ZnO Host Matrix Research Articles

Gd 3+ /Yb 3+ -Doped Zinc Oxide Quantum Dots for Dual Modal Magnetic Resonance Imaging/Computed Tomographic Imaging

The oleate-stabilized ZnO:Gd/Yb QDs was first prepared by doping rare earth ions into ZnO host matrix in ethanol solution,and then amido was grafted onto the surface by a covalent bond.These nanoprobes,with exceptionally small size and good water-dispersability,exhibited a longitudinal relaxivity r1 of 6.06 mmol/(L·s),which was higher than that of clinic contrast agent Gd-diethylenetriaminepentaacetic acid(DTPA)(4.3 mmol/(L·s)).In magnetic resonance imaging(MRI) studies,they exerted strong positive contrast effect when the Gd concentration was 1.5 mmol/L.Furthermore,computed tomography(CT) imaging showed that these nanoprobes could induce an efficient contrast enhancement when the Yb concentration was at least equal to 5.0 g/L.These nanoprobes presented relatively low toxicity or adverse affect on cell growth even at the concentration up to 1.5 mmol/L Gd3+.

Effect of Nd3+ incorporation on the microstructure and chemical structure of RF sputtered ZnO thin films

The present work aims at investigating the effects that different levels of Nd atoms incorporation can have on the microstructure and chemical structure of ZnO thin films. Undoped and Nd-doped ZnO films were deposited by RF co-sputtering from pure ZnO and metallic Nd targets in Ar plasma onto Si, quartz and glass substrates. The Nd concentration in the ZnO host matrix was varied in the range 0–26 at.% by varying the bias applied to the Nd target. A comprehensive characterization of the films properties was performed by X-ray photoelectron and Auger electron spectroscopies, X-ray fluorescence analysis, X-ray diffraction and scanning electron microscopy. At low Nd atomic concentration (Nd/Zn < 0.07) Nd atoms were successfully incorporated into the ZnO matrix, whose crystalline structure was preserved. A deterioration of the ZnO würtzite phase was observed on the contrary with increasing Nd content in the films together with the precipitation of a second phase, identified as Nd2O3.

Ni-Doping Effect on the Structural and Optical Properties of Sprayed ZnO Thin Films

Nickel-doped ZnO thin films with different Ni contents (0 - 15%) were deposited on glass substrate at 350°C by a spray pyrolysis technique. 0.1 M solutions of zinc acetate and nickel sulphate were used as the precursors with air as the carrier gas. The effect of Ni-doping on the structural and optical properties of the layers was evaluated using appropriate techniques. The X-ray diffraction studies revealed that nickel atoms were successively incorporated into ZnO host matrix without forming any detectable secondary phase. All the grown films were polycrystalline with the (002) plane as the preferred orientation and the peak position shifted towards higher diffraction angle with the increase of doping content in the films. The films had hexagonal shaped grains and the evaluated grain size varied in the range of 20 - 48 nm. The optical studies revealed a decrease of transmittance with the increase of Ni-doping content in the films and the evaluated energy band gap was found to be direct that decreased from 3.32 eV to 3.05 eV.

Alteration of Mn exchange coupling by oxygen interstitials in ZnO:Mn thin films

The un-doped and Mn doped ZnO thin films, with oxygen rich stoichiometry, were deposited onto Si (100) substrate using spin coating technique. The structural analysis revealed the hexagonal wurtzite structure without any impurity phase formation. A consistent increase in cell volume with the increase in Mn doping concentration confirmed the successful incorporation of bigger sized tetrahedral Mn2+ ions (0.83Å) in ZnO host matrix that was also endorsed by the presence of Mn 2p3/2 core level XPS spectroscopic peak. Extended deep level emission (DLE) spectra centered at ∼627nm confirmed the presence of oxygen interstitials. Moreover, the magnetic measurements of field dependent M–H curves revealed the origin of ferromagnetic ordering from Mn-defect pair exchange coupling with oxygen interstitials in ZnO host matrix.

Enhanced indirect ferromagnetic p-d exchange coupling of Mn in oxygen rich ZnO:Mn nanoparticles synthesized by wet chemical method

This paper investigates the ferromagnetism in ZnO:Mn powders and presents our findings about the role played by the doping concentration and the structural defects towards the ferromagnetic signal. The narrow-size-distributed ZnO:Mn nanoparticles based powders with oxygen rich stoichiometery were synthesized by wet chemical method using zinc acetate dihydrate and manganese acetate tetrahydrate as precursors. A consistent increase in the lattice cell volume, estimated from x-ray diffraction spectra and the presence of Mn 2p3/2 peak at ∼640.9 eV, in x-ray photoelectron spectroscopic spectra, confirmed a successful incorporation of manganese in its Mn2+ oxidation state in ZnO host matrix. Extended deep level emission spectra in Mn doped ZnO powders exhibited the signatures of oxygen interstitials and zinc vacancies except for the sample with 5 at. % Mn doping. The nanocrystalline powders with 2 and 5 at. % Mn doping concentration were ferromagnetic at room temperature while the 10 at. % Mn doped sample exhibited paramagnetic behavior. The maximum saturation magnetization of 0.05 emu/g in the nanocrystalline powder with 5 at. % Mn doping having minimum defects validated the ferromagnetic signal to be due to strong p-d hybridization of Mn ions.

Preparation and Characterization of ZnO: In Transparent Conductor by Low Cost Dip Coating Technique

Transparent conducting oxide (TCO) based on indium doped zinc oxide films in the nano scale were successfully prepared using combination between dip coating and thermal decomposition process. Structural investigations confirm the polycrystalline ZnO hexagonal wurtzite phase grown along the c-axis with nano crystallite size about 10 nm. Morphology investigation shows that ZnO films consist of fine grains of average size 40 nm. This indicates that each grain contains several crystallites with different orientations. Cross sectional image presents good adhesion of the films with the substrate and the film thickness has been determined. Compositional analysis detects the indium content in the host ZnO matrix, the In/Zn ratio is close to the calculated concentration ratios of the precursor. The optical transmittance shows that the films are transparent in the UV and VIS-IR spectral region and interference fringes were observed to be thickness dependent. Preparation parameters were investigated and optimized such as dipping rate, number of deposition cycles, precursor concentration, annealing process and In/Zn ratio. Optimization process was investigated for low resistivity, high optical spectral window transmission and easy preparation process. Dipping rate in the range 2 - 38 mm/s is the most suitable range for good film quality while dipping rate range 30 - 38 mm/s produces thicker films in lower deposition cycles. The higher dipping rate produces films with lower transparency (milky films) while the small deposition rate rate requires large number of deposition cycles in order to increase the thickness. Besides, the higher dipping rate reflects lower resistivity of the deposited films. Precursor molar concentration was observed to have an essential effect on the film thickness, film quality and transparency. Lower precursor concentration requires also large number of deposition cycles for thickening the films. The higher concentration results also milky films (high scattering process by powder film). Precursor concentrations in the range 0.7 - 0.9 mol/liter were found to be the optimal for better quality and for faster deposition process. The resistivity of the films has been reduced from the range 1.5 - 2.5 kW?cm to the range 100 - 400 W.cm as the molar concentration reaches the range 0.07 - 0.09 mol/liter. The resistivity of films increases from 330 to 1686 .cm as the decomposition temperature increases from 200C to 350C. Annealing at 450C process after completing the decomposition at 200?C results the lowest resistivity with annealing time in the range 1.5 - 2 h. In/Zn percentage in the range 1.5% - 5% produces the lowest electrical resistivity. The absorption edge of the deposited films was observed to be critical affected by the preparation parameters. The band gap change was discussed through the degenerate semiconductors as well as nanostructured semiconducting materials of the energy gap confinement effect. Deposition of TCO based on ZnO:In was optimized depending on all deposition parameters forwide area, the lower cost and good performance TCO films.

Quenching of surface traps in Mn doped ZnO thin films for enhanced optical transparency

The structural and photoluminescence analyses were performed on un-doped and Mn doped ZnO thin films grown on Si (100) substrate by pulsed laser deposition (PLD) and annealed at different post-deposition temperatures (500–800°C). X-ray diffraction (XRD), employed to study the structural properties, showed an improved crystallinity at elevated temperatures with a consistent decrease in the lattice parameter ‘c’. The peak broadening in XRD spectra and the presence of Mn 2p3/2 peak at ∼640eV in X-ray Photoelectron Spectroscopic (XPS) spectra of the doped thin films confirmed the successful incorporation of Mn in ZnO host matrix. Extended near band edge emission (NBE) spectra indicated the reduction in the concentration of the intrinsic surface traps in comparison to the doped ones resulting in improved optical transparency. Reduced deep level emission (DLE) spectra in doped thin films with declined PL ratio validated the quenching of the intrinsic surface traps thereby improving the optical transparency and the band gap, essential for optoelectronic and spintronic applications. Furthermore, the formation and uniform distribution of nano-sized grains with improved surface features of Mn-doped ZnO thin films were observed in Field Emission Scanning Electron Microscopy (FESEM) images.

Synthesis and optical properties of Mn doped ZnO thin films

AbstractStudy of optical and electrical properties of Mn doped ZnO films deposited by atmospheric barrier torch discharge technique on SiO2 substrates is reported for a wide range of Mn concentration (0.2–20 at.%). It was found that the growth of all Mn‐doped ZnO films contains secondary Mn2O3 phase even for the lowest manganese concentration (0.2%). When Mn concentration is in the range 0.2–4%, this secondary Mn2O3 phase does not conspicuously affect Raman spectra of ZnO evidencing that Mn is mostly incorporated into the ZnO host matrix. Increase of Mn concentration (8–20%) is accompanied by formation of Mn2O3 clusters manifesting itself in the appearance of a corresponding mode in the Raman spectra. These clusters influence dramatically optical and electrical properties of the films. The Mn “solubility limit” for the films growth technique used is determined to be near 8%.

Metastability of heavy lanthanides in the ZnO wurtzite structure

The introduction and stability of the heavy lanthanide Er, into ZnO was studied by HRTEM, XRD and thermal treatments. The applied synthesis route allows introducing the Er atoms in the lattice in a metastable state. The stability depends on the Er concentration. ZnO with Er concentrations of less than 2% are stable up to 800 °C, while higher concentrations result in a phase segregation at T > 700 °C. Unit cell parameters obtained from the Rietveld refinement of XRD patterns provide a conclusive evidence of the incorporation of the Er ions in the host ZnO matrix.

A molecular approach to Cu doped ZnO nanorods with tunable dopant content

A novel molecular approach to the synthesis of polycrystalline Cu-doped ZnO rod-like nanostructures with variable concentrations of introduced copper ions in ZnO host matrix is presented. Spectroscopic (PLS, variable temperature XRD, XPS, ELNES, HERFD) and microscopic (HRTEM) analysis methods reveal the +II oxidation state of the lattice incorporated Cu ions. Photoluminescence spectra show a systematic narrowing (tuning) of the band gap depending on the amount of Cu(II) doping. The advantage of the template assembly of doped ZnO nanorods is that it offers general access to doped oxide structures under moderate thermal conditions. The doping content of the host structure can be individually tuned by the stoichiometric ratio of the molecular precursor complex of the host metal oxide and the molecular precursor complex of the dopant, Di-aquo-bis[2-(methoxyimino)-propanoato]zinc(II) 1 and -copper(II) 2. Moreover, these keto-dioximato complexes are accessible for a number of transition metal and lanthanide elements, thus allowing this synthetic approach to be expanded into a variety of doped 1D metal oxide structures.

Structural, magnetic and transport properties of Ni-doped ZnO films

In this work, Ni-doped ZnO (Zn1−xNixO, x=0, 0.03, 0.06, 0.11) films were prepared using magnetron sputtering. X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), temperature dependence electrical resistance, Hall and magnetic measurements were utilized in order to study the properties of the Ni-doped ZnO films. XRD and XAS results indicate that all the samples have a ZnO wurtzite structure and Ni atoms incorporated into ZnO host matrix without forming any secondary phase. The Hall and electrical resistance measurements revealed that the resistivity increased by Ni doping, and all the Ni-doped ZnO films exhibited n-type semiconducting behavior. The magnetic measurements showed that for the samples with x=0.06 and 0.11 are room-temperature ferromagnetic having a saturation magnetization of 0.33 and 0.39μB/Ni, respectively. The bound-magnetic-polaron mediated exchange is proposed to be the possible mechanism for the room-temperature ferromagnetism in this work.

The microwave-assisted synthesis and characterization of Zn 1 − xCo xO nanopowders

In this paper, we present a simple microwave-assisted synthesis of Zn 1 − x Co x O nanopowders. With the advantages of the microwave-assisted method, we have successfully synthesized good crystalline quality and good surface morphology Zn 1 − x Co x O nanopowders. The nanopowders are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–VIS absorption, and micro-Raman spectroscopy. We found, in the synthesis process, the surfactant Triethanolamine (TEA) plays an important role on the morphology of Zn 1 − x Co x O nanoparticles. The XRD study shows that for Co doping up to 5%, Co 2+ ions are successfully incorporated into the ZnO host matrix. The absorption spectra of Zn 1 − x Co x O ( x = 1–5%) nanopowders show several peaks at 660, 611 and 565 nm, indicating the presence of Co 2+ ions in the tetrahedral sites. The Raman study shows that the linewidth of E 2 low mode increases with Co concentration, which further indicates the incorporation of Co 2+ ions into the ZnO host matrix.

Doping of ZnO Thin Film with Eu Using Ion Beams

Modification of electric and magnetic properties of ZnO thin films was achieved by low energy Eu ion irradiation. The desired doping levels as well as the depth distribution of the dopant was controlled by the ion energy and the ion flux, following a simulated interaction between the doping ion and the host ZnO matrix of epitaxial ZnO (0001) films of approximatelly 200nm, grown on c-Al2O3 by PLD. The properties of the doped ZnO film depend in a critical way on the homogeneity of the doped ions throughout the entire film. The doping levels and the depth distribution of dopants were measured by elastic recoil detection analysis (ERDA). The results show a uniform depth distribution of Eu, as well as some level of Al diffusion from the substrate and the presence of some low levels of H, N and O. PACS code: 68.49Sf; 74.78Bz

Low‐temperature synthesis and Raman scattering of Mn‐doped ZnO nanopowders

AbstractNanocrystalline Mn‐doped zinc oxides Zn1−xMnxO (x = 0–0.10) were synthesized by the sol–gel technique at low temperature. The calcination temperature of the as‐prepared powder was found at 350 °C using differential thermal analysis. A thermogravimetric analysis showed that there is a mass loss in the as‐prepared powder till 350 °C and an almost constant mass till 800 °C. The X‐ray diffraction patterns of investigated nanopowders calcined at 350 °C correspond to the hexagonal ZnO structure without any foreign impurities. The average grain size of the nanocrystal that was observed around ∼25–40 nm from transmission electron microscopy matched well with the crystallite size calculated from the line shape of X‐ray diffraction. The chemical bonding structure in Zn1−xMnxO nanopowders was examined using X‐ray photoelectron spectroscopy techniques, which indicate substitution of Mn2+ ions into Zn2+ sites in ZnO lattice. Micro Raman spectroscopy confirmed the insertion of Mn ions in the ZnO host matrix, and similar wurtzite structure of Zn1−xMnxO (x &lt; 10%) nanocrystals. Temperature‐dependent Raman spectra of the nanocrystals displayed suppression of luminescence and enhancement in full width at half maximum in pure ZnO nanocrystals with increase in temperature, which suggests an enhancement in particle size at elevated temperature. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Structural, optical and magnetic properties of Fe-doped ZnO

Zn1-xFexO (x =0.011, 0.029, 0.048, 0.10, 0.20) thin films have been grown on Al2O3 (0001) substrates by magnetron co-sputtering technique. X-ray diffraction analysis revealed that Fe atoms were successfully incorporated into ZnO host matrix, and the films exhibited wurzite structure up to x = 0.20 with reduced c-axis lattice constant compared to that of pure ZnO. There are not any secondary phases, and Fe2+ as well as Fe3+ substitutes for Zn2+ of ZnO host. With increasing x, the optical band gap is found to shift slightly to lower energies (66 meV for x = 0.20) than that of the pure ZnO. Magnetization measurement indicated that all samples were ferromagnetic at room temperature. An explanation for the dependence of the optical and magnetic properties of the samples on the value of x is also given.

Aerosol assisted chemical vapour deposition of ZnO films on glass with noble metal and p-type dopants; use of dopants to influence preferred orientation

The use of aerosol assisted chemical vapour deposition (AACVD) for the formation of zinc oxide and doped ZnO films with control of preferred orientation on glass is reported. Undoped and doped ZnO host matrix films were highly transparent with visible transmission >85%. The Cu (CuO/Cu 2O) doped ZnO thin films were highly coloured and opaque. Undoped and noble metal doped ZnO films had mainly spherical morphology. Aluminium oxide/ZnO composite films had a range of morphologies from spherical to cubic. The XRD patterns for both doped and undoped ZnO films grown at substrate temperatures less than 500 °C showed strong preferred (0 0 2) crystal lattice orientation. The undoped ZnO film at 500 °C exhibited a random crystal orientation pattern for hexagonal ZnO. The introduction of small amounts of Al 2O 3 within the ZnO to form a composite significantly altered the preferred crystal orientation to (1 0 1).

Structure and ferromagnetic properties of Co-doped ZnO powders

Single-phase Zn 1− x Co x O ( x=0.02, 0.04) powders were synthesized by a simple co-precipitation technique. X-ray diffraction analysis reveals that the Co-doped ZnO crystallizes in a wurtzite structure. The lattice constants of Co-doped ZnO powders decrease slightly when Co is doped into ZnO. Optical absorption spectra show a decrease in the bandgap with increasing Co content and also give an evidence of the presence of Co 2+ ions in tetrahedral sites. Raman spectra indicate that Co doping increased the lattice defects and induced another Raman vibration mode around at 538 cm −1, which is an indicator for the incorporation of Co 2+ ions into the ZnO host matrix. Magnetic measurement reveals that the Zn 1− x Co x O ( x=0.02, 0.04) powders clearly exhibit room-temperature ferromagnetic behavior, which makes them potentially useful as building components for spintronics.

Growing Zn0.90Co0.10O Diluted Magnetic Semiconductors by r. f. Sputtering System

AbstractZn0.90Co0.10O particles, synthesized by mechanical milling and thermal treatment, were pressed at 25 tons to form a 2” target for a radio frequency (r. f.) magnetron sputtering system. Using this target, thin films were deposited on (0001) oriented sapphire (α-Al2O3) substrates under 30W, 60W and 120W r. f. powers. Structural analyses of these films were done with X-Ray Diffractometer (XRD), Energy Dispersive X-Ray Spectrometry (EDS), X-Ray Photo Spectroscopy (XPS) and Atomic Force Microscopy (AFM). The ZnO films were deposited with (0002) preferred direction, which was coherent to (0001) ordered α-Al2O3. Impurity phases, such as Co clusters, CoO and Co3O4, were not detected with the surface analyses of Zn0.90Co0.10O thin films. Substituted Co atoms in the host ZnO matrix were identified by the binding energy peak of Co2p3/2, 781.3±0.4eV, and the energy difference of ∼15.61±0.03eV between Co2p1/2 and Co2p3/2. These results also proved that there were no Co clusters or Co3O4 phases in the lattice. Homogeneity of Co atoms in the lattice was shown by EDS spectra. It was understood that the higher r. f. power caused the more homogeneous distribution of Co and Zn atoms in thin films. Distributions of Co and Zn on the film surface, deposited under 120W, were found as 8.1±0.1% (normalized atomic ratio) and 91.7±0.7% (normalized atomic ratio), respectively, and the surface roughness of thin film was demonstrated by AFM figures as 14.2±0.1nm.

Ferromagnetism and suppression of metallic clusters in Fe implanted ZnO: a phenomenon related to defects?

We investigated ZnO(0 0 0 1) single crystals annealed in high vacuum with respect to their magnetic properties and cluster formation tendency after implant-doping with Fe. While metallic Fe cluster formation is suppressed, no evidence for the relevance of the Fe magnetic moment to the observed ferromagnetism was found. The latter along with the cluster suppression is discussed with respect to defects in the ZnO host matrix, since the crystalline quality of the substrates was lowered due to the preparation as observed by x-ray diffraction.

Substrate orientation-induced distinct ferromagnetic moment in Co:ZnO films

Dilute (3.8 at.%) cobalt-doped ZnO thin films are deposited on LiTaO 3 (LT) substrates with three different orientations [LT(1 1 0), LT(0 1 2) and LT(0 1 8)] by direct current reactive magnetron co-sputtering. The experimental results indicate that Co atoms with 2+ chemical valence are successfully incorporated into the ZnO host matrix on various oriented substrates, and the substrate orientations have a profound influence on the crystal growth and magnetization of Co:ZnO films. A large magnetic moment of 2.42 μ B/Co at room temperature is obtained in the film deposited on LT(0 1 2), while the corresponding values of the other films deposited on LT(1 1 0) and LT(0 1 8) are 1.21 μ B/Co and 0.65 μ B/Co, respectively. Furthermore, the crystal growth mode of Co:ZnO films on various oriented LT, the relationship between the microstructures and corresponding ferromagnetic properties are also discussed.