Electron energy loss spectroscopy determination of Ti oxidation state at the (001) LaAlO3/SrTiO3 interface as a function of LaAlO3 growth conditions

At the (001) interface between the two band-insulators LaAlO3 and SrTiO3, a high-mobility electron gas may appear, which has been the object of numerous works over the last four years. Its origin is a subject of debate between the interface polarity and unintended doping. Here we use electron energy loss 'spectrum images', recorded in cross-section in a scanning transmission electron microscope, to analyse the Ti3+ ratio, characteristic of extra electrons. We find an interface concentration of Ti3+ that depends on growth conditions.Comment: 6 page

Comparison of the XPS spectra from homoepitaxial {111}, {100} and polycrystalline boron-doped diamond films

International audienceIn this work, we have used X-ray photoelectron spectroscopy (XPS) to investigate the nature of surface adsorbed species and their sensitivity to the boron concentration [B] in two sets of as-grown diamond films: homoepitaxial {111} and polycrystalline. These sets cover each one at least three of the four doping ranges: low doping (5 x 10(16)2 x 10(21) cm(-3)). The results are compared to those we have previously obtained on (100) homoepitaxial films in the same doping ranges. A detailed description of both the nature and the relative concentrations of the main surface chemical species on every set of films is reported. Besides the usual CHx bonds on the diamond surface, the following oxygen-related groups: Ether (C-O-C), hydroxyl (C-OH, only on polycrystalline films), carbonyl (>C=O) and carboxyl (HO-C=O) have been found on the surface of grown diamond films, upon spontaneous oxidation under air (no oxidation treatment has been applied). The evolution of each surface chemical group according to the boron concentration in the films is

Correlation between flat-band potential position and oxygenated termination nature on boron-doped diamond electrodes

International audienc

Applied Surface Science

p. 607–612In X-ray Photoelectron Spectroscopy (XPS), binding energies and intensities of core level peaks are commonly used for chemical analysis of solid surfaces, after subtraction of a background signal. This background due to photoelectron energy losses to electronic excitations in the solid (surface and bulk plasmon excitation, inter band transitions) contains valuable information related to the near surface dielectric function ε( ω). In this work, the sensitivity of Photoelectron Energy Loss Spectroscopy (PEELS) is investigated using a model system, namely the well-controlled surface reconstruction of diamond. Boron-doped microcrystalline thin films with a mixture of (1 1 1) and (1 0 0) preferential orientations were characterized in the as-grown state, with a partially hydrogenated surface, and after annealing at 1150 ◦C in ultra high vacuum. After annealing, the bulk ( + ) plasmon of diamond at 34.5 eV is weakly attenuated but no evidence for surface graphitization is observed near 6 eV, as confirmed by electronic properties. Unexpected features which appear at 10 ± 1 eV and 19 ± 1 eV in the energy loss distribution are well described by simulation of surface plasmon excitations in graphite-like materials; alternatively, they also coincide with experimental inter band transition losses in some graphene layers. This comparative study shows that the PEELS technique gives a clear signature of weak effects in the diamond surface reconstruction, even in the absence of graphitization. It confirms the sensitivity of PEELS acquisition with standard XPS equipment as a complementary tool for surface analysis.Salvado

Sensitivity of photoelectron energy loss spectroscopy to surface termination of amorphous carbon and diamond films

International audienc

Impact of PECVD SiON stoichiometry and post-annealing on the silicon surface passivation

International audienceHydrogenated silicon oxynitride (SiON) could be used in combination with silicon nitride (SiN) to create multi-layer antireflection coatings for silicon solar cells. It could also be used as a passivation layer, especially on the back side of the cell. This work deals with the passivation effect obtained on silicon surface by SiON layer deposited by Low Frequency Plasma Enhanced Chemical Vapour Deposition (LF-PECVD). SiON layers of different compositions have been deposited by varying the gas flow mixture (NH3, SiH4 and N2O) in the reactor. Infrared and X-ray photon-electron spectroscopy were made to determine the chemical structure of SiON layer. Minority carrier lifetimes were measured by the photoconductance decay method (PCD) before and after a rapid thermal anneal. Effective lifetime, measured on 5ohm.cm FZ-silicon wafers, can reach up to several hundreds microseconds, depending on the stoichiometry of the SiON layer. Low oxygen content samples (close to SiN layer) exhibit a good surface passivation of 250??s but after annealing, this value is critically reduced to 6??s. The opposite situation is observed for oxygen-rich layers: the effective lifetime increases from 10µs to 150µs. These behaviours could be partly explained by the composition of SiON, the evolution of the main peaks values of the FTIR spectra and the disappearance of Si-H bonds with anneal

Evolution of Surface Terminations and Electrochemical Behaviors of Boron Doped Diamond Electrodes Induced by Controlled Anodic and Cathodic Pretreatements

International audienc

Sensitivity of photoelectron energy loss spectroscopy to surface reconstruction of microcrystalline diamond films

AbstractIn X-ray Photoelectron Spectroscopy (XPS), binding energies and intensities of core level peaks are commonly used for chemical analysis of solid surfaces, after subtraction of a background signal. This background due to photoelectron energy losses to electronic excitations in the solid (surface and bulk plasmon excitation, inter band transitions) contains valuable information related to the near surface dielectric function ɛ(ħω). In this work, the sensitivity of Photoelectron Energy Loss Spectroscopy (PEELS) is investigated using a model system, namely the well-controlled surface reconstruction of diamond. Boron-doped microcrystalline thin films with a mixture of (111) and (100) preferential orientations were characterized in the as-grown state, with a partially hydrogenated surface, and after annealing at 1150°C in ultra high vacuum. After annealing, the bulk (σ+π) plasmon of diamond at 34.5eV is weakly attenuated but no evidence for surface graphitization is observed near 6eV, as confirmed by electronic properties. Unexpected features which appear at 10±1eV and 19±1eV in the energy loss distribution are well described by simulation of surface plasmon excitations in graphite-like materials; alternatively, they also coincide with experimental inter band transition losses in some graphene layers. This comparative study shows that the PEELS technique gives a clear signature of weak effects in the diamond surface reconstruction, even in the absence of graphitization. It confirms the sensitivity of PEELS acquisition with standard XPS equipment as a complementary tool for surface analysis