Measurements of the adhesion energy of graphene to metallic substrates Santanu Das a , Debrupa Lahiri b , Dong-Yoon Lee c , Arvind Agarwal b , Wonbong Choi a, * a Nanomaterials and Device Laboratory, Department of Materials Science and Engineering, University of North Texas, Denton, TX 76207, USA b Nanomechanics and Nanotribology Laboratory, Mechanical and Materials Engineering Department, Florida International University, Miami, FL 33174, USA c Korea Electrotechnology Research Institute, Changwon City, Kyungnam 280-120, Republic of Korea ARTICLE INFO Article history: Received 2 January 2013 Accepted 28 February 2013 Available online 13 March 2013 ABSTRACT We report a nano-scale quantification study of the adhesion energy of chemically vapor deposited (CVD) graphene on Cu and Ni. The adhesion energy of graphene on Cu and Ni substrates was measured to be 12.8 and 72.7 Jm 2 , respectively. Density functional theory shows that the graphene/Ni interface exhibits more covalent bonding than graphene/Cu which is partially ionic, hence the reason for the higher adhesion energy for graphene/ Ni. We believe that this nano-scale adhesion energy measurement method could be further extended for measuring the adhesion energy of other 2D materials. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Quantification of the adhesion energy of directly synthesized nano-materials with substrates creates an intense research interests not only for architecting reliable devices, but also for understanding their bonding characteristics which en- ables us to develop knowledge of growth mechanism, transfer processes, and properties. Most importantly, the quantifica- tion of the adhesion energy becomes paramount importance since the property of 2D layered materials, like graphene, strongly exhibits substrate dependence. Graphene, sp 2 bonded carbon allotrope in two dimension, originated re- search booms from past 7 years due to its exceptional elec- tronic properties such as quantum Hall Effect, ballistic charge transport, high charge carrier density, tunable band gap, high thermal conductivity, etc [1]. To date, considerable works have been demonstrated in applications of graphene including transistors, Li ion batteries, super-capacitor, solar cells, etc [2–4]. As graphene is a single atomic-layer-thick material and few-layer graphene is a few atomic-layer-thick material with interlayer spacing of 0.34 nm, hence, it exhibits substrate dependent properties of electronic, photonic, ther- mal and photoelectric properties [1,5]. For example, graphene is semi-metallic with zero band gap in which the k and k / points are touching at the Brillouin zone, however, graph- ene-substrate bonding induces a band gap in a graphene structure as reported elsewhere [6]. Similarly, it has also been reported that graphene’s phonon transports are strongly sub- strate dependent as could be observed from its distinguished Raman responses [7]. Although free standing graphene exhib- its exceptional properties of electrical and thermal transport, many of graphene devices require attachment of wide range of different substrates. Therefore, it is more advantageous to understand the adhesion energy and bonding characteris- tics of graphene and substrates. On the other hand, electronic configurations and density of states (DOS) fluctuate with changing graphene-substrates electronic interactions [8]. This is due to the inconsistent interactions between an electronic band structure of 3D materials and 2D graphene which cre- ates a sharp density of state (DOS) mismatch at the interface [8]. Furthermore, substrate induced doping of graphene can readily change graphene properties whereas stable interfacial 0008-6223/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2013.02.063 * Corresponding author: Fax: +1 940 369 4824. E-mail address: Wonbong.Choi@unt.edu (W. Choi). CARBON 59 (2013) 121 – 129 Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon