Probing the Si-Si Dimer Breaking of $\mathrm{Si}(100)2\times 1$ Surfaces upon Molecule Adsorption by Optical Spectroscopy

The adsorption of atoms and molecules of several gases of the $\mathrm{Si}(100)2\times 1$ silicon reconstructed surface is investigated by surface differential reflectance spectroscopy. This UV-visible optical spectroscopy makes possible the discrimination between two adsorption modes, depending on whether or not the adsorption leads to breaking the Si-Si dimers. The observation of two different optical features is assigned to the bonding on dangling bonds or to the breaking of dimers, and gives access to the adsorption mode of hydrogen, water, oxygen, and pyridine. Moreover, the technique being quantitative, we can determine the total amount of dimers involved in the adsorption and monitor the adsorption kinetics.

Figure 1

(a) SDR spectrum after complete H adsorption on $\mathrm{Si}(100)2\times 1$ at 600 K; (b) SDR spectrum after complete H adsorption at 300 K; (c) DFT calculation corresponding to (b), from Ref. 17; (d) contribution of the dimer breaking to the SDR signal.

Figure 2

SDR spectrum after adsorption of different molecules on $\mathrm{Si}(100)2\times 1$ at 300 K. (a) saturation of water; (b) 160 L oxygen; (c) 2 L oxygen ($\times 1.5$); (d) saturation of pyridine. The schemes on the right give the most probable configurations for the molecule geometries on the surface.

Figure 3

Variation of the integrated SDR signal as a function of time during ${\mathrm{H}}_{\mathrm{at}}$ exposure at $T=600\mathrm{K}$ and pyrdine exposure at room temperature. Continuous lines are best fittings within the Langmuir model.