Confined Electron and Hole States in Semiconducting Carbon Nanotube sub-10 nm Artificial Quantum Dots

Abstract

We show that quantum confinement in the valence and conduction bands of semiconducting single-walled carbon nanotubes can be engineered by means of artificial defects. This ability holds potential for designing future nanotube-based quantum devices such as electrically driven room-temperature single-photon sources emitting at telecom-wavelength. Using Ar$^{+}$ and N$^{+}$ ion-induced defects, intrananotube quantum dots with sub-10 nm lateral sizes are created, giving rise to quantized electronic bound states with level spacings of the order of 100 meV and larger. Using low-temperature scanning tunneling spectroscopy, we resolve the energy and real space properties of the quantized states and compare them with theoretical model calculations. By solving the Schr\"odinger equation over a one-dimensional piecewise constant potential model, the effects of inhomogeneous defect scattering strength as well as surface variations in the Au(111) substrate on the quantized states structure are remarkably well reproduced. Furthermore, using ab-initio calculations, we demonstrate that defect structures such as vacancies, di-vacancies and chemisorbed nitrogen ad-atoms constitute strong scattering centers able to form quantum dots with clear signatures of discrete bound states as observed experimentally. The ab-initio simulations also allowed to study the scattering strength profile as a function of energy for different defect combinations, supporting the potential of highly stable double vacancies for practical applications at room temperature.