The design of a nanoscale molecular barrow

The design of a monomolecular barrow 1.6 nm×1.5 nm in dimension made of a central board, two rear legs and two front wheels, is discussed. This barrow is guided and driven by the tip apex of an STM which manipulates it from the rear legs. The central board has been chosen in such a way that the rotation of the front wheels can be deduced from the surface tunnelling current intensity measured during a sequence of manipulations of the barrow. Our calculations show that in UHV and without friction, the front wheels of the barrow that we designed will not rotate. This led us to design a new barrow including two ratchet molecular groups to compensate for the absence of friction.