Vapor Phase Growth of Bismuth Telluride Nanoplatelets on Flexible Polyimide Films

Abstract

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.

Solution-Based Synthesis and Processing of Metal Chalcogenides for Thermoelectric Applications

“…Currently, several methods for production of 2D metal chalcogenides have been developed, including the bottom-up synthesis by vapor-phase deposition [27,35,36], solvothermal method [37], and top-down approach by micromechanical cleavage [38]. However, those methods always suffer from harsh conditions such as high vacuum, high temperature, and/or slow throughput.…”

“…Nevertheless, the low production yield and small lateral size (typically less than 10 µm) of the exfoliated specimens hamper the practical application of this method. Synthetic approaches based on gas-phase processes such as chemical vapor deposition (CVD) [24][25][26][27] and molecular beam epitaxy growth [28,29] have been successfully applied to produce defectless, uniform thin films of metal chalcogenide materials. However, high-temperature and high-vacuum reaction conditions as well as specific substrates are required for the material growth.…”

Mechanism of Bismuth Telluride Exfoliation in an Ionic Liquid Solvent

“…This nanosheet, lying in the xy plane, was copied and repeatedly shifted in the z direction normal to the xy plane to form a four-layer stack of identical quintuple sheets. A hexagonal cross section was chosen because this is the dominant shape seen in experimental studies. , Each hexagonal quintuple layer had an approximate cross-sectional area of 379 Å 2 , 100 atoms total, a Bi/Te ratio of 2:3, and a net zero electrostatic charge. The Bi 2 Te 3 system was equilibrated in the NVT ensemble (in vacuum) for 100 ps at 298 K in a simulation box of 6 × 6 × 12 nm 3 .…”

Molecular Dynamics Simulation of Bismuth Telluride Exfoliation Mechanisms in Different Ionic Liquid Solvents

“…Currently, vapor-phase deposition , or liquid-phase synthesis , can produce two-dimensional (2D) nanosheets of Bi 2 Te 3 . However, we focus on liquid-phase synthesis, since it can potentially provide an economical route for large-scale production, and there is very little information available about the interaction of these materials with different liquid solvents.…”