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

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.