Fabrication and Characterization of Topological Insulator Bi$_2$Se$_3$ Nanocrystals

TL;DR

This paper reports the fabrication of ultra-thin Bi$_2$Se$_3$ nanocrystals, characterizes their properties, and provides a method for their production and thickness measurement, advancing nanoscale topological insulator research.

Contribution

It introduces a mechanical exfoliation technique to produce 2 nm thick Bi$_2$Se$_3$ nanocrystals and identifies a Raman spectral feature for thickness characterization.

Findings

Emergence of an additional Raman mode below 10 nm thickness

Successful fabrication of 2 nm thick nanocrystals

Provides a recipe for production and characterization of Bi$_2$Se$_3$ nanocrystals

Abstract

In the recently discovered class of materials known as topological insulators, the presence of strong spin-orbit coupling causes certain topological invariants in the bulk to differ from their values in vacuum. The sudden change of invariants at the interface results in metallic, time reversal invariant surface states whose properties are useful for applications in spintronics and quantum computation. However, a key challenge is to fabricate these materials on the nanoscale appropriate for devices and probing the surface. To this end we have produced 2 nm thick nanocrystals of the topological insulator Bi$_2$Se$_3$ via mechanical exfoliation. For crystals thinner than 10 nm we observe the emergence of an additional mode in the Raman spectrum. The emergent mode intensity together with the other results presented here provide a recipe for production and thickness characterization of Bi$_2$Se$_3$ nanocrystals.