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Xu D.-X.,NRC Institute for Microstructural Sciences
Topics in Applied Physics | Year: 2011

This chapter reviews the characteristics of SOI ridge waveguide birefringence, as governed by the waveguide cross-section geometry, the cladding stress level, and cladding thickness. Typical stress levels in dielectric cladding films such as silicon dioxide and silicon nitride are such that the stress-induced birefringence is of comparable magnitude to the waveguide geometrical birefringence. Therefore the total waveguide birefringence can be precisely controlled by counter-balancing these two factors. The application of this technique for achieving polarization independence in a variety of photonic components is described, as well as an example of polarization splitting. Passive and active tuning of the stress-induced birefringence is discussed. The use of birefringence tuning to enhance the efficiency in optical parametric processes and stress-induced Pockels electro-optic effect are also briefly addressed. © Springer-Verlag Berlin Heidelberg 2011.

Voznyy O.,NRC Institute for Microstructural Sciences
Journal of Physical Chemistry C | Year: 2011

We have performed ab initio calculations of electronic properties of the realistic Cd-rich CdSe nanocrystals with covalently bound carboxylic acid (X-type) ligands. Configurations both with and without surface traps can be prepared depending on the amount and geometry of the adsorbed ligands. We find that Cd and Se dangling bonds do not necessarily create surface traps, whereas traps originating from ligands can form near the top of the valence band. Some of the ligands are found to be mobile on the surface and this mobility is accompanied by a spectral diffusion of the associated trap energy levels. This provides the first atomistic example of the processes required to explain the emission wavelength and lifetime variations, and blinking of the nanocrystals. © Published 2011 by the American Chemical Society.

Kadantsev E.S.,NRC Institute for Microstructural Sciences | Hawrylak P.,NRC Institute for Microstructural Sciences
Applied Physics Letters | Year: 2011

A model for the evolution of conduction and valence bands of IIIA-VA (InAs, GaAs, and InP) semiconductors under (001) biaxial strain is developed. The model is based on the ab initio calculations which take into account finite strain dependent relaxation of the reference levels. The results of ab initio full potential calculations of absolute deformation potentials (ADPs) and (001) biaxial strain-modified band edges are reported. It is shown that in type I heterostructures subjected to (001) compressive biaxial strain, the corrections due to nonzero ADP of the core reference levels reduce the strained band offset for holes. © 2011 American Institute of Physics.

Kadantsev E.S.,University of Ottawa | Kadantsev E.S.,NRC Institute for Microstructural Sciences | Hawrylak P.,NRC Institute for Microstructural Sciences
Solid State Communications | Year: 2012

The electronic structure of a single MoS 2 monolayer is investigated with all electron first-principles calculations based on Kohn Sham Density Functional Theory and variational treatment of spin-orbital coupling. The topologies of the valence band maximum and conduction band minimum are explored over the whole Brillouin zone. The single MoS 2 monolayer is confirmed to be a direct band gap semiconductor. The projected density of states (PDOS) of a single monolayer is calculated and compared to that of bulk MoS 2. The effective masses and the orbital character of the band edges at high-symmetry points of the Brillouin zone are determined. The spin-splittings of the conduction band minimum (CBMIN) and valence band maximum (VBMAX) are calculated over the whole Brillouin zone. It is found that the maximum spin-splitting of VBMAX is attained at the K point of the Brillouin zone and is responsible for the experimentally observed splitting between the A 1 and B 1 excitons. © 2012 Elsevier Ltd. All rights reserved.

Finnie P.,NRC Institute for Microstructural Sciences | Lefebvre J.,NRC Institute for Microstructural Sciences
ACS Nano | Year: 2012

Individual air-suspended single-walled carbon nanotubes are imaged both spatially and spectrally in photoluminescence. At low excitation power, photoluminescence is bright and stable with high quantum efficiency; however, higher power initially causes a gradual red shift and then more severe changes. Blinking, the loss of quantum efficiency, and the appearance of new deep levels are all seen and can be explained by the introduction of defects. We propose that optical excitation induces molecular deposition onto the nanotube by optically induced van der Waals interactions, leading to physisorption and ultimately chemisorption which severely degrades the luminescence. © Published 2012 by the American Chemical Society.

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