Quantum Dots Embedded in Graphene Nanoribbons by Chemical Substitution

E Carbonell-Sanroma, P. Brandimarte, R. Balog, M. Corso, S. Kawai, A. García-Lekue, S. Saito, S. Yamaguchi, E. Meyer, D. Sánchez-Portal and J. I. Pascual
Nano Letters 17, 50 (2017)

Figure a) Model of the studied system formed by a pristine 7-aGNR region enclosed by two B-dimers 6.5 nm apart. b) Dispersion of the VB and VB-1 bands of a 7-aGNR, (left) and transmission function (right) for a pristine ribbon (red), a single boron pair (dashed green) and for the confined system formed by two boron pairs (blue). c) Projected density of states for the pristine segment. Quantized levels up to n=5 are clearly observed between the boron localized states. d) Real part of the eigenchannel functions taken at the energies corresponding to the n=2,3,4 and 5 QW levels. In the dashed panel are presented the real part of the eigenchannel functions taken at E-EF=-1.10 eV, i.e. between quantized levels. The eigenchannel corresponding to the VB shows no transmission through the boron segments, while VB-1 fully transmits through. e) Experimental results obtained using scanning tunneling spectroscopy.

The Modelization and Simulation group at CFM has been able to simulate the quantum transport properties of boron-doped graphene nanoribbons (GNRs), helping to interpret the experimental data obtained by the group of Prof. J. I. Pascual at NanoGUNE. The Figure below shows the computed transport characteristics through a pristine section of a 7-armchair GNR enclosed by two B-dimer defects situated 6.5 nm apart, mimicking the experimental situation. The results shows enhance transport at the energies corresponding to quantum well (QW) states derived from the valence band (VB). The effect is similar to that of Fabry-Perot resonances in optics. Surprisingly, the lower valence minus one (VB-1) band is almost immune to the scattering created by the B dopants and does not create any QW states at well-defined energies. This different behavior stems from the different symmetry and spatial distribution of both bands. The overall agreement with the scanning tunneling spectroscopy is remarkable.

This work was supported by the FP7 FET-ICT project PAMS (contract No. 610446), MINECO coordinated project MAT2013-46593-C6, Basque Gov. Dep. de Educación and UPV/EHU (Grant No. IT-756-13), JSPS (Grant No.15K21765) and by Swiss NSF and SNI.