Our latest work “Tuning the Fano factor of graphene via Fermi velocity modulation” has just been accepted for publication in Physica E: Low-dimensional systems and nanostructures.

The manuscript is a product of our ongoing collaboration with Prof. Jonas R. F. Lima and Prof. Anderson L. R. Barbosa at Universidade Federal Rural de Pernambuco and my departmental colleague Prof. Claudionor G. Bezerra.

The accepted paper is available here. Free access link until December 28, 2017. A free preprint version is available here.

This week we welcome a new member of the Transport in Nanostructures Group: Dr. Ana Claudia Kipper will work with us a postdoctoral associate, telecommuting from Recife. Dr. Kipper completed her Doctorate at Universidade Federal de Santa Maria, where she investigated thermal transport in carbon nanostructures via molecular dynamics simulations. Here, she will continue on that line of work, investigating heat transport in nanostructured superlattices. Welcome, Ana Claudia!

Our sixth publication of 2017 “Bimodal grain-size scaling of thermal transport in polycrystalline graphene from large-scale molecular dynamics simulations” has just been accepted in Nano Letters.

In this work we investigate the effect of grain boundaries in the thermal conductivity of graphene, which are inherent defects in wafer-scale samples prepared by chemical vapor deposition. They can strongly influence the mechanical properties and electronic and heat transport in graphene. Here, we employ extensive molecular dynamics simulations to study thermal transport in large suspended polycrystalline graphene samples. Samples of different controlled grain sizes are prepared by a recently developed efficient multiscale approach based on the phase field crystal model. In contrast to previous works, our results show that the scaling of the thermal conductivity with the grain size shows a typical bimodal behaviour with two effective Kapitza lengths. The scaling is dominated by the out-of-plane (flexural) phonons with a Kapitza length one order of magnitude larger than that of the in-plane phonons. We also show that in order to get quantitative agreement with the most recent experiments, quantum corrections need to be applied to both the Kapitza conductance of grain boundaries and the thermal conductivity of pristine graphene and the corresponding Kapitza lengths must be renormalized accordingly.

The manuscript is a product of our ongoing collaboration with Dr. Zheyong Fan, Dr. Ari Harju and Prof. Tapio Ala-Nissila at Aalto University, as well as Prof. Davide Donadio at UC Davis. It is also related to our PRB papers in 2015 and 2017.

The accepted manuscript is available here. An open-access preprint version is available here.

Coverage by UFRN news.

Our fifth paper of 2017 “Light propagation in quasiperiodic dielectric multilayers separated by graphene” has just been accepted for publication in Physical Review B. This is officially our most productive year so far.

The manuscript is my first work in graphene photonics, and is a product of a collaboration with departmental colleague Prof. Claudionor Bezerra and his former postdoc Dr. Carlos Humberto Costa, now a faculty member at the Federal University of Ceará.

The accepted manuscript is available here. A free-access preprint version is available here.

Today we kick-off the ninth edition of the Brazilian Meeting on Simulational Physics. This year we celebrate 20 years of this event, which started small and keeps growing in every edition. It has now become a traditional event in the Brazilian physics community. Although there is “Brazilian” in the title, this year we welcome more than 40 participants from a dozen different countries.

We will have two tutorial sections with 3 x 50 minute lectures, presented by David P. Landau, Ying-Wai Li and Werner Krauth. We will also have 25 speakers among invited and contributed, presenting 50 min talks each. All the talks and lectures will be available on the IIP youtube channel.

We hope that everybody enjoys the meeting as much as we enjoyed organizing it.

Here is the group photo of the meeting.

Our second graduate student, Mr. Louis Gustavo da Costa Sobral e Sá, will present his Master’s thesis on Monday (24.07.2017) at 10:00 am, in the auditorium of the Physics Department (DFTE).

The thesis, entitled “Thermal and mechanical properties of  NHG under strain”, employed non-equilibrium molecular dynamics simulations to calculate the thermal conductivity and elastic moduli of nitrogenated holey graphene.

Everybody is welcome to the public defense.

UPDATE: Louis Gustavo’s thesis was approved by the examining committee. We wish him the best of luck in his future endeavors. Congratulations!

Our fourth paper of 2017 “ Electronic, optical and thermal properties of highly stretchable 2D carbon Ene-yne graphyne” has just been accepted for publication in Carbon.

A new carbon-based two-dimensional (2D) material “carbon Ene-yne” (CEY), was successfully synthesized recently. In this work, we examine electronic, optical and thermal properties of this novel material. We studied the stretchability of CEY via density functional theory (DFT) calculations. Using the PBE and HSE06 functionals, as well as the G0W0 method and the Bethe-Salpeter equation, we systematically explored electronic and optical properties of 2D CEY. We investigated the change of band-gap and optical properties under uniaxial and biaxial strain. Ab-initio molecular dynamics simulations confirm that CEY is stable at temperatures as high as 1500 K. Using non-equilibrium molecular dynamics simulations, the lattice thermal conductivity of CEY was predicted to be anisotropic and three orders of magnitude smaller than that of graphene. We found that in the visible range, the optical conductivity under high strain levels is larger than that of graphene. This enhancement in optical conductivity may allow CEY to be used in photovoltaic cells. Moreover, CEY shows anisotropic optical responses for x- and y- polarized light, which may be suitable as an optical linear polarizer. We hope that the comprehensive insight provided by the present investigation should serve as a guide for possible applications of CEY in nanodevices.

The manuscript is another product of our ongoing collaboration with Dr. Bohayra Mortazavi and Prof. Timon Rabczuk at Bauhaus-Universität Weimar.

The paper is available here. Free access link until October 26, 2017. A preprint version is available here.

Our third paper of 2017 “Anomalous strain effect on the thermal conductivity of borophene: a reactive molecular dynamics study” has just been accepted for publication in Physica E: Low-dimensional systems and nanostructures.

Borophene, an atomically thin, corrugated, crystalline two-dimensional boron sheet, is one of the latest additions to the 2D materials family. In this work we investigate mechanical properties and lattice thermal conductivity of borophene using reactive molecular dynamics simulations. We found an anisotropy in 2D elastic moduli along perpendicular directions, dubbed zigzag and armchair directions, in analogy with the direction in graphene. We attribute the anisotropy to the buckling of the borophene structure along the zigzag direction. We performed non-equilibrium molecular dynamics simulations to calculate the lattice thermal conductivity, and found an anisotropy along the in-plane directions, also in accordance with our estimate for the effective phonon mean free paths.  In this case, the anisotropy is attributed to differences in the density of states of low-frequency phonons, with lower group velocities and possibly shorten phonon lifetimes along the zigzag direction. Finally, we found that when borophene is strained along the armchair direction there is a significant increase in thermal conductivity along that direction. Meanwhile, when the sample is strained along the zigzag direction there is a much smaller increase in thermal conductivity along that direction. Our predictions are in agreement with recent first principles results, at a fraction of the computational cost.

The manuscript is a product of our ongoing collaboration with Dr. Bohayra Mortazavi and Prof. Timon Rabczuk at Bauhaus-Universität Weimar. The thermal transport simulations were performed at the High Performance Computing Center (NPAD) at UFRN.

The paper is available here.  Free access here (until 11/Aug/2017). A preprint version is available here.

May has been an exciting month for the transport in nanostructures  group. Doctorate student Isaac de Macedo Felix has passed the written qualifying exam on his first try. Congratulations to him! We also welcome a new group member: José Roberto da Silva will pursue his doctorate under my supervision.