Ab initiostudy of adsorption and diffusion of Ag atoms on a Si(001) surface

Abstract

By employing ab initio total-energy calculations we have studied adsorption and diffusion of Ag atoms on a dimer-reconstructed Si͑001͒ surface. For a single Ag adsorption, the twofold-coordinated cave site above the fourth Si layer atom was found to be the most stable, in agreement with previous works. Inspection of the electronic structures at the cave site revealed that the Ag-Si bonds originate from low-lying 4d electrons and are covalent. Our calculations also exhibit another stable adsorption at the pedestal site that is slightly higher by 0.03 eV in energy than the cave site. Further potential-energy-surface calculations showed that the surface diffusion of a single Ag adatom is unexpectedly highly isotropic and that the energy barrier is 0.5 eV. When more Ag adatoms are adsorbed on the Si surface, the Ag adatoms are expected to form dimers. Actually, we obtained an energy gain of 0.36 eV/dimer through the dimerization. The diffusion of an Ag dimer was also investigated. Surprisingly, we found a very rapid surface-dimer diffusion with an energy barrier of 0.48 eV slightly lower than that of the single Ag adatom. In contrast to the diffusion of the single Ag adatom, the dimer diffusion is anisotropic and preferably occurs along the valley between Si dimer rows by concerted flipflop processes.

Role of surface defects in room-temperature growth of metals on Si(100)2 × 1

“…On the STM images, no diffusing adsorbate could be identified. This corresponds to a fast diffusion when compared to scanning speed ≈ 1 frame per min., in agreement with ab initio total-energy calculations [8]. Defects of missing Si dimers (A and B-type defects), appearing as dark features on the images, remain unoccupied during deposition, even if an island surrounds the defect (see the defect marked by arrow in Fig.…”

Atomically resolved nucleation and initial growth of a Ag three-dimensional island on Si(001) substrate

“…Transformation of the island occurs via emission of Ag atoms from an unstable part of the island and absorption of Ag atoms in an energetically favorable part. To date, there has been a theoretical study on the surface diffusion of Ag adatoms and Ag dimers on the clean Si(001) substrate, 16 in which diffusion barriers of ∼0.5 eV were found. To the best of our knowledge, there have been no reports of theoretical predictions for the diffusion barrier of Ag atoms on the Ag 2D layer.…”

Optical properties of amorphous and crystalline silicon surfaces functionalized with Agn adsorbates

“…The physical and electronic effects resulting from the deposition of silver nanoparticles on silicon surfaces have been studied extensively in recent experimental and theoretical work—by methods including visible range spectroscopy, surface enhanced Raman spectroscopy, scanning tunneling microscopy (STM), and surface photovoltage (SPV) techniques 23–35. Experimentally, observations of such systems reveal a sharp electronic transition from semiconducting to metallic behavior at the Ag/Si interface 33–35.…”

“…The physical and electronic effects resulting from the deposition of silver nanoparticles on silicon surfaces have been studied extensively in recent experimental and theoretical work—by methods including visible range spectroscopy, surface enhanced Raman spectroscopy, scanning tunneling microscopy (STM), and surface photovoltage (SPV) techniques 23–35. Experimentally, observations of such systems reveal a sharp electronic transition from semiconducting to metallic behavior at the Ag/Si interface 33–35. In our ongoing research, theoretical treatments of the Ag n /Si(111) surface are being used for the ab initio description of the SPV created on electronic excitation 17, 36, for the dynamics of electron transfer 37, 38, and for predictions of the energies and lifetimes of optically excited states 10.…”