Preparation of particulate films

Nanocrystalline particulate films, which exhibit pronounced quantum size effects in three dimensions, are of great interest due to applications in solar cell (108-112) and sensor (57, 113-115) applications. They exhibit novel properties due to not only the SQE manifested by individual nanoparticles but also the total surface area. Unlike MBE and MOCVD methods used to prepare quantum well electrodes, these electrodes can be prepared by conventional chemical routes described in Section 9.5.2.2. For example, II-VI semiconductor particulate films were prepared by using low concentrations of precursors and by controlling the temperature of the deposition bath. Nodes demonstrated the SQE for CdSe thin films deposited by an electroless method (98). The blue shift in the spectra of CdSe films has been demonstrated to be a function of bath temperature. As described in Section 9.5.2.1, electrodeposition of semiconductors in non-aqueous solvents leads to the formation of size-quantized semiconductor particles. On a single-crystal substrate, electrodeposition methods result in epitaxial growth (116, 117), and danonstrate quantum well properties. 

Nanoparticles can be anchored on a substrate by forming covalent bonds between the substrate and the capped nanoparticles. For example, ITO glass can be modified by (3-mercaptopropyl)trimethoxysilane (MPTMS), which leads to the formation of thiol 

Similar work has been reported by Bard and co-workers where CdS nanoparticles were attached to a gold substrate using hexanedithiol (121). Using this method, it is possible to deposit multilayers that form an addressable three-dimensional quantum dot structure. Template methods have been used to deposit semiconductors of various shapes and sizes. For example, Li demonstrated the use of anodic aluminum oxide (AAO) templates to deposit CdS nanowires with a large aspect ratio (122). 

Coulombic interaction between capped particles can be used to organize the particles on the substrate (127-129). In one such example, polyacrylate-capped CdS nanoparticles were synthesized and assembled layer by layer on poly(diallyldimethylammonium chloride) 

---