ZnO Matrices Research Articles

ZnO Matrices as a Platform for Tunable Localized Surface Plasmon Resonances of Silver Nanoparticles

In this study, the localized surface plasmon resonances (LSPRs) of Ag nanoparticles (NPs) embedded in ZnO dielectric matrices were studied. Initially, continuous Ag thin films were deposited on Corning glass substrates via magnetron sputtering, followed by post annealing, resulting in the formation of self-assembled nanoparticles. In some cases, a heated substrate holder was employed to induce NP formation during the deposition. The morphology of nanoparticles was studied using atomic force microscopy (AFM). Ultraviolet–visible spectroscopy (UV-Vis) probed the LSPRs. Subsequently, a 70 nm thick ZnO layer was deposited on top of the Ag thin films. For the Ag films, LSPR characteristics were found to depend on the initial film thickness. The ZnO capping layer induced an intense red shift, suggesting its potential as a mechanism for tailoring LSPRs. Lastly, theoretical calculations with the rigorous coupled-wave analysis (RCWA) method were carried out for comparison with the experimental results.

CO2 electro/photocatalytic reduction using nanostructured ZnO and silicon-based materials: A short review

Reducing CO2 net emissions is one of the most pressing goals in tackling the current global warming emergency. Therefore, the development of carbon recycling strategies has resulted in the application of heterogeneous catalysts toward the electro/photocatalysis reduction of CO2 into hydrocarbons with potential reusability. Their morphology is among the properties that affect the performance and selectivity of catalysts towards this reaction. Nanostructuring methods offer popular strategies for catalytic applications since they allow an increase in the area/volume ratio and versatile control over surface physicochemical properties. In this review, we summarize studies that report the use of versatile synthesis techniques for obtaining nanostructured metallic and semiconductor materials with application in the electro/photocatalytic reduction of CO2. Enhancing mechanisms to the catalytic CO2 reduction yield, such as improved charge carrier separation efficiency, defect engineering, active site concentration, and localized plasmonic behavior, are described in conjunction with the control over the morphologies of the nanostructured platforms. Special attention is given to ZnO and silicon-based matrices as candidates for developing abundant and non-toxic catalytic materials. Therefore, this work represents a guide to the efforts made to design electro/photocatalytic systems that can contribute significantly to this field.

Magnetic circular dichroism of Co nanoparticles localized in matrices of various types

Magnetic and magneto-optical properties of cobalt nanoparticles (Co-NPs) dispersed in a transparent dielectric SiO2 and semiconductor ZnO matrices have been investigated. Field and temperature dependences of the samples magnetization showed the typical behavior of an ensemble of superparamagnetic particles with a blocking temperature near and below room temperature. The spectroscopy of magnetic circular dichroism (MCD) in the visible and near-infrared light ranges has revealed a significant difference between the behavior of the Co-NPs and a solid Co film. It has been found that the MCD spectrum shape for the Co-NPs does not depend on the matrix type. The room temperature magneto-optical activity of the Co-NPs in the different matrices has been estimated as an indicator for practical applications.

In-situ growth of carbon nanotubes on ZnO to enhance thermoelectric and mechanical properties

As a high-temperature thermoelectric (TE) material, ZnO offers advantages of non-toxicity, chemical stability, and oxidation resistance, and shows considerable promise as a true ready-to-use module under air conditions. However, poor electrical conductivity and high thermal conductivity severely hinder its application. Carbon nanotubes (CNTs) are often used as a reinforcing phase in composites, but it is difficult to achieve uniform dispersion of CNTs due to van der Waals forces. Herein, we developed an effective in-situ growth strategy of homogeneous CNTs on ZnO nanoparticles by exploiting the chemical vapor deposition (CVD) technology, in order to improve their electrical conductivity and mechanical properties, as well as reducing the thermal conductivity. Meanwhile, magnetic nickel (Ni) nanoparticles are introduced as catalysts for promoting the formation of CNTs, which can also enhance the electrical and thermal transportation of ZnO matrices. Notably, the electrical conductivity of ZnO is significantly boosted from 26 to 79 S·cm−1 due to the formation of dense and uniform conductive CNT networks. The lattice thermal conductivity (κL) is obviously declined by the intensification of phonon scattering, resulting from the abundant grain boundaries and interfaces in ZnO-CNT composites. Importantly, the maximum dimensionless figure of merit (zT) of 0.04 at 800 K is obtained in 2.0% Ni-CNTs/ZnO, which is three times larger than that of CNTs/ZnO prepared by traditional ultrasonic method. In addition, the mechanical properties of composites including Vickers hardness (HV) and fracture toughness (KIC) are also reinforced. This work provides a valuable reference for dispersing nano-phases in TE materials to enhance both TE and mechanical properties.

Effects of substantial atomic-oxygen migration across silver − oxide interfaces during silver growth

The optimization of Ag wetting on oxides is essential to facilitate the synthesis of ultrathin Ag layers with ultralow electrical and optical losses. However, the primary challenge of increasing the Ag wetting on oxides is the strong cohesion and weak adhesion of Ag with chemically heterogeneous oxide substrates. In the present study, it was observed that the dissolution of excess atomic oxygen in ZnO lattices prior to Ag deposition induced the pronounced migration of atomic oxygen across the Ag − ZnO interface and subsequent incorporation into Ag lattices. The substantial intermixing of atomic oxygen in the Ag − ZnO matrices contributed to a decrease in the free energy at the interface, thereby weakening the driving force for the agglomeration of Ag nanoparticles during coalescence. This resulted in an increase in the adhesion and wetting of Ag geometries on the ZnO surfaces. These findings were confirmed based on the results of detailed experimental investigations in conjunction with numerical predictions. These outcomes elucidated the unconventional oxygen spillover dynamics from atomic oxygen-excess oxide surfaces. The findings obtained in the present study refute the existing convictions that the intermixing of oxygen at Ag − oxide interfaces is limited by weak charge transfer.

Heteroepitaxial growth of high Mg-content single-phased W-MgZnO on ZnO matrixes in various nucleation states for solar-blind and visible-blind dual-band UV photodetectors

High Mg-content single-phase wurtzite Mg0.51Zn0.49O (W-Mg0.51Zn0.49O) films were realized by radio frequency (RF) magnetron sputtering technique on quartz (SiO2) substrates. The metal-semiconductor-metal (MSM) solar-blind (SB) and visible-blind (VB) dual-band ultraviolet (DB-UV) photodetectors (PDs) were also fabricated based on heteroepitaxial growth of W-Mg0.51Zn0.49O films on ZnO buffer layer (BL) at different nucleation states. Under 270 nm of irradiation, the Au/Mg0.51Zn0.49O/ZnO (30 min) PD exhibited an optimal external quantum efficiency (EQE, 304.4%) and specific detectivity (1012), which indicated that the ZnO BL obtained with a 30 min treatment time was most efficient to improve the detection of SB-UV wavelength. The origin of these results was attributed to the contact area and adhesion strength between MgZnO and ZnO matrices. The results showed a feasible way to obtain high Mg-content wurtzite MgZnO alloys and performance improvement through ZnO BL, which is favorable to the applicability in SB/VB DB-UV PDs.

The effect of graphene+boron nitride/ZnO-based hybrid nanocomposites: synthesis, electrical, optical properties

In this study, nanocomposites ZnO-doped graphene+boron nitride nanosheets (BNNS) were produced, and their electrical and optical properties were investigated. The graphene+BN nano-hybrid layer used as a reinforcement element was synthesized using a liquid-phase exfoliation method. TEM images support the nanosheet’s structure of the graphene and boron nitride. ZnO produced by sol-gel showed nanoscale spherical particles, while the commercial ZnO showed the micrometer scale with rod-like and hexagonal shapes. Composite materials were provided by reinforcing this reinforcement element into ZnO matrices, which were commercially available and were produced using the sol-gel procedure at different ratios. To compare the results, the BN nanosheets were synthesized using liquid-phase exfoliation. Using the same method, samples for comparison were produced by reinforcing these nano-hybrid sheets into the commercially available ZnO matrix and the sol-gel synthesized ZnO matrix. A limited increase was shown for the 0.1 wt% and 0.5 wt% in the nanocomposites’ electrical conductivity ratios, along with the rise of the graphene + BN nano-hybrid sheet. The Eg values of the as-produced nanocomposites first decreased and then increased as the reinforcement ratio increased. The bandgap changing for all reinforcing types exhibits similar characters. The studied materials can be used in wide-scale electronic and optoelectronic devices, environmental, biomedical, and catalytic/photocatalytic activities.

Hybrid Ag/ZnO nanostructures for SERS detection of ammonium nitrate

Ag/ZnO composite nanostructures are produced by combined laser and ion implantation techniques. The ZnO layers are grown on SiO2 (001) and Al2O3 (r-cut) substrates by pulsed laser deposition (PLD) in vacuum and in oxygen ambient using a third-harmonic Nd:YAG laser. The ion implantation allows the introduction of Ag nanoparticles (NPs) in the surface of the ZnO matrix. These NPs are incorporated into the ZnO matrices to fabricate metal-semiconductor nanocomposites with the aim of manipulating their functionalities, exploiting the characteristics of both the matrix and the metal NPs. The composite samples are modified by laser annealing at 355 nm and 532 nm. The changes are investigated in the plasmon resonance absorption of the nanostructures before and after the annealing. The influence is explored of the different substrates used and the deposition conditions of ZnO growth on the properties of Ag/ZnO. The nanostructures obtained are efficient as SERS substrates for detection of ammonium nitrate under laser excitation at 633 nm. The SERS enhancement is attributed to the synergistic interactions between the plasmonic coupling among the surface embedded AgNPs and the enhanced charge transfer properties of the ZnO.

Single, co-doping and triple doping Fe element in the ZnO crystal matrices

Fe element settlement in the ZnO matrices has been investigated through prepared single doped, co-doped with Mg and triple doped with Mg and Cu by a systematic x-ray Photoelectron Spectroscopy (XPS) and Electron Paramagnetic Resonance (EPR) measurements as well as the structural and morphological analysis through x-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) measurements. Also, effects of different solutions, nitrate and chlorate, on the Fe doping has been studied. XRD measurements have exhibited that crystal quality of the thin films deteriorates as the Fe doping level increases. On the other hand, Fe co-doped and triple doped with Mg and Mg + Cu has converted the dominant crystal plane direction from (002) to (101) and (100), respectively. Single Fe doped ZnO thin films has shown the smoothest and uniform thin film surfaces while co-doped and the triple doped thin films has displayed overgrown surface morphology with 3D morphology. The XPS has been used to investigate the chemical environment of the Fe in the ZnO lattice and Fe element has been found to be in the Fe3+ state. Two signals have been observed at g ∼ 2.0 and g ∼ 4.3 which are attributed an electron trapped into oxygen vacancy and isolated Fe3+. As the concentration of Fe doping increases, the intensity of g ∼ 2.0 signal intensity increases significantly, while the g ∼ 4.3 signal intensity increases slowly. Temperature dependence of EPR signals in terms of intensity, linewidth and g-factor been investigated.

Water Splitting: Vapor Phase Fabrication of Nanoheterostructures Based on ZnO for Photoelectrochemical Water Splitting (Adv. Mater. Interfaces 18/2017)

In article number 1700161, Chiara Maccato and co-workers report on a hybrid vapor phase route for the growth of ZnO/Fe2O3 and ZnO/WO3 nanoheterostructures on fluorine-doped tin oxide substrates. A detailed characterization procedure allows to highligth an intimate contact and tailored interaction between the single oxides resulting in porous ZnO matrices conformally covered by tiny iron or tungsten oxide overlayers. These nanosystems show improved performances as photoanodes in solar-driven photoelectrochemical cells thanks to the enhanced separation of photogenerated charge carriers.

Room-temperature ferromagnetism in Co-, Cr-, and V-doped ZnO diluted magnetic semiconductor

In this study, diluted magnetic semiconductors Zn0.998TM0.002O (TM = Co, Cr, or V) samples were synthesized using the solid-state reaction method. X-ray diffraction measurements indicated that all the samples had a single crystalline wurtzite structure; moreover, no metallic transition metal or other secondary phases were found. The magnetization measurements showed that all the samples exhibited room-temperature ferromagnetism (RTFM) with a saturation magnetization and a coercive field of 2.310 µB/Co and ∼350 Oe, 2.479 µB/Cr and ∼325 Oe, and 2.198 µB/V and ∼170 Oe for Co-, Cr-, and V-doped ZnO, respectively. The structural and magnetic investigations demonstrate that RTFM is an intrinsic property of the samples. Thus, ferromagnetism does not originate from clusters or secondary phases; it is due to the Co/Cr/V:ZnO matrices. This study has shown that very light doping of Co, Cr, or V in ZnO results in appreciable RT ferromagnetic ordering that is useful for spintronic applications.

Enhancement of bioactivity and bioavailability of curcumin with chitosan based materials

Curcumin (CUR) has been investigated for its poor accessibility to a site of action or absorption and rapid metabolism to cope with the limited medication and cure applications. This article reviews numerous approaches, such as encapsulated surfactant/polymeric micelles, liposomes, micro/nano-spheres, nano-suspensions/composites, nanocomplex, films, and hydrogels for effective transfer of CUR to target sites. Chitosan (CS), and chitosan derivatives have been found to enhance therapeutic efficacy of CUR. CS/modified-CS based alginate, cyclodextrin, starch, dextran sulfate, ZnO, phytosomes, and poly(butyl) cyanoacrylate drug delivery matrices improved bioavailability, prolonged drug loading and permeability, sustained release rate, improved solubility and stability (prevent metabolic degradation) of CUR, consequently promoting various clinical applications. CS based polysaccharide, protein, and metal oxide drug delivery nano formulations advantageously participated to improve biological activities of CUR. We have attempted to summarize these delivery approaches, and reviewed future trends/strategies to permit the introduction of CUR as practical therapeutic drug.

XPS and DFT study of Sn incorporation into ZnO and TiO2host matrices by pulsed ion implantation

Bulk and thin films ZnO and TiO2 samples were doped with Sn by pulsed ion implantation and studied by means of X-ray photoelectron core-level and valence band spectroscopy as well as density functional theory calculations for comprehensive study of the incorporation of Sn. XPS spectral analysis showed that isovalent Sn cation substitution occurs in both zinc oxide (Sn2+ -> Zn2+) and titanium dioxide (Sn4+ -> Ti4+) for bulk and film morphologies. For TiO2 films, the implantation also led to occupation of interstitials by doped ions, which induced the clustering of substituted and embedded Sn atoms; this did not occur in ZnO:Sn film samples. Density functional theory (DFT) formation energies were calculated of various incorporation processes, explaining the prevalence of substitutional defects in both matrices. Possible mechanisms and reasons for the observed trends in Sn incorporation into the ZnO and TiO2 matrices are discussed.

Encapsulation of Glycosides from Extract Plantago Major in ZnO Matrices by Sol-Gel

Encapsulation of Glycosides from Extract Plantago Major in ZnO Matrices by Sol-Gel

Soft materials composed with lanthanide (Eu3+, Tb3+) beta-diketonates and ZnO nanoparticles through ionic liquid linkage to integrate white luminescence

Abstract In this note, 3-(2-(2-mercaptoacetoxy)ethyl)-1-methyl-1H-imidazol-3-ium bromide (SH-IL), a kind of room temperature thiol-functionalized ionic liquid compound is synthesized and used to interact with ZnO nanoparticles for the chemical affinity between S of SH-IL and Zn of ZnO. And then an anion exchange reaction is performed to introduce europium(III) and terbium(III) tetrakis β-diketonates (thenoyltrifluoroacetonate (TTA) or acetylacetonate (AcAc)) to ILs functionalized ZnO matrices. Subsequently, novel series of photoactive composites are assembled with ZnO nanoparticles and lanthanide complexes through SH-IL as bridge. Especially, it is worthy point out that the integration to white luminescence can be realized for the composite systems by adjusting the ratio of different active building units (red color for Eu complex, green color for Tb complex and blue color for ZnO unit). This result provides useful data to develop white-luminescent composite phosphors.

Influence of annealing temperature on the structural and optical properties of highly-oriented Al and Er co-doped ZnO films

High-quality c-axis oriented 7 mol% Al and 1.5 mol% Er co-doped ZnO films (ZEAO) were prepared on the quartz glass substrates by using sol–gel method. The influence of the annealing temperature on the crystal orientation, microstructure and optical properties of the ZEAO thin films were studied by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and UV–vis transmittance spectrophotometer, respectively. XRD results revealed that all the samples were polycrystalline with hexagonal structure and exhibited (002) preferential orientation. With increasing the annealing temperature, the grain size and orientation extent increased. The optical studies showed each ZEAO film had a relatively high transmittance above 85 %. The transmittance as high as 95 % was obtained at the annealing temperature of 800 °C, and the corresponding average grain size was about 50 nm. The cathodoluminescence (CL) spectra of these films were also used to characterize the luminescence properties. Strong UV emission centered at 380 nm was observed in the CL spectra taken for the pure ZnO. For the ZEAO sample, the blue-green emission is related to the 4f shell transition in the Er3+ ions of ZnO matrices, corresponding to a transition from the excited states (4F5/2).

CuO/ZnO Nanocomposite Gas Sensors Developed by a Plasma‐Assisted Route

CuO/ZnO nanocomposites were synthesized on Al(2)O(3) substrates by a hybrid plasma-assisted approach, combining the initial growth of ZnO columnar arrays by plasma-enhanced chemical vapor deposition (PE-CVD) and subsequent radio frequency (RF) sputtering of copper, followed by final annealing in air. Chemical, morphological, and structural analyses revealed the formation of high-purity nanosystems, characterized by a controllable dispersion of CuO particles into ZnO matrices. The high surface-to-volume ratio of the obtained materials, along with intimate CuO/ZnO intermixing, resulted in the efficient detection of various oxidizing and reducing gases (such as O(3), CH(3)CH(2)OH, and H(2)). The obtained data are critically discussed and interrelated with the chemical and physical properties of the nanocomposites.

Ag/ZnO nanomaterials as high performance sensors for flammable and toxic gases

Ag/ZnO nanocomposites supported on polycrystalline Al2O3 were synthesized by an unprecedented approach combining plasma enhanced chemical vapor deposition (PE-CVD) of ZnO matrices and the subsequent deposition of Ag nanoparticles (NPs) by radio frequency (RF) sputtering. The system structure, composition and morphology were investigated by glancing incidence x-ray diffraction (GIXRD), secondary ion mass spectrometry (SIMS), field emission scanning electron microscopy (FE-SEM) and energy dispersive x-ray spectroscopy (EDXS). A tailored dispersion and distribution of silver particles could be obtained under mild conditions by the sole variation of the sputtering time. Gas sensing properties toward flammable and toxic gases, both reducing (CH3CH2OH, CH3COCH3) and oxidizing (O3), were investigated in the temperature range 100–400 °C. Beside the high sensitivity, the developed sensors exhibited a response proportional to Ag content, thanks to catalytic and electronic effects promoted by silver NPs. In addition, discrimination between oxidizing and reducing analytes was enabled by a suitable choice of the adopted working temperature.

Microstructures, surface bonding states and room temperature ferromagnetisms of Zn 0.95Co 0.05O thin films doped with copper

Zn 0.95− x Co 0.05Cu x O (ZCCO, where x = 0, 0.005, 0.01 and 0.015) thin films were deposited on Si (1 0 0) substrates by pulsed laser deposition technique. Crystal structures, surface morphologies, chemical compositions, bonding states and chemical valences of the corresponding elements for ZCCO films were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and X-ray photoelectron spectroscopy (XPS). XRD and FESEM results indicate that crystallite sizes of the highly (0 0 2)-oriented ZCCO films slightly decrease with increasing Cu content. When the Cu content increases from 0 to 0.015, Zn 2 p 3/2, Co 2 p, Cu 2 p 3/2 and O 1 s peaks of the ZCCO film shift towards higher or lower binding energy regions, and the reasons for these chemical shifts are investigated by fitting the corresponding XPS narrow-scan spectra. Both in-plane and out-of-plane magnetization-magnetic field hysteresis loops of the ZCCO films reveal that all the films have room temperature ferromagnetisms (RTFMs). The conceivable origin of the RTFM is ascribed to the combined effects of the local structural disorder resulted from (Co 2+, Cu 2+, Cu 1+)-cations which substitute Zn 2+ ions in the ZnO matrices, ferromagnetic coupling between coupled dopant atoms caused by Co 2+ (3 d 74 s 0) and Cu 2+ (3 d 94 s 0) spin states, and exchange interactions between the unpaired electron spins originating from lattice defects induced by Cu doping in the Zn 0.95Co 0.05O matrices.

Structural Changes of Electrodeposited ZnO Matrices for Dye-Sensitized Solar Cells During Preparation

Nanoporous zinc oxide films can be prepared by electrochemical codeposition with the dye eosin Y (EY) as a template and its subsequent desorption with aqueous KOH. In this contribution, the partial dissolving and reorganization of the zinc oxide film during the desorption step was studied in detail using X-ray diffraction, Kelvin probe force microscopy, and atomic force microscopy. It was found that the reorganization leads to an enhancement of crystal orientation and a reduction of the oxygen defect concentration at the surface of the zinc oxide, which is supposed to be a reason for suppressed recombination of electrons in these films.