Kumar, C. N. Shyam ; Konrad, Manuel ; Chakravadhanula, Venkata Sai Kiran ; Dehm, Simone ; Wang, Di ; Wenzel, Wolfgang ; Krupke, Ralph ; Kübel, Christian (2019)
Nanocrystalline graphene at high temperatures: insight into nanoscale processes.
In: Nanoscale Advances, 1 (7)
doi: 10.1039/C9NA00055K
Artikel, Bibliographie
Kurzbeschreibung (Abstract)
During high temperature pyrolysis of polymer thin films, nanocrystalline graphene with a high defect density, active edges and various nanostructures is formed. The catalyst-free synthesis is based on the temperature assisted transformation of a polymer precursor. The processing conditions have a strong influence on the final thin film properties. However, the precise elemental processes that govern the polymer pyrolysis at high temperatures are unknown. By means of time resolved in situ transmission electron microscopy investigations we reveal that the reactivity of defects and unsaturated edges plays an integral role in the structural dynamics. Both mobile and stationary structures with varying size, shape and dynamics have been observed. During high temperature experiments, small graphene fragments (nanoflakes) are highly unstable and tend to lose atoms or small groups of atoms, while adjacent larger domains grow by addition of atoms, indicating an Ostwald-like ripening in these 2D materials, besides the mechanism of lateral merging of nanoflakes with edges. These processes are also observed in low-dose experiments with negligible electron beam influence. Based on energy barrier calculations, we propose several inherent temperature-driven mechanisms of atom rearrangement, partially involving catalyzing unsaturated sites. Our results show that the fundamentally different high temperature behavior and stability of nanocrystalline graphene in contrast to pristine graphene is caused by its reactive nature. The detailed analysis of the observed dynamics provides a pioneering overview of the relevant processes during ncg heating.
| Typ des Eintrags: | Artikel |
|---|---|
| Erschienen: | 2019 |
| Autor(en): | Kumar, C. N. Shyam ; Konrad, Manuel ; Chakravadhanula, Venkata Sai Kiran ; Dehm, Simone ; Wang, Di ; Wenzel, Wolfgang ; Krupke, Ralph ; Kübel, Christian |
| Art des Eintrags: | Bibliographie |
| Titel: | Nanocrystalline graphene at high temperatures: insight into nanoscale processes |
| Sprache: | Englisch |
| Publikationsjahr: | 23 April 2019 |
| Verlag: | Royal Society of Chemistry |
| Titel der Zeitschrift, Zeitung oder Schriftenreihe: | Nanoscale Advances |
| Jahrgang/Volume einer Zeitschrift: | 1 |
| (Heft-)Nummer: | 7 |
| DOI: | 10.1039/C9NA00055K |
| URL / URN: | https://doi.org/10.1039/C9NA00055K |
| Kurzbeschreibung (Abstract): | During high temperature pyrolysis of polymer thin films, nanocrystalline graphene with a high defect density, active edges and various nanostructures is formed. The catalyst-free synthesis is based on the temperature assisted transformation of a polymer precursor. The processing conditions have a strong influence on the final thin film properties. However, the precise elemental processes that govern the polymer pyrolysis at high temperatures are unknown. By means of time resolved in situ transmission electron microscopy investigations we reveal that the reactivity of defects and unsaturated edges plays an integral role in the structural dynamics. Both mobile and stationary structures with varying size, shape and dynamics have been observed. During high temperature experiments, small graphene fragments (nanoflakes) are highly unstable and tend to lose atoms or small groups of atoms, while adjacent larger domains grow by addition of atoms, indicating an Ostwald-like ripening in these 2D materials, besides the mechanism of lateral merging of nanoflakes with edges. These processes are also observed in low-dose experiments with negligible electron beam influence. Based on energy barrier calculations, we propose several inherent temperature-driven mechanisms of atom rearrangement, partially involving catalyzing unsaturated sites. Our results show that the fundamentally different high temperature behavior and stability of nanocrystalline graphene in contrast to pristine graphene is caused by its reactive nature. The detailed analysis of the observed dynamics provides a pioneering overview of the relevant processes during ncg heating. |
| Fachbereich(e)/-gebiet(e): | 11 Fachbereich Material- und Geowissenschaften 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft > In-Situ Elektronenmikroskopie 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft > Fachgebiet Molekulare Nanostrukturen |
| Hinterlegungsdatum: | 20 Nov 2020 11:53 |
| Letzte Änderung: | 03 Dez 2020 13:11 |
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