Helium scattering structure analyses of the c(2×8) reconstruction and the high-temperature (1×1) structures of Ge(111)

Phonon dispersion curves of theGe(111)−c(2×8)surface determined by He atom scattering

“…According to a molecular dynamics ͑MD͒ simulation based on local density functional ͑LDF͒ calculations 7 this complex rearrangement is accompanied by considerable bond stretching and contraction in the first and second layers. This buckling effect has been confirmed by scanning tunneling microscopy 11 ͑STM͒ and helium atom scattering 8 ͑HAS͒ results. The aim of the present experiments is to examine the extent to which this complex reconstruction affects the forces between the surface atoms.…”

“…The optimum He reflectivity ͑ca. 30% at RT͒ and the sharpness of the diffraction peaks in the He-diffraction spectra as well as the reproduction of previously reported HAS spectra 8,24 were taken as criteria for the sample order and cleanliness. These features are known to be very sensitive to the surface coherence length and the presence of impurities on the surface.…”

“…Whereas Si͑111͒ surfaces exhibit a ͑7 ϫ 7͒ periodicity, the Ge͑111͒ surface has a c͑2 ϫ 8͒ reconstruction, [1][2][3][4][5][6][7][8] which is similarly rich in intricate structural properties. The Ge͑111͒-c͑2 ϫ 8͒ surface has been studied by a wide variety of techniques [1][2][3][4][5][6][7][8] and, as for other semiconducting surfaces, the reconstruction is stabilized by the reduction of the number of dangling bonds present on the ideal ͑1 ϫ 1͒ surface. In this case, the process is largely brought about by two adatoms per unit cell, located at T 4 positions directly above atoms in the second layer of the unreconstructed surface.…”

Vibrational dynamics and band structure of methyl-terminated Ge(111)

“…Phonon dispersions for clean Ge(111) have been measured experimentally 6,47,48 and theoretically. 45 Clean Ge(111) reconstructs rapidly, which causes distortions of the dispersion curves; 49 however, at high temperatures, Ge(111) recovers the (1 × 1) structure such that the Rayleigh wave dispersion curves measured by HAS at 1000 K 48 can be directly compared with the present data for CH 3 -Ge(111) at low temperatures.…”

“…6 However, chemical passivation of the Ge(111) surface via hydrogenation, bromination, or alkylation leads to a reconstruction of Ge(111) that returns to the native (1 × 1) unit cell. Hydrogen or bromine atoms can passivate all of the dangling bonds above the surface Ge atoms, providing enhanced stability against surface oxidation relative to clean Ge.…”