1,170 research outputs found
Structural and magnetic properties of a series of low doped ZnCoO thin films deposited from Zn and Co metal targets on (0001) AlO substrates
We report on the synthesis of low doping ZnCoO () thin
films on (0001)-AlO substrates. The films were prepared in an oxidizing
atmosphere, using the pulsed laser deposition technique starting from Zn and Co
metallic targets. We first studied the influence of the strains of ZnO and
their stuctural properties. Second, we have investigated the structural and the
magnetic properties of the ZnCoO films. We show that at low doping,
the lattice parameters and the magnetization of the ZnCoO films
depend strongly on the Co concentration.Comment: to be published in Journal Applied Physics (June 2004) as a
proceeding of the MMM/Intermag Conferenc
Immune response & modulation of immune response induced in the guineapigs by Mycobacterium avium complex (MAC) & M. fortuitum complex isolates from different sources in the south Indian BCG trial area
A total of 139 guineapigs were used to study the immune response and its modulation induced by
Mycobacterium avium complex (MAC) and M. fortuitum complex strains obtained from different
sources in the south Indian BCG trial area. The guineapigs were divided into groups and some were
directly sensitised/immunised with different MAC strains, M. fortuitum complex strain or BCG and
others were sensitised with MAC or M. fortuitum complex and then immunised with BCG. The
resulting delayed type hypersensitivity (DTH) response in the different groups of guineapigs was
studied by skin tests using PPD-RT23 and PPD-B, and protective response was studied by challenging
the guineapigs with a south Indian low virulent strain of M. tuberculosis and enumerating the
bacilli in spleen at different points of time. The 3 strains of MAC induced similar low levels of DTH
to PPD-RT23 but much higher and varying levels of DTH to PPD-B. MAC strains from soil and
sputum induced different levels of immune modulation during subsequent immunisation with BCG
on the DTH response to PPD-RT23 and PPD-B. At 2 wk after challenge, 23.8, 81 and 90.5 per cent
protection was induced by the standard strain, soil isolate and sputum isolate of MAC, respectively,
while 33.3 per cent protection was induced by the M. fortuitum complex strain compared to the
protection induced by BCG alone. Prior exposure to MAC or M. fortuitum complex did not have
any modulatory effect on the protective immunity due to BCG at this time point. However, at 6
wk after challenge, while the guineapigs immunised with BCG were protected, modulation of the
protective response resulting from BCG was observed in the guineapigs sensitised with MAC and
M. fortuitum from soil
Evaluation of Procedures for Isolation of Nontuberculous Mycobacteria from Soil and Water
Six methods of decontamination each for the isolation of mycobacteria from soil and water were compared.
On the basis of the results obtained. three of the six methods for soil and two of the six methods for water were
further evaluated. For both soil and water samples, the method using 3% sodium lauryl sulfate in combination
with 1% NaOH yielded more positives than the other methods
Study of surface crystallinity and stoichiometry of laser annealed GaAs using time resolved reflectivity and channeling
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Study of surface crystallinity and stoichiometry of laser annealed GaAs using time resolved reflectivity and channeling
The surface crystallinity ans stoichiometry of tellurium implanted GaAs annealed with a frequency doubled Nd glass laser using time resolved reflectivity and channeling measurements has been studied. By optimizing the duration of the liquid melt, depending on the implant dose, it has been possible to laser anneal implanted layers in uncapped GaAs with good surface crystallinity and minimal loss of arsenic fue to surface decomposition. We propose a qualitative model of arsenic evaporation at the surface and subsequent replacement by arsenic displaced from the bulk by the tellurium which explains the dependence of the optimum melt duration on the dose of the implant.Physic
High Temperature Ferromagnetism with Giant Magnetic Moment in Transparent Co-doped SnO2-d
Occurrence of room temperature ferromagnetism is demonstrated in pulsed laser
deposited thin films of Sn1-xCoxO2-d (x<0.3). Interestingly, films of
Sn0.95Co0.05O2-d grown on R-plane sapphire not only exhibit ferromagnetism with
a Curie temperature close to 650 K, but also a giant magnetic moment of about 7
Bohr-Magneton/Co, not yet reported in any diluted magnetic semiconductor
system. The films are semiconducting and optically highly transparent.Comment: 12 pages, 4 figure
Cationic vacancy induced room-temperature ferromagnetism in transparent conducting anatase Ti_{1-x}Ta_xO_2 (x~0.05) thin films
We report room-temperature ferromagnetism in highly conducting transparent
anatase Ti1-xTaxO2 (x~0.05) thin films grown by pulsed laser deposition on
LaAlO3 substrates. Rutherford backscattering spectrometry (RBS), x-ray
diffraction (XRD), proton induced x-ray emission (PIXE), x-ray absorption
spectroscopy (XAS) and time-of-flight secondary ion mass spectrometry
(TOF-SIMS) indicated negligible magnetic contaminants in the films. The
presence of ferromagnetism with concomitant large carrier densities was
determined by a combination of superconducting quantum interference device
(SQUID) magnetometry, electrical transport measurements, soft x-ray magnetic
circular dichroism (SXMCD), XAS, and optical magnetic circular dichroism (OMCD)
and was supported by first-principle calculations. SXMCD and XAS measurements
revealed a 90% contribution to ferromagnetism from the Ti ions and a 10%
contribution from the O ions. RBS/channelling measurements show complete Ta
substitution in the Ti sites though carrier activation was only 50% at 5% Ta
concentration implying compensation by cationic defects. The role of Ti vacancy
and Ti3+ was studied via XAS and x-ray photoemission spectroscopy (XPS)
respectively. It was found that in films with strong ferromagnetism, the Ti
vacancy signal was strong while Ti3+ signal was absent. We propose (in the
absence of any obvious exchange mechanisms) that the localised magnetic
moments, Ti vacancy sites, are ferromagnetically ordered by itinerant carriers.
Cationic-defect-induced magnetism is an alternative route to ferromagnetism in
wide-band-gap semiconducting oxides without any magnetic elements.Comment: 21 pages, 10 figures, to appear in Philosophical Transaction - Royal
Soc.
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Dynamics of Q-switched laser annealing
Using time‐resolved optical‐reflectivity measurements, the duration of the thin liquid layer accompanying Q‐switched laser annealing in Si, Ge, and GaAs has been determined. The duration of this melted layer has been studied as a function of laser energy at 1.06‐ and 0.53‐μm wavelength for both implanted and unimplanted samples. Thresholds for initiation of melting and damaging the surface are obtained directly. With the aid of channeling–Rutherford‐backscattering measurements, the duration of melt necessary for annealing implanted samples is determined. Results for unimplanted silicon at 530 nm are compared with recent numerical calculations. In addition, measuremnts of the fall time of the reflectivity as the liquid‐solid interface approaches the surface enables us to estimate regrowth velocities. A simple scheme is also discussed for efficient annealing with dual wavelengths.Physic
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