Initial stages of the adsorption of Ge atoms on theSi(111)−(7×7)surface

Low-flux elucidation of initial growth of Ge clusters deposited onSi(111)−7×7observed by scanning tunneling microscopy

“…15͒ and Ma et al 19 for 150°C; exclusive adsorption on corner adatom sites indicates that the sites on FHUCs are the most favorable for Ge atoms at these elevated temperatures. 13,15,16,19,21 Up to the coverage of 0.05 ML deposited under the low flux, our observed results agreed with those reported. 13,15 The separation between two protrusions corresponding to two Ge atoms occupying corner adatom sites on each FHUC was measured 1.2-1.5 nm, less than the distance for Si adatoms; Ge adatoms seem shifted slightly toward the center of FHUC, which may bear high stress as explained using density-functional theory ͑DFT͒ calculations, 22,23 or the spatial distribution of electronic states seems slightly distorted.…”

“…[1][2][3][4][5][6][7][8][9][10] While Ge nanostructures have been widely studied on Si͑001͒ surfaces, 1-3 there has been growing interest for Ge nanostructures on a Si͑111͒-7 ϫ 7 reconstructed surface with dimer rows, adatoms, and stacking fault ͑DAS͒ explained by the DAS model. 11 Many reports of Ge growth on Si͑111͒-7 ϫ 7 surfaces presented thermodynamic fluctuations on morphology of nanostructures grown at different temperatures and fluxes; [6][7][8][9][10][12][13][14][15][16][17][18][19] the morphology delicately changes with growth conditions.…”

“…On the other hand, at 100°C a Ge atom was initially substituted for a Si adatom, and with increasing Ge deposition various types of clusters were formed on half unit cells ͑HUCs͒ of the 7 ϫ 7 reconstruction as a result of complex and diverse bonding configurations. [13][14][15][16][17]19 The diverse Ge nanostructures indicate that formation of self-organized nanostructures crucially depends on coverage, temperature, flux, quality of substrate, and so on, which are key factors to produce well-ordered and uniform nanostructures. [6][7][8][9][10][12][13][14][15][16][17][18][19] To elucidate the growth conditions and mechanism, systematic study is strongly recommended.…”

“…1͑a͒, remarkably brighter atoms were seen at corner adatom sites preferentially on faulted half unit cells ͑FHUCs͒, similar to those observed for deposition at 100°C. 13,15,16 The brighter ones were attributed to a Ge atom substituted for a Si atom at an adatom site since the number of bright spots increased with increasing Ge deposition. The brighter spot at a corner adatom was depicted about 0.2 Å higher than a normal Si corner adatom, seen in a line profile in Fig.…”

“…From analysis of many images we estimated that the ratio of Ge adatom occupying FHUCs with respect to UFHUCs was 20:1, in agreement that Ge atoms are preferentially adsorbed on FHUCs. 10,[12][13][14][15][16][17][18] Preferential adsorption of Ge atoms over corner sites on FHUCs and over center adatom sites on UFHUCs probably results from competition of activation energy with respect to adsorption energy for Ge atoms to diffuse over these sites. The similar results were reported by Wang et al 13 for 100°C ͑Ref.…”