Determination of Band Offsets in Heterostructured Colloidal Nanorods Using Scanning Tunneling Spectroscopy

• Published in: Nano letters Vol. 8; no. 9; pp. 2954 - 2958
• Main Authors: Steiner, Dov, Dorfs, Dirk, Banin, Uri, Della Sala, Fabio, Manna, Liberato, Millo, Oded
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01.09.2008
• Subjects: Applied sciences; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Electronics; Exact sciences and technology; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Materials science; Molecular electronics, nanoelectronics; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Physics; Quantum dots; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Localized states; Ground states; Charge separation; Zinc selenides; Nanostructures; Modelling; Band offset; Nanorod; Nanocrystal; Band structure; Charge carriers; Semiconductor materials; Optoelectronic properties; Quantum dots; Core shell structure; Theoretical study; Electron delocalization; Cadmium sulfide; Cadmium selenides; Electronic structure; Electron state; Scanning tunneling spectroscopy; Nanostructured materials; Heterostructures; Nanotechnology
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl801848x

The ability to tailor the properties of semiconductor nanocrystals through creating core/shell heterostructures is the cornerstone for their diverse application in nanotechnology. The band-offsets between the heterostructure components are determining parameters for their optoelectronic properties, dictating for example the degree of charge-carrier separation and localization. So far, however, no method was reported for direct measurement of these factors in colloidal nanocrystals and only indirect information could be derived from optical measurements. Here we demonstrate that scanning tunneling spectroscopy along with theoretical modeling can be used to determine band-offsets in such nanostructures. Applying this approach to CdSe/CdS quantum-dot/nanorod core/shell nanocrystals portrays its type I band structure where both the hole and electron ground state are localized in the CdSe core, in contrast to previous reports which predicted electron delocalization. The generality of the approach is further demonstrated in ZnSe/CdS nanocrystals where their type II band alignment, leading to electron−hole separation, is manifested.