This week I am presenting a Colloquium at the Institute of Physics (IFGW) at UNICAMP, the top ranking research university in Latin America. It is a great honour for me and I thank my host, Prof. Alexandre F. Fonseca, for this kind invitation. During the week I will also discuss new projects with Alexandre and his group.

The presentation is entitled “Exploring phonon thermal transport in 2D materials with molecular dynamics simulations”. Since its aimed at a broad audience of graduate students and faculty, it begins with a general introduction to nanotechnology, moving on to the relationship between thermal transport and dimensionality, molecular dynamics simulations and finally to our results. I will detail our quest to improve thermal conductivity calculations for graphene from 2013 to 2017, and conclude with some recent results by Ph.D. student Isaac Felix.

We just got news I have been elected Affiliated Member of the Brazilian Academy of Sciences (ABC). This is a 5-year membership for Brazilian scientists under 40 years of age, recognizing young researchers of notable talent. My term in the ABC will be from Jan. 01, 2019 to Dec. 31, 2023. This is certainly a great honor, for which I am very grateful.

My profile can be found here.

The Brazilian Academy of Sciences was founded in 1916. It is a non profit, non governmental, independent honorific scientific society. It acts as consultant for the federal government performing technical studies and studies on scientific policies. It focuses in the scientific development of the Country, the interaction among Brazilian scientists and their interaction with researchers from other nations.

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.

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

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.

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.

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