Gated Quantum Capacitive Devices

Author:

Thornton, Patrick Michael

Area of Honors:

Physics

Degree:

Bachelor of Science

Document Type:

Thesis

Thesis Supervisors:

Jorge Osvaldo Sofo, Thesis Supervisor
Prof. Richard Wallace Robinett, Thesis Honors Advisor

Keywords:

graphene
Quantum Capacitance
Density of States
gas detection

Abstract:

Graphene is a 2-dimensional allotrope of carbon which forms a honeycomb lattice. It is a material of great interest recently for the scientific community because of its unique electronic properties. Because the carbon atoms undergo sp^2 hybridization, graphene has delocalized p orbitals that form a semimetal. In our configuration, graphene is deposited on a silicon wafer with a conducting plate (top gate) located 1 cm above the surface. In this way, the configuration acts as a Field Effect Transistor (FET). The conductivity of graphene changes in a measurable way when NO and NO_2 gasses, are introduced into the region between the graphene and conducting plate. [2] We hypothesize that this change is due to the system’s sensitivity to changes in the dielectric constant of the side exposed to changing gas composition. This is enhanced by the unique density of states of graphene. The system can be modeled as two capacitors in series that share a central interface. Region 1 is the gaseous region above the graphene and region 2 is the thin non-conducting oxide layer on the outside of the silicon wafer. This method for analyzing quantum capacitance was first explored by Luryi [1] where he studied the effect of replacing the central interface with an ideal 2-dimensional quantum well. We extend this method of analysis to our graphene system. The graphene system has a high dependence on the changes in the permittivity of region 1. The introduction of dipole gasses NO and NO_2 could be the cause of this due to the relative ease of polarization by reorientation of the dipoles.