[2D01-04] Thin Film (TF)

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[2D02] Vacuum synthesis of layered borophene oxide thin films exhibiting a thermotropic liquid-crystalline phase transition

*Keita Sasaki¹, Kenichi Kaminaga¹, Hibiki Murakami¹, Shunsuke Shimizu², Takeharu Yoshii², Fumitsuna Teshima³, Ayumu Kikuchi¹, Shingo Maruyama⁴, Kiyohisa Tanaka³, Hirotomo Nishihara^2,5, Yuji Matsumoto¹ (1. Department of Applied Chemistry, Tohoku University (Japan), 2. Institute of Multidisciplinary Research for Advanced Materials (Japan), 3. UVSOR Synchrotron Facility, IMS (Japan), 4. Department of Electronics and Materials Science, Shizuoka University (Japan), 5. Advanced Institute for Materials Research (WPI-AIMR). (Japan))

Layered borophene oxide (BoL, B_4.27KO₃) has recently emerged as the first inorganic thermotropic liquid crystal (LC). Its high thermal and chemical stability make it attractive for harsh-environment devices, but BoL has so far been synthesized only as a bulk material. The thin-film fabrication is hence essential for inorganic-LC device integration. Here, we report the vacuum-synthesis of BoL thin films and their thermotropic LC phase transition. The films were fabricated by continuous-wave infrared laser deposition of KBH₄ in MeCN vapor. XRD and XPS confirmed the formation of layered BoL-C thin films with an out-of-plane periodicity and B chemical state consistent with that of bulk BoL. Upon heating, FT-IR and polarized optical microscopy revealed a dehydration-driven transition to the LC phase at 60–70°C, approximately 50°C lower than that of bulk BoL. This lowered transition temperature provides a practical advantage for BoL-based inorganic-LC applications.

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