Time-resolved investigations of growth of semiconductor nanocrystals in the bottom-up approach
D. D. Sarma
Centre for Advanced Materials
Association for the Cultivation of Science, Kolkata 700032,
It is now well understood that the bandgap, and consequently associated electronic and optical properties, of semiconducting nanoparticles can be tuned by varying the size due to quantum confinement effects. Colloidal methods constitute an important class of synthesis of such nanoparticles due to their high degree of flexibility, providing easy control over the average size. More than the average size, the entire size distribution function, controls the properties of such samples. This method of synthesis depends basically on controlling the reaction process leading to the formation of the semiconductor in a solution by controlling various factors like temperature and concentration. The primary difficulty of this method is the strong interplay between various factors in a way that is very little understood; however these very processes control the size along with the size distribution of the generated particles. Thus, the techniques of synthesis of high quality nanocrystals, indicated by the ability to grow a pre-defined size with a narrow size distribution, have remained largely in the realm of empiricism. Obviously there is a need to understand the mechanism of the growth process of the nanocrystals, though very little is known about it in such a complex reaction, often carried out in presence of a capping agent. We employ already established state-of-the-art techniques as well as a few novel approaches to study in real time the growth kinetics of a host of semiconductor materials to unravel a wide range of unexpected behaviours. We show that such studies help us to design routes to rational synthesis of high quality samples for possible device applications.
Work based on:
1. S. Sapra and
2. R. Viswanatha, S. Sapra,
T. Saha-Dasgupta and D.
3. R. Viswanatha and
4. R. Viswanatha, H. Amenitsch and D. D. Sarma, J. Am. Chem. Soc. 129, 4470 (2007).
5. R. Viswanatha, C. Das
6. R. Viswanatha et al., unpublished results.