New publication in RSC Advances – BCN hybrid graphenylene: stability and electronic properties

Our fourth publication of 2018 “BCN hybrid graphenylene: stability and electronic properties”  has just been published in RSC Advances, a publication of the Royal Society of Chemistry.

With the ever growing interest in 2D materials, we decided to investigate atomic monolayers of B, C, and N atoms arranged in the pattern carbon allotrope graphenylene. We combined density functional theory (DFT) calculations and molecular dynamics (MD) simulations to study the structural stability and electronic properties of  twenty structures with varied atomic arrangements and stoichiometries, which we call B_xC_yN_z hybrid graphenylenes. We calculated the formation energy for each arrangement, and found a  decrease as the number of B–C and N–C bonds decreases. We also found that the structure with minimum energy has stoichiometry B2CN and an atomic arrangement with BN and C stripes connected along the zigzag direction. All investigated structures were found to be semiconductors, with band gaps ranging from 0.14 to 1.65 eV. Finally, due to the presence of pores of varied sizes and shapes, we believe that these structures might be suited for molecular sieve applications.

This work is a collaboration with postdocs Aliliane Freitas and Raphael M. Tromer, and  colleagues Leonardo D. Machado, Claudionor G. Bezerra and Sergio Azevedo. Computational support was provided by our local supercomputing center NPAD.

Workshop Transport Phenomena and Non-Equilibrium Processes – Buenos Aires

I have been invited to give a presentation on thermal transport in nanostructures at the Workshop Transport Phenomena and Non-Equilibrium Processes, which takes place at Universidad Nacional de General Sarmiento in Buenos Aires, on 23 and 24 May.

The workshop is aimed at scientists and engineers from academic and industrial backgrounds. The main goal of the organizers is to exchange scientific ideas and prospect future collaborations. The event encourages the participation of  students and professionals from Physics, Engineering, Chemistry and related areas promoting an interactive environment for discussions.

Thanks to Prof. Florencia Carusela and Prof. Alejandro Monastra for organizing this great event, and also for their generous invitation.

TNG @ Autumn Meeting 2018 of the Brazilian Physical Society

The Autumn Meeting of the Brazilian Physical Society (previously the Brazilian Condensed Matter Physics Meeting) is the largest Physics meeting in Brazil, gathering  nearly 1,000 researchers from Brazil and abroad. In 2018, the event takes place in Foz do Iguaçu, Paraná, from 6 to 11 of May.

The Transport in Nanostructures Group will be represented by doctoral student Isaac M. Felix, presenting some of our latest results on thermal transport. Isaac is the only graduate student from UFRN delivering an oral presentation this year. Congrats to him!

07/05/2018 – Oral Sessions (8:30-10:00) – Room 3
ELECTRICAL & THERMAL TRANSPORT OF 2D MATERIALS
09:30 THERMAL CONDUCTIVITY OF GRAPHENE-hBN SUPERLATTICE RIBBONS
Isaac de Macêdo Félix, Luiz Felipe Cavalcanti Pereira

New publication in Scientific Reports – Thermal conductivity of graphene-hBN superlattice ribbons

Our third paper of 2018 “Thermal conductivity of graphene-hBN superlattice ribbons”  has just been published in Scientific Reports, a publication of the Nature Publishing Group.

In this work we investigate coherent (wave-like) and incoherent (particle-like) phonon thermal transport in superlattices graphene and hexagonal boron nitride, which have been produced recently with sharp edges and controlled domain sizes. We employ non-equilibrium molecular dynamics simulations to investigate the thermal conductivity of superlattice nanoribbons with equal-sized domains of graphene and BN. We analyze the dependence of the conductivity with the domain sizes and with the total length of the ribbons, and determine a minimum thermal conductivity of 89 W m−1K−1 for ribbons with a superlattice period of 3.43 nm. The effective phonon mean free path is also determined and shows a minimum value of 32 nm for the same superlattice period. Our results reveal a crossover from coherent to incoherent phonon transport at room temperature as the superlattice period becomes comparable to the phonon coherence length. Analyzing phonon populations relative to the smallest superlattice period, we attribute the minimum thermal conductivity to a reduction in the population of flexural phonons when the superlattice period equals 3.43 nm. The ability to manipulate thermal conductivity using superlattice-based two-dimensional materials, such as graphene-hBN nanoribbons, opens up opportunities for application in future nanostructured thermoelectric devices.

We are particularly proud of this work for two reasons. First, because it is a product of Isaac’s Master’s thesis, my first graduate student supervision ever. Second, because it has been completely developed and executed at UFRN, including the computational support provided by our supercomputing center NPAD. We expect to publish further developments of this work in 2018.

The open access publication is available here.

Coverage by UFRN news.

Paper accepted in Nanoscale – Borophene hydride: a stiff 2D material with high thermal conductivity and attractive optical and electronic properties

Our second paper of 2018 “Borophene hydride: a stiff 2D material with high thermal conductivity and attractive optical and electronic properties”  has just been accepted for publication in Nanoscale, published by the Royal Society of Chemistry.

In this work we investigate two-dimensional structures of hydrogenated borophene, called borophene hydride, which have been produced in recent experiments. We conducted extensive first-principles calculations to explore mechanical, electronic, optical and heat conduction properties of this novel material. The mechanical response of borophene hydride was found to be anisotropic with an elastic modulus of 131 N/m and a tensile strength of 19.9 N/m along the armchair direction. We also show that by applying mechanical loading the electronic character of borophene hydride can be altered from metallic to direct band-gap semiconductor, very appealing for application in nanoelectronics. The absorption edge of the imaginary part of the dielectric function is predicted to be in the visible range for parallel polarized light. Finally, we estimate room temperature thermal conductivities of 335 W/m-K and 293 W/m-K along zigzag and armchair directions, respectively. Our study confirms that borophene hydride presents an outstanding combination of mechanical, electronic, optical and thermal conduction properties, promising for the design of novel nanodevices.

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

The accepted paper is available here.

Bachelor’s thesis defense: Fabrizio Giovanni Oliviero

Undergraduate student Fabrizio Giovanni Oliviero will present his Bachelor’s thesis today (01.12.2017) at 10:50 am, in the seminar room #1 of the Physics Department (DFTE).

The thesis, entitled “Electronic structure of carbon nanotubes”, employed analytical and numerical approaches to investigate the electronic structure of nanotubes within the tight-binding approximation. The recursive Green’s function method was implemented to obtain the electronic density of states, reproducing results from the 1990’s.

Everybody is welcome to the public defense.

UPDATE: Fabrizio’s thesis was approved by the examining committee. He will now pursue a Master’s degree under the supervision of Prof. Rodrigo G. Pereira at UFRN. Congratulations!

Prof. Rodrigo Pereira, Fabrizio, Prof. Dory Helio, Prof. Luiz Felipe Pereira

Encontro Potiguar de Física 2017

The event “Encontro Potiguar de Física 2017” will take place on 05 and 06 of December, in the city of Caicó. This is a regional meeting  aiming to gather physicist working in Rio Grande do Norte and neighboring states, organized in collaboration with the Brazilian Physical Society.

I am on the organizing committee for this years edition, with my colleagues from UFRN, IFRN and UERN. We expect around 100 participants during this two-day event.

 

 

Although I am not presenting any works this year, our group will be represented by Dr. R. M. Tromer and Mr. I. M. Felix.

05/12/2017 – Comunicações Orais (16:00-18:00) – Física Estatística e Computacional / Física da Matéria Condensada e de Materiais / Óptica e Fotônica
16:00-16:30 A simple approach to obtain the relaxation time via Boltzmann transport theory
Raphael M. Tromer e Luiz Felipe C. Pereira
16:30 – 16:45 Controle da condutividade térmica em nanofitas de grafeno-hBN
Isaac de Macêdo Félix e Luiz Felipe C. Pereira

06/12/2017 – Comunicações Orais (15:00-17:00) – Física Estatística e Computacional / Física da Matéria Condensada e de Materiais / Óptica e Fotônica
15:30-15:45 Transporte de fônons em super-redes quase-periódicas de grafeno-hBN
Isaac de Macêdo Félix e Luiz Felipe C. Pereira

New paper accepted in Physica E – Tuning the Fano factor of graphene via Fermi velocity modulation

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.

In this work we investigate the influence of a Fermi velocity modulation on the Fano factor of periodic and quasi-periodic graphene superlattices. We use the transfer matrix method to solve the Dirac-like equation for graphene where the electrostatic potential, energy gap and Fermi velocity are piecewise constant functions of the position. We found that in the presence of an energy gap, it is possible to tune the energy of the Fano factor peak and consequently the location of the Dirac point, by a modulations in the Fermi velocity. Hence, the peak of the Fano factor can be used to identify the Dirac point in experiments. We show that for higher values of the Fermi velocity the Fano factor goes below 1/3 in the Dirac point. Furthermore, we show that in periodic superlattices the location of Fano factor peaks is symmetry when the Fermi velocity of the regions is swapped, however by introducing quasi-periodicity this  symmetry is lost. The Fano factor usually holds a universal value for a specific transport regime, therefore the possibility of controlling it in graphene is a notable result.

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.

New group member: Dr. Ana Claudia Kipper

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!

New manuscript accepted in Nano Letters – Bimodal grain-size scaling of thermal transport in polycrystalline graphene from large-scale molecular dynamics simulations

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.