Chemical Gas Sensor Based on Optical Nano Antennas Using Graphene
Open AccessThe motivation behind this work is to build a chemical gas sensor which can be sensitive and selective using optical nano antennas (Optical Nano Antenna (ONA)) or plasmonic nano antennas. ONA are devices that have their resonating frequency in the visible range. The basic principle governing the sensing mechanism for ONA is the refractive index sensing. The changes in the refractive index of the environment around the ONA lead to the change in the resonant frequency of the ONA. This inherent property of the device makes it extremely selective to different gases since different gases have different refractive index. In this work, we use this inherent quality of being selective and have also developed a technique to make these devices more sensitive to different chemical gas molecules. The ONA is covered with monolayer graphene or graphene oxide. Graphene acts as the absorbing layer for the different chemical gas molecules. Advantages of using graphene or graphene oxide include that it can be functionalized easily, transfer and removal of graphene is comparatively easier and the optical properties of the device are not aected by using graphene. This is because there is no change in the electric eld intensity pattern due to graphene. During this work, we have also developed a transfer technique for graphene, which is quick, robust and can be automated to be used in the industry. The same technique is used for Graphene transfer on the dipole ONA in this work. The advantage of using graphene or graphene oxide is that we can also perform in situ cleaning to improve the sensitivity of the device. In situ cleaning can be achievedby continuous Ultra violet (UV) illumination or by heating. Most of the semiconductor based gas sensor operate at elevated temperatures for proper operation. Temperature assisted gas sensors require on-chip heater which increases the cost of the fabrication. However, in this work, we operate the device at room temperatures and so it is comparatively simpler. In the traditional chemoresistive based gas sensors, one has to make a contact to the sensing element which is either a nanowire, a nanotube, or a 2D material like Graphene. Making these contacts has always been a challenge because of the noise introduced as well as the challenged in fabrication so as to make better contacts. In this work, there is no biasing or contacts needed to be made to the device. The sensor is completely optical and being optical in nature it is more immune to electrical noise.
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