In situ synchrotron X-ray scission of polytetrafluoroethylene chains and elucidation of dry etching

Kaito Fujitani; Kento Takenaka; Koji Takahara; Hirosuke Sumida; Akinobu Yamaguchi; Yuichi Utsumi; Satoru Suzuki

doi:10.1016/j.heliyon.2023.e15794

In situ synchrotron X-ray scission of polytetrafluoroethylene chains and elucidation of dry etching

Heliyon. 2023 Apr 29;9(5):e15794. doi: 10.1016/j.heliyon.2023.e15794. eCollection 2023 May.

Authors

Kaito Fujitani¹, Kento Takenaka², Koji Takahara¹, Hirosuke Sumida³, Akinobu Yamaguchi¹, Yuichi Utsumi¹, Satoru Suzuki¹

Affiliations

¹ Laboratory of Advanced Science and Technology for Industry, University of Hyogo, 3-1-2 Kouto, Kamigori, Ako, Hyogo 678-1205, Japan.
² Graduate School of Science, University of Hyogo, 3-2-1 Koto, Kamigori, Ako, Hyogo 678-1297, Japan.
³ Mazda Motor Corp., 3-1, Shinchi, Fuchu, Aki, Hiroshima 730-8670, Japan.

Abstract

We investigated the mechanism of polytetrafluoroethylene (PTFE) chain scission through in situ hard X-ray photoelectron spectroscopy at room temperature, 200 °C, and 230 °C. The C-C bonds in the main chain and C-F bonds in the side chains were broken, and F desorption from the PTFE surface was observed at room temperature. The formation of CF₃ was also observed from the recombination of broken C-C bonds in the main chain and detached F, which were not induced by soft X-rays. In contrast, when the PTFE substrate was irradiated with hard X-rays at 200 °C, the CF₃ intensity initially produced by recombination reactions decreased with irradiation time, and the photoelectron spectrum retained the original PTFE spectrum. Under these conditions, the F1s/C1s intensity ratio did not change with the irradiation time; hence, the fragment containing only CF₂, the chemical composition of the original PTFE, was desorbed. When the substrate temperature was 230 °C, the CF₃ intensity increased in relation to that at 200 °C. This result indicated that the formation of CF₃ via recombination reactions of broken molecular chains is enhanced by thermal assistance. These phenomena were considered to be based on the balance between recombination and desorption by photochemical and pyrochemical reactions. These results will lead to a better understanding of the use of X-ray-irradiated fluorine resins and PTFE in potential space-based environments. This study will also promote the improvement of PTFE microfabrication methods and thin-film formation using synchrotron radiation.

Keywords: HAXPES; PTFE; Polytetrafluoroethylene; Synchrotron radiation.