EXAFS and XANES investigation of (Li, Ni) codoped ZnO thin films grown by pulsed laser deposition
30 Aug 2013-Journal of Physics: Condensed Matter (IOP Publishing)-Vol. 25, Iss: 38, pp 385402-385402
TL;DR: Preliminary investigations on the Zn K-edge of the undoped and doped ZnO thin films revealed that doping has not influenced the average Zn-Zn bond length and Debye-Waller factor, which shows that both Ni and Li doping do not appreciably affect the average local environment of Zn.
Abstract: Ni doped, Li doped and (Li, Ni) codoped ZnO thin films were successfully grown using a pulsed laser deposition technique. Undoped and doped ZnO thin films were investigated using extended x-ray absorption fine structure (EXAFS) and x-ray absorption near edge spectroscopy (XANES). Preliminary investigations on the Zn K-edge of the undoped and doped ZnO thin films revealed that doping has not influenced the average Zn–Zn bond length and Debye–Waller factor. This shows that both Ni and Li doping do not appreciably affect the average local environment of Zn. All the doped ZnO thin films exhibited more than 50% of substitutional Ni, with a maximum of 77% for 2% Ni and 2% Li doped ZnO thin film. The contribution of Ni metal to the EXAFS signal clearly reveals the presence of Ni clusters. The Ni–Ni distance in the Ni0 nanoclusters, which are formed in the film, is shorter with respect to the reference Ni metal foil and the Debye–Waller factor is higher. Both facts perfectly reflect what is expected for metal nanoparticles. At the highest doping concentration (5%), the presence of Li favors the growth of a secondary NiO phase. Indeed, 2% Ni and 5% Li doped ZnO thin film shows %Nisub = 75 ± 11, %Nimet = 10 ± 8, %NiO = 15 ± 8. XANES studies further confirm that the substitutional Ni is more than 50% in all the samples. These results explain the observed magnetic properties.
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TL;DR: X-ray absorption spectroscopy (XAS) is a powerful tool for the characterization of such kinds of systems, owing to its chemical selectivity and high sensitivity in interatomic distance determination as discussed by the authors.
Abstract: Over the last three decades low-dimensional systems have attracted increasing interest both from the fundamental and technological points of view due to their unique physical and chemical properties. X-ray absorption spectroscopy (XAS) is a powerful tool for the characterization of such kinds of systems, owing to its chemical selectivity and high sensitivity in interatomic distance determination. Moreover, XAS does not require long-range ordering, that is usually absent in low-dimensional systems. Finally, this technique can simultaneously provide information on electronic and local structural properties of the nanomaterials, significantly contributing to clarify the relation between their atomic structure and their peculiar physical properties. This review provides a general introduction to XAS, discussing the basic theory of the technique, the most used detection modes, the related experimental setups and some complementary relevant characterization techniques (diffraction anomalous fine structure, extended energy-loss fine structure, pair distribution function, x-ray emission spectroscopy, high-energy resolution fluorescence detected XAS and x-ray Raman scattering). Subsequently, a selection of significant applications of XAS to two-, one- and zero-dimensional systems will be presented. The selected low-dimensional systems include IV and III–V semiconductor films, quantum wells, quantum wires and quantum dots; carbon-based nanomaterials (epitaxial graphene and carbon nanotubes); metal oxide films, nanowires, nanorods and nanocrystals; metal nanoparticles. Finally, the future perspectives for the application of XAS to nanostructures are discussed.
110 citations
TL;DR: Step-by-step SILAR deposition of CdSe films on mesoscopic TiO2 nanoparticle films is analyzed using X-ray absorption near-edge structure analysis and the interfacial structure of these films is probed.
Abstract: Successive ionic layer adsorption and reaction (SILAR) is a popular method of depositing the metal chalcogenide semiconductor layer on the mesoscopic metal oxide films for designing quantum-dot-sensitized solar cells (QDSSCs) or extremely thin absorber (ETA) solar cells. While this deposition method exhibits higher loading of the light-absorbing semiconductor layer than direct adsorption of presynthesized colloidal quantum dots, the chemical identity of these nanostructures and the evolution of interfacial structure are poorly understood. We have now analyzed step-by-step SILAR deposition of CdSe films on mesoscopic TiO2 nanoparticle films using X-ray absorption near-edge structure analysis and probed the interfacial structure of these films. The film characteristics interestingly show dependence on the order in which the Cd and Se are deposited, and the CdSe–TiO2 interface is affected only during the first few cycles of deposition. Development of a SeO2 passivation layer in the SILAR-prepared films to fo...
70 citations
63 citations
TL;DR: A high‐performance bifunctional electrode formed by vertically depositing a porous nanoplate array on the surface of nickel foam is provided, where the nanoplate is made up by the interconnection of trinary Ni–Fe–Mo suboxides and Ni nanoparticles.
Abstract: It is a great challenge to fabricate electrode with simultaneous high activity for the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Herein, a high-performance bifunctional electrode formed by vertically depositing a porous nanoplate array on the surface of nickel foam is provided, where the nanoplate is made up by the interconnection of trinary Ni-Fe-Mo suboxides and Ni nanoparticles. The amorphous Ni-Fe-Mo suboxide and its in situ transformed amorphous Ni-Fe-Mo (oxy)hydroxide acts as the main active species for HER and OER, respectively. The conductive network built by Ni nanoparticles provides rapid electron transfer to active sites. Moreover, the hydrophilic and aerophobic electrode surface together with the hierarchical pore structure facilitate mass transfer. The corresponding water electrolyzer demonstrates low cell voltage (1.50 V @ 10 mA cm-2 and 1.63 V @ 100 mA cm-2) with high durability at 500 mA cm-2 for at least 100 h in 1 m KOH.
39 citations
TL;DR: In this paper, a chunk-shaped ZnO nanostructures (CSNS) simultaneously doped with Li and Mn for varying Li/Mn concentrations have been synthesized using wet-chemical method.
Abstract: Chunk shaped ZnO nanostructures (CSNS) simultaneously doped with Li and Mn for varying Li/Mn concentrations have been synthesized using wet-chemical method. Their crystal structural, optical and magnetic properties at room temperature (RT) were then investigated, which revealed that all the samples have a single phase with the wurtzite structure. Undoped and co-doped ZnO chunk-shape structures has been demonstrated by transmission electron microscope (TEM). The Mn/Li incorporation also creates more lattice defects and disorders, which influence directly characteristic photoluminescence (PL), FTIR and UV–vis spectra of Zn1−x−yMnyLixO CSNS. Where green emission due to concentration of defects is seen. Magnetic measurements by VSM and the ferro fluid of synthesized nano ZnO by Faraday optical rotation for various concentration of Mn and Li in nano ZnO are done. Change of magnetic and magneto-optic (MO) properties due to Mn and Li ions are discussed in detail.
37 citations
References
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Abstract: Ferromagnetism in manganese compound semiconductors not only opens prospects for tailoring magnetic and spin-related phenomena in semiconductors with a precision specific to III-V compounds but also addresses a question about the origin of the magnetic interactions that lead to a Curie temperature (T(C)) as high as 110 K for a manganese concentration of just 5%. Zener's model of ferromagnetism, originally proposed for transition metals in 1950, can explain T(C) of Ga(1-)(x)Mn(x)As and that of its II-VI counterpart Zn(1-)(x)Mn(x)Te and is used to predict materials with T(C) exceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.
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