Quantification of graphene based core/shell quantum dots from first principles

Abstract

Density functional calculations are performed to study the electronic structure of recently proposed graphene/graphane based core/shell quantum dots, which have a type I band alignment and exhibit quantized carrier energy levels. Strong confinement is robust with shell thickness. The bandgap, band offset, and the number of confined carrier orbitals with different size and geometry are determined. Our findings indicate that these core/shell dots are potentially well suited for the design of advanced diode lasers and room-temperature single electron devices. The proposed method to determine the number of confined orbitals is applicable for other quantum dot systems.

Electronic Structures of Clusters of Hydrogen Vacancies on Graphene

“…Energy gap between the HOMO and LUMO drops from 2.56 eV for the cluster of 24 C atoms to 1.73 eV for the cluster of 54 C atoms, both close to the values reported in Ref. 30 for comparable configurations. It is also obvious that charge density for LUMO is more fragmented and has more nodes than that for HOMO in both examples.…”

“…H vacancies in graphane are thus defined as C atoms not bonded to H. In a more controllable manner, some H atoms can desorb from one side of graphane as a result of an applied electric field 12 13 20 , and the desorption process may continue to the extent of half hydrogenation. Patterns of H vacancies in graphane 12 13 14 15 19 21 22 23 24 can thus be formed and have attracted considerable interests 3 6 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 as partially hydrogenated graphene or, equivalently, graphane with patches or clusters of H vacancies, can have very different electronic structure from either pristine graphene or graphane, providing almost unlimited ways for designing and fine-tuning electronic circuits based on the two-dimensional composite of C and H. In this article we would like to report investigations by density functional theory (DFT) on some geometric patterns of H vacancies in graphane and their physical properties. The results can be applied to the design of nanoelectronic circuits 9 10 25 and may serve as a guide for predicting properties of larger and more complicated patterns of the C-H composites.…”

Overview of Computational Simulations in Quantum Dots

“…The contour plots of wave function squares on a cross section perpendicular to the wurtzite c ‐axis are shown in Figure for CdSe, CdSe/CdS QD, and CdSe/CdTe QD. It is worth noting that 2D monolayers can also be used to form core‐shell structures such as graphene/graphane heterostructures . A type I band alignment is discovered in the graphene/graphane core‐shell QD which exhibit quantized carrier energy levels.…”

“…First principles computational method has been widely used to investigate the effects of size and surface topology on the local structure's contribution to the density of states (DOS) of QDs, which ultimately controls the electronic and optical properties. [35][36][37][38][39] First principles method is also referred to as ab initio method, which is an approach to numerically solve the Schrodinger equation. The DFT approach is widely used to numerically solve the Schrodinger equation, or more precisely the Kohn-Sham equation.…”

“…It is worth noting that 2D monolayers can also be used to form core-shell structures such as graphene/graphane heterostructures. [38] A type I band alignment is discovered in the graphene/graphane core-shell QD which exhibit quantized carrier energy levels.…”