Dislocation Arrays in Sapphire using Femtosecond Laser Irradiation

  • PDF / 1,681,561 Bytes
  • 5 Pages / 612 x 792 pts (letter) Page_size
  • 24 Downloads / 243 Views

DOWNLOAD

REPORT


1228-KK05-56

Dislocation Arrays in Sapphire using Femtosecond Laser Irradiation Chiwon Moon,1 Shingo Kanehira,2 Kiyotaka Miura,1 Eita Tochigi3, Naoya Shibata,3 Yuichi Ikuhara3 and Kazuyuki Hirao1 1 Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan 2 Innovative Collaboration Center, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan 3 Institute of Engineering Innovation, School of Engineering, The University of Tokyo, 2-11-16, Yayoi, Bunkyo-ku, Tokyo, 113-8656, Japan

ABSTRACT We investigated the formation mechanism and thermal behaviors of defects which were _

introduced at a microscopic area inside (1120) sapphire using femtosecond laser. Cracks were _

_

formed at the focal point along the {1102} and the {1100} planes by the laser irradiation. The preferential crack formation on these planes was attributed to the different fracture surface energy between the crystallographic planes of sapphire. The cracks transformed into the array of discrete pores by the subsequent heat treatment above 1300 °C, which was due to the diffusive crack healing process. In addition, dislocations were also introduced at the interface between closed cracks.

INTRODUCTION Femtosecond laser pulses have attracted considerable attention because they can give a large amount of energy on a microscopic area in various materials without surface damage, therefore, they are widely used in microprocessing of materials with high accuracy [1, 2]. In addition, the structural changes during the laser irradiation often occur around the focal point with nanometer size, which is smaller than the center wavelength of the laser [3]. Recently, our group succeeded in fabricating and controlling a dislocation inside MgO single crystal using femtosecond laser irradiation [4].The cross-shaped pattern originated from dislocations resulted from the interaction between laser pulses and MgO single crystal with a rock-salt-type structure. Studies of the interaction between laser pulses and other single crystals have also been reported, including an amorphization of sapphire [5], and phase transformation of TiO2 single crystal [6]. Sapphire has a corundum structure and it has been used in abrasives and bearings because of its high melting point, high hardness, and low reactivity. In the last decade, the mechanical properties of sapphire have been widely investigated in terms of the deformation mechanism. For instance, dislocation, twinning, or cracks of sapphire have been studied by the indentation and uniaxial compression methods [7, 8]. However, there are few reports on the relationship between the crystal structure and the deformation mechanism under the laser irradiation. Here, we investigated the deformation mechanism of sapphire in a microscopic area during the femtosecond laser irradiation in detail. Nanocracks of approximately 30 nm width propagated

_

_

from the focal point along {1102} and {1100} planes. In addition, the crystalline phase at the focal point locally transformed to t