|We develop and apply low-temperature scanning probe techniques to study the behavior of charges in nanoscale systems. The techniques include Scanning Tunneling Microscopy and Charge Imaging -- a novel low temperature probe of electron accumulation. The method achieves an incredible sensitivity of 0.01 electrons per root hertz. Current projects include probing electrons in atomic-scale semiconductor structures and biological nanowires.|
The picture above-left shows schematically a Scanning Tunneling Microscopy image of a biological nanowire on a flat graphite substrate.
This study is a collaborative effort with Microbiologist Prof. Gemma Reguera.
These incredible bio-nanowires grow as appendages on a bacterium known as Geobacter sulfurreducens, and can reach up to several microns in length; yet they are just a few nanometers
wide. The nanowires function to conduct electrons to insoluble electron acceptors such as Fe(III) oxides and other cells within electrically-active biofilms.
This study applies our methods to probe the nature of biological electron transfer in these systems.
The picture to the right (which is also the logo for the group) shows an experiment, first published in Nature Physics,and a more recently in Nano Letters. Here we detected individual electrons entering small clusters of acceptor (dopant) atoms below the surface of a silicon semiconductor. The schematic shows a gray metallic tip positioned above two closely-spaced dopant atoms, represented as potential wells. If the atoms are close together compared to their effective Bohr radius (a few nanometers), the interaction alters the quantum structure of holes trapped on the acceptors. In this way, the study demonstrated that we can probe the smallest possible semiconductor devices -- composed of one or more individual dopant atoms.
The research described on this site is currently funded by grants from the National Science Foundation (DMR-0906939, MCB-1021948). Past support includes the MSU Foundation (Strategic Partnership Grant), the MSU Institute for Quantum Sciences and the Alfred P. Sloan Foundation.
|The background pattern is an artist's view of atomic-scale three-leaved clovers -- formed by the electronic structure of selenium atoms on the surface of Bi2Se3, a narrow-gap semiconductor (paper). The pattern results from the interaction between the surface and a subsurface substitutional defect. The study was carried out by Tessmer's first grad student (now professor), Sergei Urazhdin.|