The reproducible synthesis of high-quality quantum dots became a reality in the early 1990s when researchers at MIT pioneered a new method of producing quantum dots with uniform sizes and well-defined optical signatures. The basic recipe for making quantum dots hasn't changed much since it was first developed. A solvent is heated to almost 500 degrees Fahrenheit, and solutions containing cadmium and selenium compounds are injected. They chemically decompose and recombine as pure CdSe nanoparticles. Once these nanocrystals form, scientists can adjust their optical properties by growing them to precisely the size they want by adjusting the cooking time.
The solvent originally used for this process was trioctylphosphine oxide, or TOPO, which costs more than $150 per liter. Later, other scientists introduced a new recipe by replacing TOPO with a mixture of ODE and oleic acid.
Wong said the CBEN research team, which included CBEN Director Vicki Colvin, professor of chemistry, and Nikos Mantzaris, assistant professor of chemical and biomolecular engineering and of bioengineering, had some initial doubts about whether heat-transfer fluids could be substituted for ODE.
"They were cheap and they didn't break down at high temperatures, but no one uses these compounds for chemical reactions," said Wong. In addition to finding that other quantum dot nanostructures could be made in heat- transfer fluids, the team concluded that any solvent could be used to replace ODE. Thanks to a mathematical modeling approach developed by Mantzaris, the team now has a method for predicting the particle size and growth behavior of quantum dots based on only three physical properties of a given solvent: viscosity, surface free