Department of Physics

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Subject: search.filters.subject.Chemical vapor deposition

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    Strain-mediated rapid growth of vertically oriented 2D MoSe₂: Insights into the growth mechanism
    (Elsevier, 2025-11) Gangopadhyay, Subhashis
    Horizontally aligned transition metal dichalcogenides (TMDCs) are well-suited for charge transport applications, while vertically oriented TMDCs are advantageous for high surface area applications such as catalysis, water splitting, and energy storage. However, the mechanism governing these structural and morphological transition remains unclear. This study provides a comprehensive growth time profile and demonstrates that parameters such as strain, distribution of grain boundaries, randomness and interlayer distance plays the critical role in driving the desirable morphological evolution. Here, we investigate the growth dynamics of MoSe₂ thin films synthesized via chemical vapor deposition (CVD), with a focus on understanding and optimizing the horizontal-to-vertical transition as a function of growth time. Scanning electron microscopy and high-resolution transmission electron microscopy (HRTEM) were used to trace the stacking and structural order, while Raman spectroscopy and photoluminescence spectroscopy (PL) were used to investigate the variation of stacking and optical order. X-ray photoelectron spectroscopy (XPS) was used to investigate the chemical environment of the films, and field-effect transistors (FET) measurements were used to assess electrical properties such as mobility and surface carrier density. To support the experimental findings, a computational multilayer stacking framework was developed to project desirable randomness in a controlled manner through the variation of interlayer distance and simulating extent of strain mediation through wide range of unstrained, compressive, tensile and even highly diffusive strain states. This model helps to establish the relationship between the interlayer distortion and randomness with the optical asymmetry, providing insights into strain-mediated widely distributed direct to indirect optical transitions. This can further serve as an optical marker especially for these highly randomized directional vertical oriented flakes. Overall, this study presents a fundamental understanding of strain-induced morphological transitions in MoSe₂ thin films and offers a framework for tracing and tuning the optical and electronic properties in anisotropic 2D materials.
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    Chemical vapor deposition growth of large-area molybdenum disulphide (MoS2) dendrites
    (Elsevier, 2024-12) Dey, Srijata
    Molybdenum disulphide (MoS2) has emerged as a popular transition metal dichalcogenide (TMDC) in the recent decade because of its potential applications in electronic devices, optoelectronics, and fuel cells. Specifically, dendritic MoS2 has been shown to efficiently catalyse various hydrogen evolution reactions. We report the growth of dendritic MoS2 flakes on SiO2/Si wafers using a sophisticated atmospheric pressure chemical vapor deposition (APCVD) system. High-resolution optical microscopy reveals a morphology comprising different star-shaped dendrites, in addition to large MoS2 domains, which merge to form a continuous film. Our observations reveal that the dendrites originate from the nucleation centre of a monolayer MoS2 island, and their branches develop preferentially along the grain boundaries of this island. Raman spectroscopy, Atomic force microscopy (AFM), Field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS) measurements were carried out to characterize the as-grown MoS2 dendrites and further confirm these observations.
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    Formation and morphology of InGaN nanoislands on GaN(0001)
    (AIP, 2007-04) Gangopadhyay, Subhashis
    The morphology and density of InGaN nanoislands can be controlled by the choice of proper growth conditions for metal organic vapor phase epitaxy. Scanning tunneling microscopy has been used to investigate the dependence of InGaN island morphology on the growth parameters. A heterogeneous nucleation of large InGaN islands with a complex structure is observed after growth at in conjunction with a high In partial pressure. For and low In partial pressure, however, the homogeneous nucleation of small islands of sizes suitable for three-dimensional quantum confinement is found, with very high densities of ⁠. The influence of the growth temperature and the In partial pressure is discussed in terms of thermally activated diffusion and surface mobility.