  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.
