Researchers from KTH Royal Institute of Technology developed a technique that enables scalable production of the nanoscale electrodes
A team of researchers from the Department of Micro and Nanosystems at KTH tested a technique to form vast number of viable nanoscale molecular junctions. These junctions are extremely small pairs of electrodes. The nanometer-sized gap between these electrodes trap and probe molecules. According to KTH researchers, a 100 mm diameter slice of thin materials can generate around 20 million electrodes in a span of five hours. The team used gold film on top of a brittle material that forms cracks. Moreover, the team trapped and studied a most preferred reference molecule at the van der Zant Lab at TU Delft. To ensure that the fabrication method did not inhibit the formation of molecular junctions, the molecule was trapped in the nanometer-wide space between the electrodes.
The team focused on producing gaps that enable a phenomenon called tunneling. Electrons overcome the break in a circuit in the tunneling effect. A break junction contains a gap the size of a few atoms that breaks the flow of electrons through it. However, the short gap causes the electrons with sufficient energy to jump across this expanse. Tunneling electrons are capable of sustaining a considerable amount of current that is extremely sensitive to the size of the gap. Tunneling break junctions are generated one gap at a time. This restricts the development of any application that includes tunneling junctions outside a research laboratory.
The team used photo lithography to pattern a stack of gold on titanium nitride (TiN). This stack is placed on a silicon slice and the notched structures that are formed to concentrate stress. Removal of silicon directly underneath the stack is called release etching, which leads to formation of tiny cracks at the pre-determined locations in the TiN to release the stress. This causes deformation of gold that spreads it into atomically thin wires stretching across these cracks. Breaking of the wires leads to formation of gaps as small as a molecule. The research was published in the journal Nature Communications on August 24, 2018.