Structural and photoluminescence properties of nanostructured zinc oxide synthesized by immersion method / Azlinda Ab. Aziz

In this present work, Zinc oxide (ZnO) nanostructures on gold-coated silicon (Si)
substrate were prepared from zinc nitrate hexahydrate (Zn(N03)2.6HO) and urea
(CH4N2O) using a low-temperature solution-immersion method. High hierarchical
structure of ZnO with high surface area were successfully synthesised by the
immersion method through optimization of the reaction parameters, such as different
substrate surface, alignment of substrate, concentration of precursor, ratio of stabiliser
in solution, and different heat temperature. FESEM, EDX, XRD, AFM and PL were
the selected characterization tools to analyse the morphological, structural, surface
analysis and optical properties of ZnO nanostructures. FESEM images revealed that
ZnO flowerlike microspheres consist of nanosheets was the dominant structure growth
along synthesis parameter. The results give evidence that the smallest diameter -11-13
|um of ZnO micro-flowers was successfully formed on gold-coated Si substrate, and
gold served as a nucleation sites for the growth of ZnO micro-flowers. Low average
surface roughness of ZnO nanostructures had shown the uniformity of particles size
on gold-coated Si surface. The alignment of substrate tilt towards 60 ° was the better
alignment towards smallest crystallite size 28.5 nm. PL emission spectra of ZnO
nanostructures consistently produced UV (398-416 nm) and visible emissions (450-
750 nm). UV peak corresponds to the ZnO nanostructures while peak at visible range
relates to ZnO defects. PL results indicated that 0.40 M concentration of zinc nitrate
and urea at 1:1 ratio had successfully formed ZnO micro-flowers consist of
nanostructures with high intensity of UV emission, confirming high optical properties
of the samples. At 500 °C of thermal treatment, ZnO nanostructures gave extremely
high PL intensity which improved its optical property with better crystallization.
Furthermore, additional analysis by PL temperature dependence of ZnO
nanostructures sample had shown that the emission energies and intensities of the ZnO
nanostructured strongly affected by the applied temperature. A plausible mechanism
of the dissociation-deposition formation of micro-flower assembly of ZnO nanosheets
from Zn(N03)2 and urea solution was also proposed.