14th international conference on hyperfine interactions| foz do iguacu-pr (original) (raw)
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Characterization of ZnO and Zn0.95Co0.05O prepared by sol-gel method using PAC spectroscopy
Hyperfine Interactions, 2007
The measurement of the electric field gradient (efg) with PAC spectroscopy was used to follow the heat treatment during the preparation of ZnO samples using sol-gel method. In particular, the investigation was carried out on samples of intrinsically n-type II-VI wurtzite semiconductor ZnO and Codoped Zn 0.95 Co 0.05 O samples prepared by sol-gel methodology from pure metallic Zn(99.9999%). Carrier-free 111 In nuclei were introduced in the samples by thermal diffusion. 111 In solution was added to the precursor sol-gel solution prior to the formation of gel material. PAC measurements were carried out to follow the formation of the ZnO. Two undoped ZnO samples, which were heated in air and argon atmosphere, show different results. PAC measurements were also used to follow the 111 In diffusion in a commercially purchased ZnO (99.99%) sample as well as to compare the results with the measurements taken with sol-gel prepared samples. The results show that samples prepared by sol-gel process followed by heating in argon produce better quality ZnO samples. The results also show that the Co atoms in Zn 0.95 Co 0.05 O are in substitutional sites.
Local investigation of hyperfine interactions in pure and Co-doped ZnO
Journal of Magnetism and Magnetic Materials, 2010
In the present work bulk samples of pure as well as Co-doped ZnO with different concentrations were prepared by sol-gel method from highly pure metallic Zn (99.9999%) and Co (99.9999%). The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray microanalysis (EDS) and perturbed gamma-gamma angular correlation (PAC) spectroscopy. Carrier-free 111 In nuclei were introduced during preparation of the samples and used as probe nuclei at Zn sites for PAC measurements. PAC results show that both pure and Zn 1Àx Co x O (xr0:15) samples have the same electric quadrupole frequency when Co-doped samples are annealed in air, argon or nitrogen atmosphere at 1173 K. SEM and EDS results showed that Co-doped samples are homogeneous without any secondary Co phases. These observations indicate that Co ions are substituted for Zn ions and have a similar electronic structure of Zn ions. A weak local magnetism was observed at temperatures below about 300 K for Co concentration of 10% when sample was annealed in Nitrogen.
IEEE Transactions on Magnetics, 2000
Both ZnO and Zn 0 99 Co 0 01 O semiconductors were synthesized through solid state reaction via mechanical milling and thermal treatment. Initially the wurtzite ZnO structures of the synthesized particles were characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Since these techniques were unable to identify both contamination atoms and Co distribution, energy dispersive X-ray spectrometry (EDS) was used. EDS showed a successful doping of Co atoms with the atomic ratio of 0.9 0.1%, and also showed a contamination of tungsten (W) atoms, in the atomic ratio of 1.6 0.2% for Zn 0 99 Co 0 01 O, and 1.3 0.2% for ZnO. Substitutions of Co +2 ions with Zn +2 host atoms in the ZnO lattice were exposed through X-ray photo spectroscopy (XPS) data of Co 2p electronic energy levels. UV-vis absorption spectroscopy (UV-vis) was also used to prove Co substitutions in the ZnO lattice. This was revealed by a decrease in band gap from 3.25 0.01 eV to 3.03 0.01 eV, and the existence of newly permitted transitions between intra ionic levels. The ferromagnetic effect of Co doping in ZnO lattice was revealed by the coercivity of 154 50 Oe and positive Curie-Weiss temperature, 79 1 K. Beside ferromagnetic interactions, the calculated effective Bohr Magnetron ( e ), 0 32 0 01 B , suggested anti-ferromagnetic interactions due to be less than the theoretical spin based magnetic moment of Co 2+ ions, 3.0 B . Index Terms-Doping, magnetic semiconductors, zinc alloys.
Study of Structural and Optoelectronic Properties of ZnO Codoped with Ca and Mg
Indian Journal of Materials Science, 2013
ZnO codoped with Ca and Mg in various proportions was prepared by a chemical method and annealed at 600 C. The structural and optical properties of these oxide samples were systematically studied by XRD, SEM, EDS, and PL spectrometer. XRD pattern shows a hexagonal wurtzite structure. The size of particle as shown by XRD machine and calculated by Scherer’s formula is found in the nano range. The formation of particles showed that they were polycrystalline. Due to larger ionic and covalent radii of Ca than those of Zinc, a lattice deformation occurs with the development of strain field. New phases were observed in XRD pattern of few samples ZnO-2.2 and ZnO-2.4. SEM micrograph shows the formation of nanoparticles. EDS study confirms the codoping of ZnO with Ca and Mg. Optical properties like photoluminescence emission showed a blue shift in peak wavelength. General conductivity and photoconductivity were found high in samples containing certain proportion of Ca and Mg in comparison wit...
Electronic and Optical Properties of ZnO Between 3 and 32 eV
2008
The dielectric response functions of bulk ZnO for electric field polarizations parallel and perpendicular to the c-axis are obtained in the spectral range from 3 to 32 eV by analysis of ellipsometric data. Anisotropics are observed between ε|| and ε⊥. Electronic transitions involving Zn-3d and O-2s bands are detected. Ab-initio band structure calculations performed at the DFT-LDA level help to
Electrical and optical spectroscopy on ZnO:Co thin films
Applied Physics A-materials Science & Processing, 2007
Magnetic oxide semiconductors, for example the highly transparent and intrinsically n-type conducting zinc oxide doped with the 3d transition metal Co (ZnO:Co), are promising for the emerging field of spintronics [1]. We investigated n-conducting ZnO:Co thin films with a Co content of nominal 0.02, 0.20, or 2.00 at. %. The substitution of Co cations in the tetrahedral sites of wurtzite ZnO with Zn was confirmed at low temperature by the 1.877 eV photoluminescence between crystal field split d-levels of Co2+ (d7) ions. Based on theoretical studies, it is predicted that the formation of electron levels with zinc interstitials (IZn) or hole levels with zinc vacancies (VZn) is necessary to induce ferromagnetism, whereas the formation of electron levels with oxygen vacancies (VO) is detrimental for ferromagnetism in ZnO:Co [2]. Cobalt generates a hole level in ZnO [3]. We investigated the generation of electron levels in n-conducting ZnO:Co in dependence on the Co content by means of deep level transient spectroscopy (DLTS). However, because of the ambiguous categorization of deep defects in n-conducting ZnO (VO, IZn), an optimization of defect-related ferromagnetism in ZnO:Co is not possible at the moment.
Co-doped ZnO: synthesis and structural, electrical and optical properties
Journal of Materials Science: Materials in Electronics, 2015
This paper reports the synthesis, crystal structure and electrical conductivity properties of Co-doped ZnO powders (in the range of 0.25-15 mol%). I-phase samples, which were indexed as single phase with a hexagonal (wurtzite) structure in the Co-doped ZnO system, were determined by X-ray diffraction. The solubility limit of Co ions in the ZnO structure was found to be 15 mol% at after heating at 950°C. The impurity phase was determined to be Co 3 O 4 at lower temperatures than 950°C. The research focused on single I-phase samples which were synthesized at 950°C. For I-phase samples (after heating at 950°C), the lattice parameters a and c decreased with increasing Co concentration. Electrical conductivity of undoped ZnO and 15 mol% Co-doped ZnO (after heating at 950°C) were found to be 7.8*10-7 and 1.05*10-4 X-1 cm-1 , respectively, at 25°C and 1.15 and 37.15 X-1 cm-1 , respectively, at 950°C. Thus, it appears that electrical conductivity slightly increases with Co doping. Also, activation energy of the all I-phase samples (after heating at 950°C) was calculated and the values were found to be range from 0.774 to 1.201 eV. UV/vis absorption spectras of undoped and the all I-phase samples (after heating at 950°C) were recorded and optical band gap values were found to be between 3.351 and 3.416 eV.
111Cd-doped ZnO physicaB FINAL
In this work, we present results of Time-Differential g-g Perturbed-Angular-Correlations (PAC) experiments performed in 111 Cd-doped ZnO semiconductor. The PAC technique has been applied in order to characterize the electric-field-gradient (EFG) tensor at (111 In (EC)-) 111 Cd nuclei located, as was later demonstrated, at defect-free cation sites of the ZnO host structure. The PAC experiments were performed in the temperature range of 77-1075 K. At first glance, the unexpected presence of lowintensity dynamic hyperfine interactions was observed, which were analyzed with a perturbation factor based on the Bäverstam and Othaz model. The experimental EFG results were compared with ab initio calculations performed with the Full-Potential Augmented Plane Wave plus local orbital (FP-APWþ lo) method, in the framework of the Density Functional Theory (DFT), using the Wien2K code. The presence of the dynamic hyperfine interactions has been analyzed enlightened by the FP-APW þ lo calculations of the EFG performed as a function of the charge state of the cell. We could correlate the large strength of the dynamic hyperfine interaction with the strong variation of the EFG due to changes in the electronic charge distribution in the Cd vicinity during the time-window of the PAC measurement. It was also revealed that the Cd impurity decays to a final stable neutral charge state (Cd 2 þ) fast enough (in few ns) to produce the nearly undamped observed PAC spectra.