Isotope dependence of the lifetime of the vibration of oxygen in silicon

Temperature dependence of phonon-defect interactions: phonon scattering vs. phonon trapping

The interactions between thermal phonons and defects are conventionally described as scattering processes, an idea proposed almost a century ago. In this contribution, ab-initio molecular-dynamics simulations provide atomic-level insight into the nature of these interactions. The defect is the Si|X interface in a nanowire containing a δ-layer (X is C or Ge). The phonon-defect interactions are temperature dependent and involve the trapping of phonons for meaningful lengths of time in defect-related, localized, vibrational modes. No phonon scattering occurs and the momentum of the phonons released by the defect is unrelated to the momentum of the phonons that generated the excitation. The results are extended to the interactions involving only bulk phonons and to phonon-defect interactions at high temperatures. These do resemble scattering since phonon trapping occurs for a length of time short enough for the momentum of the incoming phonon to be conserved.

Rotational and vibrational excitations of a hydrogen molecule trapped within a nanocavity of tunable dimension

The rotational and vibrational transitions of a hydrogen molecule weakly adsorbed on the Au(110) surface at 10 K were detected by inelastic electron tunneling spectroscopy with a scanning tunneling microscope. The energies of the j=0 to j=2 rotational transition for para-H(2) and HD indicate that the molecule behaves as a three-dimensional rigid rotor trapped within the tunnel junction. An increase in the bond length of H(2) was precisely measured from the downshift in the rotational energy as the tip-substrate distance decreases.

The spectral bandshape of the ν(3) (1136 cm(-1)) vibration of oxygen in silicon and dilute silicon-germanium alloys

At room temperature, the ν(3) (1136 cm(-1)) absorption band of oxygen in silicon and Si(1 - x)Ge(x) alloys consists of dozens of components, masking the properties of the individual transitions. Here, experimental data are presented for the evolution of the ν(3) band in the temperature range 0 < T < 300 K and the composition range 0 ≤ x ≤ 0.066. The vibrational potential for Si:O is developed to provide accurate fits to the absorption data. The potential predicts properties consistent with published studies, including hydrostatic stress experiments. Extending the model to Si(1 - x)Ge(x) allows the properties of the alloy-induced O(i)-I, O(i)-II and O(i)-III components to be investigated accurately to higher values of x than hitherto. The properties of O(i)-I are understood as perturbations by Ge atoms of Si:O, and O(i)-III is rationalized in terms of off-axis movement of the O atom resulting from the nearby Ge atom. Challenges to theory are: the behaviour of O(i)-II, understanding the strain fields generated by Ge atoms in Si, and the reduced coupling of the ν(2) and ν(3) modes with increasing amplitude in the ν(2) mode.