Nanoscale Modification of Graphene Transport Properties by Ion Irradiation
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1203-J09-02
Nanoscale modification of graphene transport properties by ion irradiation F. Giannazzo 1, S. Sonde1,2,V. Raineri1, E. Rimini1,3 1 CNR-IMM, Strada VIII, 5, 95121, Catania (Italy) 2 Scuola Superiore di Catania, Via San Nullo, 5/i, 95123, Catania (Italy) 3 Dipartimento di Fisica ed Astronomia, Università di Catania, Via S. Sofia, 64, 95123, Catania (Italy) ABSTRACT Single layers of graphene (SLG) mechanically exfoliated from highly oriented pyrolytic graphite and deposited on SiO2/Si were irradiated with C+ ions at different fluences (from 1013 to 1014 cm-2), in order to modify the transport properties in controlled way. Using a method based on scanning probe microscopy, local measurements of the electron mean free path (l) have been carried out both on pristine and ion irradiated SLG. A lateral inhomogeneity of l was found in both cases, with an increasing spread in the distribution of l for larger fluences. Before irradiation, the spread was explained by the inhomogeneous distribution of charged impurities on SLG surface and/or at the interface with SiO2. After irradiation, lattice vacancies cause a local reduction of l in the damaged regions. INTRODUCTION Graphene is the subject of great research interest, due to its outstanding transport properties making it an attractive candidate for post-Si electronics [1-4]. In the case of ideal (i.e., freestanding, defects and impurities free) graphene layers, values of the electron mobility µ≈2×105 cm2V-1s-1 (corresponding to an electron mean free path l≈2.3 µm) have been estimated for a carrier density n≈1012 cm-2 and at room temperature (300 K) [3]. However, in most practical cases, graphene is placed on a substrate (SiO2 or other dielectrics) and is subjected to lithographic processes (for patterning and/or contact formation), which leave chemical residuals. In these cases, the reported µ values are typically ranging from 103 to 104 cm2V-1s-1, corresponding to mean free paths from ∼10 to ∼100 nm. Many experimental [3] and theoretical [5,6] works are focused on the role of the different scattering mechanisms limiting l and µ (i.e. scattering by charged impurities, point defects, lattice phonons…). The screened Coulomb interaction between charged impurities and the two-dimensional-electron-gas (2DEG) in graphene causes “long range” scattering and represents the main mechanism limiting l in most of practical cases. However, there is a significant interest on the role played by point defects, which are sources of “short range” scattering [7]. In this context, plasma treatments [8], electron [9] or ion irradiation [10,11] have been proposed as means to introduce defects in single layers of graphene. Among all of these methods, ion irradiation allows a better control of the damage, through the control of the irradiated fluence. In this paper, irradiation with energetic ions was carried out on single layers of graphene (SLG) on SiO2 and the effect on the electron mean free path was investigated as a function of ion fluence. While µ and l are commonly obtained by mea
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