5,721 research outputs found
Structural, electrical and optical properties of copper selenide thin films deposited by chemical bath deposition technique
Detection of crystal structure of chemically-deposited copper selenide thin films
A low cost Chemical Bath Deposition (CBD) system has been developed in our laboratory for the preparation of copper selenide thin film. Good quality thin films of smooth surface of copper selenide thin films of compositions Cu2-xSe (x = 0.1–0.5) and Cu3Se2 were deposited using sodium selenosulfate as a source of selenide ions. Crystal structure of copper selenide (Cu1.8Se and Cu3Se2) thin films has been identified by X-ray diffraction (XRD) method. When the film is annealed at 250ºC in air, the phases of Cu1.8Se and Cu3Se2 become crystalline, with structures of cubic (berzelianite) and tetragonal, respectively, whereas the as-deposited film was found to be disorder. The crystallinity is very low in as-deposited samples, which improves on annealing in air at 250ºC. The grain size of the as-deposited samples was very small, which was increased about 30% owing to annealing in air at 250ºC.Author Affiliation: Al-Mamun, S H Firoz and A B M O Islam
1.Department of Physics, University of Dhaka, Dhaka-1000, Bangladesh
2.Institute of Glass and Ceramic Research and Testing
Bangladesh Council for Scientific and Industrial Research (BCSIR), Dhaka-1205, Bangladesh
E-mail : [email protected] of Physics, University of Dhaka, Dhaka-1000, Bangladesh
2.Institute of Glass and Ceramic Research and Testing
Bangladesh Council for Scientific and Industrial Research (BCSIR), Dhaka-1205, Banglades
Consequences of critical interchain couplings and anisotropy on a Haldane chain
Effects of interchain couplings and anisotropy on a Haldane chain have been
investigated by single crystal inelastic neutron scattering and density
functional theory (DFT) calculations on the model compound SrNiVO.
Significant effects on low energy excitation spectra are found where the
Haldane gap (; where is the intrachain exchange
interaction) is replaced by three energy minima at different antiferromagnetic
zone centers due to the complex interchain couplings. Further, the triplet
states are split into two branches by single-ion anisotropy. Quantitative
information on the intrachain and interchain interactions as well as on the
single-ion anisotropy are obtained from the analyses of the neutron scattering
spectra by the random phase approximation (RPA) method. The presence of
multiple competing interchain interactions is found from the analysis of the
experimental spectra and is also confirmed by the DFT calculations. The
interchain interactions are two orders of magnitude weaker than the
nearest-neighbour intrachain interaction = 8.7~meV. The DFT calculations
reveal that the dominant intrachain nearest-neighbor interaction occurs via
nontrivial extended superexchange pathways Ni--O--V--O--Ni involving the empty
orbital of V ions. The present single crystal study also allows us to
correctly position SrNiVO in the theoretical - phase
diagram [T. Sakai and M. Takahashi, Phys. Rev. B 42, 4537 (1990)] showing where
it lies within the spin-liquid phase.Comment: 12 pages, 12 figures, 3 tables PRB (accepted). in Phys. Rev. B (2015
High-field spectroscopy of singlet-triplet transitions in the spin-dimer systems Sr3Cr2O8 and Ba3Cr2O8
Magnetic excitations in the isostructural spin-dimer systems Sr3Cr2O8 and
Ba3Cr2O8 are probed by means of high-field electron spin resonance at
sub-terahertz frequencies. Three types of magnetic modes were observed. One
mode is gapless and corresponds to transitions within excited states, while two
other sets of modes are gapped and correspond to transitions from the ground to
the first excited states. The selection rules of the gapped modes are analyzed
in terms of a dynamical Dzyaloshinskii-Moriya interaction, suggesting the
presence of phonon-assisted effects in the low-temperature spin dynamics of
Sr3Cr2O8 and Ba3Cr2O8Comment: 6 pages, 4 figures, all comments are welcome and appreciate
Rotating Hairy Black Holes
We construct stationary black holes in SU(2) Einstein-Yang-Mills theory,
which carry angular momentum and electric charge. Possessing non-trivial
non-abelian magnetic fields outside their regular event horizon, they represent
non-perturbative rotating hairy black holes.Comment: 13 pages, including 4 eps figures, LaTex forma
Tunable Electron Multibunch Production in Plasma Wakefield Accelerators
Synchronized, independently tunable and focused J-class laser pulses are
used to release multiple electron populations via photo-ionization inside an
electron-beam driven plasma wave. By varying the laser foci in the laboratory
frame and the position of the underdense photocathodes in the co-moving frame,
the delays between the produced bunches and their energies are adjusted. The
resulting multibunches have ultra-high quality and brightness, allowing for
hitherto impossible bunch configurations such as spatially overlapping bunch
populations with strictly separated energies, which opens up a new regime for
light sources such as free-electron-lasers
Chemical and biological investigations of Delonix regia (Bojer ex Hook.) Raf.
U radu je opisana izolacija pet sastojaka petroleterske i diklormetanske frakcije metanolnog ekstrakta kore biljke Delonix regia: lupeol (1), epilupeol (2), β-sitosterol (3), stigmasterol (4) i p-metoksibenzaldehid (5). Nadalje, testirano je antimikrobno djelovanje različitih ekstrakata difuzijskom metodom na disku (15 μg mm2). Zone inhibicije za sastojke topljive u petroleteru, tetraklormetanu i diklormetanu bile su 914 mm, 1113 mm, odnosno 920 mm, dok je zona inhibicije standarda kanamicina bila 2025 mm. U biološkom pokusu smrtnosti morskih kozica najveću toksičnost pokazali su spojevi topljivi u tetraklormetanu (LC50 = 0,83 μg mL1), dok je topljivost sastojaka topljivih u petroleteru i diklormetanu bila LC50 14,94, odnosno 3,29 μg mL1, a standarda vinkristin sulfata 0,812 μg mL1. Ovo je prvo izvješće o izolaciji sastojaka, antimikrobnom djelovanju i citotoksičnosti biljke D. regia.In this study five compounds, lupeol (1), epilupeol (2), β-sitosterol (3), stigmasterol (4) and p-methoxybenzaldehyde (5) were isolated from the petroleum ether and dichloromethane fractions of a methanolic extract of the stem bark of Delonix regia. Antimicrobial screening of the different extracts (15 μg mm2) was conducted by disc diffusion method. The zones of inhibition demonstrated by the petroleum ether, carbon tetrachloride and dichloromethane fractions ranged from 914 mm, 1113 mm and 920 mm, respectively, compared to kanamycin standard with the zone of inhibition of 2025 mm. In brine shrimp lethality bioassay, the carbon tetrachloride soluble materials demonstrated the highest toxicity with LC50 of 0.83 μg mL1, while petroleum ether and dichloromethane soluble partitionates of the methanolic extract revealed LC50 of 14.94 and 3.29 μg mL1, respectively, in comparison with standard vincristine sulphate with LC50 of 0.812 μg mL1. This is the first report on compounds separation from D. regia, their antimicrobial activity and cytotoxicity
Systematics of electronic and magnetic properties in the transition metal doped SbTe quantum anomalous Hall platform
The quantum anomalous Hall effect (QAHE) has recently been reported to emerge
in magnetically-doped topological insulators. Although its general
phenomenology is well established, the microscopic origin is far from being
properly understood and controlled. Here we report on a detailed and systematic
investigation of transition-metal (TM)-doped SbTe. By combining density
functional theory (DFT) calculations with complementary experimental
techniques, i.e., scanning tunneling microscopy (STM), resonant photoemission
(resPES), and x-ray magnetic circular dichroism (XMCD), we provide a complete
spectroscopic characterization of both electronic and magnetic properties. Our
results reveal that the TM dopants not only affect the magnetic state of the
host material, but also significantly alter the electronic structure by
generating impurity-derived energy bands. Our findings demonstrate the
existence of a delicate interplay between electronic and magnetic properties in
TM-doped TIs. In particular, we find that the fate of the topological surface
states critically depends on the specific character of the TM impurity: while
V- and Fe-doped SbTe display resonant impurity states in the vicinity
of the Dirac point, Cr and Mn impurities leave the energy gap unaffected. The
single-ion magnetic anisotropy energy and easy axis, which control the magnetic
gap opening and its stability, are also found to be strongly TM
impurity-dependent and can vary from in-plane to out-of-plane depending on the
impurity and its distance from the surface. Overall, our results provide
general guidelines for the realization of a robust QAHE in TM-doped
SbTe in the ferromagnetic state.Comment: 40 pages, 13 figure
120{\deg} Helical Magnetic Order in the Distorted Triangular Antiferromagnet alpha-CaCr2O4
{\alpha}-CaCr2O4 is a distorted triangular antiferromagnet. The magnetic Cr3+
ions which have spin-3/2 and interact with their nearest neighbors via
Heisenberg direct exchange interactions, develop long-range magnetic order
below T_N=42.6 K. Powder and single-crystal neutron diffraction reveal a
helical magnetic structure with ordering wavevector k=(0,~1/3,0) and angles
close to 120{\deg} between neighboring spins. Spherical neutron polarimetry
unambiguously proves that the spins lie in the ac plane perpendicular to k. The
magnetic structure is therefore that expected for an ideal triangular
antiferromagnet where all nearest neighbor interactions are equal, in spite of
the fact that {\alpha}-CaCr2O4 is distorted with two inequivalent Cr3+ ions and
four different nearest neighbor interactions. By simulating the magnetic order
as a function of these four interactions it is found that the special pattern
of interactions in {\alpha}-CaCr2O4 stabilizes 120{\deg} helical order for a
large range of exchange interactions.Comment: 13 pages, 12 figure
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