Observation of strain in the Si(111) 7×7 surface

Silicon backbond strain effects on NH3 surface chemistry: Si(111)-(7 × 7) compared to Si(100)-(2 × 1)

“…Since the surface Si atoms can be classified into adatoms and rest atoms, the Si-Si backbonds associated with them can also be classified into adatom backbonds and rest atom backbonds (Figure 3a). While both types of backbonds involve triply coordinated surface Si atoms, there is in fact a significant difference between these two types of silicon backbonds in that the adatom backbonds are strained while the rest atom backbonds are not [12,13]. The important role of these strained (and therefore weaker) Si backbonds in controlling surface chemistry has been recognized by Boland [14].…”

Diffraction refinement of localized antibonding at the Si(111)7×7surface

“…Another unusual feature of the DAS structure are the buried dimer atoms which have previously been shown to exhibit bond lengths 6±2% longer than bulk values [20], indicating a slightly weaker bond compared to the bulk value. We have refined the value of the dimer bond density against the diffraction data to be 0.37±0.04 e -(92% of the bulk value) by allowing the charge clouds within the BCPA model to vary in magnitude with all dimers treated identically.…”

Structure Factor Determination in Surface X-ray Diffraction

“…The former is usually constant and can be ignored for in-plane measurements, while the sin 28 dependence of the latter acts like a second Lorentz factor. The procedure implicit in equation (3) has been used in several in-plane surface structure determinations with success (Bohr et al 1985;Feidenhans'l et al 1987;Robinson et al 1988). Agreement between calculated and observed intensities is in the 5-10% range.…”