Pentamers with interstitial atoms as the building blocks of the Ge(3 3 1)-5 × 1 surface

Comment on “Experimental Evidence for a New Two-Dimensional Honeycomb Phase of Silicon: A Missing Link in the Chemistry and Physics of Silicon Surfaces?”

“…To have an idea of the magnitude of the DFA surface energy, we recall that Si(001), Si(110), Si(331), and Si(113) surface energies fall in the range 88−97 meV/Å 2 and that 85 meV/Å 2 was found for Si(111)-7 × 7 DAS. 11,12 The above figures are in line with established experimental evidence showing that Si(111)-7 × 7 is the most stable surface of silicon. 13 The formation energy of the proposed "two-dimensional honeycomb phase of silicon" (DFA) exceeds the above figures by a factor of about two.…”

“…We agree that some questions remain regarding our understanding of the 7 × 7 structure and its physical properties. However, according to our density functional calculations, and considering the relative energy of the DAS reconstruction and that of other Si surfaces with different orientations, , the DAS structure of Si(111)-7 × 7 is still the best model available. The work of Demuth , has the merit of raising a series of issues regarding the DAS model.…”

Crucial role of vibrational entropy in the Si(111)-7$\times$7 surface structure stability

“…First-principles electronic structure methods, most notably density functional theory (DFT), have been widely used as a powerful tool to solve surface structures and to study their electronic properties. Due to its technological importance, semiconductor silicon has been a benchmark for studying surface physics, with several surface structures being extensively investigated [1][2][3][4][5][6][7][8][9][10]. When Si surface structures are composed of different building blocks as, for example, 2 × 1, 2 × 2 and 7 × 7 reconstructions on Si(111), their surface energy differences are usually significant (above 1 meV/ Å2 ), facilitating a reliable identification of the lowest energy atomistic configuration [11,12].…”