  Coupled semiconductor nanostructures with a high degree of tunability are
fabricated using local oxidation with a scanning force microscope. Direct
oxidation of the GaAs surface of a Ga[Al]As heterostructure containing a
shallow two-dimensional electron gas is combined with the local oxidation of a
thin titanium film evaporated on top. A four-terminal quantum dot and a double
quantum dot system with integrated charge readout are realized. The structures
are tunable via in-plane gates formed by isolated regions in the electron gas
and by mutually isolated regions of the Ti film acting as top gates. Coulomb
blockade experiments demonstrate the high quality of this fabrication process.
