ORIGINAL PAPER Microstructural, compositional, topological and optical properties of plasma polymerized cyclohexane amorphous thin films Md. Abdul Momin 1 & Khandker Saadat Hossain 2 & Abu Hashan Bhuiyan 1 Received: 16 November 2018 /Accepted: 20 February 2019 # The Polymer Society, Taipei 2019 Abstract Synthesis of plasma polymerized cyclohexane (PPCHex) thin films on to glass substrates has been done using a capacitively coupled parallel plate low-pressure glow discharge technique from cyclohexane at room temperature. From scanning electron microscopy, smooth and homogeneous surface of PPCHex thin films is observed and atomic force microscopic micrographs show the roughness of 0.815 to 0.364 nm which also confirm the smooth, homogenous, pinhole free and uniform surface of the PPCHex thin films. The presence of 73.1 and 74.7 percentage of carbon in PPCHex thin films of thicknesses 220 and 350 nm with a small percentage of oxygen is confirmed by the energy dispersive x-ray analysis. The PPCHex thin film is thermally stable up to about 510 K. The structure of PPCHex thin films is observed to vary with film’ s thickness by forming new chemical bonds such as O-H stretching, C=C stretching, C≡C stretching, C-O stretching compared to that of the monomer. Allowed direct band gaps of PPCHex thin films are found between 2.97 and 3.61 eV for different thicknesses and allowed indirect band gaps are found to be 1.83 to 2.31 eV. Therefore, the PPCHex could be used in different type of optoelectronic devices. Keywords Cyclohexane . Plasma polymerization . AFM . Band gaps . Topography . Optoelectron Introduction In the last few decades, plasma polymerized organic thin films have attracted scientists and researchers for their applications, such as chemical, physical and biological sensors, microelectron- ic devices, optoelectronic devices, molecular devices, coating for chemical fibers, etc. [1–4]. Plasma polymerization (PP) method, an inexpensive and straightforward method, is of particular in- terest for synthesizing thin films of various thickness from or- ganic vapor with assorted surface and definite bulk qualities [2, 5]. The PP technique is largely recognized since it enables pro- duction of very thin films of smooth and uniform surface and that might not be the same as other methods. Studies on organic thin films by many researchers reveal that characteristics of or- ganic thin films depend on the monomer and methods of depo- sition [6–10]. Therefore, it is of much attention to develop organic polymer thin films of high quality for a variety of indus- trial applications. A recent study [11] on plasma polymerized polypyrrole thin films reported that increasing plasma power modified the chemical structure of the polymer due to monomer fragmentation and oxidation of the polymer. The root mean square surface roughness (R q ) and optical band gaps (E g ) were found near about 3.42 nm and 2.53 eV, respectively. Polythiophene thin films [12] were prepared by PP method un- der atmospheric pressure. The content of carbonyl (C=O), al- kyne (C≡C-H) and aliphatic groups was increased comparing with thiophene due to the high reactivity of plasma phase. The R q was increased from 17 to 25.7 nm after exposing in the air for 7 days. Rahman and Bhuiyan [13] studied plasma polymerized o-methoxyaniline (PPOMA) thin films prepared using a capac- itively coupled parallel plate reactor. Uniform, pinhole free and fracture free surface of PPOMA thin films was found. The direct (E g(d) ) and indirect (E g(i) ) band gaps of the studied PPOMA thin films of various thicknesses were 2.90 to 3.08 eV and 1.68 to 2.08 eV, respectively. Manaa et al. [14] reported optical proper- ties of plasma polymerized cyclohexane (PPCHex) thin films deposited by radio frequency (RF) plasma enhanced chemical vapor deposition technique at different RF powers onto glass and silicon substrates. The values of R q are 2.67 and 0.35 nm for the films deposited at different plasma powers and as the RF power * Md. Abdul Momin mamomin89bd@gmail.com 1 Department of Physics, Bangladesh University of Engineering and Technology (BUET), Dhaka 1000, Bangladesh 2 Department of Physics, University of Dhaka, Dhaka 1000, Bangladesh Journal of Polymer Research (2019) 26:83 https://doi.org/10.1007/s10965-019-1745-1