DC electric field induced phase array self-assembly of Au nanoparticles

In this work we report the discovery of phase array self-assembly, a new way to spontaneously make periodic arrangements of metal nanoparticles. An initially random arrangement of gold (Au) or silver (Ag) nanoparticles on SiO2/Si substrates was irradiated with linearly polarized (P) laser light in the presence of a dc electric (E) field applied to the insulating substrate. For E fields parallel to the laser polarization (E parallel to P), the resulting periodic ordering was single-crystal like with extremely low defect density and covered large macroscopic areas. The E field appears to be modifying the phase between radiation scattered by the individual nanoparticles thus leading to enhanced interference effects. While phase array behavior is widely known in antenna technology, this is the first evidence that it can also aid in nanoscale self-assembly. These results provide a simple way to produce periodic metal nanoparticles over large areas.