Engineering quantum wires states on hydrogen terminated silicon for atom scale circuitry

Result of the Month

Author: Max Yuan, Lucian Livadaru, Roshan Achal, Jason Pitters, Furkan Altincicek, and Robert Wolkow Institute: ''Department of Physics, University of Alberta, Canada'' ACS Nano
URL: https://doi.org/10.1021/acsnano.6c05873
Date: 8/2026 Instruments: LT STM Lab

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.

Two prototype atomic silicon integrated circuits are shown to demonstrate current capabilities to fabricate complex error-free silicon DB structures using STM-based HL on an H- terminated surface. (a) 1.3 V, 50 pA STM image of a three-input combination OR gate and AND gate with atom-defined SET readout formed out of 69 DBs. (b) 1.3 V, 50 pA STM image of a two-input multiplexing DB circuit made of several gates and a fanout formed out of 56 DBs. Both circuit layouts were made using gate designs from binary atomic silicon logic and were based on modelling and simulation software for silicon DB logic systems.

Characterizing a 12-dimer long wire using dI/dV spectroscopy, imaging, and DFT simulations.

(a) An atom diagram indicating the location of the dI/dV spectroscopy with respect to the wire. (b) A 1D dI/dV map taken over the 12-dimer long wire using a 1.8 V and 50 pA tip set point over H−Si. Apparent band edges are shown in blue (VB) and red (CB). (c) Constant height dI/dV images of the wire from the same set point. Energies were chosen to correspond to states shown in (b). (d) Simulated dI/dV images for the first several states in the band gap. (e) A calculated energy level diagram for the dimer wire showing the manifold of filled (blue) and empty (red) states for the wire, analogous to the experimental data in (b).

Quantum transport calculation through 4- and 8-long dimer wires on Si nanoclusters sandwiched between metal electrodes, predicted using the NEGF-DFT method in the limit of low to zero bias. (a) The compiled values of the transmission function as a function of bias for various wire lengths and types, indicated in the legend. GS stands for the “ground state” configuration of the wire. The lines connecting the symbols are just a visualization aid. The remaining panels indicate the ground-state geometries used in the calculations of four wire types: (b) 4-long single dimer wire; (c) 4-long double dimer wire; (d) 8-long single-dimer wire; (e) 8-long double dimer wire. Si atoms are depicted in yellow, H atoms in white, Ag atoms in gray, with the Si atoms hosting DBs being highlighted in light green. Only the far-side electrode is shown for clarity.

Engineering quantum wires states on hydrogen terminated silicon for atom scale circuitry

Result of the Month

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