Al-doped ZnO Nanoparticles Research Articles

Structural and photoluminescence properties of Al-doped zinc oxide nanoparticles synthesized in polyol

Al-doped ZnO (AZO) nanoparticles have been prepared using a modified polyol process that makes use of di-ethylene glycol as a solvent. This procedure allows for obtaining nanoparticles with a narrowed size distribution, a controlled morphology and a high crystal quality. The prepared AZO nanoparticles were annealed at 400°C. We studied the effect of doping and annealing on structural and optical properties. The structural investigations of the products confirmed the hexagonal wurtzite structure for all products and having a most preferred orientation along (101) plane. The results obtained by TEM revealed that the average particle size of the products decreases by doping and increases by annealing temperature. Energy dispersive spectroscopy (EDS) confirms the substitution of Al into ZnO lattice. Raman scattering analysis shows that the crystallinity of the material was improved by increasing the concentration of the dopant Al3+ and the photoluminescence spectra shows that the UV emission peak position of AZO nanoparticles exhibited a slight blue shift from 384 to 383nm, and the intensity decreased with increasing the Al concentration, which is attributed to an increase in nonradiative recombination. However the UV emission peak position of AZO (0.2% and 0.6%) nanoparticles annealed at 400°C exhibited a slight red shift due to the influence of the size effect on the energy level of confined excitons, because of the average size of the nanoparticles obviously became bigger with the increase of annealing temperature.

Highly sensitive gas sensor based on Al-doped ZnO nanoparticles for detection of dimethyl methylphosphonate as a chemical warfare agent simulant

In this paper, we report a dimethyl methylphosphonate (DMMP) gas sensor using synthesized Al-doped ZnO nanoparticles (NPs) via a hydrothermal method. The average particle size of the Al-doped ZnO NPs is ∼25nm. The single crystalline phase was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. The variation in the response of the Al-doped ZnO NP sensors within operating temperatures showed the highest response and recovery at 2 and 96s, respectively, at 10ppm in DMMP at 350°C compared with undoped ZnO NP sensors. Our results showed remarkable sensitivity and selectivity of the Al-doped ZnO NPs sensor toward DMMP. Such increased O2 vacancies and surface reactions with small nanocrystals in the Al-doped ZnO NP sensors offer outstanding sensing performance for DMMP detection.

Polymer Solar Cells with Efficiency >10% Enabled via a Facile Solution‐Processed Al‐Doped ZnO Electron Transporting Layer

A facile and low‐temperature (125 °C) solution‐processed Al‐doped ZnO (AZO) buffer layer functioning very effectively as electron accepting/hole blocking layer for a wide range of polymer:fullerene bulk heterojunction systems, yielding power conversion efficiency in excess of 10% (8%) on glass (plastic) substrates is described. The ammonia‐treatment of the aqueous AZO nanoparticle solution produces compact, crystalline, and smooth thin films, which retain the aluminum doping, and eliminates/reduces the native defects by nitrogen incorporation, making them good electron transporters and energetically matched with the fullerene acceptor. It is demonstrated that highly efficient solar cells can be achieved without the need for additional surface chemical modifications of the buffer layer, which is a common requirement for many metal oxide buffer layers to yield efficient solar cells. Also highly efficient solar cells are achieved with thick AZO films (>50 nm), highlighting the suitability of this material for roll‐to‐roll coating. Preliminary results on the applicability of AZO as electron injection layer in F8BT‐based polymer light emitting diode are also presented.

Structural and optical properties of (Mg,Al)-codoped ZnO nanoparticles synthesized by the autocombustion method

Structural and optical properties of 1% Al-doped Zn1−xMgxO (x=0–8%) nanoparticles prepared by autocombustion method were systematically investigated by means of X-ray diffraction, scanning electron microscopy, ultraviolet–visible absorbance measurement and photoluminescence spectra. All the nanoparticles retained hexagonal wurtzite structure of ZnO, and the average sizes of the nanoparticles were about 80nm. The band gap and near band emission energies determined from absorbance and photoluminescence spectra both increased linearly with increasing Mg content, which implied that the Mg worked effectively on ZnO band gap engineering, irrespective of Al codoping. The Stokes shift remained nearly unchanged, which demonstrated that the carrier concentration and resistivity of Al-doped ZnO nanoparticles changed slightly after Mg codoping, i.e. the Al doping efficiency was not heavily destroyed in band gap engineering. Meanwhile, there is no obvious difference in structural and optical properties between unannealed and annealed samples, which indicated that annealing was not necessary for combustion synthesis processing.

Influence of Transition Metal (Cu, Al) Ions Doping on Structural and Optical Properties of ZnO Nanopowders

Al doped ZnO, Cu doped ZnO Nanoparticles were successfully synthesized by Sol-Gel Method and Zinc Chloride(ZnCl2),Potassium Hydroxide(KOH), Aluminum Nitrate(Al(NO3)2, Copper Nitrate (Cu(NO3)2) and Ethanol(C2H6O) were used as a precursors . The structural and optical properties of Nanoparticles were analyzed by means of XRD (X-Ray Diffraction), SEM (Scanning Electron Microscopy) and FTIR (Fourier Transform Infra Red spectroscopy). The results of Cu doped ZnO and Al-doped ZnO nanoparticles were also compared to investigate the structural and optical properties. XRD analysis reveals that both the samples crystallizes in hexagonal wurtzite structure and exhibit no impurity phase . The crystalline size of 28.43nm and 6.87nm are obtained in Cu doped ZnO and Al doped ZnO Nanoparticles. Therefore, the decrease in the crystalline size can be seen with the change in doping element. The optical properties also depend on the type of doping due to the Al-N bond intensity, The Al doped ZnO powder is stronger than Cu doped ZnO.

Experimental investigation on structural and optical properties of ZnO: AZO nano particles by hydrothermal synthesis

The undoped and Al-doped ZnO (AZO) nanostructures were synthesized by using simple hydrothermal process with two different pH values 6 and 10. The structural and optical properties of the ZnO and 0.5 % AZO nano particles were investigated using field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscope, atomic force microscope, X-ray diffraction (XRD), Ultraviolet–visible (UV) spectroscopy and photoluminescence (PL). It is observed from XRD results; on aluminium doping the crystalline size reduces significantly. It can be clearly seen from the FESEM images that Al doping causes the crystalline structure of ZnO to agglomerated small grain nano particles and TEM confirms that the particles are of nanometer size. The UV absorption indicates that blue shift of the samples increases the optical band gap, and decreases the average crystallite size. In the PL spectra, undoped ZnO exhibit an excitonic peak in the UV region and a defect-related peak in the visible region, whereas Al doping leads to a suppression of c lattice parameter and blue shift of luminescence with blue and green emission.

Degradation kinetics for photocatalytic reaction of methyl orange over Al-doped ZnO nanoparticles

Al-doped ZnO nanoparticles with different Al concentrations were prepared and employed as photocatalysts for the degradation of methyl orange. The samples were characterized by XRD, FE-SEM, XPS, BET, UV–vis DRS and photoluminescence techniques. The kinetic behavior could be described in terms of the Langmuir–Hinshelwood model. The adsorption equilibrium constant increased with increasing Al concentration and the reaction rate constant showed a maximum at 3% Al. It can be deduced that the enhancement of photocatalytic activity of ZnO by addition of Al could be attributed not to increase of surface area but to effective suppression of photoinduced electrons and holes.

O K-Edge X-ray Absorption Spectroscopy in Al-Doped ZnO Materials: Structural vs Electronic Effects

This work reports an O K-edge X-ray absorption spectroscopy (XAS) study of Al-doped ZnO nanoparticles and films showing room-temperature ferromagnetism (RTFM). The origin of this ferromagnetism remains controversial as different conclusions are derived for analogous systems. Among those, charge-transfer effects and the presence of vacancies are often suggested, based on the modification of similar XAS spectra with respect to that of undoped ZnO. We present here a critical re-examination of the reported O K-edge absorption in these materials, by comparing the experimental spectra to ab initio theoretical calculations, paying special attention to the role of structural modifications, instead of the currently accepted electronic interpretation, into driving the observed spectral modifications. Our results indicate that the reported variations of the XAS spectral profile are not due to the charge-transfer effects involving Al and O, but are associated with the structural modification of the oxygen next-neighboring arrangement. Indeed, the structural changes are in agreement with the formation of interfaces between ZnO and alumina-based regions, upon the reaction between ZnO and Al. According to previous studies, the RTFM likely resides in these interfaces associated with the oxygen ions.

Thermoelectric properties of n-type Bi2Te2.7Se0.3 with addition of nano-ZnO:Al particles

Nano Al-doped ZnO (AZO) particles were added into n-type Bi2Te2.7Se0.3 alloys by ball milling and hot pressing method. The power factor was improved by ∼22% with addition of nano-AZO particles, accompanied with a ∼40% decrease of lattice thermal conductivity, leading to peak ZT of ∼0.85 at 323 K for Bi2Te2.7Se0.3(AZO)0.005 sample. The effects of the addition of AZO nanoparticles on the microstructure and thermoelectric transport properties are discussed.

Ferromagnetism induced by the charge transfer in Al-doped ZnO nanoparticles

The mechanism of ferromagnetism in Al-doped ZnO was investigated both theoretically and experimentally. The density functional theory calculations were carried out to explore the electronic structure origin of ferromagnetism. The Al dopants both doping in a bulk ZnO and absorbing on the ZnO surface are taken into account. Based on the Bader charge analysis for the clear and adsorbed ZnO surface, it is found that the ionic state of Zn decreases after Al doping. The corresponding room temperature ferromagnetism was also confirmed by experiments. Moreover, the experimental analysis rules out that the ferromagnetism results from zinc vacancy or oxygen vacancy. Thus, the physical origin of the induced magnetism was indicated originating from the charge transfer between Zn atoms and adsorbed Al atoms.

Microstructure and blueshift in optical band gap of nanocrystalline AlxZn1−xO thin films

In this paper, we report the structural and optical properties of Al doped ZnO (AZO) thin films grown on glass substrates using the sol–gel process. To understand the effect of Al doping on the structural and optical response of ZnO nanoparticles thin films, the prepared samples have been characterized using X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), photoluminescence (PL), UV–vis absorption and Raman spectroscopy. X-ray diffraction results show that Al doped ZnO nanoparticles have hexagonal phase similar to ZnO nanoparticles. TEM images as well as XRD data exhibit the estimated size of nanoparticles to be in the range 35–45nm. The optical band gap has been determined from optical absorption spectra. The band gap varied from 3.27eV for undoped ZnO film to 3.87eV for AZO film having 3atwt% Al. The blue shift in energy band gap mainly related to carrier concentration induced by Al-donor doping, and to the degree of crystalline order. Photoluminescence study further confirms the blue shift in UV emission when Al doping concentration is increased, as a consequence of extension in band gap.

Synthesis, Characterization and Sensing Properties of AZO and IZO Nanomaterials

Al-doped ZnO (AZO) and In-doped ZnO (IZO) nanopowders were prepared by a sol-gel route and subsequent drying in ethanol under supercritical conditions. The morphological and microstructural properties were investigated by transmission electron microscopy (TEM) analysis and X-ray powder diffraction (XRD). The characterization study showed that the AZO and IZO nanoparticles were crystalline and exhibited the hexagonal wurtzite structure. Chemoresistive devices consisting of a thick layer of synthesized nanoparticles on interdigitated alumina substrates have been fabricated and their electrical and sensing characteristics were investigated. The sensor performances of the AZO and IZO nanoparticles for carbon monoxide (CO) were reported. The results indicated that both doped-sensors exhibited higher response and quick response/recovery dynamics compared to a ZnO-based sensor. These interesting sensing properties were discussed on the basis of the characterization data reported.

Synthesis of Al doped ZnO nanoparticles by aqueous coprecipitation

Al-doped ZnO particles were obtained by a simple route: soda addition in aqueous cationic solution. The effects of temperature, hydrolysis duration, reagent concentration and time were investigated. A non-topotactic reaction mechanism, involving firstly the precipitation of various hydroxide compounds depending on the route (low or high pH), followed by the dissolution–recrystallization of the hydroxide species into ZnO was demonstrated. The Al concentration in the final ZnO nanopowders did not exceed 0.3at.% which correspond to the solubility limit of Al in ZnO. The different experimental conditions allow the morphology of ZnO particles to be controlled from isotropic nanoparticles of several tens of nanometers, platelets of several hundreds of nanometers or agglomerates of needle like particles.

Synthesis and optical characterization of aluminum doped ZnO nanoparticles

This paper reports on the structural and optical properties of Al doped ZnO nanoparticles prepared through a sol–gel method. Different atomic ratio's of Al were doped into ZnO ranging from 1 at% to 6 at%. X-ray diffraction (XRD) and FE-SEM results showed that the average crystallite size of ZnO nanoparticles decreased with increasing Al concentration. A compressive strain induced in ZnO with Al doping was calculated using W–H plot analysis. The band gap increased monotonously as Al concentration was increased from 1 at% to 6 at%. ZnO nanocrystals showed an emission peak positioned at 396 nm. The intensity of this peak decreases with Al doping for all concentrations. The decrease of the intensity of 396 nm emission peak is due to the worsening of the crystal quality due to Al doping. In addition to this, another peak at 437 nm is developed with Al doping and it is speculated to be due to the zinc interstitial defects.

Al-doped ZnO for highly sensitive CO gas sensors

Al-doped ZnO (AZO) nanoparticles have been prepared using a modified sol–gel technique. The as-prepared AZO nanoparticles were annealed at 400°C, and their morphologies and microstructural characteristics were investigated using transmission electron microscopy (TEM) and x-ray powder diffraction (XRD) analyses. Crystallites with an average size of approximately 60–70nm and ZnO as a primary phase were observed in all samples. In addition, smaller nanoparticles (less than 5nm) with an Al-rich structure covering the surface of larger ZnO crystallites were also noted on the Al-doped samples.Chemoresistive devices consisting of a thick layer of AZO nanoparticles on interdigitated alumina substrates have been fabricated, and their electrical and sensing characteristics for carbon monoxide were investigated. Al-doping provided a remarkable decrease in the electrical resistance of the sensing layer at the working temperature of the sensors (250–300°C). The sensors based on Al-doped ZnO exhibited a higher response than the pure ZnO sample, allowing the detection of CO at sub-ppm concentrations in air. The enhancement in sensing properties was discussed in terms of the characterization and electrical data.

Al-doping effects on structure and optical properties of ZnO nanostructures

Al-doped ZnO (AZO) nanoparticles are prepared by the homogeneous precipitation method, which were characterized by X-ray diffraction, scanning electron microscope, ultraviolet and visible spectrophotometer and an infrared spectrometer. It is found that the AZO particles are of hexagonal wurtzite phase. With increase of Al doping, the particle size become smaller. A minimum diameter of 20nm is obtained doped with 5mol% Al. The band gap is found to broaden with increasing dopant concentration, and the ultraviolet absorption peak appeared blue shift. When doped with 5mol% Al, the ultraviolet absorption rate and the visible light transmittance are 98% and 90%, respectively.

Study of structural and optical properties of Zn1−xAlxO nanoparticles

Al doped ZnO nanoparticles (Zn1−xAlxO, 0.00≤x≤0.05) have been synthesized by the co-precipitation method at temperature of 500°C for 2h in air. The synthesized samples were characterized by powder X-ray diffraction (XRD), FE-SEM/EDS, TEM and UV–visible spectrophotometer. The prepared nanoparticles exhibit a hexagonal wurtzite structure with an average particle size of 26nm as evident from XRD measurements. The calculated average crystalline size of particle varied from 20 to 39nm with increase in Al concentrations. The increase in lattice parameters reveals the easy fit of Al into ZnO lattice. It was observed that the Al doped ZnO nanoparticles (Zn1−xAlxO, 0.00≤x≤0.05) exhibit higher transmittance i.e. above 77% at 400nm wavelength as compared to the un-doped ZnO nanoparticles (70%) due to its smaller crystal size (23.9nm) as compared to un-doped ZnO nanoparticles (77.4nm). Also, Al doped ZnO nanoparticles showed higher optical energy band gap as compared to un-doped ZnO nanoparticles.

Al-Doped ZnO Nanoparticles Synthesized by Sonochemical-Assisted Method

Al-doped ZnO nanoparticles were synthesized by sonochemical method from zinc acetate dehydrate and aluminum acetate as starting precursors. The deionized (DI) water was selected as the solvent. Sonication of the precursor was performed by a Sonics Model VCX 750 for 30 minutes until precipitated product was finally obtained. The as-precipitated powders were calcined at different temperature range of 550-1100 °C for 2 hr. For all samples, their crystal structures were investigated by X-ray diffraction (XRD) and surface morphologies were observed by scanning electron microscope (SEM). The XRD results revealed that, the purity of as-synthesized powders increases when the calcination temperature increases. Moreover, it is noticed that the AlZnO partial peaks will appear when the as-synthesized powders were calcined at 800 – 1000 °C. In addition, SEM micrographs show the increase of agglomeration and the particles when the calcination temperature increases.

Solution Processed Al-Doped ZnO Nanoparticles/TiOx Composite for Highly Efficient Inverted Organic Solar Cells

We investigated the electrical properties of solution processed Al-doped ZnO (AZO) nanoparticles, stabilized by mixing with a TiOx complex. Thin solid films cast from the solution of AZO-TiOx (AZOTi) (Ti/Zn ∼0.4 in the bulk and ∼0.8 on its surface) is processable in inert environment, without a need for either ambient air exposure for hydrolysis or high temperature thermal annealing commonly applied to buffer layers of most metal-oxides. It was found that the electronic structure of AZOTi matches the electronic structure of several electron acceptor and donor materials used in organic electronic devices, such as solar cells. Inverted solar cells employing a bulk heterojunction film of poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester, cast on an indium-tin-oxide/AZOTi electrode, and capped with a tungsten oxide/aluminum back electrode, give rise to a nearly 70% fill factor and an optimized open-circuit voltage as a result of efficient hole blocking behavior of AZOTi. The resulting electron collecting/blocking capability of this material solves crucial interfacial recombination issues commonly observed at the organic/metal-oxide interface in most inverted organic bulk heterojunction solar cells.

Effects of aluminium doping on structural and photoluminescence properties of ZnO nanoparticles

Structural and optical properties of Al doped ZnO nanoparticles prepared by the thermal decomposition method are presented. X-ray diffraction studies confirmed the substitution of Al on Zn sites without changing the hexagonal structure of ZnO. Also, lattice parameters, the crystallite size and other physical parameters such as strain, stress and energy density were calculated from various modified forms of W–H equation and their variation with the doping of Al is discussed. A blue shift in the energy band gap attributed to increase in carrier concentration (Burstein Moss Effect) is observed by absorption spectra. Photoluminescence studies show a strong and dominant peak corresponding to the near band edge emission in ultraviolet range and a broad band in the range 420–520nm corresponding to defects and oxygen vacancies. Phonon modes were studied by FTIR measurements. The tunability of the band gap of ZnO nanoparticles could eventually be useful for potential optoelectronic applications.