arXiv subjects

Jahid Emon

Publications and source records attributed to Jahid Emon.

4 recordsLinked to original sources

arXiv2026

Defect configuration, not nitrogen content, governs the mechanical integrity of nitrogen-doped graphene: a molecular dynamics study

The mechanical reliability of nitrogen-doped graphene is often attributed to its nitrogen content, yet nitrogen occurs in chemically distinct configurations whose individual mechanical roles, and whose interactions with other defects, remain unresolved. Here, molecular dynamics simulations of uniaxial tension are used to separate the contributions of nitrogen chemistry, missing atoms, and defect arrangement to the strength and fracture of graphene. Three size-matched defects, a graphitic-nitrogen cluster, a void, and a pyridinic-nitrogen cluster, are compared so that two controlled contrasts isolate the effects of edge chemistry and of the vacancy independently. The graphitic cluster leaves the mechanical properties essentially unchanged (a strength reduction of <1 %), whereas the void degrades the ultimate strength by ~23 % and the pyridinic cluster, which combines the same vacancy with edge nitrogen, is the most damaging (~30 %), failing abruptly from its nitrogen-decorated rim rather than through the damage-tolerant process of the bare void. The mechanical impact of a nitrogen cluster is therefore governed by whether it carries vacancies, not by nitrogen itself. When a nitrogen cluster and a void coexist, their interaction is controlled by orientation relative to the load: in-line defects interact negligibly and fail at the more severe member, whereas side-by-side defects couple through overlapping stress fields and weaken the sheet progressively as they approach, an interaction that persists to separations of ~80 {\AA}. These results establish that the mechanical integrity of nitrogen-modified graphene is determined by the configuration of defects, the bonding environment of nitrogen, and the arrangement of coexisting defects relative to the load, rather than by nitrogen content or defect density alone, thereby providing a basis for defect-tolerant design.

cond-mat.mtrl-sci↗

arXiv2026

Peripheral Nitrogen Topology as a Defect-Chemical Switch for Electronic and Magnetic States in Graphene: A First-Principles Study of Pyridinic, Pyridazinic, Pyrrolic, and Pyrazolic Configurations

Defect and heteroatom engineering offer powerful routes for tuning the electronic and magnetic properties of graphene, yet the role of specific peripheral nitrogen topologies around graphene voids remains insufficiently understood. Here, spin-polarized first-principles calculations were performed to investigate how four heterocyclic -- like peripheral nitrogen configurations -- pyridinic, pyridazinic, pyrrolic, and pyrazolic modify the structural stability, charge redistribution, electronic structure, and magnetic response of graphene containing a central void. Among the four peripheral N configurations, the pyridinic N provides the most favorable structural-energetic balance among the investigated motifs. Bond-length analysis reveals that nitrogen topology strongly controls local lattice reconstruction. Charge-density, charge-density-difference, and Bader analyses demonstrate that the peripheral N atoms act as electron-accumulating centers and reshape the local electronic environment around the vacancy rim. Spin-resolved band structures show that pyridinic, pyridazinic, and pyrrolic configurations retain metallic or near-metallic defect-state character, whereas pyrazolic graphene opens a narrow band gap. Magnetic analysis further reveals that pyrazolic graphene is spin-compensated, with zero net magnetization, unlike the other systems, which possess finite spin-polarized moments. Spin-density and SPDOS analyses indicate that the magnetism originates from N-modulated vacancy-edge states involving both N 2p and neighboring C 2p orbitals. These findings establish peripheral nitrogen topology not merely as a structural defect descriptor, but as a deterministic defect-chemical switch, offering a metal-free route to pattern active spintronic and semiconducting domains directly into the graphene lattice through controlled vacancy-edge nitrogen coordination.

cond-mat.mtrl-sci↗

arXiv2025

Impact of Nitrogen Atom Clusters and Vacancy Defects on Graphene: A Molecular Dynamics Investigation

Graphene's exceptional mechanical properties are crucial for its integration into advanced technological applications. However, real-world synthesis and functionalization processes introduce structural modifications that can compromise its mechanical integrity. Nitrogen doping, while beneficial for electronic property tuning, often results in atomic clustering rather than uniform distribution, while concurrent vacancy defect formation represents another common structural alteration during processing. This study systematically investigates the comparative effects of nitrogen atom clusters and equivalent sized vacancy defects on the mechanical behavior of graphene sheets through molecular dynamics simulations. The Nitrogen clustering significantly degraded mechanical performance almost similarly to random doping. In comparison, systems with equivalent-sized vacancy defects showed higher stiffness and lower ductility than those with clusters. The study revealed distinct failure mechanisms between doped and defective configurations, with nitrogen clusters showing modified crack propagation patterns while vacancies acted as pronounced stress concentrators, leading to premature failure. However, this study also showed that defect morphology critically influences mechanical properties. These findings provide important insights for optimizing graphene synthesis and processing protocols, highlighting the differential mechanical risks associated with dopant clustering versus vacancy formation. The results inform defect-tolerant design strategies for graphene-based nanoelectronics, composites, and sensors, where mechanical reliability is paramount for device performance and longevity.

cond-mat.mtrl-sci↗

arXiv2025

Scaling Laws Governing Droplet Spreading and Merging Dynamics on Solid Surfaces: A Molecular Simulation Study

This study employs molecular dynamics simulations to investigate droplet dynamics when a stationary droplet on a solid surface is struck by another droplet of similar size from above. The focus is on the jumping behavior of the merged droplet and the associated energy conversion. The process is primarily governed by the amount of energy converted into kinetic energy after dissipation. At high impact velocities, the energy conversion efficiency becomes constant, with only about 1% lost due to surface adhesion, an effect that diminishes with increasing velocity. Factors such as impact velocity, droplet size, surface texture, and wettability significantly influence the jumping velocity. Scaling laws are developed for the maximum spreading time, spreading factor, and restitution coefficient based on the Weber (We) and Reynolds (Re) numbers, which differ from those for single droplet impacts. On superhydrophobic surfaces, the spreading time is approximated as three times droplet radius to impact velocity, and its dimensionless form scales linearly with We 0.31. The general scaling laws for the spreading factor for velocity dependent and velocity independent spreading regimes are developed.

physics.flu-dyn↗