Ki-Soo Lim
Chungbuk National University, Korea
Title: Self-organized periodic nanostructures on the surfaces of semiconductors and dielectrics by scanning femtosecond laser pulses
Biography
Biography: Ki-Soo Lim
Abstract
We report the self-formed nanogratings on the surfaces of semiconductors (ZnO and GaN) and dielectric materials (fused silica, borate glass, LiTaO3, LiVO3, sapphire) prepared by scanning focused femtosecond laser pulses at 800 nm with a repetition rate of 1 kHz. Laser fluence range for nanograting self-formation is very narrow. We find a series of periodic-structure orientation is perpendicular to the linear laser polarization. The period of grating structures on the dielectric surface depends on laser power and scan speed, and increases in the range of 200∼300 nm with scan speed and laser pulse energy. In contrast, GaN shows about 600 nm period in the same power range as the dielectric materials. Its period decreases to 450 nm when the laser power is reduced ten times. It also has much lower laser ablation threshold than dielectrics and ZnO, indicating characteristics of metal-like nanogratings due to its high plasma density, large thermal conductivity, and multiphoton absorption coefficients at 800nm. Emission from nanograting area of sapphire indicates the existence of oxygen vacancies. Figure 1 shows the nanograting structure formed by scanning femtosecond laser pulses at 40 μm/s speed of on the surfaces of LiVO3 and ZnO with 0.13 and 0.09 mW power respectively.
For applications, surface nanostructures can be used to improve out-coupling of light in LED. Material absorption can be also significantly enhanced due to surface nano-structures produced by fs-laser pulse processing, applicable to sensing and solar cells.
