Tetrakis(trimethylsilyloxy)silane for nanostructured SiO 2 -like films deposited by PECVD at atmospheric pressure J. Schäfer a, ⁎, J. Hnilica b , J. Šperka b,c , A. Quade a , V. Kudrle b , R. Foest a , J. Vodák d , L. Zajίčková b,c a Leibniz Institute for Plasma Science and Technology e.V., Felix-Hausdorff-Straße 2, 17489 Greifswald, Germany b Department of Physical Electronics, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czech Republic c CEITEC — Central European Institute of Technology, Masaryk University, Kamenice 753/5, CZ-62500 Brno, Czech Republic d Institute of Physical Engineering, Faculty of Mechanical Engineering, Brno University of Technology, Technická 2896/2, CZ-61669 Brno, Czech Republic abstract article info Article history: Received 16 May 2015 Revised 21 August 2015 Accepted in revised form 26 September 2015 Available online 3 October 2015 Keywords: Tetrakis(trimethylsilyloxy)silane Tetrakis(trimethylsiloxy)silane Plasma jet Silicon dioxide Plasma enhanced chemical vapor deposition (PECVD) from tetrakis(trimethylsilyloxy)silane (TTMS) has been studied at atmospheric pressure. TTMS has been chosen because of its unique 3D structure with potential to form nano-structured organosilicon polymers. Despite the widespread surveying of various silicon-organic mol- ecules for PECVD, the use of TTMS in AP-PECVD has not been investigated deeper yet. PECVDs have been per- formed with two different plasma jets. While they are alike regarding the geometry and injection of TTMS, they differ in input power and excitation frequency. The radiofrequency plasma jet operates at lower power den- sities as compared to the microwave plasma jet. Despite this all the deposited films exhibit similar chemical prop- erties resembling that of silicon dioxide (Si:O = 1:2) with carbon content below 5%. The films demonstrate a broad variety of morphologies from compact smooth films to nano-dendritic 3D structures depending on the par- ticular process. © 2015 Elsevier B.V. All rights reserved. 1. Introduction If complex organosilicon precursors are used for PECVD, the chemis- try and properties of the resulting films are heavily influenced by the operational conditions. Depending on temperature, power density or gas mixture (e.g. oxygen content) inorganic SiO 2 [1,2] films are ob- served as well as branched and/or cross-linked structures of polymethylsiloxanes [3]. Often, the incorporation of a high content of organic functional groups, in particular methyl groups is causing a po- rous or less dense film structure with inferior chemical and mechanical stability. Hence, the independent adjustment of the morphological and chemical film properties by variation of the process parameters at atmo- spheric pressure is a challenging task. Much of current effort is dedicat- ed to this issue [4,5]. In particular, a stability against chemical or mechanical impact is desirable for coatings in a wide range of morphol- ogies. For instance, permeation barriers rely on compact pin-hole free coatings [6] whereas surfaces for heterogeneous catalysis require hier- archically nano-structured films with large surface area and their cata- lysts centered in chemically stable matrices [7,8]. The importance of hybrid materials production from molecular precursors leads to investi- gation of organosilicates from complex precursors. For example, precur- sors of the general formula (CH 3 O) 3 SiRSi(OCH 3 ) 3 are under investigation for the preparation of hybrid materials by sol-gel polycon- densation [9]. In the present study it is demonstrated that such different morpholo- gical structures can be obtained using tetrakis(trimethylsilyloxy)silane (TTMS, C 12 H 36 O 4 Si 5 ) as thin film precursor for PECVD, while the chemical composition remains essentially SiO 2 –like. Among other complex silicon organic molecules commonly in use for PECVD, the TTMS molecule (see Fig. 1) exhibits several advantages, with regard to forming structured coatings at suitable conditions. The molecular structure of TTMS is char- acterized by the presence of five rigid tetrahedral sub-units: the central unit SiO 4 and four peripheral units OSi(CH 3 ) 3 . The central unit represents the elementary cell of quartz-like structures in dense SiO 2 films. The aver- age valence angle of SiOSi in TTMS is 146° [10] and hence wider than in usually used hexamethyldisiloxane (HMDSO, (CH 3 ) 3 Si–O–Si(CH 3 ) 3 ) where 130° is found [11]. Thus, the rotation around the Si c –O bonds 1 in TTMS is virtually more unrestricted than in HMDSO. This causes a rela- tively flexible conformation of TTMS [12]. Consequently, this flexible con- formation can play a crucial role for the self-adapted growth of nano- structured films. In addition, this precursor is non-flammable, non- toxic, and has reasonably high vapor pressure. After studies [13] and [14], the present work is the first utilizing TTMS in atmospheric pressure high-frequency PECVD processes. Surface & Coatings Technology 295 (2016) 112–118 ⁎ Corresponding author. E-mail address: jschaefer@inp-greifswald.de (J. Schäfer). 1 The index c denotes the central atom of the molecules. http://dx.doi.org/10.1016/j.surfcoat.2015.09.047 0257-8972/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat