Correlating Electronic Transport to Atomic Structures in Self-Assembled Quantum Wires
Shengyong Qin,1 Tae-Hwan Kim,1 Yanning Zhang,2 Wenjie Ouyang,2 Hanno H. Weitering,3 Chih-Kang Shih,4 Arthur P. Baddorf,1 Ruqian Wu,2 and An-Ping Li1
1-Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
2-Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA
3-Department of Physics and Astronomy, The University of Tennessee, Knoxville, TN 37996, USA
4-Department of Physics, The University of Texas at Austin, Austin, TX 78712, USA
Quantum wires are extremely narrow one-dimensional (1D) materials where electron motion is allowed only along the wire direction, and is confined in the other two directions. Quantum wires, as a smallest electronic conductor, are expected to be a fundamental component in all quantum electronic architectures. The electronic conductance in quantum wires, however, is often dictated by structural instabilities and electron localization at the atomic scale. Here we report on the evolution of electronic transport as a function of temperature and interwire coupling as the quantum wires of GdSi2 are self-assembled on Si(100) wire-by-wire. Individual nanowires have a width of 16.7 Å, a height of 4 Å, and lengths of micrometers, and embody one of the closest realizations of 1D conductors. Amazingly, these nanowires can be grown either in the form of isolated nanowires or bundles with a number of constituent wires separated by an atomic interwire spacing. We have examined the correlation between structure, electronic properties, and electronic transport in the quantum wire system by combining nanoscale transport measurements, scanning tunneling microscopy, and density functional theory calculations. A metal-insulator transition (MIT) is revealed in isolated nanowires, while a robust metallic state is obtained in wire bundles at low temperature. Observations are interpreted as atomic defects leading to electron localization in isolated nanowires, and interwire coupling which stabilizes the structure and promotes metallic states in wire bundles.
In this paper, we have performed the first correlated study of electronic properties by utilizing both scanning tunneling microscopy and nanotransport measurements on the same nanowire as the nanowires are assembled wire-by-wire. The approach takes advantage of our developments in fabricating nanocontacts using a field-induced atom emission process to bridge the atomic wires and the mesoscopic transport electrodes. The competition of defect-induced localization and interwire coupling in 1D systems has been argued for decades. The 1D metallic phase is inherently unstable with respect to symmetry-lowering lattice deformation and defect-induced localization. Adding interwire coupling can often lead to the formation of change density waves. In both cases, the metallic state is not stable and a metal to insulator transition occurs at low temperature. Our results now indicate that robust metallic conductance can be stabilized by interwire coupling, while the isolated single nanowires exhibit a metal to insulator transition due to quantum localization. The results provide a rare glimpse of the intrinsic structure-transport relations and the influence of local environments at an unprecedented atomic scale.
This work was published online in Nano Letters on January 23, 2012. This research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division by the Office of Basic Energy Sciences, U.S. Department of Energy. Theoretical work at UCI was supported by DOE grant DE-FG02-05ER46237.
Citation for the highlight: “Correlating Electronic Transport to Atomic Structures in Self-Assembled Quantum Wires,” Shengyong Qin, Tae-Hwan Kim, Yanning Zhang, Wenjie Ouyang, Hanno H Weitering, Chih-Kang Shih, Arthur P. Baddorf, Ruqian Wu, and An-Ping Li, Nano Letters, DOI: 10.1021/nl204003s.