Single Molecular Rotor at the Nanoscale Christian Joachim 1 , James Kazimiez Gimzewski 2 1 Centre d'Elaboration de Mate Âriaux et d'Etudes Structurales-Centre National de la Recherche Scienti®que CEMES-CNRS), 29 rue J. Marvig, 31055 Toulouse Cedex, France 2 IBM Research, Zurich Research Laboratory, 8803 Ru Èschlikon, Switzerland E-mail: gim@zurich.ibm.com The design of a monomolecular engine such as a rotating motor ®rst requires the preparation of a semi-classical rotating motion of the rotor part of the engine. We show that this can be achieved either by a careful quantum control of the time evolution of an initially prepared rotating quantum wave packet or by controlling the interaction of the rotor or stator) with a reservoir. This second alternative is illustrated experimentally through the realization of the rotary motion of a hexa-tert-butyl-decacyclene molecule self-assembled in an homomolecular cavity on an ultraclean Cu100) surface. The conditions to transform such a molecular rotor into a motor with a given motive power are also discussed. Keywords: Molecular rotor, Motive power, Decoherence, Classical motion, Quantum control, Nano-thermodynamics 1 Introduction ...................................... 2 2 The Rotation of a Nanoscale Material Object .............. 3 3 The Motive Power of a Quantum-State Superposition ....... 5 4 Decoherence and Classical Motion ...................... 8 5 Observation of the Semi-Classical Rotation of a Single Molecular Rotor .......................... 11 6 Towards Nano-Thermodynamics ....................... 15 7 Conclusion ....................................... 16 8 References ....................................... 17 List of Abbreviations STM scanning tunneling microscope ESQC elastic scattering quantum chemistry AFM atomic force microscope HBDC hexa-tert-butyl-decacyclene molecule UHV ultrahigh vacuum Structure and Bonding, Vol. 99 Ó Springer-Verlag Berlin Heidelberg 2001