Effect of Cr doping on the photoelectrochemical performance of hematite nanorod photoanodes

ZnO nanoparticles doped with Li (Zn1−yLiyO, y ≤ 0.1) have been investigated with emphasis on the correlation between their magnetic, electronic, and structural properties. In particular, defects such as interstitial Li and Zn atoms, substitutional Li atoms, and oxygen vacancies have been identified by X-ray photoelectron spectroscopy (XPS) and their respective roles in stabilization of the magnetic moment are discussed. X-ray diffraction (XRD) and XPS give clear evidence of Li presence at both substitutional and interstitial sites. XPS studies further show that the amount of substitutional Li defects (Lizn) and interstitial Li defects (Lii) vary non-monotonically with the Li concentration, with the Lii defects being noticeably high for the y = 0.02, 0.08, and 0.10 concentrations, in agreement with the XRD results. Magnetization studies show room temperature ferromagnetism in these nanoparticles with the moment being largest for the particles with high concentration of interstitial lithium and vice versa. Both interstitial Zn (Zni) defects and Zn-O bonds were determined from the Zn LMM Auger peaks; however, the variation of these with Li concentrations was not large. Oxygen vacancies (Vo) concentrations are estimated to be relatively constant over the entire Li concentration range. We relate the Lii and Zni defects to the formation and stabilization of Zn vacancies and thus stabilizing the p-type ferromagnetism predicted for cation (zinc) vacancy in the ZnO type oxides.

https://scholarscompass.vcu.edu/cgi/viewcontent.cgi?article=1193&context=phys_pubs

Ferromagnetism in Li doped ZnO nanoparticles: The role of interstitial Li

This study investigated the microstructure, optical, and magnetic properties of Zn1−xMnxO powder samples with x = 0.02–0.08 synthesized by a solid-state reaction route. X-ray diffraction revealed that the cell parameters, a and c, increased with the increase in Mn content, which indicated that Mn ions substitute into the lattice of ZnO. UV–vis measurements revealed that the band gap decreased due to the incorporation of Mn. Photoluminescence studies confirmed the formation of oxygen vacancies (VO) in all samples. Magnetic measurements revealed that all samples exhibited room temperature ferromagnetism (RTFM), and the average magnetic moment per Mn atom decreased as the Mn content, and annealing temperature (TA) increased. However, our results indicate that the ferromagnetic property is an intrinsic property of the ZnO:Mn samples due to VO and/or defects, and it does not originate from any secondary magnetic phase.

Structural, optical, and magnetic properties of Mn-doped ZnO samples

Magnetic and optical properties of manganese doped ZnO nanoparticles synthesized by sol–gel technique

With a view to study structural, optical, vibrational, and magnetic properties of solgel derived Zn1−xNixO (x = 0.02, 0.04, and 0.06) nanoparticles, systematic investigations have been carried out. The Rietveld refinement of X-ray powder diffraction data revealed a single hexagonal phase with space group P63mc. The secondary phase of NiO appeared only in 6% Ni doped sample. Phonon modes in Ni doped ZnO nanoparticles were studied through Fourier transform infrared measurements. Furthermore, the enhancement in optical band gap with Ni doping from 3.29 to 3.32 eV has been observed through UV-visible spectroscopic analysis. Photoluminescence spectra of Zn1−xNixO show the UV-emission peak showing the blue shift with increase in doping concentration followed by broad visible (blue) emission corresponding to the defect emission whose intensity decreased with increasing Ni concentration. A clear room temperature ferromagnetism is observed in all samples but saturation magnetization decreased with increasing Ni co...

Structural, optical, vibrational, and magnetic properties of sol-gel derived Ni doped ZnO nanoparticles

This paper reports the temperature-dependent tailoring of acceptor defects in oxygen rich ZnO thin films, for enhanced p-type conductivity. The oxygen rich p-type ZnO thin films were successfully grown by pulsed laser deposition on silicon substrate at different postdeposition annealing temperatures (500–800 °C). The oxygen rich ZnO powder was synthesized by wet chemical method using zinc acetate dihydrate [Zn(CH3COO)2·2H2O] and potassium hydroxide (KOH) as precursors. The powder was then compressed and sintered to make pellets for pulsed laser deposition system. The x-ray diffraction analysis exhibits an improved crystallinity in thin films annealed at elevated temperatures with a temperature-dependent variation in lattice constants. An analysis of Auger Zn L3M4,5M4,5 peak reveals a consistent decrease in interstitial zinc (Zni) exhibiting its temperature-dependent reversion to zinc lattice sites. Room temperature photoluminescence of the p-type ZnO shows a dominant deep level emission peak at ∼3.12 eV r...

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Oxygen rich p-type ZnO thin films using wet chemical route with enhanced carrier concentration by temperature-dependent tuning of acceptor defects

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

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 � 640.9eV, in x-ray photoelectron spectroscopic spectra, confirmed a successful incorporation of manganese in its Mn 2þ 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 0.05emu/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. V C 2012 American Institute of Physics. [doi:10.1063/1.3679129]

https://www3.ntu.edu.sg/home/hdsun/group/publication/2012/JApplPhys_111_033503[1].pdf

Li Fengji

Papers

Oxygen rich p-type ZnO thin films using wet chemical route with enhanced carrier concentration by temperature-dependent tuning of acceptor defects

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

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