Edoardo Busetto

Recording of x-ray holograms on a position-sensitive detector

An unconventional x-ray fluorescence holography experiment was carried out by using an area detector in combination with an absorption filter. The high angular resolution and the very precise detection of intensities allowed the reconstruction of images of distant, as well as light, atoms. The simultaneous recording of the full hologram opens the possibility of one-shot imaging at atomic resolution. The hologram of a CoO single crystal was recorded on the imaging plate and the images of atoms located up to more than 7 A far from the emitter were obtained.

Location of Mn sites in ferromagnetic Ga1-xMnxAs studied by means of X-ray diffuse scattering holography

A three-dimensional image of the local neighbourhood of Mn atoms in a Ga 1-x Mn x As (x = 0.02) layer has been obtained by using X-ray diffuse scattering holography. The first and second nearest neighbours of the Mn atoms correspond to the local structure around Ga atoms in the zinc-blende GaAs structure. Accordingly, the Mn atoms are situated in substitutional positions.

Imaging of interstitial atoms in Ga1−xMnxAs layers by means of X-ray diffuse scattering

The local atomic structure of a Ga1−xMnxAs (x = 0.07) layer during the annealing process was studied by means of X-ray diffuse scattering. The difference between the pair-distribution functions before and after annealing indicated the fraction of atoms that changed concentration and identified them to be exclusively interstitial atoms at the centres of gallium and/or arsenic tetrahedra in the GaMnAs unit cell.

X-ray diffuse scattering holography of a centrosymmetric sample

The hologram based on the measurement of anomalous x-ray diffuse scattering is presented for the first time. The experiment was carried out using a rubidium chloride single crystal and anomalous scattering from Rb atoms close to the rubidium K-absorption edge. Holographic oscillations of a few percent of a total detected signal were achieved by choosing a suitable pair of photon energies. The real-space images of nearest neighbors of rubidium atoms were obtained using the standard Helmholz–Kirchhoff reconstruction algorithm.

Multi-energy anomalous diffuse scattering

A new approach to local structure determination is presented. A three-dimensional region of the reciprocal space of a SrTiO(3) single crystal was mapped by measuring x-ray diffuse scattering patterns at different sample orientations in order to reconstruct the local atomic structure. The phase problem was solved by means of anomalous scattering from strontium atoms at photon energies near their K absorption edge. Real-space reconstruction provides the average short-range order atomic arrangement in the vicinity of anomalous scatterers up to a distance of several unit cells.