arXiv subjects

Shang-Fen Ren

Publications and source records attributed to Shang-Fen Ren.

4 recordsLinked to original sources

arXiv2006

Self-diffusion on Si(001) mono-hydride surfaces revisited: The role of adatom clustering

First-principles total-energy calculations of the H/Si(001)-2x1 surfaces reveals a dual diffusion process for the Si adatoms: single along the dimer row while pairing up across the row. The calculated diffusion barrier along the dimer row is 1.1 eV, which is, however, too small to account for the hydrogen-induced growth disruption seen by experiments. Instead, we find that the adatom diffusion, in the presence of H, leads to the formation of immobile fourfold-ring Si tetramers which are difficult to break. This could explain the adverse effects of H on Si homoepitaxy.

physics.comp-ph↗

arXiv2002

Calculations on Electronic States in QDs woth Saturated Shapes

Electronic States of Si and Ge QDs of 5 to 3127 atoms with saturated shapes in a size range of 0.57 to 4.92 nm for Si and 0.60 to 5.13 nm for Ge are calculated by using an empirical tight binding model combined with the irreducible representations of the group theory. The results are compared with those of Si and Ge quantum dots with spherical shape. The effects of the shapes on electronic states in QDs are discussed.

cond-mat.mtrl-sci↗

arXiv2001

Calculations on the Size Effects of Raman Intensities of Silicon Quantum Dots

Raman intensities of Si quantum dots (QDs) with up to 11,489 atoms (about 7.6 nm in diameter) for different scattering configurations are calculated. First, phonon modes in these QDs, including all vibration frequencies and vibration amplitudes, are calculated directly from the lattice dynamic matrix by using a microscopic valence force field model combined with the group theory. Then the Raman intensities of these quantum dots are calculated by using a bond-polarizability approximation. The size effects of the Raman intensity in these QDs are discussed in detail based on these calculations. The calculations are compared with the available experimental observation. We are expecting that our calculations can further stimulate more experimental measurements.

cond-mat.mtrl-sci↗

arXiv2001

Microscopic interface phonon modes in structures of GaAs quantum dots embedded in AlAs shells

By means of a microscopic valence force field model, a series of novel microscopic interface phonon modes are identified in shell quantum dots(SQDs) composed of a GaAs quantum dot of nanoscale embedded in an AlAs shell of a few atomic layers in thickness. In SQDs with such thin shells, the basic principle of the continuum dielectric model and the macroscopic dielectric function are not valid any more. The frequencies of these microscopic interface modes lie inside the gap between the bulk GaAs band and the bulk AlAs band, contrary to the macroscopic interface phonon modes. The average vibrational energies and amplitudes of each atomic shell show peaks at the interface between GaAs and AlAs. These peaks decay fast as their penetrating depths from the interface increase.

cond-mat.mtrl-sci↗