Metal Island Films for Write-Once Optical Data Storage Media

Abstract

Write-once (WO) optical disks with high reflectance are becoming attractive data storage media for small production runs of specific compact discs (CD) or Digital Video Discs (DVD). A metal island film is one of the interesting media proposed for such WO optical disk media [1-3]. The metal island film is composed of metal nanoclusters (i.e., islands) and exhibits resonance-type absorption in a visible - near infrared region. Near the resonance peak wavelength, it has not only large absorptance but also high reflectance due to the resonance of free electrons in the metal islands. As the optical characteristics of the metal island film are greatly changed by heating the film, it can be used as heat-mode WO media. The metal island films have some advantages over other WO media, i.e. (1) high reflectance, (2) large absorbance, and (3) low stress in the films from those discontinuous island structure. In addition, the very short recording time is expected since the optical characteristics of the metal island films can be greatly changed by the slight changes of the nanometer-size metal islands [1,3]. We have investigated gold (Au), silver (Ag), copper (Cu), and aluminum (Al) island films for the WO optical data storage media. In this paper, we show the optical changes of those island films at the commercially useful wavelength of 800 nm and demonstrate the highly reflective WO media with the reflectance of 70 % using the Ag island films. It seems that those island films are useful as CD-DVD compatible WO optical data storage media.