Bei elektrisch isolierenden Polymeren kann durch Beimischung leitfähiger Partikel eine Leitfähigkeit erreicht werden. Polymere mit einem strukturell geordneten, ungesättigten Polymerkörper besitzen bereits eine intrinsische Leitfähigkeit. Dünne Polymerschichten, wie sie mit Plasmaverfahren erzeugt werden, unterscheiden sich ganz wesentlich in ihrer Struktur von den klassischen Polymeren. So besitzen Plasmapolymerschichten aus leitfähigen Polymeren nur sehr geringe Leitfähigkeiten. Diese kann durch eine Dotierung mit Jod bei erhöhter Temperatur verbessert werden. Da eine Dotierung während des Plasmaprozesses mit elementarem Jod schwierig ist, wurde am Fraunhofer-Institut für Angewandte Materialforschung ein neues Plasmaverfahren entwickelt und in einer Laboranlage erprobt. Die Anlage arbeitet mit einem Argon-Mikrowellenplasma, dem jodhaltige aromatische Monomere (2-lodthiophen) zugesetzt wird. Die elektrische Leitfähigkeit der erzeugten Plasmapolymerschicht ist gut; ihr Aufbau und molekulare Struktur wurden mit ESCA und IR-Spektroskopie untersucht.
Intrinsically conductive plasma polymers were formed in a 2.45 GHz microwave low pressure plasma. The electrical conductivity and structure of the polymeric films were compared with those of electrochemically polymerized polythiophene. A new method of doping was tested using the iodine-containing monomer 2-iodothiopene. Films with high electrical conductivity (10-1 down to 10-6 S cm-1) could be produced, and their chemical structure was studied by X-ray photoelectron spectroscopy and Fourier transform IR spectroscopy. The IR spectra give a strong indication that the chemical structure of these films is comparable with that of electrochemically deposited polythiophene. Optical emission spectroscopy was used to give in-situ information about the fragmentation mechanism in the plasma.
Plasma polymer films of vinyltrimethylsilane (VTMS) were deposited by radiofrequency (RF. 13.56 MHz) or Microwave (MW, 2.45 GHz) discharges in two reactors of the same volume and geometry. — The polymer films were characterized by electron spectroscopy for chemical analysis (ESCA) and infrared spectroscopy (FTIR). It turned out, that the RF — and the MW — polymers had almost the same Si/C-composition ratio of 1/5 in the entire range of RF-and MW-power (60-150 W). Although the Si/C film-composition remains almost constant, the binding states of Si-and C-atoms in the respective ESCA-spectra are changing. While the CSi part of the C1s-peak increases with the RF-or MW-power, the C-H/C-C part of the peak decreases, indicating a loss of hydrogen in the polymer films. — Obviously the fragmentation of the VTMS-monomer is quite different for the two types of plasma discharges. While films of the RF-plasma clearly show strong contributions of the methyl and vinyl groups, these groups are completely missing for the MW-plasma polymers. — From these results structure models of the plasma polymers have been developed.
Structural investigations of electrical conducting plasma polymerized films from 2-iodothiophene
(1993)
Thin plasma polymerized films were produced in a microwave (2.45 GHz) plasma discharge using 2-iodothiophene as the initial monomer. The structure of these electrically conducting films (10-6-10-1 S/cm), the chemical state of the doping element iodine and the elemental homogeneity at the surface and in the films have been investigated by XPS, FTIR and AES. An interesting relationship was found that indicates some similarity to conventional polythiophene, prepared by electrodeposition. Besides covalently bound iodine, considerable amounts of I 3- and I 5- were detected and also a small number of O-I bonds were identified.