Synthesis and Characterization of Atomically Flat Methyl-Terminated Ge(111) Surfaces

Abstract

Atomically flat, terraced H–Ge(111) was prepared by annealing in H2(g) at 850 °C. The formation of monohydride Ge–H bonds oriented normal to the surface was indicated by angle-dependent Fourier-transform infrared (FTIR) spectroscopy. Subsequent reaction in CCl3Br(l) formed Br-terminated Ge(111), as shown by the disappearance of the Ge–H absorption in the FTIR spectra concomitant with the appearance of Br photoelectron peaks in X-ray photoelectron (XP) spectra. The Br–Ge(111) surface was methylated by reaction with (CH3)2Mg. These surfaces exhibited a peak at 568 cm–1 in the high-resolution electron energy loss spectrum, consistent with the formation of a Ge–C bond. The absorption peaks in the FTIR spectra assigned to methyl “umbrella” and rocking modes were dependent on the angle of the incident light, indicating that the methyl groups were bonded directly atop surface Ge atoms. Atomic-force micrographs of CH3–Ge­(111) surfaces indicated that the surface remained atomically flat after methylation. Electrochemical scanning–tunneling microscopy showed well-ordered methyl groups that covered nearly all of the surface. Low-energy electron diffraction images showed sharp, bright diffraction spots with a 3-fold symmetry, indicating a high degree of order with no evidence of surface reconstruction. A C 1s peak at 284.1 eV was observed in the XP spectra, consistent with the formation of a C–Ge bond. Annealing in ultrahigh vacuum revealed a thermal stability limit of ∼400 °C of the surficial CH3–Ge­(111) groups. CH3–Ge­(111) surfaces showed significantly greater resistance to oxidation in air than H–Ge(111) surfaces.

Integration of 3D nanographene into mesoporous germanium

“…. 45 The XPS peaks at binding energies of 29.3 eV and 29.9 eV correspond to Ge elementary 3d 5/2 and 3d 3/2 , respectively. The small peak at 30.8 eV represents the σ bonding between Ge and oxygen (GeO).…”

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

“…The surfaces investigated herein were therefore instead prepared using a two-step halogenation-alkylation that produces atomically flat, methyl-terminated Ge(111) surfaces. 13 Briefly, a thoroughly cleaned and rinsed Ge(111) wafer was hydrogenated by exposure to a flow of H 2 at 850…”

“…11,12 Recently, highly ordered, atomically flat CH 3 -Ge(111)-(1 × 1) surfaces have been prepared, resulting in improved chemical and electrical passivation. 13 Several standard surface analytical techniques have revealed the chemical composition, surface structure, surface conductance, and methyl vibrational modes of methylated Ge(111) surfaces.…”

“…[11][12][13] The vibrational modes of CH 3 -Ge(111) have been investigated by use of transmission infrared spectroscopy (TIRS), high-resolution electron-energy loss spectroscopy (HREELS), and density functional perturbation theory (DFPT).…”

“…13,14 Additionally, methylated germanane (a single-layer crystal of germanium terminated with hydrogen) has recently been synthesized, and X-ray diffraction data indicate a hexagonal spacing with a lattice constant of a = 3.96 Å. 15 Despite extensive structural characterization, the dynamics of CH 3 -Ge(111) remain largely unexplored, whereas the dynamics of a surface analog, CH 3 -Si(111), have been thoroughly studied both experimentally [16][17][18][19][20][21] and theoretically.…”