Conduction in Colloidal Systems: A Kinetic Study of Ag_2S Semiconductor Nanoparticle Formation

摘要

The synthesis of metal and semiconductor nanoparticles has received widespread attention by the scientific community due to the large number of technological applications they find in nanoscaled systems. The mechanism of nanoparticle growth is, in general, still an open question. The general picture that emerges from previous works is that nanostructures form from the self assembly of atoms and nuclei in solution. The driving forces involved in this self assembly are not well known. There is little doubt that electrostatic and magnetic interactions among atoms and small nuclei play an important role in the synthesis and growth of nanostructures. We have employed real time-conductivity measurements to measure the kinetics of Ag_2S nanoparticle growth. Conductivity measurements reflect the electrical stability and order of the colloid, which are well known to result from a delicate balance of electrostatic and magnetic forces. Ag_2S semiconductor nanoparticles absorb light deep in the UV (about 230-240 nm). Conductivity measurements on this synthesis are an attractive approach to study the mechanism of nucleation. In this work a stopped flow system is used to study reaction growth kinetics of the formation of Ag_2S nanoparticles. The kinetic data obtained indicates that the reaction mechanism involves multiple steps.rnConductivity and optical absorption measurements indicate that the semiconductor, nucleation and coalescence of particles occur in a time scale shorter than 5 seconds after the flow of Ag~+ and S~(-2) is brought to a stop.