We propose an improved wet chemical process for preparing a high-quality hydrogen-terminated Si(111)-(1× 1) surface and show an atomically ordered and ultraclean surface without carbon and oxygen contamination. The vibrational properties and surface morphology are investigated by high-resolution electron energy loss spectroscopy (HREELS), atomic force microscopy (AFM), and scanning tunneling microscopy (STM). The HREELS spectra and images of AFM and STM reveal the precise aqueous NH4F etching process of Si(111) and indicate the high controllability of steps and terraces at the atomic scale. The surface cleanliness and morphology strongly depend on the etching time. At the etching time of 10 min, we obtain an ultraclean and atomically ordered surface with wide terraces of 36±7 nm step distance. It is confirmed by AFM and STM that 1.0% ammonium sulfite is useful for removing dissolved oxygen in the 40% NH4F etching solution and for preparing a high-quality H:Si(111)-(1× 1) surface with a low density of etch pits. The onset of tunneling current and the gap of 1.39 eV are measured by scanning tunneling spectroscopy. There is no peak at -1.3 eV in comparison with the previous report [Phys. Rev. Lett. 65 (1990) 1917].

The surface phonon dispersion was investigated by high-resolution electron-energy-loss spectroscopy on the deuterium-terminated Si͑111͒-͑1 ϫ 1͒ prepared by an improved wet chemical method. The phonon modes were recorded over the entire surface Brillouin zone and compared with the theoretical phonon dispersion curves derived on the basis of semiempirical total-energy scheme calculated by Sandfort et al. ͓Phys. Rev. B 51, 7139 ͑1995͔͒ and by Gräschus et al. ͓Surf. Sci. 368, 179 ͑1996͔͒. The present results of the observation fairly agree with the theoretical curves, except a discrepancy for B 3 and R 1 branches exhibiting a sizable dispersion between 35 and 55 meV, which was predicted to have no dispersion by the theory. The suface-projected bulk phonon is distributed below 65 meV of the vibration energy, and the Si-D modes with higher energies than that are independent of SPBP. The Si-D vibrations with energies between 35 and 65 meV strongly intermix with bulk phonons, and below 35 meV, the Si-D's move together in phase and the surface phonons are the same as those of hydrogen-terminated Si͑111͒-͑1 ϫ 1͒.

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We review a wet chemical process to prepare the high quality hydrogen-terminated Si( 111)-(1×1) surface and show that the two key issues for the high reproducibility are the etching time and the oxygen in the etching solution. We add ammonium sulfite to remove the oxygen according to the previous report [Appl. Surf. Sci. 130, 146 (1998)]. To elucidate the optimal etching time, the vibrational properties and the surface morphology are investigated by high-resolution electron-energy-loss spectroscopy (HREELS), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The HREELS spectra and images of AFM and STM reveal the precise aqueous NH4F etching process of Si( 111) and indicate the high controllability of steps and terraces with atomic scale. The surface cleanliness and morphology strongly depend on the etching time. At the etching time of 10 min, we obtain an ultra-clean and atomically ordered surface with wide terraces of 36 ± 7 nm step distance. It is confirmed by AFM and STM that the 1.0% ammonium sulfite is useful to remove dissolved oxygen in the 40% NH4F etching solution and to prepare a high quality H:Si(111)-(1×1) surface with low density of etch pits. The measurement of scanning tunneling spectroscopy(STS) shows the Schottky diode character of the surface. This surface is well applied to the initial stages of the nano-particle and film growth of Ag atoms and Pentacene molecules.