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Nanopatterned sapphire substrates were fabricated by annealing of patterned Al thin films. Square-patterned Al thin films with the diagonal length of 600 nm, period of 1 um and height of ∼200 nm were obtained by the Laser Interference Lithography and Reactive Ion Etching. Patterned Al thin films were subsequently subjected to dual stage annealing due to the melting temperature of Al thin films (660 C). The first comprised a low temperature oxidation anneal. The hillocks formation on Al thin films was minimized with an oxidation annealing at 450 C for 24 h. The little change in the morphology of patterned Al thin films was observed at 450 C for 24 h. This was followed by a high temperature annealing to induce growth of the underlying sapphire single crystal to consume the oxide layer. The SEM results show the patterns were retained on sapphire substrates after high temperature annealing at less than 1200 C. The XRD and Raman results reveal that the orientation of island patterns by dual stage annealing of patterned Al thin films for 24 h at 450 C, and 1 h at 1000 C, was the same as that of the sapphire (0001) substrates. [ABSTRACT FROM AUTHOR]

Large-scale nanopatterned sapphire substrates were fabricated by annealing of patterned Al thin films. Patterned Al thin films were obtained by soft UV-nanoimprint lithography and reactive ion etching. The soft mold with 550-nm-wide lines separated by 250-nm space was composed of the toluene-diluted polydimethylsiloxane (PDMS) layer supported by the soft PDMS. Patterned Al thin films were subsequently subjected to dual-stage annealing due to the melting temperature of Al thin films (660°C). The first comprised a low-temperature oxidation anneal at 450°C for 24 h. This was followed by a high-temperature annealing in the range of 1,000°C and 1,200°C for 1 h to induce growth of the underlying sapphire single crystal to consume the oxide layer. The SEM results indicate that the patterns were retained on sapphire substrates after high-temperature annealing at less than 1,200°C. Finally, large-scale nanopatterned sapphire substrates were successfully fabricated by annealing of patterned Al thin films for 24 h at 450°C and 1 h at 1,000°C by soft UV-nanoimprint lithography.

Abstract: Sapphire single crystals grown by an improved Kyropoulos-like method are irradiated by fast neutron flux. The irradiated doses of neutron are 1018 and 1019 n/cm2. The infrared transmission spectra of sapphire were studied before and after irradiation. The irradiated samples were annealed at 200, 400, 600, 800 and 1000°C for 10min in ambient atmosphere. Positron annihilation studies have been carried out before and after neutron irradiation. The experimentally measured positron lifetime in the pristine specimen is 143ps. There were aluminum vacancies produced in sapphire crystals after neutron irradiation. The positron lifetime increased with the dose of neutron flux. A longer value τ 2 was found after annealing at 600°C, which indicated vacancies were aggregated with each other. The second long-time component τ 2 has been found to increase with the annealing temperature. There was almost no change in peak position of the CDB spectra after neutron irradiation and isothermal annealing. The chemical environment of core in sapphire did not change greatly after neutron irradiation. [Copyright &y& Elsevier]

In this paper, ZnO thin films with different thicknesses grown on Si (1 0 0) substrates by atomic layer deposition (ALD) method were annealed in nitrogen at the temperatures ranging from 200 to 900 °C. The influences of film thickness and annealing temperature on the structural and optical properties of the ZnO films were systematically investigated by XRD, SEM and RT-PL. All the ALD-ZnO thin films show polycrystalline hexagonal wurtzite structure and a high preferential c -axis orientation. The results show that the crystallinity quality and luminescence performance are both improved by increasing the film thickness. In addition, the loss of oxygen which results in the formation of oxygen vacancies (V O ) is the main reason for the green emission dominating visible band of annealed ZnO thin films. The visible band is dominated by different kinds of defects including oxygen vacancies (V O and V O + ), and interstitial oxygen (I O ) with increasing annealing temperature. High-quality ZnO thin films with good luminescence performance can be obtained for the films annealed at 800 °C in nitrogen. [ABSTRACT FROM AUTHOR]

Nanopatterned sapphire substrates were prepared by solid state reaction of patterned Al films obtained by E-Beam lithography of a PMMA/copolymer bilayer resist and lift-off. The effect of exposure parameters and annealing on the structure and morphological properties of nanopatterned sapphire substrates prepared by solid state reaction were investigated by a scanning electron microscope (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and Raman, respectively. The circular Al patterns with diameter/spacing being 500nm/1000nm were obtained by optimal exposure diameter/exposure dosage of 400nm/200μC/cm2. Patterned Al films were subsequently subjected to solid state reaction by dual stage annealing due to the melting temperature of Al thin films (660°C). The hillocks formation on Al films was minimized with an oxidation anneal at 450°C. Moreover, the little change in the morphology of Al patterns was observed after annealing at 450°C. The SEM and AFM results show the patterns were retained on sapphire substrates after high temperature annealing at less than 1200°C. The XRD and Raman results reveal that the composition and orientation of island patterns prepared by solid state reaction for 24h at 450°C, and 1h 1000°C were the same as that of the sapphire (0001) substrates. [ABSTRACT FROM AUTHOR]

Highlights: [•] N-doped Ga2O3 films were deposited on sapphire substrates by radio frequency magnetron sputtering. [•] The samples were annealed in N2, O2, air, respectively. [•] The influence of annealing atmosphere on the structure, morphology and transmittance was investigated. [•] Annealing in nitrogen showed smooth surface and higher transmission in visible range. [•] The red shift of the optical band gap was observed after annealing. [ABSTRACT FROM AUTHOR]

Abstract: ZnO thin films were prepared on sapphire (0001) substrates by the dip-coating sol–gel technique. Then, ZnO thin films with thicknesses of 50nm, 150nm, 250nm, and 350nm were annealed at 800°C and with thickness of 250nm were annealed at 600°C, 700°C, 800°C, and 900°C, respectively. The effect of film thickness and annealing temperature on the structure and optical properties of sol–gel ZnO thin films on sapphire substrates were investigated by XRD, SEM, RT-PL. All the sol–gel ZnO thin films show polycrystalline hexagonal wurtzite structure and a high preferential c-axis orientation. The XRD and SEM results show that the better structural quality, high c-axis preferred orientation, uniform, compact sol–gel ZnO thin films 250nm thick were obtained when annealed at 700°C in air. Room-temperature PL spectrum of sol–gel ZnO thin films can be divided into the UV emission and the visible broad band emission. The UV emission can be attributed to the near band edge emission (NBE) and the visible broadband emission can be ascribed to the deep level emissions (DLE). The visible emission is suppressed with the annealing temperature of 600–700°C. By analyzing our experimental results, we concluded that the deep-level emission corresponds to oxygen vacancies (V O ). The biggest ratio of the PL intensity of UV emission to that of visible emission (I NBE/I DLE) is observed from sol–gel ZnO thin films 250nm thick annealed at 700°C. Therefore, we suggest that film thickness of 250nm and annealing temperature of 700°C are the most suitable conditions for obtaining high quality, high c-axis preferred orientation, uniform, compact sol–gel ZnO thin films with good luminescence performance. [Copyright &y& Elsevier]

Abstract: ZnO thin films were epitaxially grown on sapphire (0001) substrates by radio frequency magnetron sputtering. ZnO thin films were then annealed at different temperatures in air and in various atmospheres at 800°C, respectively. The effect of the annealing temperature and annealing atmosphere on the structure and optical properties of ZnO thin films are investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL). A strong (002) diffraction peak of all ZnO thin films shows a polycrystalline hexagonal wurtzite structure and high preferential c-axis orientation. XRD and AFM results reveal that the better structural quality, relatively smaller tensile stress, smooth, uniform of ZnO thin films were obtained when annealed at 800°C in N2. Room temperature PL spectrum can be divided into the UV emission and the Visible broad band emission. The UV emission can be attributed to the near band edge emission (NBE) and the Visible broad band emission can be ascribed to the deep level emissions (DLE). By analyzing our experimental results, we recommend that the deep-level emission correspond to oxygen vacancy (VO) and interstitial oxygen (Oi). The biggest ratio of the PL intensity of UV emission to that of visible emission (I NBE/I DLE) is observed from ZnO thin films annealed at 800°C in N2. Therefore, we suggest that annealing temperature of 800°C and annealing atmosphere of N2 are the most suitable annealing conditions for obtaining high quality ZnO thin films with good luminescence performance. [Copyright &y& Elsevier]