New Mechanisms for Chemistry at Surfaces

Abstract

It is becoming increasingly apparent that chemistry at surfaces, whether it be heterogeneous catalysis, semiconductors etching, or chemical vapor deposition, is controlled by much more than the nature and structure of the surface. Recent experiments that principally make use of molecular beam techniques have revealed that the energy at which an incident molecule collides with a surface can be the key factor in determining its reactivity with or on the surface. In addition, the collision energy of an incident particle has proven essential to the finding of new mechanisms for reaction or desorption of molecules at surfaces, collision-induced activation and collision-induced desorption. These phenomena are often responsible for the different surface chemistry observed under conditions of high reactant pressure, such as those present during a heterogeneous catalytic reaction, and of low pressure of reactants (< 10(-4) torr), such as those present in an ultrahigh vacuum surface science experiment. This knowledge of the microscopic origins of the effect of pressure on the chemistry at surfaces has allowed the development of a scheme to bypass the high-pressure requirement. Reactions that are normally observed only at high reactant pressures, and which are the ones most often of practical importance, can now be carried out in low-pressure, ultrahigh vacuum environments.

Aktivierung der C‐H‐Bindung von Methan bei Raumtemperatur durch nacktes [P4O10].+

“…[13] Durch eine elegante Kombination von experimentellen und theoretischen Untersuchungen konnten sie zeigen, dass [SO 2 ]C + eine effektive Aktivierung von Methan ermöglicht [Gl. (2)]. Die Ge-…”

CVD in Weakly Rarefied Rotating Disk Flows

“…For dissociative chemisorption, the associated sticking coefficient (defined as the probability of a gas/surface collision resulting in reaction, analogous to the reaction rate constant) is sensitive to the temperature of the molecules striking the surface, rather than the disk temperature. [14] Consequently, when slip is taken into account, the surface reaction rate, based on the molecular temperature, can be substantially different from that based on the disk temperature, which can be adopted only when the flow is continuous. Second, many gas molecules participating in surface reactions are produced by gas-phase reactions.…”

The interaction of hyperthermal argon atoms with CO-covered Ru(0001): Scattering and collision-induced desorption

“…During gas-surface interactions in industrial catalytic processes (under high pressure and temperature conditions), such phenomena may play an important role. 1,2 This motivates the study of collisioninduced processes for a wide variety of systems. This paper is concerned primarily with one of those processes-collisioninduced desorption (CID)-and its effect on the associated scattered particles.…”

“…16 Combined experimental and theoretical studies were undertaken for the N 2 -Ru(0001) 17 and Xe-Pt(111) systems. 18 Various mechanisms have been proposed for collision-induced processes (desorption, diffusion, and absorption) 1,2,19,20 and dynamic displacement. 21 Generally speaking, the mechanisms proposed can be separated into two classes: prompt processes, where the primary impact by the fast particle immediately causes the observed effect, and secondary processes, where the primary impact transfers energy to the adsorbate-substrate system which responds in a subsequent step by using this energy to produce a measurable effect.…”