Towards Applications of Quantum Dots: Surface Modification and Novel Electronic Properties

摘要

The possibility of quantum confinement causing the intense visible luminescence seen in porous Si, first mentioned by Canham in 1991, led to enormous interest in that material. The large blue-shift in the band gap and increase in luminescent efficiency attributed to quantum confinement in porous Si, while still controversial, continues to fuel research on colloidal Si nanoparticles prepared by sonicating porous Si, and by solution chemistry. This interest continues, and has led naturally to an interest in colloidal Ge nanoparticles, since the elements are both indirect gap semiconductors, and the exciton of Ge has a larger Bohr radius. The earliest preparation of Ge nanoparticles by a colloidal chemistry method started as a continuation of the previous work on Si, but required either high temperatures and pressures, or laser annealing to produce crystalline nanoparticles. There has been only limited work on colloidal Ge nanoparticles prepared by sonicating porous Ge, with interest instead focused primarily on solution preparation of colloidal Ge nanoparticles. The reaction between Mg{sub 2}T and TCl{sub 4} in refluxing diglyme produced silicon and germanium nanoparticles in high yields, and the surface of these nanoparticles may be terminated using Grignard reagents. Since the particles produced by the initial metathesis reaction are from 2-10 nm in diameter, from 10-30% of their atoms are on the surface. With such a large proportion of atoms at the surface, its termination is vital to controlling their properties. Surface termination with Grignard reagents forms a robust protective layer at the surface of the nanoparticle, and provides an opportunity for further chemical manipulation. Though a considerable amount of work remains, chemically manipulating the surface of the nanoparticles may provide the ability to further tailor their properties and incorporate them into composite materials or devices. The ability to chemically change the surface of the nanoparticles yet retain the luminescence due to quantum confinement is unique to this preparative method.