ScholarWorks@경상국립대학교

초록

Electron-beam irradiation of carbon materials induces apparently paradoxical structural transformations: amorphous carbon evolves into more ordered configurations, whereas crystalline graphite undergoes amorphization. Although such behavior has been widely reported, ordering and amorphization have typically been treated as separate phenomena, and the dominant mechanism governing these transformations remains unresolved. Here, we investigate electron-beam-induced phase transformations in carbon by comparing glassy carbon and highly oriented pyrolytic graphite (HOPG) as representative amorphous and crystalline allotropes, respectively, under identical 300-keV transmission electron microscopy irradiation conditions. Glassy carbon reorganizes into carbon nano-onions at both current densities, whereas HOPG undergoes amorphization. Most notably, amorphized HOPG does not remain structurally static but subsequently transitions to turbostratic graphite. This sequential amorphization–ordering behavior strongly indicates the need for a unified mechanism capable of encompassing these opposing transitions. By combining finite-element thermal analyses with Monte Carlo simulations, we show that these transformation sequences arise from the interplay between beam heating and thermal transport. Localized beam heating, driven by Auger-electron energy dissipation, promotes structural reorganization, while thermal conductivity governs the balance between heating-assisted ordering and beam-induced disordering. Glassy carbon and amorphized graphite, both characterized by low thermal conductivity, readily accumulate heat under irradiation and therefore favor structural ordering, whereas HOPG exhibits high thermal conductivity, facilitating rapid heat dissipation and thereby favoring beam-induced disorder and amorphization. Together, these findings establish a unified mechanistic framework for irradiation-induced structural ordering and amorphization in carbon materials.

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