Success in Fabrication of Polymer Nanowires Using Pulsed Laser!

2008.09.30

National Institute for Materials Science

NIMS discovered that polymer nanowires form when a polymer film containing dispersed organic molecules is subjected to convergent irradiation by a pulsed laser with optimized light intensity, and also succeeded in time resolution measurement of the growth process of the polymer nanowires using an ultra-high speed camera.

Abstract

  1. A team led by NIMS Senior Researcher Masahiro Goto and Group Leader Masahiro Tosa, Materials Reliability Center, National Institute of Materials Science (President: Prof. Teruo Kish) discovered that polymer nanowires form when a polymer film containing dispersed organic molecules is subjected to convergent irradiation by a pulsed laser with optimized light intensity, and also succeeded in time resolution measurement of the growth process of the polymer nanowires using an ultra-high speed camera.
  2. Accompanying progress in nanotechnology, various types of nanowires have been fabricated, and development of applications in a variety of fields is continuing. As part of this trend, interest in organic materials has increased dramatically. The fabrication of polymer nanowires and their applications have been a particular focus. Research on physical properties, beginning with quantum size effects,3) and application of polymer nanowires to light-emitting devices, optical waveguides, optical switches, and other devices taking advantage of their flexibility and other unique properties is expected. However, because fabrication of the nanowire itself is not easy, a simple method of forming new polymer nanowires had been awaited.
  3. In order to solve this problem, in this work, we considered the possibility of fabricating polymer nanowires by a completely different method utilizing the laser technology possessed by NIMS, and in various experiments, succeeded in developing a method of forming polymer nanowires which is different from the conventional process. First, a polymer film which serves as the material for the wire is prepared. Molecules which absorb laser light (for example, organic molecules such as coumarin, perylene, etc.) are dispersed in this film. When the film is subjected to one pulse of convergent irradiation by pulsed laser light (e.g., wavelength: 440nm, pulse width: 900ps) using objective lens, it was found that the molecules are excited, and an extremely fine polymer nanowires (diameter: 5-200nm, length: 10-2000μm; can be controlled depending on the conditions) are formed by this energy.　At the same time, in order to elucidate the formation process of these nanowires, measurements were performed using an ultra-high speed camera and gate CCD camera. The formation time was approximately 1μs, and it was possible to form all of the polymer nanowires (PMMA, PEMA, PBMA, polystyrene) which have been attempted to date. Fabrication of wires was also possible when the species of dispersed molecules was changed, but in all cases, optimization of the laser light intensity was necessary in formation of the polymer nanowires.
  4. Using the new polymer nanowire fabrication technique developed in this research, extremely simple formation of polymer nanowires with different sizes and lengths was possible by a dry process4) in the atmosphere. Considering the fact that many types of polymer materials can be used, wide-ranging development to physical research in connection with size effects and various types of optical and electronic devices, ultra-high sensitivity nanosensors, and other applications is expected.
  5. We wish to thank Shimadzu Corporation and Hamamatsu Photonics K.K. for their support in experimental observations of the polymer nanowire formation process using the ultra-high speed camera and gate CCD camera.