Nanoparticles and Nanostructures Fabricated Using Femtosecond Laser Pulses

Abstract

Recently, the processing of materials by femtosecond (fs) laser pulses has attracted a great deal of attention, because fs pulse energy can be precisely and rapidly transferred to the materials without thermal effects (Stuart et al., 1995). In particularly, periodic microstructures can be produced in almost any materials using fs pulses directly and without the need for masks or chemical photoresists to relieve the environmental concerns. For instance, nanoripples (Hsu et al., 2007; Luo et al., 2008; Sakabe et al., 2009; Jia et al., 2010; Yang et al., 2010; Bonse & Kruger, 2010; Okamuro et al., 2010; Huang et al., 2009), nanoparticles (Jia et al., 2006; Luo et al., 2008; Teng et al., 2010), nanocones (Nayak et al., 2008), and nanospikes (Zhao et al., 2007b) have been induced in various materials using single-beam fs laser pulses in air. In addition, fs laser ablation for metals and semiconductors in a vacuum environment (Amoruso et al., 2004; Liu et al., 2007a) and in liquid (Tsuji et al., 2003) have also been extensively investigated. These results are a strong indicator of the application potential of fs laser pulses in science and industry. In this chapter, we demonstrate the generation of nanoparticles and nanostructures (including ripples and dots) using fs laser pulses. Initially, we selected the II-VI semiconductor ZnSe to demonstrate the fabrication of nanoparticles. Following the irradiation of fs laser pulses at a wavelength of 800 nm and pulse duration of 80 fs, many hexagonal-phase ZnSe nanoparticles formed on the surface of an undoped (100) cubic ZnSe single-crystal wafer. The interesting phase transition from the cubic structure of ZnSe singlecrystal wafer to the hexagonal structure of ZnSe nanoparticles may have been caused by the ultra-high ablation pressure at the local area due to the sudden injection of high-energy leading to solid-solid transition. This chapter discusses the details of the mechanisms underlying this process. In the second part of this chapter, we introduce controllable nanoripple and nanodot structures to high-Tc superconducting YBa2Cu3O7 (YBCO) thin films. We also introduce the surface morphology of YBCO thin films under single-beam and dual-beam fs laser irradiation. The generation of periodic ripple and dot structures is determined by the application of laser fluence, the number of pulses, polarization and the incident angles of the laser beam. The period and orientation of ripples and even the size and density of dots can be controlled by these parameters.