We study electronic and optical properties of single layer phosphorene quantum dots with various shapes, sizes, and edge types (including disordered edges) subjected to an external electric field normal to the structure plane. Compared to graphene quantum dots, in phosphorene clusters of similar shape and size there is a set of edge states with energies dispersed at around the Fermi level. These states make the majority of phosphorene quantum dots metallic and enrich the phosphorene absorption gap with low-energy absorption peaks tunable by the electric field. The presence of the edge states dispersed at around the Fermi level is a characteristic feature that is independent of the edge morphology and roughness.
The structure stability and electronic properties of edge carboxylated hexagonal and triangular graphene quantum dots are investigated by using density functional theory. The calculated binding energies show that the hexagonal clusters with armchair edges have the highest stability among all other flakes. The binding energy of carboxylated graphene quantum dots increases by increasing the number of attached carboxyl groups. Our study shows that the total dipole moment significantly increases by adding COOH with the highest values observed in triangular clusters. The edge states in triangular graphene with zigzag edges produce completely different energy spectrum from other shapes as (a) the energy gap in triangular zigzag cluster is very small compared to other clusters and (b) the highest occupied molecular orbital is localized at the edges which is in contrast to other clusters where it is distributed over the cluster surface. The enhanced reactivity and the controllable energy gap by shape and edge termination make graphene quantum dots ideal nanodevices for various applications such as sensors. The infrared spectra for different flakes are presented for confirmation and detection of the obtained results.
The stability and electronic properties of hexagonal and triangular silicene quantum dots are investigated under the effect of edge passivation by different elements and molecular groups. The structures experience a considerable alternation in shape depending on the attached elements or groups. The most noticeable alternations occur in zigzag triangular flakes passivated with sulfur and in all selected flakes when OH groups are attached to the edge atoms. The resulting structure has a spherical shape with a large total dipole moment. All the studied clusters have been proven to be stable by the calculated positive binding energies. Flexible structure transformation from insulator (conductor) to conductor (insulator) is obtained in zigzag hexagonal-H (zigzag triangular-H) and zigzag hexagonal-S (zigzag triangular-OH), respectively. The magnetic properties of triangular zigzag depend on the parity of the total number of Si atoms such that flakes with an even number of Si atoms will have antiferromagnetic properties while flakes with an odd number of Si atoms can have ferromagnetic or antiferromagnetic properties depending on the attached element or group. Thus, a proper choice of the attached functional groups or elements to silicene flakes allows tailoring of their properties to different application. In particular, hydrogenated or fluorinated flakes are highly interactive with the surrounding and can be used for sensor applications while clusters passivated with S or OH are insensitive to edge defects and have tunable electronic properties that make them promising in semiconductor device applications.
To cite this version:Hazem Abdelsalam, Mohamed Talaat, Igor Lukyanchuk, M. Portnoi, V. Saroka. Electro-absorption of silicene and bilayer graphene quantum dots. Journal of Applied Physics, American Institute of Physics, 2016, 120 (1) We study numerically the optical properties of low-buckled silicene and AB-stacked bilayer graphene quantum dots subjected to an external electric field, which is normal to their surface. Within the tight-binding model, the optical absorption is calculated for quantum dots, of triangular and hexagonal shapes, with zigzag and armchair edge terminations. We show that in triangular silicene clusters with zigzag edges a rich and widely tunable infrared absorption peak structure originates from transitions involving zero energy states. The edge of absorption in silicene quantum dots undergoes red shift in the external electric field for triangular clusters, whereas blue shift takes place for hexagonal ones. In small clusters of bilayer graphene with zigzag edges the edge of absorption undergoes blue/red shift for triangular/hexagonal geometry. In armchair clusters of silicene blue shift of the absorption edge takes place for both cluster shapes, while red shift is inherent for both shapes of the bilayer graphene quantum dots. Published by AIP Publishing.
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