In recent years atomic chains on surfaces came into the focus of research. Due to the reduced dimensions, atomic chains can exhibit extraordinary electronic properties like endstates [1], i.e. the zero-dimensional analogy to surface states, or 1D confinement states [2]. There are two approaches to prepare one-dimensional structures on surfaces: one is the manipulation of single atoms with an STM-tip. The other approach is the self-organized growth on an appropriate surface, which acts as a template for the deposited atoms. As previously shown by Hammer et al. [3], the Ir(001) surface is an ideal template for the self-organized formation of one-dimensional nanostructures. The clean Ir(001) surface layer rearranges in a quasi-hexagonal (5×1)-reconstruction, which shows trenches running along the <110>-directions. Deposited Fe atoms form chains, which consist of two parallel atomic rows sitting in a trench of the surface reconstruction [3].
We have studied the structural and electronic properties of Fe/Ir(001) using scanning tunneling microscopy (STM) and spectroscopy (STS). At submonolayer coverage our growth studies confirm the results of Ref. [3] concerning the formation of chains (< 0.25 ML), the lifting of the reconstruction (> 0.25 ML) and the formation of an alloy layer (~0.8 ML). In addition, we find a transition from anisotropic (≤ 2 ML) to isotropic growth (≥ 3 ML) at higher coverages. Low-temperature STS data (T=13 K) obtained on the bi-atomic Fe chains reveal a remarkable change in the electronic density of states at the ends of the chains compared to the chain center. While we observed these endstates there is no evidence for 1D confinement states.
[1] J. Crain et al., Science, 307, 703 (2005)
[2] S. Fölsch et al., Phys. Rev. Lett., 92, 056803 (2004)
[3] L. Hammer et al., Phys. Rev. B, 67, 125422 (2003) |