  We demonstrate for the first time controlled patterning by inducing
nucleation of material from a dense aqueous dispersion or solution in an
optical tweezers. A hot spot is formed on a glass surface by the trapping laser
due to which a water vapor bubble is formed causing Gibbs-Marangoni convection
of material around the bubble. This results in accretion of material around the
bubble, which eventually nucleates into a crystalline state of the material.
The nucleation site, when moved by translating the microscope stage of the
optical tweezers apparatus, forms a pattern. We have demonstrated the technique
using exotic inorganic materials such as soft oxometalates, and organic
materials such as glycine, paracetamol, and a fluorescent dye such as perylene.
We have written patterns over lengths of nearly 1 mm at the rate of 1 Hz, with
best resolution of about 1 micron. The technique has potential for a wide range
of applications ranging from solution processed printable electronics to
controlled catalysis.
