Preparation and study of the electrical properties of plasma polymerized thin films of N, N, 3,5 tetramethylaniline

Abstract

Plasma polymerized N, N, 3, 5 tetramethylaniline (PPTMA) thin films were deposited on to glass substrates at room temperature by a capacitively coupled parallel plate reactor. The as-grown PPTMA thin films were characterized by elemental analysis (EA), infrared (IR) spectroscopy, differential thermal analysis (DTA)/ thermogravimetric analysis (TGA), ultraviolet-visible(Uv-vis) spectroscopy and dc electrical measurements. The EA and IR spectroscopic analyses indicate that the PPTMA is chemically and structurally different from that of the N, N, 3, 5 tetramethylaniline (TMA) monomer. The empirical formula of the PPTMA film is C7.70HIO,JoN1.5000.80' The structural investigation reveals that PPTMA thin films may be formed with certain amount of conjugation. The DTA/TGA analyses shows that the degradation in the structure and evaluation of gases may occur temperatures between 373 to 873K most probably due to dehydrogenation and oxidative reactions in the thin films. It is observed that the PPTMA films are thermally stable up to about 505 K. From the Uv-vis absorption spectra, allowed direct transition (Eqd),allowed indirect transition (Eqi) energy gaps, Tauc parameter, B and extinction coefficient were determined. The Eqdand Eqi are 2.80 and 1.44eV respectively. The value ofB is 188cm'l/2 (eVr1l2. The current density-voltage(J-V) measurements were performed on the PPTMA thin films of different thicknesses in a aluminium/PPTMA/aluminium configuration over 0 to 13 V and temperature range from 300 to 450 K. The J-V characteristics ofPPTMA showed a power law dependence, J 00 Vn , with a lin~ar behavior (n ""I) at the lower voltage region followed by a non ohmic dependence with an exponent about 2 at higher voltage region. These results emphasize that the conduction mechanism is space charge limited (SCL) conduction. Measurements of current density as a function of temperature at constant applied voltages yielded different activation energies. The values obtained are 0.81 :t 0.02 and 0.85 :t 0.05 eV for 2(ohmic) and 10 V( non ohmic) in the high temperature region respectively and 0.19:t 0.01 and O.l9:t 0.02 eV in the low temperature region respectively. The conduction in PPTMA may be dominated by hopping of carriers between the localized states at low temperatures and thermally excited carriers from energy levels within the band gap in the vicinity of high temperature.