Diffusion by bond hopping of hydrogen atoms on the Si(111)-7×7 surface

Abstract

Site-specific adsorption and diffusion of atomic hydrogen on the Si͑111͒-7ϫ7 surface at elevated temperatures are studied by scanning tunneling microscopy. Hydrogen atoms are found to adsorb preferentially on rest-atom sites rather than adatom sites with a binding-energy difference of ϳ0.2 eV. The adsorption causes a reverse charge transfer from rest atoms back to adatoms. Above ϳ280°C, atomic hopping between two rest-atom sites within a half-cell can occur which is mediated by an adatom site. Above ϳ330°C, H atoms start to hop across the cell boundary via two adatom sites, or they can diffuse across the surface. The activation barrier for hopping from a rest-atom site to a corner adatom site is ϳ50 meV lower than that to an edge adatom site. Thus, in cross boundary jumps, they hop preferentially via two corner adatom sites. From Arrhenius plots, the hopping barriers within the cell and across the cell boundary are determined. The hopping paths, relative binding energies, and site selectivity of hydrogen atoms on the Si͑111͒-7ϫ7 surface agree in general with theoretical results, but our result are both site and path specific. The dynamic behavior of two to three H atoms inside a half-cell is also investigated. ͓S0163-1829͑98͒00939-4͔

Dissociative adsorption of pyrrole on Si(111)-(7×7)

“…From filled-state images, the adsorption of H atom on a rest atom site was found to enhance the brightness of the three neighboring unreacted adatoms, not seen in the empty-state images. 38 In our work, one adatom adjacent to the reacted rest atom is darkened upon reaction. The remaining two unreacted adatoms indeed become brighter.…”

Surface diffusion of Pb atoms on the Si(553)-Au surface in narrow quasi-one-dimensional channels

“…Usually, the diffusion of atoms on low-index surfaces is two dimensional and rather isotropic, like in the case of various adsorbates on the Si(111) surface [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. However, the movement of atoms can become strongly anisotropic or even quasi-one-dimensional in the presence of a specific surface reconstruction or on stepped (vicinal) templates [23][24][25][26][27][28].…”

Study by scanning tunneling microscopy of hydrogen adsorption and desorption on Si(111)7×7 at room temperature and at high temperature

“…It was found that the Si adatoms of the (7×7) structure are the preferential sites for H adsorption at low coverage. In contrast, high-temperature STM studies of H/Si(111)7×7 have shown that the rest atoms acted as preferential adsorption sites and it was argued that the room temperature results might not correspond to the thermodynamically stable final state [9,10]. One issue of this work is devoted to this controversy more specifically by adsorption experiments both at room and at elevated temperature.…”

“…Note that for better visibility of adsorption on rest atoms a negative value of the sample bias must be applied [9,10]. It is evident from the images, however, that reaction of the Si adatoms with H occurs from the beginning of the adsorption experiments at both room and elevated temperatures.…”

“…Such surfaces have been obtained by wet chemical etching [2]. In more recent times scanning tunneling microscopy (STM) has been widely used to follow the adsorption and reaction of atomic H with Si(111)7×7 under ultrahigh vacuum (UHV) and to explore the extent to which an ideal (111) H-terminated surface can be obtained [3,4,5,6,7,8,9,10,11]. In initial studies the atomic sites for adsorption in its initial stage were identified [3].…”