The kinetics of a surface-chemical reaction: A time-of-flight secondary ion mass spectrometry study

• Published in: Applied surface science 1989, Vol.37 (2), p.147-159
• Main Authors: van Velzen, P.N.T., Ponjeé, J.J., Benninghoven, A.
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; Kinetics and mechanisms; Organic chemistry; Reactivity and mechanisms
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/0169-4332(89)90477-7

Time-of-flight secondary ion mass spectrometry, in combination with neutron activation analysis, has been used to study the kinetics of a surface-chemical reaction, namely the bromomethyldimethylsilylation of oxidized silicon wafers at room temperature in toluene. The anticipated quasi-first-order kinetics are not observed over the entire surface-coverage range. Instead, the apparent rate constant of this “two-dimensional” reaction appears to decrease gradually with increasing coverage up to one third of the maximum packing of one monomolecular layer. Two factors that can contribute to this phenomenon are elaborated in detail. From the calculations presented it can be concluded that the presence of two types of hydroxyl sites (geminal versus lone) at the surface can adequately explain the observed kinetics. On the other hand, a description of the steric hindrance by means of a coverage-dependent energy barrier for molecules approaching the surface also yields reasonable results. On the basis of the data available a distinction between these two extremes cannot be made.