Advanced Materials Research Vols. 887-888

Abstract: We present a self-collimation-based beam splitter in a two-dimensional photonic crystal (2D-PC) by introducing defects near the termination. From the equi-frequency contour (EFC) calculations and the finite-difference time-domain (FDTD) simulations, we show that the defects can give rise to the splitting of self-collimated beams in 2D-PCs and the directivity of the deflected beam can be improved by the defect along the PC surface. In order to get different kinds of beam splitters, including the Y-shaped, one-to-three, one-to-four structures, and so on, we only need to modify the structure of the output surface (along X-M direction). The proposed splitter may have practical applications in integrated photonic circuits.

Abstract: The molecular geometries, frontier molecular orbital properties, absorption and emission properties of seven 4-thiophene-1,8-naphthalimide derivatives are studied. The ground state optimized structures are obtained by density functional theory (DFT). The lowest singlet states are studied with the configuration interaction singles (CIS) approach. The transition energies of absorption and emission are obtained using time-dependent density functional theory (TD-DFT). It was found that, the 1,8-naphthalimide derivatives with an electron-donating group on the thiophene ring have enhanced fluorescence properties. Our calculations are in good agreement with the experiment results.

Abstract: A simple and easy method is demonstrated for the fabrication of the shape controllable micro-lenses, which are widely used in biomedical systems for improving the image quality as their ability to efficiently focus light into the devices. The micro-lenses were drop on demand printed on the glass micro-holes based on a simple drop on demand printing technique. The shape controllable micro-lenses with a fixed diameter resulting from boundary confinement effect of the micro-holes and the surface wetting conditions are controlled by printing different numbers of drops per micro-lens. The influence of the geometrical shape changes on the optical properties is also investigated. The micro-lens array with different numerical apertures (NA) can be fabricated by controlling the number of drops of the micro-holes as the boundary confinement and hydrophobic effect of the micro-holes.

Abstract: An optically transparent microwave absorbing material based on the destructive interference theory was studied in this paper. The destructive interference phenomenon has been discussed and verified in the transparent microwave absorbing material. According to the destructive interference theory, we designed a type of three-layer microwave absorbing structure to enlarge the absorbing bandwidth. And its reflection coefficient curve stays below -10dB in the range of 7.5GHZ to 17.0GHz.

Abstract: A two-dimensional (2D) triangular lattice photonic crystal coupled-cavity waveguide is designed and optimized. The transmission spectrum of the PC waveguide with TE polarization is calculated by using the finite-difference time-domain (FDTD) method, and the group velocity of c/131.18 at the wavelength is obtained. Through optimizing the parameters of photonic crystal waveguide, different resonance length are obtained by changing the number of the continous air holes. The smallest group velocity is obtained to be c/2209 in the coupled-cavity waveguide with 15 air holes. The mechanism of slow light in the coupled-cavity waveguide of photonic crystal is analyzed.

Abstract: Heavily P type In_0.51Ga_0.49As was grown with hole concentration from 3.3E19cm^-3 to 4.6E19cm^-3. Standard (001) surface Raman backscattering geometry was used to measure samples. Two mode behavior and LO phonon-plasmon-coupled mode (LOPC) were observed obviously. Raman peak of LOPC mode is insensitive to hole concentration. The full width at half maximum (FWHM) of LOPC and the intensity ratio of GaAs-like LO mode and LOPC mode depend on hole concentration. The coupling strength of GaAs-like LO mode and plasmons is weak when hole concentration is very high and Raman peak of LOPC mode is independence with increasing hole concentration.

Abstract: The epitaxial growth of Gallium Nitride (GaN) on 2 inch Si (1 1 1) substrates was investigated, and it was found that by inserting a surface nitridation layer prior to Aluminum Nitride (AlN) nucleation upon substrate, the discoid defects and cracks on the surface were suppressed. Furthermore, compared with the GaN epitaxial layer grown without nitridation, the one with a 30 sec. nitridation layer showed a twice brighter integrated photoluminescence (PL) spectra intensity and a (0 0 2) High-resolution X-ray diffraction (HRXRD) curve width of 13.6 arcminute. The crystalline quality of GaN epitaxial layer became worse when the nitridation time exceeded a critical value, and even more cracks appeared on the surface although no discoid defect appeared anymore.

Abstract: Ho³⁺:BaY₂F₈(Ho:BYF) single crystal was grown by the Czochralski method. The optimal technical parameters obtained are as follows: the pulling rate is 0.5mm/h, the rotation rate is 5rad/min, the cooling speed is 10°C/h.The result of XRD curve shows that as-grown Tm:BYF crystal belongs to the monoclinic system and space group C12/m1. The cell parameters calculated are a=0.642nm,b=1.03293nm,c=0.42621nm,β= 99.62o.The absorption and fluorescence spectra of the Ho:BYF crystal were measured.FWHM is 8 nm on 884 nm wavelength,absorption coefficient and absorption cross-section calculated are 1.21cm^-1 and 1.21×10^-21cm².

Abstract: In order to improve the surface properties of SiO₂ particles, SiO₂ particles were modified by vinyl triethoxysilane, SiO₂ particles and vinyl triethoxysilane modified SiO₂ particles were characterized by FTIR, SEM and XRD techniques. The results showed that vinyl triethoxysilane has been successfully grafted onto SiO₂ particles and basically there are no changes in the size of SiO₂ particles before and after the modification by vinyl triethoxysilane. XRD results show that the synthesized SiO₂ particles have certain crystallinity.

Abstract: Porous silicon (PSi) was fabricated by using electrochemical anodic etching method. Then acid treatment and cathode reduction treatment were employed to improve the luminescence properties and stability of PSi material. Photoluminescence (PL) measurements and scanning electron microscope (SEM) were used to observe the luminescence properties and microstructure of samples, respectively. The results of PL measurements showed that the PL intensity and the stability of luminescence of samples after cathodic reduction and acid treatment were significantly improved. The SEM images showed that the porosity of PSi may be increased through the cathodic reduction treated.