NASA’s Glenn Research Center has developed a groundbreaking new microsensor that detects toxic gases and explosives in a variety of environments. Most devices can perform only a unidirectional sensing task, lacking a switching feature that would allow the device to return to baseline operation after the volatile species is removed or has dissipated. Glenn’s nano-Switch Sensor Schottky Diode (nanoSSSD) device consists of a thin film of graphene deposited on a specially prepared silicon wafer. Graphene’s two-dimensional properties make this technology both extremely sensitive to different gases and highly reliable in harsh, enclosed, or embedded conditions. The nanoSSSD can be connected to a visual and/or sound alarm that is autonomously triggered as the sensor detects a selected gas, and then is returned to its passive mode when the gas is no longer present. The innovation has applications in biomedical devices, combustion engines, and detection/switching devices used in mass transit systems.
The graphene-based nanoSSSD provides dual-use functionality and reversibility characteristics in a compact and reliable package. The nanoSSSD can be connected to an alarm that autonomously triggers in the presence of specially selected gases, such as ammonia, hydrogen, hydrocarbons, nitrogen oxides, or carbon monoxide. The device includes a doped substrate, an insulating layer disposed on the substrate, an electrode formed on the insulating layer, and one or more thin films of graphene deposited on an electrodized, doped silicon wafer. The graphene film acts as a conductive path between a gold electrode deposited on top of a silicon dioxide layer and the reversible side of the silicon wafer, so as to form a Schottky diode. The substrate in Glenn’s innovative device can be fabricated with either n-doped or p-doped silicon, allowing the device to achieve enhanced compatibility with specific silicon-based nanoelectronic circuits as required.
The graphene’s two-dimensional nature maximizes the sensing area, and the device itself contains no moving parts, unlike other devices offering dual switching/sensing functionality that often make use of mechanical actuators such as cantilevers. Those devices are more complex to fabricate and more likely to reduce the mean-time-to-failure. By contrast, the relative simplicity of the Glenn nanoSSSD makes it more robust and therefore lends itself to settings where frequent replacement is not an option. It features a simplified fabrication process and a vertical configuration, which reduces cost and frees up circuit area.
Potential applications include detecting harmful gases and explosives, optimizing internal combustion engine and turbine performance, security screening for airports, monitoring air quality underground (e.g., in mines) and underwater (e.g., in nuclear submarines), and biomedical microelectromechanical and nanoelectromechanical systems.