SiO2/TiO2 distributed Bragg reflector near 1.5 μm fabricated by e-beam evaporation
The authors report on the fabrication and characterization of SiO2/TiO2 distributed Bragg reflector (DBR) mirrors operating at the eye safe and optical communication wavelength window, λ = 1.5 μm. Our experimental results demonstrated that SiO2/TiO2 DBR mirrors with reflectivity exceeding 95% at λ = 1.5 μm can be achieved using e-beam evaporation in conjunction with postdeposition thermal annealing process in ambient air. It was found that the postdeposition annealing process transformed the crystal structure of the as-deposited TixOy to TiO2, leading to a significant reduction in optical absorption. Erbium doped III-nitride semiconductors incorporating DBR mirrors at 1.5 μm emission may open up many novel applications, including infrared emitters, optical amplifiers, and high power infrared lasers.
Structural modification, photoluminescence, and magnetic property enhancement with Er3+ doping, of sol–gel TiO2 thin films
Nanocrystalline undoped and Er3+ doped TiO2 thin films were prepared by sol–gel dip-coating technique onto glass substrates. Post-deposited films were annealed at 450 °C for 1 h. Differential scanning calorimetric analysis showed that undoped film crystallization occurred at 339 °C, while it appears at lower temperature for Er:TiO2. X-ray diffraction and Raman spectroscopy results indicate that the films crystallize only into anatase phase, and the crystallite size decreases from 24.3 to 21.16 nm with increasing Er3+ doping ratio. The photoluminescence (PL) spectra are composed of two broad peaks at 520–570 nm and 640–680 nm assigned to (2H11/2, 4S3/2)–4I15/2 and 4F9/2–4I15/2 transitions of Er3+ ions, respectively. PL emission intensities increase gradually raising the erbium doping ratio. Vibrating sample magnetometer results of undoped TiO2 thin films reveal a ferromagnetic behavior at room temperature and erbium doping leads to an enhancement of the saturated magnetic moment (Ms).
The unfolded universe of elementary particles. A geometric explanation of the standard model structure
We propose a geometric explanation of the standard model of Glashow, Weinberg and Salam for the known elementary particles. Our model is a generic Quantum Field Theory in dimension four, obtained by developing along a Lorentz sub-manifold the lagrangian of Einstein and Dirac in dimension twelve. The main mechanism which gives birth to the standard model is a certain gauge fixing of triality, which permits to identify the multiplicity of fermions, as seen from the four dimensional world, with the eight unseen dimensions of the generating universe. In this way we get the known tables of particles, explaining the series of fermions and the gauge bosons. We suggest that the Higgs field dynamics could appear through a bosonization of the right handed neutrino and correspond to a displacement in the unseen dimensions. We also propose hypotheses for dark matter, and perhaps dark energy. Then we suggest predictions to go beyond the standard model.