Browsing by Author "Anupam Giri"

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Large-Area Epitaxial Film Growth of van der Waals Ferromagnetic Ternary Chalcogenides
(John Wiley and Sons Inc, 2021) Anupam Giri; Chandan De; Manish Kumar; Monalisa Pal; Hyun Hwi Lee; Jun Sung Kim; Sang-Wook Cheong; Unyong Jeong
Following the first experimental realization of intrinsic ferromagnetism in 2D van der Waals (vdW) crystals, several ternary metal chalcogenides with unprecedented long-range ferromagnetic order have been explored. However, the synthesis of large-area 2D ternary metal chalcogenide thin films is a great challenge, and a generalized synthesis has not been demonstrated yet. Here, a quick and scalable synthesis of epitaxially aligned ferromagnetic ternary metal chalcogenide thin films (Cr2Ge2Te6, Cr2Si2Te6, Mn3Si2Te6) is reported. The synthesis is based on the flux-controlled surface diffusion of Te on metal (Cr, Mn)-deposited wafer (Ge, Si) substrates. Magnetic anisotropy study of the epitaxial ternary thin films reveals the intrinsic magnetic easy axis; out-of-plane direction for Cr2Ge2Te6 and Cr2Si2Te6, and in-plane direction for Mn3Si2Te6. In addition to the synthesis, this work creates an opportunity for transfer-free device fabrication for realizing magnetoelectronics based on the electrical control of both charge and spin degrees of freedom in 2D ferromagnetic semiconductors. © 2021 Wiley-VCH GmbH.
One-Step Room Temperature Synthesis of Printable Carbon Quantum Dots Ink for Visual Encryption and High-Performance Photodetector
(John Wiley and Sons Inc, 2024) Baishali Thakurta; Sobhan Hazra; Alapan Samanta; Adnan Nasir; Amresh Kumar Singh; Deepak Maurya; Bama Charan Mondal; Anupam Giri; Bhola Nath Pal; Monalisa Pal
Carbon quantum dots (CQDs) have emerged as promising materials for optoelectronic applications and have garnered much interest as potential competitors to conventional inorganic or hybrid semiconductor quantum dots because of carbon's intrinsic merits of high stability, low cost, and environment-friendliness. The ability of easy formulation of functional ink of CQDs is necessary for the development of industrial-scale, reliable, inexpensive printing/coating processes, for its full exploitation in the ever-growing class of applications in sensors, optoelectronics, and energy storage and conversion. Here a facile one-step room-temperature synthesis of printable, fluorescent CQD ink is demonstrated. The as-synthesized fluorescent CQD ink is used for invisible fingerprint stamps, printing of micro-patterns, and soft lithographic patterning with a resolution down to 1.5 µm. This functional CQD ink is also used to fabricate a high-performance CQD-ZnO heterojunction ultraviolet (UV) photodetector with a photo-responsivity of 3.85 A W−1, detectivity of 6.78 × 1010 Jones, and an external quantum efficiency (EQE) of 15.3%. The enhanced device performance can be attributed to CQD's high photocurrent generation efficiency and rational combination of the asymmetric electrode materials. This work enables a high-temperature stable CQD fluorescent ink synthesis method to fulfill the processing requirements of printing and soft lithographic patterning for visual encryption and optoelectronics. © 2024 Wiley-VCH GmbH.
Plasmonic Grating on Monolayer MoS2for Strong Photoluminescence Enhancement and Ultrasensitive Surface-Enhanced Raman Scattering (SERS) Detection
(American Chemical Society, 2025) Chetna Gautam; Sandeep Yadav; Abhay Kumar; Monalisa Pal; Anup Kumar Ghosh; Anupam Giri
Monolayer MoS2, a key 2D transition metal dichalcogenide (TMDC), offers strong potential for next-generation optoelectronic devices due to its direct bandgap and tunable optical properties. However, its ultrathin structure results in inherently weak light–matter interactions and limited photoluminescence (PL) output. Here, we demonstrate a scalable strategy for enhancing the optical response of monolayer MoS2using plasmonic nanoresonators patterned via capillary-force-assisted assembly of the thermoresponsive polymer poly(ε-caprolactone) (PCL), eliminating complex nanofabrication. Subsequent deposition of plasmonic metals (Au, Ag, Al) forms well-defined resonator arrays, enabling sequential fabrication of multiple patterns on a single layer. Optimized Au gratings (818 nm width, 2.6 nm thickness) achieved over 390-fold PL enhancement through efficient exciton–plasmon coupling. Moreover, the crossbar-type Au–Au gratings on MoS2exhibited remarkable surface-enhanced Raman scattering (SERS) sensitivity, enabling detection of rhodamine 6G down to 10–18M. This practical approach significantly amplifies light–matter interactions in 2D materials, advancing their integration into flexible photonic, sensing, and optoelectronic systems. © 2025 American Chemical Society
Surface Diffusion and Epitaxial Self-Planarization for Wafer-Scale Single-Grain Metal Chalcogenide Thin Films
(John Wiley and Sons Inc, 2021) Anupam Giri; Manish Kumar; Jaeseon Kim; Monalisa Pal; Writam Banerjee; Revannath Dnyandeo Nikam; Junghyeok Kwak; Minsik Kong; Seong Hun Kim; Kaliannan Thiyagarajan; Geonwoo Kim; Hyunsang Hwang; Hyun Hwi Lee; Donghwa Lee; Unyong Jeong
Although wafer-scale single-grain thin films of 2D metal chalcogenides (MCs) have been extensively sought after during the last decade, the grain size of the MC thin films is still limited in the sub-millimeter scale. A general strategy of synthesizing wafer-scale single-grain MC thin films by using commercial wafers (Si, Ge, GaAs) both as metal source and epitaxial collimator is presented. A new mechanism of single-grain thin-film formation, surface diffusion, and epitaxial self-planarization is proposed, where chalcogen elements migrate preferentially along substrate surface and the epitaxial crystal domains flow to form an atomically smooth thin film. Through synchrotron X-ray diffraction and high-resolution scanning transmission electron microscopy, the formation of single-grain Si2Te3, GeTe, GeSe, and GaTe thin films on (111) Si, Ge, and (100) GaAs is verified. The Si2Te3 thin film is used to achieve transfer-free fabrication of a high-performance bipolar memristive electrical-switching device. © 2021 Wiley-VCH GmbH
Wafer scale growth of single crystal two-dimensional van der Waals materials
(Royal Society of Chemistry, 2024) Chetna Gautam; Baishali Thakurta; Monalisa Pal; Anup Kumar Ghosh; Anupam Giri
Two-dimensional (2D) van der Waals (vdW) materials, including graphene, hexagonal boron nitride (hBN), and metal dichalcogenides (MCs), form the basis of modern electronics and optoelectronics due to their unique electronic structure, chemical activity, and mechanical strength. Despite many proof-of-concept demonstrations so far, to fully realize their large-scale practical applications, especially in devices, wafer-scale single crystal atomically thin highly uniform films are indispensable. In this minireview, we present an overview on the strategies and highlight recent significant advances toward the synthesis of wafer-scale single crystal graphene, hBN, and MC 2D thin films. Currently, there are five distinct routes to synthesize wafer-scale single crystal 2D vdW thin films: (i) nucleation-controlled growth by suppressing the nucleation density, (ii) unidirectional alignment of multiple epitaxial nuclei and their seamless coalescence, (iii) self-collimation of randomly oriented grains on a molten metal, (iv) surface diffusion and epitaxial self-planarization and (v) seed-mediated 2D vertical epitaxy. Finally, the challenges that need to be addressed in future studies have also been described. © 2024 The Royal Society of Chemistry.
Wafer-scale synthesis of two-dimensional ultrathin films
(Royal Society of Chemistry, 2023) Amresh Kumar Singh; Baishali Thakurta; Anupam Giri; Monalisa Pal
Two-dimensional (2D) materials, consisting of atomically thin layered crystals, have attracted tremendous interest due to their outstanding intrinsic properties and diverse applications in electronics, optoelectronics, and catalysis. The large-scale growth of high-quality ultrathin 2D films and their utilization in the facile fabrication of devices, easily adoptable in industrial applications, have been extensively sought after during the last decade; however, it remains a challenge to achieve these goals. Herein, we introduce three key concepts: (i) the microwave assisted quick (∼1 min) synthesis of wafer-scale (6-inch) anisotropic conducting ultrathin (∼1 nm) amorphous carbon and 2D semiconducting metal chalcogenide atomically thin films, (ii) a polymer-assisted deposition process for the synthesis of wafer-scale (6-inch) 2D metal chalcogenide and pyrolyzed carbon thin films, and (iii) the surface diffusion and epitaxial self-planarization induced synthesis of wafer-scale (2-inch) single crystal 2D binary and large-grain 2D ferromagnetic ternary metal chalcogenide thin films. The proposed synthesis concepts can pave a new way for the manufacture of wafer-scale high quality 2D ultrathin films and their utilization in the facile fabrication of devices. © 2024 The Royal Society of Chemistry.