Transport & Nanostructures Group

Our fourth publication of 2020 “Electronic, optical and thermoelectric properties of boron-doped nitrogenated holey graphene”  has just been published in Physical Chemistry Chemical Physics.

Following-up form our previous publications on the physical properties of nitrogenated holey graphene (NHG), we now employed first principles calculations to investigate the electronic, optical, and thermoelectric properties of ten boron-doped NHG monolayers. We find that most of the proposed structures remain stable during ab initio molecular dynamics simulations, in spite of their increased formation energies. Density functional theory calculations employing a hybrid functional predict band gaps ranging from 0.73 eV to 2.30 eV. In general, we find that boron doping shifts optical absorption towards the visible spectrum, and also reduces light reflection in this region. On the other hand, the magnitude of optical absorption coefficients are reduced. Regarding the thermoelectric properties, we predict that boron doping can enhance the figure of merit ZT of NHG by up to 55%. Our results indicate that boron-doped NHG monolayers may find application in solar cells and thermoelectric devices.

This work results from collaboration with colleagues at Universidade Federal do Rio Grande do Norte, Universidade Federal da Paraíba, and Leibniz Universität Hannover. Most calculations were carried out within our research group at UFRN, and we are grateful for the computational support provided by the local supercomputing center NPAD.

Our third publication of 2020 “Suppression of coherent thermal transport in quasiperiodic graphene-hBN superlattice ribbons”  has just been published in Carbon.

Nanostructured superlattices are promising materials for novel electronic devices due to their adjustable physical properties. Periodic superlattices facilitate coherent phonon thermal transport due to constructive wave interference at the boundaries between the materials. However, it is possible to induce a crossover from coherent to incoherent transport regimes by adjusting the superlattice period. In 2018 we observed such crossover in periodic graphene-boron nitride nanoribbons as the length of individual domains was increased. In general, transport properties are dominated by translational symmetry and the presence of unconventional symmetries leads to unusual transport characteristics. In this work we perform non-equilibrium molecular dynamics simulations to investigate phonon heat transport in graphene-hBN superlattices following the Fibonacci quasiperiodic sequence, which lie between periodic and disordered structures. We show that the quasiperiodicity can suppress coherent phonon thermal transport in these superlattices. This behavior is related to the increasing number of interfaces per unit cell as the Fibonacci generation increases, hindering phonon coherence along the superlattice. The suppression of coherent thermal transport in graphene-hBN superlattices enables a higher degree of control on heat conduction at the nanoscale, and shows potential for application in the design of novel thermal management devices.

We are rather proud of this work. It is an extension of Isaac’s Master’s thesis and also part of his PhD dissertation. It was completely carried out within our research group, and we are grateful for the computational support provided by the supercomputing center at UFRN (NPAD).