X-ray absorption and magnetic circular dichroism characterizations of Mn doped ZnO

Thakur, P.; Chae, Keun Hwa; Kim, J.-Y.; Subramanian, M.; Jayavel, R.; Asokan, K.

doi:10.1063/1.2794764

Cited by 69 publications

(49 citation statements)

References 17 publications

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“…Starting from higher oxidation states the spectra obtained for the samples after reduction at 873 K and after reaction showed a sharp peak at 640 eV with some satellites that can be attributed to the Mn 2+ state [58]. Both spectra exposed very similar features compared to spectra of MnO reported in literature [59,60] as well as to homovalent standards like MnSO 4 and MnCl 2 [61,62] demonstrating that the Mn ions in the surface near region are predominantly present as Mn 2+ .…”

Section: Nexafs At the Mn L-edgesupporting

confidence: 61%

Optimizing the synthesis of cobalt-based catalysts for the selective growth of multiwalled carbon nanotubes under industrially relevant conditions

Becker

Xia

Tessonnier

et al. 2011

Carbon

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A An industrially applicable cobalt-based catalyst was optimized for the production of multiwalled carbon nanotubes (CNTs) from ethene in a hot-wall reactor. A series of highly active Co-Mn-Al-Mg spinel-type oxides with systematically varied Co : Mn ratios was synthesized by precipitation and calcined at different temperatures. The addition of Mn drastically enhanced the catalytic activity of the Co nanoparticles resulting in an extraordinarily high CNT yield of up to 249 gCNT/gCat. All quaternary catalysts possessed an excellent selectivity towards the growth of CNTs. The detailed characterization of the obtained CNTs by electron microscopy, Raman spectroscopy and thermogravimetry demonstrated that a higher Mn content results in a narrower CNT diameter distribution, while the morphology of the CNTs and their oxidation resistance remains rather similar. The temperature-programmed reduction of the calcined precursors as well as in-situ X-ray absorption spectroscopy investigations during the growth revealed that the remarkable promoting effect of the Mn is due to the presence of monovalent Mn(II) oxide in the working catalyst, which enhances the catalytic activity of the metallic Co nanoparticles by strong metal-oxide interactions. The observed correlations between the added Mn promotor and the catalytic performance are of high relevance for the production of CNTs on an industrial scale.

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Section: Nexafs At the Mn L-edgesupporting

confidence: 61%

Optimizing the synthesis of cobalt-based catalysts for the selective growth of multiwalled carbon nanotubes under industrially relevant conditions

Becker

Xia

Tessonnier

et al. 2011

Carbon

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“…This is due to the fact that, as 'Co' concentration increases, more and more 'Co' unoccupied 3d states are being introduced within the band gap of the ZnO that hybridizes with the O 2p orbitals. The appearance of similar feature has been reported [30][31][32] in case of thin films. It is also evidenced that, this pre-edge peak also present in the case of pure ZnO.…”

Section: Resultssupporting

confidence: 57%

“…The relative intensity of XMCD signal at L 3 edge increases with 'Co' concentrations, due to the increase of 'Co' ions in the host lattice. It is also seen that, there is a weak signal at the L 2 -edge; this would suggests the presence of large orbital contribution of the magnetic moment [30,32,34].…”

Section: Resultsmentioning

confidence: 86%

Spectroscopic investigation of an intrinsic room temperature ferromagnetism in Co doped ZnO nanoparticles

Srinatha

Angadi

Nair

et al. 2014

Journal of Electron Spectroscopy and Related Phenomena

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a b s t r a c tPure and Co substituted ZnO nano crystalline particles were prepared by solution combustion technique using l-Valine as a fuel. As synthesized powder samples were characterized by X-ray diffractometer and SQUID magnetometer to confirm the formation of single phase wurtzite structure and to study the bulk magnetic response of the sample, respectively. Magnetic studies show that Co doped ZnO nanoparticles exhibit ferromagnetism (FM) at room temperature (RT). Furthermore, the electronic structure and element specific magnetic properties were investigated by near-edge X-ray absorption fine structure (NEXAFS) and X-ray magnetic circular dichroism (XMCD) measurements, respectively. The effect of Co substitution on the spectral features of Co-ZnO at O K-edge, Co L 3,2 edge, Zn L 3,2 edge have been investigated. The spectral features of NEXAFS at Co L 3,2 edge is entirely different from the spectral features of metallic clusters and other impurity phases, which rules out the presence of impurity phases. The valence state of 'Co' ion is found to be in +2 state. The FM nature of the sample was confirmed through XMCD spectra, which is due to the incorporation of divalent 'Co' ions. Hence the presented results confirm the substitution of 'Co' ions at 'Zn' site in the host lattice, which is responsible for the RTFM.

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“…[2][3][4][5][6]8) An important consequence of the previous paragraph is that O-substitution can thus explain the observed 4+ charge state of minority fractions of Mn impurities in ZnO thin films. 4,14,15 Moreover, the fact that for those studies the impurities were not incorporated by ion implantation but during growth, indicates that minority anion substitution may be a general phenomenon in transition metal doped ZnO. In principle, the concentration of transition metal impurities in anion sites increases with (1) decreasing energy cost of incorporating an atom of a given impurity element in an O site and (2) increasing available energy.…”

Section: Resultsmentioning

confidence: 99%

“…13 However, some observations do not completely conform to the scenario where all impurities occupy Zn substitutional sites in ZnO. X-ray absorption near-edge structure spectroscopy (XANES) 4,14 and X-ray photoelectron spectroscopy (XPS) 15 experiments have shown that Mn impurities can be incorporated in ZnO with charge states of up to 4+. Because Zn-substitutional Mn is expected to have a 2+ charge state with the 2+/3+ and 3+/4+ donor levels below the valence band maximum (thus not ionized), 16 these reports indicate that minority fractions may in fact occupy other lattice sites.…”

Section: Introductionmentioning

confidence: 98%

Mixed Zn and O substitution of Co and Mn in ZnO

et al. 2011

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The physical properties of an impurity atom in a semiconductor are primarily determined by the lattice site it occupies. In general, this occupancy can be correctly predicted based on chemical intuition, but not always. We report on one such exception in the dilute magnetic semiconductors (DMS) Co-and Mn-doped ZnO, experimentally determining the lattice location of Co and Mn using β − emission channeling from the decay of radioactive 61 Co and 56 Mn implanted at the ISOLDE facility at CERN. Surprisingly, in addition to the majority substituting for Zn, we find up to 18% (27%) of the Co (Mn) atoms in O sites, which is virtually unaffected by thermal annealing up to 900 • C. We discuss how this anion site configuration, which had never been considered before for any transition metal in any metal oxide material, may in fact have a low formation energy. This suggests a change in paradigm regarding transition metal incorporation in ZnO and possibly other oxides and wide-gap semiconductors.

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X-ray absorption and magnetic circular dichroism characterizations of Mn doped ZnO

Cited by 69 publications

References 17 publications

Optimizing the synthesis of cobalt-based catalysts for the selective growth of multiwalled carbon nanotubes under industrially relevant conditions

Optimizing the synthesis of cobalt-based catalysts for the selective growth of multiwalled carbon nanotubes under industrially relevant conditions

Spectroscopic investigation of an intrinsic room temperature ferromagnetism in Co doped ZnO nanoparticles

Mixed Zn and O substitution of Co and Mn in ZnO

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