3,064 research outputs found
Synthesis and properties of Co-doped titanate nanotubes and their optical sensitization with methylene blue
Here we report on a novel chemical route to synthesize homogenous cobalt
doped titanate nanotubes (CoTNT), using an amorphous Co-doped precursor. The
influence of the synthesis temperature, autoclave dwell time and metal doping
on the structural and microstructural as well as on the optical properties of
the synthesized titanate nanotubes is studied and discussed. The optical band
gaps of the CoTNT samples are red shifted in comparison with the values
determined for the undoped samples, such red shifts bringing the absorption
edge of the CoTNT samples into the visible region. CoTNT materials also
demonstrate particular high adsorption ability for methylene blue, the amount
of the adsorbed dye being higher than the one predictable for a monolayer
formation. This suggests the possibility of intercalation of the dye molecule
between the TiO6 layers of the TNT structure. It is also shown that the
methylene blue sensitized Co-doped nanostructures are highly stable under UV
radiation and present a strong and broad absorption in the visible region.Comment: 31 pages, 3 tables, 7 figure
Synthesis of sub-5 nm Co-doped SnO nanoparticles and their structural, microstructural, optical and photocatalytic properties
A swift chemical route to synthesize Co-doped SnO nanopowders is
described. Pure and highly stable SnCoO (0 x
0.15) crystalline nanoparticles were synthesized, with mean grain sizes <
5 nm and the dopant element homogeneously distributed in substitutional sites
of the SnO matrix. The UV-visible diffuse reflectance spectra of the
SnCoO samples reveal red shifts, the optical bandgap
energies decreasing with increasing Co concentration. The Urbach energies of
the samples were calculated and correlated with their bandgap energies. The
photocatalytic activity of the SnCoO samples was
investigated for the 4-hydroxylbenzoic acid (4-HBA) degradation process. A
complete photodegradation of a 10 ppm 4-HBA solution was achieved using 0.02%
(w/w) of SnCoO nanoparticles in 60 min of
irradiation.Comment: 29 pages, 2 tables, 10 figure
Ferromagnetic Ga₁ˍₓ Mnₓ As produced by ion implantation and pulsed-laser melting
We demonstrate the formation of ferromagneticGa₁ˍₓMnₓAsfilms by Mn ion implantation into GaAs followed by pulsed-laser melting. Irradiation with a single excimer laser pulse results in the epitaxial regrowth of the implanted layer with Mn substitutional fraction up to 80% and effective Curie temperature up to 29 K for samples with a maximum Mn concentration of x≈0.03. A remanent magnetization persisting above 85 K has been observed for samples with x≈0.10, in which 40% of the Mn resides on substitutional lattice sites. We find that the ferromagnetism in Ga₁ˍₓMnₓAs is rather robust to the presence of structural defects.The work at the Lawrence Berkeley National Laboratory
was supported by the Director, Office of Science, Office of
Basic Energy Sciences, Division of Materials Sciences and
Engineering, of the U.S. Department of Energy under Contract
No. DE-AC03-76SF00098. The work at Harvard was
supported by NASA Grant No. NAG8-1680. One of
the authors ~M.A.S.! acknowledges support from an NSF
Graduate Research Fellowship
Ferromagnetic order in aged Co-doped TiO2 anatase nanopowders
Oxide based diluted magnetic semiconductor (DMS) materials have been a
subject of increasing interest due to reports of room temperature
ferromagnetism in several systems and their potential use in the development of
spintronic devices. However, concerns on the stability of the magnetic
properties of different DMS systems have been raised. Their magnetic moment is
often unstable, vanishing with a characteristic decay time of weeks or months,
which precludes the development of real applications. This paper reports on the
ferromagnetic properties of two-year-aged Ti1-xCoxO2-{\delta} reduced anatase
nanopowders with different Co contents (0.03<x<0.10). Aged samples retain
rather high values of magnetization, remanence and coercivity which provide
strong evidence for a quite preserved long-range ferromagnetic order. In what
concern Co segregation, some degree of metastability of the diluted Co doped
anatase structure could be inferred in the case of the sample with the higher
Co content.Comment: 15 pages, 5 figure
Rooting Pattern Distribution and Spatial Variability of Italian Ryegrass (Lolium Multiflorum Lam) in a Mediterranean Region
It is estimated that less than 10% of the studies on pastures and forages have evaluated the subterranean biomass production. The objective of this study was to evaluate for a Mediterranean region the rooting characteristics and spatial variability of Italian ryegrass (Lolium multiflorum Lam) under two different soil water status conditions
Zoneamento de risco climático para o girassol no Estado do Ceará.
Objetivou-se identificar as regiões com menor risco climático e a melhor época de semeadura para a cultura do girassol no Estado do Ceará, definindo-se datas de semeadura para o ciclo médio (115 dias), em três tipos de solos: tipo 1(CAD = 30 mm), tipo 2(CAD = 50 mm) e tipo 3(CAD = 75 mm), visando à obtenção de maiores rendimentos agrícolas. Utilizou os softwares Sarrazon, para o cálculo de ISNA e o SPRING 4.0, para analise dos dados, gerando mapas e tabelas. O período de semeadura indicada ao cultivo de girassol foi de 05/11 a 15/03. O total de municípios aptos para o cultivo de girassol foram de 126 para solo tipo 3, uma vez que apresentam maior capacidade de armazenamento de água em comparação aos solos do tipo 2 e 1, pois em termos granulométricos possuem teores de argila superiores a 35%. Para os municípios situados ao norte, é recomendado que o cultivo ocorra preferencialmente, de 25/12 a 15/02, uma vez que o período chuvoso nessa região se estende durante os meses de abril a maio, coincidindo com a fase critica da cultura
Magnetic properties of Co-doped TiO(2) anatase nanopowders
This letter reports on the magnetic properties of Ti(1-x)Co(x)O(2) anatase phase nanopowders with different Co contents. It is shown that oxygen vacancies play an important role in promoting long-range ferromagnetic order in the material studied in addition to the transition-metal doping. Furthermore, the results allow ruling out the premise of a strict connection between Co clustering and the ferromagnetism observed in the Co:TiO(2) anatase system
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