Photoluminescence quenching response of as prepared and surface modified porous silicon sensors in presence of organic analytes in gas phase was studied. Surface modification aimed at increasing of operational stability and modification of sensoric response was performed by a hydrosilylation reaction with various organic compounds - methyl 10-undecenoate, haemin, cinchonine and quinine. These sensors were tested for a homological set of aliphatic alcohols from methanol to hexanol. We have systematically measured changes in porous silicon photoluminescence intensity as a function of concentration of detected analytes and evaluated sensitivity, detection limit and linear dynamic range of our sensors. Speed of the sensoric response was of the order of seconds. The obtained sensoric parameters were correlated with chemical and physical properties of both the compounds used for derivatization and the detected analytes.
Ivan Pelant, Katerina Luterova, Petr Fojtik, Jean-Luc Rehspringer, Dominique Muller, Jean-Jacques Grob, Juraj Dian, Jan Valenta, Rolandas Tomasiunas, Bernd Honerlage
We review critically recent results of investigation of hydrogenated amorphous silicon (a-Si:H) and Si+- implanted SiO2 films from the point of view of light- emission applications. Wide bandgap a-Si:H with the energy gap ranging from 2.0 to 2.2 eV exhibits room temperature photoluminescence in the visible region. Electroluminescence, however, occurs after previous recrystallization of a-Si:H only and seems not to be perspective for large scale applications. Si+-implanted SiO2 films contain, after proper annealing at 1000 - 1100 degrees Celsius, Si nanocrystals that luminesce in the red. In parallel another emission band can occur (in the blue region) which is related to post-implantation defects. We demonstrate that in SiO2 films homogeneously implanted across the entire film thickness red electroluminescence can be easily observed, presumably due to injection of electron-hole pairs into Si nanocrystals. Finally, the present status of prospects of stimulated emission achievement in low-dimensional Si structures is briefly summarized.
Room temperature visible photoluminescence (PL) and electroluminescence (EL) of wide band gap hydrogenated amorphous silicon thin films prepared in SiH4 microwave plasma strongly diluted with He is reported. The emission spectra are peaked at approximately 1.5 eV. Films were characterized by means of optical and IR absorption and hydrogen thermal desorption. The band gap of a-Si:H films varies within the interval 2.0-2.2 eV. The strong evidence for two distinct types of PL processes is presented: one being linked with oligosilanes and the second one attributed to electron-hole recombination in tail states. EL has been investigated in p-i-n and p+-p-n-n+ structures with CrNi/ITO contacts. The EL occurs after initial forming in reverse bias only and its external quantum efficiency is approximately 10-5 percent. The shape and spectral position of EL spectra suggest that the light emission in this case is probably due to simultaneous excitation of the oligosilane units and impact ionization by hot electrons.
Langmuir—Blodget (LB) films are thin or ultrathin molecular layer systems. They are good basis for the creation of molecular encembles with predetermined architecture including superlattices and quasi two-dimensional systems. This opens new possibilities for a detailed investigation of various intermolecular coupling. In this paper we present preliminary fluorescence hole burning data of metal-free tetra-4-terc-butyl phthalocyanine (H2TTBPc) in LB film.
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