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Graphene/Complex Oxide Heterostructures
Superlattice patterning on Graphene/LAO/STO
Superlattice patterning on Graphene/LAO/STO
Superlattices have attracted great interest because their use may make it possible to modify the spectra of two-dimensional electron systems and, ultimately, create materials with tailored electronic properties. The two-dimensional electron gas (2DEG) appearing at the Lanthanum aluminate-strontium titanate (LaAlO3/SrTiO3) interface makes it an ideal substrate to pattern superlattice on graphene through Conductive atomic force microscopy (c-AFM) lithography [1]. Owing to the high dielectric constant of SrTiO3 in low temperature, it is possible to heavily dope graphene and tune the carrier density dramatically. Thus, LAO3/STO3 makes it possible to tune the fermi level and created nanostructures reversibly on graphene.
The growth of the graphene is achieved by atmospheric pressure chemical vapor deposition (APCVD) on ultra-flat diamond turned copper substrates [2]. Then the Graphene is transferred to LAO/STO substrated and patterned to a hall bar structure with an amorphous perfluoropolymer Hyflon AD60, which will leave less residue compared with PMMA. Superlattice was written by Conductive atomic force microscopy (c-AFM) lithography with alternating positive and negative five volts. As a control group, Rxx2 region was written uniformly with 5V.
The propagation of nearly free electrons through a weak periodic potential results in the opening of bandgaps near points of the reciprocal lattice. In the graphene superlattices, there is no gap opening at the Dirac point. Instead, a new set of Dirac points will emergent at an energy determined by the superlattice size [3]. Longitudinal resistance was measured as a function of back-gate under 5 Tesla at 2K. In the Landau fan diagram, a replica of Dirac point shows up next to the charge neutrality point only in the superlattice region, which is a sign of superlattice potential.
Cen, C. et al. "Nanoscale Control of an Interfacial Metal-Insulator Transition at Room Temperature," Nat Mater 7, 298-302(2008).
http://dx.doi.org/10.1038/nmat2136S. Dhingra, J.-F. H., I. Vlassiouk, and B. D’Urso. "Chemical Vapor Deposition of Graphene on Large-Domain Ultra-Flat Copper," Carbon 69 (2014).
http://dx.doi.org/10.1016/j.carbon.2013.12.014Ando, T. & Nakanishi, T. "Impurity Scattering in Carbon Nanotubes – Absence of Back Scattering –," J. Phys. Soc. Jpn. 67, 1704-1713.
http://dx.doi.org/10.1143/JPSJ.67.1704
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