The objective of this research is to develop a highly sensitive uncooled Infrared (IR) sensor using polymer/epitaxial few layer graphene (FLG) composite film as a novel sensing element, utilizing the extraordinary material properties of epitaxial FLG films on SiC. The approach is based on: (i) Designing polymer/FLG sensor through modeling and finite element simulations, (ii) Growing FLG films on doped 6H-SiC substrate, (iii) Fabrication and characterization of the polymer/FLG sensor layer, and (iv) Evaluation of the sensor for IR detection.
Intellectual Merit: Success of the proposed research will lead to the development of a novel uncooled and inexpensive IR sensor that can far exceed the state-of-the-art performance of uncooled IR sensors, and rival those utilizing cryogenic cooling. The sensor would offer very high sensitivity along with very short response time, addressing the critical limitations of other uncooled IR sensors that suffer from high noise floor, high thermal time constant, and dependence on optical transduction. The highly sensitive deflection transduction method utilizing substrate gating, can also foster the development of next generation nanoelectromechanical devices based on suspended graphene.
Broader Impacts: The project is expected to have broad technological impacts in the areas of defense, homeland security, astronomy, law enforcement, and environmental monitoring. For educational and outreach activities, the PIs would involve one undergraduate and one high school student every year in their research, ensuring one minority student participation. The PIs would also develop a graduate course, and disseminate research results through conference participation, and utilizing individual research group, and departmental websites.
This project resulted in the development of novel graphene heterojunction and suspended graphene membrane based sensor devices that can be used to detect chemicals, biomolecules and infrared radiation based on changes in conductivity or capacitance. Graphene, which consist of hexagonal (honeycomb) arrangement of single layer of carbon atoms have exceptional electrical and mechanical properties that can be used to develop extremely sensitive physical, chemical, and biological sensors. In this project, graphene heterojunctions and composites have been used to develop these sensors by first synthesizing graphene on Cu foil, followed by transfer to appropriately patterned substrates, and finally deposition of contacts for external probing. The graphene sensors were found to be extremely sensitive to donor or acceptor type molecules, while electronically tunable sensitivity of the sensor devices was demonstrated for the first time in this project. Large changes in the infrared reflectance properties of graphene due to "molecular doping" of graphene, caused by adsorption of the donor and acceptor type molecules, was also discovered, which can also be used for sensing. The graphene/Si "chemi-diode" type sensor developed in this project resulted in orders of magnitude higher sensing response compared to commonly used chemi-resistor type sensors, while consuming much less power. Graphene synthesized on SiC as well as on Cu foil were utilized to realize graphene bridge type transistor devices, whose conductance and capacitance could be modulated using a back-gate. These devices have opened up a new paradigm for highly sensitive detection of chemicals, bio-molecules and radiation. Overall, the project led to 7 journal publications, 1 invention disclosure, 35 conference presentations, and 3 invited talks. The project activities also led to very significant technological and educational broader impacts. In terms of technological broader impact, the development of the novel graphene/Si heterojunction diode based microcantilever sensor has opened up the possibility to detect a whole range of chemical, biological, and nuclear analytes. The project also resulted in the training of five doctoral students, three undergraduate and two high school students and research engagement with one high school teacher. The training that the students obtained from this project enabled them to find employment in reputed companies such as Intel and Northrop Grumman. The project also led to the creation of research infrastructure (in terms of specialized equipment, test beds, and software), knowledge base, and expertise in the PI’s lab, which is expected to open up further applications in a large variety of fields.
