Nitro group as a means of attaching organic molecules to silicon: nitrobenzene on Si(100)-2 x 1.

This paper will present the computational and experimental infrared studies of the reactions of nitrobenzene on a Si(100) surface, a prototypical model reaction for understanding the behavior of bifunctional molecules on semiconductor surfaces. The initial reaction of nitrobenzene with the Si(100)-2 x 1 occurs via 1,3-dipolar cycloaddition of the nitro group to the silicon surface dimer. Computational exploration of the initial adsorption configurations suggests that two stable structures can be formed: one with the phenyl ring essentially perpendicular to the surface; the other one with the tilt angle of approximately 113 degrees with respect to the surface normal. The barrier for converting the latter into the former, more stable by approximately 13 kJ/mol, is 19.1 kJ/mol. Further thermal reactions are analyzed, and the reaction pathways are compared for the computational models with fixed vs relaxed subsurface silicon atoms. While all the surface species resulting from nitrobenzene transformations on the Si(100)-2 x 1 surface studied here are thermodynamically stable, most of the reaction pathways can be ruled out on the basis of the analysis of the transition states leading to these species and on the comparison of predicted and measured vibrational spectra. As a result, the exact adsorption configurations can be pinpointed.