Femtosecond Irradiation Yields Luminescent Silica

A team at Harvard University in Cambridge, Mass., has reported that microstructuring silicon in air with femtosecond pulses of radiation generates a silicon-rich silica that produces visible luminescence under less than 10 mW of excitation. The material, which the team described in the Sept. 9 issue of Applied Physics Letters, may ease the integration of electronics and optoelectronics.

The researchers exposed silicon surfaces to trains of 100-fs pulses of 800-nm laser radiation. Subsequent exposure of the samples to 488-nm light from an argon-ion laser caused them to emit light visible to the naked eye, with a peak wavelength at approximately 560 nm. Rutherford backscattering spectrometry revealed that the luminescence is attributable to the oxidation of silicon on the microstructured surface. Annealing the samples increases the intensity of the response and results in the appearance of another peak at 620 nm, which the researchers believe is caused by quantum confinement in clusters of nonoxidized silicon embedded in the oxidized silicon lattice.