Few-layer Nanoplates of Bi2Se3 and Bi2Te3 with Highly Tunable Chemical Potential

TL;DR

This paper reports the synthesis of ultrathin Bi2Se3 and Bi2Te3 nanoplates with thickness down to 3 nm, demonstrating their potential for enhanced surface state effects due to high surface-to-volume ratio and tunable chemical potential.

Contribution

It introduces a catalyst-free vapor-solid growth method for ultrathin TI nanoplates and shows their effective electrical gating and chemical potential tuning.

Findings

Nanoplates have thickness down to 3 nm (3 quintuple layers).

Electrical gating effectively tunes the chemical potential.

Nanoplates exhibit thickness-dependent optical contrast.

Abstract

Topological insulator (TI) represents an unconventional quantum phase of matter with insulating bulk bandgap and metallic surface states. Recent theoretical calculations and photoemission spectroscopy measurements show that Group V-VI materials Bi2Se3, Bi2Te3 and Sb2Te3 are TI with a single Dirac cone on the surface. These materials have anisotropic, layered structures, in which five atomic layers are covalently bonded to form a quintuple layer, and quintuple layers interact weakly through van der Waals interaction to form the crystal. A few quintuple layers of these materials are predicted to exhibit interesting surface properties. Different from our previous nanoribbon study, here we report the synthesis and characterizations of ultrathin Bi2Te3 and Bi2Se3 nanoplates with thickness down to 3 nm (3 quintuple layers), via catalyst-free vapor-solid (VS) growth mechanism. Optical images reveal thickness-dependant color and contrast for nanoplates grown on oxidized silicon (300nm SiO2/Si). As a new member of TI nanomaterials, ultrathin TI nanoplates have an extremely large surface-to-volume ratio and can be electrically gated more effectively than the bulk form, potentially enhancing surface states effects in transport measurements. Low temperature transport measurements of a single nanoplate device, with a high-k dielectric top gate, show decrease in carrier concentration by several times and large tuning of chemical potential.