Vertically-oriented zinc oxide (ZnO) nanowires were synthesized on glass and silicon substrates by Pulsed Laser Deposition and without the use of a catalyst. An intermediate c-axis oriented nanotextured ZnO seed layer in the form of nanowall network with honey comb structure allows the growth of high quality, self-forming, and vertically-oriented nanowires at relatively low temperature (<400 °C) and under argon atmosphere at high pressure (>5 Torr). Many parameters were shown to affect the growth of the ZnO nanowires such as gas pressure, substrate–target distance, and laser energy. Growth of a c-axis-crystalline array of nanowires growing vertically from the energetically favorable sites on the seed layer is observed. Nucleation occurs due to the matching lattice structure and the polar nature of the ZnO seed layer. Morphological, structural, and optical properties were investigated. X-ray diffraction (XRD) revealed highly c-axis aligned nanowires along the (002) crystal plane. Room temperature photoluminescence (PL) measurements showed a strong and narrow bandwidth of Ultraviolet (UV) emission, which shifts to lower wavelength with the increase of pressure.

The carbon dioxide highly sensitive ultra-thin optical sensor using plasmonic nanoparticles distributed uniformly on the nanowall honeycomb structure with a footprint in the millimeter range is presented in this work. The zinc oxide (ZnO) honeycomb nanowall structure is grown by the pulsed laser deposition (PLD) method. Moreover, the performance of the fabricated structure as a gas nanosensor is simulated using the finite difference time domain (FDTD) method in the visible and near-infrared regions. A graphene layer is mounted on the top of the nanowall, and then, plasmonic nanoparticles are distributed on the nanowall sides. Furthermore, the effect of gas concentration on the pressure and consequently on the dielectric constant of the gas are also illustrated in this article. Red-shift in the absorption has been noticed with different refractive indices and intensity sensitivities. The obtained refractive index sensitivity of the proposed nano optical sensor is 874 nm/RIU, and the intensity sensitivity is 5,174 RIU−1 with the figure of merit of 12.5 and quality factor (Q-factor) of 281 at a carbon dioxide (CO2) concentration of 5,500 ppm. Finally, the absorbed power of the incident light is calculated using different polarization angles, from 10° to 80° with a step10°.

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