Efficient determiniation of multilayer relaxation in the Pt(210) stepped and densely kinked surface

Facet-Dependent Strain Determination in Electrochemically Synthetized Platinum Model Catalytic Nanoparticles

Studying model nanoparticles is one approach to better understand the structural evolution of a catalyst during reactions. These nanoparticles feature well-defined faceting, offering the possibility to extract structural information as a function of facet orientation and compare it to theoretical simulations. Using Bragg Coherent X-ray Diffraction Imaging, the uniformity of electrochemically synthesized model catalysts is studied, here high-index faceted tetrahexahedral (THH) platinum nanoparticles at ambient conditions. 3D images of an individual nanoparticle are obtained, assessing not only its shape but also the specific components of the displacement and strain fields both at the surface of the nanocrystal and inside. The study reveals structural diversity of shapes and defects, and shows that the THH platinum nanoparticles present strain build-up close to facets and edges. A facet recognition algorithm is further applied to the imaged nanoparticles and provides facet-dependent structural information for all measured nanoparticles. In the context of strain engineering for model catalysts, this study provides insight into the shape-controlled synthesis of platinum nanoparticles with high-index facets.

Surface X-ray scattering of stepped surfaces of platinum in an electrochemical environment: Pt(331) = 3(111)-(111) and Pt(511) = 3(100)-(111)

Real surface structures of the high-index planes of Pt with three atomic rows of terraces (Pt(331) = 3(111)-(111) and Pt(511) = 3(100)-(111)) have been determined in 0.1 M HClO(4) at 0.1 and 0.5 V(RHE) with the use of surface X-ray scattering (SXS). The surfaces with two atomic rows of terraces, Pt(110) = 2(111)-(111) and Pt(311) = 2(100)-(111) = 2(111)-(100), are reconstructed to a (1 × 2) structure according to previous studies. However, the surfaces with three atomic rows of terraces have pseudo-(1 × 1) structures. The interlayer spacing between the first and the second layers, d(12), is expanded 13% on Pt(331) compared to that of the bulk, whereas it is contracted 37% on Pt(511). The surface structures do not depend on the applied potential on either surface.

Catalytic reduction of NO2 with hydrogen on Pt field emitter tips: kinetic instabilities on the nanoscale

The catalytic reduction of NO(2) with hydrogen on a Pt field emitter tip is investigated using both field electron microscopy (FEM) and field ion microscopy (FIM). A rich variety of nonlinear behavior and unusually high catalytic activity around the {012} facets are observed. Our FEM investigations reveal that the correlation function exhibits damped oscillations with a decaying envelope, showing that molecular noise will influence the dynamics of the oscillations. The dependence of the oscillatory period on the P(H(2))/P(NO(2)) pressure ratios is analyzed. Similar patterns are reported under FIM conditions. Corresponding density functional theory (DFT) calculations for the adsorption of NO(2) on Pt{012} in the presence of an external electric field are performed in order to gain an atomistic understanding of the underlying nonlinear phenomena.

The Structure of the Chiral Pt{531} Surface: A Combined LEED and DFT Study

The structure of the chiral kinked Pt531 surface has been determined by low-energy electron diffraction intensity-versus-energy (LEED-IV) analysis and density functional theory (DFT). Large contractions and expansions of the vertical interlayer distances with respect to the bulk-terminated surface geometry were found for the first six layers (LEED: d12 = 0.44 A, d23 = 0.69 A, d34 = 0.49 A, d45 = 0.95 A, d56 = 0.56 A; DFT: d12 = 0.51 A, d23 = 0.55 A, d34 = 0.74 A, d45 = 0.78 A, d56 = 0.63 A; dbulk = 0.66 A). Energy-dependent cancellations of LEED spots over unusually large energy ranges, up to 100 eV, can be explained by surface roughness and reproduced by applying a model involving 0.25 ML of vacancies and adatoms in the scattering calculations. The agreement between the results from LEED and DFT is not as good as in other cases, which could be due to this roughness of the real surface.

Energy-dependent cancellation of diffraction spots due to surface roughening

The low-energy electron diffraction (LEED) pattern of the step-kinked Pt{531} surface at 200 K shows energy-dependent cancellation of diffraction spots over unusually large energy ranges, up to 100 eV. This cannot be reproduced theoretically when a flat surface geometry is assumed. A relatively simple model of roughening, however, involving 0.25 ML of vacancies and adatoms leads to very good agreement with the experiment. The cancellation of intensities within a very narrow range of adatom or vacancy coverages is caused by the interference of electrons emerging from different heights but similar local environments. This is a rare example where the energy dependence of integrated LEED spot intensities is dramatically affected by the long-range arrangement of atoms.