arXiv subjects

Pedro Alves da Silva Autreto

Publications and source records attributed to Pedro Alves da Silva Autreto.

17 recordsLinked to original sources

arXiv2026

In-Situ TEM Observation of Solid-State Phase Evolution in High-Entropy Alloy Nanoparticles

The emergence of new materials has gone beyond conventional design principles. Among them are high entropy alloys (HEAs), in which multiple metallic elements coexist within a single unit cell. In this case, each atomic position in a solid material has a different chemical environment, leading to configurational entropy as high as that in the fully random or melted state, which has been frozen to a solid solution. However, the behaviour of such alloy systems at pre-melting temperatures is largely unknown, where atoms gain sufficient mobility and time to rearrange, leading to an enthalpic rather than an entropic interplay. This study demonstrated the phase transformation of HEA nanoclusters (CoCrFeMnNi) under high-resolution transmission electron microscopy (HRTEM) at different temperatures, including room temperature (RT), 550 °C, and 850 °C. The clustered nanoparticles coarsen into larger clusters, accompanied by compositional heterogeneity due to surface and lattice diffusion. This experimental finding of atomic mobility was further corroborated using molecular dynamics, which provides a detailed mechanistic description.

cond-mat.mtrl-sci↗

arXiv2026

Controlling HER activity and stability of $γ$- and 6,6,12-Graphyne through engineered B-N doping: DFT and Reactive MD simulations

Graphynes offer a chemically heterogeneous $sp/sp^{2}$ carbon framework with distinct electronic regimes and site-selective reactivity. Here, Density Functional Theory and Reactive Molecular Dynamics Simulations are combined to evaluate pristine, B-doped, N-doped, and B-N co-doped $γ$-graphyne and 6,6,12-graphyne (meta/ortho/para). $γ$-graphyne is a semiconductor, while 6,6,12-graphyne exhibits an anisotropic Dirac-like semi-metallic dispersion. B/N substitution reconstructs near-$E_F$ states via dopant $π$ hybridization, and B-N pairing stabilizes defects through donor-acceptor compensation, with the ortho substitutions being the most favorable. Hydrogen adsorption remains weak on pristine lattices but becomes locally optimized upon doping, with near thermo-neutral $ΔG_{\mathrm{ads}}$ 'hot spots' predominantly on $sp$-proximate carbon sites adjacent to the dopants. Reactive MD at 300 K further reveals an activity stability trade-off: B-N ortho in $γ$-graphyne sustains controlled hydrogen uptake without catastrophic bond scission, whereas B-N meta/para degrade, and 6,6,12-graphyne is generally more susceptible to over-hydrogenation. These results identify the B-N geometry as a key design variable for graphyne-based HER catalysts, which require both a favorable $ΔG_{\mathrm{ads}}$ and finite-temperature hydrogenation stability.

cond-mat.mtrl-sci↗

arXiv2025

Pyrite Bismuth Telluride Heterojunction for Hybrid Electromagnetic to Thermoelectric Energy Harvesting

The rapid proliferation of wireless networks and connected devices has led to pervasive electromagnetic (EM) energy dissipation into the environment, an underutilized resource for energy harvesting. Here, we demonstrate a pyrite (FeS$_2$)-bismuth telluride (Bi$_2$Te$_3$) heterojunction that enables hybrid electromagnetic-to-thermoelectric energy conversion. Fabricated via a simple cold-press compaction of powders, the heterojunction forms a Schottky interface at FeS$_2$, facilitating efficient RF absorption and localized heating. This heat is harvested by Bi$_2$Te$_3$ through thermoelectric conversion. Under 35~MHz RF irradiation at 1~W input power, the device achieved a local temperature rise of 46~$^\circ$C and a thermal gradient of 5.5~K across the Bi$_2$Te$_3$, resulting in a peak power density of approximately 13~mW/cm$^2$. Molecular dynamics (MD) simulations and density functional theory (DFT) calculations further elucidate the heat transport behavior and interfacial thermoelectric performance. This work introduces a new class of heterostructures for RF-responsive energy harvesting, offering a scalable route toward self-powered IoT and wireless sensing systems.

cond-mat.mtrl-sci↗

arXiv2025

Enhancing catalyst activity of two-dimensional C$_4$N$_2$ through doping for the hydrogen evolution reaction

This study investigates the structural, electronic, and catalytic properties of pristine and doped C$_4$N$_2$ nanosheets as potential electrocatalysts for the hydrogen evolution reaction. The pristine C$_{36}$N$_{18}$ nanosheets exhibit limited HER activity, primarily due to high positive Gibbs free energies ($>$ 2.2 eV). To enhance catalytic performance, doping with B, Si, or P at the nitrogen site was explored. Among these systems, B-doped C$_{36}$N$_{17}$ nanosheets exhibit the most promising catalytic activity, with a Gibbs free energy close to zero ($\approx -0.2$ eV), indicating efficient hydrogen adsorption. Band structure, projected density of states, charge density, and Bader charge analyses reveal significant changes in the electronic environment due to doping. While stacking configurations (AA$'$A$''$ and ABC) have minimal effect on catalytic performance, doping -- particularly with B -- substantially alters the electronic structure, optimizing hydrogen adsorption and facilitating efficient HER. These findings suggest that B-doped C$_{36}$N$_{17}$ nanosheets could serve as efficient cocatalysts when combined with metallic materials, offering a promising approach to enhance catalytic efficiency in electrocatalytic and photocatalytic applications.

cond-mat.mtrl-sci↗

arXiv2024

TPDH-Graphene as a New Anodic Material for Lithium Ion Battery: DFT-Based Investigations

The potential of tetra-penta-deca-hexagonal graphene (TPDH-gr), a recently proposed 2D carbon allotrope as an anodic material in lithium ion batteries (LIB), was investigated through density functional theory (DFT) calculations. The results indicate that Li-atom adsorption is moderate (around 0.70 eV), allowing for easy desorption. Moreover, energy barrier, diffusion coefficient, and open circuit voltage (OCV) calculations show rapid Li atom diffusion on the TPDH-gr surface, stable intercalation of lithium atoms, and good performance during the charge and discharge cycles of the LIB. These findings, combined with the intrinsic metallic nature of TPDH-gr, indicate that this new 2D carbon allotrope is a promising candidate for use as an anodic LIB material.

cond-mat.mtrl-sci↗

arXiv2024

Exploring the Electronic and Mechanical Properties of TPDH-Nanotube: Insights from Ab initio and Classical Molecular Dynamics Simulations

Tetra-Penta-Deca-Hexa-graphene (TPDH) is a new 2D carbon allotrope with attractive electronic and mechanical properties. It is composed of tetragonal, pentagonal, and hexagonal carbon rings. When TPDH-graphene is sliced into quasi-one-dimensional (1D) structures like nanoribbons, it exhibits a range of behaviors, from semi-metallic to semiconducting. An alternative approach to achieving these desirable electronic (electronic confinement and/or non-zero electronic band gap) properties is the creation of nanotubes (TPDH-NT). In the present work, we carried out a comprehensive study of TPDH-NTs combining Density Functional Theory (DFT) and Classical Reactive Molecular Dynamics (MD). Our results show structural stability and a chiral dependence on mechanical properties. Similarly to standard carbon nanotubes, TPDH-NT can be metallic or semiconductor. MD results show Young's modulus values exceeding $700$ GPa, except for nanotubes with very small radii. However, certain chiral TPDH-NTs (n,m) display values both below and above $700$ GPa, particularly for those with small radii. The analyses of the angle and C-C bond length distributions underscore the significance of the tetragonal and pentagonal rings in determining the mechanical response of TPDH-NTs (n,0) and (0,n), respectively.

cond-mat.mtrl-sci↗

arXiv2024

Selective Hydrogenation Promotes Anisotropic Thermoelectric Properties of TPDH-Graphene

We have combined DFT calculations with the Boltzmann semiclassical transport theory to investigate the effect of selective hydrogenation on the thermoelectric properties of tetra-penta-deca-hexagonal graphene (TPDH-gr), a recently proposed new 2D carbon allotrope. Our results show that the Seebeck coefficient is enhanced after hydrogenation. The conductivity along the x direction is increased almost eight times while being almost suppressed along the y direction. This behavior can be understood in terms of the electronic structure changes due to the appearance of a Dirac-like cone after the selective hydrogenation. Consistent with the literature, the electronic contribution to thermal conductivity displays the same qualitative behavior as the conductivity, as expected from the Wiedemann-Franz law. The increase in thermal conductivity with temperature limits the material's power factor. The significant increase in the Seebeck coefficient and conductivity increases also contribute to the thermal conductivity increase. These results show that hydrogenation is an effective method to improve the TPDH-gr thermoelectric properties, and this carbon allotrope can be an effective material for thermoelectric applications.

cond-mat.mtrl-sci↗

arXiv2023

Machine Learning-based Analysis of Electronic Properties as Predictors of Anticholinesterase Activity in Chalcone Derivatives

In this study, we investigated the correlation between the electronic properties of anticholinesterase compounds and their biological activity. While the methodology of such correlation is well-established and has been effectively utilized in previous studies, we employed a more sophisticated approach: machine learning. Initially, we focused on a set of $22$ molecules sharing a common chalcone skeleton and categorized them into two groups based on their IC50 indices: active and inactive. Utilizing the open-source software Orca, we conducted calculations to determine the geometries and electronic structures of these molecules. Over a hundred parameters were collected from these calculations, serving as the foundation for the features used in machine learning. These parameters included the Mulliken and Lowdin electronic populations of each atom within the skeleton, molecular orbital energies, and Mayer's free valences. Through our analysis, we developed numerous models and identified several successful candidates for effectively distinguishing between the two groups. Notably, the most informative descriptor for this separation relied solely on electronic populations and orbital energies. By understanding which computationally calculated properties are most relevant to specific biological activities, we can significantly enhance the efficiency of drug development processes, saving both time and resources.

physics.comp-ph↗

arXiv2020

Ballistic Properties of Highly Stretchable Graphene Kirigami Pyramid

Graphene kirigami (patterned cuts) can be an effective way to improve some of the graphene mechanical and electronic properties. In this work, we report the first study of the mechanical and ballistic behavior of single and multilayered graphene pyramid kirigami (GKP). We have carriedout fully atomistic reactive molecular dynamics simulations. GPK presents a unique kinetic energy absorption due to its topology that creates multi-steps dissipation mechanisms, which block crack propagation. Our results show that even having significantly less mass, GKP can outperform graphene structures with similar dimensions in terms of absorbing kinetic energy.

cond-mat.mtrl-sci↗

arXiv2018

Silver Hardening via Hypersonic Impacts

The search for new ultra strong materials has been a very active research area. With relation to metals, a successful way to improve their strength is by the creation of a gradient of nanograins (GNG) inside the material. Recently, R. Thevamaran et al. [Science v354, 312-316 (2016)] propose a single step method based on high velocity impact of silver nanocubes to produce high-quality GNG. This method consists of producing high impact collisions of silver cubes at hypersonic velocity (~400 m/s) against a rigid wall. Although they observed an improvement in the mechanical properties of the silver after the impact, the GNG creation and the strengthening mechanism at nanoscale remain unclear. In order to gain further insights about these mechanisms, we carried out fully atomistic molecular dynamics simulations (MD) to investigate the atomic conformations/rearrangements during and after high impact collisions of silver nanocubes at ultrasonic velocity. Our results indicate the co-existence of polycrystalline arrangements after the impact formed by core HCP domains surrounded by FCC ones, which could also contribute to explain the structural hardening.

physics.app-ph↗

arXiv2018

Improving Graphene-metal Contacts: Thermal Induced Polishing

Graphene is a very promising material for nanoelectronics applications due to its unique and remarkable electronic and thermal properties. However, when deposited on metallic electrodes the overall thermal conductivity is significantly decreased. This phenomenon has been attributed to the mismatch between the interfaces and contact thermal resistance. Experimentally, one way to improve the graphene/metal contact is thorough high-temperature annealing, but the detailed mechanisms behind these processes remain unclear. In order to address these questions, we carried out fully atomistic reactive molecular dynamics simulations using the ReaxFF force field to investigate the interactions between multi-layer graphene and metallic electrodes (nickel) under (thermal) annealing. Our results show that the annealing induces an upward-downward movement of the graphene layers, causing a pile-driver-like effect over the metallic surface. This graphene induced movements cause a planarization (thermal polishing-like effect) of the metallic surface, which results in the increase of the effective graphene/metal contact area. This can also explain the experimentally observed improvements of the thermal and electric conductivities.

cond-mat.mes-hall↗

arXiv2017

Hydrogenation Dynamics of Biphenylene Carbon (Graphenylene) Membranes

The advent of graphene created a revolution in materials science. Because of this there is a renewed interest in other carbon-based structures. Graphene is the ultimate (just one atom thick) membrane. It has been proposed that graphene can work as impermeable membrane to standard gases, such argon and helium. Graphene-like porous membranes, but presenting larger porosity and potential selectivity would have many technological applications. Biphenylene carbon (BPC), sometimes called graphenylene, is one of these structures. BPC is a porous two-dimensional (planar) allotrope carbon, with its pores resembling typical sieve cavities and/or some kind of zeolites. In this work, we have investigated the hydrogenation dynamics of BPC membranes under different conditions (hydrogenation plasma density, temperature, etc.). We have carried out an extensive study through fully atomistic molecular dynamics (MD) simulations using the reactive force field ReaxFF, as implemented in the well-known Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code. Our results show that the BPC hydrogenation processes exhibit very complex patterns and the formation of correlated domains (hydrogenated islands) observed in the case of graphene hydrogenation was also observed here. MD results also show that under hydrogenation BPC structure undergoes a change in its topology, the pores undergoing structural transformations and extensive hydrogenation can produce significant structural damages, with the formation of large defective areas and large structural holes, leading to structural collapse.

cond-mat.mes-hall↗

arXiv2016

Graphone (one-side hydrogenated graphene) formation on different substrates

In this work we present a fully atomistic reactive (ReaxFF force field) molecular dynamics study of the structural and dynamical aspects of the one-side hydrogenation of graphene membranes, leading to the formation of the so-called graphone structure. We have considered different substrates: graphene, few-layers graphene, graphite and platinum at different temperatures. Our results showed that the hydrogenation rates are very dependent on the substrate and thermal effects. Our results also showed that, similarly to graphane, large hydrogenated domains are unlikely to be formed. These hydrogenation processes occur through the formation of uncorrelated cluster domains.

cond-mat.mes-hall↗

arXiv2016

Carbon Nanoscrolls at High Impacts: A Molecular Dynamics Investigation

The behavior of nanostructures under high strain-rate conditions has been object of interest in recent years. For instance, recent experimental investigations showed that at high velocity impacts carbon nanotubes can unzip resulting into graphene nanoribbons. Carbon nanoscrolls (CNS) are among the structures whose high impact behavior has not yet been investigated. CNS are graphene membranes rolled up into papyrus-like structures. Their unique open-ended topology leads to properties not found in close-ended structures, such as nanotubes. Here we report a fully atomistic reactive molecular dynamics study on the behavior of CNS colliding at high velocities against solid targets. Our results show that the velocity and scroll axis orientation are key parameters to determine the resulting formed nanostructures after impact. The relative orientation of the scroll open ends and the substrate is also very important. We observed that for appropriate velocities and orientations, the nanoscrolls can experience large structural deformations and large-scale fractures. We have also observed unscrolling (scrolls going back to planar or quasi-planar graphene membranes), unzip resulting into nanoribbons, and significant reconstructions from breaking and/or formation of new chemical bonds. Another interesting result was that if the CNS impact the substrate with their open ends, for certain velocities, fused scroll walls were observed.

cond-mat.mtrl-sci↗

arXiv2016

One Side-Graphene Hydrogenation (Graphone): Substrate Effects

Recent studies on graphene hydrogenation processes showed that hydrogenation occurs via island growing domains, however how the substrate can affect the hydrogenation dynamics and/or pattern formation has not been yet properly investigated. In this work we have addressed these issues through fully atomistic reactive molecular dynamics simulations. We investigated the structural and dynamical aspects of the hydrogenation of graphene membranes (one-side hydrogenation, the so called graphone structure) on different substrates (graphene, few-layers graphene, graphite and platinum). Our results also show that the observed hydrogenation rates are very sensitive to the substrate type. For all investigated cases, the largest fraction of hydrogenated carbon atoms was for platinum substrates. Our results also show that a significant number of randomly distributed H clusters are formed during the early stages of the hydrogenation process, regardless of the type of substrate and temperature. These results suggest that, similarly to graphane formation, large perfect graphone-like domains are unlikely to be formed. These findings are especially important since experiments have showed that cluster formation influences the electronic transport properties in hydrogenated graphene.

cond-mat.mtrl-sci↗

arXiv2016

Graphene healing mechanisms: A theoretical investigation

Large holes in graphene membranes were recently shown to heal, either at room temperature during a low energy STEM experiment, or by annealing at high temperatures. However, the details of the healing mechanism remain unclear. We carried out fully atomistic reactive molecular dynamics simulations in order to address these mechanisms under different experimental conditions. Our results show that, if a carbon atom source is present, high temperatures can provide enough energy for the carbon atoms to overcome the potential energy barrier and to produce perfect reconstruction of the graphene hexagonal structure. At room temperature, this perfect healing is only possible if the heat effects of the electron beam from STEM experiment are explicitly taken into account. The reconstruction process of a perfect or near perfect graphene structure involves the formation of linear carbon chains, as well as rings containing 5, 6, 7 and 8 atoms with planar (Stone-Wales) and non-planar (lump like) structures. These results shed light on the healing mechanism of graphene when subjected to different experimental conditions. Additionally, the methodology presented here can be useful for investigating the tailoring and manipulations of other nano-structures.

cond-mat.mes-hall↗

arXiv2013

Species Fractionation in Atomic Chains from Mechanically Stretched Alloys

Bettini et al. [Nature Nanotech 1, 182 (2006)] reported the first experimental realization of linear atomic chains (LACs) composed of different atoms (Au and Ag). Different contents of Au and Ag were observed in the chains from what found in the bulk alloys, which rises the question of what is the wire composition if in equilibrium with a bulk alloy. In this work we address the thermodynamic driving force for species fractionation in LACs under tension, and we present density-functional theory results for Ag-Au chain alloys. A pronounced stabilization of wires with an alternating Ag-Au sequence is observed, which could be behind the experimentally observed Au enrichment in LACs from alloys of high Ag content.

cond-mat.mtrl-sci↗