arXiv subjects

Luiz A. Ribeiro Junior

Publications and source records attributed to Luiz A. Ribeiro Junior.

24 records · Page 2Linked to original sources

arXiv2022

A DFT Study of the Electronic, Optical, and Mechanical Properties of a Recently Synthesized Monolayer Fullerene Network

Closely packed quasi-hexagonal and quasi-tetragonal crystalline phase of C$_{60}$ molecules (named qHPC$_{60}$) was recently synthesized. Here, we used DFT simulations to investigate the electronic, optical, and mechanical properties of qHPC$_{60}$ monolayers. qHPC$_{60}$ has a moderate direct electronic bandgap, with anisotropic mechanical properties. Their elastic modulus ranges between 50 and 62 GPa. The results for optical properties suggest that qHPC$_{60}$ can act as UV collectors for photon energies until 5.5 eV since they present low reflectivity and refractive index greater than one. The estimated optical bandgap (1.5-1.6 eV) is in very good agreement with the experimental one (1.6 eV).

cond-mat.mtrl-sci↗

arXiv2021

On the Adsorption Mechanism of Caffeine on MAPbI3 Perovskite Surfaces: A Combined UMC--DFT Study

Recently, it was experimentally shown that the performance and thermal stability of the perovskite MAPbI$_3$ were improved upon the adsorption of a molecular layer of caffeine. In this work, we used a hybrid methodology that combines Uncoupled Monte Carlo (UMC) and Density Functional Theory (DFT) simulations to carry out a detailed and comprehensive study of the adsorption mechanism of a caffeine molecule on the surface of MAPbI$_3$. Our results showed that the adsorption distance and energy of a caffeine molecule on the MAPbI$_3$ surface are 2.0 Å and -0.3 eV, respectively. The caffeine/MAPbI$_3$ complex presents a direct bandgap of 2.38 eV with two flat intragap bands distanced 1.15 and 2.18 eV from the top of valence bands. Although the energy band levels are not significantly shifted by the presence of caffeine, the interaction MAPbI$_3$/perovskite is enough to affect the bands' dispersion, particularly the conduction bands.

cond-mat.mtrl-sci↗

arXiv2020

Tuning Magnetic Properties of Penta-Graphene Bilayers Through Doping with Boron and Oxygen

Penta-graphene (PG) is a carbon allotrope that has recently attracted the attention of the materials science community due to its interesting properties for renewable energy applications. Although unstable in its pure form, it has been shown that functionalization may stabilize its structure. A question that arises is whether its outstanding electronic properties could also be further improved using such a procedure. As PG bilayers present both sp$^2$ and sp$^3$ carbon planes, it consists of a flexible candidate for functionalization tuning of electromagnetic properties. In this work, we perform density functional theory simulations to investigate how the electronic and structural properties of PG bilayers can be tuned as a result of substitution doping. Specifically, we observed the emergence of different magnetic properties when boron was used as dopant species. On the other hand, in the case of doping with oxygen, the rupture of bonds in the sp$^2$ planes does not induce a magnetic moment in the material.

cond-mat.mtrl-sci↗

arXiv2020

Predicting the Energetic Stabilization of Janus-MoSSe/AlN Heterostructures: A DFT Study

The packing mechanisms between Janus-MoSSe and Aluminum-Nitride (AlN) sheets were systematically investigated by using Density Function Theory calculations. Results show that the stabilization (packing) energies vary from -35.5 up to -17.5 meV depending on the chemical species involved in the interface. The packing energies were obtained using the improved Lennard-Jones (ILJ) potential. The SeMoS/AlN heterostructures, when the MoS face is interacting with the AlN sheet, presented the lowest packing energies due to the sulfur's higher degree of reactivity. Importantly, the calculated bandgap values ranged within the interval 1.61-1.87 eV, which can be interesting for photovoltaic applications.

cond-mat.mtrl-sci↗

arXiv2020

Intrinsic Properties of Bipolarons in Armchair Graphene Nanoribbons

We performed an investigation concerning bipolaron dynamics in armchair graphene nanoribbons (AGNRs) under the influence of different electric field and electron-phonon coupling regimes. By studying the response to the electric excitation, we were able to determine the effective mass and terminal velocity of this quasiparticle in AGNRs. Remarkably, bipolarons in narrower AGNRs move as fast as the ones in conjugated polymers. Our findings pave the way to enhance the understanding of the behavior of charge carriers in graphene nanoribbons.

cond-mat.mtrl-sci↗

arXiv2020

On the Mechanical and Thermal Stability of Free-standing Monolayer Amorphous Carbon

Recently (C.-T. Toh et al., Nature 577, 199 (2020)), the first synthesis of free-standing monolayer amorphous carbon (MAC) was achieved. MAC is a pure carbon structure composed of five, six, seven and eight atom rings randomly distributed. MAC proved to be surprisingly stable and highly fracture resistant. Its electronic properties are similar to boron nitride. In this work, we have investigated the mechanical properties and thermal stability of MAC models using fully-atomistic reactive molecular dynamics simulations. For comparison purposes, the results are contrasted against pristine graphene (PG) models of similar dimensions. Our results show that MAC and PG exhibit distinct mechanical behavior and fracture dynamics patterns. While PG after a critical strain threshold goes directly from elastic to brittle regimes, MAC shows different elastic stages between these two regimes. Remarkably, MAC is thermally stable up to 3600 K, which is close to the PG melting point. These exceptional physical properties make MAC-based materials promising candidates for new technologies, such as flexible electronics.

cond-mat.mtrl-sci↗