Study Of Physical Characteristics Of Heat-treated Silver Nanoparticle Containing Silica Thin Films

Noble metallic nanostructures are attracting increasing interest as an importantclass of photonic components to control and manipulate light on the nanometer scale.When the surface of noble metallic nanostructures is excited by electromagneticradiation, the conductive electronic oscillations result in surface Plasmon resonance(SPR) and produce surface plasmons (SPs) spread along the surface of the particles.Plasmonic excitations provide a means to focus light to subwavelength dimensions,which would overcome optical diffraction limits and enable the design of nanoscaleoptical devices, such as waveguides. The intense local electromagnetic fields ofmetallic nanostructures accompanying plasmon resonance can also be exploited forsurface enhanced spectroscopy. The theoretical studies and experimental work havesuggested that the exact position and intensity of SPR is extremely sensitive toparticle size and shape, as well as to the optical and electronic properties of themedium surrounding the particles.Nanoparticle clusters of noble metals can be introduced into a dielectric matrixvia different. Due to the low processing temperature, homogeneity as well aschemical purity of the resulting samples, easy adjusting of metal concentration toprepare nano-sized metal particles with a narrow particle size distribution, andpossibility of adding reducing and oxidizing agents in small concentrations, thesol–gel method has been considered as one of the most useful and versatiletechniques oxide film fabrication. Ag particles have been incorporated by dissolvingsilver salts in the precursor sols followed by reduction of the silver ions to metallicparticles by heat-treatment or UV irradiation. During the formation of Ag colloids ina heat-treatment, temperature is an important parameter for changing the size, shapeand the chemical state of the resulting silver nanoclusters. It will affect the opticaldensity and absorption characteristics of the Ag nanoparticles.Metal NPs are mostly characterized by transmission electron microscopy(TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis(EDX), X-ray photoelectron spectroscopy (XPS) and UV-visible spectroscopy. TEMis valuable for studying thin sections of samples to examine internal structures. Italso provides useful data on the size and shape distribution of the nanoparticlesThe present dissertation describes the synthesis, characterization, andincorporation of stabilized silver nanoparticles into silica matrices as well as theirpotential applications. Silver nanoparticles were synthesized and their antibacterialactivity of different concentration of nanosilver coating was extensively investigated.Silica films containing various concentrations of Ag nanoparticles weredeposited on glass slides using a sol–gel process and then heat-treated in air atdifferent temperatures. The films were analysed by using UV–visiblespectrophotometry, atomic force microscopy (AFM), scanning electron microscopy(SEM), transmission electron microscopy (TEM) and x-ray photoelectronspectroscopy (XPS) for their optical, surface morphological as well as structural,and chemical properties.At the first step, a facile route to synthesis silver nanoparticles into silica (SiO2)as an inorganic matrix using sol-gel method has been developed. The influence ofmatrices on the size and optical properties of silver nanoparticles were studied. It isfound that the particle size can be tailored by changing the AgNO3as a nanosilverprecursor. Silica-based coatings because of their unique properties like chemicaldurability and biocompatibility were interesting for our purpose to be a substrate ofbiocide silver.Sol–gel coatings containing biocide silver ions are prepared for the preventionof biofilm formation on implanted surfaces. High-temperature processing of suchcoatings can lead to diffusion of nano silver and reduce the amount of availablesilver for lasting effect. Here, we present the preparation of silane based matrices,containing different amount of Ag nanoparticles, using a low-temperature sol–gelmethod. The incorporation of a silver salt into sol–gel matrix resulted in a desiredsilver release, i.e., with high initial release rate in de-ionized water followed by alower sustained release for more than15days, as determined by inductively coupledplasma mass spectrometry (ICP-MS). Scanning Electron Microscopy (SEM) hasbeen employed to investigate the morphology of the film surfaces before and afterimmersion in a nutrient-rich bacterial suspension of approximately108CFU/ml,which was incubated for15and30days at37°C. From SEM images, it was foundthat thin films containing35nm particles could prevent formation of biofilm forover30days.After heat-treatment, the optical absorption peaks of Ag nanoparticles show ablueshift and an intensity reduction due to particle size reduction and AgOxnanoparticle formation, respectively. The particle size reduction and surfacemorphology changes in the films were observed by AFM and TEM as a function ofheat-treatment temperature and Ag concentration. Using AFM and XPS analyses, wehave found that the Ag nanoparticles accumulated on the surface diffuse into thesubstrate as the heat-treatment temperature increases. XPS analysis also showed thatthe silver oxidation occurs during the heat-treatment, causing the reduction ofabsorption intensity. By controlling the Ag concentration and the heat-treatmenttemperature, we could change the silica structure, and tailor the average size of the silver nanoparticles down to less than4nm.