Atom-by-Atom Construction of a Cyclic Artificial Molecule in Silicon

Abstract

Hydrogen atoms on a silicon surface, H–Si (100), behave as a resist that can be patterned with perfect atomic precision using a scanning tunneling microscope. When a hydrogen atom is removed in this manner, the underlying silicon presents a chemically active site, commonly referred to as a dangling bond. It has been predicted that individual dangling bonds fUnction as artificial atoms, which, if grouped together, can form designer molecules on the H–Si (100) surface. Here, we present an artificial ring structure molecule spanning three dimer rows, constructed from dangling bonds, and verified by spectroscopic measurement of its molecular orbitals. We found that removing 8 hydrogen atoms resulted in a molecular analog to 1,4-disilylene-hexasilabenzene (Si8H8). Scanning tunneling spectroscopic measurements reveal molecular π and π* orbitals that agree with those expected for the same molecule in a vacuum; this is validated by density functional theory calculations of the dangling bond system on a silicon slab that show direct links both to the experimental results and to calculations for the isolated molecule. We believe the unique electronic structure of artificial molecules constructed in this manner can be engineered to enable future molecule-based electronics, surface catalytic functionality, and templating for subsequent site-selective deposition.

Atomic-scale control of tunneling in donor-based devices

“…The Si:P SETs are fabricated on a hydrogen-terminated Si(100)2 × 1 substrate (3 10 15 cm À3 boron doped) in an UHV environment with a base pressure below 4 10 À9 Pa (3 10 À11 Torr). Detailed sample preparation, UHV sample cleaning, hydrogen-resist formation, and STM tip fabrication and cleaning procedures have been published elsewhere 11,18,33 . A low 1 × 10 −11 Torr UHV environment and contamination-free hydrogen-terminated Si surfaces and STM tips are critical to achieving highstability imaging and hydrogen-lithography operation.…”

“…In this study, we overcome previous challenges by uniquely combining hydrogen lithography that generates atomically abrupt device patterns 10,11 with recent progress in low-temperature epitaxial overgrowth using a locking-layer technique [12][13][14] and silicide electrical contact formation 15 to substantially reduce unintentional dopant movement. These advances have allowed us to demonstrate the exponential scaling of the tunneling resistance on the tunnel gap separation in a systematic and reproducible manner.…”

Ionic charge distributions in silicon atomic surface wires

“…[30][31][32] Experimental exploration of such behaviours has so far been limited to scanning tunneling microscopy (STM) measurements at energies outside the band-gap of the material, where the expected ground state ordering of DB wire structures is convoluted with higher energy features associated with the perturbative nature of a necessary tunneling current. [33][34][35][36][37] In this work, we compliment these former studies with the use of the less perturbative AFM. We explore energies within the Si band gap revealing characteristics more easily associated to the charge state of DBs within these confined 1-D structures.…”

Extended iron phthalocyanine islands self-assembled on a Ge(001):H surface

“…Importantly, hydrogen-passivated Si/Ge surfaces may also act as platforms for nanostructurization by the atomically precise desorption of individual hydrogen atoms and the creation of unsaturated dangling bonds (DBs) or DB systems with predesigned architecture [ 30 – 31 ]. In such a way, different atomic nanostructures could be fabricated in a controllable manner; artificial molecules [ 32 ] or surface logic gates [ 33 ] could act as examples. Further, such nanostructures may be applied in hybrid systems to couple organic molecules with the underlying surface in a controlled way [ 34 – 35 ], or even provide pivot points for nanoscale rotors [ 30 ].…”