Surface and bulk thermal annealing effects on ZnO crystals (original) (raw)
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Emission modification in ZnO nanosheets at thermal annealing
MRS Online Proceeding Library
Photoluminescence (PL) and its temperature dependences, as well as the X ray diffraction (XRD), have been studied in the freshly prepared amorphous phase ZnO nanosheets, obtained by the electrochemical (anodization) method, and in the crystalline annealed ZnO nanosheets. The freshly prepared samples have been divided in two groups. One of these groups has been annealed at 400 °C for 2 hours in ambient air. Defect related PL bands with the peaks at 2.10-2.13, 2.42-2.46 and 2.65-2.69 eV are detected in amorphous state. Appreciable changes in the size of nanosheets as a function of thermal treatments have been revealed. XRD study has shown that annealing stimulates the Zn oxidation and the creation of ZnO with a wurtzite crystal lattice. In crystalline ZnO seven PL bands appeared with the PL peaks 1.46, 1.58, 2.02, 2.43, 2.70, 2.93 and 3.16 eV at 10K. The reasons of emission transformation and the nature of optical transitions related to the studied PL bands have been discussed. It is shown that the anodization method permits by a controllable way to obtain the wide range ZnO emission that is interesting for the future applications in room temperature "white" light-emitting diodes.
Effects of annealing temperature on morphologies and optical properties of ZnO nanostructures
Superlattices and Microstructures, 2008
Electroplated depositions of Sm were prepared using a vertical well-type electrodeposition unit with an aqueous ammonium acetate electrolyte system, with an average deposition yield just over 87%. The depositions were analyzed for morphology and thickness by scanning electron microscopy (SEM) and chemical composition by energy dispersion X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) before and after firing. The depositions were fired at 125-700°C, while varying the heating rate from 0.5 to 10°C/min in either an oxidizing or reducing atmosphere. A heating rate of 10°C/min was slow enough to prevent disruption of the deposition morphology during firing. A gas sweep enhanced the removal of any organic substituents, with an oxidizing environment being more advantageous than a reducing environment.
An effect of annealing on In implanted ZnO
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003
The behavior of In implants, 170 keV, 1  10 16 ions/cm 2 , in ZnO after annealing was investigated in the temperature range of 750-850°C. The In depth profiles reveal the anomalous behavior due to the plateau region in profiles. In diffusion coefficients were estimated from the plateau region of the profiles, and the temperature dependence was described as D In ½cm 2 =s ¼ 1:1 expðÀ259 AE 17 ½kJ=mol=RT Þ. The feature in the In profiles resulted from the complex defects formed by In and radiation damages. The annealing leads to an intense emission at around 525 nm in photoluminescence spectrum. This emission is due to the defects related to the oxygen vacancy.
Optical doping of ZnO with Tm by ion implantation
Physica B: Condensed Matter, 2003
ZnO [0 0 0 1] single-crystals were implanted at room temperature with 150 keV Tm + ions at a fluence of 5 Â 10 15 cm À2 . Each sample was then subjected to one single 30 min air annealing at 800 C, 950 C and 1050 C. The Tm lattice site location and defect recovery were investigated with Rutherford Backscattering/Channeling Spectroscopy. Detailed angular scans along the [0 0 0 1] direction show that 94% of the Tm ions occupy substitutional Zn sites (S Zn ) in the as-implanted sample. All the annealing temperatures lead to a reduction of this fraction to 30%. Also, progressive damage recovery and Tm segregation to the surface were observed, being enhanced at 1050 C. Photoluminescence (PL) studies with above band gap excitation performed on these samples revealed no luminescence on the as-implanted state. The 800 C air annealing promotes the Tm 3+ optical activation and a well-defined nearinfrared intraionic emission is observed. For higher annealing temperatures, in spite of no change of the Tm fraction at S Zn sites, a decrease of the Tm intraionic emission was observed. These results suggest that optical activation of Tm ions is related with the defect density in their environment.
Effect of Annealing Temperature on Structural and, Morphological Properties of Zno Thins Films
In this work, thins films of zinc oxide were deposited on n-type silicon substrates by chemical electrodeposition. The effect of annealing temperature from 200 ° C to 600 ° C, with a step of 100 ° C, on the structural and morphological properties of ZnO layers has been studied. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and contact angle measurements were used to characterize the morphology and structure of ZnO without and with annealing. The XRD patterns of unannealed ZnO thins films indicate the presence of three intense peaks along (100), (002) and (101) planes, while for the annealed ZnO layers the XRD patterns show also the three major peaks but the intensity of these peaks is increased except for a temperature of 600 ° C where is decreased. The comparison of the XRD patterns of the ZnO layers without and with annealing, reveal a shift in the 2θ diffraction angle, the calculation of the crystallinity confirms the obtained results. The contact angle measurements...
Influence of Annealing Treatment on the Structural and Optical Properties of ZnO Nanorods
MRS Proceedings, 2010
In this paper, we have reported the influence of annealing treatment on structural, optical, electrical, and thermoelectric properties of MBE-grown ZnO on Si substrate. After growth, a set of as grown ZnO was annealed in oxygen environment at 500-800°C and another set was annealed in different environments (vacuum, oxygen, zinc, and vacuum + zinc) at 600°C for one hour in a programmable furnace. X-ray diffraction (XRD) results demonstrated that all annealed samples exhibited a major diffraction peak related to (002) plane. The full width at half maximum (FWHM) of this plane decreased and crystalline size increased for oxygen annealed sample and it increased when samples were annealed in zinc, vacuum, and successively annealed in vacuum and zinc. Further, photoluminescence spectrum revealed that the intensity of band edge emission increased and defect emission decreased as annealing temperature (oxygen environment) increased while it decreased for rest of annealing ambient. It is suspected that annealing in oxygen environment causes compensation of the oxygen vacancies by the incoming oxygen flux, while annealing in zinc and vacuum generates more oxygen vacancies. Hall and Seebeck measurements are also consistent with these arguments.
Thin Solid Films, 2007
Undoped (as-grown) ZnO films grown by pulsed laser deposition on Al 2 O 3 (0001) substrates were doped with nitrogen by means of an ion implantation process. Post-implantation annealing behavior in the temperature range between 500 and 700°C has been studied by photoluminescence and Hall effect measurements. The implanted films show no peak other than the excitonic recombination emission in the asimplanted state, however, after rapid thermal annealing at 700°C they reveal a nitrogen acceptor related emission at 3.273 eV. The as-implanted ZnO films show more electron concentrations than the as-grown, unimplanted ZnO film. In contrast, after annealing, the electron concentration in the implanted films is significantly reduced, indicating that the incorporated nitrogen becomes activated after the thermal annealing, then produces holes and eventually compensates for certain amount of electrons. The results imply that a proper nitrogen implantation and subsequent annealing may be a way to produce p-type ZnO films.
Annealing effects on photoluminescence of ZnO nanoparticles
Materials Letters, 2013
In this study, the effects of annealing temperature on photoluminescence (PL) of ZnO nanoparticles were studied. ZnO was annealed at various temperatures between 600 and 900 1C. The X-ray diffraction (XRD) results demonstrated that grain size increased with increase of annealing temperature. As the annealing temperature increased from 600 to 800 1C, the intensities of both UV peak and that of green luminescence (GL) enhanced monotonously but reduced at 900 1C. The enhancement in the UV peak intensity is attributed to the decrease of grain boundaries and surface states; whereas, the remarkable improvement in the GL is assigned to the out-diffusion of oxygen from the sample up to 800 1C. It supports that GL is induced by the singly ionized oxygen vacancies. These oxygen vacancies are saturated due to the finiteness of the defects at 800 1C. So, it is speculated that the deterioration of GL intensity at 900 1C is due to the evaporation of Zn which is predominant at temperatures higher than 850 1C.
Energy Shift of Native 2.45 eV Related Defects in Annealed ZnO Films
IOP Conference Series: Materials Science and Engineering, 2010
We study the influence of annealing temperature on the structural and optical properties of ZnO. Zinc oxide films were prepared by thermal oxidation of metallic Zn films. First, high quality (5N) Zn was evaporated onto sapphire substrate. Then zinc films were annealed in the oxygen atmosphere at several temperatures from 500 o C to 1100 o C. The surface was analyzed by Scanning Electron Microscopy (SEM) and structural properties were studied by XRD. Photoluminescence (PL) was measured from 350 nm to 800 nm, at two temperatures -80 K and 300 K. Ordinary PL spectra could be divided into two parts. One band observed at ~3.3 eV (UV PL) and second at 2.2 -2.5 (VIS PL as "visible") -the maximum energy depends on annealing temperature. The origin of UV PL is in recombination of free excitons and bound excitons to donors and acceptors [1]. However, for VIS PL exact mechanism of emission recombination is still not fully understood. The main discussion is related to the native defects such as zinc vacancies or oxygen vacancies or oxygen antisite [2] but impurities like Cu [3] and/or hydrogen donors [4] are also candidates. Sample annealing temperature influenced the peak position of VIS PL and intensity of both part of the PL spectrum
Applied Surface Science, 2012
The effects of annealing parameters on the surface morphology, crystallinity, and optical properties of ZnO disc were investigated. Variations in the annealing temperatures and gas flow rates were found to have a profound impact; grain growth was enhanced even at the low annealing temperature of only 400 • C. SEM and AFM revealed smooth and uniform grain growth after annealing treatment, especially at 800 • C. A unique secondary growth of ZnO nanoparticles and multilayer grain growth that have not been reported elsewhere were also observed. The annealing treatment was also found to improve grain crystallinity as illustrated by the lowering of intrinsic compressive stress based on the XRD lattice constant and FWHM data. The PL spectra of the M-Disc showed a huge band edge emission at 371-376 nm. In contrast, the N-Disc exhibited a dominant and broad visible PL emission in the green band with peaks at 519-533 nm. These peaks were attributed to a very high concentration of structural defects (oxygen vacancies and zinc/oxygen interstitials). The annealing conditions had a significant effect on the properties of ZnO. Increased percentage of oxygen in the O/Ar from 50% to 100% did not change the M-Disc spectra. However, the XRD pattern of the N-Disc revealed that the (0 0 2) peak intensity decreased, the position of the (1 0 1) peak slightly shifted toward a higher angle, and the FWHM of the (1 0 1) peak improved. The experimental results showed that thermal annealing could enhance the different properties of ZnO discs.