Fabrication of Ultraviolet Photodetectors Based on Fe-Doped ZnO Nanorod Structures.

In this paper, 100 nm-thick zinc oxide (ZnO) films were deposited as a seed layer on Corning glass substrates via a radio frequency (RF) magnetron sputtering technique, and vertical well-aligned Fe-doped ZnO (FZO) nanorod (NR) arrays were then grown on the seed layer-coated substrates via a low-temperature solution method. FZO NR arrays were annealed at 600 °C and characterized by using field emission scanning microscopy (FE-SEM) and X-ray diffraction spectrum (XRD) analysis. FZO NRs grew along the preferred (002) orientation with good crystal quality and hexagonal wurtzite structure. The main ultraviolet (UV) peak of 378 nm exhibited a red-shifted phenomenon with Fe-doping by photoluminescence (PL) emission. Furthermore, FZO photodetectors (PDs) based on metal-semiconductor-metal (MSM) structure were successfully manufactured through a photolithography procedure for UV detection. Results revealed that compared with pure ZnO NRs, FZO NRs exhibited a remarkable photosensitivity for UV PD applications and a fast rise/decay time. The sensitivities of prepared pure ZnO and FZO PDs were 43.1, and 471.1 for a 3 V applied bias and 380 nm UV illumination, respectively.

Fast Detection and Flexible Microfluidic pH Sensors Based on Al-Doped ZnO Nanosheets with a Novel Morphology.

In this study, a flexible and stable pH sensor based on aluminum-doped zinc oxide nanosheets (Al-doped ZnO NSs) was developed by a low-cost hydrothermal method. The results obtained from this study indicated that Al ions could be doped successfully into the ZnO nanostructure, which could change the morphology and improve the pH-sensing properties. The pH sensitivity of Al-doped ZnO nanosheets reached 50.2 mV/pH with a correlation coefficient of around 0.99468 when compared with that of ZnO film (34.13 mV/pH) and pure ZnO nanowires (45.89 mV/pH). The test range of pH values was widened by Al-doping, and the Al-doped ZnO NS sensor could detect the pH value ranging from 2 to 12. It was observed that in a more acidic environment, especially at pH 2, the sensor, Al-doped ZnO nanosheet, was strongly stable over 12 weeks of testing. It was noted that the response time was utterly fast and the response time of the sensors for each pH standard buffer solutions was around 0.3 s. Thus, the response time and performance were quite stable. The microchannel provided a novel testing method for the pH sensor, where the liquid to be tested was just 5 mL. Hence, it was suggested to be useful for many medical diagnoses and treatments. The benefits of Al-doped ZnO nanosheet pH sensor were high sensitivity, good long-term usage, good flexible property, and requirement of a small amount of test liquid, which could make the sensors viable candidates for practical applications.

High Sensitivity of NO Gas Sensors Based on Novel Ag-Doped ZnO Nanoflowers Enhanced with a UV Light-Emitting Diode.

An ultraviolet-enhanced (UV-enhanced) nitric oxide (NO) sensor based on silver-doped zinc oxide (ZnO) nanoflowers is developed using a low-cost hydrothermal method. The results indicate that silver (Ag) ions were doped into the ZnO nanostructure successfully, thus changing the morphology. In the high-resolution transmission electron microscopy images, we also found that some Ag ions were separated out onto the surface of the ZnO nanoflowers and that the Ag-doped and Ag nanoparticles improved the sensing property. The NO sensing property increased from 73.91 to 89.04% through the use of a UV light-emitting diode (UV-LED). The response time was approximately 120 s without the UV-LED, and the UV-enhanced Ag-doped ZnO nanoflower sensor exhibited a reduced response time (60 s). The best working temperature could be reduced from 200 to 150 °C using UV light illumination, and it was found that the NO response increased by 15.13% at 150 °C. The UV photoresponse of the Ag-doped ZnO nanoflowers and the mechanisms by which the improvement of NO sensing property occurred through the use of UV light illumination are discussed. The property of the gas sensor can be calibrated using a self-photoelectric effect under UV light illumination. These interesting UV-enhanced Ag-doped ZnO nanoflowers are viable candidates for practical applications.

Annealing effect and photovoltaic properties of nano-ZnS/textured p-Si heterojunction.

The preparation and characterization of heterojunction solar cell with ZnS nanocrystals synthesized by chemical bath deposition method were studied in this work. The ZnS nanocrystals were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Lower reflectance spectra were found as the annealing temperature of ZnS film increased on the textured p-Si substrate. It was found that the power conversion efficiency (PCE) of the AZO/ZnS/textured p-Si heterojunction solar cell with an annealing temperature of 250°C was η = 3.66%.

Surface plasma resonant effect of gold nanoparticles on the photoelectrodes of dye-sensitized solar cells.

In this study, we prepared different shapes of gold nanoparticles by seed-mediated growth method and applied them on the photoelectrodes of dye-sensitized solar cells (DSSCs) to study the surface plasma resonant (SPR) effect of gold nanoparticles on the photoelectrodes of dye-sensitized solar cells. The analyses of field emission scanning electron microscopy show that the average diameter of the spherical gold nanoparticles is 45 nm, the average length and width of the short gold nanorods were 55 and 22 nm, respectively, and the average length and width of the long gold nanorods were 55 and 14 nm, respectively. The aspect ratio of the short and long gold nanorods was about 2.5 and 4, respectively. The results of ultraviolet-visible absorption spectra show that the absorption wavelength is about 540 nm for spherical gold nanoparticles, and the absorption of the gold nanorods reveals two peaks. One is about 510 to 520 nm, and the other is about 670 and 710 nm for the short and long gold nanorods, respectively. The best conversion efficiency of the dye-sensitized solar cells with spherical gold nanoparticles and short and long gold nanorods added in is 6.77%, 7.08%, and 7.29%, respectively, and is higher than that of the cells without gold nanoparticles, which is 6.21%. This result indicates that the effect of gold nanoparticles on the photoelectrodes can increase the conductivity and reduce the recombination of charges in the photoelectrodes, resulting in the increase of conversion efficiency for DSSCs. In addition, the long gold nanorods have stronger SPR effect than the spherical gold nanoparticles and short gold nanorods at long wavelength. This may be the reason for the higher conversion efficiency of DSSCs with long gold nanorods than those of the cells with spherical gold nanoparticles and short gold nanorods.