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.