arXiv subjects

Khushboo Dange

Publications and source records attributed to Khushboo Dange.

6 recordsLinked to original sources

arXiv2026

Strain-Engineered s-C$_3$N$_6$ Monolayer for Efficient Water Splitting: A first-principles study

Photocatalytic water splitting offers a sustainable route for solar-to-hydrogen energy conversion, yet identifying stable, metal-free semiconductors with suitable electronic, optical, and band-alignment properties remains challenging. Here, we investigate the structural, mechanical, electronic, optical, and photocatalytic properties of the two-dimensional s-C$_3$N$_6$ monolayer using first-principles calculations. Ab initio molecular dynamics and elastic constant analysis confirm its thermal and mechanical stability. Hybrid HSE06 calculations reveal pristine s-C$_3$N$_6$ is a direct-band-gap semiconductor (2.62 eV). However, its conduction-band minimum lies below the hydrogen reduction potential, preventing spontaneous hydrogen evolution. To overcome this limitation, we employ biaxial and uniaxial strains (-10% to +10%) to modulate its electronic structure. We find that compressive biaxial strains of -8% and -10% uniquely tune the band edges to straddle the redox potentials, enabling spontaneous overall water splitting. Crucially, these photocatalytically active states remain mechanically and thermally stable. Optical properties calculations show the fundamental gap in both pristine and strained structures is optically dark, with the primary absorption peak in the UV region. Furthermore, a strain-induced mobility mismatch between electrons and holes facilitates efficient charge separation. However, thermodynamic modeling of surface kinetics reveals that the s-C$_3$N$_6$ surface binds intermediates strongly, necessitating a co-catalyst to overcome kinetic barriers. Our results establish strain engineering as an effective strategy to tailor band-edge alignment, carrier dynamics, and optical transitions in s-C$_3$N$_6$, highlighting its potential for stable 2D photocatalytic water splitting.

cond-mat.mtrl-sci↗

arXiv2025

Electric-field induced half-metallicity in a two-dimensional ferromagnetic Janus VSSe bilayer

Two-dimensional (2D) half-metals with intrinsic ferromagnetism hold great potential for applications in spintronics. In this study, we aim to expand the known space of such 2D ferromagnetic (FM) half-metals by investigating bilayer of Janus VSSe, an FM semiconductor. Its structural, electronic, and magnetic properties are examined using density functional theory, employing the DFT+$U$ method, coupled with the PBE functional. The stability of the bilayer is examined using ab initio molecular dynamics simulations at finite temperatures up to 400 K. To ensure the stability further, the elastic constants of the system have also been investigated and we found that VSSe bilayer manifests an easy plane of magnetization similar to its monolayer counterpart. At the DFT+$U$ level, the considered VSSe bilayer exhibits a tendency towards half-metallicity with a small band gap of 0.11 eV for the majority spin carriers, and of 0.66 eV for the minority ones. To include a transition from a semiconductor to a half-metal, the bilayer is subjected to an external electric field of varying strengths normal to the plane. The lack of horizontal mirror symmetry in the bilayer allows bidirectional tuning of the band gap, with different values for the field in "upward" and "downward" directions. The band gaps for the two spin channels increase with the increasing upward electric field, while the opposite happens for the downward fields, with the majority carrier gap closing at 0.16 V/$\unicode{x212B}$, making the material a spin gapless semiconductor. Further increase in the electric field renders the material half metallic at 0.18 V/$\unicode{x212B}$. Given the fact that these values of the external electric field are achievable in the lab suggests that the FM Janus VSSe bilayer is a promising candidate for spintronic devices.

cond-mat.mtrl-sci↗

arXiv2025

Two dimensional transition metal dichalcogenide based bilayer heterojunctions for efficient solar cells and photocatalytic applications

This work presents a first-principles study of the optoelectronic properties of vertically-stacked bilayer heterostructures composed of 2D transition-metal dichalcogenides (TMDs). The calculations are performed using the density-functional theory (DFT) and many-body perturbation theory within $G_0W_0$-BSE methodology. We aim to propose these TMD heterostructures for solar cell applications. The TMD monolayers comprising the heterojunctions considered in this work are $MoS_2$, $WS_2$, $MoSe_2$, and $WSe_2$ due to their favorable band gaps, high carrier mobility, robust absorption in the visible region, and excellent stability. These four TMD monolayers provide the basis for six heterostructures. Consequently, we have examined the structural, electronic, and optical properties of six heterostructures ($WS_2/MoS_2$, $MoSe_2/MoS_2$, $MoSe_2/WS_2$, $WSe_2/MoS_2$, $WSe_2/MoSe_2$, and $WSe_2/WS_2$). At the DFT level, all the six considered TMD heterostructures meet the essential criterion of type II band alignment, a critical factor in extending carrier lifetime. However, according to $G_0W_0$ results, $MoSe_2/WS_2$ does not exhibit the type II band alignment, instead it shows type I band alignment. The large quasiparticle gaps obtained from $G_0W_0$ approximation suggest the presence of strong electron-correlation effects. The quality of these heterojunction solar cells is estimated by computing their power conversion efficiencies (PCE). The PCEs are calculated at both the HSE06 and $G_0W_0$ levels, and the maximum PCE predicted by HSE06 calculations on our designed solar cells can reach up to 19.25% for the $WSe_2/WS_2$ heterojunction. In addition, all six TMD heterostructures are examined for their potential applications in photocatalysis for hydrogen evolution reaction, and the three of them, namely, $WS_2/MoS_2$, $MoSe_2/MoS_2$, and $WSe_2/MoS_2$ heterostructures qualify for the same.

cond-mat.mtrl-sci↗

arXiv2024

Enhanced hydrogen evolution reaction activity of nitrogen deficient $hg-C_{3}N_{4}$ quantum dot

The present study investigates the catalytic performance of a $hg-C_{3}N_{4}$ quantum dot aimed at enhancing electrochemical water splitting, using the first-principles density functional theory. The size of the considered quantum dot lies within the range reported experimentally (2nm - 4nm) [Zhou et al. ACS Nano 9, 12480 (2015)]. The nitrogen vacancies are created in the considered $hg-C_{3}N_{4}$ structure to simulate the realistic scenario, as the presence of nitrogen and carbon defects are reported in the synthesized $hg-C_{3}N_{4}$ quantum dots. First, the structural and vibrational properties are computed to ensure the stability of the nitrogen deficient $hg-C_{3}N_{4}$ quantum dots, and subsequently, their electronic and hydrogen evolution reaction (HER) properties are investigated. The calculate HER parameters, i.e., adsorption energies, Gibbs free energies, and overpotentials demonstrate that the considered $hg-C_{3}N_{4}$ quantum dot with nitrogen vacancies can be used as a moderately effective electrocatalyst for HER performance. We also considered the quantum dot to be dissolved in water and ethanol, and find that the overpotential gets drastically reduced to 16 mV for the alcohol dissolved quantum dot, while some significant reduction is seen for the aqueous solution also. As a result, this study suggests that the nitrogen-deficient $hg-C_{3}N_{4}$ quantum dots dissolved in ethanol are excellent candidates for catalysis aimed at sustainable hydrogen production via electrochemical water splitting.

cond-mat.mtrl-sci↗

arXiv2023

Tuning the electronic and optical properties of hg-C$_3$N$_4$, quantum dots with edge-functionalization: A computational perspective

In this work, we have systematically investigated the structural, electronic, vibrational and optical properties of the edge-functionalized hg-C3N4 quantum dots with the aim of exploring their possible applications in solar cells and other optoelectronic devices such as light-emitting diodes. The functional groups considered in this work are methyl (-CH$_3$), fluorine (-F), and oxygenated groups such as aldehyde (-CHO), carboxyl (-COOH), ketone (-COCH$_3$), and hydroxyl (-OH) groups. The edge-functionalization resulted in significant tuning of the electronic, vibrational, and optical properties. Thus, their structural fingerprints are present in both their vibrational and optical properties, thereby allowing their detection both in the Raman as well as optical spectroscopies. It is observed that edge functionalization broadens the energy range of optical absorption, leading to coverage of most of the ultraviolet and visible regions. This implies that the edge-functionalization of hg-C$_3$N$_4$ quantum dots can be used in a variety of optoelectronic devices such as solar cells and light emitting diodes.

cond-mat.mtrl-sci↗

arXiv2023

Engineering the electronic, magnetic, and optical properties of GaP monolayer by substitutional doping: a first-principles study

In this paper we present a thorough first-principles based density functional theory study of the structural stability, electronic, magnetic, and optical properties of pristine and doped gallium phosphide (GaP) monolayers. The pristine GaP monolayer is found to have a periodically buckled structure, with an indirect band gap of 2.15 eV. The doping by X (B, Al, In, C, Si, Ge, Sn, Zn, Cd) at the Ga site, and Y (N, As, Sb, O, S, Se, Te, Zn, Cd) at the P site is considered, and an indirect to direct transition is observed after doping by In at the Ga site. For several cases, significant changes in the band gap are seen after doping, while system becomes metallic when O is substituted at the P site. The spin-polarized band structures are calculated for the monolayers with doping-induced magnetism, and we find that for some cases a direct band gap appears for one of the spin orientations. For such cases, we investigate the intriguing possibility of spin-dependent optical properties. Furthermore for several cases, the band gap is very small for one of the spin orientations, suggesting the possibility of engineering half metallicity by doping. For the layers with direct band gaps, the calculated optical absorption spectra are found to span a wide energy range in the visible and ultraviolet regions. The calculated formation energies of both the pristine and doped structures are quite small, indicating that the laboratory realization of such structures is quite feasible. On the whole, our results suggest that the doped GaP monolayer is a material with potentially a wide range of applications in nanoelectronics, spintronics, optoelectronics, solar cells, etc.

cond-mat.mtrl-sci↗