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Modification of surface morphology and lattice order in nanocrystalline ZnO thin films prepared by spin-coating sol–gel method

Journal of Sol-Gel Science and Technology volume 100, pages 55–67 (2021)Cite this article

Abstract

The surface morphology and structure of zinc oxide thin films play a key role in many applications such as chemical sensors and photocatalysts. In this study, ZnO thin films are prepared on Si/SiO2 substrates by spin-coating sol–gel technique. New element in the films preparation is the application of drying with hot air flow (Th= 90–95 °C), as first step of the drying procedure, followed by furnace drying as second step. It is shown that hot air drying has significant influence on the films properties. It reduces the internal stress, strongly affects the films surface morphology, gives assistance to the effusion of organic remains and results in a better crystallinity and lower defect density in the as-prepared films when compared with the films prepared by furnace drying only. Besides, first data on the modification of sol–gel ZnO films by post-deposition irradiation with a nanosecond infrared laser are obtained, giving an alternative to the standard furnace annealing. They indicate that laser irradiation of as-prepared ZnO films gives rise to certain improvement in crystal structure and slight increase in crystallite size, followed by the increase of micro-strain. It also reduces the number of defects playing role of non-radiative recombination centers, as well as the size and density of small cracks and pores on the surface of as-prepared films.

Left: X-ray diffraction patterns of as-prepared and annealed at 400 °C ZnO films prepared by furnace drying only, the patterns are taken on non-irradiated and laser-irradiated films. Middle: Experimental and fitted E2high Raman mode in the spectra of non-irradiated and laser-irradiated samples prepared by two-step drying, as - the asymmetry fitting parameter. Right: Optical and AFM surface images of annealed ZnO films prepared by one-step drying; the AFM images were obtained at two different scales.

Highlights

  • Zinc oxide thin films of densely packed nanograins are prepared by sol–gel method.

  • Hot air drying during films preparation and post-deposition infrared laser irradiation are applied.

  • The hot air drying has strong influence on the internal strain and surface morphology.

  • The laser irradiation reduces the size and density of pores and cracks on the surface.

  • Defect density decreases but internal strain increases upon the laser annealing.

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Availability of data and material (data transparency)

All data described in the manuscript are available to all co-authors.

Code availability (software application or custom code)

Graphics program used: OriginPro 8.6.0 (64-bit) Sr3, Serial Number: GF3S5-6089-7606559, Registration ID: UHD-6YQ-8A1.

The AFM image analysis was done by means of Nanoscope 7.30 programme.

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Acknowledgements

RG-D gratefully acknowledge the financial support provided by the Bulgarian Ministry of Education and Science, National program “Young scientists and postdoctoral researchers” approved by DCM N577, 17.08.2018. DN and IB acknowledge the financial support provided by the European Regional Development Fund within the OP “Science and Education for Smart Growth 2014 - 2020”, project No BG05M2OP001-1.001-0008. MS, MG-B, and ZP are thankful to the Institute of Physics, Belgrade and Ministry of Education, Science and Technological Development of the Republic of Serbia. All authors are thankful to the Bulgarian Academy of Sciences and Serbian Academy of Sciences and Arts (bilateral project “Preparation and characterization of nanostructured semiconductor thin films for sensor application”).

Funding

(information that explains whether and by whom the research was supported). RG-D gratefully acknowledge the financial support provided by the Bulgarian Ministry of Education and Science, National program “Young scientists and postdoctoral researchers” approved by DCM N577, 17.08.2018. DN and IB acknowledge the financial support provided by the European Regional Development Fund within the OP “Science and Education for Smart Growth 2014 - 2020”, project No BG05M2OP001-1.001-0008. MS, MG-B and ZP are thankful to the Institute of Physics, Belgrade and Ministry of Education, Science and Technological Development of the Republic of Serbia. All authors are thankful to the Bulgarian Academy of Sciences and Serbian Academy of Sciences and Arts (bilateral project „Preparation and characterization of nanostructured semiconductor thin films for sensor application“).

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Authors and Affiliations

  1. G. Nadjakov Institute of Solid State Physics, Bulgarian Academy of Sciences, 72, Tzarigradsko Chaussee Blvd, 1784, Sofia, Bulgaria

    R. Gegova-Dzhurkova, D. Nesheva, V. Dzhurkov, I. Bineva, V. Mihailov, Z. Levi & E. Manolov

  2. Center for Solid State Physics and New Materials, Institute of Physics, University of Belgrade, Pregrevica 118, Belgrade, 11080, Serbia

    M. Šćepanović, M. Grujić-Brojčin & Z. V. Popović

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  1. R. Gegova-Dzhurkova
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  2. D. Nesheva
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  3. V. Dzhurkov
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  4. M. Šćepanović
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  5. M. Grujić-Brojčin
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  7. V. Mihailov
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  8. Z. Levi
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All authors whose names appear in the application have contributed significantly to the concept or design of the work; acquisition, analysis or interpretation of data.

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Correspondence to D. Nesheva.

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Gegova-Dzhurkova, R., Nesheva, D., Dzhurkov, V. et al. Modification of surface morphology and lattice order in nanocrystalline ZnO thin films prepared by spin-coating sol–gel method. J Sol-Gel Sci Technol 100, 55–67 (2021). https://doi.org/10.1007/s10971-021-05635-6

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Keywords

  • Sol–gel
  • Drying
  • ZnO nanostructured layers
  • Laser irradiation
  • Surface morphology
  • Lattice strain