Fabrication of a Nanogap on a Metal Nanowire Using Scanning Probe Lithography

A molecular electronics device (MED), which makes use of the functionality of one or several molecules, is a very attractive nanotechnology. However, it is necessary to both fabricate conductive metal nanowire circuits and insert the desired functional molecule at any position on the circuits in order to realize superintegrated circuits using molecular electronics. Therefore, a technique for fabricating nanogaps at any position on a metal nanowire is very important. We patterned an electron-beam negative resist SAL601 using the scanning probe lithography (SPL) technique and the resist patterns were transferred to the underlying titanium film by wet etching. We fabricated a continuous 20-µm-long Ti nanowire, thus this method can be combined with conventional photolithography. Using this combination, we fabricated a Ti nanowire connected to a large Pt pad electrode, and measured its current–voltage property with an atomic force microscopy (AFM) conductive tip. Moreover, we fabricated nanogaps on this line pattern by switching off the voltage bias between the AFM tip and the sample for a short time. Using these techniques, we fabricated nanogap electrodes with both nanometer-scale width and gap. It is expected that the electrodes can also be applied for electric measurement of one or several molecules.