One-Dimensional Silica Nanostructures and Metal–Silica Nanocomposites: Fabrication, Characterization, and Applications

Among Si-based nanostructures, silica nanowires are gaining a great scientific and technological interest due to their potential applications such as new electronic devices, biosensors, nanoscale optical devices. Furthermore, the silica nanowires chemical and physical properties, and so their performances in devices, can be enhanced if embed or if decorated on surface by metal nanoparticles due to local plasmonic effects. In fact, properties such as surface-enhanced-Raman-spectroscopy (SERS) and optical wave-guiding of the silica nanowires gain enormous benefit from the presence of the metal nanoparticles. In particular, SERS effects in metal nanoparticles/silica nanowires are extremely promising for diagnostics with rapid screening. Examples include identification of cancer malignancies and classification in oncology research and monitoring of drug recipient interaction in pharmaceuticals. The majority of single-molecule detection studies have utilized aggregates of metal nanoparticles, which are particularly likely to form hot spots where Raman scattering is even more strongly enhanced due to electromagnetic coupling between nanoparticles, and the coupling with silica nanowires leads to a further improvement of the light interaction due to the waveguide properties of the nanowires. Despite the importance of the one-dimensional metal/silica nanocomposite systems, a key question towards their device applications concerns the development of simple, low-cost, and versatile methodologies for their mass production directly on surface and for the wide-range control of their structural characteristics. So, in this chapter we review, first of all, the most promising fabrication methods of one-dimensional metal/silica nanocomposite systems focusing our attention, primarily, on the basic microscopic mechanisms, processes and general concepts suitable for the materials properties interpretation and the structure-properties correlations. The chapter aims, in addition, to a comprehensive schematization of the main technological applications of such nanocomposites actually worldwide in development so as the future possible ones. The chapter is, so, organized as follows: - Review of the most promising methods to fabricate, in controlled way, one-dimensional Silica and metal/silica nanocomposite systems highlighting the connections between the resulting structural and morphological characteristics of the nanocomposites and the processing parameters. In this section, in addition, the review of the physical properties (electrical, optical) of such systems is presented highlighting, also, in this case the connections between such properties and the nanocomposites structural and morphological characteristics. Comparisons between various proposed fabrication techniques, highlighting strengths and weakness, are carried out. - Review of the most promising technological applications of the one-dimensional Silica and metal/silica nanocomposite systems highlighting the technological potentialities of such systems, the actual limitations to real device applications and proposing solutions to overcame such limitations. Concerning the technological applications, those exploiting the SERS and electrical properties of the one-dimensional metal/silica nanocomposite systems towards bio-recognition and gas-sensors are particularly emphasized.