Intramolecular Hgπ interactions of d-character with non-bridging atoms in mercury-aryl complexes.

Mercury 5d-orbitals are involved in intramolecular π-interactions with carbon and sulfur nearest and next-nearest neighbors in mercury-aryl complexes. This unexpected character of the electron cloud of mercury was revealed by high energy-resolution XANES spectroscopy readily interpreted in terms of a final-state local (l,m)-projected density of states (DOS).

Electronic structure and local distortions in epitaxial ScGaN films.

High energy resolution fluorescence-detected x-ray absorption spectroscopy and density functional theory calculations were used to investigate the local bonding and electronic structure of Sc in epitaxial wurtzite-structure ScxGa1-xN films with x ≤ 0.059. Sc atoms are found to substitute for Ga atoms, accompanied by a local distortion involving an increase in the internal lattice parameter u around the Sc atoms. The local bonding and electronic structure at Sc are not affected strongly by the strain state or the defect microstructure of the films. These data are consistent with theoretical predictions regarding the electronic structure of dilute Sc(x)Ga(1-x)N alloys.

Setup for optimized grazing incidence x-ray absorption experiments on thin films on substrates.

We present a state-of-the-art experimental apparatus and a proper setup to perform x-ray absorption spectroscopy (XAS) experiments in grazing incidence mode. This geometry is appropriate for doped thin films or interfaces buried at moderate depth in a thick matrix, whenever the scattering and/or fluorescence from the matrix has to be strongly attenuated. Both the calculation and the experimental data demonstrate that the specific setup that consists in a grazing incidence and grazing collection geometry is extremely advantageous. In fact, with respect to the standard geometry used to perform XAS experiments in fluorescence mode, the present setup allows an enhancement in the interesting fluorescence signal from the surface layer without a corresponding increase in the elastic scattering contribution from the matrix. The sample holder especially designed for this kind of experiment can work in vacuum and at low temperature. An easy and quick automatic sample alignment procedure is detailed.

A new procedure for the quantitative analysis of extended x-ray absorption fine structure data in total reflection geometry.

A novel code for the analysis of extended x-ray absorption fine structure (EXAFS) data collected in total reflection mode (reflEXAFS) is presented. The procedure calculates the theoretical fine structure signals appearing in the reflectivity spectrum starting from the ab initio EXAFS calculations. These signals are then used in complex structural refinement (i.e., also including multiple scattering paths) with usual fitting programs of EXAFS data. A test case consisting in the analysis of a gold film collected at different incidence angles is presented in detail.

Controlled aggregation of magnetic ions in a semiconductor: an experimental demonstration.

The control on the distribution of magnetic ions into a semiconducting host is crucial for the functionality of magnetically doped semiconductors. Through a structural analysis at the nanoscale, we give experimental evidence that the aggregation of Fe ions in (Ga,Fe)N and consequently the magnetic response of the material are affected by the growth rate and doping with shallow impurities.