Nanoscale devices fabricated by direct machining of GaAs with an atomic force microscope

We demonstrate a lithography wherein the tapping mode of an atomic force microscope the Si tip is used as a chiseling tool for direct machining of a GaAs surface. Single-groove drawing movements in a vector-scan mode result in approximately 3-4 nm deep and 30 nm wide furrows, which can be combined to arbitrary noncontiguous polygon patterns. Beneath such a groove a barrier arises in the electron channel of a GaAs/A1GaAs modulation-doped field effect transistor (MODFET). Using appropriate sub-100 nm line patterns we prepared quantum point contacts and single electron devices. At T = 4.2 K the transconductance characteristics of these nanoscale MODFETs exhibit structures, which represent signatures of either the quantized conductance or Coulomb-blockade effects.