Applied Surface Science 305 (2014) 554–561 Contents lists available at ScienceDirect Applied Surface Science journal h om epa ge: www.elsevier.com/locate/apsusc Hydrophobicity enhancement of Al 2 O 3 thin ﬁlms deposited on polymeric substrates by atomic layer deposition with perﬂuoropropane plasma treatment Kamran Ali a , Kyung-Hyun Choi a,∗ , Chang Young Kim b , Yang Hoi Doh c , Jeongdai Jo d a Department of Mechatronics Engineering, Jeju National University, Jeju, 690-756, Republic of Korea b Research Institute for Basic Sciences and Department of Physics, Jeju National University, Jeju, 690-756, Republic of Korea c School of Electronic Engineering, Jeju National University, Jeju, 690-756, Republic of Korea d Korean Institute of Machinery and Materials, Yuseong-Gu, Daejeon 305-343, Republic of Korea a r t i c l e i n f o Article history: Received 9 January 2014 Received in revised form 21 March 2014 Accepted 21 March 2014 Available online 30 March 2014 Keywords: Al2O3 Atomic layer deposition C3F8 Hydrophobicity Contact angle PEN a b s t r a c t The optoelectronics devices such as organic light emitting diodes are greatly vulnerable to moisture, which reduces their functionality and life cycle. The Al 2 O 3 thin ﬁlms are mostly used as barrier coat- ings in such electronic devices to protect them from water vapors. The performance of the Al 2 O 3 barrier ﬁlms can be improved by enhancing their hydrophobicity. Greater the hydrophobicity of the barrier ﬁlms, greater will be their protection against water vapors. This paper reports on the enhancement of hydropho- bicity of Al 2 O 3 thin ﬁlms through perﬂuoropropane (C 3 F 8 ) plasma treatment. Firstly, good quality Al 2 O 3 ﬁlms have been fabricated through atomic layer deposition (ALD) on polyethylene naphthalate (PEN) substrates at different temperatures. The fabricated ﬁlms are then plasma treated with C 3 F 8 to enhance their hydrophobicity. Hydrophobic Al 2 O 3 thin ﬁlms have shown good morphological and optical prop- erties. Low average arithmetic roughness (Ra) of 1.90 nm, 0.93 nm and 0.88 nm have been recorded for the C 3 F 8 plasma treated ﬁlms deposited at room temperature (RT), 50 ◦ C and 150 ◦ C, respectively. Optical transmittance of more than 90% has been achieved for the C 3 F 8 plasma treated ﬁlms grown at 50 ◦ C and 150 ◦ C. The contact angle has been increased from 48 ◦ ± 3 to 158 ◦ ± 3 for the ﬁlms deposited at RT and increased from 41 ◦ ± 3 to 148 ◦ ± 3 for the ﬁlms deposited at 150 ◦ C. © 2014 Elsevier B.V. All rights reserved. Introduction The development of electronic devices such as solar cell, organic light emitting diode (OLED), organic light emitting transistors (OLET), organic thin ﬁlm transistors device (OTFT) and memristor on ﬂexible substrates would result in great advantages like reduced weight, low cost, continuous production and high ﬂexibility[1–7]. However, there are some challenges in fabricating these devices on polymeric substrates and one of them is the high permeability of ﬂexible substrates to water vapors which can result in damage such as corroding the cathodes of the devices [8–12]. Therefore, the ∗ Corresponding author at: Department of Mechatronics Engineering, Jeju National University, Room 221, Engineering building #4, Jeju City, Jeju 690-756, Republic of Korea. Tel.: +82 64 754 3713; fax: +82 64 752 3174. E-mail addresses: Kamran ali1214@yahoo.com (K. Ali), amm@jejunu.ac.kr (K.-H. Choi), ﬁrstyoung77@naver.com (C.Y. Kim), yhdoh@jejunu.ac.kr (Y.H. Doh), micro@kimm.re.kr (J. Jo). permeability of polymeric substrates must be reduced with addi- tional barrier coatings such as thin ﬁlms of Al 2 O 3 in order to improve the efﬁciency and life time of the devices. Al 2 O 3 is non- toxic, non-ﬂammable material and has a melting point of 2050 ◦ C. In controlled conditions Al 2 O 3 forms highly even and uniform sur- face ﬁlms, and has been considered as an excellent diffusion barrier [13]. The Al 2 O 3 thin ﬁlms can be efﬁciently produced on ﬂexible substrates through atomic layer deposition [14]. The ALD tech- nique is known to produce densely packed, virtually defect-free and highly conformal ﬁlms and can therefore be used to deposit high- quality permeation barriers. A typical ALD process involves a binary reaction sequence in which two independent surface reactions are separated in time [15]. Al 2 O 3 ALD using trimethylaluminum [Al (CH 3 ) 3 , TMA] and water (H 2 O) is one of the most studied ALD systems. Al 2 O 3 can be deposited on thermally sensitive polymers because Al 2 O 3 ALD can be conducted at temperatures as low as 33 ◦ C [16]. The passivation properties of Al 2 O 3 barrier thin ﬁlms can be enhanced by enhancing the hydrophobicity or water repellency http://dx.doi.org/10.1016/j.apsusc.2014.03.135 0169-4332/© 2014 Elsevier B.V. All rights reserved.