Modified-edge-support heat treatment method of polyimide for crystalline, large-area, and self-standing ultrathin graphite films

• Published in: Carbon (New York) Vol. 181; pp. 348 - 357
• Main Authors: Murashima, Kensuke, Kawashima, Yuki, Ozaki, Shuhei, Tatami, Atsushi, Tachibana, Masamitsu, Watanabe, Takeo, Harada, Tetsuo, Murakami, Mutsuaki
• Format: Journal Article
• Language: English
• Published: New York Elsevier Ltd 30.08.2021; Elsevier BV
• Subjects: Basal plane; Chemical vapor deposition; Edge-support method; electrical conductivity; Electrical resistivity; graphene; Graphite; Graphite ultrathin film; Heat conductivity; Heat treatment; Large-area graphite film; Modulus of elasticity; Nanoparticles; oxygen; Polyimide heat treatment method; Reactive ion etching; Self-standing graphite film; tensile strength; Thickness; Thin films; Ultimate tensile strength; Graphite ultrathin film; Large-area graphite film; Edge-support method; Polyimide heat treatment method; Self-standing graphite film
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/j.carbon.2021.05.036

Using a newly developed edge-support heat treatment method of polyimide, self-standing graphite thin films (GTFs) with a frame were prepared. The graphite basal plane in the GTF was oriented in the direction of the film surface, resulting in GTFs with high quality, large area, and a uniform thickness of 50–120 nm. The thickness distribution (3σ) with an area of 25 mm × 25 mm and a thickness of 54 nm sample was 5.17 nm (measurement area 7.8 mm × 10.4 mm). The electric conductivity of a similarly prepared sample was 1.81 × 104 S/cm. The Young's modulus and ultimate tensile strength of a 60-nm-thick GTF were 1.02 × 102 and 5.34 GPa, respectively. Approximately 50 nm thick GTF samples were thinned by reactive ion etching using oxygen to fabricate a thickness between 10 and 20 nm. A film with an area of 10 mm × 10 mm and thickness of 16.7 nm exhibited a 3σ value of 1.80 nm which means that the thickness difference corresponds to 5 layers of graphite. The conductivity of a 16.2-nm-thick GTF was 1.79 × 104 S/cm. These results indicate that the etching proceeded uniformly. The proposed top-down method is an industrially superior method that overcomes the drawbacks of conventional bottom-up methods. Using a modified ES method of polymer HT and its combination with RIE, crystalline GTFs at a thickness of 10–120 nm with an area within the cm scale were successfully fabricated. The GTF was fabricated with no substrate and exhibited good crystallinity, excellent thickness uniformity at the ±10% level, no wrinkles, and higher Young's modulus and UTS. Photograph of the produced GTF with 16.7 nm thick (a) and 25 × 25 mm2 area. and with 10.7 nm thick and 10 × 10 mm2 area (b). [Display omitted]