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Introduction
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| Nanostructures are nanoscale arrangements of atoms or molecules. The term nanostructure has a broad definition, and the functions of such structures range from magnetic information stoage to single molecule detectors to qubits for quantum computing. Magnetic structures take advantage of the inherent ferromagentic properties of the individual molecules built into the spins of the atoms bound in the molecules.
In order to understand and analyze the properties of the nanostructures, it is necessary to probe the electronic and magnetic characteristics of these molecules. Research has focused on using a spin polarized STM in order to study the magnetic properties of single molecules and atoms with electronic spectroscopy and topography studies. Using a homebuilt STM as well as Low Temperature (LT) and Variable Temperature (VT) systems, research is done in ultra-high vacuum and low temperature.
The main tool for investigation of magnetic nanostructures is the spin polarized STM (SP-STM).
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Spin-Polarised Scanning Tunneling Microscopy (SP-STM)
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A conventional scanning tunneling microscope (STM) allows for atomically resolved topographic images to be obtained from flat metallic surfaces. By varying the voltage of the STM tip, the electronic density of states (DOS) can be obtained and probed spatially. In most cases, this DOS is spin-averaged, with electrons from the majority and minority bands tunneling with equal probability. By growing a magnetic crystal at the end of a STM tip, however, a spin-polarized STM (sp-STM) can be achieved which changes the tunneling probability for electrons depending on the direction of their spin. This effect, combined with the ultra-high spatial resolution of an STM, produces a very powerful probe for understanding magnetism at the atomic level. The goal of our project is to see what happens to the spin of single magnetic atoms when they are placed in different environments. Such environments include atoms which are small building blocks of larger magnetic crystals, single atoms chemically bonded within a molecule, or single atoms that are sitting on a magnetic surface and can be moved with a STM tip.
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Magnetic Islands
Most relevant for the magnetic storage industry, probing such structures with a sp-STM allows us to spatially resolve how the spin-polarized electronic structure varies with size and environment.
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Magnetic molecules
Measurements performed on large ensembles of these systems have indicated that each molecule behaves as a large quatum spin. Tunneling into such a molecule with a sp-STM should reveal many more details about their electronic and magnetic structure.
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Single atoms
Single atoms can be moved around with an STM tip to create customized structures. By manipulating magnetic atoms with a sp-STM, we should be able to create controlled systems to probe magnetism at it’s absolute limit.
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© Crommie Group 2007. All Rights Reserved
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