Structure of the Ge(111)-c(2 × 8) surface as determined from scattered X-ray intensities along crystal truncation rods

Abstract

In an X-ray diffraction study of the c(2 x 8) reconstructed Ge( 11 1) surface we have measured intensity profiles along integer-order rods of Bragg scattering perpendicular to the surface plane. The diffracted intensity profiles are explained in terms of a simple adatom model for the reconstruction. The adatoms are found to occupy T4 sites on a distorted bulk-like substrate. We rule out any model for c(2 x 8) reconstruction that is based on stacking faults in the substrate. For the adatom model we give best-fit values for the positions of the atoms at the surface and compare them with those obtained from total-energy and Keating-energy minimisation calculations.

Reconstructions and phase transitions at semiconductor surfaces: Ge(111)

“…This is found to be lower in energy than the ideal (1 X 1) surface by ~ 0.33 eV/(1 X 1) cell, and lower than Ge(lll)2 X 1 by ~ 0.05 eV/(1 X 1) cell. The agreement between our atomic coordinates and X-ray experiments [17] is excellent: Silfhout has shown that the structure factor intensity along the (10) rod calculated using our atomic positions (averaged to yield a (2 X 2) cell) fits the X-ray as well as his best fit coordinates [11]. Since we do not impose a (2 X 2) unit cell, our surface structure does not have threefold symmetry.…”

“…On the other hand the c(2 × 8) recon-3 struction involves the saturation of ~ of the surface dangling bonds by extra atoms called the "adatoms", forming a so-called "simple adatom" structure [14][15][16][17]. Experiments have shown that the adatoms sit at T 4 sites [15][16][17], above 2nd layer Ge atoms, and are arranged in a way that the c(2 X 8) structure can be decomposed in alternating (2 X 2) and c(2 X 4) subunits [14]. Electronic charge transfer from the 1 adatoms to the restatoms (i.e.…”

Photoelectron Diffraction and Synchrotron Radiation

“…The spectra were taken at a polar emission angle Θ of 51° off normal and at two different azimuths, [-110] and 30° off. The stucture of this reconstucted surface was solved by surface X-ray diffraction [41], but there was some controversy about the assignment of the two surface-shifted components [42,43]. At the top of Fig.…”

STM andab initiostudy of holmium nanowires on a Ge(111) surface

“…Consideration of the bonding requirements of the two trivalent Ho atoms per 5×1 unit cell also leads to the conclusion that Ho atoms cannot be adsorbed atop a simple bulk-terminated Ge surface since in such a situation the Ge surface would provide only 5 dangling bonds to be quenched by the two trivalent Ho atoms. On the other hand, the lower layer of the nanorod is too high above the rest atoms of the Ge substrate to be a simple adatom layer (0.66Å above the rest atoms in clean Ge(111)-c(2×8) [15]). A visual comparison with surrounding areas of the c(2×8) reconstruction in the empty states STM images suggests an atomic density in the lower nanorod layer which is greater than that of a dilute (e.g.…”

“…Features within the top layer of the nanorod can now be resolved, especially when the image contrast is adjusted as in the left half of the figure. In the empty states STM images the top layer of the nanorod was measured as being 3.1Å above the Ge adatom layer (and thus 3.8Å above the rest atom layer since the adatom layer is known to be 0.66Å above the rest atom layer [15]). …”