Near-threshold ultraviolet-laser ablation of Kapton film investigated by x-ray photoelectron spectroscopy

Abstract

Near-threshold ultraviolet-laser (355 nm) ablation of 125-μm thick Kapton films was investigated in detail using x-ray photoelectron spectroscopy. Different from the irradiation at higher fluences, the contents of the oxygen, amide group, and C–O group on the ablated surface increased with an increase in the pulse number, whereas the carbon contents decreased, although the contents of the nitrogen and the carbonyl group (C = O) decreased slightly. This implied that there was no carbon-rich residue on the ablated surface. Near the ablation threshold, only photolysis of the C–N bond in the imide rings and the diaryl ether group (C–O) took place due to a low surface temperature rise, and the amide structure and many unstable free radical groups were created. Sequentially, the oxidation reaction occurred to stabilize the free radical groups. The decomposition and oxidation mechanism could explain the intriguing changes of the chemical composition and characteristics of the ablated surface. In addition, the content of the C–O group depended on the opposite factors: the thermally induced decomposition of the ether groups and the pyrolysis of the Caryl–C bond. Upon further irradiation, the cumulative heating may induce the breakage of the Caryl–C bond and enhance the oxidation reaction, resulting in an increase of the content of the C–O group.

Thermal oxidation of PEPA-terminated polyimide

“…Finally, the peak at 288.6 eV (peak 5) corresponds to the carbonyl carbon from the imide ring. 29,31…”

“…Finally, the peak at 288.6 eV (peak 5) corresponds to the carbonyl carbon from the imide ring. 29,31 As shown in Figure 11(b), XPS spectra from the oxidized surface showed distinct differences from the interior. In particular, the shift of the carbonyl peak from 288.6 eV to 288.2 eV reflects consumption of imide rings and generation of oxidation products on the polymer surface.…”

“…The first of these peaks (peak 1), the broad peak at 284.6 eV, includes (a) the sp 2 carbon from the alkene groups of the cross-linked endcap, (b) aromatic rings that are not attached to an imide ring, and (c) aromatic carbon of the p-ODA moiety, not directly connected with N or O. 26,[28][29][30] The second peak (peak 2), at 285.2 eV, arises from (a) carbon atoms shared by the imide ring and the aromatic ring on the endcap, (b) from the C-N bond, and (c) the unsubstituted C in the PMDA aromatic ring. 31 The third peak (285.7 eV, peak 3) corresponds to the aromatic carbon connected with the imide ring in the backbone.…”

Damage-free polymer surface modification employing inward-type plasma

“…In the literature, decomposition schemes of PI by ultraviolet laser ablation have been proposed. 36,37) The plausible scheme consists of three steps: first, breakage of the -N-(CO)bond in the imide ring; second, breakage of the C-O-C in the aryl ether group; and third, decomposition of the aromatic group (see the chemical structure of PI illustrated in Fig. 2).…”