Electrochemical and spectroelectrochemical investigations on Quantum Dots of CdSe, CdTe and their composites

Abstract

Colloidal composite semiconductor quantum dots (Q-dots) have attracted great attention due to their unique and intricate optical and electronic properties, which depends on specific material, size, shape and the composition. These characteristics arise from several phenomena viz. quantum confnement of charge carriers, surface effects and geometrical conffnement of phonon etc. This turned semiconductor Q-dots into promising material for many applications such as, biological imaging, nanosensors, biomedical tags for uoroimmunoassays, biographic optical memories, light emitting diodes, lasers, photonic band gap crystals and ultrafast photonic switches. However, the development of nanotechnology using these dots would demand an exact knowledge of the band structure and physicochemical properties of the semiconductor Q-dots, which in turn depends mainly on the band edge positions of these Q-dots. Due to the lack of direct experimental measurements for the determination of these values, a common approach taken so far has been to assume band edge positions of the bulk material or of epitaxial super lattices. However, in case of colloidal Q-dots, the band edge values can differ considerably from that of the bulk. Optical spectroscopy has routinely been used for the estimation of band gap values, which provides the energies of allowed electronic transitions between the conduction band and valence band. However, it fails to predict the actual positions of these band edges, separately. On the contrary, these parameters are routinely determined from Scanning Tunneling Spectroscopy and Photo-electron Spectroscopy. However, the difficulties with these techniques is the involvement of serious instrumentation and tedious sample preparation protocols.