Conductance decay of a surface hydrogen tunneling junction fabricated along a Si(001)-(2×1)-H atomic wire

Abstract

On a Si(001)-$(2\ifmmode\times\else\texttimes\fi{}1)$-H substrate, electrons tunneling through hydrogen atomic junctions fabricated between two surface dangling-bond (DB) wires are theoretically investigated using the elastic-scattering quantum-chemistry method. The surface states introduced in the Si band gap by removing H atoms from a Si(001)-$(2\ifmmode\times\else\texttimes\fi{}1)$-H surface were calculated and also analyzed using a simple tight-binding model. The two-channel surface conductance of a DB wire results from a combination of through-space and through-lattice electronic couplings between DB states. The conductance of the DB wire-H-junction-DB wire structure decreases exponentially with the length of H junction with an inverse decay rate ranging from 0.20 to $0.23\text{ }{\text{\AA{}}}^{\ensuremath{-}1}$, depending on the energy. When the DB wire-H-junction-DB wire structure is contacted by Au nanoelectrodes, the transmission resonances corresponding to the DB wire states split, demonstrating a coupling of the DB wires through short surface hydrogen atomic junctions. This splitting decreases with the length of H junction between the DB wires with an inverse decay length ranging from 0.22 to $0.44\text{ }{\text{\AA{}}}^{\ensuremath{-}1}$, indicating that such an atomic scale surface tunneling junction is not a very good insulator.