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Local Structure of Fe Impurity Atoms in ZnO: Bulk versus Surface
McLeod, J. A.,Boukhvalov, D. W.,Zatsepin, D. A.,Green, R. J.,Leedahl, B.,Cui, L.,Kurmaev, E. Z.,Zhidkov, I. S.,Finkelstein, L. D.,Gavrilov, N. V.,Cholakh, S. O.,Moewes, A. American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.10
<P>By studying Fe-doped ZnO pellets and thin films with various X-ray spectroscopic techniques, and complementing this with density functional theory calculations, we find that Fe-doping in bulk ZnO induces isovalent (and isostructural) cation substitution (Fe<SUP>2+</SUP> → Zn<SUP>2+</SUP>). In contrast to this, Fe-doping near the surface produces both isovalent and heterovalent substitution (Fe<SUP>3+</SUP> → Zn<SUP>2+</SUP>). The calculations performed herein suggest that the most likely defect structure is the single or double substitution of Zn with Fe, although, if additional oxygen is available, then Fe substitution with interstitial oxygen is even more energetically favorable. Furthermore, it is found that ferromagnetic states are energetically unfavorable, and ferromagnetic ordering is likely to be realized only through the formation of a secondary phase (i.e., ZnFe<SUB>2</SUB>O<SUB>4</SUB>), or codoping with Cu.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-10/jp411219z/production/images/medium/jp-2013-11219z_0010.gif'></P>
Gabor Neumann,Dennis J. O'Dowd,Penny J. Gullan,Peter T. Green 한국응용곤충학회 2016 Journal of Asia-Pacific Entomology Vol.19 No.1
Detailed assessment of scale insect (Hemiptera: Coccoidea) faunas on islands may help predict impacts of invasive ants (Hymenoptera: Formicidae) and informoptions for theirmanagement, including biological control.Mutualism between scale insects and the invasive ant Anoplolepis gracilipes on Christmas Island, Indian Ocean, threatens the conservation of the island's endemic land crab fauna, alters rainforest structure and composition, and disrupts ecosystem processes. Diversity and endemism of the scale insect fauna were assessed through broad survey across rainforest, targeted search on endemic plant species, and inspection of ornamental and horticultural plants in settled areas. Emphasis was placed on honeydew-producing species that sustain ant supercolonies and detection of endemic scale insects that could be non-target species in a biological control programme for honeydew-producing scale insects. Origins of the fauna were inferred using scale insect databases and interception records at Ports-of-Entry for the United States and Korea. Twenty-eight scale insect species in seven families are identified for the island. Four honeydew-producing species, the lac scale Tachardina aurantiaca (Kerriidae) and three soft scale species (Coccidae), are abundant in rainforest and tended by ants. No endemic species were found. Compositionally, the scale insect fauna resembles that of many other tropical islands: almost all species are biogeographically widespread, host-plant generalists, and routinely intercepted in humanmediated dispersal pathways. The likely source bioregion is Sundaland where 27 of the 28 species on the island have been recorded andwhich has been the major pathway for movement of plant material to the island for over a century.
Gabor Neumann,Dennis J. O'Dowd,Penny J. Gullan,Peter T. Green 한국응용곤충학회 2014 Journal of Asia-Pacific Entomology Vol.17 No.1
Pulvinaria urbicola Cockerell, a pulvinariine soft scale (Hemiptera: Coccidae), is a broad host-plant generalist, produces honeydew and is commonly tended by ants, including the invasive yellow crazy ant Anoplolepis gracilipes Smith and big-headed ant Pheidole megacephala (Fabricius). Pu. urbicola is implicated in dieback of forest dominated by Pisonia grandis (Nyctaginaceae) on many Indo-Pacific islands. Here we report detection of Pu. urbicola on Christmas Island (Indian Ocean), describe the potential impacts of the association of this trophobiontwith introduced ants, and briefly outline biosecurity and management issues. On Christmas Island, Pu. urbicola represents a threat to stands of Pi. grandis, potentially threatens the dominant forest tree Pi. umbellifera, and could exacerbate supercolony formation and impacts of the yellow crazy ant.
Su Ping Ong,Dennis J. O’Dowd,Peter T. Green 한국응용곤충학회 2019 Journal of Asia-Pacific Entomology Vol.22 No.2
Development and reproduction of the hymenopteran parasitoid Tachardiaephagus somervilli Mahdihassan (Chalcidoidea: Encyrtidae) were studied in its native range in Malaysia as part of a classical biological control program on Christmas Island (Indian Ocean). Tachardiaephagus somervilli was reared in the laboratory on its target host, the yellow lac scale, Tachardina aurantiaca Cockerell (Coccoidea: Kerriidae). The developmental time, survival, and sex ratio of F1 offspring from two different sources of F0 adults (field-collected F0 adults [=‘wild-caught’] and F0 adults that emerged from parasitized hosts in the laboratory [=‘laboratory-emerged’]) were compared. Sources of F0 adults did not affect the developmental time of either male or female offspring, which ranged from 23 to 25 days. Furthermore, per capita fecundity of laboratory-emerged F0 females was three times greater than wild-caught F0 females. The number of emerged F1 adults was positively related to host size. Tachardiaephagus somervilli has a short generation time relative to its female Tachardina hosts (~23 vs ~90 days), high fecundity (~16 emerged offspring per laboratory-emerged female) and can potentially complete 12–15 generations per year. This rearing protocol produced sufficient quantities of adult T. somervilli for the export and successful introduction to Christmas Island (Indian Ocean) for the biological control of invasive T. aurantiaca, with near 100% survival rates for both sexes during transit.
Structural defects induced by Fe-ion implantation in TiO<sub>2</sub>
Leedahl, B.,Zatsepin, D. A.,Boukhvalov, D. W.,Green, R. J.,McLeod, J. A.,Kim, S. S.,Kurmaev, E. Z.,Zhidkov, I. S.,Gavrilov, N. V.,Cholakh, S. O.,Moewes, A. American Institute of Physics 2014 Journal of Applied Physics Vol.115 No.5
X-ray photoelectron spectroscopy and resonant x-ray emission spectroscopy measurements of pellet and thin film forms of TiO2 with implanted Fe ions are presented and discussed. The findings indicate that Fe-implantation in a TiO2 pellet sample induces heterovalent cation substitution (Fe2+ -> Ti4+) beneath the surface region. But in thin film samples, the clustering of Fe atoms is primarily detected. In addition to this, significant amounts of secondary phases of Fe3+ are detected on the surface of all doped samples due to oxygen exposure. These experimental findings are compared with density functional theory calculations of formation energies for different configurations of structural defects in the implanted TiO2:Fe system. According to our calculations, the clustering of Fe-atoms in TiO2:Fe thin films can be attributed to the formation of combined substitutional and interstitial defects. Further, the differences due to Fe doping in pellet and thin film samples can ultimately be attributed to different surface to volume ratios. (C) 2014 AIP Publishing LLC.
Leedahl, B.,Zatsepin, D. A.,Boukhvalov, D. W.,Kurmaev, E. Z.,Green, R. J.,Zhidkov, I. S.,Kim, S. S.,Cui, L.,Gavrilov, N. V.,Cholakh, S. O.,Moewes, A. American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.48
<P>Herein we systematically study a range of dopants (Cr, Fe, Ni, Cu, and an MnCo alloy) in ZnO and TiO<SUB>2</SUB> using several X-ray spectroscopic techniques. We identify the dopant’s local environment and interaction with the host lattice by employing crystal field multiplet calculations and hence clarify their potential applicability for spintronic technologies. Our density functional theory (DFT) calculations predict a decreasing probability of direct cation (Zn/Ti) substitution by dopant atoms as atomic number increases, as well as a much greater likelihood of metallic clustering in TiO<SUB>2</SUB>. Our spectroscopic measurements confirm that in all cases, except Mn, metallic clusters of dopant atoms form in the TiO<SUB>2</SUB> crystal lattice, thus making it unfit for spintronic capabilities. On the other hand, in ZnO, the dopants substitute directly into zinc sites, which is promising for spintronic technologies.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-48/jp509761c/production/images/medium/jp-2014-09761c_0011.gif'></P>