Atoms at the ends of self-assembled atomic chains act like anchors with lower energy levels than the "links" in the chain, according to new measurements by physicists at the National Institute of Standards and Technology (NIST).
The two images above show the energy levels (vertical scale) and spatial positions (white lines) of electrons within a three-atom chain. The top image shows the calculated or theoretical results; the bottom image shows the measured energy levels in a physical experiment. Electrons are most likely to be located in the red areas and least likely in the blue areas. Both images indicate that the electrons in the outermost atoms (positioned on the far left and right at the bottom) have lower energy than those within the center atom.
The first-ever proof of the formation of "end states" in atomic chains may help scientists design nanostructures, such as electrical wires made "from the atoms up," with desired electrical properties.
The NIST experiments, described in the Feb. 4 issue of the journal Science,* involved measuring and comparing the electronic properties of gold atoms in short chains assembled on silicon surfaces. Energy levels of the electrons within the end atoms of the chains were lower than those of inner atoms. This condition arises because the structural, chemical and electronic symmetry of a chain is broken at each end, and the atoms electrons are redistributed to lower the chains energy. The electronic structure of atomic chains is comparable to the electronic structure of bulk crystals, in which surface atoms have different properties than atoms inside the crystal.
Laura Ost | EurekAlert!
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