Wurtzite Zinc Oxide Research Articles

Self-Powered Piezoelectric Nanogenerator Based on Wurtzite ZnO Nanoparticles for Energy Harvesting Application

We report the synthesis procedure of hexagonal wurtzite structure of zinc oxide (ZnO) nanoparticles via hydrothermal route to use as a main component of piezoelectric nanogenerator. The ZnO nanoparticles are dispersed into polydimethylsiloxane (PDMS) to fabricate the high performance flexible piezoelectric nanogenerator (FPNG).The output voltage and power generated from the FPNG is around 20 V and 20 μW respectively. It is also capable to charge up the capacitors within very short span of time (for example, about 2V is reached at 96s). It is demonstrated that the output power generated from the FPNG can directly drive several commercial blue light emitting diodes (LEDs)that ensuring the applicability as a self-powered energy harvester.

High aspect-ratio semiconducting ZnO nanowires formed by anodic oxidation of Zn foil and thermal treatment

Arrays of zinc oxide (ZnO) nanowires with diameter of about 200nm and length of >20µm were successfully obtained by simple anodic oxidation of Zn foil in sodium bicarbonate electrolyte and thermal post-treatment. The as formed anodic film consists of overlapping nanowire bundles forming a flower-like or grass-like structure. Thermal annealing in air at temperatures higher than 150°C results in the conversion of initially formed hydroxycarbonate precursor to crystalline wurtzite ZnO. The crystallinity of ZnO nanowires increases with increasing annealing temperature. On the other hand, optical band-gap energy of obtained semiconducting nanowires was found to be independent of the temperature applied during the thermal treatment. It is expected that the described method can be further scaled up and offers a great potential even for technological applications.

Highly selective gas sensors from photo-activated ZnO/PANI thin films synthesized by mSILAR

Zinc oxide (ZnO) nano-polycrystalline thin films has been prepared by cost-effective microwave assisted successive ionic layer adsorption and reaction (mSILAR) technique. ZnO/PANI prepared by in situ polymerization technique and thin films were fabricated using spin coating. X-ray Diffraction analysis confirms the presence of hexagonal wurtzite ZnO structure in the ZnO/PANI composite. The field emission scanning electron microscope revealed the porous nature of ZnO/PANI films with nanosized grains. We observed PANI intensively affected the structural and electrical properties of ZnO films. The examination of sensors was carried out in the liquefied petroleum gas (LPG) concentration range of 30 to 450ppm. It was noticed that ZnO/PANI nanocomposite film possesses excellent LPG sensing properties at a room temperature compared with other volatile organic compounds, at an applied voltage of 1.5V. The composite films also exhibited significant sensing response of ∼6.11×102 towards temperature and light with recovery and response time of ∼3.5min and 2.16min, respectively. Finally, the fabricated sensor showed good repeatability and sensitivity upon cyclic exposure to gas, light, and temperature. The ZnO/PANI nanocomposite film demonstrated overall sensing behavior in terms of sensor recovery time and response as well as repeatability.

Zinc oxide hierarchical nanostructures as potential NO2 sensors

A superficial thermal evaporation method has been employed for the fabrication of hierarchical zinc oxide (ZnO) nanostructured films, composed of nanorods (NR's) and bunch of nanowires (BNW's), on glass substrate and the diverse atmospheric annealing effect on their structural, morphological, compositional, and gas sensing properties has been systematically studied and reported. Structural investigation corroborates the formation of crystalline hexagonal wurtzite ZnO. The arrays of vertically aligned nanorods and bunch of nanowires of ZnO were observed on the substrate surface. As-prepared ZnO NR's and BNW's are utilized as a sensing material for detection of toxic nitrogen dioxide (NO2). The ZnO sensors exhibit high response to NO2 along with rapid response and recovery time values @200°C. In addition, ZnO sensors respond to a very small exposure of NO2 gas i.e. 1ppm. Furthermore, the developed sensors attain excellent stability and reproducibility in response. Finally, the interaction of NO2 gas molecules with hierarchical nanostructured ZnO sensors has successfully been studied and discussed by employing an electrochemical impedance spectroscopy measurement.

The electron transport that occurs within wurtzite zinc oxide and the application of stress

ABSTRACTWe examine how stress has the potential to shape the character of the electron transport that occurs within ZnO. In order to narrow the scope of this analysis, we focus on a determination of the velocity-field characteristics associated with bulk wurtzite ZnO. Monte Carlo simulations of the electron transport are pursued for the purposes of this analysis. Rather than focusing on the impact of stress in of itself, instead we focus on the changes that occur to the energy gap through the application of stress, i.e., energy gap variations provide a proxy for the amount of stress. Our results demonstrate that stress plays a significant role in shaping the form of the velocity-field characteristics associated with ZnO. This dependence could potentially be exploited for device application purposes.

The influence of oxygen partial pressure on the shape transition of ZnO microstructure by thermal evaporation

One-dimensional (1-D) and two-dimensional (2-D) wurtzite zinc oxide (ZnO) microstructures were grown on indium tin oxide (ITO)/borosilicate glass substrates via oxygen-assisted thermal chemical vapor deposition (CVD) using zinc (Zn) powder as a precursor with different flow rates of ultra-high purity nitrogen carrier gas (N2) at the total pressure of 450Pa and temperature of 550°C. The structural and optical properties of the synthesized ZnO microstructures were investigated using field-emission scanning electron microscopy, X-ray diffraction (XRD) and photoluminescence (PL) as a term of oxygen (O2) partial pressure. The obtained microstructure evolved from micropin to micropillar and to microsheet in correspondence with the increase of O2 partial pressure. XRD confirmed the transition from 1-D to 2-D microstructure with defects observed from PL spectra. The experiment suggested that the increase of supersaturation in the vapor-solid (VS) growth mechanism caused the shape transition.

IONIC LIQUID ASSISTED SYNTHESIS AND CHARACTERISATION OF ZnO NANOPARTICLES

A green approach has been developed for the synthesis of nanocrystalline zinc oxide (ZnO) with the aid of room-temperature synthesized ionic liquids (RTIL's) as crystal growth modifiers by low-temperature precipitation technique. The role of RTIL's (propylammonium acetate (PAA), propylammonium formate (PAF), 3-hydroxy propylammonium acetate (3-HPAA), 3-hydroxy propylammonium formate (3HPAF) and their concentration effect on the particle size is studied in this protocol. The formed nanoparticles are characterized by XRD, TEM, FT-IR and UV-DRS. XRD spectra of nanoparticles exhibit typical diffraction peaks of hexagonal phase with wurtzite ZnO structure corresponding to JCPDS 36-1451. TEM results revealed that spherical nanoparticles obtained with an average particle size in the range of 5-20 nm. UV-Vis-DRS spectra of the ZnO nanoparticles shows blue shift compared to the bulk ZnO, attributed to quantum confinement effect.

Photoluminescence quenching and enhanced spin relaxation in Fe doped ZnO nanoparticles

Cost-effective ultrasonically assisted precipitation method is utilized to synthesize Zinc oxide (ZnO) nanoparticles (NPs) at room temperature and the effect of Iron (Fe) doping on structural, optical and spin relaxation properties also presented. As-synthesized pure and Fe doped ZnO NPs possess a perfect hexagonal growth habit of wurtzite zinc oxide, along the (101) direction of preference. With Fe doping, ‘c/a’ ratio and compressive lattice strain in ZnO NPs are found to reduce and increase, respectively. Raman studies demonstrate that the E1 longitudinal optical (LO) vibrational mode is very weak in pure which remarkably enhanced with Fe doping into ZnO NPs. The direct band gap energy (Eg) of the ZnO NPs has been increased from 3.02 eV to 3.11 eV with Fe doping. A slight red-shift observed with strong green emission band, in photoluminescence spectra, is strongly quenched in 6 wt.% Fe doped ZnO NPs. The field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) reveals spherical shape of ZnO NPs with 60–70 nm, which reduces substantially on Fe doping. The energy dispersive X-ray spectrum and elemental mapping confirms the homogeneous distribution of Fe in ZnO NPs. Moreover, the specific relaxation rate (R2sp = 1/T2) has been measured using Carr-Purcell-Meiboom-Gill (CPMG) method and found to be maximum in 6 wt.% Fe doped ZnO NPs. Further, the correlation of structural, optical and dynamic properties is proposed.

Pure and Al-doped ZnO obtained by the modified Pechini method applied in ethanolic transesterification of cottonseed oil

Abstract Pure zinc oxide (ZnO) and 5% Al-doped ZnO (ZNAL) were synthesized using the modified Pechini method and characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), Raman spectroscopy, infrared spectroscopy and UV-visible spectroscopy. XRF confirmed the theoretical stoichiometry, while XRD and Raman spectroscopy indicated that Al3+ was incorporated into the ZnO wurtzite lattice with no secondary phases, leading to a decrease in the band gap value and to a meaningful increase of the Lewis basic sites. Pure and doped ZnO were used as catalysts in the ethylic transesterification of cottonseed oil using a factorial design to determine the best synthesis conditions. Oil conversion into biodiesel was evaluated by viscosity measurements and 1H NMR spectroscopy. The results analyzed by factorial design indicated that the catalyst type and temperature were the determinant factors in the conversion indices. The highest basicity of the ZNAL lead to a significant increase of the catalytic potential, reaching a reduction of the oil viscosity next to 71% at 130 °C and greater than 85% at 200 °C.

Influence of Carbon Modification on the Morphological, Structural, and Optical Properties of Zinc Oxide Nanoparticles Synthesized by Pneumatic Spray Pyrolysis Technique

This paper reveals the influence of doping on the morphological, structural, and optical properties of zinc oxide (ZnO) nanoparticles (NPs) synthesized by pneumatic spray pyrolysis technique (PSP), using zinc ethoxide ZnO2CH32 as the precursor. The prepared samples were characterized by XRD, HRTEM, SEM-EDX, UV-Vis spectroscopy, and RS. RS analysis has revealed that the unmodified ZnO and carbon modified ZnO samples have characteristic Raman optic modes at 325 cm−1, 373 cm−1, and 432 cm−1 belonging to Wurtzite ZnO structure. The XRD ZnO (C:ZnO) NPS have characteristic peaks of hexagonal Wurtzite ZnO structure. HRTEM analysis has revealed that the synthesized ZnO NPs have particle size range of 8.8–11.82 nm. EDX spectra of both unmodified and modified ZnO nanoparticles have revealed prominent peaks at 0.51 keV, 1.01 keV, 1.49 keV, 8.87 keV, and 9.86 keV. The occurrence of these peaks in the EDX spectra endorses the existence of Zn and O atoms in the PSP synthesized ZnO NPs. The UV-Vis spectroscopy has revealed a red shift of the absorption edge, with the increase in C dopant level. The effect of nanocrystallite size and the gradual prominence of C into ZnO matrix due to increase in C dopant level in the PSP synthesized ZnO NPs was meticulously elaborated through Raman spectroscopy analysis.

Investigation of intrinsic defect magnetic properties in wurtzite ZnO materials

Theoretical and experimental investigations of the ferromagnetism induced by intrinsic defects inside wurtzite zinc oxide structures are performed using magnetic field-dependent circular dichroism (MCD-H), direct magnetization measurement (M-H) by superconducting quantum interference device (SQUID) as well as by generalized gradient density functional theory (GGA-DFT). To investigate localized magnetic moments of bulk material intrinsic defects - vacancies, interstitial atoms and Frenkel defects, various-size periodic supercells are calculated. It is shown that oxygen interstitial atoms (Oi) or zinc vacancies (Znv) generate magnetic moments of 1,98 и 1,26µB respectively, however, the magnitudes are significantly reduced when the distance between defects increases. At the same time, the magnetic moments of oxygen Frenkel defects are large (~1.5–1.8µB) and do not depend on the distance between the defects. It is shown that the origin of the induced ferromagnetism in bulk ZnO is the extra spin density on the oxygen atoms nearest to the defect. Also dependence of the magnetization of ZnO (101̅0)and(0001) thin films on the positions of Oi and Znv in subsurface layers were investigated and it is shown that the magnetic moments of both defects are significantly different from the values inside bulk material. In order to check theoretical results regarding the defect induced ferromagnetism in ZnO, two thin films doped by carbon (C) and having Zn interstitials and oxygen vacancies were prepared and annealed in vacuum and air, respectively. According to the MCD-H and M-H measurements, the film, which was annealed in air, exhibits a ferromagnetic behavior, while the other does not. One can assume annealing of ZnO in vacuum should create oxygen vacancies or Zn interstitial atoms. At that annealing of the second C:ZnO film in air leads to essential magnetization, probably by annihilation of oxygen vacancies, formation of interstitial oxygen atoms or zinc vacancies. Thus, our experimental results confirm our theoretical conclusions that ZnO magnetization origin are Oi or Znv defects.

A Comparative Study on Structural and Optical Properties of ZnO Micro-Nanorod Arrays Grown on Seed Layers Using Chemical Bath Deposition and Spin Coating Methods

In this study, Zinc Oxide (ZnO) seed layers were prepared on Indium Tin Oxide (ITO) substrates by using Chemical Bath Deposition (CBD) method and Sol-gel Spin Coating (SC) method. ZnO micro-nanorod arrays were grown on ZnO seed layers by using Hydrothermal Synthesis method. Seed layer effects of structural and optical properties of ZnO arrays were characterized. X-ray diffractometer (XRD), Scanning Electron Microscopy (SEM) and Ultraviolet Visible (UV-Vis) Spectrometer were used for analyses. ZnO micro-nanorod arrays consisted of a single crystalline wurtzite ZnO structure for each seed layer. Besides, ZnO rod arrays were grown smoothly and vertically on SC seed layer, while ZnO rod arrays were grown randomly and flower like structures on CBD seed layer. The optical absorbance peaks found at 422 nm wavelength in the visible region for both ZnO arrays. Optical bandgap values were determined by using UV-Vis measurements at 3.12 and 3.15 eV for ZnO micro-nanorod arrays on CBD seed layer and for ZnO micro-nanorod arrays on SC-seed layer respectively. DOI: http://dx.doi.org/10.5755/j01.ms.22.4.13443

Effect of ethyl cellulose on thermal resistivity of thixotropic ZnO nano-particle paste for thermal interface material in light emitting diode application

A large amount of heat trapped inside Light Emitting Diode (LED) is the consequence of large thermal resistance between the heat source and the heat sink. Zinc oxide (ZnO) thick film was screen-printed from thixotropic paste that consisted of binder, filler and solvent to act as thermal interface material. Structural, surface morphology, vibrational and thermal properties of the samples were studied by means of Field Emission Scanning Electron Microscopy (FESEM), Atomic Force Measurement (AFM), Fourier Transform Infrared Spectroscopy (FTIR) and Thermal Transient Tester (T3ster). XRD analysis revealed that the formation of hexagonal wurtzite ZnO powder, which is free of hydroxide. FESEM results indicated that 50wt% of filler loading in the thick film had created longer thermal transportation chain. The surface roughness of thick film displays variation in the range of from 64.8 to 218nm. The presence of ZnO and binder were confirmed by FTIR spectrum at 518cm−1 and 668cm−1 to 2974cm−1, respectively. Thermal characterization reveals a drop in film’s resistivity with the higher content of filler loading of 50wt% and 55wt%. The lowest rise in junction temperature of tested LED is reported to be 14.7°C of 50wt% of filler loading.

Kinetics-Driven Crystal Facets Evolution at the Tip of Nanowires: A New Implementation of the Ostwald-Lussac Law

Nanocrystal facets evolution is critical for designing nanomaterial morphology and controlling their properties. In this work, we report a unique high-energy crystal facets evolution phenomenon at the tips of wurtzite zinc oxide nanowires (NWs). As the zinc vapor supersaturation decreased at the NW deposition region, the NW tip facets evolved from the (0001) surface to the {101̅3} surface and subsequently to the {112̅2} surface and eventually back to the flat (0001) surface. A series of NW tip morphology was observed in accordance to the different combinations of exposed facets. Exposure of the high-energy facets was attributed to the fluctuation of the energy barriers for the formation of different crystal facets during the layer-by-layer growth of the NW tip. The energy barrier differences between these crystal facets were quantified from the surface area ratios as a function of supersaturation. On the basis of the experimental observation and kinetics analysis, we argue that at appropriate deposition conditions exposure of the crystal facets at NW growth front is not merely determined by the surface energy. Instead, the NW may choose to expose the facets with minimal formation energy barrier, which can be determined by the Ehrlich-Schwoebel barrier variation. This empirical law for the NW tip facet formation was in analogy to the Ostwald-Lussac law of phase transformation, which brings a new insight toward nanostructure design and controlled synthesis.

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.

Butane/Propane Gas Sensing Using Zinc Oxide Film Grown by Successive Ionic Layer Adhesion and Reaction

This study was aimed to test the ability of zinc oxide (ZnO) film fabricated by successive ionic layer adsorption and reaction (SILAR) to detect liquid petroleum gas consisting of a mixture of butane/propane gas. The film was fabricated by alternate dipping of pre-cleaned glass substrates in a sodium zincate bath and in a 95°C hot water bath using an automated dipping machine to control the sequence and dipping time. Scanning electron microscopy (SEM) revealed a uniform film consisting of wurtzite ZnO nanorods for the sample grown using 0.1M concentration of sodium zincate and 200 dippings. Current-voltage characterization of the samples showed an average resistivity of 1.343 Ω-m. EDS analysis of the film confirmed the existence of zinc oxide with 65.9% zinc and 34.1% oxygen. The ZnO film exhibited an ability to detect the gas with an average gas response of 0.44, average response time of 14 seconds and average recovery time of 25 seconds using a gas concentration in air of 1.5 % by volume. Response time is the time for the sensor to reach the peak voltage output from the start of gas exposure while recovery time is the time for the voltage output to return to the initial value without gas when the gas is removed from the chamber. The zinc oxide film also showed a voltage output of 100, 109.31, 118.92, 123.61, 133.5, and 149.52 mV when exposed to percent volume gas concentrations of 0, 0.5, 0.75, 1.0, 1.25, and 1.5, respectively with a correlation coefficient of 0.97. The sensor sensitivity is 32 Δ(mV)/Δ(%conc).

Anatase TiO2 (101) and wurtzite ZnO (001) modified polymer for visible light-photocatalytic efficiency enhancement

ABSTRACTPhotocatalytic property of titanium dioxide and zinc oxide was used in several of application in the environmental field due to their high oxidation power and a self-sensitized degradation in a wide range of organic compound. Unfortunately, the large band gap of these metal oxides absorbs only UV radiation and limits the photocatalytic efficiency results in high cost of photocatalytic degradation of environmental pollutant. To be used under visible light irradiation, time-dependent density functional theory was applied to study anatase titanium dioxide (101) and wurtzite zinc oxide (001) with modified organic materials. Four modified structures, including polyisoprene ring, polyisoprene chain, polyacethylene, and polyphenylenevinylene, were investigated. The electronic structure and simulated UV-Vis spectra were analyzed.

Low Temperature Synthesis and Annealing effect of Transparent ZnO Thin Films on ITO Substrate by Sol-Gel Method

Objectives: Transparent Zinc oxide (ZnO) thin films to be prepared and annealed on the Indium tin oxide - ITO substrate using simple solution gel dip coating technique. Methods/Analysis: Thin films have been carried out by different characterization techniques such as X-ray diffractometer - XRD, Scanning Electron Microscopy - SEM, Energy dispersive analysis - EDAX, UV spectroscopic and FTIR spectroscopy. In the contemporary work, the ZnO films have been prepared on ITO substrate by dipping in the solution and annealed at the 300 °C. Findings: XRD pattern reveals that the annealed thin film is standard wurtzite zinc oxide hexagonal structure. SEM Morphological studies have been investigated using scanning electron microscopy and the elemental analysis confirmed by EDAX. Optical measurement shows the greatly transparent and the thin films are direct energy gap Eg of 3.70eV. FTIR confirm the metal oxide bond in the molecular structure. Novelty/Improvement: This research work helps for the future researcher’s preparation of undoped Zinc oxide thin film for solar cell applications.

Hydrothermal controllable synthesis to convert ZnO hexagonal nanotubes to hexagonal nanorods and their photocatalytic application

Zinc oxide (ZnO) thick films were analyzed by high-resolution X-ray diffraction (HR-XRD), field emission scanning electron microscopy, and photoluminescence (PL) spectroscopy at room temperature. The films were grown on glass substrates using different molar concentrations of aqueous solution (0.02, 0.04, and 0.06 M) via a simple hydrothermal method. This method uses glass bottles with rubber caps as reactor vessels (100 mL) and, thus, is classified as a green chemistry technique. Hexahedral zinc nitrate (Zn (NO3)2·6H2O), hexamethylenetetramine (C6H12N4), and deionized water were used as starting materials and were reacted in the presence of heat. HR-XRD measurements confirmed that the diffraction peaks of the polycrystalline structure films can be assigned to the hexagonal-shaped wurtzite ZnO. In addition, the PL spectra show that the integrated intensity decreases with the increase in ZnO content. The SEM images also revealed the existence of hexagonal ZnO nanotubes in the 0.02 M sample, and these nanotubes are gradually converted into hexagonal nanorods with the increase in ZnO content. Moreover, the photocatalytic activity of both nanostructures was measured based on the degradation of methyl blue (MB) by using ultraviolet light (λ = 366 nm). Results showed that the ZnO nanotubes degraded MB more effectively than the nanorods.

Elucidating the Impact of Cobalt Doping on the Lithium Storage Mechanism in Conversion/Alloying‐Type Zinc Oxide Anodes

AbstractHerein, an in‐depth investigation of the influence of transition‐metal doping on the structural and electrochemical characteristics of a hybrid conversion/alloying‐type lithium‐ion anode material is presented. Therefore, pure zinc oxide (ZnO) and cobalt‐doped ZnO (Zn0.9Co0.1O) were investigated comparatively. Characterization by using X‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) confirmed the successful incorporation of the cobalt (Co) dopant into the wurtzite ZnO structure, which led to a decreased particle size for the doped compound. The in situ electrochemical XRD analysis of the first de‐/lithiation of ZnO and Zn0.9Co0.1O revealed the highly beneficial impact of the transition‐metal dopant on the reversible degradation of lithium oxide (Li2O) and suppression of zinc crystallite growth upon lithiation; both effects are essential for greatly improved electrochemical performance. As a result, Co doping leads to a substantially increased specific capacity from 326 mAh g−1 for pure ZnO to 789 mAh g−1 for Zn0.9Co0.1O after 75 full charge–discharge cycles.