Operating Individual Quantum Molecular Machines
Department of Physics & Astronomy, Ohio University, OH 45701, USA
Nanoscience and Technology Division, Argonne National Laboratory, IL 60439, USA.
A recent emergent research direction is the development of complex molecular machines suitable to operate on solid surfaces. Biological machines have the sizes from tens of nanometers to a few microns –a range where classical machine concepts hold while artificially designed molecular machines can be in the size range of a few nanometers or less, which is in the range of quantum processes. Unlike biological counterparts, the synthetic molecular machines may tolerate a more diverse range of conditions, and thus they can be advantageous for the complex functions with low power consumption suitable to operate in solid state devices. Development of molecular machines demands novel quantum mechanical engineering concepts, and requires testing their operation mechanisms. We use low temperature scanning tunneling microscopy, spectroscopy, and molecular manipulation schemes to investigate fundamental operations of synthetic molecular switches and molecular motors on metallic surfaces [1-5]. Using an inelastic electron tunneling process, individual molecules can be switched from one state to another in a controlled manner. Controlled directional rotation of molecular motors can also be performed using the same technique. In addition to single molecule operations, synchronization of molecular motors can be achieved in hexagonal assembly of dipolar motors due to the degeneracy of ground state dipole energy. Moreover, we find that the defects are essential to induce electric torque required for the rotation of the motors in the networks. At the low excitation energy regime, slight reorientations of individual motors can occur resulting in the motor arms pointing in different directions. Analysis reveals that the rotator arm directions here are not random, but are coordinated to minimize energy via cross talk among the motors through dipolar interactions.
Figure 1. Dipolar motor assembly (Left). A rotating motor on Au(111) (middle), and the corresponding motor structure (right).
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