Spectroscopy of Electronic States in Atomic Chains

Jason N. Crain, NIST Electron Physics Group

The interaction of electrons in reduced dimensional systems leads to unexpected and exciting properties that are different than in higher dimensions. We explore the electronic structure of a promising set of reduced-dimensional materials, metallic surface states on silicon. Using stepped wafers that are miscut at different angles from (111) enables the confinement of states to one dimension via the self-assembly of atomic chains. Angle-resolved photoemission measurements directly show the one-dimensional nature of the chains through measurements of the Fermi surfaces, and show that the two-dimensional coupling between the chains varies with the chain spacing [1].
Since a single defect breaks an atomic chain, individual defects play a crucial role in determining the electronic properties of these chain reconstructions. Since photoemission provides only spatially averaged electronic properties, scanning tunneling microscopy (STM) is required to investigate the electronic structure in real space. Using STM we find the formation of quantized states in isolated chains segments. Furthermore, we find evidence for localized states at the boundaries of finite chains. These "end states" can be thought of as zero-dimensional analogs to two-dimensional surface states that occur at bulk surfaces [2].

[1] J. N. Crain et al., Phys. Rev. Lett. 90, 176805 (2003).
[2] J. N. Crain and D. T. Pierce, Science 307, 703 (2005).

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