We report the growth of bismuth telluride, Bi 2 Te 3 , nanoplatelets on flexible polyimide films (Kapton films), using a chemical vapor transport process. Hexagonal, triangular, and ribbon-shaped nanoplatelets can be routinely synthesized on Kapton films. We developed a dry transfer technique to transfer these as-grown nanoplatelets from the Kapton films onto SiO 2 (300 nm)/Si substrates for atomic force microscopy (AFM) characterization. The thickness of the as-grown nanoplatelets is 10-100 nm, and thinner than those grown on glass and silicon susbtrates. We further suggest the possible growth mechanism based on our AFM obervations. Owning to their unique crystal structure, universal van der Waals epitaxy 12,13 is the applied principle for synthesizing 2D nano sheets of these topological insulator chalcogenides, and consequently their unusual properties arise. The crystal has a rhombohedral structure 12,15 with space group D 5 3d (R3m), 12,15 and it is a layered structure in which individual layers consist of atoms of one kind. A five atomic layer stacking, in the order of Te (1) -Bi-Te (2) -Bi-Te (1) along the c-axis, forms a ∼1 nm thick, charge-neutral sheet, i.e., a quintuple sheet.12,15 These quintuple sheets constitute the stacking units in the crystal, and the bonding between neighboring quintuple sheets (i.e., between adjacent Te (1) layers) is a weak van der Waals interaction. Van der Waals epitaxy of these topological insulator chalcogenides results in an in-plane growth rate much faster than an out-of-plane growth rate, and crystal growths can be achieved regardless of lattice mismatches between these 2D nano sheets and substrates.Nanoplatelets of Bi 2 Te 3 and other related chalcogenides have thus far been synthesized by chemical vapor transport, 12,13 molecular beam epitaxy, 16 and hydro/solvothermal processes. 7,8,17 Solution processes are facile, scalable, and can produce nanoplatelets of high crystallinity, but they lack size and position control. These drawbacks make this method unsuitable for micro/nano-device applications. Instead, vapor phase growths (chemical vapor transport or molecular beam epitaxy) produce nanoplatelets with high crystallinity and good thickness control; consequently, they are preferable for practical micro/nano-devices. Recently, Peng, Liu, and coworkers 13 have synthesized Bi 2 Te 3 and Bi 2 Se 3 nanoplatelets on a mica surface using a facile chemical vapor transport method. Precise orientation and position control of those nanoplatelets further demonstrated their potential as flexible infrared transparent electrodes.18 Towards future device applications, one of the imperative tasks is to grow these topological insulator nanoplatelets on low-cost and flexible plastic substrates.
