Superhydrophobic polytetrafluoroethylene thin films with hierarchical roughness deposited using a single step vapor phase technique Sushant Gupta a, ⁎, Arul Chakkaravarthi Arjunan b , Sameer Deshpande c , Sudipta Seal c , Deepika Singh b , Rajiv K. Singh a a Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, United States b Sinmat Incorporated, 2153 SE Hawthorne Road, #129, Gainesville, Florida 32641, United States c Advanced Material Processing and Analysis Center, University of Central Florida, Orlando, Florida 32816, United States abstract article info Article history: Received 13 May 2008 Received in revised form 8 December 2008 Accepted 18 December 2008 Available online 2 January 2009 Keywords: Polytetrafluoroethylene Pulsed electron deposition Superhydrophobicity Dual-scale roughness Thin films Atomic force microscopy Superhydrophobic polytetrafluoroethylene films with hierarchical surface roughness were deposited using pulse electron deposition technique. We were able to modulate roughness of the deposited films by con- trolling the beam energy and hence the electron penetration depth. The films deposited at higher beam energy showed contact angle as high as 166°. The scanning electron and atomic force microscope studies revealed clustered growth and two level sub-micron asperities on films deposited at higher energies. Such dual-scale hierarchical roughness and heterogeneities at the water–surface interface was attributed to the observed contact angle and thus its superhydrophobic nature. Published by Elsevier B.V. 1. Introduction Superhydrophobic surfaces are highly desirable for various appli- cations such as self-cleaning surfaces, microfluidics, antifogging appli- cations [1,2], anticorrosion [3] and microelectromechanical systems [4] etc. Considerable efforts have been made to control microstructure of the surfaces since surface roughness is known to influence the wetting properties of the surface. Wenzel and Cassie–Baxter models describe the role of roughness in surface wetting properties. According to Wenzel model, the presence of protrusions on the hydrophobic surface increases the surface area thereby enhancing its hydrophobic nature. In Cassie state, the surface roughness results in the reduction of liquid–solid contact area with concomitant increase in the fraction of liquid–air interface, thus increasing the contact angle. A number of reports have shown that the presence of multi-scale roughness is essential to achieve superhydrophobic surfaces [1,2,5–8]. To em- phasize the importance of such multi-scale roughness, Xiu et al. recently showed that the superhydrophobicity was only achieved when nanoscale roughness was constructed on the silicon pyramids [5]. Herminghaus proposed a model to understand the role of multi- scale roughness in superhydrophobic behavior shown by certain plant leaves [9]. Extensive research efforts have been focused on controlling the microstructure of the surface at nanometer scale in addition to the micrometer scale to achieve dual/multi-scale roughness. Most of the methods adopted to achieve dual roughness involve use of two separate steps for example (a) deposition of the films and (b) con- trolling the surface roughness by techniques such as plasma treat- ment or etching [10,11]. The deposition or surface functionalization on patterned surface is another approach involving photolithogra- phy followed by surface coating or treatment [12,13]. Bormashenko et al obtained multi-scale roughness by coating the substrate with a colloidal suspension of the polyvinylidene fluoride beads in a dis- solved polymer matrix followed by the evaporation of the solvent [14]. Other methods include laser-etching [15], phase-separation micromolding methods using soluble polymers [2], sol–gel method [16,17], electrohydrodynamics technique [7], plasma polymeriza- tion [18–20] etc. In this paper, we demonstrate an electron beam technique to deposit dual-roughness superhydrophobic films using a single processing step. Under the optimized energy density con- dition of the electron beam, superhydrophobic films with two levels of roughness can be fabricated using pulse electron deposition (PED) technique. Polytetrafluoroethylene (PTFE) or commonly known as Teflon was used in this study. It is commonly used material for Thin Solid Films 517 (2009) 4555–4559 ⁎ Corresponding author. E-mail address: sushant3@ufl.edu (S. Gupta). 0040-6090/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.tsf.2008.12.048 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf