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SYCO: Cluster auf Oberflächen

SYCO 1: Electronic Properties

SYCO 1.7: Hauptvortrag

Donnerstag, 14. März 2002, 14:00–14:45, H 36

Scanning Tunneling Spectroscopy of Semiconductor Quantum Dots and Quantum Rods — •O. Millo¹, D. Katz¹, T. Mokari², S.-H. Kan², and U. Banin² — ¹Racah Institute of Physics, The Hebrew University, Jerusalem, Israel — ²Department of Physical Chemistry, The Hebrew University, Jerusalem, Israel

We employ scanning tunneling microscopy and spectroscopy in studies of single nanocrystal InAs and InAs / ZnSe (core / shell) quantum dots, and CdSe quantum rods in the double-barrier tunnel junction configuration. The tunneling spectra reveal the size-dependent level structure of these particles and clearly manifest the symmetry of each system. In particular, s-like and p-like levels are observed for the dots, manifested both in the tunneling spectra and in wavefunction images measured for the core / shell particles, while the rods depict the transition from the zero-dimensional to the one-dimensional regime. We shall also discuss the effects of the tunnel junction symmetry on the spectra, due to both the voltage division between the two junctions and the different tunneling rates. We observe resonant tunneling through nanocrystal states without charging when the tip is retracted from a nanocrystal deposited directly on a conducting substrate. Charging is regained upon reducing the tip-nanocrystal distance, making the junctions more symmetric. In contrast, charging-free resonant tunneling was not found for nanocrystals anchored to the substrate via linker molecules, which enhance the substrate-nanocrystal tunnel barrier. Computer simulations showing the effects of both level structure and junction symmetry will be presented.