Dynamics of hydroxyl dissociation of methanol and water on silicon surfaces

The ability to affix organic molecules to silicon surfaces could bring together two well established technologies and create opportunities for new functional materials. A deeper understanding of the dynamics and kinetics of bonds between organic molecules and silicon surfaces can help develop ways to manufacture and finetune these materials. While spectroscopic information is available for many organic-silicon reactions, the reaction dynamics of relatively few systems have been investigated.

Bohamud et al. report the dynamics of the hydroxyl dissociation of methanol and water on silicon surfaces. In addition to controlling parameters that define the silicon surface, the group used molecular beam techniques to control the kinetic energy of the incoming molecules. They were able to measure the initial sticking probability as a function of the kinetic energy of the incoming molecules and temperature of the silicon surface.

“So far, the adsorption of many molecules on silicon has been investigated and many reaction mechanisms are well understood,” said Michael Dürr, an author on the paper. “However, this has been typically done with thermal gas molecules. Using a molecular beam allows us to investigate the potential energies involved and the forces which drive these reactions in much more detail.”

Adsorption of organic molecules on semiconductor surfaces normally proceeds by way of an intermediate state. For both methanol and water, the authors found a low conversion barrier from the intermediate state into the final bonded state, likely due to proton transfer from the OH-group of the datively bonded molecules to the silicon surface atoms. However, even in that case, they found that the intermediate state determines the reaction dynamics.

Dürr hopes this work will eventually lead to better control over which chemical entities react on silicon surfaces, and perhaps extending the approach to more complex systems.

Source: “Dynamics of proton transfer reactions on silicon surfaces: OH-dissociation of methanol and water on Si(001),” by T. Bohamud, M. Reutzel, M. Dürr, and U. Höfer, Journal of Chemical Physics (2019). The article can be accessed at https://doi.org/10.1063/1.5092804 .