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  • Küçük Resim
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    Atomic-scale probing of defect-assisted Ga intercalation through graphene using ReaxFF molecular dynamics simulations
    (Elsevier Ltd., 2022) Nayir, Nadire; Şengül, Mert Y.; Costine, Anna L.; Reinke, Petra; Rajabpour, Siavash; Bansal, Anushka; Kozhakhmetov, Azimkhan
    We report a joint theory and experimental investigation on the defect-mediated surface interactions of gallium (Ga) metals and trimethyl-gallium (TMGa) molecules with graphene. A combination of Raman spectra, X-ray photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy (STM/STS) reveal defects in graphene, which can act as pathways for Ga intercalation. These experimental results are connected to ReaxFF simulations, which further confirm that the Ga and TMGa adsorption on graphene is strongly impacted by the presence and size of defects. These defects catalyze the surface reactions by lowering the temperature for Ga-deposition on the surface. Moreover, multivacancy defects promote Ga intercalation through graphene by reducing the kinetic barrier while the migration through single vacancy or 5-8-5 defect is kinetically hindered. The ReaxFF results indicate that TMGa exposure leads to defect healing by the passivation of carbon-dangling bonds by hydrocarbon and organometallic adducts, which is supported by the decreased Raman D:G ratio in Ga-intercalated graphene and by STM images. Since probing and controlling graphene defects constitutes a key step in the intercalation mechanism, this work provides an in-depth atomic scale understanding into the complex interplay between defects and precursors, thus providing an effective way to design defects for 2D metal fabrication.
  • Küçük Resim
    Öğe
    Development and applications of ReaxFF reactive force fields for group-III gas-phase precursors and surface reactions with graphene in metal-organic chemical vapor deposition synthesis
    (American Chemical Society, 2021) Rajabpour, Siavash; Mao, Qian; Nayir, Nadire; Robinson, Joshua A.; van Duin, Adri C.T.
    Two-dimensional (2D) materials exhibit a wide range of optical, electronic, and quantum properties divergent from their bulk counterparts. To realize scalable 2D materials, metal-organic chemical vapor deposition (MOCVD) is often used. Here, we report two ReaxFF reactive force fields, GaCH-2020 and InCH-2020, which were developed to investigate the MOCVD gas-phase reactions of Ga and In film growth from trimethylgallium (TMGa) and trimethylindium (TMIn) precursors, respectively, and the surface interactions of TMGa and TMIn with graphene. The newly developed force fields were applied to determine the optimal conditions for the thermal decomposition of TMGa/TMIn to achieve Ga/In nanoclusters with low impurities. Additionally, the cluster formation of Ga/In on a graphene substrate with different vacancies and edges was studied. It was found that a graphene with Ga-functionalized monovacancies could help conduct directional Ga cluster growth via covalent bonds. Moreover, under specific growth conditions, we found that Ga atoms growing on armchair-edged graphene not only exhibited a superior growth ratio to In atoms but also produced a widely spread 2D thin layer between graphene edges.