A nanometer scale gap can be built using conventional microscale fabrication techniques such as optical lithography, electron-beam evaporation, and lift-off. Using electron-beam evaporation and lift-off of a metal line, it is possible to transfer the positive slope at the developed pattern edge in positive photoresist to a corresponding negative (undercut) slope in the resulting edge of the metal line. This negative slope on the metal pattern edge is subsequently used as a shadow for a second, thinner metal layer. Using this shadow, we demonstrate that a nanometer scale gap, denoted as a step junction, can be built between the two metal layers. The current-voltage characteristics of the resulting gaps have been characterized and the gaps have been imaged using scanning electron microscopy. To illustrate the application of a step junction structure as a nanoscale gap electrode, conductive bridges consisting of organic monolayers and nanoscale gold clusters were formed between the two electrodes. The observation of the clusters in scanning electron microscope (SEM) images and enhanced conductivity in the devices indicates that the step junction structure provides a means to realize efficient electrical contacts to nanoscale conductive elements.

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