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Electron beam-induced polymerization (EBIP) has been widely explored in coatings, adhesives, and nanostructure fabrication, relying on electron irradiation to generate reactive species that initiate polymerization via radical pathways [1]. While its efficiency in solid and thin-film systems is well established [2], real-time observation of gas-phase polymerization at the nanoscale remains challenging due to the lack of suitable experimental platforms. In this study, we employ a custom-built ultrathin (UT) membrane gas-cell chip for in-situ closed-cell environmental transmission electron microscopy (ETEM). This platform offers enhanced reciprocal and spectral visibility, enabling precise tracking of crystallinity through diffraction patterns and gas composition through electron energy loss spectroscopy (EELS) [3-5]. By allowing real-time observation of polymerization kinetics under controlled electron irradiation, this work aims to elucidate the fundamental mechanisms governing EBIP in the gas phase, addressing a critical knowledge gap in electron beam-driven chemical reactions. 

2D nanomaterials have garnered significant attention due to their unique physicochemical properties. MXene, a type of twodimensional transition metal carbide, nitride, or carbonitride, has become a focal point in materials science due to its excellent metallic conductivity, tunable chemical functional groups, outstanding mechanical properties, and unique surface chemistry [1,2]. Compared to traditional metal oxides, MXenes exhibit superior mechanical strength and flexibility, making them ideal candidates for high-performance energy storage devices (such as lithium-ion batteries and supercapacitors) as well as flexible electronic devices [3]. However, there are still some limitations, such as the self-stacking phenomenon, which restricts the improvement of its performance. Researchers have gradually expanded various types of MXene structures, enhancing their value in fields such as energy, electronics, sensing, nanofluids, computing, and the environment by tuning the element composition, surface functional groups, interlayer structure, and composite structure design [4,5]. 

Environmental transmission electron microscopy (E-TEM) enables direct observation of nanoscale chemical processes crucial for catalysis and materials design. However, the high-energy electron probe can dramatically alter reaction pathways through radiolysis, the dissociation of molecules under electron beam irradiation. While extensively studied in liquid-cell TEM, the impact of radiolysis in gas phase reactions remains unexplored. Here, we present a numerical model elucidating radiation chemistry in both gas and liquid E-TEM environments. Our findings reveal that while gas phase E-TEM generates radiolytic species with lower reactivity than liquid phase systems, these species can accumulate to reaction-altering concentrations, particularly at elevated pressures. We validate our model through two case studies: the radiation-promoted oxidation of aluminum nanocubes and disproportionation of carbon monoxide. In both cases, increasing the electron beam dose rate directly accelerates their reaction kinetics, as demonstrated by enhanced AlOx growth and carbon deposition. Based on these insights, we establish practical guidelines for controlling radiolysis in closed-cell nanoreactors. This work not only resolves a fundamental challenge in electron microscopy but also advances our ability to rationally design materials with subÅngstrom resolution.