ABSTRACT
We present a measurement scheme that enables quantitative detection of the shot noise in a scanning tunnelling microscope while scanning the sample. As test objects we study defect structures produced on an iridium single crystal at low temperatures. The defect structures appear in the constant current images as protrusions with curvature radii well below the atomic diameter. The measured power spectral density of the noise is very near to the quantum limit with Fano factor F = 1. While the constant current images show detailed structures expected for tunnelling involving d-atomic orbitals of Ir, we find the current noise to be without pronounced spatial variation as expected for shot noise arising from statistically independent events.
ABSTRACT
We directly image the interior of GaAs/AlGaAs axial and radial nanowire heterostructures with atomic-scale resolution using scanning tunneling microscopy. We show that formation of monolayer sharp and smooth axial interfaces are possible even by vapor-phase epitaxy. However, we also find that instability of the ternary alloys formed in the Au seed fundamentally limits axial heterostructure control, inducing large segment asymmetries. We study radial core-shell nanowires, imaging even ultrathin submonolayer shells. We demonstrate how large twinning-induced morphological defects at the wire surfaces can be removed, ensuring the formation of wires with atomically flat sides.
Subject(s)
Aluminum/chemistry , Arsenicals/chemistry , Crystallization/methods , Gallium/chemistry , Microscopy, Scanning Tunneling/methods , Nanostructures/chemistry , Nanostructures/ultrastructure , Nanotechnology/methods , Macromolecular Substances/chemistry , Materials Testing , Molecular Conformation , Particle Size , Surface PropertiesABSTRACT
Using the highly localized current of electrons tunneling through a double barrier scanning tunneling microscope junction, we excite luminescence from a selected C60 molecule in the surface layer of fullerene nanocrystals grown on an ultrathin NaCl film on Au(111). In the observed fluorescence and phosphorescence spectra, pure electronic as well as vibronically induced transitions of an individual C60 molecule are identified, leading to unambiguous chemical recognition on the single-molecular scale.
