arXiv subjects

Douglas S. Galvao

Publications and source records attributed to Douglas S. Galvao.

At least 19 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

High-Entropy Nitride Photocatalysts for Visible-Light Antibiotic Degradation: Structural Stability, In Situ Interfacial Visualization, and Molecular-Level Mechanistic Insights

High-entropy nitrides (HENs) have emerged as a promising class of advanced materials with tunable electronic structures, high stability, and abundant active sites. The incorporation of nitrogen enhances visible-light absorption, promotes efficient charge separation, and improves structural robustness, making these materials highly suitable for photocatalytic applications. In this study, (MnFeCoNiCu)N-based HEN nanoparticles (NPs) were synthesized as visible-light-assisted photocatalysts for the degradation of antibiotics, including sulfamethoxazole (SME) and tetracycline (TCL). The catalyst exhibited excellent performance, achieving 96% degradation of SME and 94% removal of TCL within 2 h of visible-light irradiation. The photocatalytic activity was systematically evaluated under varying operational parameters, including solution pH, catalyst dosage, pollutant concentration, and the presence of coexisting ions. Notably, the catalyst maintained high efficiency in real water matrices, demonstrating its practical applicability. The entropy-stabilized nitride framework exhibited negligible metal leaching, excellent thermal and structural stability as confirmed by temperature-dependent synchrotron angle-dispersive X-ray diffraction, and stable performance over multiple reuse cycles. Furthermore, in situ liquid-cell transmission electron microscopy provided real-time insight into catalyst-pollutant interactions, while complementary molecular simulations revealed the structural stability of the HEN NPs during molecular adsorption and the distinct interaction modes of the two antibiotics. Phytotoxicity tests using Vigna radiata confirmed the effective detoxification of treated solutions. Overall, this work establishes (MnFeCoNiCu)N HENs as efficient and durable visible-light-driven photocatalysts for the removal of antibiotics from complex aqueous environments.

cond-mat.mtrl-sci↗

arXiv2026

Hopping-Mediated Charge Transport in Graphene Beyond the Ballistic Regime

We present a trajectory-resolved framework for charge transport in graphene and related two-dimensional carbon systems beyond the ideal ballistic and fully coherent limits. Transport is described by kinetic Monte Carlo hopping on a predefined atomic lattice, allowing the combined treatment of disorder, thermal activation, and external fields. Current and effective transmittance are extracted directly from stochastic carrier trajectories, without phenomenological transport coefficients. We apply the method to graphene under bias voltage (0-0.10 V), temperature (300-900 K), magnetic field (0-10 T), in-plane strain (2-10%, uniaxial and biaxial), and vacancy concentration (0-10%). Pristine graphene shows an almost ohmic response, with currents of about 7-8 uA, effective transmittance near 0.98-1.00, and conductance of about (5.8-7.8) x 10^-5 S at 0.10 V, depending on direction. Vacancies strongly suppress transport, reducing transmittance to about 0.45-0.75 at 10% vacancy. Higher temperature accelerates hopping and partly restores transport, but cannot overcome severe connectivity loss. Magnetic fields further reduce transport, especially in disordered networks. The framework provides a unified computational scheme for realistic two-dimensional carbon materials and also yields diffusion coefficients and effective mobilities from carrier displacements and transit times.

cond-mat.mes-hall↗

arXiv2026

Endohedral Derivatives of the Recently Synthesized Two-Dimensional Fullerene Networks: Electronic and Optical Insights from First-Principles Calculations

The quasi-hexagonal phase of the two-dimensional fullerene network (qHPC$_{60}$), recently synthesized, has emerged as a stable carbon-based material with distinct structural and electronic features. In this work, we employed density functional theory (DFT) calculations to investigate the electronic and optical properties of its endohedral derivatives. The encapsulation of nitrogen, cerium, and strontium atoms inside fullerene cages was systematically analyzed at different concentrations. Our results show that encapsulation preserves the semiconducting backbone of pristine qHPC$_{60}$ while introducing localized electronic states that alter the bandgap and enable new transition channels. Nitrogen encapsulation produces intragap states with potential relevance for discrete optical emission, whereas cerium and strontium generate intraband states near the conduction edge. These modifications induce a red shift of the absorption onset into the visible spectrum, accompanied by enhanced refractive and absorptive responses. The robustness of the electronic structure under reduced concentrations indicates that the fully encapsulated limit adequately represents the system. Overall, the findings highlight impurity-endowed qHPC$_{60}$ as a promising platform for optoelectronic and light-harvesting applications.

cond-mat.mtrl-sci↗

arXiv2026

Stacking-Tunable Electronic Properties in Recently Synthesized Hydrogen-Substituted Graphdiyne

Recent progress in porous carbon materials has highlighted the importance of structural design in controlling emergent physicochemical properties. In this context, hydrogen-substituted graphdiyne (HsGDY), a three-dimensional framework derived from graphdiyne (GDY), has recently emerged as a promising architecture whose stacking-dependent behavior remains largely unexplored. Here, we present a comprehensive first-principles investigation of the structural, electronic, and optical properties of HsGDY across distinct stacking sequences. Our results identify the AA and ABC configurations as the most energetically favorable, with AA corresponding to the global minimum, consistent with recent experimental observations. Electronic-structure analysis reveals that HsGDY is an indirect semiconductor with an electronic band gap of 0.89 eV (optB88-vdW), primarily governed by interlayer coupling and van der Waals interactions. The optical response exhibits pronounced absorption features spanning the visible to ultraviolet regions, highlighting strong potential for optoelectronic applications. \textit{Ab initio} molecular dynamics (AIMD) simulations at 700 K confirm the thermal robustness of the framework, with negligible structural distortions. Collectively, these findings elucidate the stacking-dependent stability and semiconducting character of HsGDY, providing a solid theoretical foundation for its integration into next-generation nanoelectronic and energy-harvesting technologies.

cond-mat.mtrl-sci↗

arXiv2025

On the Electronic, Mechanical and Optical Properties of Superhard Cross-Linked Carbon Nanotubes (Tubulanes)

We have investigated the electronic, optical, and mechanical properties of six structures belonging to the Tubulanes-cross-linked carbon nanotube family. Our results highlight the remarkable anisotropic mechanical behavior of these materials, distinguishing them from isotropic structures, such as diamond. Notably, the 8-tetra-22 structure has a higher Young's modulus ($Y_M$) along the $z$-direction compared to diamond. Unlike diamonds, the mechanical properties of Tubulanes are direction-dependent, with significant variations in Young's Modulus (2.3 times). Additionally, the Poisson's ratio is highly anisotropic, with at least one direction exhibiting an approximately zero value. The inherent anisotropy of these materials enables tunable mechanical properties that depend on the direction of applied stress. Regarding their electronic properties, all Tubulane structures studied possess indirect electronic band gaps, dominated by $2p$ orbitals. The band dispersion is relatively high, with band gaps ranging from 0.46 eV to 2.74 eV, all of which are smaller than that of diamond. Notably, the 16-tetra-22 structure exhibits the smallest bandgap (0.46 eV), making it particularly interesting for electronic applications. Additionally, these structures exhibit porosity, which provides an advantage over denser materials, such as diamond. Considering the recent advances in the synthesis of 3D carbon-based materials, the synthesis of tubulane-like structures is within our present-day technological capabilities.

cond-mat.mtrl-sci↗

arXiv2025

Visible-Light Photocatalytic Degradation of Cresols using Sustainable 3D-Printed Bi4O5I2-Hematite Scaffold

In photocatalysis, the reusability limit of catalysts can contribute to secondary pollution, posing ecological risks. Addressing this, the present study explores the integration of additive manufacturing with photocatalysis by decorating Bi$_4$O$_5$I$_2$ onto a 3D-printed hematite scaffold (Bi$_4$O$_5$I$_2$@3DH) for the degradation of cresols. The 3D-printed hematite grid, fabricated via direct ink writing, exhibited excellent rheological behavior ($τγ= 24$ Pa), allowing precise shape retention. The sintered Bi$_4$O$_5$I$_2$ was subsequently immobilized via a facile dip-coating method. Under optimized conditions, the composite achieved 99.78\% degradation of 20 mg/L p-cresol within 240 min of irradiation. Notably, hematite served as a porous substrate and contributed to photocatalytic activity. Density functional theory simulations with Hubbard correction (DFT+U) indicated an interfacial charge transfer of approximately -0.9 electrons from hematite to Bi$_4$O$_5$I$_2$, confirming a S-scheme heterojunction between hematite and Bi$_4$O$_5$I$_2$ semiconductors, validating experimental observations. The composite demonstrated strong performance across varied water matrices and in the presence of other cresol isomers. It also retained 84.28\% degradation efficiency after 10 cycles, with negligible catalyst leaching. Furthermore, in vitro and in silico ecotoxicity analyses revealed reduced toxicity of the degradation products. The current work presents a novel and scalable strategy, advancing the use of earth-abundant hematite minerals in sustainable environmental remediation.

physics.chem-ph↗

arXiv2025

Chiral Phonons in Graphyne

Chiral phonons, quantized lattice vibrations with circular polarization and non-zero angular momentum, offer new perspectives for phononic and quantum device engineering. Graphyne could be a promising candidate due to its unique lattice geometry, valley-structured electronic bands, and thermal transport capabilities. However, chiral phonons in graphyne remain unexplored owing to the existence of inversion ($\mathscr{P}$) and time-reversal ($\mathscr{T}$) symmetries. Herein, we have demonstrated the existence of chiral phonons in graphynes, achieved by breaking combined $\mathscr{PT}$ symmetry through atomic-selective substitutional doping. We find that the B, N, dopants and ortho BN co-dopant in 6-6-12 and $γ$-graphynes induce localized structural deformations. These deformations lift phonon degeneracies away from $Γ$ point and give rise to circularly polarized vibrational modes. We further established a strong correlation between chiral phonon angular momentum and electron affinity of dopants. Electron-rich dopants increase local electron density which could enable chiral phonon modes to couple more effectively with electronic environment. This in turn increases phonon angular momentum, indicating potential role of electron-phonon interactions in angular momentum modulation of chiral phonons. Our prosposed approach provides a tunable route for controlling chiral phonon behavior, paving way for development of advanced phononic devices.

cond-mat.mes-hall↗

arXiv2025

All Photonic Isolator using Atomically Thin (2D) Bismuth Telluride (Bi2Te3)

This study demonstrates that two-dimensional (2D) Bi2Te3 exhibits strong light-matter interaction, enabling a broadband Kerr nonlinear optical response. This characteristic is advantageous for nonreciprocal light propagation in passive photonic isolators. Using Spatial Self-Phase Modulation (SSPM) spectroscopy, self-induced diffraction patterns in the far field were observed at excitation wavelengths of 650 nm, 532 nm, and 405 nm to calculate the nonlinear refractive index (n2) and the third-order nonlinear optical susceptibility (chi^(3)) of the synthesized 2D Bi2Te3. The results show that 2D Bi2Te3 possesses a significantly higher nonlinear refractive index than graphene. The laser-induced hole coherence effect is responsible for the large magnitude of the third-order nonlinear susceptibility. Surface engineering techniques were also employed to enhance the response speed of the photonic system. Complementary ab initio simulations were performed to gain further insight into the observed nonlinear behavior. Leveraging the strong Kerr nonlinearity of 2D Bi2Te3, a nonlinear photonic isolator that breaks time-reversal symmetry and enables unidirectional light propagation was demonstrated. This work establishes Bi2Te3 as a novel 2D material for nonlinear photonics, expanding its potential applications in detectors, modulators, and optical switches.

physics.optics↗

arXiv2025

First-Principles and Machine Learning Investigation of the Structural and Optoelectronic Properties of Dodecaphenylyne: A Novel Carbon Allotrope

We report the computational discovery and characterization of Dodecaphenylyne (DP), a novel carbon allotrope with a distinctive geometric arrangement. DP structural, thermodynamic, mechanical, electronic, and optical properties were evaluated using density functional theory and a machine learning interatomic potential trained explicitly for this material. The formation energy of -7.98 eV/atom indicates high thermodynamic stability, further supported by the absence of imaginary phonon modes and the preservation of structural integrity up to 1000 K in ab initio molecular dynamics simulations. Mechanical analysis reveals high in-plane stiffness with directional dependence: Young's modulus values of 469.09 GPa and 600.41 GPa along the x and y directions, respectively. Electronic band structure and projected density of states analyses confirm the DP semiconducting character. Calculations of carrier mobility using the deformation potential theory reveal pronounced anisotropy, with maximum values reaching up to $30.6 \times 10^4$ cm$^2$/V$\cdot$s (electrons, e) and $8.4 \times 10^4$ cm$^2$/V$\cdot$s (holes, h), much higher than the observed for other 2D materials. DP also exhibits anisotropic optical absorption in the visible and ultraviolet spectrum, highlighting its potential for optoelectronic applications.

cond-mat.mtrl-sci↗

arXiv2025

Potassium Decoration on Graphenyldiene Monolayer for Advanced Reversible Hydrogen Storage

Potassium-decorated graphenyldiene (K@GPD) is investigated as a promising two-dimensional material for reversible hydrogen storage using first-principles density functional theory calculations. Potassium atoms bind strongly to the GPD monolayer, and ab initio molecular dynamics (AIMD) simulations confirm the thermal stability of the functionalized system at 300 K. Hydrogen adsorption energies range from -0.11 to -0.14 eV per H$_2$, denoting reversible storage. At full coverage (18 H$_2$ molecules), the system reaches a storage capacity of 8.82 wt\%, exceeding the U.S. DOE target. AIMD simulations reveal spontaneous H$_2$ desorption at ambient temperature, demonstrating excellent reversibility.

cond-mat.mtrl-sci↗

arXiv2025

A Novel Graphyne-Like Carbon Allotrope: 2D Dewar-Anthracyne

Anthracyne (2DDA). 2DDA consists of chains of Dewar-anthracenes connected by acetylenic linkages. DFT-based simulations show that 2DDA is thermally stable and exhibits no imaginary phonon modes, confirming its dynamic stability. 2DDA is metallic with Dirac-like features near the Fermi level, dominated by C pz orbitals. It shows marked mechanical anisotropy, with Young's modulus of 176.24 N/m (x) and 31.51 N/m (y), shear modulus up to 69.14 N/m, and Poisson's ratio varying from 0.27 to 0.87. The material also exhibits strong anisotropic optical absorption in the visible and ultraviolet ranges. Raman and IR spectra reveal intense bands at 648 cm-1 (Raman) and 1292 cm-1 (Infrared). Nanoribbon structures derived from 2DDA exhibit diverse electronic behaviors, from metals up to bandgap values of up to 0.42 eV, depending on the edge-type terminations and width. These findings demonstrate the 2DDA potential for nanoelectronic and optoelectronic applications.

cond-mat.mtrl-sci↗

arXiv2025

Nano-size fragmentation of Tantalum in Copper composite using additive manufacturing

The biggest challenge in manufacturing an immiscible system is phase segregation and non-uniformity inside the composite matrix. Additive manufacturing has the potential to overcome these difficulties due to the high cooling rate achieved during the process. Here we have developed immiscible Copper-based composites reinforced with Tantalum, which were fabricated using the powder bed fusion melting (PBF-M) technique. The distinct advantage of utilizing Tantalum in this process resides in its high melting point, allowing it to remain in particle form within the composite and contribute to its mechanical and surface/wear properties. The PBF-M results in the in situ fragmentation of micron-size Tantalum particles into nanoparticle form through a surface roughening process during laser interaction, enhancing its mechanical and wear properties. The microstructural evolution of Cu-Ta composites is explained through multiscale numerical modeling. The enhanced yield strength and the dynamics of the Ta particles were corroborated by molecular dynamics simulations. The maximum yield strength is exhibited by Cu-5wt%Ta of 80 MPa. Addition of Ta also have significant improvement in wear properties of composites. The current results can be exploited to develop complex shape, high energy efficient copper-based composites.

cond-mat.mtrl-sci↗

arXiv2025

Ultrasensitive Electrochemical Sensor for Perfluorooctanoic Acid Detection Using Two-dimensional Aluminium Quasicrystal

Per- and polyfluoroalkyl substances (PFAS), often referred as "forever chemicals," are pervasive environmental pollutants due to their resistance to degradation. Among these, perfluorooctanoic acid (PFOA) poses significant threats to human health, contaminating water sources globally. Here, we have demonstrated the potential of a novel electrochemical sensor based on two-dimensional (2D) aluminium-based multicomponent quasicrystals (2D-Al QC) for the ultrasensitive sub-picomolar level detection of PFOA. The 2D-Al QC-inked electrode was employed here to detect PFOA by differential pulse voltammetry (DPV). The limit of detection (LoD) achieved is 0.59 +/- 0.05 pM. The sensor was evaluated for selectivity with other interfering compounds, repeatability of cycles, and reproducibility for five similar electrodes with a deviation of 0.8 %. The stability of the sensor has also been analysed after ninety days ,which shows a minimal variation of 15%. Spectroscopic techniques and theoretical calculations were further utilized to understand the interaction between the 2D-Al QC and PFOA. The results demonstrate that the 2D-Al QC offers a promising platform for the rapid and sensitive detection of PFOA, potentially addressing current environmental monitoring challenges.

cond-mat.mtrl-sci↗

arXiv2024

A 2D T-carbon 2-(111) structure with tunable electric and optical properties via chemical decorations: a first-principles investigation

We proposed a new two-dimensional carbon material named 2-(111) planar T-carbon, which is obtained by slicing bulk T-carbon along its (111) crystallographic direction. 2-(111) planar T-carbon's optical and electrical properties can be engineered via surface decoration. Comparing the DFT phonon spectra of pristine and five decorated 2-(111) planar T-carbon obtained by first-principles calculations, we conclude that surface decoration presents a promising, effective, and feasible strategy to improve the structural stability of 2-(111) planar T-carbon. The calculated band structures and electronic properties show direct electronic band gap values between 0.17 eV (-O= decorated) and 2.21 eV (Hydrogenated). Chemical decoration also promises blue or red energy shifts in its optical properties.

cond-mat.mtrl-sci↗

arXiv2024

Non-thermal Magnetic Deicing Using Two-Dimensional Chromium Telluride

Two-dimensional (2D) chromium telluride Cr2Te3 exhibits strong ferromagnetic ordering with high coercivity at low temperatures and paramagnetic behaviour when approaching room temperature. The spin states of monolayer Cr2Te3 show ferromagnetic ordering in the ground state, and in-situ Raman analysis shows reversible structure transformation and hence a ferromagnetic to paramagnetic transition during low-temperature heating cycles (0 - 25 °C). The magnetic phase transition near room temperature in the 2D Cr2Te3 prompted the exploration of these layered materials for energy application. We demonstrate that the low-temperature ferromagnetic behavior can be used to magnetically deice material surfaces using an external magnetic source, avoiding the use of harsh chemicals and high temperatures. The hydrophobic nature and dipole interactions of H2O molecules with the surface of the 2D Cr2Te3 coating aid in the condensation of ice droplets formed on the surface. First-principles calculations also confirm the observed crystal structure, surface interaction, and magnetic properties of 2D Cr2Te3.

cond-mat.mtrl-sci↗

arXiv2024

Tuning the Electronic and Optical Properties of Two-Dimensional Diboron-Porphyrin by Strain Engineering: A Density Functional Theory Investigation

In the present work, we have carried out DFT simulations to investigate the electronic and optical properties of a porphyrin-based 2D crystal named 2D Diboron-Porphyrin (2DDP). We showed that it is possible to use strain to tune the 2DDP electronic properties (from semiconductor to metal) depending on the direction of the applied strain. 2DDP exhibits optical activity from the infrared to the ultraviolet region. Similarly to electronic bands, strain can also modulate the optical activity response. 2DDP can be a promising candidate for some electro-opto-mechanical applications.

cond-mat.mtrl-sci↗

arXiv2024

From Pure Mathematics to Macroscale Applications: The Genesis of Schwarzites

Schwarzites are porous (spongy-like) carbon allotropes with negative Gaussian curvatures. They were proposed by Mackay and Terrones inspired by the works of the German mathematician Hermann Schwarz on Triply-Periodic Minimal Surfaces (TPMS). This review presents and discusses the history of schwarzites and their place among curved carbon nanomaterials. We summarized the main works on schwarzites available in the literature. We discuss their unique structural, electronic, thermal, and mechanical properties. Although the synthesis of carbon-based schwarzites remains elusive, the recent advances in the synthesis of zeolite-templates nanomaterials bring them closer to reality. Atomic-based models of schwarzites have been translated into macroscale ones that have been 3D printed. These 3D printed models have been exploited in many real-world applications, including water remediation and biomedical ones.

cond-mat.mtrl-sci↗