A flexible and wearable terahertz scanner

Transcription

1 A flexible and wearable terahertz scanner Daichi Suzuki 1, Shunri Oda 1, and Yukio Kawano 1* 1 Laboratory for Future Interdisciplinary Research of Science and Technology, Tokyo Institute of Technology, , Ookayama, Meguro-ku, Tokyo , Japan * kawano@pe.titech.ac.jp Figure S1 The details of the CNT film. a, Photographic images of an inch-sized CNT film. The mechanical strength of the film endows it with high flexibility, as shown in the right-hand photograph. b, THz absorption spectrum obtained via THz time-domain spectroscopy. c, Schematic representation of the THz response measurements. NATURE PHOTONICS 1

2 Figure S2 Simulated results concerning the thermal conduction of the CNT film. a, Illustration of the simulation model. b, Temperature profile and the experimental result of the thermal image of the THz detector. The electrode functions as a heat source; consequently, a temperature gradient is generated at the interface between the CNT film and the electrode. c, Simulated temperature gradients for different electrode materials (Au, Al, Mo, Ni, and Ti). d, Simulated temperature gradient as a function of the electrode thickness (Au). e, Simulated thermal conduction of a CNT film instrumented with electrodes of two different materials (Al and Ti). Because of the difference in thermal conductivity between Al and Ti, a temperature gradient is generated even when the entire CNT device is illuminated with THz waves. f, The experimental result of the thermal image of a CNT film with electrodes of Al and Ti. The temperature on the side of the Al electrode is higher than that on the side of the Ti electrode. 2 NATURE PHOTONICS

3 SUPPLEMENTARY INFORMATION Figure S3 Performance comparison between a detector array fabricated with electrodes of the same material (Al Al) and a detector array fabricated with electrodes of two different materials (Ti Al). a, Illustration of the 8-element detector array and the measurement system. b, THz transmission image recorded using the Al Al detector array. c, Line profile of the THz response for one element of the Al Al detector array. d, THz transmission image recorded using the Ti Al detector array. e, Line profile of the THz response for one element of the Ti Al detector array. A 29-THz source was used for all measurements. NATURE PHOTONICS 3

4 Figure S4 Demonstration of flexible scan with 29 THz irradiation. a, Schematic illustration of flexible THz imaging for bent mask (an aluminum mask). b, THz transmission image of a bent mask acquired at 29 THz. Even for a bent object, the scanner flexibly conforms to the sample surface and produces a clear THz image. 4 NATURE PHOTONICS

5 SUPPLEMENTARY INFORMATION Figure S5 Fermi-level control for the thick CNT film via the electron double layer technique with an ionic liquid. a, Sketch of the electron double layer CNT transistor by using N,N-diethyl-N-methyl-(2-methoxyethyl)ammonium bis(trifluoromethane sulfonyl)imide (DEMETFSI, Kanto Kagaku Co.). b, The gate voltage V g dependence of the current I sd of a at the source-drain voltage V sd of 100 mv. The Fermi level was controlled by the gate voltage V g even for the CNT film above 100 m thickness. c, The gate voltage V g dependence of the current and the THz response of a at the source-drain voltage V sd of 10 mv. This result shows that the THz response is peaked near the van Hove singularities, because it is proportional to the Seebeck coefficient, i.e., the derivation of the density of state at Fermi level. NATURE PHOTONICS 5

6 Figure S6 THz response of the p-n junction CNT device. a, Photographic images of the p-n junction CNT device. The left-hand side of the CNT film (originally p-type) was immersed into the ionic liquid and consequently was doped to the n-type. b, Line profile of THz response distribution of a for 39 THz irradiation (0.3 mw). The large negative response was seen at the p-n junction. d, The comparison of THz response between the p-n junction and the p-type. The THz response at the p-n junction is 4 times larger than that of the interface between the CNT and the electrode. 6 NATURE PHOTONICS

7 SUPPLEMENTARY INFORMATION Figure S7 Thermal network model and pressure dependence of THz response of the CNT device. a, The thermal network model of the CNT detector. Here, R CNT is thermal resistance of the CNT film, R outside is total external thermal resistance, T is a temperature of the CNT film, TT is a temperature at the infinite. According to the heat equation, the thermal gradient is described as Q (1/R CNT + 1/R outside) -1. b, The pressure dependence of the THz response. Because R outside becomes high with decreasing the pressure of the surrounding air, the temperature gradient T and the resulting THz response become higher. As a result, the detection sensitivity under high vacuum condition became about 3 times higher than that in the air. NATURE PHOTONICS 7