Ångström-level, real-time control of the formation of quantum devices

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Abstract
We report a novel approach for the realization of quantum devices which require device structures of sub-10 nm dimensions and position control better than 1 nm. In this approach we combine three methods from nano-technology: (i) an aerosol technique for the fabrication of metallic and semiconducting nano-crystals or nano-particles with diameters in the range 5-50 nm, (ii) extreme electron beam lithography to define contact gap geometries with dimensions of 10-50 nm and (iii) a manipulation technique based on atomic-force microscopy, combined with in situ electrical measurements of the device characteristics, by which pre-fabricated nano-structures can be positioned with high accuracy. We present details of room-temperature measurements on quantized conductance devices, formed in the neck structures between neighbouring gold particles. These necks or wires have a cross-section of only one or a few gold atoms, leading to quantized conductance of , with values of n between 1 and 10 having been observed. Such lateral quantum resistor devices are found to be remarkably stable, frequently maintaining the conductance levels on the time scale of hours. We also discuss the prospect for novel devices in which a single nano-particle or a single molecule is controllably positioned with high accuracy, with tunnel gaps surrounding the island.