The adsorption of pyridine onto the Ge(100) surface has been studied using both real-time scanning tunneling microscopy (STM) and ab initio pseudopotential density functional calculations. The results show that pyridine molecules adsorb on the electron-deficient down-Ge atoms of the Ge=Ge dimers via Ge-N dative bonding, with the pyridine ring tilted to the surface. The electron-rich up-Ge atoms remaining after adsorption of pyridine induce an asymmetric dimer row, which is mainly reconstructed to the c(4 x 2) structure. At pyridine coverage of 0.25 ML, the adsorbed pyridine molecules form a perfectly ordered monolayer. The entire Ge substrate underlying this organic monolayer rearranges into the c(4 x 2) structure.

We present an atom‐resolved analysis method that traces physical quantities such as the root‐mean‐square bond length fluctuation and coordination number for individual atoms as functions of temperature or time. This method is applied to explain the temperature‐dependent behaviors of three types of NiN (N=12,13,14) clusters. The detailed studies for the three types of clusters reveal characteristics as follows: (a) as the temperature increases, all three types of clusters undergo two‐stage melting, irrespective of the existence of vacancy or adatom on the icosahedral surfaces, (b) the melting of icosahedral clusters with vacancy starts with vacancy hopping, which has not been observed for any type of small clusters (N<34), (c) the melting of the icosahedral clusters with adatom (N=14) is initiated by adatom hopping, followed by the site exchange between the adatom and surface atoms. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 380–387, 2000

We have performed ab initio pseudopotential calculations in order to investigate the atomic and electronic structure of pyridine adsorbed on the Ge(100) surface. A large number of pyridine/Ge(100) adsorption configurations possibly resulting from cycloadditions and Lewis acid−base reactions are presented. The configuration having the Ge−N linkage formed by dative bonding with adsorbed pyridine molecules tilted is the most stable, which explains the experimental STM images well. The dative bonding character is investigated by comparing the charge densities for the clean and pyridine-adsorbed Ge(100) surfaces. Finally the difference between the Ge(100) and Si(100) surfaces is discussed.

The adsorption structures and thermal desorption behavior of C 2 H 2 on Ge͑100͒ were studied in ultrahigh vacuum by scanning tunneling microscopy ͑STM͒ and temperature programmed desorption ͑TPD͒. The STM investigation revealed that, at low coverage, C 2 H 2 initially adsorbs onto the Ge͑100͒ surface with two types of configurations: ͑i͒ a diconfiguration on top of a single Ge-Ge dimer ͑on-top͒ and ͑ii͒ a tetra-configuration parallel to the dimer axes, bridging two neighboring Ge dimers (p-bridge͒. TPD measurements show that chemisorbed C 2 H 2 desorbs from Ge͑100͒ nondissociatively with two different desorption features, denoted as ␣ ͑520 K͒ and ␤ ͑560 K͒. In addition, it was found that the desorption of C 2 H 2 follows first order kinetics for both states and that the desorption energies of the ␣ ͑520 K͒ and ␤ ͑560 K͒ states are 1.3 and 1.4 eV, respectively. STM studies of the adsorption of C 2 H 2 at various Ge surface temperatures indicate that the ␣ and ␤ features correspond to the on-top and p-bridge configurations, respectively.

The atomic-scale structural evolution of Ge͑100͒ surfaces etched by H͑g͒ and D͑g͒ at T s ϭ400 K is studied using scanning tunneling microcopy ͑STM͒ and field emission-scanning electron microscopy ͑FE-SEM͒. The STM investigation reveals that etching of the Ge͑100͒ by H͑g͒ and D͑g͒ proceeds initially via the production of single atom vacancies ͑SV͒, dimer vacancies ͑DV͒, and subsequently, line defects along the Ge dimer rows. It is also observed that D͑g͒ etches the Ge͑100͒ surface eight times faster than H͑g͒ does. After extensive exposures of the surface to H͑g͒, the FE-SEM images show square etch pits with V-groove shapes, indicating that H͑g͒ etching of the Ge͑100͒ surface proceeds anisotropically.