Band‐gap Modification in a Nanoscale Region of Polyethylene by Fast Electrons

Abstract

Drastic change: A nanoscale spot of polyethylene (PE) can change its electrical properties dramatically after exposure to fast electrons-from a representative insulator, via a semiconductor, to a hopping conductor (see picture). These modifications of the chemical and energy-band structures of PE are extremely localized, thus opening a new way to use this conventional polymer in nanotechnology. Herein, a nanoscale area on a polyethylene film is investigated by an electron-microscope-electron-spectroscopy system after exposure to various doses of fast electrons. Therefore, modifications in its physical and chemical properties and the spatial size of a beam-affected area are measured. The results show that the modifications of PE by electrons are significant enough to rebuild the chemical and energy-band structures. Hydrogen is removed through scission while pi bonds are formed by cross-linking between main chains. These changes cause the energy band of PE to show dramatic variation from a wide to a narrow (down to approximately 0.8 eV) band-gap. At the highest dose (10(10) C m(-2)) used herein, an illuminated area of PE becomes quite similar in properties to graphitic amorphous carbon. On the other hand, the size of the beam-affected area is as small as roughly 50 nm in diameter. Since the extent of the modifications can be tailored in a controllable way by the dose, these findings may be fundamental for the utilization of a conventional polymer in nanotechnology.

Modifications in Electronic Properties of Polystyrene Methacrylic Acid by Neutralization and Fast Electrons

“…Recently it has been reported that, when irradiated by focused electrons, nanoscale areas of conventional polymers can change their chemical and energy-band structures dramatically in a controllable manner. , Since the transformation can be made to a conductor, different kinds of electrical materials can be constructed in various scales and dimensions in an insulating polymer by electrons. These results may be useful for employment of cheap conventional polymers in optical and electronic nanodevices.…”

“…Covalent cross-linking and scission by irradiation may be added to vulnerability by neutralization, responsible for the severe modifications of highly irradiated Ba-PSMAA. Scission can remove hydrogen from the polymer while covalent cross-linking can form new π bonds between main chains. , It is interesting that neutralization can make an ionic copolymer more vulnerable to irradiation while enhancing its mechanical properties. One possible explanation is that since the backbones are expected to be strained in all directions the net strain on a macroscopic scale properties may be small as opposed to the directional residual strain caused by cold working or heat treatment .…”