X-Irradiation-Induced Disorganization of Cytoskeletal Filaments and Cell Contacts in HT29 Cells

Organization of cytoskeleton and cell contacts were studied by immunochemistry and electron microscopy in confluent HT29 cultured cells following exposure to 0.5 and 1.0 Gy doses of X-ray. Microtubules were resistant to irradiation, whereas, the actin and intermediate filaments disrupted rapidly following the treatment and their components appeared as clumps of actin and cytokeratin aggregates in the cytoplasm as demonstrated by immunochemistry. Loss of cell contacts and decrease in the number of desmosomes was also characteristic of irradiated cells. Electron microscopy revealed intact desmosomes in control cells and abnormal desmosomes in the irradiated samples characterized by the absence of tonofilaments. The perinuclear filament network and cortical filaments were well detectable by electron microscopy. Under the effect of irradiation, the perinuclear filaments almost disappeared and, at the same time, small bundles of filaments were formed irregularly in the cytoplasm associated with amorphous material

Doublet structures in quantum well absorption spectra due to Fano-related interference

In this theoretical investigation we predict an unusual interaction between a discrete state and a continuum of states, which is closely related to the case of Fano-interference. It occurs in a GaAs/AlxGa1-xAs quantum well between the lowest light-hole exciton and the continuum of the second heavy-hole exciton. Unlike the typical case for Fano-resonance, the discrete state here is outside the continuum; we use uniaxial stress to tune its position with respect to the onset of the continuum. State-of-the art calculations of absorption spectra show that as the discrete state approaches the continuum, a doublet structure forms which reveals anticrossing behaviour. The minimum separation energy of the anticrossing depends characteristically on the well width and is unusually large for narrow wells. This offers striking evidence for the strong underlying valence-band mixing. Moreover, it proves that previous explanations of similar doublets in experimental data, employing simple two-state models, are incomplete.Comment: 21 pages, 5 figures and 5 equations. Accepted for publication in Physical Review

Polarization insensitive InGaAs/InGaAsP/InP amplifier using quantum well intermixing

NRC publication: Ye

Focused ion beam lithography of multiperiod gratings for a wavelength-division-multiplexed transmitter laser array

Wavelength-division multiplexing with closely spaced multiple wavelengths is of great interest for high-capacity data transmission. One major and very critical requirement of such a system is the fabrication of a laser array with very small wavelength separations ( 3c2 nm). In this paper, the design, fabrication, and performance of an integrated eight-channel system is described. Focused ion beam lithography, with the beam deflection sensitivity modified from its calibrated value, is used to write the critical stepped-period distributed-Bragg-reflector gratings required to provide the tightly controlled multiple laser frequencies. The outputs of the lasers are combined via curved waveguides into a single optical output.NRC publication: Ye

Bandgap tuning of semiconductor quantum well structures using ion implantation

Ion induced QW intermixing using broad area and focused ion beam (FIB) implantation was investigated at low energy (32 and 100 keV respectively) in three different material systems (GaAs/AlGaAs, InGaAs/GaAs, and lattice matched InGaAs/InP). Repeated sequential ion implants and rapid thermal anneals (RTAs) were successful in delivering several times the maximum QW bandgap shift achievable by a single implant/RTA cycle. The effectiveness of broad area high energy implantation (8 MeV As4+) on QW intermixing was also established for GRINSCH (graded-index separate confinement heterostructure) QW laser structures grown in InGaAs/GaAs. Lastly, preliminary work illustrating the effects of implant temperature and ion current density was carried out for InGaAs/GaAsQWs.NRC publication: Ye

Quantum-well intermixing for optoelectronic integration using high energy ion implantation

The technique of ion-induced quantum-well (QW) intermixing using broad area, high energy (2\u20138 MeV As4+) ion implantation has been studied in a graded-index separate confinement heterostructure InGaAs/GaAs QW laser. This approach offers the prospect of a powerful and relatively simple fabrication technique for integrating optoelectronic devices. Parameters controlling the ion-induced QW intermixing, such as ion doses, fluxes, and energies, post-implantation annealing time, and temperature are investigated and optimized using optical characterization techniques such as photoluminescence, photoluminescence excitation, and absorption spectroscopy.NRC publication: Ye