Thermal Stability Of ZnO Research Articles

White light-emitting ZnO:Dy3+ nanophosphors: delving into the spectroscopic parameters via Judd-Ofelt analysis.

Developing a single-phase white emitting nanophosphor with high quantum efficiency has become a hotspot for scientific world. Herein, single-phase white-light emitting Zn1-xO:xDy3+ nanophosphors have been synthesized via a sonochemical method. X-ray diffraction analysis and Raman spectroscopy-based investigations confirmed the hexagonal wurtzite phase for Zn1-xO:xDy3+ nanophosphors with preferential growth along the (101) plane. Scanning electron microscopy images showed the formation of a ribbon-shaped morphology with a diameter of ∼25 nm. The emission spectra of the Dy3+-activated ZnO nanophosphors exhibited three distinct peaks, namely blue (480 nm), yellow (572 nm), and red (635 nm) emissions, under near-UV excitations related to the 4F9/2 → 6HJ (J = 15/2, 13/2, and 11/2) transitions of Dy3+ ions. The values of CIE chromaticity coordinates for the optimized phosphor (x = 0.329, y = 0.334) with correlated color temperature (CCT) of 5657 K indicated cool white-light emission from the phosphor. The thermal stability of ZnO:Dy3+ nanophosphors was probed by temperature-dependent luminescence. Quantitative evaluation of Judd-Ofelt intensity parameters, radiative parameters, luminescence decay, and quantum efficiency of Zn1-xO:xDy3+ using the J-O theory suggests that these nanophosphors are promising luminescent media for commercial white LEDs and other display devices.

Physical characterizations and methane gas–sensing of AlxZn1-xO nanoparticles

The effects of the Al ratio on the morphological and structural parameters, thermal stability, surface area, optical band gap, and methane (CH4) gas–sensing of AlxZn1-xO nanoparticles were investigated. The homogeneous precipitation method was used to prepare AlxZn1-xO nanoparticles (x = 0, 0.5, 1, 2, and 4 at.%) and their compositions were revealed by EDX mapping. The hexagonal crystal structure of ZnO was obtained by annealing at 600 °C and wasn’t affected by the Al ratio. The crystallite/particle size was decreased while dislocation density and stacking fault were increased as Al content increased. The Al ratio controls the morphology of AlxZn1-xO e.g., rod-like, and nano-sheet shapes were observed for higher Al ratios. UV–visible absorption spectroscopy was utilized to investigate the optical absorbance and optical band gap (Eg), e.g., increasing the Al content increased Eg from 3.38 eV (for ZnO) up to 5.8 eV for Al0.04Zn0.96O. Al-doped ZnO has a considerable impact on both the surface area and the thermal stability of ZnO. The maximum surface area (189.72 m2/g) was achieved for the Al0.005Zn0.995O. The sensing parameters as a function of operating temperature and Al doping ratio have been thoroughly tested. The Al0.005Zn0.995O revealed the best sensing performance toward CH4 gas.

Synthesis, Fabrication and Characterization of ZnO-Based Thin Films Prepared by Sol–Gel Process and H2 Gas Sensing Performance

In this paper, an attempt is made to deposit ZnO thin films using sol–gel process followed by dip-coating method on p-silicon (100) substrates for intended application as a hydrogen gas sensor owing to the low toxic nature and thermal stability of ZnO. The thin films are annealed under annealing temperatures of 350, 450 and 550 °C for 25 min. The crystalline quality of the fabricated thin films is then analyzed by field-emission scanning electron microscopy and transmission electron microscope. The gas sensing performance analysis of ZnO thin films is demonstrated at different annealing temperatures and hydrogen gas concentrations ranging from 100 to 3000 ppm. Results obtained show that the sensitivity is significantly improved as annealing temperature increases with maximum sensitivity being achieved at 550 °C annealing temperature and operating temperature of 150 °C. Hence, the modified ZnO thin films can be applicable as H2 gas sensing device showing to the improved performance in comparison with unmodified thin-film sensor.

Thermal stability of ZnO/ZnCdO/ZnO double heterostructures grown by pulsed laser deposition

The thermal stability of ZnO / Zn 1 − x Cd x O / ZnO double heterostructures grown by pulsed-laser deposition was studied by annealing them for 30 min in air at temperatures from 620 to 970 °C. In photoluminescence spectroscopy measurements on the as-grown samples emission with energies between 3.122 and 3.044 eV were observed, corresponding approximately to Cd-contents between 2.7% and 3.6%. Due to the annealing a monotonic blue-shift of the Zn 1 − x Cd x O - related luminescence was found with increasing annealing temperature. The shift was small for annealing temperatures of up to 720 °C, thus a stability of the heterostructures up to this temperature was concluded. The underlying diffusion process was investigated to determine the diffusion coefficient for the different annealing temperatures. The temperature dependence of the diffusion coefficient shows an activation enthalpy in the range between 2.1 and 3.5 eV, depending on the growth conditions.

GaN Growth on Si Using ZnO Buffer Layer

AbstractZnO films were deposited by Pulsed Laser Deposition (PLD) onto silicon substrates to serve as a buffer layer for GaN films grown by MOCVD. A ZnO buffer layer was found to improve the quality of GaN grown on Si. The thermal stability of ZnO as a buffer layer was also examined. It was determined that exposure of ZnO/Si to NH3 at high temperature (> 600°C) results in the decomposition of ZnO and subsequent poor nucleation of GaN. The ZnO layer thickness on GaN quality was found to be important.

Influence of deposition conditions on the thermal stability of ZnO:Al films grown by rf magnetron sputtering

The resistivity and the thermal stability of transparent conducting ZnO layers doped with aluminum have been correlated with the conditions of the sputtering process. Layers deposited at low rf power density (∼1.3 to 2.6 W/cm2) exhibit a low resistivity of 9×10−4 Ω cm, predominantly due to a high concentration of intrinsic donor type defects. These donors are compensated during annealing at high temperature in a vacuum; the low resistivity increases and the layers are not thermally stable. At rf power densities of ∼3.2 W/cm2 and more, the deposition conditions yield a high growth rate and the extrinsic aluminum dopant is incorporated on vacant cation sites. These substitutional donors are thermally stable therefore a low resistivity is retained after annealing at 550 °C.