Applied Surface Science 256 (2010) 4672–4676 Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc Humidity effect on the interaction between carbon nanotubes and graphite David Chabrier a,b , Bharat Bhushan a,∗ , Sophie Marsaudon b a Nanoprobe Laboratory for Bio- & Nanotechnology & Biomimetics, The Ohio State University, 201 W 19th Ave., Columbus, OH 43210, USA b Centre de Physique Moleculaire Optique et Hertzienne, Université Bordeaux 1, 351 Cours de la liberation, Talence 33405, France article info Article history: Received 4 December 2009 Received in revised form 12 February 2010 Accepted 22 February 2010 Available online 1 March 2010 Keywords: SWNT MWNT HOPG Force curve abstract An atomic force microscope is used to study the effect of humidity on the interaction between carbon nanotubes anchored to atomic force microscopy tips and various samples. Commercial silicon tips were also used for comparison. Adhesion force and dissipative energy were measured between these tips and highly oriented pyrolytic graphite (HOPG) and PMMA in contact mode. The data provides a detailed understanding of carbon nanotube interactions as a function of humidity. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Since their discovery in 1991 by Iijima [1], a lot of research has been carried out on carbon nanotubes (CNTs). There are a large number of applications due to their exceptional properties such as high electrical conductivity (comparable to copper) [2], ther- mal conductivity (comparable to diamond), and low deformation (a hundred times stronger than steel and six times lighter) [3,4]. CNTs are being used in microelectronic devices such as actuators and sensors [5,6]. For example, a microelectromechanical switch is operated by electrically driving a moving part to produce a physical motion which results in the opening or closing of an electric circuit. An example of a nanoelectromechanical switch is a single-walled carbon nanotube (SWNT) that can slip into a multi-walled carbon nanotube (MWNT) and touch a second MWNT, forming a closed circuit. A voltage is applied to the SWNT to push out and touch the second MWNT. Adhesion forces between the CNT ends maintain the conductive state [7]. CNTs are also used to improve material toughness. One can find composites reinforced with CNTs [8–10]. Other applications include nanofluidics, where CNTs are used as nanochannels [11–13]. These are used as a filter to permit passage for small molecules [11,14]. With nanofluidics, CNTs are also used for the characterization of biological molecules and/or control of the placement of a molecule [15]. One last application is drug car- riers due to their high aspect ratio, which enables cell penetration and possibilities of introducing a drug via the CNT [16]. ∗ Corresponding author. E-mail address: bhushan.2@osu.edu (B. Bhushan). In all of these applications, CNTs come in contact with the mat- ing surface. Moreover, all these applications require use in different environments, including relative humidities (RH). Therefore, we need to understand the effect of RH on CNT interactions. Nanoscale surface effects are different compared with commonly understood macroscale surface effects [17]. A number of studies have been carried out to study adhesion force or friction force as a function of RH [17]. For example, the- oretical adhesion force and its dependence on contact angle and radius of the tip are discussed by Stifter et al. [18] and Chen and Lin [19]. Adhesion and friction experiments at nominal and various humidities have been carried out by Bhushan and Dan- davate [20], Bhushan [21], Bhushan and Ling [22], and Bhushan et al. [23,24]. Adhesion force is a combination of the electrostatic force, the van der Waals force, the capillary force, and forces due to chemical bonds or acid–base interactions [25]. That explains why it is so difficult to predict adhesion force at different RH, and different trends in adhesion force vs. RH are found for dif- ferent samples and different tips. For example, Chen et al. [26] reported that with a Si 3 N 4 tip on highly oriented pyrolytic graphite (HOPG) there exists a hump on the adhesion force at 55–80% of RH. Studies have also been conducted using AFM dynamical mode in which force–distance curves have been obtained. For example, force–distance curve mode studies with CNT tips show hystere- sis behavior (e.g. [27,28]). Using frequency mode, interpretation of the contribution of the dissipative and conservative part of CNTs on HOPG has been provided [29] or of CNTs and soft sample [30]. In this article, the adhesion force and dissipative energy of CNTs on HOPG are investigated at different relative humidities. Changes in the adhesion force are calculated from the force–distance curves. 0169-4332/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2010.02.070