Didier Sébilleau

On the computation of the integrated products of three spherical harmonics

Gaunt coefficients, the integrated products of three spherical harmonics, are widely used in several branches of physics. Here, I review the most recent methods to calculate them efficiently (i.e. with an extensive use of their symmetry properties) and propose a new one which is faster and remarkably stable in terms of accuracy in the range of energies generally encountered in electron spectroscopies.

MSPHD: A full multiple scattering code for low energy photoelectron diffraction

We describe a Full Multiple Scattering (MS) code for the calculation of photoelectron diffraction (PD) patterns from solid surfaces. The use of a complex potential allows the calculation of complex phase shifts which describe realistically the damping of the electronic wave during its path to the detector. Full convergence in the scattering path expansion due to the inversion of the multiple scattering matrix makes this method particularly reliable in the surface sensitive energy range of the photoelectron, where approximate solutions in terms of series expansion and/or real potential calculations lead to inaccuracies in the determination of structural parameters. In this form the code is suitable to applications to clean surfaces such as Surface Core Level Shift Photoelectron Diffraction (SCLS-PD).

Angle-resolved x-ray photoemission study of GaAs(001) surfaces

Angle-resolved X-ray photoelectron spectroscopy (XPS) has been used to characterise chemically etched GaAs(001) versus epitaxially grown surfaces. The measured amplitude of X-ray photoelectron diffraction (XPD) modulation is then an excellent probe of the local structural environment around the emitter atom in the near-surface substrate. The observed modulations are here compared to the results of single- and double-scattering cluster calculations with a fine agreement. Moreover, because of our choice of the emission plane and taking into account the similarity in the scattering factors of Ga and As atoms, XPD effects can be almost eliminated from the angular variation of the fractional peak ratio IAs(IAs + IGa) which is then easily related to the arsenic concentration profile CAs(z). A best-fitting procedure is used to select the experimental concentration depth profile which characterises the surface under study. Samples exposed to different technological treatments, like ion implantation, chemical etching and annealing have been studied and compared. The concentrations of As atoms at the surface for As-capped, MBE-grown (001) samples after annealing around 350°C and for chemically etched GaAs(001) wafers indicate the same type of surface (As-terminated) as far as composition and structure are concerned.

Multiple-scattering approach with complex potential in the interpretation of electron and photon spectroscopies

We present a unitary cluster approach to the calculation of several electron and photon spectroscopies, ranging from core and valence level photoelectron diffraction and absorption to electron, Auger and anomalous diffraction. Electron energy loss and Auger–photoelectron coincidence spectroscopies can also be treated in the same frame. This approach is based on multiple-scattering theory with a complex optical potential of the Hedin–Lundqvist type and is valid for all electron kinetic energies. Similarities and differences between these diffraction techniques are examined and cluster size convergence is discussed in connection with the electron mean free path. Applications to selected problems ar ep resented to illustrate the method, both for structural and electronic analysis.

Multiple scattering theory for non-local and multichannel potentials

Methodological advances in multiple scattering theory (MST) in both wave and Greens function versions are reported for the calculation of electronic ground and excited state properties of condensed matter systems with an emphasis on core-level photoemission and absorption spectra. Full-potential MST is reviewed and extended to non-local potentials. Multichannel MST is reformulated in terms of the multichannel density matrix whereby strong electron correlation of atomic multiplet type can be accounted for in both ground and excited states.

X-RAY PHOTOELECTRON DIFFRACTION STUDY OF YBAS/GAAS(001) AND SCAS/GAAS(001)HETEROSTRUCTURES

Polar angle distributions of core level photoemission intensities recorded on YbAs/GaAs(001) and ScAs/GaAs(001) heterostructures are presented. They allow first the surface roughness of thin YbAs overlayers to be seen, second to estimate the tetragonal distortion of a strained ScAs film and, third, the most interesting point, to demonstrate in a direct fashion that the mixed (Yb‐As) (010) planes of YbAs grow in the prolongation of the As planes of GaAs. The results are compared to those obtained by other authors with various techniques. The main advantage of the photoelectron diffraction method over the other techniques is that it can be performed on very thin epitaxial films (some monolayers) directly in situ under ultrahigh vacuum.

Layer-resolved study of Mg atom incorporation at the MgO/Ag(001) buried interface.

By combining x-ray excited Auger electron diffraction experiments and multiple scattering calculations we reveal a layer-resolved shift for the Mg KL23L23 Auger transition in MgO ultrathin films (4-6 Å) on Ag(001). This resolution is exploited to demonstrate the possibility of controlling Mg atom incorporation at the MgO/Ag(001) interface by exposing the MgO films to a Mg flux. A substantial reduction of the MgO/Ag(001) work function is observed during the exposition phase and reflects both band-offset variations at the interface and band bending effects in the oxide film.

Epitaxial Fe-Ge thin films on Ge(111): Morphology, structure, and magnetic properties versus stoichiometry

We have studied the growth and magnetic properties of thin Fe-Ge films synthesized (codeposited at room temperature and postannealed at

Formation of a body-centered-cubic Fe-based alloy at the Fe/GaAs(001) interface

250\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}

Induced work function changes at Mg-doped MgO/Ag(001) interfaces: Combined Auger electron diffraction and density functional study

) on Ge(111) wafers versus stoichiometry. Morphology and crystal structure have been investigated in situ by means of scanning tunneling microscopy, low-energy electron diffraction, and x-ray photoelectron diffraction and ex situ with x-ray diffraction. The magnetic properties were characterized ex situ by conventional polar and longitudinal magneto-optical Kerr effect and transverse biased initial inverse susceptibility and torque measurements. It is found that the growth is epitaxial for Ge content up to