Crystalline Zinc Oxide Research Articles

The Relationship between the Mechanism of Zinc Oxide Crystallization and Its Antimicrobial Properties for the Surface Modification of Surgical Meshes.

Surgical meshes were modified with zinc oxide (ZnO) using a chemical bath deposition method (CBD) at 50 °C, 70 °C, or 90 °C, in order to biologically activate them. Scanning electron microscopy (SEM), mass changes, and X-ray diffraction measurements revealed that at low temperatures Zn(OH)2 was formed, and that this was converted into ZnO with a temperature increase. The antimicrobial activity without light stimulation of the ZnO modified Mersilene™ meshes was related to the species of microorganism, the incubation time, and the conditions of the experiment. Generally, cocci (S. aureus, S. epidermidis) and yeast (C. albicans) were more sensitive than Gram-negative rods (E. coli). The differences in sensitivity of the studied microorganisms to ZnO were discussed. The most active sample was that obtained at 90 °C. The mechanism of antimicrobial action of ZnO was determined by various techniques, such as zeta potential analysis, electron paramagnetic resonance (EPR) spectroscopy, SEM studies, and measurements of Zn(II) and reactive oxygen species (ROS) concentration. Our results confirmed that the generation of free radicals was crucial, which occurs on the surface of crystalline ZnO.

ZnO/Au nanocatalysts for enhanced decolorization of an azo dye under solar, UV-A and dark conditions

Abstract Plasmonic nanoparticles have emerged as a promising material for enhancing catalytical properties of wide-bandgap semiconductors. In this work, we report a well-controllable synthesis of new nanocatalysts based on star-shaped zinc oxide (ZnO) decorated with gold nanoparticles for enhanced decolorization of methylene blue under solar, UV-A and dark conditions. ZnO particles were prepared using precipitation method at room temperature and decorated with Au nanoparticles via a simple photodeposition methodology. Morphology, crystallinity, and optical properties of bare ZnO and hybrid ZnO/Au nanocatalysts were fully characterized by standard analytical techniques. The catalytic properties for decolorizing aqueous methylene blue (MB) solutions of these materials were tested via 3 different methods: photocatalysis using UV-A irradiation, photocatalysis using solar irradiation, and sonocatalysis in dark conditions, under low frequency ultrasound. The results revealed the plasmon-enhanced performance of ZnO/Au nanocatalysts when the system is exposed with solar irradiation, which could be attributed to the efficient charge separation of photogenerated electron/hole pairs, as inferred from PL studies. Finally, it was found that the photocatalysis efficiency is influenced by variations on the [MB]/mcatalyst ratio and the size/concentration of dopping Au nanoparticles.

Preparation of electron buffer layer with crystalline ZnO nanoparticles in inverted organic photovoltaic cells

Zinc oxide (ZnO) nanoparticles synthesized through sol-gel method were used to fabricate the electron buffer layer in inverted organic photovoltaic cells (OPVs) after thermal treatment. To investigate the effect of thermal treatment on the formation of crystalline ZnO nanoparticles, the amorphous ZnO nanoparticles were treated via hydrothermal method. The crystalline phase of ZnO with well-ordered structure could be obtained when the amorphous phase of ZnO was processed under hydrothermal treatment at 170°C. The crystalline structure of ZnO thin film in inverted organic solar cell could be obtained under relatively low annealing temperature by using thermally treated ZnO nanoparticles. The OPVs fabricated by using crystalline ZnO nanoparticles for electron buffer layer exhibited higher efficiency than the conventional ZnO nanoparticles. The best power conversion efficiency (PCE) was achieved for 7.16% through the ZnO film using the crystalline ZnO nanoparticles. The proposed method to prepared ZnO nanoparticles (NPs) could effectively reduce energy consumption during the fabrication of OPVs, which would greatly contribute to advantages such as lower manufacturing costs, higher productivity and application on flexible substrates.

Stable p–i–n FAPbBr3 Devices with Improved Efficiency Using Sputtered ZnO as Electron Transport Layer

Radio‐frequency magnetron sputtering is demonstrated as an effective tool to deposit highly crystalline thin zinc oxide (ZnO) layer directly on perovskite absorber as an electron transport layer (ETL). As an absorber, formamidinium lead tribromide (FAPbBr3) is fabricated through a modified single‐step solution process using hydrogen bromide (HBr) as an additive resulting in complete surface coverage and highly crystalline material. A planar p–i–n device architecture with spin‐coated poly‐(3,4‐ethylenedioxythiophene):poly‐styrenesulfonic acid (PEDOT:PSS) as hole transport material (HTM) and sputtered ZnO as ETL results in a short circuit current density of 9.5 mA cm−2 and an open circuit potential of 1.19 V. Numerical simulations are performed to validate the underlying loss mechanisms. The use of phenyl C60 butyric acid methyl ester (PCBM) interface layer between FAPbBr3 and sputter‐coated ZnO offers shielding from potential plasma‐related interface damage. The modified interface results in a better device efficiency of 8.3% with an open circuit potential of 1.35 V. Such devices offer better stability under continuous illumination under ambient conditions in comparison with the conventional organic ETL (PCBM)‐based devices.

Highly Sensitive Electrospun Multiwalled Carbon Nanotubes Embedded Zinc Oxide Nanowire Based Interface for Label Free Biosensing

We demonstrate synthesis of Multiwalled carbon nanotubes (MWCNTs) embedded highly oriented Zinc Oxide (ZnO) nanowires targeted towards development of ultrasensitive electrochemical nanobiosensors using electrospinning method. The synthesized composite nanowires combines advantages of ZnO such as biocompatibility, electrostatic affinity towards biomolecules with the excellent conductivity and surface functionalization capabilities of MWCNTs. Calcination temperature is optimized so as to ensure MWCNTs are present in their original form and at the same time highly crystalline ZnO is obtained. The key advantage of this process is that there is no separate functionalization process is required to create functional groups on MWCNTs. Furthermore, the electrochemical activity of MWCNTs embedded ZnO nanowires is much higher as compared to pure ZnO nanowires. We have demonstrated the performance of electrochemical nanobiosensor using Biotin-streptavidin interaction as model system. The sensor exhibits excellent sensitivity in the range 10 μgmL-1 - 0.5 fgmL-1 of streptavidin with 0.5fgmL-1 limit of detection.

Effect of pH on the properties of electrochemically prepared ZnO thin films

Zinc Oxide (ZnO) thin films have been electrochemically deposited on fluorine doped tin oxide (FTO) coated glass substrates from an aqueous electrolyte. Deposition potential −0.96V was optimized by cyclic voltammetry experiment for slow scan rate 5mV/s with moderate agitation of electrolyte. The effect of pH on the electrodeposition of ZnO is studied by cyclic voltammetry, X-ray diffraction (XRD), scanning electron microscopy (SEM), optical spectroscopy and photoelectrochemical I-t transient characteristics. It is revealed that the pH of the electrolyte has significant influence on the surface morphology and structural properties. Highly crystalline ZnO layers with hexagonal crystal structure deposited for all pH of the solutions. A systematic shift observed in the reflections (002) and (101) is correlated with an effective tensile strain developed in the crystal lattice. A remarkable improvement in the crystallinity was noticed in the as-deposited ZnO samples with increasing pH and upon heat treatment. Optical direct band gap ~ 3.26–3.33eV and transmittance ~70 −80% was measured by optical spectroscopy. PL measurement showed the band edge emission at 375–382nm and a visible light emission at 410–550nm. The intensities of emission peaks are found to be affected by the pH of bath. The compact, densely packed and well adherent thin films of ZnO electrodeposited in zinc nitrate bath for pH 2.0, 3.5 and 6.0. The surface morphology has been changed from granular to disc shaped and finally a large hexagonal sheets were obtained with an increase in the pH of bath. Nearly stoichiometric ZnO thin films are electrodeposited at −0.96V versus Ag/AgCl reference electrode for pH 6.0. The photoelectrochemical (PEC) measurement (I-t transient curve) shows the enhancement in photocurrent with increasing the pH of zinc nitrate solution. After heat treatment the photocurrent is increased by 54%, 98% and 130% in the samples deposited from 2.0, 3.5 and 6.0pH of the bath. I-V measurements were further confirmed the current enhancement in all samples after heat treatment.

Structural and optical properties of Cr-doped ZnO thin films

In the present work, chromium (Cr)-doped zinc oxide (ZnO) thin films were prepared on silicon and glass substrates by using the sol–gel spin-coating technique. The influence of chromium doping on the structural and optical properties of zinc oxide films was investigated. The X-ray diffraction results reveal that the films are polycrystalline in nature with hexagonal wurtzite structure. The absence of secondary diffraction peaks other than those for zinc oxide suggests that the chromium ions successfully replaced zinc (Zn) ions and were incorporated into the crystal-lattice positions. The average grain size and the strain arising due to the introduction of chromium ions in the lattice were obtained by using Williamson–Hall analysis. The surface morphology of the films was observed by field emission scanning electron microscopy. The Raman spectra of the films show a peak at 434 cm−1 corresponding to E2 (high) mode of crystalline zinc oxide wurtzite structure, and the intensity of this mode decreases with increase in chromium doping. The films are highly transparent (∼90%) in the visible region, which reduces with chromium doping.

Structural and Morphological study of ZnO-Ag thin films synthesized by reactive magnetron co-sputtering

Zinc oxide (ZnO) is well-known to present, among other properties, a good antibacterial activity which could be enhanced by the addition of Ag. The efficiency of ZnO-Ag films is correlated to the Ag concentration which should not exceed a threshold of a few atomic percent. Therefore it is necessary to develop a synthesis method allowing a perfect control of the film properties which can be easily transferred to the industry. In this context, we have developed a reactive magnetron co-sputtering process, in which, a Zn and an Ag metallic targets are co-sputtered in Ar-O2 gas mixtures. ZnO-Ag thin films were successfully grown, in which the Ag concentration can be tuned with a precision of 0.2%. The experimental data reveal that the incorporation of Ag disturbs the ZnO crystalline structure, and that Ag migrates to the film surface and agglomerates as a function of time for at.%Ag > 1.5%. The latter phenomenon takes place several days after the film synthesis when they are stored under ambient conditions, and is associated to oxydo-reduction reactions between oxygen and silver atoms.

Improved photo-catalytic activity of novel nano-dimension Ce/Zn composite oxides deposited on flat-glass surface for removal of Acid Black 4BN dye pollution

In this research, we studied an easy method to prepare pure cerium oxide nano particle (CeONP), pure zinc oxide nano particle (ZnONP) and Ce/Zn nano composite (Ce/ZnONP) coupled oxide by one pot reaction of cerium and zinc nitrate as precursors in aqueous solution using a Teflon-lined stainless autoclave at 120 °C for 12 h. Model water pollutant Acid Black 4BN as a di-azo textile dye was used to compare the photo-catalytic activity of (CeONP), (ZnONP) and (CeZnONP) deposited on flat-glass surface to overcome the problem of nano catalyst separation from suspension. Thermal, structural and spectral characterization of nano-structures were studied by thermo-gravimetric analysis, X-ray diffraction method, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy. The elemental analysis using energy dispersive X-ray spectroscopy proved the existence of cerium and zinc in immobilized nano-structures Ce/Zn oxides. The X-ray diffraction result of the composite showed high crystalline cubic cerium oxide and hexagonal wurtzite zinc oxide. The photo-catalytic activity of Ce/Zn nano composite oxide coated on flat-glass surface for degradation dia-azo dye was enhanced compared to their single oxide counterparts. This heterogeneous photo-catalytic degradation of dia-azo dye can be applied as an alternative to suspended oxide powders and over-come drawbacks of filtration of photo-catalysts. This study for the first time showed the potential application of Ce/Zn nano composite for removal of organic pollutant from water.

Tuning of Structural and Optical Properties of Graphene/ZnO Nanolaminates

Zinc oxide (ZnO) and graphene (G) have been extensively studied because of their unique physical properties. Here, graphene–zinc oxide (G/ZnO) nanolaminates were fabricated, respectively, by chemical vapor deposition and low-temperature atomic layer deposition technique. The number of obtained G/ZnO layers was tuned from 1 to 11 with a total thickness of 100 nm for all prepared nanolaminates. The structure, optical properties, and interaction between G and ZnO were studied by X-ray methods, TEM, AFM, Raman, and optical spectroscopy. The obtained results were interpreted and analyzed taking into account strain and charge effects of graphene in G/ZnO nanostructures. We demonstrate that the bottom graphene used as a substrate stimulated the formation of ZnO crystalline structure. n-Doping of graphene caused by charge transfer from ZnO to graphene has been detected by blue-shift of G-band of Raman spectra of the nanolaminates. ZnO photoluminescence intensity was found to be dependent on the number of graphene...

Low cerium doping investigation on structural and photoluminescence properties of sol-gel ZnO thin films

Undoped and cerium (Ce)-doped zinc oxide (ZnO) thin films with various doping concentrations of cerium (0.1–0.9 at.%) were prepared on glass substrates by the sol-gel dip-coating process. The effects of Ce doping on the structural, morphological and optical properties were studied by X-ray diffraction, energy-dispersive X-rays, atomic force microscopy, UV–visible spectrophotometry and photoluminescence spectroscopy. The diffraction patterns showed that all the samples are characterized by a hexagonal wurtzite crystalline ZnO structure with (0002) preferred orientation. The crystal quality and crystallite size were found to decrease with the Ce doping level. From the atomic force microscopy images analysis it was revealed that both of the grain size and the surface roughness decrease with the increasing of the Ce concentrations. According to UV–visible measurements all the films are highly transparent with average visible transmittance values ranging from 79% to 82%, and the optical band gap is sensitive to the dopant concentration. Room temperature photoluminescence spectra put into evidence that UV and visible emissions decrease significantly as the Ce concentration increases from 0.1 to 0.9 at.%.

Green mediated synthesis of zinc oxide nanoparticles for the photocatalytic degradation of Rose Bengal dye

Zinc oxide (ZnO) nanoparticles were synthesised by a simple method using leaf extract of jackfruit (Artocarpus heterophyllus). The phytochemicals present in the leaf act as stabilising agents. The green synthesised ZnO nanoparticles were characterized by X-ray diffraction (PXRD), Scanning Electron microscopy (FESEM), Energy dispersive spectroscopy (EDS) and Transmission electron microscopy (TEM). XRD pattern confirmed the formation of crystalline ZnO nanoparticles. The SEM images showed porous, sponge-like agglomerated structures. TEM analysis showed the ZnO nanoparticles formed to have hexagonal wurtzite structure and the particles ranging between 15 and 25nm. The green synthesised ZnO nanoparticles exhibited excellent photodegradation efficiency (>80%, 0.24g/L, 1h) against Rose Bengal dye, a main water-pollutant released by the textile industries. The characterisation results confirmed that the ZnO nanoparticles can be efficiently synthesised using jackfruit leaf extract as stabiliser and the photodegradation results proved the efficiency of the green synthesised ZnO nanoparticles for the degradation of Rose Bengal dye.

Effect of Hydroxyl Concentration on the Structural and Optical Properties of Zinc Oxide Nanoparticles

Zinc oxide (ZnO) nanoparticleswere successfully synthesized by chemical precipitation method at different hydroxyl concentrations. The resulting nanoparticles are characterized by transmission electron microscopy (TEM), ultraviolet-visible (UV-VIS) and photoluminescence (PL) spectroscopy. From TEM images, the measured average sizes of the nanoparticles were 4.45 nm to 5.26 nm. Selected area diffraction(SAED) patternsconfirmed that the nanoparticles were of highly crystalline ZnO having wurtzitephase structure.The energy band gap values red-shifted from 3.79 to 3.64 eV based from excitonic absorption peaks. All the samples exhibited a strong visible emission and decreasing peak intensity in increasing OH- concentration.

One step biofunctionalized electrospun multiwalled carbon nanotubes embedded zinc oxide nanowire interface for highly sensitive detection of carcinoma antigen-125

Ovarian cancer is the most leading cause of cancer-related death in women . The carcinoma antigen-125, which is found on the surface of many ovarian cancer cells is known to be a gold standard clinical biomarker associated with life-threatening gynecological malignancy. In this work, we demonstrate a novel biosensor platform based on multiwalled carbon nanotubes embedded zinc oxide nanowire for the ultrasensitive detection of carcinoma antigen-125. Label free detection of the carcinoma antigen-125 was accomplished by differential voltammetry technique that demonstrated excellent sensitivity (90.14µA/(U/mL)/cm2) with a detection limit of 0.00113UmL−1 concentration. The fabricated immunosensor exhibits good performance with wider detection range (0.001UmL−1–1kUmL−1), reproducibility, selectivity, acceptable stability, and thus is a potential cost-effective methodology for point-of-care diagnosis. The multiwalled carbon nanotubes (MWCNTs) embedded highly oriented zinc oxide (ZnO) nanowires were synthesized by simple, low cost electrospinning technique. Compared to pure ZnO nanowires, electrochemical activity of MWCNTs embedded ZnO nanowires was found to be much higher. The calcination temperature was optimized to avoid any decomposition of the CNTs and to obtain multiwalled carbon nanotubes embedded highly crystalline ZnO nanowires. The salient feature of this biosensing platform is that one step calcination process is enough to create the functional groups on MWCNT-ZnO nanowire surface that are effective for the covalent conjugation of antibody without further surface modification. To the best of our knowledge, this is the first report on MWCNT-ZnO nanowire based immunosensor explored for the detection of cancer biomarker.

Novel Biomimatic Synthesis of ZnO Nanorods Using Egg White (Albumen) and Their Antibacterial Studies.

Zinc oxide (ZnO) is well-recognized as a biocompatible multifunctional material with outstanding properties as well as low toxicity and biodegradability. In this work, a simple and versatile technique was developed to prepare highly crystalline ZnO nanorods by introducing egg white to a bio-inspired approach. X-ray diffraction (XRD) and selected area electron diffraction (SAED) pattern results indicated that the ZnO nanorods have single phase nature with the wurtzite structure. Field emission scanning electron microscopy (FESEM) and Transmission electron microscopy (TEM) results showed the nanometer dimension of the nanorods. Raman, FTIR, and TGA/DTA analyses revealed the formation of wurtzite ZnO. The antibacterial properties of ZnO nanorods were investigated using both Gram-positive and Gram-negative microorganisms. These studies demonstrate that ZnO nanorods have a wide range of antibacterial activities toward various microorganisms that are commonly found in environmental settings. Survival ratio of bacteria decreased with increasing powder concentration, i.e., increase in antibacterial activity. The antibacterial activity of the ZnO nanorods toward Pseudomonas aeruginosa was stronger than that of Escherichia coli and Staphylococcus aureus. Surprisingly, the antibacterial activity did not require specific UV activation using artificial lamps, rather activation was achieved under ambient lighting conditions. Overall, the experimental results suggest that ZnO nanorods could be developed as antibacterial agents against a wide range of microorganisms to control and prevent the spreading and persistence of bacterial infections. This research introduces a new concept to synthesize ZnO nanorods by using egg white as a biological template for various applications including food science, animal science, biochemistry, microbiology and medicine.

Antibacterial, Structural and Optical Characterization of Mechano-Chemically Prepared ZnO Nanoparticles.

Structural investigations, optical properties and antibacterial performance of the pure Zinc Oxide (ZnO) nanoparticles (NPs) synthesized by mechano-chemical method are presented. The morphology, dimensions and crystallinity of the ZnO NPs were controlled by tweaking the mechanical agitation of the mixture and subsequent thermal treatment. ZnO nanoparticles in small (< 20 nm) dimensions with spherical morphology and narrow size distribution were successfully obtained after treating the mechano-chemically prepared samples at 250°C. However, higher temperature treatments produced larger particles. TEM, XRD and UV-Vis spectroscopy results suggested crystalline and phase pure ZnO. The NPs demonstrated promising antibacterial activity against Gram negative foodborne and waterborne bacterial pathogens i.e. Enteropathogenic E. coli (EPEC), Campylobacter jejuni and Vibrio cholerae as well as Gram positive methicillin resistant Staphylococcus aureus (MRSA), thus potential for medical applications. Scanning electron microscopy and survival assay indicated that most probably ZnO nanoparticles cause changes in cellular morphology which eventually causes bacterial cell death.

Room Temperature Deposition of Crystalline Nanoporous ZnO Nanostructures for Direct Use as Flexible DSSC Photoanode.

A facile approach to fabricate dye-sensitized solar cells (DSSCs) is demonstrated by depositing (001) oriented zinc oxide (ZnO) nanostructures on both glass and flexible substrates at room temperature using pulsed laser deposition. Unique crystallographic characteristics of ZnO combined with highly non-equilibrium state of pulsed laser-induced ablated species enabled highly crystalline ZnO nanostructures without aid of any chemically induced additives or organic/inorganic impurities at room temperature. Film morphology as well as internal surface area is tailored by varying ambient oxygen pressure and deposition time. It is revealed that the optimization of these two experimental factors was essential for achieving structure providing large surface area as well as efficient charge collection. The DSSCs with optimized ZnO photoanodes showed overall efficiencies of 3.89 and 3.4 % on glass and polyethylene naphthalate substrates, respectively, under AM 1.5G light illumination. The high conversion efficiencies are attributed to elongated electron lifetime and enhanced electrolyte diffusion in the high crystalline ZnO nanostructures, verified by intensity-modulated voltage spectroscopy and electrochemical impedance measurements.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1437-2) contains supplementary material, which is available to authorized users.

New CVD-based method for the growth of high-quality crystalline zinc oxide layers

High-quality zinc oxide (ZnO) layers were grown using a new chemical vapour deposition (CVD)-based low-cost growth method. The process is characterized by total simplicity, high growth rates, and cheap, less hazardous precursors. To produce elementary zinc vapour, methane (CH4) is used to reduce a ZnO powder. By re-oxidizing the zinc with pure oxygen, highly crystalline ZnO layers were grown on gallium nitride (GaN) layers and on sapphire substrates with an aluminum nitride (AlN) nucleation layer. Using simple CH4 as precursor has the big advantage of good controllability and the avoidance of highly toxic gases like nitrogen oxides. In photoluminescence (PL) measurements the samples show a strong near-band-edge emission and a sharp line width at 5K. The good crystal quality has been confirmed in high resolution X-ray diffraction (HRXRD) measurements. This new growth method has great potential for industrial large-scale production of high-quality single crystal ZnO layers.

Evaluation of polarization rotation in the scattering responses from individual semiconducting oxide nanorods.

We investigate the interaction of visible light with the solid matters of semiconducting oxide nanorods (NRs) of zinc oxide (ZnO), indium tin oxide (ITO), and zinc tin oxide (ZTO) at the single nanomaterial level. We subsequently identify an intriguing, material-dependent phenomenon of optical rotation in the electric field oscillation direction of the scattered light by systematically controlling the wavelength and polarization direction of the incident light, the NR tilt angle, and the analyzer angle. This polarization rotation effect in the scattered light is repeatedly observed from the chemically pure and highly crystalline ZnO NRs, but absent on the chemically doped NR variants of ITO and ZTO under all measurement circumstances. We further elucidate that the phenomenon of polarization rotation detected from single ZnO NRs is affected by the NR tilt angle, while the phenomenon itself occurs irrespective of the wavelength and incident polarization direction of the visible light. Combined with the widespread optical and optoelectronic use of the semiconducting oxide nanomaterials, these efforts may provide much warranted fundamental bases to tailor material-specific, single nanomaterial-driven, optically modulating functionalities which, in turn, can be beneficial for the realization of high-performance integrated photonic circuits and miniaturized bio-optical sensing devices.

Synthesis, characterization, and hydrogen gas sensing properties of AuNs-catalyzed ZnO sputtered thin films

Hydrogen present in concentration up to 4 vol.% forms an explosive mixture with air. Its propensity to escape in the event of leak, could lead to quick build-up and formation of an explosive mixture with air in confined spaces, such as an automobile. This necessitates its detection at very low concentration. Zinc oxide (ZnO) is a well-known wide band gap (∼3.37eV) semiconducting oxide that has been widely used for gas sensing applications. This work reports on the fabrication, characterization and gas sensing performance of nanogold decorated ZnO thin films made by DC reactive sputtering. The sensor films were fabricated by depositing a very thin layer of gold on the sputtered ZnO thin film. The as deposited Au@ZnO films were converted into highly crystalline ZnO film covered with gold nanostructures (AuNs@ZnO) by mild heat treatment. The structural and morphological as well as the compositional homogeneity of the as-deposited and heat-treated ZnO, Au@ZnO and AuNs@ZnO thin films were ascertained. The gas sensing behavior of the AuNs@ZnO thin films towards hydrogen as a function of temperature at different H2 concentrations was investigated and compared with that of pure and heat-treated ZnO films. The effect of the presence of gold nanoparticles on imparting improvement (in terms of higher response signal, high reproducibility and complete reversibility) was established; the optimal operating temperature was about 400°C. A plausible mechanism for the observed enhancement in the sensing behavior of AuNs@ZnO films towards H2 is proposed.