Deposition, electrical, optical, and mechanical properties of plasma polymer films made from thiophenes

Over the last years is a growing interest in organic electrical conducting thin films, which can applied in many fields of microelectronics, for examples as light-emitting diodes. The deposition of conducting polymer thin films by means of a vacuum technologies could be introduce possibilities of further applications. The plasma polymerization as a plasma assisted chemical vapor deposition process is a well-known and efficient method to produce organic thin films. The objective of our work was to fabricate thin plasma polymer films from the monomers thiophene and iodothiophene without additional doping and to investigate the physical properties of these films. The plasma polymer films were deposited by AC-plasma polymerization, whereby an additional embedding of silverparticles is possible. The electrical power was supplied by a 50 Hz generator to a pair of two parallelstainless steel electrods. The monomer was introduced in the reactor with a flow rate of 0.8 1/min and could be contro lled by needle valve. The plasma polymerization power density for the deposition ranged from 0. 1 to 0.6 W/cm(-2). Optical emission spectroscopy was applied during the film deposition to characterize the plasma at various energy input levels and various monomer partial pressures. Among this in-situ analysis of the gas phase during plasma polymerization of thiophene and iodothiophene, the film thickness was measured by optical interferometry, the film surface was observed by scanning electron microscopy and atomic force microscopy. Furthermore, the adhesive forces were determined for films deposited on various preparation conditions. The youngs modulus was determined by nanoindentation. The electrical direct current conductivity for films deposited at various preparation conditions was calculated based on the measured current voltage relationships. The maximum conductivity of an undoped thiophene films was sigma = 1.3Xl0(exp -6) ohm (-1).