Synthesis and characterization of two-dimensional and three-dimensional arrays of metal and semiconductor nanoparticles of tunable sizes in supercritical carbon dioxide.

摘要

The interest in nanoscale materials stems from the fact that new properties are acquired at this scale and, equally important, that these properties change with their size or shape. This, together with the ability to make nanoparticles in different sizes and shapes, makes them potentially useful for the application in photonic and optoelectronic devices or in catalysis.; Reverse micelles, phase transfer and solvated metal atom dispersion (SMAD) techniques are, among others, well known in making metal and semiconductor nanoparticles for the past few years. These techniques have been used with some success in synthesizing numerous semiconductor and metal nanoparticles and making nanoarrays, but the results obtained and the procedures used still need to be improved for commercial applications. Supercritical fluid carbon dioxide (SC-CO2) is capable of dissolving precursors of advanced materials and depositing them into small nanometer-sized structures. Its penetration power and tunable solvation strength make it an attractive medium for synthesizing and manipulating organized arrays of nanoparticles. Development of similar but improved techniques for making metallic nanoparticles' superlattices using water-in-oil microemulsions, and the use of the experience acquired in this process in order to find supercritical fluid CO2 conditions in making the same materials with controllable size are presented here.; Relatively few semiconductor nanomaterials have included nanoparticles produced by supercritical fluid methods, which have their own unique characteristics. These comprise being able to produce narrow size distributions over a wide range of sizes and also to discover appropriate coatings or shell formations that can reduce surface defects. In this way, photoluminescence yields for the exciton peaks are increased. Size tuning of CdS and ZnS nanoparticles by varying the density of supercritical carbon dioxide was explored here with further stabilization of the nanoparticles with fluorinated thiols.; The characterization of these new nanomaterials, by using various surface analysis techniques including transmission electron microscopy (TEM), transmission electron diffraction (TED), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and energy dispersive X-ray fluorescence spectroscopy (EDS) was also achieved. Their optical properties were studied using spectroscopic techniques, mainly UV-Visible absorption and photoluminescence (PL). Potential applications of this new technology for developing sensors and nanoelectronics were explored.