Highly brilliant X-rays are essential for many of the powerful techniques that allow the routine study of surfaces and interfaces. While the pioneering work in surface diffraction was focussed on clean surfaces under ultra-high vacuum conditions, buried surfaces have gained interest in more recent work, mainly due to the fact that such interfaces are closer to those in real applications. Nonetheless, the classical technique of crystal truncation rod analysis can still be exploited for buried interfaces as well as for fluorescence analysis during standing wave excitation. The ideal methods for studying complex near-surface structures involve scattering techniques at grazing incidence and exit angles. These techniques, grazing-incidence diffraction (GID) and grazing-incidence small-angle scattering (GISAXS), have been developed by several groups taking advantage of the high brilliance of the ESRF's X-rays. Since a wide range of length scales can be studied, from the atomic to the micrometre scale, both parallel and perpendicular to the interfaces, these techniques are ideally suited to the characterisation of samples relevant for future developments in nano-technology.

There are several beamlines at the ESRF where such experiments can be performed. The newly formed ESRF group "Surface and Interface Science", constituted by the beamlines ID1, ID3 and ID32, provides all the above mentioned techniques and a wide variety of relevant sample environments. ID1 is especially well suited for the grazing-incidence techniques, both GID and GISAXS, which can be performed simultaneously without the necessity of remounting the sample and in combination with anomalous scattering. At the Surface Diffraction beamline ID3, an improvement on the monochromator has been very recently implemented which would allow for increased flux at the sample. In addition to the "traditional" surface crystallography work, studies of dynamic processes and of surface magnetism are performed in the UHV end-station. At ID32, diffraction (XSW - X-ray standing waves) and X-ray photoelectron spectroscopy (XPS) can be combined. An electron energy analyser can be used for up to 4800 eV kinetic energies of the electrons. The surface characterisation laboratory at ID32 is now in full operation, with several ultra-high vacuum machines, a scanning tunnelling microscope and transfer chambers to the diffractometer. In addition, the beamline ID10B is available for surface and interface studies using grazing incidence techniques. This is a multipurpose device allowing for near-surface structural studies of solid and liquid interfaces thanks to a deflector that declines the beam downwards.

The following reports highlight the research done at the ESRF during the past year. The first contribution represents pioneering work in fundamental research showing the importance of non-dipolar effects in XPS for the proper analysis of XSW and high energy X-ray photoemission data. In the two successive studies from ID3, measurements of crystal truncation rods have been used to study the transition from a clean to a covered surface in order to investigate the possible structural changes of the buried interfaces. Approaching now the physics on the nanometre scale, the next contribution deals with structural changes following laser excitation. In the present case, the timescale, which is limited by the

X-ray pulse length, was reduced to an unprecedented 25 ps which demonstrates the unique potential for time-resolved measurements at ID9. The last three examples use grazing-incidence methods to study nano-structured materials. First, multilayers consisting of a periodic stack of bilayers with magnetic and nonmagnetic material have been investigated. GISAXS, specular reflectivity and GID have been combined to study the structure of the multilayer in order to confirm that the predicted electron channelling was not an artefact of the crystal perfection. In the next contribution the authors report on the self-organisation of the stacking of GaN quantum dots embedded in AlN. This material is interesting for optical applications in the blue-ultraviolet wavelength range. Again GISAXS and GID are shown to be ideally suited for the characterisation of the internal structure of quantum dot multilayers. Finally, exit-angle-resolved GID measurements are used to investigate the re-orientation of micro-channels in thin zeolite films on Si wafers as a function of the film thickness.