Surfaces and Interfaces 23 (2021) 100989 Available online 4 February 2021 2468-0230/© 2021 Elsevier B.V. All rights reserved. Silicon Dioxide Deposited Using Atmospheric Pressure Plasma Chemical Vapor Deposition for Improved Adhesion and Water Intrusion Resistance for Lightweight Manufacturing Zachary Jeckell a , Dhruval Patel a , Andrew Herschberg a , Tag Choi a , David Barlaz a , Lucia Bonova a, c , Ivan Shchelkanov b , Brian Jurczyk b , David Ruzic b a Department of Nuclear, Radiological, and Plasma Engineering, University of Illinois at Urbana-Champaign, 201 S Goodwin Ave, Urbana, IL 61802 b Starfre Industries 2109 S Oak St, Champaign, IL 61820 c Advanced Technologies Research Institute, Faculty of Materials Science and Technology in Trnava, Slovak University of Technology in Bratislava, J´ ana Bottu 25, 91724 Trnava, Slovakia A R T I C L E INFO Keywords: Atmospheric pressure plasma chemical vapor deposition silicon oxide lap shear strength barrier coating ABSTRACT This work aims to demonstrate the barrier coating, and adhesion promoting properties of silica-based coatings deposited using an atmospheric pressure plasma torch (APPT). This is achieved by applying an industrial grade adhesive to silica thin flms deposited, on the surfaces to be joined, using atmospheric pressure plasma chemical vapor deposition (APP-CVD), to make single joint lap shear samples of different metal combinations commonly found in lightweight manufacturing, such as aluminum and magnesium as well as steel. To deposit these thin flms, two separate silicon based organic precursors, hexamethyldisiloxane (HMDSO), and tetraehylorthosilicate (TEOS), are used. Samples are bonded using DuPont Betamate 1486 adhesive, and the lap shear results for these flms are compared to the lap shear results of a chemically cleaned control using the same adhesive. The APPT uses a microwave power supply and gas mixtures of N 2 and Ar. The adhesion of the flms are tested using lap shear, and elevated temperature water soaks are conducted on the joints as well to simulate environmental exposure. Lap shear results, from samples with silica thin flms, have an increase of max shear stress of 25%- 115% compared to control samples depending on material. After exposure to water soak the max shear strength of the joints decreased by less than 15%, which demonstrates the flms capabilities as a water barrier. Film morphology is examined using Scanning Electron Microscopy (SEM), and the flm’s composition and approxi- mate thickness are obtained using Rutherford Backscattering Spectroscopy (RBS). 1. Introduction As the automotive industry shifts towards lightweight manufacturing there is a need for a cost-effective method to bond dissimilar metals commonly used in manufacturing, such as aluminum and magnesium. For this reason, the automotive industry is looking for methods that improve the performance of dissimilar metal joints bonded using ad- hesives. The primary method for this procedure was, until recently, the Alodine dip coating process, an dipping process where entire parts are submerged in a solution to clean and deposit a conversion coating [1]. The Alodine treatment coats the entire part, when typically only small joints require the coating. This process is inherently wasteful, and because this is typically done off site it adds transportation costs and creates chemical waste which can both endanger workers and incurs costly disposal [1]. A newer technique to improve adhesion involves using a laser which roughens and cleans the surface, as well as removes the native oxide [2–4]. Silicon dioxide thin flms are versatile and offer many potential ad- vantages for lightweight manufacturing. Signifcant research has been published on the oxygen and water barrier properties of silicon dioxide thin flms, which is of great interest for the food packing and medical industries [5–8]. Thin silicon dioxide flms have been demonstrated to improve the barrier and corrosion resistance of various materials including aluminum [9], steel [10], magnesium [11–13], and even carbon fber reinforced polymers [6–8,14–18] . Research has also been done that highlights silica thin flms for their ability to act as an Abbreviations: APPT, Atomospheric pressure plasma torch; APP-CVD, atmospheric pressure plasma chemical vapor deposition; HMDSO, hexamethyldisiloxane; TEOS, tetraethylorthosilicate; RBS, Rutherford Back Scattering. Contents lists available at ScienceDirect Surfaces and Interfaces journal homepage: www.sciencedirect.com/journal/surfaces-and-interfaces https://doi.org/10.1016/j.surfn.2021.100989 Received 10 December 2020; Received in revised form 21 January 2021; Accepted 30 January 2021