Goniometry Versus Profilometry Studies of Contact Angle for PEDOT:PSS Deposited Onto Silicon and Fused Silica Substrates
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Goniometry Versus Profilometry Studies of Contact Angle for PEDOT:PSS Deposited Onto Silicon and Fused Silica Substrates Kenneth D. Shaughnessy1, Emma G. Langford1, Chester Szwejkowski2, Patrick Hopkins2, Costel Constantin1 1 Department of Physics and Astronomy, James Madison University, Harrisonburg, VA 22807 2 Departmnet of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, VA 22904 ABSTRACT This paper presents a comparative study on the effects of plasma type and duration on the contact angle of silicon (Si) and fused silica (FS) for the deposition of Poly (3,4 ethyldioxythiophene) Polystyrene Sulfonate (PEDOT:PSS) via drop casting. The two methods used to measure contact angles were goniometry and profilometry. Both methods agreed that the lowest contact angles were given by: 1) 30 seconds in nitrogen/oxygen mix for Si substrates, and 2) 10 minutes in pure oxygen plasma for FS substrates. INTRODUCTION Conjugated polymers such as Poly (3,4 ethyldioxythiophene) Polystyrene Sulfonate (PEDOT:PSS) combine the advantages of conventional polymers and conventional semiconductors. From the polymeric side, it includes the advantages of low weight, easy processability, and flexibility, while in the same time it behaves as a semiconductor from optical absopsion/emission perspective and, furthermore, its electrical conductivity can be easily tuned [1-6]. Plastic electronics is in dire need for such polymers to act as charge transport layer or electrical interconnect. In some of these applications, PEDOT:PSS needs to be spin-coated onto non-flexible substrates such as silicon (Si) and fused silica (FS) and the wettability between PEDOT:PSS and the host substrate can hinder of help the functionality of the devise. Therefore, the cleaning procedure of substrates like Si and FS are very important, other works have studied the effects of UV ozone and oxygen plasma on the functionality of Flextrodes (i.e. flexible transparent electrods) [7]. We present here contact angle measurements comparison between goniometry and profilometry techniques of oxygen and nitrogen plasma treated Si and FS substrates as a priori cleaning procedure to PEDOT:PSS thin film deposition. It was found that both techniques predict the same conditions for the lowest contact angle. Namely, the optimal condition for Si substrates consists in an exposure to 100 parts O2 and 3 parts N2 plasmas for 30 seconds. For the FS, the optimal conditions are obtained with 100 parts O2 for 10 minutes. EXPERIMENTAL The PEDOT:PSS polymer used in our experiments were 3.0 – 4.0 % polymer suspended in water and it was the conductive grade purchased from Sigma Aldrich. The sonicator used was a Branson 3800 and the plasma etcher used was a March Px-250. We cut substrates in 1x1 inch size and the Si used were low conductivity grade with 1 side polished silicon test wafers purchased from University Wafers. The FS substrates used were double side polished wafers purchased also from University Wafers. These samples were then cleaned first using sonification
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