Local surface conductivity mapping of single-layer graphene subject to low energy argon bombardment: Energy loss mechanism and defect induction efficiency Tanmoy Basu a,b,⇑ , Milan Blaskovic a , Sudhiranjan Tripathy c , Feng Tian a , Ranveer Singh d , Tapobrata Som d , Slaven Garaj a,e , Jeroen Anton van Kan b,e,⇑ a Centre for Advanced 2D Materials, National University of Singapore, Singapore 117546, Singapore b Center for Ion Beam Applications, Department of Physics, National University of Singapore, Singapore 117542, Singapore c Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), Innovis 08-03, 2 Fusionopolisway, Singapore 138634, Singapore d SUNAG Laboratory, Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005, India e Department of Physics, National University of Singapore, Singapore 117542, Singapore article info Article history: Received 15 April 2019 Received in revised form 24 August 2019 Accepted 6 September 2019 Available online 10 September 2019 Keywords: Graphene Ion irradiation Defects abstract An ion-beam exposure can be applied to form defects in supported graphene which can be tuned with energies and fluence. However, recent results show that nuclear energy loss process is the dominant mechanism in defect formation. In the present work, it is shown that in low energy regime (1–10 keV Ar + ions), both nuclear and electronic energy losses play an important role in forming different types of defects. Here we show a linear relation between defect induction efficiency and energy loss. Conductive atomic force microscopy shows a significant reduction in the current through supported graphene after ion beam exposure. Ó 2019 Elsevier B.V. All rights reserved. 1. Introduction Recently, nanoporous graphene is emerging as a promising material for Li-ion batteries, DNA sequencing, and molecular- sieving [1]. In this regard, various approaches have been used to create pores or defects in graphene [2]. While creating pore size <2 nm is challenging with lithographic techniques, broad beam ion irradiation technique can play a major role to induce controlled atomic scale defects in graphene lattice. It has been pointed out earlier that in case of graphene, nuclear energy loss (S n ) dominates the defect formation mechanism and contribution of electronic energy loss (S e ) becomes negligible [3,4]. However, one of the most contentious topics is the substrate effect during ion irradiation of graphene. For example, Compagnini et al. have shown that single-layer graphene on SiO 2 is more susceptible to defect forma- tion than multilayers [4] while Mathew et al. found that graphene supported by SiO 2 is stronger than free standing graphene under 2 MeV proton beam irradiation [5]. Subsequently, Buchowicz et al. suggested that the sputtered atoms from the SiO 2 substrate do not contribute to form defects in graphene [6]. However, recently Li et al. has shown experimentally that the substrate con- tributes to defect formation. These contradictory results indicate that the key mechanism of the defect formation in supported gra- phene remains to be understood [7]. In addition, evaluation of ion irradiation can be done by probing local change in surface conductivity upon ion bombardment using non-destructive techniques like conductive atomic force micro- scopy (CAFM). Here surface conductivity differences of pristine and ion irradiated supported graphene layer is analyzed. Detailed influence of S n /S e and the effect of substrate on defect formation in graphene are discussed using Raman spectroscopy. 2. Experimental The preparation, irradiation, and characterization methods are presented in supplementary information. 3. Results and discussion Final sample with graphene is shown in Fig. 1(a). CAFM measurement is shown in Fig. 1(b) schematically. Fig. 1(c) and (d) show topography and CAFM images, respectively, taken on https://doi.org/10.1016/j.matlet.2019.126638 0167-577X/Ó 2019 Elsevier B.V. All rights reserved. ⇑ Corresponding authors at: Center for Ion Beam Applications, Department of Physics, National University of Singapore, Singapore 117542, Singapore. E-mail addresses: c2dtb@nus.edu.sg (T. Basu), phyjavk@nus.edu.sg (J. Anton van Kan). Materials Letters 256 (2019) 126638 Contents lists available at ScienceDirect Materials Letters journal homepage: www.elsevier.com/locate/mlblue