Angle‐Scanned Photoelectron Diffraction: Probing crystalline ultrathin films

Abstract

Electrons emitted from the core levels of a photon-irradiated crystalline sample undergo scattering by atoms in the vicinity of the emitting species. Subsequent interference phenomena between the electron wave portions propagating to the detector produce intensity modulations as a function of the direction of detection. This process constitutes the physical basis of the anglescanned X-ray photoelectron diffraction (XPD) technique. The resulting modulations, properly interpreted, are rich in structural information concerning the near-surface atomic layers. In this review, after an introduction to the principles of XPD, some selected results in the field of ultrathin epitaxial films will be reported in order to outline the merits of the technique. Qualitative structural information (e.g., growth modes and lattice distortions) is directly obtained from the experimental raw data without the need for theoretical simulation. On the other hand, quantitative structural parameters, as well as the presence of stacking faults and other structural defects, may be deduced by using a trial-and-error fitting procedure based on simple scattering models.

Estimating soft-mode frequencies of surface overlayers by means of photoelectron diffraction: The(2×2)surface-V2Sambi1, Surnev2, Kresse3 et al. 2003Phys. Rev. B3000View full textAdd to dashboardCite

“…The (2ϫ2) structure revealed by low-energy electron diffraction ͑LEED͒ and STM has been interpreted on the basis of density functional theory ͑DFT͒ calculations, which support a model leading to an excellent agreement of simulated and experimental STM images. 2 As reported in a recent short communication, 6 the system has been investigated by means of angle scanned x-ray photoelectron diffraction [7][8][9] ͑XPD͒ as well, which confirms the DFT/STM model and gives ͑a͒ direct experimental evidence for the proposed atomic arrangement and ͑b͒ an estimate of the V-O interlayer spacing. However, single scattering cluster ͑SSC͒ simulations of XPD curves for V 2p emission from s-V 2 O 3 , compared to experimental scans, revealed a peculiar anisotropic broadening of V-O forward scattering ͑FS͒ maxima in the experiment, which cannot be explained in the framework of a simple Debye-Waller ͑DW͒ isotropic vibration model.…”

Bottom-Up Assembly of Single-Domain Titania Nanosheets on(1×2)−Pt(110)

“…2) have been acquired in the polar angle range 28 66 (with respect to the sample normal), i.e., in the range where the main forward scattering (FS) events are expected for a lepidocrocite nanosheet. Actually, XPD in the FS regime (at photoelectron KE close to 1000 eV) provides a direct fingerprint of the local atomic arrangement surrounding each emitter: The main intensity maxima correspond to interatomic directions and give information regarding the atomic stacking in three dimensions [15,24]. The SSC-SW simulations of XPD 2 plots based on the DFT model are also reported in Fig.…”

Silver nanostructures on a c(4×2)-NiOx/Pd(100) monolayer

“…Exploiting the observed symmetry, the whole set of XPD data has been fourfold averaged; the polar angle ranges from h = 0°to h = 66°. As the photoelectron kinetic energy is rather high, the interpretation of the Ag 3d XPD pattern can be carried out by a simple kinematical single-scattering model, where the strongest intensity enhancements are interpreted as derived from a forward-focusing effect [40]. Starting with the lowest coverage (Fig.…”

“…In order to obtain crystallographic information on the Ag NPs and to detect any possible epitaxial ordering, we have undertaken an angle-scanned XPD investigation [39,40]. In Fig.…”