Researchers at Rice University have created a coaxial cable that is about a thousand times smaller than a human hair and has higher capacitance than previously reported microcapacitors. The nanocable was produced with techniques pioneered in the burgeoning graphene research field and could be used to build next-generation energy-storage systems.
The tiny coaxial cable is similar in makeup to the ones that carry cable television signals into millions of homes and offices. The heart of the cable is a solid copper wire that is surrounded by a thin sheath of insulating copper oxide. A third layer, another conductor, surrounds that. In the case of TV cables, the third layer is copper again, but in the nanocable it is a thin layer of carbon measuring just a few atoms thick. The coaxial nanocable is about 100 nanometers wide.
The three-layer, metal-insulator-metal structure can be used to build energy-storage devices called capacitors. Unlike batteries, which rely on chemical reactions to both store and supply electricity, capacitors use electrical fields. A capacitor contains two electrical conductors, one negative and the other positive, that are separated by thin layer of insulation. Separating the oppositely charged conductors creates an electrical potential, and that potential increases as the separated charges increase and as the distance between them – occupied by the insulating layer — decreases. The proportion between the charge density and the separating distance is known as capacitance, and it’s the standard measure of efficiency of a capacitor. The Rice University study reports that the capacitance of the nanocable is at least ten times greater than what would be predicted with classical electrostatics.