"We want to measure the spatial variations in electronic properties," Jochen Weber of the Max Planck Institute for Solid State Research told nanotechweb.org. "An array of tips allows you to perform time-correlated experiments while monitoring the variation in potential of several sites at the same time."

The device is made using conventional semiconductor processing techniques such as e-beam lithography, etching and evaporation. This gives the team the option of including further electronics directly on the chip alongside the tips to boost the performance of the probe.

To obtain an accurate picture of the sample surface, it is desirable that the probes share similar electrical characteristics. After etching, the array substrate is polished with a focused ion beam to obtain clean and uniform tips. The SETs are formed by a number of aluminium evaporation and oxidation steps, which take place within an ultra-high vacuum environment so that the process can be well controlled.

"Reproducibility is of utmost importance as it makes no sense to call the device an array if most of the SETs do not work," commented Weber.

Currently, the yield is around 60% for the several hundred devices that have been made so far. The resistance of working single-electron transistors within the same array varies by a factor of about two, which is already sufficient to obtain useful results.

The researchers presented their work in Nanotechnology.