Steps on Pt stereodynamically filter sticking of O ₂

Abstract

Low coordinated sites on catalytic surfaces often enhance reactivity, but the underlying dynamical processes are poorly understood. Using two independent approaches, we investigate the reactivity of O2impinging onto platinum and resolve how step edges on (111) terraces enhance sticking. At low incident energy, the linear dependence on step density, independence of step type, and insensitivity to O2’s molecular alignment show that trapping into a physisorbed state precedes molecular chemisorption and dissociation. At higher impact energies, direct molecular chemisorption occurs in parallel on steps and terraces. While terraces are insensitive to alignment of the molecule within the (111) plane, steps favor molecules impacting with their internuclear axis parallel to the edge. Stereodynamical filtering thus controls sticking and dissociation of O2on Pt with a twofold role of steps.

Setting benchmarks for modelling gas–surface interactions using coherent control of rotational orientation states

“…Strong magnetic and electric field gradients, offer a well-known method for separating particles with different magnetic or electronic quantum states by selective deflection of their trajectories 28 . For O 2 , which is a paramagnetic molecule, passing the beam through a magnetic field gradient is all that is required to enhance one of the rotational projection states and perform alignment sensitive scattering 29 and reactivity measurements 30 . However, this approach cannot be used for the more general case of ground state closed shell molecules such as H 2 .…”

“…The initial rotational orientation of molecules has also been shown to change how molecules interact with a surface in previous studies which have used collision induced rotational polarisation in molecular beam expansions 51 , paramagnetic 30 and vibrationally excited 52 molecules to prepare molecules with an anisotropic distribution of m J states before the gas-surface collision. The experimental method we employ, which does not perturb the molecular ground state, allows us to also study how the quantum state (rotational orientation) of the H 2 molecule just before the collision, changes the probability of the molecule to scatter into a particular diffraction channel (regardless of its final quantum state).…”

Effect of Dielectric Thickness on Resistive Switching Polarity in TiN/Ti/HfO2/Pt Stacks

“…The RS mechanisms proposed could be further favored by a high negative voltage value needed to carry the forming process (although as it was earlier discussed, negative forming resulted in better performance and overall higher number of functional devices but was not mandatory). In addition, it must be mentioned that, although chemically inert, Pt is often used as a catalyst to adsorb O 2 on its surface [43,44], this could help the previously mentioned mechanisms by generating oxygen vacancies near the Pt surface.…”

Chiral Surface Characterisation and Reactivity Toward H–D Exchange of a Curved Platinum Crystal

“…The approach using vicinal surfaces requires that the same reaction is studied on several different surface structures to extract site-specific reactivities [24][25][26][27][28]. Comparing reactivities of single crystals with varying number densities of particular types of terraces, steps, or kinks may yield direct and quantifiable evidence for the influence of each particular type of site on the reaction.…”