to undergo the semiconductor to metal transition. All these data can be interpreted consistently with an incomplete surface-melting scenario.

Cluster-assembled carbon films with different nanostructures: a spectroscopic study

Abstract Carbon thin films with different nanostructures grown by Cluster Beam Deposition are studied by means of Raman Spectroscopy, X-ray photoemission spectroscopy (XPS), and electron energy loss spectroscopy (EELS). Raman and EELS of the as-grown specimens show a correlation between the properties of the free carbon clusters and the properties of the films obtained by deposition of different sized clusters. In contrast, the inhomogeneous character of the films is not reflected in the valence band states as seen by XPS.

Molecular gap and energy level diagram for pentacene adsorbed on filled d-band metal surfaces

The authors present a combined photoemission and scanning-tunneling spectroscopy study of the filled electronic states, the molecular energy gap, and the energy level diagram of highly ordered arrays of pentacene deposited on the Cu(119) vicinal surface. The states localized at the interface are clearly singled out, comparing the results at different pentacene thicknesses and with gas-phase photoemission data. The molecular gap of 2.35eV, the hole injection barrier of 1.05eV, and the electron injection barrier of 1.30eV determine the energy level diagram of the states localized at the pentacene molecules.

Electronic structure of K doped C60 monolayers on Ag(001)

Abstract The doping of a C60/Ag(100) interface with K is studied by high resolution valence band photoemission spectroscopy. With increasing potassium exposure the progressive filling of the C60 lowest unoccupied molecular orbital (LUMO) derived band is observed. The charge transfer onto the C60 molecules is quantified from the observed binding energies of the LUMO derived band. Up to a half filled LUMO no rigid band shift is found. Furthermore the intensity of the highest occupied molecular orbital is not constant but shows in normal emission a pronounced dip between half and complete LUMO filling.

Covalency in the electronic structure of Fe3O4: An ultraviolet inverse photoemission investigation

The unoccupied electronic structure of an opend-shell transition metal oxide, namely Fe3O4, has been addressed by measuring ultraviolet angle-integrated inverse photoemission (IP) spectra acquired in the isochromat mode (hv=10.2-24 eV). Exploitation of photon energy dependence of symmetry-projected IP cross-sections and comparison with the O 1s X-ray absorption spectrum allow us to recognize a strong covalent admixture of Fe [3d; 4 (sp)]-and O (2p)-derived states in this compound.

High resolution photoemission study of C60 on Si(111) as a precursor of SiC growth

We characterized the room temperature (RT) growth of C 60 on the Si(111) (7 ×7) surface and the SiC formation upon annealing using high resolution photoelectron spectroscopy techniques. Si 2p core level spectra for RT C 60 deposition unambiguously show the strong attenuation of the rest-atoms components and the growth of at least one new component at I ML coverage. This new component grows with annealing temperature and at T > 1020 K an abrupt change occurs, corresponding to the formation of SiC, as confirmed by the C Is core level emission.

The empty electron-states in MoS2: an inverse photoemission spectroscopy investigation

k-integrated Bremsstrahlung isochromat spectra, collected at different UV-photon energies (hv=13.2−24 eV), from 2H-MoS2 are presented. Two structures (energy separation=1.2 eV) of d-character are resolved close to the Fermi level. A third broad spectral feature appears at higher energy values and is assigned to hybridised metal-cation sp derived states. The results are compared to different electron-states calculations and are found to give support to the theoretical predictions derived within a LCAO scheme.