Fabrication of large addition energy quantum dots in graphene

TL;DR

This paper introduces a straightforward cryogenic method to create graphene quantum dots with large addition energies by controlled rupture, resulting in clean, substrate-free quantum dots with significant energy level spacing.

Contribution

A novel in-situ fabrication technique for graphene quantum dots that minimizes contamination and substrate effects, enabling large addition energies and level spacings.

Findings

Quantum dots with addition energy up to 180 meV

Level spacing as large as 25 meV

Suspended, contamination-free quantum dots

Abstract

We present a simple technique to fabricate graphene quantum dots in a cryostat. It relies upon the controlled rupture of a suspended graphene sheet subjected to the application of a large electron current. This results in the in-situ formation of a clean and ultra-narrow constriction, which hosts one quantum dot, and occasionally a few quantum dots in series. Conductance spectroscopy indicates that individual quantum dots can possess an addition energy as large as 180 meV and a level spacing as large as 25 meV. Our technique has several assets: (i) the dot is suspended, thus the electrostatic influence of the substrate is reduced, and (ii) contamination is minimized, since the edges of the dot have only been exposed to the vacuum in the cryostat.