arXiv subjects

Anagha Gopinath

Publications and source records attributed to Anagha Gopinath.

3 recordsLinked to original sources

arXiv2026

Charge transfer mediated anomalous photoluminescence enhancement in monolayer MoS2 graphene heterostructure via polystyrene assisted wet transfer

Van der Waals MoS2 graphene heterostructures are compelling candidates for high performance electronic and optoelectronic device applications. However, the interlayer charge transfer typically quenches the photoluminescence of monolayer MoS2, limiting the use of these heterostructures in light emitting applications. In this work, we report an anomalous photoluminescence enhancement in n-type monolayer MoS2 by integrating it with monolayer graphene via polystyrene assisted wet transfer process. Photoluminescence spectroscopy reveals a dominant trion to exciton conversion in the heterostructure. Kelvin probe force microscopy shows a 600 meV increase in the work function of MoS2 upon heterostructure formation. This work function shift, together with the higher work function of graphene, signifies electron transfer from MoS2 to graphene. Shifts in the graphene G and 2D Raman modes further corroborate the interlayer charge transfer. Hydroxyl and epoxy functionalization of graphene following heterostructure formation is evidenced by X ray photoelectron spectroscopy. DFT based Bader charge analysis quantifies the role of these functional groups in facilitating interlayer charge transfer. Collectively, our findings establish polystyrene assisted wet transfer as a practical interface engineering strategy for enhancing excitonic emission in MoS2 graphene heterostructures, thereby advancing their potential for scalable optoelectronic devices.

cond-mat.mes-hall↗

arXiv2026

Nanoscale mapping of stacking-dependent work function and local photoresponse in CVD-grown MoS2 bilayers by KPFM

Stacking order in bilayers of transition metal dichalcogenides (TMDs) controls structural symmetry and layer-to-layer interactions, offering a direct route to tune their electronic properties and enable optoelectronic applications. The work function is a key parameter that determines the electronic and optoelectronic device performance. However, a comprehensive understanding of the influence of stacking order on work function of TMDs remains limited. Herein, we employ Kelvin Probe Force Microscopy (KPFM) to probe spatial variations in surface potential and thereby determine the work function of AA'- and AB-stacked MoS2 bilayers grown using NaCl-assisted chemical vapor deposition (CVD) technique. The work function increases with layer number in both AA'- and AB-stacked MoS2, with a larger work function difference in AB-stacked layers, reflecting their stronger interlayer coupling. KPFM measurements clearly resolve local electronic heterogeneities arising from carrier trapping at residual surface particulates from CVD growth. Photoinduced surface potential variations imply n-type doping in MoS2 due to enhanced photogating from trapped holes and Na+ ions at the MoS2/SiO2 interface. Our study demonstrates the competing effects of interlayer coupling, substrate-induced photogating, and carrier trapping by surface particulates in determining the localized optoelectronic response of MoS2 bilayers. Correlative atomic force microscopy measurements in lateral force microscopy and force modulation microscopy modes probe the nanomechanical response to electronic variations. These findings provide new insights into the localized optoelectronic response of CVD-grown AA'- and AB-stacked MoS2, with significant implications for the design and reliability of optoelectronic devices.

cond-mat.mes-hall↗

arXiv2025

High-energy electron-beam induced defect engineering of monolayer MoS2 for tunable optical properties

Structural defects in 2D-transition metal dichalcogenides are critical in modulating their optical and electrical behavior. Nevertheless, precise defect control within the monolayer regime poses a significant challenge. Herein, a high-energy (1MeV) electron beam irradiation strategy is harnessed to induce defects in monolayer MoS2. Controlled variation of electron-beam irradiation time tunes the defect density, as reflected by the evolution of defect-mediated photoluminescence characteristics. The optically active defect emission appearing at approx. 200-300meV below the A exciton at 85K exhibits a systematic increase in intensity with prolonged exposure and saturates at higher laser excitation power. Circular polarization-resolved photoluminescence spectroscopy reveals strong suppression of valley polarization of the A exciton after irradiation. Complementary x-ray photoelectron spectroscopy identifies enhanced Mo-O bonding signatures in MoS2 following irradiation. Kelvin probe force microscopy indicates the transition to p-type doping behaviour. A detailed temperature and power-dependent photoluminescence measurements further elucidate the optical behaviour of these defect states. Density functional theory calculations using these configurations establish that the transition between the conduction band and acceptor states within the bandgap accounts for the defect emission. This work presents a tunable route for defect engineering in monolayer TMDs, enabling controlled tailoring of their structural and optical properties for optoelectronic, electronic and valleytronic applications.

cond-mat.mes-hall↗