Nanometre spaced electrodes on a cleaved AlGaAs surface

We present a novel technique for fabricating nanometre spaced metal electrodes on a smooth crystal cleavage plane with precisely predetermined spacing. Our method does not require any high-resolution nanolithography tools, all lateral patterning being based on conventional optical lithography. Using molecular beam epitaxy we embedded a thin gallium arsenide (GaAs) layer in between two aluminium gallium arsenide (AlGaAs) layers with monolayer precision. By cleaving the substrate an atomically flat surface is obtained exposing the AlGaAs–GaAs sandwich structure. After selectively etching the GaAs layer, the remaining AlGaAs layers are used as a support for deposited thin film metal electrodes. We characterized these coplanar electrodes by atomic force microscopy and scanning electron microscopy; this revealed clean, symmetric and macroscopically flat surfaces with a maximum corrugation of less than 1.2 nm. In the case of a device with a 20 nm thick GaAs layer the measured electrode distance was 22.5 nm with a maximum deviation of less than 2.1 nm. To demonstrate the electrical functionality of our device we positioned single colloidal gold nanoparticles between the electrodes by an alternating voltage trapping method; this resulted in a drop of electrical resistance from ∼11 G Ω to ∼1.5 k Ω at 4.2 K. The device structure has large potential for the manipulation of nanosized objects like molecules or more complex aggregates on flat surfaces and the investigation of their electrical properties in a freely suspended configuration.