arXiv subjects

Douglas S. Galvão

Publications and source records attributed to Douglas S. Galvão.

At least 19 recordsLinked to original sources

arXiv2026

Corrugated Niobene: Stability, Mechanical and Electronic Properties from First-Principles Calculations

The growing diversity of two-dimensional (2D) materials has expanded opportunities in electronics, energy technologies, catalysis, and optical applications. Within this landscape, understanding how corrugated architectures accommodate metallic bonding and influence the stability and properties of monoelemental niobium sheets remains an open research direction. Here, we propose a corrugated niobene nanosheet, denoted c-Nb, and investigate its structural, energetic, vibrational, mechanical, electronic, and optical properties using density functional theory simulations. The optimized structure adopts a centrosymmetric P-3m1 symmetry, with six atoms per primitive cell and a geometrical thickness of 4.279 Angstrom. Its cohesive energy of -6.03 eV/atom indicates strong binding relative to isolated atoms, although bulk BCC Nb remains energetically favored by 2.49 eV/atom. The absence of imaginary phonon frequencies along the investigated high-symmetry path and the positive-definite in-plane stiffness matrix support dynamical and mechanical structural stability. Despite its pronounced corrugation, the nanosheet exhibits isotropic in-plane elasticity, with Young's and shear moduli of 43.66 N/m and 13.66 N/m, respectively, and a Poisson's ratio of 0.598. Electronic states near the Fermi level are dominated by Nb 4d orbitals, establishing multiband metallicity. These findings identify a corrugated structural candidate that combines strong cohesion, elastic compliance, and metallic electronic behavior, extending the structural diversity of monoelemental 2D metals and providing a basis for further exploration of niobium nanosheets in electronic and ultraviolet-responsive systems.

cond-mat.mtrl-sci↗

arXiv2026

Interfacial Charge Transfer and Morphology Govern Magnetism in Ultrathin VOx/MoSe2 Heterostructures

Engineering magnetism in two-dimensional semiconductors through interfacial interactions offers an attractive alternative to substitutional doping and provides opportunities for integrating magnetic and optoelectronic functionality within the same heterostructure. Here, we investigate ultrathin VOx films deposited on monolayer MoSe2 and demonstrate a pronounced enhancement of the magnetic response upon formation of the VOx/MoSe2 interface. Combined structural, spectroscopic, magnetic, and first-principles analyses support a consistent picture in which finite VOx clusters possess intrinsic magnetic moments that are further enhanced by electron transfer from MoSe2 to the oxide. The predicted charge transfer is also consistent with the increased trion contribution observed in the photoluminescence response of the heterostructure. Beyond this interfacial enhancement, the magnetic behavior is strongly governed by the morphology of the ultrathin oxide. A crossover from discontinuous clusters to more continuous films produces qualitatively different temperature dependences: the continuous-film regime exhibits conventional thermal demagnetization and coercive softening, whereas the clustered regime displays an unusual increase in magnetization and nonmonotonic coercivity with increasing temperature. These contrasting responses are captured by a phenomenological model in which morphology determines the collective magnetic dynamics through a distribution of effective reversal barriers and their thermally activated accessibility. Together, the results establish a unified picture in which interfacial charge transfer enhances the local magnetic moments of VOx, while nanoscale morphology governs their collective magnetic dynamics, providing complementary routes for controlling magnetism in oxide/transition-metal dichalcogenide heterostructures.

cond-mat.mes-hall↗

arXiv2026

Multiproperty Atomistic Characterization of a Synthesized Pyrazinic Nitrogen-Doped Porous Armchair Graphene Nanoribbon

Graphene nanoribbons (GNRs) obtained by on-surface synthesis combine a width-controlled band gap with atomic precision, making chemical decoration of their edges and interiors a practical route to designed electronic and optical behavior. Ullmann coupling of a phenazine-bearing precursor yields a nine-atom-wide armchair ribbon that is periodically perforated and carries two two-coordinated nitrogen atoms at every pore rim. Here we characterize this ribbon across the properties relevant to device operation, alongside the pristine and undoped porous ribbon, disentangling the roles of pore formation and nitrogen incorporation. Perforation primarily governs mechanical and thermal response, whereas nitrogen substitution predominantly controls electronic and optical properties. Perforation removes the atomic row carrying frontier states, opening the gap into the range measured by tunneling spectroscopy while substantially reducing stiffness and thermal conductivity. Substitution leaves the mechanical response essentially unchanged and contributes a secondary conductivity reduction through phonon spectrum reweighting. Its primary effect is electronic: it selectively narrows the conduction band, binds the lowest exciton by 414 meV, and displaces the absorption edge into the red. The effective phonon mean free path we obtain, 9.9 nm, matches the length to which the synthesis presently limits these ribbons, placing reported samples at the ballistic-to-diffusive crossover. Adsorption on Au(111), Ag(111), and Cu(111) is energetically nearly indistinguishable and remains van der Waals in character, accounting for the substrate tolerance observed experimentally. Finally, graphitic rather than pyrazinic nitrogen would make the ribbon metallic, except when two atoms occupy pore-rim sites, yielding a ferromagnetic semiconducting state having a magnetic moment of 2 mu_B per unit cell.

cond-mat.mtrl-sci↗

arXiv2026

Metallic Organometallic and Semiconducting Covalent Phases of Free-Standing $γ$-Graphdiyne Molecular Wires

One-dimensional carbon allotropes combining sp and sp2 hybridizations provide a versatile platform for atomically precise quantum wires with tunable electronic, vibrational, and mechanical responses. Recent on-surface synthesis has realized the $γ$-graphdiyne molecular wire on Au(100) in two interconvertible phases sharing an identical aromatic backbone but distinct linkage chemistry: an organometallic intermediate with C-Au-C bridges and a fully covalent product with diacetylenic linkages. While experimental techniques characterize the on-surface periodicity and C$\equiv$C Raman signatures, the intrinsic properties of the free-standing wires remain inaccessible. Here, we address this gap using hybrid-functional first-principles calculations. The covalent phase is a semiconductor with a direct band gap of 2.02 eV, a polyynic bond-length alternation of 0.117 Å, and a chain periodicity reproducing experiment within -0.5%. Conversely, the organometallic phase exhibits partial cumulenization and 1D metallic behavior, with spin channels crossing the Fermi level. Both isolated polymers demonstrate dynamic stability with Young's moduli of 995 nN and 861 nN, respectively, where the C-Au-C bridge acts as a soft link absorbing 9.2% of axial deformation at +6% macroscopic strain. Species-resolved vibrational analysis identifies an effective-conjugation-coordinate band at 1408 cm$^{-1}$ for the covalent phase and Au-projected modes below 400 cm$^{-1}$ for the intermediate, offering diagnostic fingerprints for phase discrimination during thermal or chemical conversion.

cond-mat.mtrl-sci↗

arXiv2026

Ion-Engineered Insulator-to-Semiconductor Transition in Natural 2D Biotite

Naturally occurring layered silicates offer an abundant yet unexplored class of 2D materials, but their insulating nature limits their functional utility. Here, we demonstrate a chemical strategy that transforms liquid-phase-exfoliated biotite nanosheets into a tunable 2D semiconductor through controlled NaOH treatment. The resulting insulator-to-semiconductor transition originates from Na incorporation, defect generation, and local structural reconstruction while largely preserving the layered framework. Structural and chemical analyses reveal lattice distortion, interlayer reorganization, hydroxylation, and partial Na+-K+ exchange, establishing the origin of the electronic restructuring. This transformation broadens the optical response, shifting the approximately 221 nm absorption toward approximately 280 and 975 nm, reducing the optical bandgap from approximately 5.2 to 3.2-3.5 eV, and introducing low-energy transitions at approximately 1.12-1.17 eV. Electrical measurements reveal nonlinear transport with currents reaching close to 10 microA, demonstrating activated carrier conduction. Ultrafast transient absorption reveals pronounced excited-state absorption, with carrier cooling (0.16-0.38 ps) followed by fast (35-60 ps) and long-lived (336-491 ps) relaxation associated with trap-mediated recombination. Fluence-dependent dynamics reveal a hot-phonon bottleneck at elevated carrier densities. Together with density functional theory calculations, these results establish chemical defect and ion engineering as a powerful route for converting naturally abundant layered minerals into electronically tunable 2D materials for emerging optoelectronic and ultrafast photonic technologies.

cond-mat.mtrl-sci↗

arXiv2026

Structure-Property Correlation of Cr/Cu-MnFeCoNi High-Entropy Alloys for Alkaline Water Electrolysis

High-entropy alloys (HEAs), with their unique compositional-complexity and tunable surface chemistry, have emerged as promising electrocatalysts for energy conversion. The catalytic activity of HEA often arises from the interplay between the intrinsic activity of the individual elements and the synergistic effects generated at the interfaces. Even a single-element substitution in a multicomponent HEA can substantially alter the surface-chemistry and electrochemical kinetics of the active surface. Here we investigated the structure-property relationship of CrMnFeCoNi (HEA-Cr) and MnFeCoNiCu (HEA-Cu) HEAs by comparing the alkaline hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity. Under the same experimental condition, HEA-Cu outperforms HEA-Cr towards both HER and OER. Substituting Cr with Cu significantly enhances the bifunctional activity, where HEA-Cu achieved a lower overpotential (538 mV) and Tafel slope (165 mVdec-1) when compared with HEA-Cr. Computational analysis corroborates these findings, showing that Cu substitution modulates the electronic-structure to provide favorable binding energies for reaction intermediates (H*, O*, OH*, and OOH*). Interestingly, unlike HER, recovered HEA-Cu after OER showed migration of Cu forming a Cu-rich outer layer shell with a multimetallic core. These findings demonstrate the potential of single-element substitution in HEAs as a strategy for designing high-performance, cost-effective catalysts for efficient water electrolysis.

cond-mat.mtrl-sci↗

arXiv2026

Plasmonic Mediated Atomically Engineered 2D Aluminium Quasicrystals for Dopamine Biosensing

Dopamine levels are linked to neurological illnesses like Parkinson's and Alzheimer's. Thus, reliable and sensitive detection of dopamine is crucial for early diagnosis and surveillance of neurodegenerative diseases. Non-noble-metal-based nanomaterials are ideal for light-mediated sensing of organic molecules. Among these, 2D quasicrystal structures consisting of five elements, namely Al70Co10Fe5Ni10Cu5, provide active sites due to their high surface-to-volume ratio, making them excellent for organic chemical sensing. Here, we propose a simple, label-free, spatial self-phase-modulation (SSPM)-based sensing method in liquid form. SSPM-based time evolution of the diffraction pattern for varied mixing levels of a 1100 ppb dopamine solution shows a shift in the active 2D Al QC solution. The 1100 ppb solution shows a distinct value, indicating a change in the nonlinear refractive index. Time-evolution analysis is used to calculate sensitivities to changes in the nonlinear refractive index and time constant. The SPR-activated 2D Al QC nanostructure is used to demonstrate dopamine sensing and to perform qualitative and quantitative evaluations. The SSPM-based sensing has been further compared with other optical-based sensing methods such as Raman spectroscopy, UV-Vis spectroscopy, and FTIR spectroscopy. The experimental observations are also explained using DFT-based simulations. The current SSPM method can be used for rapid, large-scale medical diagnostics.

cond-mat.mtrl-sci↗

arXiv2026

Chiral Epitaxy: Enantioselective Growth of Chiral Nanowires on Low-Symmetry Two-Dimensional Materials

Chiral crystals exhibit useful handedness-dependent properties, including spin selectivity and circularly polarized light sensitivity, yet controlling which enantiomer forms during synthesis remains a central challenge. Existing approaches utilize molecules in solution to template crystal growth, which restricts processing conditions and introduces organic contaminants incompatible with device fabrication. Enantioselective growth of a chiral crystal on a chiral surface via vapor-phase synthesis (chiral epitaxy) has not yet been demonstrated. Here, we show chiral epitaxy of aligned tellurium nanowires on a low-symmetry two-dimensional material, ReSe2. In situ electron microscopies suggest a mechanism where handedness is determined at nucleation by the interface energy difference between Te enantiomers and the chiral substrate surface. Chiral epitaxy provides a solvent-free, vapor-solid route to homochiral crystals compatible with semiconductor and quantum manufacturing processes.

cond-mat.mtrl-sci↗

arXiv2026

Topology as a Design Variable for Multiproperty Engineering in Synthesized 4-5-6-8 Carbon Nanoribbons

Nonbenzenoid carbon frameworks expand low-dimensional material design via controlled asymmetry. Here, we show the experimentally realized 4-5-6-8 carbon nanoribbon establishes a topology-driven paradigm for multiproperty engineering, not just a graphene variant. Using hybrid DFT, tight-binding, and molecular dynamics in a multiscale framework, we demonstrate the symmetry-broken lattice stabilizes hierarchical bonds within standard energy ranges. This geometry produces a robust semiconducting state (hybrid gap >1 eV) and enables strain as a controllable modulation parameter. A tight-binding Hamiltonian fitted only at equilibrium accurately captures strain-dependent band evolution, proving the essential physics is topology-dominated. Mechanical analysis reveals high stiffness with fracture governed by the largest polygons, showing asymmetry redistributes stress without compromising integrity. Intrinsic phonon scattering suppresses thermal conductance, enabling favorable thermoelectric performance without extrinsic disorder. Optical response confirms non-equivalent ring connectivity reorganizes interband transitions, promoting strong visible absorption and efficient photocarrier generation. These results position topology as a governing parameter coupling elasticity, electronics, thermal transport, and optics, establishing the 4-5-6-8 nanoribbon as a unified platform for predictive design of multifunctional carbon materials.

cond-mat.mes-hall↗

arXiv2026

Multiscale Mechanical Response of 3D-Printed Diamondiynes: From Movable Interlocked Lattices to Architected Metamaterials

Diamondynes are a recently synthesized three-dimensional carbon allotrope, with interlocked and movable sublattices that introduce deformation modes not present in standard architected materials. Here, we report the first multiscale mechanical assessment of Diamondiyne-derived architectures by combining quasi-static compression of 3D-printed specimens with reactive molecular dynamics simulations of the corresponding atomic-scale models. We generate four geometries (3F, 2F-SY, 4F, and 2F-USY). All structures resulted in lower density in the range of 0.20-0.38 g.cm^-3. Experiments indicate that the symmetric two-sublattice structure (2F-SY) delivers the best performance, reaching a specific yield strength of 5.91 MPa.g^-1cm^-3 and a specific energy absorption of 279 J.g^-1, whereas 2F-USY architecture yielded the lowest values, with 0.77 MPa.g^-1.cm^-3 and 16 J.g^-1. The 4F geometry provided a specific energy absorption of 254 J.g^-1. The structures deformed through geometric collapse and strut buckling, which was due to diagonal shear in 2F-USY and progressive compaction in 2F-SY and 3F. Molecular dynamics simulations also confirmed these experimental trends and revealed strong directional anisotropy due to the arrangement of interlocked sublattices, with a stiffness of 24.1 GPa along the z-direction in the case of 4F architecture. Overall, Diamondiyne-derived architectures display geometry-dominated mechanical behavior and serve as a promising platform for lightweight, energy-absorbing metamaterials.

physics.app-ph↗

arXiv2025

A Three-Dimensional Dodecaphenylyne-Derived Carbon Allotrope with Anisotropic and Auxetic-Like Mechanical Behavior

We introduce 3D-DPhyne, a novel three-dimensional (3D) carbon allotrope derived from the dodecaphenylyne framework, and investigate its structural, electronic, optical, and mechanical properties using first-principles calculations. The proposed structure forms a tetragonal, topologically complex network of four-, six-, and twelve-membered carbon rings with mixed sp/sp^2 hybridization and a formation energy of -7.87 eV/atom, comparable to other stable carbon allotropes. Phonon dispersion calculations show no imaginary modes, and ab initio molecular dynamics simulations at 1000~K confirm robust thermal stability without bond breaking. Electronic structure analysis reveals metallic character, with multiple bands crossing the Fermi level and dominant contributions from carbon p orbitals, consistent with a fully delocalized 3D $π$-conjugated network. The optical response is anisotropic, exhibiting strong absorption in the visible and ultraviolet regions and low reflectivity across a broad range of photon energies. Mechanical analysis reveals pronounced elastic anisotropy, with Young's modulus varying from approximately 40 to 490 GPa depending on direction. Poisson's ratio displays unconventional directional behavior, including auxetic-like responses.

cond-mat.mtrl-sci↗

arXiv2025

Kagome Topology in Two-Dimensional Noble-Metal Monolayers

Two-dimensional (2D) metallic lattices with kagome topology provide a unique platform for exploring the interplay between geometric frustration, reduced coordination, and lattice stability in elemental systems. Motivated by the recent experimental realization of atomically thin gold layers and kagome goldene, we present a first-principles investigation of free-standing kagome monolayers of Cu, Ag, and Au. Using density functional theory combined with lattice dynamics and ab initio molecular dynamics, we systematically assess their structural, mechanical, dynamical, and thermal stability. All kagome monolayers satisfy the 2D Born criteria and exhibit relatively low in-plane stiffness compared to graphene and hexagonal goldene, reflecting the porous nature of the kagome lattice and its metallic bonding. Among the three systems, the Au-based lattice displays the highest in-plane Young's modulus. Phonon calculations reveal that the unstrained kagome phase is dynamically unstable for all metals. However, a moderate biaxial tensile strain of 5% stabilizes the Ag and Au monolayers, while Cu retains residual unstable modes. Finite-temperature simulations further show that Cu rapidly reconstructs toward a trigonal lattice, Ag remains metastable at low temperature but collapses at room temperature, and Au exhibits competing kagome and trigonal motifs at 300 K, indicating near-degeneracy between these phases. These results establish that strain engineering and atomic size are key determinants of the stability of metallic kagome monolayers and provide guidance for future substrate-supported realizations.

cond-mat.mtrl-sci↗

arXiv2025

Quadrene: A Novel Quasi-2D Carbon Allotrope with High Carrier Mobility

We present a comprehensive first-principles investigation of a novel carbon allotrope characterized by quasi-tetragonal atomic motifs and quasi-two-dimensional structural behavior. Structural analysis reveals an open framework composed of alternating diamond-like and square units, while thermodynamic assessments indicate a negative formation energy, suggesting high intrinsic stability. Phonon spectra confirm dynamical robustness, and \textit{ab initio} molecular dynamics simulations at 1000~K validate its thermal resilience. Furthermore, the system exhibits an indirect bandgap of 1.58 eV at the HSE06 level, anisotropic mechanical behavior, and a broadband optical response, reinforcing its potential for nanoelectronic and optoelectronic applications. The highly anisotropic mechanical behavior is characterized by an in-plane Young's modulus ranging from 80 to 550 GPa, depending on crystallographic direction. Additionally, the electronic transport properties exhibit pronounced anisotropy, with hole mobilities reaching up to 5.83 x 10^6 cm^2/V . s and electron mobilities up to 6.40 x 10^6 cm^2/V . s along different crystallographic directions, highlighting the material's potential for directionally selective nanoelectronic device applications.

cond-mat.mtrl-sci↗

arXiv2025

From Glaphene to Glaphynes: A Hybridization of 2D Silica Glass and Graphynes

Hybrid two-dimensional (2D) materials have attracted increasing interest as platforms for tailoring electronic properties through interfacial design. Very recently, a novel hybrid 2D material termed glaphene, which combines monolayers of 2D silica glass and graphene, was experimentally realized. Inspired by glaphenes, we proposed a new class of similar structures named glaphynes, which are formed by stacking SiO$_2$ monolayers onto $α$-, $β$-, and $γ$-graphynes. Graphynes are 2D carbon allotropes with the presence of acetylenic groups (triple bonds). The glaphynes' structural and electronic properties were investigated using the density functional tight-binding (DFTB) method, as implemented in the DFTB+ package. Our analysis confirms their energetic and structural stability. We have observed that in the case of glaphynes, the electronic proximity effect can indeed open the electronic band gap, but not for all cases, even with the formation of Si-O-C bonds between silica and graphynes.

cond-mat.mtrl-sci↗

arXiv2025

A Concise Review of Recently Synthesized 2D Carbon Allotropes: Amorphous Carbon, Graphynes, Biphenylene and Fullerene Networks

Two-dimensional (2D) carbon allotropes have received considerable attention due to their unique properties and potential applications in several fields, including electronics, catalysis, energy storage, and sensing. Following the experimental realization of graphene, numerous other 2D carbon structures have been proposed and, in some cases, successfully synthesized. This work presents a concise review of the recently experimentally realized 2D carbon allotropes, including graphynes, biphenylene-based networks, fullerene networks, and monolayer amorphous carbon. For each class, we discuss structural characteristics, theoretical predictions, and synthesis methods, with emphasis on the interplay between theory and experiment. We also highlight instances where experimental studies overlooked relevant theoretical contributions. Finally, we identify theoretically predicted structures that remain unexplored experimentally, suggesting opportunities for synthesis-driven investigations.

cond-mat.mtrl-sci↗

arXiv2025

Magnetism Induced by Azanide and Ammonia Adsorption in Defective Molybdenum Disulfide and Diselenide: A First-Principles Study

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention due to their tunable structural, electronic, and spin-related properties, particularly in the presence of point defects and molecular adsorbates. Motivated by these aspects, we have investigated using first-principles methods the magnetic properties induced by azanide (NH$_2$) and ammonia (NH$_3$) adsorption on defective monolayers of Molybdenum Disulfide (MoS$_2$) and Diselenide(MoSe$_2$). Spin-polarized density functional theory (DFT) was employed to investigate the impact of mono- and di-vacancies on the local spin environment and the role of molecular adsorption in modifying magnetic behavior. The results show that pristine chalcogen vacancies do not generate magnetism, whereas the adsorption of NH$_2$ and NH$_3$ creates localized magnetic moments in Mo-based dichalcogenides. A notable case occurs for MoSe$_2$, where NH$_3$ dissociation into NH$_2$ and H fragments on the same side of the surface produces a net magnetic moment of 2.0 $μ_B$. Tests performed on W-based dichalcogenides under equivalent conditions showed no magnetic response, and are reported here only for comparison. These findings demonstrate that molecular adsorption combined with defect engineering can be a practical approach to tune magnetism in 2D materials, with potential relevance for spintronic and sensing applications.

cond-mat.mtrl-sci↗

arXiv2025

Defect Engineered Layer Dependent Nonlinear Optical Response in Two Dimensional Muscovite for Efficient Optical Limiting

Light-matter interactions in two-dimensional (2D) materials have gained significant interest due to their distinctive optical and electronic properties. Recently, silicates have emerged as a promising new class of 2D materials, but their nonlinear optical properties remain largely unexplored. In this study, we demonstrate layer-dependent nonlinear absorption and optical limiting capabilities of 2D muscovite using femtosecond laser excitation at 450 nm. The two-photon absorption (TPA) coefficient is highly sensitive to both the number of layers and excitation intensity, increasing markedly from (3.91+/-0.06)x10^3 cm GW^-1 in multilayer structures to (6.94+/-0.17)x10^5 cm GW^-1 in the monolayer limit at a peak intensity of 68 GW cm^-2, highlighting a strong layer-dependent enhancement in nonlinear absorption. Additionally, monolayer muscovite exhibits an optical limiting threshold of 1.46 mJ cm^-2, outperforming graphene and other 2D dichalcogenides. This enhanced TPA arises from quantum confinement and intrinsic lattice defects that facilitate nonlinear optical transitions. Density functional theory reveals that liquid-phase exfoliation disrupts potassium interlayers and induces oxygen vacancies, generating mid-gap electronic states that significantly enhance TPA. These insights open new avenues for designing low-fluence, high-efficiency optical limiters using 2D silicates.

physics.optics↗

arXiv2025

Alpha-, Beta-, and Gamma-TODD-G: Novel 2D Planar Carbon Allotropes

We present a comprehensive first-principles investigation of three novel two-dimensional carbon allotropes: alpha-, beta-, and gamma-TODD-Graphene (TODD-G), composed of 3-8-12-16, 3-8-12-16, and 3-4-8-12 interconnected carbon rings with sp/sp2 hybridization, respectively. Structural optimization, phonon spectra, and ab initio molecular dynamics simulations confirm their thermal and dynamical stability. All phases exhibit metallic electronic behavior, with distinct Dirac-like features and tilted Dirac cones that suggest anisotropic charge transport. Mechanical analysis reveals tunable anisotropy: alpha-TODD-G is strongly anisotropic, beta-TODD-G shows moderate anisotropy, and gamma-TODD-G displays an almost isotropic mechanical response. Optical spectra further differentiate the phases, with gamma-TODD-G showing strong absorption in the infrared region, while alpha- and beta-TODD-G mainly absorb in the visible and ultraviolet ranges.

cond-mat.mtrl-sci↗