No abstract

International audienceThree types of Ag-coated arrays from porous anodic aluminum oxide (AAO) were prepared and studied as substrates for surface-enhanced Raman scattering (SERS). They were compared with Ag-coated porous silicon (PSi) samples. AAO-based substrates were prepared by the vapor deposition of silver directly onto the surface of porous AAO with different morphologies of the pores, whereas SERS-active island films on the PSi were prepared by immersion plating. The resulting metallic nanostructures were characterized by UV-vis absorption spectroscopy and scanning electron microscopy (SEM). Thermal evaporation leads to the formation of granular arrays of Ag nanoparticles on the surface of AAO. SERS activity of the substrates was tested using water-soluble cationic Zn(II)-tetrakis (4-N-methylpyridyl) porphyrin (ZnTMPyP4) as a probe molecule. The results indicate that all AAO-based substrates studied here exhibit some degree of SERS activity. Noteworthy, for excitation at 532 nm, signals from AAO-based substrates were comparable with those from the PSi-based ones, whereas for 441.6 nm excitation they were about twice higher. The strongest SERS- enhancement at 441.6 nm excitationwas provided by the AAO substrates with silver deposited on the monolith (originally nonporous) side of AAO. Preferential SERS-enhancement of the bands ascribed to the vibrations of the N-methylpyridinium group of ZnTMPyP4 when going to blue excitation was found

543.422+621.357Luminescent properties of anodic alumina fabricated in anodizing solutions containing oxalic, sulfuric, and phosphoric acids in addition to those modified by thermal annealing are investigated. Comparison of the obtained data shows that F + -centers are responsible for the luminescence band at 390 nm. The intense photoluminescence band of porous anodic alumina substrates at 450-500 nm is associated with oxalate anions.Introduction. One of the main areas of progress in nanotechnology is the fabrication and formation of nanostructures with regularly distributed nanoclusters of a certain size and shape. This is due to a large extent by the fact that such geometric properties and the position of the clusters have a critical influence on many important properties of nanomaterials such as optical, electronic, magnetic, etc. Anodic alumina (AA) fabricated by electrochemical oxidation of aluminum in acidic electrolytes has much potential in this sense [1]. The grown AA substrates consist of an ordered periodic structure of nanopores that are perpendicular to the substrate surfaces and have diameters (10-300 nm) and distances between them (20-900 nm) that are regulated by the process conditions. Recently AA membranes have been widely used to fabricate nanostructures for application in solar energy, quantum electronics, and optics [2]. Detailed information on their properties, including optical, is needed in order to develop new nanocomposites based on substrates and films of porous alumina and to predict the properties of the fabricated materials.Questions about the photoluminescence of AA films have been discussed for 30 years. Even in the first research reports on AA films prepared under various fabrication conditions and annealing temperatures it was demonstrated that the photoluminescence spectra and intensity were independent of the purity of the starting aluminum and the impurities in it [3,4]. The strongest luminescence was observed if a solution of oxalic acid was used as the electrolyte. The hypothesis was formulated [3, 4] that the photoluminescence was associated with adsorption of H 2 O at active centers (defects) on the surface of the oxide film. Subsequent research on AA films fabricated in various electrolytes and with variable anodizing regimes [5] showed that the emission intensity was much greater if solutions of organic acids were used. The conclusion was drawn that carboxylic groups incorporated into the oxide films during the anodizing process were the luminescence centers. A similar viewpoint was expressed later [6, 7] that considered the photoluminescence due to traces of oxalic acid present in the AA as an impurity. Based on the obtained temperature dependences of photoluminescence and absorption spectra in addition to electron paramagnetic resonance [8,9], it was proposed that the photoluminescence and optical absorption in the wavelength range 200-600 nm was due to oxygen vacancies (F + -centers) in alumina membranes. Finally, the conclusion was made [10-12] that photoluminescence

No abstract