Letter pubs.acs.org/NanoLett
Doping of Graphene by Low-Energy Ion Beam Implantation: Structural, Electronic, and Transport Properties Philip Willke,† Julian A. Amani,‡ Anna Sinterhauf,† Sangeeta Thakur,§ Thomas Kotzott,† Thomas Druga,† Steffen Weikert,‡ Kalobaran Maiti,§ Hans Hofsas̈ s,‡ and Martin Wenderoth*,† †
IV. Physikalisches Institut and ‡II. Physikalisches Institut, Georg-August-Universität Göttingen, 37077 Göttingen, Germany § Department of Condensed Matter Physics and Materials’ Science, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India S Supporting Information *
ABSTRACT: We investigate the structural, electronic, and transport properties of substitutional defects in SiC-graphene by means of scanning tunneling microscopy and magnetotransport experiments. Using ion incorporation via ultralow energy ion implantation, the influence of different ion species (boron, nitrogen, and carbon) can directly be compared. While boron and nitrogen atoms lead to an effective doping of the graphene sheet and can reduce or raise the position of the Fermi level, respectively, 12C+ carbon ions are used to study possible defect creation by the bombardment. For low-temperature transport, the implantation leads to an increase in resistance and a decrease in mobility in contrast to undoped samples. For undoped samples, we observe in high magnetic fields a positive magnetoresistance that changes to negative for the doped samples, especially for 11B+- and 12C+-ions. We conclude that the conductivity of the graphene sheet is lowered by impurity atoms and especially by lattice defects, because they result in weak localization effects at low temperatures. KEYWORDS: Graphene, scanning tunneling microscopy/spectroscopy, ion implantation, boron-doped graphene, nitrogen-doped graphene, magnetotransport
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Here, we report a comparative study using scanning tunneling microscopy/spectroscopy (STM/S) as well as transport measurements to study SiC-graphene doped with nitrogen/boron atoms. In contrast to nitrogen-doped graphene, boron-doping has rarely been studied up to now6 especially for epitaxially grown graphene on SiC. Figure 1a shows an STM image of a pristine graphene sheet on SiC. Besides the graphene lattice the 6 × 6 reconstruction is clearly visible.16 In Figure 1b, we introduced substitutional boron atoms into the system that manifest in a pronounced electronic contrast. Besides their influence on doping, these defects change the local structural and electronic properties and serve as atomic scattering centers for electron transport. This becomes apparent in Figure 1c where we show the magnetoresistance (MR) of the two systems. While the MR for the undoped system increases for increasing magnetic field, it strongly decreases for the doped systems that we attribute to an additional contribution of weak localization.17 This connection between the microscopic structure and the transport properties reveals the processes taking place for electron scattering at substitutional atoms and additional defects in graphene and are in the focus of this paper.
ailoring the electronic properties of graphene is an important requirement for its application in future electronic devices. Essentially, the position of the Fermi level and a corresponding tuning of the number of charge carriers are one of the major challenges. To achieve doping in graphene different approaches have been explored, including adsorption of adlayers1 and intercalation of atomic layers,2−4 but also a direct incorporation of foreign atoms into the graphene sheet.5−14 This direct substitution can be realized during the growth process as usually done for graphene grown by chemical vapor deposition (CVD).5,6 Besides other techniques7−9 ion bombardment has been established as a suitable way,10,11 allowing doping of graphene on different substrates.12−14 This doping technique has the advantage of being easily transferable to other dopant atoms and other two-dimensional atomic crystals in the context of van der Waals heterostructures15 like boron nitride (BN), tungsten disulfide (WS2), and molybdenum disulfide (MoS2). Moreover, it allows an easy control of the dopant concentration through the ion fluence. The influence of doping by atomic substitution on transport processes remains important for device physics: the presence of foreign atoms as well as the possible creation of additional defects hinders the electronic performance by introducing atomic scale scattering centers. Therefore, it is crucial to connect the electronic properties of doped graphene sheets with their microscopic structure and their behavior in transport experiments. © XXXX American Chemical Society
Received: April 2, 2015 Revised: June 10, 2015
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DOI: 10.1021/acs.nanolett.5b01280 Nano Lett. XXXX, XXX, XXX−XXX
Letter
Nano Letters
graphene on the Si-terminated side are achieved by a heating step for 2 min at 1400−1600 °C in ultrahigh vacuum (UHV) (
