Study of oriented growth of oligofluorene–thiophene films onto aligned vacuum-deposited polytetrafluoroethylene layers

An analysis of a vacuum-deposited fluorene-thiophene-based material 5,5′-Di(9,9′-di-(butyl)-fluorene-2,2′-bithiophene) (DBFBT) onto different substrates, which can act as dielectric gate for organic field-effect transistor is made. Also a new method for preparation of high-quality dielectric thin films made of polytetrafluoroethylene (PTFE) is described. This method includes film formation by means of a special kind of vacuum deposition polymerization (VDP) of PTFE, assisted by electron cloud activation. Rubbing of these layers makes them orienting substrate materials which induce spontaneous ordering of deposited organic semiconductor layers. We investigated structure and morphology of PTFE layers deposited by vacuum process in dependence on deposition parameters: deposition rate, deposition temperature, electron activation energy and activation current. The molecular structure of the PTFE films was investigated by use of infrared spectroscopy. By means of ellipsometry, values of refractive index between 1.33 and 1.36 have been obtained for PTFE films in dependence on deposition conditions. Using the cold friction technique orienting PTFE layers with unidirectional grooves are obtained. We have shown that DBFBT layers growth on top of rubbed PTFE films present a certain alignment suitable for building organic field-effect transistors with better transport parameters.