Single-walled carbon nanotubes (SWCNTs) have unique electrical properties and are ideal for a host of applications, such as single-electron and field-effect transistors, chemical sensors and in transparent electronics. The most common method to produce such devices is electron-beam lithography but exposing the nanotubes to electron irradiation can damage them. This means that their intrinsic physical properties can not be studied, something that is crucial for improving future devices.

Now, Zhenan Bao and colleagues have put forward a new technique that employs dip-pen nanolithography (DPN), a scanning probe-based technique that combines both the nanoscale resolution of electron-beam lithography with the ability to print micron-sized contacts. DPN has already proved its merit because it works with a variety of "inks", including the widely used alkanethiols, conducting polymers, biological molecules and metal nanoparticles.

Bao's team has shown that DPN can be used to pattern electrical contacts in nanoelectronic devices made from SWCNTs. The researchers use a scanning probe tip coated with alkylthiol ink that acts as a nanoscale "quill" to selectively deposit the ink on top of a thin film of gold covering the carbon nanotubes. The resulting alkythiol pattern plays the role of a mask and protects against subsequent chemical etching, which reveals gold contacts to isolated nanotubes, explains team member Maria Wang.

"DPN has many advantages over electron-beam lithography, including minimal damage during fabrication," she told nanotechweb.org. "It can also image nanostructures and pattern electrical contacts using one system operating under ambient conditions."

The contacts formed using DPN are comparable in terms of quality to those made via electron-beam lithography, and Bao and co-workers report on three different DPN-generated CNT devices – semi-metallic, semiconducting and metallic.

The team will now study how the structure and chemical environment of CNTs affect their final electrical properties.

The results were published in ACS Nano.