Activation process-dependent characteristics of novel thermionic oxide cathodes for CRT application

The emission and conductivity characteristics of oxide cathodes depend largely on the activation process. In this paper, the electrical properties of new type of oxide cathodes for cathode ray tube (CRT) application, supplied by LG Philips Displays, have been investigated in relation to different cathode activation regimes. The influence of the activation process over different durations has been investigated. A temperature of T=1425 K was chosen to be higher than the optimum cathode activation temperature (T=1200 K), and the other temperature of T=1125 K was lower than that. The electron activation energy (E) was found to vary in the range from 0.58 to 2.28 eV for cathodes activated at the higher temperature regime, and from 1.08 to 1.9 eV for those activated at the lower temperature regime. Scanning electron microscopy (SEM) and electron diffraction X-ray (EDX) analyses show a structural phase transformation in the oxide material that was activated at 1125 K for a period of 1-12 hours. The SEM mapping shows a large contamination of Ba in the top layer of oxide material. The activator agents tungsten and aluminum are found to penetrate into the BaO/spl bsol/SrO layer in two different ways.     

Planar silicon nitride waveguides for biosensing

The principles of attenuation of the light intensity due to multiple reflections are realised in a planar silicon oxide (SiO(2))silicon nitride (Si(3)N(4)) waveguiding structure for the purpose of developing optical biosensors with improved sensitivity. The analysis of the experimental data shows that the large difference in refractive indices of core and cladding layers gives rise to an increase in sensitivity by a factor of 3 over previously reported structures. Composite polyelectrolyte self-assembled thin films containing cyclo-tetra-chromotropylene as an indicator and enzymes glucose oxidase or urease were employed in the superstrate as a sensing membrane. Individual enzyme reactions as well as their inhibition by pesticides were studied by monitoring the intensity of light output from the planar waveguide. The results were compatible with those obtained by conventional ultraviolet-visible absorption spectroscopy. The instrument detection limit for Imidacloprid pesticide was found to be as low as 10 ppb in concentration.     

Optical study on II-VI semiconductor nanoparticles in Langmuir-Blodgett films

Cadmium sulfide (CdS) nanoparticles formed within Langmuir-Blodgett (LB) films of stearic acid and calix[8]arene were studied with different optical methods including surface plasmon resonance (SPR), ellipsometry and UV-visible absorption and fluorescence spectroscopies. For the first time, the process of formation of CdS nanoparticles within LB films was monitored in-situ with SPR. The results of ellipsometry, SPR and UV-vis absorption spectroscopy were analyzed to evaluate simultaneously the thickness, refractive index and extinction coefficient of LB films. It was shown that all three parameters increase as a result of formation of CdS nanoparticles. Photoluminescence measurements provided direct confirmation directly for previous observation with UV-vis absorption spectroscopy of the blue spectral shift caused by CdS particles formation. The observed large Stoke's shift of the luminescence band is discussed in terms of the formation of "dark excitons" in the platelet-type CdS nanoclusters. AFM study shows the formation of pseudo-two dimensional platelets of CdS with the lateral dimensions in the range of 20-30 nm.     

Resistivity network and structural model of the oxide cathode for CRT application

In this paper, the electrical properties of oxide cathode and oxide cathode plus, supplied by LG Philips Displays, have been investigated in relation to different cathode activation regimes and methods. Oxide cathode activation treatment for different durations has been investigated. The formations of the compounds associated to the diffusion of reducing elements (Mg, Al, and W) to the Ni cap surface of oxide cathode were studied by a new suggestion method. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) was used as analytical techniques. Al, W, and Mg doping elements take place during heating to 1080 K (Ni-Brightness) under a rich controlled Ba-SrO atmosphere through an acceleration life test. The chemical transport of these elements was occurred mainly by the Ni cap grain boundary mechanism with significant pile-up of Mg compounds. Al and W show a superficial concentrations and distribution. A new structural and resistivity network model of oxide cathode plus are suggested. The new structural model shows a number of metallic and metallic oxide pathways are exist at the interface or extended through the oxide coating. The effective values of the resistances and the type of the equivalent circuit in the resistivity network model are temperature and activation time dependent.     

Optical investigation of thin films of liquid–crystalline lutetium bisphthalocyanine

Thin films of bis[4,5,4,5,4,5,4,5]-octakis(hexylthiophthalocyanine) of lutetium(III) were prepared by spin coating at different speeds in the range of 2000–6000 rpm. The films undergo phase transition on heat treatment at temperatures above 120 °C and the formation of a mesophase. The Q-bands in the visible absorption spectra of the films are broader and become red shifted compared to ones obtained for molecules in chloroform solution. Heat treatment produces molecular ordering, which is believed to be due to the edge-to-edge interaction between neighboring Pc moieties. Reduced film thickness and changes in optical constants are also attributed to thermally induced molecular reorganization corresponding to the liquid crystalline phase. AFM and polarized microscopy images are consistent with the phase transformations.     

noloco: An efficient implementation of van der Waals density functionals based on a Monte-Carlo integration technique

The treatment of van der Waals interactions in density functional theory is an important field of ongoing research. Among different approaches developed recently to capture these non-local interactions, the van der Waals density functional (vdW-DF) developed in the groups of Langreth and Lundqvist is becoming increasingly popular. It does not rely on empirical parameters, and has been successfully applied to molecules, surface systems, and weakly-bound solids. As the vdW-DF requires the evaluation of a six-dimensional integral, it scales, however, unfavorably with system size. In this work, we present a numerically efficient implementation based on the Monte-Carlo technique for multi-dimensional integration. It can handle different versions of vdW-DF. Applications range from simple dimers to complex structures such as molecular crystals and organic molecules physisorbed on metal surfaces.     

Investigation of gas-sensing properties of copper phthalocyanine films

In this work, the sensor response of thin films of octasubstituted copper phthalocyanine derivative (CuPcR₈) with bulky substituents on R = –N(SO₂C₆H₅–CH₃)CH₂(CH₂)₈CH₃ to the vapour of benzene, chloroform, ethanol and butanol were investigated by surface plasmon resonance technique. The application and some advantages of total internal reflection ellipsometry method for determination of the organic vapours are also demonstrated.     

Lead sulphide/phthalocyanine nanocomposite spun films

Composite lead sulphide/phthalocyanine thin films were produced for the first time by exposure of thin spun films of a lipophilic lead phthalocyanine derivative to H/sub 2/S gas. The formation of lead sulphide was confirmed by Raman and X-ray photoelectron spectroscopy measurements. UV-visible absorption and photoluminescence spectral measurements as well as a film morphology study using atomic force microscopy indicate the formation of lead sulphide clusters. From the blue spectral shift of the fundamental adsorption band, the size of the PbS clusters was estimated to be 2.24 nm.