Quantum Capacitance of Graphene Finally Measured

Since it was first discovered in 2004, graphene has been one of the materials largely touted as having the potential to completely revolutionize the world, at least in terms of electronic devices. Believed to be a sustainable alternative to the silicon used in modern chips, the carbon compound has proven its abilities in the field of quantum computing as well, exhibiting peculiar electrical, chemical and physical properties. Recently, using an electrochemical gate method, Arizona State University (ASU) Biodesign Institute researcher N.J. Tao has managed to measure and document one of the fundamental properties of graphene, known as quantum capacitance.

In his paper, published in the latest issue of the respected scientific journal Nature Nanotechnology Letters, the expert also underlines the potential applications graphene could play an important role in, ranging from microchips, chemical-sensing instruments, and biosensors to ultracapacitance devices and flexible displays. He also recalls the days in which the material was first synthesized, after more than a decade of theoretical assumptions as to its existence. “When they found it was a stable material at room temperature, everyone was surprised,” Tao recalls.

The expert explains that there are two kinds of capacitances – one having to do with classical physics, and the other with quantum physics. In the first case, capacitance is the property of a material to repel electrical charges. That is to say, if electrons of a certain energy enter the material, after a certain level, the material begins to repel them, and a higher intensity needs to be applied just to contain the electrical field. In the quantum version of the theory – which makes use of the Pauli exclusion principle – the electron charges, once reaching a threshold, need to move to higher energy levels.

This is the same, Tao says, as people occupying a building. Once the first floor is full, newcomers move to the second, and so on, until the building is full. In his experiments with graphene, the expert applied voltage through the material via two electrodes, and measured both the classical and the quantum capacitance of the carbon compound. He learned that the theoretical predictions on graphene quantum conductance did not match those in practice, because of the impurities in the samples he was able to obtain and work on.