4 research outputs found
Self-assembled MgxZn1−xO quantum dots (0 ≤ x ≤ 1) on different substrates using spray pyrolysis methodology
By using the spray pyrolysis methodology in its classical configuration we have grown self-assembled MgxZn1−xO quantum dots (size [similar]4–6 nm) in the overall range of compositions 0 ≤ x ≤ 1 on c-sapphire, Si (100) and quartz substrates. Composition of the quantum dots was determined by means of transmission electron microscopy-energy dispersive X-ray analysis (TEM-EDAX) and X-ray photoelectron spectroscopy. Selected area electron diffraction reveals the growth of single phase hexagonal MgxZn1−xO quantum dots with composition 0 ≤ x ≤ 0.32 by using a nominal concentration of Mg in the range 0 to 45%. Onset of Mg concentration about 50% (nominal) forces the hexagonal lattice to undergo a phase transition from hexagonal to a cubic structure which resulted in the growth of hexagonal and cubic phases of MgxZn1−xO in the intermediate range of Mg concentrations 50 to 85% (0.39 ≤ x ≤ 0.77), whereas higher nominal concentration of Mg ≥ 90% (0.81 ≤ x ≤ 1) leads to the growth of single phase cubic MgxZn1−xO quantum dots. High resolution transmission electron microscopy and fast Fourier transform confirm the results and show clearly distinguishable hexagonal and cubic crystal structures of the respective quantum dots. A difference of 0.24 eV was detected between the core levels (Zn 2p and Mg 1s) measured in quantum dots with hexagonal and cubic structures by X-ray photoemission. The shift of these core levels can be explained in the frame of the different coordination of cations in the hexagonal and cubic configurations. Finally, the optical absorption measurements performed on single phase hexagonal MgxZn1−xO QDs exhibited a clear shift in optical energy gap on increasing the Mg concentration from 0 to 40%, which is explained as an effect of substitution of Zn2+ by Mg2+ in the ZnO lattice
Mn2þ-induced room-temperature ferromagnetism and spin-glass behavior in hydrothermally grown Mn-doped ZnO nanorods
The magnetic properties of Mn-doped ZnO (ZnO:Mn) nanorods
grown by hydrothermal process at a temperature of 200 8C
and a growth time of 3 h have been studied. The samples were
characterized by using powder X-ray diffraction with Rietveld
refinement, scanning electron microscopy, energy-dispersive
X-ray analysis and SQUID magnetometry. Mn (3 wt%) and
(5 wt%)-doped ZnO samples exhibit paramagnetic and
ferromagnetic behavior, respectively, at room temperature.
The spin-glass behavior is observed from the samples with
respect to the decrease of temperature. At 10 K, both samples
exhibit a hysteresis loop with relatively low coercivity. The
room-temperature ferromagnetism in 5 wt% Mn-doped ZnO
nanorods is attributed to the increase in the specific area of grain
boundaries, interaction between dopant Mn2þ ions substituted
at Zn2þ site and the interaction between Mn2þ ions and Zn2þ
ions from the ZnO host latticeCochin University of Science and TechnologyPhys. Status Solidi A 211, No. 5, 1155–1161 (2014
Enhanced UV emission from ZnO nanoflowers synthesized by the hydrothermal process
ZnO nanoflowers were synthesized by the hydrothermal process at an optimized growth
temperature of 200 â—¦C and a growth/reaction time of 3 h. As-prepared ZnO nanoflowers were
characterized by x-ray diffraction, scanning electron microscopy, UV–visible and Raman
spectroscopy. X-ray diffraction and Raman studies reveal that the as-synthesized flower-like
ZnO nanostructures are highly crystalline with a hexagonal wurtzite phase preferentially
oriented along the (1 0 1 1) plane. The average length (234–347 nm) and diameter (77–106 nm)
of the nanorods constituting the flower-like structure are estimated using scanning electron
microscopy studies. The band gap of ZnO nanoflowers is estimated as 3.23 eV, the lowering of
band gap is attributed to the flower-like surface morphology and microstructure of ZnO. Room
temperature photoluminescence spectrum shows a strong UV emission peak at 392 nm, with a
suppressed visible emission related to the defect states, indicating the defect free formation of
ZnO nanoflowers that can be potentially used for UV light-emitting devices. The suppressed
Raman bands at 541 and 583 cm−1 related to defect states in ZnO confirms that the ZnO
nanoflowers here obtained have a reduced presence of defectsCochin University of Science and TechnologyJ. Phys. D: Appl. Phys. 45 (2012) 425103 (6pp