Surface Of ZnO Nanorods Research Articles

Silver nanoparticles coupled ZnO nanorods array prepared using photo-reduction method for localized surface plasmonic effect study

Coupling of selected metal nanoparticles (NPs) on the surface of ZnO nanorods (NRs) array grown on conductive glass substrates is one of the approaches to tailor the optical properties of ZnO NRs. It is a metal oxide deposition process followed by an annealing treatment to convert the deposits to metal NPs. However, the conductive glass substrates could easily deform during this annealing process. This issue limits the application of ZnO NRs array that grown on glass substrates for the fabrication of ZnO based devices. Thus, the development of metal NPs deposition technique without the need of post-deposition annealing is highly desired. This work demonstrated a successful and controlled deposition of silver (Ag) NPs on ZnO NRs array grown on fluorine doped tin oxide (FTO) glass substrates without any post-deposition annealing and, the product has exhibited localized surface plasmonic resonance (LSPR) phenomenon. The ZnO NRs arrays were grown on FTO glass substrates that pre-seeded with ZnO layer using hydrothermal method. The controlled coupling of Ag NPs particles on ZnO NRs was performed by adjusting the duration of photo-reduction process. The optical bandgap ZnO NRs was widened because of Ag NPs coupling, i.e. from 3.16 to 3.22 eV; as estimated from the result of UV–Vis measurement. The shift of near band-edge emission (NBE) in room temperature photoluminescence (RTPL) suggests that the presence of Ag NPs on the surface of ZnO NRs could block the transitions of electrons in ZnO whereas the shift in defect-related emission indicates the generation of defects at the interfaces between Ag NPs and ZnO NRs. The 5-folds increment of IUV/Vis ratio of Ag NPs/ZnO NRs in RTPL, indicating the specimens experienced LSPR effect. The LSPR effect of Ag NPs/ZnO NRs could be used to improve the performance of ZnO-based devices such as solar cells, light-emitting diodes and photocatalysts applications.

A green synthesis of CISe nanocrystal ink and preparation of quantum dot sensitized solar cells

I–III–VI chalcopyrite copper indium selenium is one of therepresentatives of the light absorbing layer material, and is often used for a thin-film solar cell. With the development of nano-technology, CuInSe2 quantum dots (CISe QDs) which have intermediate belt and excitation effect characteristics are applied to the solar cells as an alternative of Cd- or S-based QDs. Most conventional methods for the synthesis of CISe QDs using solution involve the dangerous and environmentally unfriendly Oleylamine or phosphine coordination compounds. In this work, CISe QDs were synthesized by a green, safe and low-temperature method in triethylene glycol. Through controlling the growth temperature and time, the diameter can be adjusted from 3[Formula: see text]nm to 10[Formula: see text]nm. The samples exhibit quantum confinement effect, and have a controllable optical band gap. QDs were deposited on the surface of ZnO nanorods to obtain a photoanode, which were fabricated into quantum dot-sensitized solar cells. The device exhibits size-dependent performance. And the open circuit voltage shows a fluctuation up to 0.26[Formula: see text]V. When the size is 4[Formula: see text]nm, the short circuit current density is the largest (15[Formula: see text]mA/cm2).

Improving performance of perovskite solar cells based on ZnO nanorods via rod-length control and sulfidation treatment

The structure and properties of electron transport layers play an important role in determining device performance of perovskite solar cells (PSCs). PSCs based on one-dimensional ZnO nanorods still suffer from serious efficiency losses. In this work, length of ZnO nanorods was firstly optimized by exploring steady photoluminescence quenching of perovskite films deposited on ZnO nanorods of various lengths and their photovoltaic performance. PSCs fabricated on ZnO nanorods of ~400 nm yield the best power conversion efficiency of ~10% due to their relatively balanced charge carrier transfer and transport properties. On this basis, sulfidation treatment was applied on these ZnO nanorods to further improve device performance. It is found that the sulfidation treatment of ZnO nanorods may play a role in at least three aspects: (I) passivating defects on the surface of ZnO nanorods; (II) facilitating charge carrier transfer and transport by forming ZnO/ZnS type II heterojunctions; (III) alleviating perovskite dissociation to some extent. Due to these benefits, the power conversion efficiency of perovskite solar cells based on ZnO nanorods was improved to 11.72%, along with less hysteresis. This work not only demonstrates the importance of rod-length and sulfidation treatment on device performance of perovskite solar cells based on ZnO nanorods but also provides a feasible method to improve their power conversion efficiency.

Study on the enhanced electron-hole separation capability of IrxZn1-xO/Ti electrodes with high photoelectrocatalysis efficiency

Making full use of low-energy photons and reducing photogenerated carriers' recombination rate have been considered important ways to raise photoelectrocatalysis (PEC) efficiency. In this study, Ir-doped ZnO PEC electrodes were prepared by thermal decomposition method, first principles calculations were used to study the effects of Ir content on the electronic structure and optical properties of IrxZn1-xO coatings, the PEC degradation mechanism of the IrxZn1-xO/Ti electrodes was also tentatively presented. The results indicated that with numbers of Zn atoms replaced by Ir atoms, impurity energy level appeared in ZnO band gap, which reduced the electron transition barriers and increased the number of photogenerated carriers. Besides, IrO2 nanoparticles covered on ZnO nanorods surface, acting as highly efficient electron transfer channels and electrocatalytic active sites, could separate photogenerated electron-hole pairs and enhance PEC performance effectively. PEC performance of IrxZn1-xO/Ti electrodes with different Ir contents under UV irradiation was evaluated by rhodamine B (RhB) removal rate. Compared with pure ZnO electrodes, IrxZn1-xO/Ti ones exhibited much stronger degradation capacity. Specifically, Ir0.09375Zn0.90625O/Ti electrodes showed the highest degradation rate of 99.4 %, and a relatively high rate of 95.2 % after working 100 h continuously, indicating its excellent long-term stability.

Construction of ZnO/CdS three-dimensional hierarchical photoelectrode for improved photoelectrochemical performance

Three-dimensional ZnO/CdS hierarchical films with uniform CdS deposition on the ZnO nanorods surface is prepared by a two-step hydrothermal method. The morphology of CdS nanostructure can be adjusted from particles to sheets and then blocks by changing amount of the surfactant in the precursor solution. The ZnO/CdS hierarchical film as photoelectrode with optimized morphology shows significant enhancement to the light harvesting and photoelectrochemical performance. Under light irradiation of 100 mW/cm2, the three-dimensional ZnO/CdS hierarchical film yields a photocurrent density of 4.5 mA/cm2, approximately two times higher than that of film without three-dimensional structure. The photoelectrochemical property improvement is attributed to the (1) enhanced light absorption due to the multi-scattering and multi-reflection of the unique three-dimensional hierarchical structure, (2) improved photogenerated carrier separation and transportation because of the hierarchical and heterojunction structure, and (3) facilitated hole transfer and reaction at the photoelectrode-electrolyte interface due to the large surface area.

In-situ pulsed laser induced growth of CdS nanoparticles on ZnO nanorods surfaces

Herein we present a process for the in-situ growth of CdS nanoparticles using a pulsed laser irradiation. A Nd-YAG laser was applied to ZnO nanorods previously submerged in an aqueous precursor solution containing cadmium chloride and thiourea. For optimum values of the laser fluence, around 40 mJ/cm2 it was possible to fabricate a highly homogeneous film of CdS nanoparticles covering the ZnO nanorods surface. Cathodoluminescence measurements of the ZnO/CdS structure show the quenching of the ZnO yellow and green luminescence, indicating the ZnO surface defects passivation by CdS nanostructures. Although lasers have been already used for inducing growth in solution, this work presents new evidence of in-situ growth on the surface of nanostructured materials. The laser based technique presented is simple, easy to implement, scalable and it could be applied in the fabrication of nanostructured solar cells and other devices.

Intrinsic Control in Defects Density for Improved ZnO Nanorod-Based UV Sensor Performance.

Hitherto, most research has primarily focused on improving the UV sensor efficiency via surface treatments and by stimulating the ZnO nanorod (ZNR) surface Schottky barriers. However, to the best of our knowledge, no study has yet probed the intrinsic crystal defect generation and its effects on UV sensor efficiency. In this study, we undertake this task by fabricating an intrinsic defect-prone hydrothermally grown ZNRs (S1), Ga-doped ZNRs (S2), and defect-free microwave-assisted grown ZNRs (S3). The defect states were recognized by studying X-ray diffraction and photoluminescence characteristics. The large number of crystal defects in S1 and S2 had two pronged disadvantages. (1) Most of the UV light was absorbed by the defect traps and the e–h pair generation was compromised. (2) Mobility was directly affected by the carrier–carrier scattering and phonon scattering processes. Hence, the overall UV sensor efficiency was compromised based on the defect-induced mobility-response model. Considering the facts, defect-free S3 exhibited the best UV sensor performance with the highest on/off ratio, the least impulse response time, the highest recombination time, and highest gain-induced responsivity to 368 nm UV light, which was desired of an efficient passive metal oxide-based UV sensor. Our results were compared with the recently published results.

Effects of catalyst surfaces on adsorption revealed by atomic force microscope force spectroscopy: photocatalytic degradation of diuron over zinc oxide.

Controlling adsorption of a heterogeneous catalyst requires a detailed understanding of the interactions between reactant molecules and the catalyst surface. Various characteristics relevant to adsorption have been theoretically predicted but have yet to be experimentally quantified. Here, we explore a model reaction based on diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] photo-degradation over a ZnO particle catalyst. We used atomic force microscope (AFM)-based force spectroscopy under ambient conditions to investigate interactions between individual functional groups of diuron (NH2, Cl, and CH3) and surfaces of ZnO particles (polar Zn and O-terminated, and nonpolar Zn-O terminated). We were able to distinguish and identify the two polar surfaces of conventional ZnO particles and the nonpolar surface of ZnO nanorods based on force-distance curves of functionalized probe/surface pairs. We posit that the reaction involved physisorption and could be described in terms of Hamaker constants. These constants had an order-of-magnitude difference among the probe/surface interacting pairs based on polarity. Hence, we confirmed that van der Waals interactions determined the adsorption behavior. We interpreted the electronic distribution models of the probe-modifying molecules. The functional group configurations inferred the diuron adsorption configurations during contact with each ZnO facet. The adsorption affected characteristics of the reaction intermediates and the rate of degradation.

Electrical properties of nanoscale p-n heterojunctions formed between a single ZnO nanorod and GaN substrate

We study electronic transport in single vertically oriented n-type ZnO nanorods on p-type GaN substrates using a nanoprobe in a scanning electron microscope. The ZnO nanorods are prepared by chemical bath deposition on both plain GaN substrates and the substrates locally modified by focused ion beam. The heterojunctions on focused ion beam-modified substrates show rectifying current-voltage characteristics, while the characteristics of the plain structures are symmetrical. Adsorption/desorption processes on the surface of ZnO nanorods strongly affect their electrical properties. We demonstrate that the electronic transport in the nanorods grown on focused ion beam-modified substrates is less sensitive to adsorption/desorption processes, which is related to their uniform nucleation and higher crystalline quality.

The dependence of the optical properties of ZnO nanorod arrays on their growth time

As a multifunctional optoelectronic material, ZnO nanorod array has attracted wide attention. In this work, transparent and highly c-axis oriented ZnO nanorod arrays were grown by a simple chemical solution method using zinc acetate and urea as raw materials. Compared with widely used zinc nitrate and hexamethyltetramine, zinc acetate and urea are safer and cheaper. The relationship between crystallization quality, surface defects, optical properties and growth time of ZnO nanorods was investigated. The results show that with the rise of growth time, the length of ZnO nanorods gradually increases, and the crystalline quality gradually improves. The transmittance in the visible range is gradually enhanced, and the absorption edge near 375 nm becomes steeper. The photoluminescence spectra show that as the growth time increases, the intrinsic emission of the ZnO nanorods, i.e., the ultraviolet emission, is gradually enhanced, and the visible emissions related to the defects are gradually weakened. X-ray photoelectron spectroscopy (XPS) analysis show that the oxygen-related defects on the surface of ZnO nanorods gradually decrease with the increase of growth time, which is consistent with the results of the photoluminescence spectra.

Photocatalytic green fabrication of Au nanoparticles on ZnO nanorods modified membrane as flexible and photocatalytic active reusable SERS substrates

Surface-enhanced Raman Scattering (SERS) is an optical detection means that provides utilities over traditional assay detection technologies. In this study, a UV-irradiation was exploited as an ease non-toxic photochemical method for a one-step reduction-deposition of gold nanoparticles (AuNPs) on zinc oxide nanorods supporter (AuNPs@ZnO) patterned on a flexible and porous membrane. Here, we were able to fabricate a self-cleaned and recyclable SERS-active flexible substrate for the quantitative analysis of hazard organic contaminants. The photocatalytic activity of AuNPs@ZnO nanorods was significantly improved under UV- irradiation and after the deposition of AuNPs of ∼21 nm on the surface of ZnO nanorods of average particle size ∼ 60 nm. The morphology, crystallinity, structural phase and optical behaviors of AuNPs@ZnO nanorods modified flexible membrane were characterized using scanning electron microscopy (SEM, SEM-EDX, SEM-Mapping), X-ray powder diffraction (XRD) and SERS analysis. The photocatalytic capabilities of AuNPs@ZnO nanorods modified flexible membrane were exploited to reuse it as SERS substrates for five cycles without losing significant sensitivity through UV-sensitized photocatalytic self-cleaning. As a result, the optimized AuNPs@ZnO; used for SERS analysis of rhodamine 6 G (R6 G) and erythrosine B (EryB), was able to degrade probe-analytes within ∼10 min and a resultant detection limit of 10−10 and 10-9 M, respectively. Additionally, the calculated enhancement factor was 4.96 × 105 and ∼1.73 × 105 for R6 G and Ery B, respectively. Particularly, this contribution is an attempt to lead the potential of cutting-edge research toward practical food biosensor manufacturing for rapid and sensitive monitoring using without-sample-loss preparation methods.

Bayberry-like Pt nanoparticle decorated ZnO nanorods for the photocatalytic application

The preparation of the nanocomposites zinc oxide/platinum (ZnO/Pt) has attracted much attention with regard to improving the photocatalytic efficiency of ZnO, but most studies have focused on the use of ZnO/Pt in conventional powdered spherical nanocrystals only. In this experiment, bayberry-like Pt nanoparticles (NPs) were successfully synthesized and deposited on the surfaces of ZnO nanorods (NRs) that were hydrothermally grown on glass substrates. The bayberry-like Pt NPs, which had a diameter range of 40–70 nm and consisted of many nanodots with a diameter < 5 nm, were spread uniformly on the surface of the ZnO NRs via the drop-casting method. The presence of the Pt NPs increased the photocatalytic activity of ZnO NRs for methylene blue (MB) degradation by 54% and 32% under UV and visible light irradiation, respectively. This improvement can be attributed to the presence of Pt, which acted as an electron trap and can inhibit the rate of electron–hole recombination. It may also be credited to the morphology of the bayberry-like Pt NPs, which consisted of many nanodots that can trap light in the surroundings of the nanodots, thereby enhancing the light scattering and absorption and enlarging the surface area for oxygen and hydroxyl ion adsorption.

Metal Decoration and Magnetic Field Effect on the Electrical Breakdown Voltage for ZnO Nanorods Gas Ionization Sensor

ZnO nanorod arrays with sharp tips were synthesized via chemical vapor deposition and utilized as the anode for gas ionization sensor. The effects of metal (Mn, Ni81Fe19 and Au) decoration and magnetic field on the electrical breakdown voltage were studied. Compared with the bare ZnO nanorod, metal decorated ZnO nanorod arrays in the magnetic field can effectively reduce the breakdown voltage for the air to 20 V. The possible mechanism is that metal decoration produces small size protuberance on the surface of ZnO nanorods and then enhances the electrical field near the tips. The magnetic field exerts action on the motion of the electron and therefore increases electron impact ionization efficiency and second electron emission efficiency.

Enhancing charge transfer for ZnO nanorods based triboelectric nanogenerators through Ga doping

Triboelectric nanogenerator (TENG) has been developed as a promising green energy source, but the working mechanism as regard to the surface condition in charge transfer is still under investigation. Therefore, the work is devised to study the charge transfer efficiency by varying electron concentration at the surface of ZnO nanorods (NRs) arrays through Ga doping as a means to change surface chemistry of a given material when rubbing with PDMS and nylon. The hydro-thermally grown ZnO NRs arrays remain vertically aligned upon Ga doping from 0.18 to 0.69 at%, effectively generating free electron concentrations from 2.63× 1014 to 1.80× 1018 cm−3, compared to 4.24 × 1016 cm−3 corresponding to the un-doped ZnO NRs. The triboelectric output voltage, current density and tribo-charges density of the Ga-doped ZnO NRs are remarkably enhanced by up to ~13, ~90 and ~15 times, respectively, compared to the un-doped ZnO NRs. This work verifies the concept of n-type semiconductors in favor of transferring electrons to the counter materials bound to receiving electrons such as PDMS in the triboelectric series and vice versa to the materials bound to donating electrons such as nylon. This behavior is mainly ascribed to the work function difference in proposed band diagrams with surface band bending as well as the kinetic constraints to the ease of charge transfer. This work not only deepens the understanding into the fundamental charge transfer mechanism governing the triboelectrification efficiency but provides a facile method to maximize the range of positions in the triboelectric series for a given semiconductor to optimize device design for TENG.

X-ray diffraction investigations of nanostructured ZnO coated with reduced graphene oxide.

Nowdays, nanocomposites containing ZnO with various morphologies and graphene, graphene oxide (GO) or reduced graphene oxide (rGO) have been attracting many researchers according to their properties and board application in optoelectronic devices. In this study, rGO/ZnO nanorods were synthesized using different procedures. In the first procedure, ZnO nanorods prepared by using the hydrothermal method. In the second procedure, the surface of ZnO nanorods was coated with rGO using the drop coating process. The pure ZnO, rGO and rGO/ZnO nanorods were characterized by X-ray diffraction (XRD) and the average crystallite size was calculated using Debye-Scherrer equation.

Stable Electrochemical Measurements of Platinum Screen-Printed Electrodes Modified with Vertical ZnO Nanorods for Bacterial Detection

The study is aimed at investigating the stability of electrochemical and biosensing properties of ZnO nanorod-based platinum screen-printed electrodes (SPEs) applied for detection of bacterial pathogens. The platinum SPEs were designed and patterned according to standard photolithography and lift-off process on a silicon wafer. ZnO nanorods (NRs) were grown on the platinum working electrode by the hydrothermal method, whereas Salmonella polyclonal antibodies were selected and immobilized onto ZnO NR surface via a crosslinking process. Morphological and structural characteristics of ZnO NRs were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results showed that the ZnO NRs were grown vertically on platinum electrodes with a diameter around 20-200 nm and a length of 5-7 μm. These modified electrodes were applied for detection of Salmonella enteritidis at a concentration of 103 cfu/mL by electrochemical measurements including cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The ZnO NR-modified platinum electrodes could detect Salmonella bacteria well with stable measurements, and the signal to noise ratio was much higher than that of 3 : 1. This study indicated that ZnO NR-modified platinum SPEs could be potential for the development of biochips for electrochemical detection of bacterial pathogens.

Template-Free Electrochemical Growth of Ni-Decorated ZnO Nanorod Array: Application to an Anode of Lithium Ion Battery.

ZnO nanorods (NRs) decorated with Ni nanoparticles were synthesized using a template-free electrochemical deposition in an ultra-dilute aqueous electrolyte and a subsequent galvanic reaction. The electrochemical properties of the ZnO NRs as an anode material for rechargeable Li-ion batteries were evaluated for different binder morphologies (film and close-packed spherical particles) of polyvinylidene fluoride (PVDF). Results showed that the close-packed spherical PVDF simultaneously improved electrochemical capacity and cyclability because the free-volume between the spherical PVDF helped to accommodate the volume change in the anode caused by the Li ions discharge and charge processes. Furthermore, the Ni nanoparticles decorated on the surface of ZnO NRs enhanced the electrical conductivity of the ZnO NR anode, which enabled faster electronic and ionic transport at the interface between the electrolyte and the electrode, resulting in improved electrochemical capacity. The free-volume formed by the close-packed spherical PVDF, and the decoration of metal nanoparticles are expected to provide insight on the simultaneous improvement of electrochemical capacity and cyclability in other metal oxide anode nanostructures.

Enhanced piezo-phototronic effect of ZnO nanorod arrays for harvesting low mechanical energy

Abstract In this paper, ZnO photocatalytic activity was enhanced by a built-in piezoelectric field due to the piezoelectric effect of ZnO nanorods (NRs). A simple, practical, and self-powered device was designed to simulate and harvest the very low energy of ocean waves. By testing the degradation efficiency of ZnO for different polar dyes (methyl orange, natural red and rhodamine B), the role of the dynamic built-in electric field in the photocatalytic process was illustrated. The changing piezoelectric field acts as a “photo-induced carrier storage” in that the photo-induced carriers would be separated, stored, and released on the ZnO NR surfaces incessantly, improving the separation efficiency of photo-induced carriers in the ZnO NR array. The intensity and frequency of the built-in oscillating piezoelectric field are proportional to the ZnO NR array photocatalytic efficiency. The sustainable piezo-photocatalytic performance of the ZnO NR arrays should promote further applications of ZnO photocatalyst in pollution degradation.

ZnO nanorods decorated with nanocrystalline (nc) Au Particles:Electronic structure and magnetic behaviours

Electronic structures and magnetic behaviours of zinc oxide nanorods (ZnO-NRs) decorated with nanocrystalline “Au”-particles (nc-Au) have been studied using different spectroscopies, superconducting quantum interference device-type magnetometer and plane wave pseudopotential density functional theory calculations. The presence of intrinsic defects viz. zinc interstitials (Zni) and/or oxygen vacancies (VO) are established using different spectroscopies measurements. Ultraviolet photoelectron spectroscopy and valence band photoemission spectroscopy suggests that the valence band density of states of O 2p - Zn 4sp hybridized states of nc-Au/ZnO-NRs is higher than pure ZnO-NRs that could be correlated with its higher ferromagnetic behaviour. An enhanced room temperature ferromagnetism has been observed when nanocrystalline (nc) gold (Au) particles are decorated on the surface of ZnO-nanorods (ZnO-NRs). This enhanced magnetic moment in nc-Au/ZnO-NRs comes from the metallic electrons of nc-Au that induces large orbital magnetic moment at the nc-Au/ZnO-NR interface. Theoretical calculations shows the enhancement of the density of states at the valence band region of ZnO with a decoration of optimum content nc-Au particles along with the increase of oxygen vacancies in nc-Au/ZnO-NRs; that further confirms the enhancement of magnetization.

Study of Structural Properties of BiOI on ZnO Thin Films and ZnO Nanorods

We report the study of ZnO nanorods (ZnO-NR) decorated with BiOI nanoplatelets by the simple precipitation of BiOI in aqueous solution containing ZnO-NR powders. Likewise, as a reference for the decoration of ZnO-NR, BiOI thin films were prepared by the SILAR technique on RF magnetron-sputtered ZnO thin films. The scanning electron microscopy analysis showed that BiOI grew on the ZnO-NR surfaces in nanoplatelet shape with an order of magnitude smaller in size, with respect to the platelets observed in BiOI thin films. Analysis by X-ray diffraction exhibited the hexagonal P63mc phase of ZnO and the tetragonal P4nmm crystal phase of BiOI. On the other hand, BiOI thin films are nonuniform and strongly adherent and, besides they exhibited the P4nmm tetragonal crystal structure of BiOI, they have highly preferential orientation along (001) direction (9.66°). Optical characterization of ZnO-NR/BiOI by absorbance showed a widened peak slightly shifted to infrared compared with the ZnO-NR absorbance peak, suggesting the increase of the absorption wavelength ranges from the ultraviolet to visible for ZnO-NR. Similarly, the results of the optical characterization by absorbance, for BiOI thin films, indicated the bandgap energy of the samples was between 1.78 eV and 1.88 eV, values previously reported for BiOI.