Polaronic transport and current blockades in epitaxial silicide nanowires and nanowire arrays

1. CNMS Staff Science Highlight Polaronic transport and current blockades in epitaxial silicide nanowires and nanowire arrays Scientific Achievement (b) Four-probe scanning tunneling microscopy (STM) of epitaxial nanowires elucidates electronic conduction mechanism of individual and arrays of nanowires. Individual nanowires exhibit thermally-assisted tunneling of small polarons between atomic-scale defect centers. Complex wire networks show significant electronic crosstalk between the nanowires, due to long-range Coulomb fields of polaroniccharge fluctuations. 22nm 450nm Significance and Impact (a)(b) STM images of YSi2 nanowire bundles. (c) Cross sectional structure of a wire bundle. Electrical characteristics of nanowires approaching the 1D limit are heavily influenced by atomic-scale charge trapping defects and the resulting polarization of the surroundings. This imposes severe constraints on the materials quality and circuit designs of future nanoarchitectures. This work establishes a semi-quantitative correlation between the density and distributions of atomic-scale defects and resulting current-voltage characteristics of nanoscale network devices. Research Details • Ultrathin epitaxial YSi2 nanowires are grown on Si(001) and the conductance is measured with a four-tip STM. • Individual nanowire I-V follows a universal curve indicative of thermally-assisted polaron hopping between defect centers. • Analysis of wire, probe, and negative differential resistances of nanowire networks indicates significant interwire coupling. Above: I-V of a single nanowire at all temperatures fall on a universal curve Right: I-V of a nanowire network show nonlinear (92K) to linear change (180K, 293K) with temperature V. Iancu, X.-G. Zhang, T.-H. Kim, L. D. Menard, P. R. C. Kent, M. E. Woodson, J. M. Ramsey, A.-P. Li, H. H. Weitering, Nano Lett. DOI: 10.1021/nl401574c Work was performed at CNMS-ORNL and at the University of Tennessee

2. CNMS Staff Science Highlight How electrical current flows in silicide nanowires and nanowire networks (b) Scientific Achievement Novel measurements of both individual and arrays of nanometer-scale wires (nanowires) reveals unusual ways that electric current is carried. In a single nanowire, electrons hop from one defect to the next assisted by nanowire deformation. In nanowire networks, electrons in one nanowire can influence those in another nanowire via the substrate that supports the nanowires causing the conductance to vary nonlinearly with the applied voltage. 22nm 450nm Significance and Impact (a)(b) STM images of YSi2 nanowire bundles. (c) Cross sectional structure of a wire bundle. Nanoscale electronic devices will inevitably contain networks of wires whose cross-sections will be so small as to represent one-dimensional conductors with novel transport properties. Understanding how these nanowires conduct electricity will pave the way for major achievements in nanoscale electrical engineering. Research Details • The current-voltage characteristics of nanowires and nanowire arrays are measured with a four-tip STM. • These measurements show that at low temperatures nanowires and nanowire arrays do not behave like ordinary wires. • The unusual behaviors are analyzed using theory based on quantum mechanics. Above: I-V of a single nanowire at all temperatures fall on a universal curve. Right: I-V of a nanowire network show nonlinear (92K) to linear change (180K, 293K) with temperature. V. Iancu, X.-G. Zhang, T.-H. Kim, L. D. Menard, P. R. C. Kent, M. E. Woodson, J. M. Ramsey, A.-P. Li, H .H. Weitering, Nano Lett. DOI: 10.1021/nl401574c Work was performed at CNMS-ORNL and at the University of Tennessee