Hydrogen termination surface states

Both a 1x1 phase obtained by polishing and a 2x2/2xl phase obtained by annealing to above 1000 C were observed by LEED. (LEED cannot distinguish between a true 2x2 or disordered domains of 2x1 for this surface the similarity of the angle-resolved photoemission to that of Si and Ge suggests the latter.) No surface states were observed in the gap for the 1x1 diamond surface. However, recent experiments have shown that this is a hydrogen-terminated surface. The 2x2/2xl surface, on the other hand, is believed... 

Figure 10.14 Angle-resolved photoelectron spectra of the clean C(lll)2xl surface scanning the surface Brillouin zone along a line through K. The resonance S corresponds to the surface state, K is reached for a polar angle of ft 45. The zero of the energy axis is the Fermi level. In the upper panel one spectrum for the hydrogen-terminated surface is shown to demonstrate the absence of S for that surface. (Data from Ref [57].)...

Deuterium-terminated PS shows the same microstructure and VB energy shift, but the PL is significantly blue shifted if compared to hydrogen-terminated PS. This indicates that the surface vibration of terminated atoms couples to the excited energy states of quantum-confined charge carriers [Mall]. 

At low temperatures the PLE of hydrogen-terminated PS reveals that phonons and the exciton exchange splitting contribute significantly to the observed Stokes shift [Ca6, Ku4, Ro5, Ka8, Kol3]. For oxidized PS the picture is not usually so clear, due to a recombination path that may involve surface states. 

Boukherroub, R. Chemical reactivity of hydrogen-terminated crystalline silicon surfaces. Current Opinion in Solid State Materials Science 9, 66 (2005). 

HCl to NH40H). Polyhydrides are found to be more stable than monohydride. Hydrogen termination also serves to passivate grain boundaries. Terrace monohydride has different stability from step monohydride. As a result of hydrogen passivation, HF-treated silicon surface exhibits a very low density of surface states in various acids over a wide concentration range. ... 

According to Memming and Schwandt, surface states are always present on silicon electrodes in acidic aqueous solutions. The energy levels depend on whether fluoride ions are present the surface states in acidic fluoride solutions are associated with the dissolution of the silicon. The quantity of the surface states depends on the type of silicon and the illumination intensity. When fluoride ions are present in the solution, the n-Si surface, being oxide free and terminated by hydrogen, exhibits a low density of surface states. ... 

A rare exception is the hydrogen terminated (111) surface of silicon in acidic fluoride solutions, where flie surface state density is extremely small. 

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