Inherent Surface Properties of Adsorbent-Free Ultrathin Bi2Se3 Topological Insulator Platelets

Mesoporous Semiconductive Bi2Se3 Films

Bi₂Se₃ is a semiconductive material possessing a bandgap of 0.3 eV, and its unique band structure has paved the way for diverse applications. Herein, we demonstrate a robust platform for synthesizing mesoporous Bi₂Se₃ films with uniform pore sizes via electrodeposition. Block copolymer micelles act as soft templates in the electrolyte to create a 3D porous nanoarchitecture. By controlling the length of the block copolymer, the pore size is adjusted to 9 and 17 nm precisely. The nonporous Bi₂Se₃ film exhibits a tunneling current in a vertical direction of 52.0 nA, but upon introducing porosity (9 nm pores), the tunneling current increases significantly to 684.6 nA, suggesting that the conductivity of Bi₂Se₃ films is dependent on the pore structure and surface area. The abundant porous architecture exposes a larger surface area of Bi₂Se₃ to the surrounding air within the same volume, thereby augmenting its metallic properties.

Silica Coated Bi2Se3 Topological Insulator Nanoparticles: An Alternative Route to Retain Their Optical Properties and Make Them Biocompatible

Localized surface plasmon resonance (LSPR) is the cause of the photo-thermal effect observed in topological insulator (TI) bismuth selenide (Bi₂Se₃) nanoparticles. These plasmonic properties, which are thought to be caused by its particular topological surface state (TSS), make the material interesting for application in the field of medical diagnosis and therapy. However, to be applied, the nanoparticles have to be coated with a protective surface layer, which prevents agglomeration and dissolution in the physiological medium. In this work, we investigated the possibility of using silica as a biocompatible coating for Bi₂Se₃ nanoparticles, instead of the commonly used ethylene-glycol, which, as is presented in this work, is not biocompatible and alters/masks the optical properties of TI. We successfully prepared Bi₂Se₃ nanoparticles coated with different silica layer thicknesses. Such nanoparticles, except those with a thick, ≈200 nm silica layer, retained their optical properties. Compared to ethylene-glycol coated nanoparticles, these silica coated nanoparticles displayed an improved photo-thermal conversion, which increased with the increasing thickness of the silica layer. To reach the desired temperatures, a 10-100 times lower concentration of photo-thermal nanoparticles was needed. In vitro experiments on erythrocytes and HeLa cells showed that, unlike ethylene glycol coated nanoparticles, silica coated nanoparticles are biocompatible.

Hydrothermal synthesis of Bi2Se3 nanosheets by using gallic acid as a reductant

In this work, a simple and reproducible hydrothermal synthesis was employed to synthesize two-dimensional Bi2Se3 nanosheets by using gallic acid as a reductant. Meanwhile, the effects of the amounts of gallic acid and sodium hydroxide and the surfactant Triton X-100 on phase composition and morphology of the obtained Bi2Se3 were also studied. The results reveal that gallic acid could effectively reduce Se4+ to Se2- and gave rise to the formation of Bi2Se3. Additionally, keeping the reaction conditions of molar ratio of gallic acid to the precursor elements (Bi + Se) at 1 to 1 (or higher) and using strong alkaline solutions were the key factors to synthesize high purity crystalline Bi2Se3 nanosheets. Furthermore, flower-like Bi2Se3 composed of nanosheets with a dozen nanometer thickness could be easily fabricated by adding appropriate amounts of Triton X-100. This work provides a novel approach for synthesis of ultra-thin Bi2Se3 nanosheets in a controllable manner.