Growth, Structure, Electronic and Transport Properties of Yttrium Disilicide Nanowires

The electronic properties of low-dimensional materials deviate significantly from their bulk counterparts. Especially in quasi one-dimensional (1D) materials, a small number of structural defects can lead to strong electron localization. Electrons may also display unusual collective behavior in 1D. As integrated circuits continue to shrink in size, there is an increasing need for understanding and possibly manipulating electronic transport in quasi 1D materials. Here, we focus on electrical transport in self-assembled YSi₂ [yttrium disilicide] nanowires on Si(001). Being just a few atoms wide, these nanowires are one of the closest experimental realizations of a 1D conductor. YSi₂ nanowires are particularly attractive because they can be integrated into silicon based electronic circuits. Little is known about their electrical transport properties, however, because it is extremely difficult to connect these atomically thin wires to macroscopic measurement contacts. This technical obstacle was overcome by developing an in-situ method for contacting these atomically thin nanowires in ultrahigh vacuum. Here, one wire end is contacted to a macroscopic contact pad via shadow mask deposition, while the other end is contacted with the tip of a scanning tunneling microscope. The nanowires turn out to be very resistive and the relation between the measured resistance and wire length is highly non-linear. From the resistance measurements, we infer a localization length that is comparable to the atomic defect spacing in the wire, thus confirming the 1D nature of the transport and highlighting the importance of charge trapping by defects. Whereas the nanowires on Si(001) grow into orthogonal directions, nanowires on Si(110) all grow in the same direction. They exhibit a clear preference of nucleating at step edges when these edges are aligned along the [1-10] growth direction. This suggests a promising avenue for the fabrication of regular nanowire arrays with controlled wire separation, by varying the miscut angle of the Si wafer. We have demonstrated the feasibility of controlling nanowire growth, including their orientation, and related the nanowire resistance with the atomic dimensions and atomic-scale features of the wires. These insights will be increasingly relevant as nanoscale interconnects will ultimately approach the atomic limit.