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In this study, the sol–gel method was used to prepare ZnO seed layer for synthesizing ZnO nanorods, and we would investigate the effects of different Zn(CH₃COO)₂ and C₆H${}_{12}$N₄ concentrations on the synthesized characteristics of ZnO nanorods. First, the ZnO gel was dipped on the surface of the $P$-type $\mathrm{\text{Si}}〈100〉$ wafer as a seed layer. Then, the hydrothermal method with different Zn(CH₃COO)₂ and C₆H${}_{12}$N₄ concentrations as precursors was used to synthesize ZnO nanorods on $P$-type $\mathrm{\text{Si}}〈100〉$ wafer. X-ray diffraction (XRD) pattern, focused ion beam-field emission scanning electron microscopy (FIB-FESEM) and photoluminescence (PL) spectrometry were employed to observe and analyze the crystal properties, surface morphologies, and optical properties of the prepared ZnO seed layer and synthesized ZnO nanorods. $90^{\circ }$C and 60 min were used as the synthesis temperature and time, and we found that Zn(CH₃COO)₂ and C₆H${}_{12}$N₄ concentrations had an apparent effect on the height, diameter, total surface area, total volume, density, and PL property of ZnO nanorods. The maximum PL emission intensity of ZnO nanorods presented in the samples with Zn(CH₃COO)₂ and C₆H${}_{12}$N₄ concentrations of 0.2 M. The results of XRD patterns suggest that ZnO nanorods have the property of $c$-axis preferred orientation. We showed that the different Zn(CH₃COO)₂ concentrations had large effects on the average height, average diameter, aspect ratio, total surface area (S, nm${}^2)$, total volume (V, nm${}^3)$, S/V ratio, and PL property of ZnO nanorods.

In this work, ZnO nanorods (ZnO NRs) were successfully synthesized on FTO-glass via hydrothermal technique. Two steps were followed to grow ZnO NRs. In the first step, the seed layer of ZnO nanocrystals was deposited by using a drop cast method. The second step was represented by the hydrothermal growth of ZnO NRs on a pre-coated FTO- glass with the seed layer. The hydrothermal growth was conducted at 90^∘C for 2h. The resulted structure, morphology and optical properties of the produced layers were analyzed by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray (EDX) and UV-visible spectrophotometer, respectively. The analysis confirmed that the ZnO NRs grown by the hydrothermal method have a hexagonal crystal structure which was grown randomly on the FTO surface. The crystallite size was recorded 50nm and a slight microstrain (0.142%) was calculated. The bandgap was found to be in the range of 3.14–3.17eV. The ZnO NRs have a high density and large aspect ratio. A pH sensor with high sensitivity was fabricated using a two-electrode cell configuration. The ZnO NRs sensor showed the sensitivity of $-$59.03mV/pH, which is quite promising and close to the theoretical value ($-$59.12mV/pH).

In this paper, ZnO nanorods were grown by wet chemical method on p-Si (100) substrate to form n-ZnO nanorods/p-Si (100) heterojunction. The optical, electrical, structural properties of n-ZnO nanorods/p-Si(100) heterojunction were analyzed by the photoluminescence (PL) spectroscopy, $I$–$V$ measurement, X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. The room temperature PL spectra reveal the good optical property of the heterojunction with strong UV peak at 385nm. The ZnO nanorods were vertically well-aligned on p-Si (100) and had an average height of about 1.6$\mu$m. The n-ZnO nanorods/p-Si (100) heterojunction also exhibits diode-like-rectifying-behavior.

We report efficient second harmonic generation (SHG) of femtosecond (fs) pulses using ZnO nanorods grown by chemical bath deposition (CBD) method with drop-casted seed layer. The SHG behavior of the nanorods are tested using an amplified Ti:sapphire fs laser of pulse duration of 100fs at 800nm. The SHG signal from the ZnO nanorods is found to be of very high intensity as detected by a low cost, compact spectrometer. In a comparative study, the SHG signal from ZnO nanorods grown over seed layer is found to be 12 times higher than the SHG signal observed from the ZnO nanorods grown on substrate without any seed layer. The efficient SHG in former case is due to the growth of high density, well oriented nanorods whereas the lower signal in the later case is due to growth of low density, randomly oriented nanorods. The polarization dependence behavior of the SHG signal is studied both experimentally and theoretically.

In this paper, it is described that the motion of water droplets on the hydrophobic surface of ZnO nanorod array impregnated lubricant, is called slippery liquid-infused porous surface (SLIPS). The energy gradient required to induce the motion of the droplets is created on the boundary of superhydrophobic ZnO nanorod array and SLIPS. Because of the lower viscous force of SLIPS, the water droplet can rapidly move for longer distance on the surface. In view of changing the release distance of water droplet, the mechanism for the rapid movement is discussed. The results indicate that the movement distance of water droplet markedly increases with the increasing of the release distance. Because the potential energy of the height is converted into kinetic energy, the water droplet intensively collides the interface between ZnO nanorod array and SLIPS. This impact makes the water droplet distort, which enhances the driving force. These new findings will not only deepen our understanding of the relationship between surface structure and dynamic wetting properties, but also afford the new notion and beneficial reference for designing liquid droplet transportation devices in micro-fluidic systems.

Zinc oxide (ZnO) nanorods (NRs) have been synthesized as a template to fabricate TiO₂ nanotubes (TiNTs) on hemispherical diamond film by liquid-phase deposition (LPD) method. The process concerning the formation of TiNTs was analyzed. Based on the results of XRD and Raman spectroscopy, it is demonstrated that TiNTs was successfully obtained after removing ZnO NRs by chemical etching at room temperature. The TiNTs on hemispherical diamond film show higher performance photocatalysis, examined by the degradation of the reactive yellow 15 (RY15) solution. The corresponding mechanism is discussed.

Innovative vertically aligned ZnO/In_xS_y nanorod (NR) electrodes were prepared by successive ion layer adsorption and reaction (SILAR) technique. The In_xS_y shell layer was deposited on top of ZnO NR electrodes of two different lengths, ~1.6 μm and ~3.2 μm. Two sulfur contents on the In_xS_y shell layer with different layer thicknesses were analyzed. These electrodes were fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), Energy-dispersive x-ray spectroscopy (EDS), Infrared spectroscopy (FT-IR), x-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS) and then applied in dye-sensitized solar cells (DSC). Power conversion efficiency of 2.32% was observed when a low-sulfur content In_xS_y shell layer was applied in comparison to the stoichiometric In₂S₃ shell layer (0.21%) or the bare ZnO NRs (0.87%). In the case of low sulfur content, a shell layer of In(OH)_xS_y or/and In(OH)₃ is formed as observed by the presence of –OH observed by FTIR analyses. The presence of higher amounts of hydroxide groups modifies the bandgap and work function of the In_xS_y shell and facilitates dye adsorption, increasing the final solar cell performance.

S-doped C₃N₄ quantum dots (SCNQDs) were synthesized successfully by a low-temperature solid-phase method. The as-synthesised SCNQDs were decorated on ZnO nanorods by a dipping method. The ZnO nanorod films were prepared through a two-stage method, including pulse electrodeposition for depositing ZnO seed layer on fluorine doping SnO₂ glass (FTO) and chemical bath for growing ZnO nanorods on the ZnO seed layer. The prepared samples were characterized via scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS). The photoelectrochemical performances of the prepared samples were estimated using linear sweep voltammograms, electrochemical impedance spectra (EIS), Mott–Schottky, transient photocurrent and incident photon-to-current conversion efficiency (IPCE). The results show that the light absorption edge of the prepared SCNQDs increases from 326nm (CNQDs) to 349nm after S doping. The CNQD decorated ZnO photoanode film exhibits 1.34 times as high photocurrent as bare ZnO photoanode film. Importantly, the photocurrent increased to 1.79 times than bare ZnO photoanode film by S doping at 1.0V (versus Ag/AgCl), which is attributed to a wider light absorption of SCNQDs and a better efficiency of electron transfer in the interface between SCNQDs and ZnO.

The interconnected three-dimensional Ni–Co–S nanosheets were successfully deposited on ZnO nanorods by a one-step potentiostatic electrodeposition. The Ni–Co–S nanosheets provide a large electrode/electrolyte interfacial area which has adequate electroactive sites for redox reactions. Electrochemical characterization of the ZnO@Ni–Co–S core–shell nanorods presents high specifc capacitance (1302.5F/g and 1085F/g at a current density of 1 A/g and 20 A/g), excellent rate capabilities (83.3% retention at 20A/g) and great cycling stability (65% retention after 5000 cycles at a current density of 30A/g). The outstanding electrochemical performance of the as-prepared electrode material also can be ascribed to these reasons that the special structure improved electrical conductivity and allowed the fast diffusion of electrolyte ions.

Development of a low-cost hand-held nitric oxide (NO) sensor with high selectivity, sensitivity and low detection limit is attractive for environment and health monitoring applications. NO gas sensor was fabricated using hydrothermally grown ZnO nanorods (ZnO NRs). The sensing performance like sensor response, sensitivity, detection limit has been improved significantly by attaching gold nanoparticles (Au NPs) with ZnO NRs. Au NPs were synthesized by chemical reduction method from gold chloride trihydrate. The attachment of Au NPs on nanorods was done by spin coating method. The maximum sensor response and sensitivity were obtained at $\sim 100^{\circ }$C operating temperature with $300\mu$l gold loading. The interference study of the sensor was carried out with acetone, ammonia, carbon monoxide, hydrogen peroxide and propanol. It demonstrated high selectivity towards the interfering gases and high humid condition. Au-decorated ZnO NRs exhibited very low detection limit $\sim 6.6$ppb, which is attractive for biomedical applications.

The use of solar energy for photoelectrochemical (PEC) water splitting is seen as an alternate strategy for addressing the problems of fossil fuels and global warming. In order to achieve the desired PEC performance for the evolution of hydrogen, such as high solar to hydrogen efficiency, incident photo to current conversion efficiency, and long-term stability, significant strategies have been developed on the basis of the bottom-up approach. Inorganic metal oxides, like zinc oxide (ZnO), are thought to be among the most promising photoelectrode materials because of their high carrier mobility, high exciton binding energy and non-toxic nature. Herein, we have summarized and reviewed ZnO nanostructured-based photoanode used in PEC applications.