Band-gap modification in a nanoscale region of polyethylene by fast electrons.
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.
Kim
Hansoo
H
Microscopy and Imaging Center, Texas A&M, College Station, Texas 77843, USA. hkim@mic.tamu.edu