Key Engineering Materials Vols. 277-279

Abstract: The photopolymerization of aromatic methacrylate in organic-inorganic nanocomposite films for holographic recording media was investigated. Thick photopolymer films (thickness>200 µm) were prepared using organic-inorganic hybrid solutions containing high refractive index monomers, through the sol-gel process. These photopolymer films were polymerized upon exposure to a visible light with high photo conversions. The photopolymerization was highly effective under visible light irradiation and could be applied to a holographic medium with high diffraction efficiency (>95 %) by using a 532nm laser. The diffraction efficiency of the film was much affected by morphology, which might affect monomer diffusion during the recording.

Abstract: Nanostructured iron and cobalt ferrite particles were prepared from iron chloride and cobalt chloride, respectively, using the sonochemical method. The particles were compared with those synthesized using the co-precipitation method. The properties of the particles were characterized using various techniques, such as XRD, TEM, VSM and a SQUID magnetometer. The iron ferrite particles had an average particle size of about 15 nm and a magnetization value of 83 emu/g at a magnetic field of 50 kOe, while the particle size of cobalt ferrite was about 5 nm and its magnetization value was 33 emu/g at the same magnetic field.

Abstract: We investigate the third order harmonic generation for model atoms interacting with intense short laser pulses. We focus on the cases where the ponderomotive energy is not big enough to generate high-order harmonics, and where resonant transitions between bound states are also as important as multi-photon ionization and low-order harmonic generation. We find that the third order harmonic intensity from a model hydrogen atom can decrease as the laser frequency draws near a resonance between bound states. We explain this result by looking into the ionization and Rabi oscillation from the numerical calculation of the time-dependent 1-D Schrödinger equation. In order to support our explanation we also investigate the populations of bound states that play an important role in this atomic process.

Abstract: This paper presents a simple and novel model for low-frequency noise generation in polycrystalline-Si resistors within the number fluctuation model. The grain boundary in polycrystalline-Si thin films is the major source of noise and is modeled as independent symmetric Schottky barriers in series, face-to-face. It has been found that trapping and detrapping of the carriers at the traps in the space charge region of the grain boundary via thermal activation modulate the barrier height and generate the low-frequency noise. The model successfully explains the experimental data and gives useful information about the defects in the space charge region of the grain boundary. As a result, the Hooge parameter is interpreted in terms of defect density, among other parameters.

Abstract: Photoexcitation of “proton sponge” 1,8-bis (dimethylamino) naphthalene (DMAN) leads to charge transfer (CT) emission. This work demonstrates that substitution of DMAN with a strong electron acceptor group (CN) results in CN-DMAN and leads to a stronger orbital decoupling between the Donor and Acceptor groups and to a more effective CT process (λF = 630 nm). The theoretical absorption spectrum calculated for CN-DMAN using the ZINDO method on its ground state ab initio [HF/6-31G(d)] optimized geometry reproduces a better experimental spectrum than that calculated using the RCIS method. It also shows that AM1 excited state (1La) optimization reveals two quasi-degenerated states with anti-quinoidal (A) and quinoidal (B) structures and the CT nature. Both structures may contribute more or less equally to the fluorescence of CN-DMAN in a solution.