X-ray scattering from stepped and kinked surfaces: An approach with the paracrystal model

A general formalism of X-ray scattering from different kinds of surface morphologies is described. Based on a description of the surface morphology at the atomic scale through the use of the paracrystal model and discrete distributions of distances, the scattered intensity by non-periodic surfaces is calculated over the whole reciprocal space. In one dimension, the scattered intensity by a vicinal surface, the two-level model, the N-level model, the faceted surface and the rough surface are addressed. In two dimensions, the previous results are generalized to the kinked vicinal surface, the two-level vicinal surface and the step meandering on a vicinal surface. The concept of crystal truncation rod is generalized considering also the truncation of a terrace by a step (yielding a terrace truncation rod) and a step by a kink (yielding a step truncation rod).Comment: 33 pages, 18 figure

The morphology of growing nanoparticles by Grazing Incidence Small Angle X-Ray Scattering

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Silver layers on oxide surfaces: morphology and optical properties

International audienc

Wetting and interfacial chemistry of metallic films on the hydroxylated α − Al 2 O 3 ( 0001 ) surface

International audienc

GranFilm: a software for calculating thin-layer dielectric properties and Fresnel coefficients

International audienc

Dielectric study of the interplay between charge carriers and electron energy losses in reduced titanium dioxide

International audienceThe transport mechanism in titanium dioxide through polarons is an open issue. High-resolution electron energy-loss spectroscopy (HREELS) is in principle of great relevance in such context, provided the fingerprints on the loss spectrum of the charge carriers involved in the material are disclosed. This paper aims at evidencing those fingerprints. Through a suitable parametrization of the dielectric function, a theoretical analysis of EELS excitations in defective TiO2 rutile is developed in the framework of the semiclassical dielectric theory. The focus is put on the interplay between phonons, interband transitions, and defect-related excitations, namely, plasmon and band-gap states. Transport properties are demonstrated to be more efficiently grasped through the screening they induce on phonons than through the existence of a defined surface plasmon peak. While the corresponding imaginary part of the dielectric function only yields a slight broadening and temperature dependence of the quasielastic peak due to the large static dielectric function and electron effective mass, a sizable upward shift in energy and a decrease in intensity of phonons due to the real part are predicted. Band-gap states also screen phonons but with downward shift in energy loss. Due to its large oscillator strength, the high-energy-lying surface phonon at 95 meV is a very sensitive reporter of the combined effects of transport behavior and band-gap states. Finally, it is highlighted that extracting quantitative information out of EELS experiments requires an accurate modeling of the depth profile

Probing surfaces and interfaces morphology with Grazing Incidence Small Angle X-Ray Scattering

International audienceNanoscience and nanotechnology are tremendously increasing fields of research that aim at producing, characterizing and understanding nanoobjects and assemblies of nanoobjects. Their new physical or chemical properties, which arise from confinement effects, intimately depend on their morphological properties, i.e. their shapes, their sizes and their spatial organization. This calls for dedicated morphological characterization tools, among which is the Grazing Incidence Small Angle X-Ray Scattering (GISAXS). This reciprocal space technique has emerged in the last two decades as a powerful tool that allows investigating in a non-destructive way the morphological properties from one to billions of nanoparticles, either on a surface, or embedded in a matrix, with sizes ranging from 1 nm to several microns. The advantages of the technique are that it is non-destructive; it yields statistical information averaged on a large number of nanoparticles; it allows probing both the surface or deep below it, by changing the incident angle of the X-ray beam; it can be used in very different sample environments, in particular in situ in the course of a given process such as growth, annealing, gas exposure; and it may be given chemical sensitivity by use of anomalous scattering. This report presents a review of the GISAXS technique, from experimental issues to the theories underlying the data analysis, with a wealth of examples. The physical morphological information contained in GISAXS data and its analysis are presented in simple terms, introducing the notions of particle form factor and interference function, together with the different cases encountered according to the size/shape dispersion. The theoretical background of X-ray diffuse scattering under grazing incidence is presented in a general way, and then applied to the particular case of grazing incidence small angle X-ray scattering from assemblies of particles either on a substrate, or buried below it. Most of the GISAXS measurements published to date are reported, covering the fields of ex situ studies of embedded metallic nanoparticles, granular multilayered systems, implanted systems, embedded or stacked or deposited semi-conductor nanostructures, porous materials and copolymer thin films. A special emphasis is brought on in situ experiments, performed either in ultra-high vacuum during nanoparticle growth by molecular beam epitaxy, or in gas-reactors during catalytic reactions. This covers a very broad field, from (i) the 3D island (VolmerWeber) growth of metals on oxides surfaces to (ii) the organized growth of metals on surfaces that are nanopatterned either by surface reconstruction or by underlying dislocation networks or by deposit-induced nanofacetting, to (iii) the in situ investigation of the self-organized StranskiKrastanow hetero-epitaxial growth of semi-conductor quantum dots on semi-conductor surfaces, or (iv) the in situ surface nanopatterning by ion bombardment. Many examples are discussed in detail, to illustrate the large diversity of systems and morphologies that can be addressed as well as the different analysis issues and the conclusions of the technique in terms of growth mode

Structural investigation of nanoporous alumina film with grazing incidence small angle X-ray scattering

International audienceNanoporous alumina films (NPAF) have been elaborated by anodization of an aluminum film on silicon wafer. Ex situ structural characterization of the films has been achieved with grazing incidence small angle X-ray scattering under ultra high vacuum atmosphere and using a synchrotron source. The comparison of the experimental patterns with suitable modeling confirms the cylindrical geometry of the pores well as the good local hexagonal order. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei