"For most physicists, the idea of materials held together by light is still foreign," says Colin Bain of Durham University. But materials held together by light are exactly what Bain and his colleague Christopher Mellor have accomplished.

Their "optical matter" arrays consist of polystyrene nanospheres that are trapped by light that has been scattered off a prism. The spheres are attracted by a laser-generated "evanescent field" above the prism surface and spontaneously assemble into 2D arrays.

Their process provides a new method of self-assembly, and opens a window to study even smaller scales of matter. "As well as being a new way to assemble matter on the nanoscale," says Bain, "such arrays may also provide a way of visually studying, in real time, the processes that occur invisibly in crystals on sub-nanoscales."

To follow up this study, Bain (photo above), plans to explore how particles with different shapes and sizes assemble, and to extend the optical matter arrays into 3D.