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 mi croscope the Si tip is used as a chiseling tool for direct machining of a G aAs surface. Single-groove drawing movements in a vector-scan mode result i n approximately 3-4 nm deep and 30 nm wide furrows, which can be combined t o arbitrary noncontiguous polygon patterns. Beneath such a groove a barrier arises in the electron channel of a GaAs/AlGaAs modulation-doped field eff ect transistor (MODFET). Using appropriate sub-100 nm line patterns we prep ared quantum point contacts and single electron devices. At T = 4.2 K the t ransconductance characteristics of these nanoscale MODFETs exhibit structur es, which represent signatures of either the quantized conductance or Coulo mb-blockade effects. (C) 2000 Elsevier Science B.V. All rights reserved.