In this paper, a metal-insulator-metal plasmonic biosensor based on two adjacent disk resonators and the unidirectional reflectionless propagation effect is proposed and investigated. The numerical results obtained from the finite difference time domain simulations are verified analytically by means of the coupled-mode theory. The resonant properties of the proposed structure including the full-width at half-maximum and quality factor are optimized by determining the suitable geometrical parameters. The presented biosensor is then utilized to detect some biomaterials such as ether, ethyleneglycol, chlorobenzene, and quinoline. It is shown that the proposed structure shows high sensitivity of ~1500nm/RIU, large figure of merit of 242.66RIU-1 and large quality factor of 242.8, compared to the previously reported optical biosensors. Moreover, the effect of the dielectric used in the waveguides is also inspected.

Integrating different semiconductor materials, taking merits of each component’s advantages and synergistic properties, hold great promise to enhance the performance of gas sensors. In the present study, a multistep fabrication process, involving the environment-friendly hydrothermal process and simple sol-gel techniques is proposed for the fabrication of star-shaped BaTiO3/ZnO heterostructures based sensors. Sensors with different molar ratios of BaTiO3 to ZnO were fabricated and exploited for the detection of volatile organic compounds. Characterizations of the BaTiO3/ZnO heterostructures using X-ray diffraction spectroscopy, field emission scanning electron microscopy, and energy dispersive spectroscopy provided clear evidence of high-purity star-shaped heterostructure formation. Gas sensing measurement results illustrate that the BaTiO3/ZnO heterostructure based sensor with a molar ratio of 1:2 exhibits an abrupt and reliable gas response to ethanol and acetone at the optimum working temperature of 300 °C. Moreover, the BaTiO3/ZnO heterostructure sensor with a molar ratio of 1:3 shows a significant response to methanol at the optimum working temperature of 260 °C. The enhanced sensing characteristics of the sensor are attributed to the formation of heterojunctions at the interface of BaTiO3 and ZnO and surface area enhancement provided by its star-shaped morphology.

Line nanopatterns are produced on the positive photoresist by scanning near‐field optical microscope (SNOM). A laser diode with a wavelength of 450 nm and a power of 250 mW as the light source and an aluminum coated nanoprobe with a 70 nm aperture at the tip apex have been employed. A neutral density filter has been used to control the exposure power of the photoresist. It is found that the changes induced by light in the photoresist can be detected by in situ shear force microscopy (ShFM), before the development of the photoresist. Scanning electron microscope (SEM) images of the developed photoresist have been used to optimize the scanning speed and the power required for exposure, in order to minimize the final line width. It is shown that nanometric lines with a minimum width of 33 nm can be achieved with a scanning speed of 75 µm/s and a laser power of 113 mW. It is also revealed that the overexposure of the photoresist by continuous wave laser generated heat can be prevented by means of proper photoresist selection. In addition, the effects of multiple exposures of nanopatterns on their width and depth are investigated.