  We perform electronic structure and quantum transport studies of dangling
bond loops created on H-passivated Si(100) surfaces and connected to carbon
nanoribbon leads. We model loops with straight and zigzag topologies as well as
with varying lenght with an efficient density-functional based tight-binding
electronic structure approach (DFTB) . Varying the length of the loop or the
lead coupling position we induce the drastic change in the transmission due to
the electron interference. Depending if the constructive or destructive
interference within the loop takes place we can noticeably change transport
properties by few orders of magnitude. These results propose a way to engineer
the closed electronically driven nanocircuits with high transport properties
and exploit the interference effects in order to control them.
