Preparation of nanoscale semiconductors through the rapid expansion of supercritical solution (RESS) into liquid solution

The preparation of nanoscale lead sulfide (PbS) particles using a supercrit ical fluid processing technique is reported. The method is based on two sim ultaneous modifications to the conventional RESS (rapid expansion of superc ritical solution) process. The first is to expand the supercritical solutio n into a liquid solution instead of a gas, and the second is to use a react ing system, in which one reactant is dissolved in the supercritical solutio n and one in the liquid receiving solution. Supercritical ammonia, methanol , and acetone solutions are used for rapid expansion, and the PbS nanoparti cles obtained with the different solvents are rather similar. RESS experime nts are also carried out under different experimental conditions, but the c hanges in processing parameters apparently have only marginal effects on th e produced PbS nanoparticles. Mechanistic considerations on the RESS into s olution method and issues concerning the use of the semiconductor nanoparti cles in nanocomposite materials are discussed.