Engineering Quantum Wires States on Hydrogen Terminated Silicon for Atom Scale Circuitry.

Abstract

Recent advances in hydrogen lithography on silicon surfaces now enable the fabrication of complex and error-free atom-scale circuitry. To illustrate these capabilities and highlight the importance of reliable interconnects, two prototype integrated atomic circuits are presented. Central to their operation are continuous atomic wires required to actuate and transmit signals. At this scale, wire geometry is critical because the precise position of each atom determines the resulting electronic structure. A systematic comparison of different wire geometries is therefore essential to identify the most effective configurations for signal transmission. In this study, low-temperature (4.5 K) scanning tunneling microscopy (STM) and spectroscopy (STS) were employed to fabricate and characterize six silicon dangling bond (DB) wire geometries on the degenerately As doped H-Si(100) surface. All measurements were performed at the same location and under identical tip conditions, enabling a direct comparison of the intrinsic electronic properties of each wire. dI/dV maps, proportional to the local density of states (LDOS) of each wire, were obtained to identify midgap electronic states which could support transport while minimizing leakage to bulk states. Complementary density functional theory (DFT) and nonequilibrium Green's function calculations were conducted to compute LDOS distributions and transmission coefficients for the most promising wire geometries. The results indicate that dimer wires exhibit good transmission (T = 0.7) with evidence of ballistic conductance and some resiliency toward hydrogen defects. Wider wires, such as the double dimer wire support more transverse eigenchannels, increasing conducting modes and resulting in enhanced transmission (T = 1.4) and improved defect tolerance.