arXiv subjects

Douglas S. Galvao

Publications and source records attributed to Douglas S. Galvao.

At least 37 records · Page 2Linked to original sources

arXiv2023

Thickness dependent mechanical properties of soft ferromagnetic two-dimensional CoTe2

Two dimensional (2D) layered transition-metal-based tellurides (chalcogens) are known to harness their surface atoms characteristics to enhance topographical activities for energy conversion, storage, and magnetic applications. High surface energy due to unsaturated dangling bonds and larger lateral size than the thickness (volume) makes them a potential candidate for emerging electronics. Nevertheless, the gradual stacking of each sheet alters the surface atoms' subtle features, such as lattice expansion, leading to several phenomena and rendering tunable properties. In the present work, we have monitored thickness-dependent properties of the 2D CoTe2 sheets from nanoscale mechanics, tribology, surface potential distributions, interfacial interaction and magnetism using atomically resolved spectroscopy and different surface probe techniques, in conjunction with theoretical investigations: density functional theory (DFT) and molecular dynamics (MD). The variation in properties observed in theoretical investigation unleashes the crucial role of crystal planes of the CoTe2. The presented results are beneficial in expanding the use of 2D telluride family in flexible electronics, piezo sensors, tribo-generator, and next-generation memory devices.

cond-mat.mtrl-sci↗

arXiv2023

Topological engineered 3D printing of Architecturally Interlocked Petal-Schwarzites

The topologically engineered complex Schwarzites architecture has been used to build novel and unique structural components with a high specific strength. The mechanical properties of these building blocks can be further tuned, reinforcing with stronger and high surface area architecture. In the current work, we have built six different Schwarzites structures with multiple interlocked layers, which we named architecturally interlocked petal-schwarzites (AIPS). These complex structures are 3D printed into macroscopic dimensions and compressed using uniaxial compression. The experimental results show a strong dependency of mechanical response on the number of layers and topology of the layers. Fully atomistic molecular dynamics compressive simulations were also carried out, and the results are in good agreement with experimental observations. They can explain the underlying AIPS mechanism of high specific strength and energy absorption. The proposed approach opens a new perspective on developing new 3D-printed materials with tunable and enhanced mechanical properties.

cond-mat.mtrl-sci↗

arXiv2023

Mechanical Energy Absorption of Architecturally Interlocked Petal-Schwarzites

We carried out fully atomistic reactive molecular dynamics simulations to study the mechanical behavior of six newly proposed hybrid schwarzite-based structures (interlocked petal-schwarzites). Schwarzites are carbon crystalline nanostructures with negative Gaussian curvature created by mapping a TPMS (Triply Periodic Minimal Surface) with carbon rings containing six to eight atoms. Our simulations have shown that petal-schwarzite structures can withstand uni-axial compressive stress up to the order of GPa and can be compressed past 50 percent strain without structural collapse. Our most resistant hierarchical structure has a calculated compressive strength of 260~GPa and specific energy absorption (SEA) of 45.95 MJ/kg, while possessing a mass density of only 685 kg/m$^3$. These results show that these structures could be excellent lightweight materials for applications that require mechanical energy absorption.

cond-mat.mtrl-sci↗

arXiv2023

On the Mechanical, Electronic, and Optical Properties of 8-16-4 Graphyne: A 2D Carbon Allotrope with Dirac Cones

Due to the success achieved by graphene, several 2D carbon-based allotropes were theoretically predicted and experimentally synthesized. We used density functional theory and reactive molecular dynamics simulations to investigate the mechanical, structural, electronic, and optical properties of 8-16-4 Graphyne. The results showed that this material exhibits good dynamical and thermal stabilities. Its formation energy and elastic moduli are -8.57 eV/atom and 262.37 GPa, respectively. This graphyne analogue is a semi-metal and presents two Dirac cones in its band structure. Moreover, it is transparent, and its intense optical activity is limited to the infrared region. Remarkably, the band structure of 8-16-4 Graphyne remains practically unchanged at even moderate strain regimes. As far as we know, this is the first 2D carbon allotrope to exhibit this behavior.

cond-mat.mtrl-sci↗

arXiv2023

Transforming 2D carbon allotropes into 3D ones through topological mapping: The case of biphenylene carbon (graphenylene)

In this work, we propose a new methodology for obtaining 3D carbon allotrope structures from 2D ones through topological mapping. The idea is to select a 3D target structure and 'slice' it along different structural directions, creating a series of 2D structures. As a proof of concept, we chose the Tubulane structure 12-hexa(3,3) as a target. Tubulanes are 3D carbon allotropes based on cross-linked carbon nanotubes. One of obtained 2D 'sliced' structures was mapped into the biphenylene carbon (BPC). We showed that compressing BPC along different directions can generate not only the target Tubulane 12-hexa(3,3) but at least two other structures, bcc-C6 and an unreported member of the Tubulane family, which we called Tubulane X. The methodology proposed here is completely general, it can be used coupled with any quantum method. Considering that new 2D carbon allotropes, such as the biphenylene carbon network, which is closely related to BPC, have been recently synthesized, the approach proposed here opens new perspectives to obtain new 3D carbon allotropes from 2D structures.

cond-mat.mtrl-sci↗

arXiv2023

Hydrogen atom/molecule adsorption on 2D metallic porphyrin: A first-principles study

Hydrogen is a promising element for applications in new energy sources like fuel cells. One key issue for such applications is storing hydrogen. And, to improve storage capacity, understanding the interaction mechanism between hydrogen and possible storage materials is critical. This work uses DFT simulations to comprehensively investigate the adsorption mechanism of H/H$_2$ on the 2D metallic porphyrins with one transition metal in its center. Our results suggest that the mechanism for adsorption of H (H$_2$) is chemisorption (physisorption). The maximum adsorption energy for atomic hydrogen was $-3.7$ eV for 2D porphyrins embedded with vanadium or chromium atoms. Our results also revealed charge transfer of up $-0.43$ e to chemisorbed H atoms. In contrast, the maximum adsorption energy calculated for molecular hydrogen was $-122.5$ meV for 2D porphyrins embedded with scandium atoms. Furthermore, charge transfer was minimal for physisorption. Finally, we also determined that uniaxial strain has a minimal effect on the adsorption properties of 2D metallic porphyrins.

cond-mat.mtrl-sci↗

arXiv2023

Tetra-penta-deca-hexagonal-graphene (TPDH-graphene) hydrogenation patterns: dynamics and electronic structure

The advent of graphene has renewed the interest in other 2D carbon-based materials. Bhattacharya and Jana have proposed a new carbon allotrope, composed of different polygonal carbon rings containing 4, 5, 6, and 10 atoms, named Tetra-Penta-Deca-Hexagonal-graphene (TPDH-graphene). This unusual topology created material with interesting mechanical, electronic, and optical properties and several potential applications, including UV protection. Like other 2D carbon structures, chemical functionalizations can be used to tune their TPDH-graphene properties. In this work, we investigated the hydrogenation dynamics of TPDH-graphene and its effects on its electronic structure, combining DFT and fully atomistic reactive molecular dynamics simulations. Our results show that H atoms are mainly incorporated on tetragonal ring sites (up to 80% at 300 K), leading to the appearance of well-delimited pentagonal carbon stripes. The electronic structure of the hydrogenated structures shows the formation of narrow bandgaps with the presence of Dirac cone-like structures, indicative of anisotropic transport properties.

cond-mat.mtrl-sci↗

arXiv2022

The Effect of Element Composition on the Structural and Electronic Properties of Carbon, Silicon, Silicon Carbide, and Boron Nitride Gyroid Schwarzites

Schwarzites are porous structures that present negative Gaussian curvatures. Although initially proposed for carbon, in principle, schwarzites of other elements are possible. In this work, we have carried out a detailed investigation of the effect of element composition (C, Ge, Si, SiC, and BN) on the structural, electronic and optical properties of a gyroid schwarzite structure, the so-called G688. The DFT simulations were carried out using the well-known SIESTA code. Our results showed that formation energy values are in similar range of other related allotrope structures and are thermally stable (up to 1000~K). From the electronic analyses, our results indicate that all structures, except the carbon one, present semiconductor characteristics. From the optical properties, except for the infrared region where only silicon and germanium show some absorption, the other structures exhibit optical activity only in the visible and ultra-violet regions, and all of them have large refractive index values. For reflectivity, except for Si and Ge schwarzites that reflect almost 40\% of light, the other schwarzites exhibit low reflectivity. These characteristics make them good candidates for optoelectronic applications, such as infrared/ultraviolet absorbers, and ultraviolet blockers.

cond-mat.mtrl-sci↗

arXiv2022

Two-dimensional (2D) d-Silicates from abundant natural minerals

In the last decade, the materials community has been exploring new 2D materials (graphene, metallene, TMDs, TMCs, MXene, among others) that have unique physical and chemical properties. Recently, a new family of 2D materials, the so-called 2D silicates, have been proposed. They are predicted to exhibit exciting properties (such as high catalytic activity, piezoelectricity, and 2D magnetism). In the current work, we demonstrate a generic approach to the synthesis of large-scale 2D silicates from selected minerals, such as Diopside (d). Different experimental techniques were used to confirm the existence of the 2D structures (named 2D-d-silicates). DFT simulations were also used to gain insight into the structural features and energy harvesting mechanisms (flexoelectric response generating voltage up to 10 V). The current approach is completely general and can be utilized for large-scale synthesis of 2D silicates and their derivatives, whose large-scale syntheses have been elusive.

cond-mat.mtrl-sci↗

arXiv2022

Investigating thermal transport in knotted graphene nanoribbons using non-equilibrium molecular dynamics

In this work, we investigated the effect of knots in the thermal transport of graphene nanoribbons through non-equilibrium molecular dynamics simulations. We considered the cases of one, two, and three knots are present. Temperature jumps appear in the temperature profile where the knots are located, which indicates that they introduce thermal resistances in the system, similar to interfacial Kapitza resistance present between two different materials and/or single materials with defects and/or lattice distortions. We found that the thermal resistance introduced by each individual knot is essentially the same as the overall resistance increase linearly with the number of knots, as they behave as thermal resistances associated in series. Also, the relative position between each knot in the arrangement does not strongly affect the thermal current produced by the temperature gradient, showing a weak thermal rectification effect.

cond-mat.mes-hall↗

arXiv2022

'Guided' Fractures in Graphene Mechanical Diode-like Structures

The concept of the diode is usually applied to electronic and thermal devices but very rarely for mechanical ones. A recently proposed fracture rectification effect in polymer-based structures with triangular voids defects has motivated us to test these ideas at the nanoscale using graphene membranes. Using fully-atomistic reactive molecular dynamics simulations we showed that robust rectification-like effects exist. The fracture can be 'guided' to easier propagate along one specific direction than its opposite. We also observed that there is an optimal value for the spacing between each void for the rectification effect.

cond-mat.mtrl-sci↗

arXiv2021

Schwarzite and schwarzynes based load-bear resistant radial cellular griding-based 3D printed structures

Nature-occurring structures exhibiting unique topological features such as complex and gradient porosity has been the basis to create new materials and/or structures. Most studies have been focused on complex periodic porous structures but gradient porous ones have not been yet fully investigated for stable structural designs. In this work, we have proposed and tested a new approach to create cellular griding structures, in which the mass density varies from the center to the borders, i.e, a radial gradient. To create these new structures we exploited the topology of two carbon-based families with different pore sizes, the schwarzites, and schwarzynes. We created fully atomistic models that were translated into macroscale ones that were then 3D printed. The mechanical behavior of the gradient structures was investigated by molecular dynamics simulations and mechanical compression tests of the printed models. Our results show that their mechanical response can be engineered (for instance, in terms of energy absorption, ballistic performance, etc.) and can outperform their corresponding density uniform structures.

cond-mat.mtrl-sci↗

arXiv2021

Scalable synthesis of 2D van der Waals superlattices

Heterostructure materials form the basis of much of modern electronics, from transistors to lasers and light-emitting diodes. Recent years have seen a renewed focus on creating heterostructures through the vertical integration of two-dimensional materials, including graphene, hexagonal boron nitride, and transition metal dichalcogenides (TMDCs). However, fundamental challenges associated with materials processing have limited material quality and impeded scalability. We demonstrate a method to convert sub-nanometer metal films deposited on silicon and sapphire into TMDC heterostructures through vapor-phase processing. The resulting heterostructures and superlattices exhibit novel properties compared with stand-alone TMDCs, including reduced bandgap, enhanced light-matter coupling, and improved catalytic performance. This robust and scalable synthetic method provides new opportunities to generate a wide range of artificially stacked 2D superlattices with controlled morphology and composition.

cond-mat.mtrl-sci↗

arXiv2021

Two-dimensional Cobalt Telluride as Piezo-tribogenerator

Two-dimensional (2D) materials have been shown to be efficient in energy harvesting. Here, we report utilization of waste heat to generate electricity via combined piezoelectric and triboelectric property of 2D Cobalt Telluride (CoTe2). The piezo-triboelectric nanogenerator (PTNG) produced an open-circuit voltage of ~5V under 1N force and the effect of temperature in the 305-363 K range shows a four-fold energy conversion efficiency improvement. The 2D piezo-tribogenerator shows excellent characteristics with a maximum voltage of ~10V, fast response time and high responsivity. Density functional theory was used to gain further insights and validation of the experimental results. Our results could lead to energy harvesting approaches using 2D materials from various thermal sources and dissipated waste heat from electronic devices.

physics.app-ph↗

arXiv2021

Multifold enhancement in magnetization of atomically thin Cobalt Telluride

Magnetism in semiconductor two-dimensional (2D) materials is gaining popularity due to its potential application in memory devices, sensors, spintronic and biomedical applications. Here, 2D Cobalt Telluride (CoTe) has been synthesized from its bulk crystals using a simple and scalable liquid-phase exfoliation method. The atomically thin CoTe shows over four hundred times enhancement in its magnetic saturation values compared to the bulk form. The UV-Vis absorption spectra reveal superior absorption in the high energy region, suggesting a semiconducting nature. Furthermore, we explain bandgap and origin of high magnetic behavior by density functional theory (DFT) calculations. The 2D CoTe shows a larger magnetism compared to bulk CoTe due to the reduced coordination number of the surface atoms, shape anisotropy and surface charge effect.

physics.app-ph↗

arXiv2021

Apparent Ferromagnetism in Exfoliated Ultra-thin Pyrite Sheets

Experimental evidence for ferromagnetic ordering in isotropic atomically thin two-dimensional crystals has been missing until a bilayer Cr2Ge2Te6, and a three-atom thick monolayer CrI3 are shown to retain ferromagnetic ordering at finite temperatures. Here, we demonstrate successful isolation of a non-van der Waals type ultra-thin nanosheet of FeS2 derived from naturally occurring pyrite mineral (FeS2) by means of liquid-phase exfoliation. Structural characterizations imply that (111) oriented sheets are predominant and is supported theoretically by means of density functional theory surface energy calculations. Spin-polarized density theory calculations further predicted that (111) oriented three-atom thick pyrite sheet has a stable ferromagnetic ground state different from its diamagnetic bulk counterpart. This theoretical finding is evaluated experimentally employing low temperature superconducting quantum interference device measurements and observed an anomalous ferromagnetic kind of behavior.

cond-mat.mtrl-sci↗

arXiv2021

A Reactive Molecular Dynamics Study of Hydrogenation on Diamond Surfaces

Hydrogenated diamond has been regarded as a promising material in electronic device applications, especially in field-effect transistors (FETs). However, the quality of diamond hydrogenation has not yet been established, nor has the specific orientation that would provide the optimum hydrogen coverage. In addition, most theoretical work in the literature use models with 100% hydrogenated diamond surfaces to study electronic properties, which is far from the experimentally observed hydrogen coverage. In this work, we have carried out a detailed study using fully atomistic reactive molecular dynamics (MD) simulations on low indices diamond surfaces i.e. (001), (013), (110), (113) and (111) to evaluate the quality and hydrogenation thresholds on different diamond surfaces and their possible effects on electronic properties. Our simulation results indicate that the 100% surface hydrogenation in these surfaces is hard to achieve because of the steric repulsion between the terminated hydrogen atoms. Among all the considered surfaces, the (001), (110), and (113) surfaces incorporate a larger number of hydrogen atoms and passivate the surface dangling bonds. Our results on hydrogen stability also suggest that these surfaces with optimum hydrogen coverage are robust under extreme conditions and could provide homogeneous p-type surface conductivity in the diamond surfaces, a key requirement for high-field, high-frequency device applications.

cond-mat.mtrl-sci↗

arXiv2021

Mechanical Properties of 3D-Printed Pentadiamond

In this work, We combined fully atomistic molecular dynamics and finite elements simulations with mechanical testings to investigate the mechanical behavior of atomic and 3D-printed models of pentadiamond. Pentadiamond is a recently proposed new carbon allotrope, which is composed of a covalent network of pentagonal rings. Our results showed that the stress-strain behavior is almost scale-independent. The stress-strain curves of the 3D-printed structures exhibit three characteristic regions. For low-strain values, this first region presents a non-linear behavior close to zero, followed by a well-defined linear behavior. The second regime is a quasi-plastic one and the third one is densification followed by structural failures (fracture). The Young's modulus values decrease with the number of pores. The deformation mechanism is bending-dominated and different from the layer-by-layer deformation mechanism observed for other 3D-printed structures. They exhibit good energy absorption capabilities, with some structures even outperforming kevlar. Interestingly, considering the Ashby chart, 3D-printed pentadiamond lies almost on the ideal stretch and bending-dominated lines, making them promising materials for energy absorption applications.

physics.app-ph↗