All-Carbon Molecular Tunnel Junctions

This Article explores the idea of using nonme-
tallic contacts for molecular electronics. Metal-free, all-carbon
molecular electronic junctions were fabricated by orienting a
layer of organic molecules between two carbon conductors with
high yield (>90%) and good reproducibility (rsd of current
density at 0.5 V <30%). These all-carbon devices exhibit current
density
voltage (J
V) behavior similar to those with metallic
Cu top contacts. However, the all-carbon devices display
enhanced stability to bias extremes and greatly improved
thermal stability. Completed carbon/nitroazobenzene(NAB)/
carbon junctions can sustain temperatures up to 300 C in vacuum for 30 min and can be scanned at (1 V for at least 1.2  109 cycles in air at 100 C without a significant change in J
V characteristics. Furthermore, these all-carbon devices can withstand much higher voltages and current densities than can Cu-containing junctions, which fail upon oxidation and/or electromigration of the copper. The advantages of carbon contacts stem mainly from the strong covalent bonding in the disordered carbon materials, which resists electromigration or penetration into the molecular layer, and provides enhanced stability. These results highlight the significance of nonmetallic contacts for molecular electronics and the potential for integration of all-carbon molecular junctions with conventional microelectronics.