Diffusion of Ag adatom on the H-terminated and clean Si(111) surfaces: A first-principles study

Abstract

Using a first-principles calculation method, we investigate the adsorption and diffusion of a Ag adatom on the H-terminated and clean Si͑111͒ surface, which would be useful in understanding the initial stages of metal growth on semiconductor substrates. We perform extensive searches for metastable surface structures induced by the Ag adatom adsorption, and then find its diffusion barriers and pathways on both kinds of the substrates. The calculated barrier for the Ag atom on the H-terminated surface is only 0.14 eV. On the clean surface, the diffusion barriers inside a half-unit cell ͑HUC͒ and between HUC's are calculated at 0.27 and 0.88 eV, respectively. The present results provide a qualitative description of the Ag growth modes on the Si͑111͒ surfaces: the three-dimensional island growth on the H-terminated surface and the formation of the wetting layer on the clean surface. In addition, the calculated barrier of 0.88 eV agrees well with the diffusion barrier measured by recent scanning-tunneling microscopy.

Influences of H on the Adsorption of a Single Ag Atom on Si(111)-7 × 7 Surface

“…The calculations also show that the surface atomic charge distribution is much more uniform once all 19 surface DBs have been saturated by H, which is consistent with the previous results reported by Stauffer and Minot [40]. The more uniformity of the surface charge distribution may decrease the Ag diffusion barrier on H-terminated Si(111) surface [20]. …”

Adatom-dependent diffusion mechanisms on aAg/Si(111)3×3surface

“…In this way, the exchange repeats in each diffusion step. The calculated energy barrier for the ST→ LT process decreases to 0.22 eV, which is comparable to that of Ag diffusion on a H-terminated Si͑111͒ surface, 22 where adatom migration is very active. Assuming the same prefactor as above, we obtain attempting frequencies of 10 5 -10 8 s −1 and 10 −9 -10 −6 s −1 for RT and 65 K, respectively.…”

“…We use a 13 Ry cut-off energy for the plane-wave basis and a 2 ϫ 2 k-point mesh for the surface Brillouin zone sampling which produce wellconverged results. 15,16,22 The pathways and activation energies for the adatom diffusion processes are calculated using the nudged elastic band method. [22][23][24] …”

Segregation of H as a surfactant during the formation of an Ag cluster on H-terminated Si(111): First-principles total-energy calculations

“…Thus, in this study, we theoretically investigate the roles of H atoms in metal growth, focusing on H segregation for Ag on the H-terminated Si͑111͒ surface, which has been extensively studied in the last decades from both academic and practical points. 1, 3,4,[13][14][15][16][17][18][19] As for H position in the Ag growth on the H / Si͑111͒ surface, there are two different arguments. The first one states that the H layer remains at the Ag-Si interface even at the later stages of overlayer growth.…”

“…15 This looks plausible considering the Si-H bond energy of 3.45 eV ͑rela-tive to a spin-polarized H atom͒ and the fact that a single Ag adatom migrates just on H / Si͑111͒ without distinct surface reconstruction. 19 Conversely, Fukutani et al performed a nuclear reaction analysis ͑NRA͒ for Ag on H / Si͑111͒ suggesting that the H atoms are partially removed from the interface even at the low temperature of 110 K. 17 They assumed that H segregation is a thermally activated process due to the difference in bond strengths of Ag-Si and H-Si. However, our total energy calculation reveals that the Si-H bond is stronger than the Ag-Si bond ͓bond energy: less than 2.2 eV ͑Ref.…”