Fabrication of quantum point contacts by engraving GaAs/AlGaAs-heterostructures with a diamond tip

We use the all-diamond tip of an atomic force microscope for the direct engraving of high quality quantum point contacts in GaAs/AlGaAs-heterostructures. The processing time is shortened by two orders of magnitude compared to standard silicon tips. Together with a reduction of the line width to below 90 nm the depletion length of insulating lines is reduced by a factor of two with the diamond probes. The such fabricated defect free ballistic constrictions show well resolved conductance plateaus and the 0.7 anomaly in electronic transport measurements.