Cairo University

MTPR Journal

 

STM INVESTIGATION OF INTERFACIAL BAND BENDING IN AU-TIPPED CD-CHALCOGENIDES HYBRID NANOSTRUCTURES

2016-12-17
Hassan Talaat
Faculty of science, Ain Shams University
Vol./Issue: 16 , id: 186

The interfacial electronic structure of Au-tipped CdX (X = S, Se and Te) hybrid nanostructures (HNSs) have been studied by UHV scanning tunneling spectroscopy (STS) at room temperature. Au-tipped CdX (X = S, Se and Te) HNSs were synthesized by phase transfer chemical methods. The dimensions were determined by the scanning tunneling microscope (STM), the high resolution transmission electron microscope (HRTEM) and the optical absorption. The measured dimensions using these techniques are consistent, giving Au tip average size within the range of [2.5, 3.5] nm and Cd-chalcogenides quantum dots (QDs) nanoparticles (NPs) average size within the range of [3.5, 4] nm. The STS at the interface of Au-tipped CdS and CdSe HNSs detects a downward band bending towards the interface ~0.25 ± 0.01 eV and 0.18 ± 0.03 eV respectively, indicating an electron accumulation at these interfaces. However, an upward band bending towards the interface of ~0.78 ± 0.01 eV is measured by the STS at the interface of Au-tipped CdTe HNS, indicating electron depletion at the interface. The band bending values were also confirmed using the corresponding calculated models of the energy band diagrams. These different behaviors were also observed in the UVevis absorption of Autipped CdS and CdSe HNSs, which shows exciton bleaching features, but an exciton increasing feature is observed in the case of Au-tipped CdTe HNS. These later results are explained as a result of the presence of electron accumulation at the interface of Au-tipped CdS and CdSe HNSs, and also an electron depletion at the interface of Autipped CdTe HNS. Such determinations of the interfacial band bending in Au-tipped Cd-chalcogenides HNSs have significant consequences on the charge separation efficiency and the photo-response behavior. Furthermore, the presence of these bands has a direct impact in the field of applying plasmonics for improved photovoltaic solarcells.