Effect of film thickness on topographic, microstructural, optical and dielectric behaviour of PPMBA thin films

Abstract

Plasma polymerized 2-methyl butylacrylate (PPMBA) thin films of varied thicknesses (d) were deposited on to glass substrates via plasma polymerization technique. FESEM images exhibited that the film of lower thickness was comparatively smoother and uniform than that of the film of higher thickness. Topographic analysis revealed that with the decrease of d from 300 to 120 nm, the mean roughness and root-mean-square roughness decreased from 0.60 to 0.48 and 1.50 to 0.62 nm, respectively. The XRD pattern showed amorphous nature of the PPMBA films. The FTIR band intensity of the spectra of monomer and PPMBA was altered due to change of band energy. The optical T (%) increased rapidly in the lower wavelengths and became nearly constant at higher wavelengths. Refractive index and optical conductivity were reduced from 1.4842 to 1.1252 and 4.2663 × 1014 to 0.1892 × 1014, respectively with the increase in d. The ac conductivity was increased rapidly with frequency (f) but decreased with the increase of d. The dielectric constant (ɛ′) showed a strong dependence on f and d. The maximum ɛ′ was found 4.50 for 300 nm film at 103 Hz. The tanδ peaks shifted a little towards higher f with increasing d, indicating reduction of relaxation time.

Keywords

• Plasma polymerization
• Atomic force microscopy
• Optical parameter
• Ac dielectric behavior