Scientific Reports Top 100 in Physics 2018

Scientific Reports, an online, multidisciplinary, open access journal from the publishers of Nature (Springer Nature Publishing) has released a list of their most highly accessed physics articles in 2018 (#SREPTop100). The list is based on nature.com web analytics, covering accesses from January to December 2018. According the Scientific Reports, the list features authors from around the World, and the papers highlight valuable research within physics from an international community.

Our paper “Thermal conductivity of graphene-hBN superlattice ribbons” is one of the Top 25 most accessed papers. Being more precise, it received 1836 article views in 2018, making  it the 11th most accessed paper out of more than 1133 papers published by Scientific Reports in 2018 including all areas of physics.

We are particularly proud of this work for two main reasons. First, because it is a product of Isaac M. Felix 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. Isaac is currently on the final year of his Doctoral studies.

Coverage by UFRN news and Blog do BG.

New paper in Carbon – Mechanical, optical and thermal transport properties of graphene-like BC3 and BC6N

Our third publication of 2019 “Outstanding strength, optical characteristics and thermal conductivity of graphene-like BC3 and BC6N semiconductors” has just been accepted for publication in Carbon.

Carbon-based 2D materials with honeycomb lattices, such as graphene, polyaniline carbon-nitride, and boron-carbide exhibit exceptional physical properties. Here, we propose two novel graphene-like materials with BC6N stoichiometry. We employ first-principles calculations to explore mechanical, optical and thermal transport characteristics of graphene-like BC3 and BC6N monolayers. The absence of imaginary phonon frequencies confirm the dynamical stability of BC3 and BC6N monolayers. First principles results also reveal that BC3 and BC6N present high elastic moduli and tensile strengths. Electronic structure calculations show that BC3 and BC6N monolayers are indirect and direct bandgap semiconductors, respectively. An analysis of their optical absorption spectra reveals absorption peaks for in-plane polarization in the visible range. Finally, ab-initio based anharmonic lattice dynamics calculations predict room temperature lattice thermal conductivities of 410 and 1710  W/-K, respectively. Notably, the thermal conductivity of BC6N is one of the highest among 2D materials. Our results indicate that those new BC6N monolayers are promising candidates for the design of novel nanodevices.

This work is our most recent collaboration with Dr. Bohayra Mortazavi and Prof. Timon Rabczuk at Bauhaus-Universität Weimar.

Physics education paper accepted in Revista Brasileira de Ensino de Física

My first ever publication in a physics education journal, “Total entropy variation for an object in contact with heat reservoirs: the path to reversibility” has just been accepted for publication in Revista Brasileira de Ensino de Física, published by the Brazilian Physical Society.

In this paper we explore the second law of thermodynamics, which is one of the least understood fundamental physical laws among science and engineering students, possibly due to its subtleness and alternative statements. We consider the entropy variation of an isolated system composed of an object and one or more heat reservoirs, as the absolute temperature of the object varies due to heat exchange with the reservoirs, one at a time. We obtain a general expression for the total entropy variation, ∆S, in terms of the object’s heat capacity and the number of reservoirs, N. We employ a simple numerical routine to show that ∆S decreases as N increases, approaching zero as N becomes very large. Since the temperature difference between subsequent reservoirs becomes infinitesimal as N increases, we analytically show that ∆S vanishes, in accordance with the second law of thermodynamics. In the manuscript we also propose an undergraduate exam problem based on this demonstration.

The idea for this work came to me when I was preparing a problem set for the undergraduate Statistical Physics course, which I taught at UFRN in 2017 and 2018. The course was based on “Fundamentals of Statistical and Thermal Physics” by F. Reif, which contains a similar problem in its Chapter 4. The analytical solution was presented by one of the students in the class, Lucas R.D. Freitas, who co-authored the manuscript with me.

Colloquium at UNICAMP

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.

Paper accepted in Physical Review E – Dirac wave transmission in Lévy disordered systems

Our first paper of 2019 “Dirac wave transmission in Lévy disordered systems” has just been accepted for publication in Physical Review E, an American Physical Society journal.

In this paper we investigate the propagation of electronic waves described by the Dirac equation subject to a certain disorder distribution. The disorder takes the form of potential barriers following an unusual statistical distribution, know as the Lévy distribution. Our numerical calculations reveal a phase transition from anomalous to standard to anomalous localization as the incidence energy increases. In contrast, electronic waves described by the Schrödinger equation do not present such transition. We obtain the phase diagram delimiting anomalous and standard localization regimes, and argue that these transitions can also be characterized by the dispersion of the transmission. We attribute the transition to an abrupt reduction in transmittance when the incidence angle is higher than a critical value, which induces a decrease in transmission fluctuations.

This work is a collaboration with Jonas R. F. Lima and Anderson L. R. Barbosa, both at Universidade Federal Rural de Pernambuco. A.L.R. Barbosa was also my graduate school colleague at UFPE back in 2003-2005. Networking does pay off.

Brazilian Academy of Sciences

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.

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.