Graphene Golay micro-cell arrays for a color-sensitive terahertz imaging sensor E. Betz-Güttner1, N. Cefarin2, S. Dal Zilio3, M. Lazzarino3 1
University of Trieste, Trieste, TS, 34100, Italy 2 Elettra Sincrotrone, Trieste, TS, 34100, Italy 3 CNR-IOM, Trieste, TS, 34100, Italy
Abstract—Our aim in this research is the improvement of currently existing sensors with the use of advanced materials and technology, for the use in the field of terahertz imaging. The new sensor will be much faster and economic with respect to current industrial devices, with specific frequency-dependent sensitivity (color-like) bringing new possibilities in this field.
I. INTRODUCTION
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N the electromagnetic spectrum, just between the microwaves that we use in our WiFi and Bluetooth devices and the infrared light, there is a mostly unexplored region, named the TeraHertz (THz) gap, consisting of electromagnetic (EM) waves with frequencies comprised between 0.1 to 10 THz, which is waiting to be exploited[1]. While affordable THz laser sources are available on the market since the demonstration of the first quantum cascade THz laser by a group of Italian scientists in 2002[2], partner of this proposal, the development of affordable and lost cost THz detectors for imaging (the equivalent of the CCD for the visible light) was much slower. The bulky array of gear currently used to measure terahertz waves is clunky and expensive, making it impractical outside of a lab. Our project aims to apply new advanced materials and technology like graphene and microlithography to improve the responsiveness and efficiency of the Golay cell sensor invented and used in the astronomical field for the detection of infrared radiation, to broaden its field of application to terahertz radiation. Furthermore, we intend to design a final device that includes an array of this sensor leading to a high spatial resolution in comparison with current commercial sensors.
Fig. 1. Expansion of the graphene membrane of a single cell golay sensor by heating the cell through a peltier element. In particular, it is possible to observe how the initially corrugated membrane is relaxed by pressure and then relax at a constant temperature.
The relaxation of the membrane, on the other hand, may be due to an air leak present inside the cell during heating. These heating tests have also been repeated cyclically over time demonstrating the cell's ability to preserve its properties even subject to fatigue stress conditions. Parallel to the single-cell sensors, the first arrays of cells covered by graphene were manufactured, however the collapse of the graphene covering some cells prevents validating the data in comparison to the single cell and it s still in progress. III. SUMMARY Prototypes of advanced golay cells have been effectively designed and built, in which graphene plays a fundamental role as it seals the golay cell and at the same time has a high deformability in the presence of a modest pressure variation close to ambient temperature. This demonstrates the potential of this new generation of terahertz radiation sensors capable of offering good performance at a lower cost than commercial analogues.
II. RESULTS The Graphene-based Golay Micro-cell (GGM) were fabricated by micromachining technology on suspended silicon nitride membrane and sealed transferring a graphene monolayer to cover the hole. To measure the cell's sealing properties and graphene's ability to adhere to the substrate, a preliminary test was carried out in which a prototype of a single Golay cell was subjected to heating with the intention of observing the expansion of the air present inside the cell. The graphene deflection was evaluated with an optical profilometer and the heating of the cell took place through a Peltier element placed under it. During the heating phase an expansion of the membrane was observed, followed by a relaxation during the temperature maintenance phase. This indicates a variation in the pressure inside the cell during the experiment, showing that the system allows sealing of a small space, responding quickly to the variation in the internal pressure due to heating.
REFERENCES [1] [2]
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A. Y. Pawar, D. D. Sonawane, K. B. Erande, and D. V. Derle, “Terahertz technology and its applications,” Drug Invention Today. 2013. R. Köhler et al., “Terahertz semiconductor-heterostructure laser,” Nature, 2002.
