Gallium arsenide (GaAs) nanocrystals with diameters ranging from 1 to 36 nm can be reliably produced and stored for as much as a year, according to researchers at Duke University (Durham, NC). The process involves combining sodium arsenide and potassium arsenide with gallium trichloride and selected solvents to form GaAs nanocrystals. The solvents control the size of the quantum structures produced: polyethers such as diglyme and monoglyme yield structures 10 and 17 nm in diameter, respectively, while toluene and dioxane produce 36-nm crystals. Duke researchers Richard Wells and Shreyas Kher believe the long-chain molecules of the solvents occupy the bonding sites on the gallium atoms, limiting crystal growth. Kher can routinely reproduce the nanocrystal sizes for a given solvent. After quantum structure formation the solvents are replaced by methanol, leaving the crystals in colloidal suspension. They are robust in this state, remaining stable for at least a year and withstanding repeated exposure to air. Possible applications for the nanocrystals include solar cells and optical computing. The grou¥is also collaborating with researchers at the University of North Carolina (Chapel Hill, NC), who are exploring the nonlinear optical properties of the structures.