Gigahertz-Based Visible Light Detection Enabled via CdS-Coated TiO₂ Nanotube Layers

Abstract

Detection of visible light is a key component in material characterization techniques and often a key component of quality or purity control analyses for health and safety applications. Here in this work, to enable visible light detection at gigahertz frequencies, a planar microwave resonator is integrated with high aspect ratio TiO2 nanotube (TNT) layer-sensitized CdS coating using the atomic layer deposition (ALD) technique. This unique method of visible light detection with microwave-based sensing improves integration of the light detection devices with digital technology. The designed planar microwave resonator sensor was implemented and tested with resonant frequency between 8.2 and 8.4 GHz and a resonant amplitude between −15 and −25 dB, depending on the wavelength of the illuminated light illumination on the nanotubes. The ALD CdS coating sensitized the nanotubes in visible light up to ∼650 nm wavelengths, as characterized by visible spectroscopy. Furthermore, CdS-coated TNT layer integration with the planar resonator sensor allowed for development of a robust microwave sensing platform with improved sensitivity to green and red light (60 and 1300%, respectively) compared to the blank TNT layers. Moreover, the CdS coating of the TNT layer enhanced the sensor’s response to light exposure and resulted in shorter recovery times once the light source was removed. Despite having a CdS coating, the sensor was capable of detecting blue and UV light; however, refining the sensitizing layer could potentially enhance its sensitivity to specific wavelengths of light in certain applications.

Wide-range soft anisotropic thermistor with a direct wireless radio frequency interface

“…dielectric changes due to soil moisture variation or ice accumulation 21 , 22 , or vital signs using wearable antennas 23 . Moreover, RF sensor readout has been widely used based on additional functional sensors including 2D materials 24 , conductive polymers 25 , 26 , inorganic sensitive materials 27 , lumped sensors 28 , and even bacterial cultures 29 . For gas sensing, it was shown that reading the response of resistive sensors at kHz frequencies can improve their linearity and sensitivity 30 .…”

Optically controlled n −Si/p −SeO2/p −SiO2 microwave resonators designed for 5G/6G communication technology

“…This change can be in the refractive index, polarization, or other properties of light passing through the material. Some of the materials that performed as dielectric materials that showed electro-optic properties are TiO 2 and SiO 2 [6,7]. Heterojunction devices made of TiO 2 /SiO 2 electro-optic multilayers are controlled by applying a 100 V bias to the ends of altered the resonant modes [8].…”

“…These devices use light to control the resonance properties of a microwave cavity. They have wide range of applications including communication, sensing and signal processing [1][2][3][4][5][6][7][8][9][10][11][12]. The currently constructed resonator benefits from selenium dioxide as a sandwiched p-type layer between n-Si and p-SiO 2 .…”