Surface defects and their influence on surface properties

Abstract

Surface defects have a profound influence on many attributes of materials, therefore experimental techniques and specific studies focused on their controlled generation and properties are mandatory. We have carried out a thorough study of the role of surface defects on a variety of physico-chemical properties of metals and oxides, using different experimental techniques and molecular dynamics simulations. In particular, we have studied the defects formed upon bombardment with Ar+ ions in a reconstructed Au(100) surface at very low ion doses. At room temperature, the pristine defects are mainly single vacancies, which diffuse by collective atomic motions, then cluster and collapse, resulting in 2D dislocation dipoles. These dislocations exhibit an enhanced chemical reactivity due to the elastic stress of their cores. We have also performed indentation tests of flat and stepped Au(111) samples with an atomic force microscope, revealing noticeable differences in their mechanical behavior when probed at the nanoscale. Thus, the stepped sample has a 20% smaller Young's modulus, 40% smaller yield point and 50% smaller shear stress. These differences, as well as reversible, quasiplastic behavior of the stepped sample up to a critical load, are due to the active role of steps as dislocation nucleation centers. In contrast, a TiO2(110) surface, modified with ion bombardment, does not show noticeable changes in its nanomechanical properties, which is an indication of the very different mechanical responses of oxides compared to simple metals at the nanoscale. Finally, we show how surface defects affect the chemical activity of a Pt(111) surface when exposed to methanol. The nature of the adsorbed species and the dynamics of the surface reactions are modified in the presence of surface defects, rendering the defective surface into a more robust state against catalytic poisoning.

Formation of titanium monoxide (001) single-crystalline thin film induced by ion bombardment of titanium dioxide (110)

“…L ow-energy ion bombardment (LEIB) is a common tool to achieve the controlled generation of surface defects and self-organized nanostructures [1][2][3] . In this sense, oxides are interesting targets for ion-induced modifications, as their tolerance to non-stoichiometry allows the exploration of a wide range of induced morphologies and properties.…”

Modification of Oxide Thin Films with Low-Energy Ion Bombardment

“…), it can generate a broad spectrum of surface defects (surface vacancies, adatoms, linear steps, vacancy islands, etc. ), which can be subsequently studied for whatever phenomenon of interest [13,14]. Also, the kinetics of flattening of an initially rough surface, with the roughness induced with LEIB, has been studied for different types of materials (among them, also oxides).…”

Strain engineering of H/transition metal systems

“…Ar + ion sputtering has been used more recently [5] to distribute stress across Au(100) surfaces and an increase in chemical reactivity was seen at the defected, or locally stressed, sites. Strain has also been seen across the surfaces of metallic nanoparticles -for example, Pd@Pt [6], Pt [7] and Au [8][9] -and both oxide nanoparticles and thin-films [10][11].…”