Morphology and conductivity control in hexagonal ZnO nanorods through annealing for gas sensor applications
N.A. Klychkov1, V.V. Simakov1, I.V. Sinev1, A.M. Zakharevich1, V.V. Efanova2
1 Saratov State University
2 Volga State Transport University
DOI: 10.26456/pcascnn/2025.17.649
Original article
Abstract: This study investigates the influence of the annealing temperature (300-500°C) on the electrophysical properties of nanostructured zinc oxide (ZnO) layers synthesized by a sol–gel method. The obtained samples consist of an ensemble of hexagonal nanorods. Quantitative morphological analysis revealed that the kinetics of the nanorods growth in the temperature range of 300-450°C follows an Arrhenius-type dependence with the activation energy of 0,35 eV, which corresponds to a surface diffusion-controlled mechanism. Experimental data demonstrate a non-monotonic relationship between the conductivity and annealing temperature, with a distinct minimum observed between 350°C and 400°C. It was found that annealing at 400°C for five hours results in stabilization of the electronic properties, yielding a minimal conductivity drift of 0,19 %/h. The observed effect is attributed to a competition between two processes: a decrease in the concentration of bulk donors (oxygen vacancies and zinc interstitials) and an increase in the average crystallite size with rising the annealing temperature, leading to the formation of shunting conductive channels. The dependence of the steady-state conductivity of the ZnO sample in dry air on the annealing temperature, as calculated using a flat-band model, satisfactorily describes the experimental data. The obtained results open prospects for the targeted synthesis of highly sensitive and stable sensing elements for chemical resistive gas sensors based on ZnO.
Keywords: zinc oxide, sol-gel synthesis, thermal annealing, electrical conductivity, gas sensor, nanostructured materials
- Nikita A. Klychkov – 4th year postgraduate student, Physics Institute, Saratov State University
- Viacheslav V. Simakov – Dr. Sc., Professor, Material Sciences, Technologies and Quality Management Department, Saratov State University
- Ilya V. Sinev – Ph. D., Docent, Material Sciences, Technologies and Quality Management Department, Saratov State University
- Andrey M. Zakharevich – Ph. D., Head of the Laboratory for Diagnostics of Nanomaterials and Structures, Saratov State University
- Vera V. Efanova – Dr. Sc., Professor, Volga State Transport University
For citation:
Klychkov N.A., Simakov V.V., Sinev I.V., Zakharevich A.M., Efanova V.V. Upravlenie morfologiej i provodimostyu geksagonalnykh nanosterzhnej ZnO s pomoshchyu termoobrabotki dlya prilozhenij gazovoj sensoriki [Morphology and conductivity control in hexagonal ZnO nanorods through annealing for gas sensor applications], Fiziko-khimicheskie aspekty izucheniya klasterov, nanostruktur i nanomaterialov [Physical and chemical aspects of the study of clusters, nanostructures and nanomaterials], 2025, issue 17, pp. 649-657. DOI: 10.26456/pcascnn/2025.17.649. ⎘
Full article (in Russian): download PDF file
References:
1. Smirnov A.V., Grebennikov A.I., Gribov A.N. et al. Otklik gazochuvstvitel`noj mikrosistemy` na zapax peregretoj izolyacii e`lektricheskogo kabelya [Response of a gas-sensitive microsystem to the smell of overheated electrical cable insulation], Nano-i mikrosistemnaya tekhnika [Nano- and Microsystems Technology], 2014, no. 2, pp. 53-56. (In Russian).
2. Sinev I.V., Klychkov N.A., Timoshenko D.A., Simakov V.V. Vliyanie osveshcheniya na raspoznavatelnuyu sposobnost multisensornikh mikrosistem na osnove nitevidnikh nanokristallov dioksida olova [Illumination effect on recognition ability of multisensor microsystems based on tin oxide nanowhiskers], Fiziko-khimicheskie aspekty izucheniya klasterov, nanostruktur i nanomaterialov [Physical and chemical aspects of the study of clusters, nanostructures and nanomaterials], 2020, issue 12, pp. 713-721. DOI: 10.26456/pcascnn/2020.12.713.
3. Wang Y., Li X., Wang N. et al. Controllable synthesis of ZnO nanoflowers and their morphology-dependent photocatalytic activities, Separation and Purification Technology, 2008, vol. 62, issue 3, pp. 727-732. DOI: 10.1016/j.seppur.2008.03.035.
4. Gupta S.K., Joshi A., Kaur M. Development of gas sensors using ZnO nanostructures, Journal of Chemical Sciences, 2010, vol. 122, issue 1, pp. 57-62. DOI: 10.1007/s12039-010-0006-y.
5. Fan S.W., Srivastava A.K., Dravid V.P. Nanopatterned polycrystalline ZnO for room temperature gas sensing, Sensors and Actuators B: Chemical, 2010, vol. 144, issue 1, pp. 159-163. DOI: 10.1016/j.snb.2009.10.054.
6. Gurylev V., Perng T.P. Defect engineering of ZnO: Review on oxygen and zinc vacancies, Journal of the European Ceramic Society, 2021, vol. 41, issue 10, pp. 4977-4996. DOI: 10.1016/j.jeurceramsoc.2021.03.031.
7. Fang Z.B., Yan Z.J., Tan Y.S. et al. Influence of post-annealing treatment on the structure properties of ZnO films, Applied Surface Science, 2005, vol. 241, issues 3-4, pp. 303-308. DOI: 10.1016/j.apsusc.2004.07.056.
8. Lee J., Choi Y., Park B.J. et al. Precise control of surface oxygen vacancies in ZnO nanoparticles for extremely high acetone sensing response, Journal of Advanced Ceramics, 2022, vol. 11, issue 5, pp. 769-783. DOI: 10.1007/s40145-022-0570-x.
9. Klychkov N.A., Simakov V.V., Sinev I.V., Efanova V.V., Zakharevich A.M. Vliyanie parov vodi na provodimost i otklik k param etanola gazochuvstvitelnikh nanostrukturirovannikh sloyov ZnO pri komnatnoi temperature [The effect of water vapor on the conductivity and response of gas-sensitive nanostructured ZnO layers to ethanol vapors at room temperature], Fiziko-khimicheskie aspekty izucheniya klasterov, nanostruktur i nanomaterialov [Physicochemical Aspects of the Study of Clusters, Nanostructures and Nanomaterials], 2024, issue 16, pp. 891-905. DOI: 10.26456/pcascnn/2024.16.891. (In Russian)
10. Klychkov N.A., Simakov V.V., Sinev I.V. Vliyanie glubokikh poverkhnostnikh aktseptornikh sostoyanii na temperaturnuyu zavisimost provodimosti sloyov oksida tsinka [The effect of deep surface acceptor states on the temperature-dependent conductivity of zinc oxide nanoparticles], Fiziko-khimicheskie aspekty izucheniya klasterov, nanostruktur i nanomaterialov [Physicochemical Aspects of the Study of Clusters, Nanostructures and Nanomaterials], 2024, issue 16, pp. 906-921. DOI: 10.26456/pcascnn/2024.16.906. (In Russian)
11. Gwyddion – Free SPM (AFM, SNOM/NSOM, STM, MFM, …) data analysis software. Available at: www.url: http://gwyddion.net (accessed 15.07.2025).
12. Borah M. Theoretical insights into growth mechanisms of ZnO nanorods, Journal of Nanoscience and Technology, 2025, vol. 10, issue 2, pp. 995-998. DOI: 10.30799/inst.357.25100201.
13. Nandi R., Major S.S. The mechanism of growth of ZnO nanorods by reactive sputtering, Applied Surface Science, 2017, vol. 399, pp. 305-312. DOI: 10.1016/j.apsusc.2016.12.097.
14. Kim D.S., Gösele U., Zacharias M. Surface-diffusion induced growth of ZnO nanowires, Journal of Crystal Growth, 2009, vol. 311, issue 11, pp. 3216-3219. DOI: 10.1016/j.jcrysgro.2009.03.026.
15. Simakov V., Voroshilov A., Grebennikov A. et al. Gas identification by quantitative analysis of conductivityvs-concentration dependence for SnO2 sensors, Sensors and Actuators B: Chemical, 2009, vol. 137, issue 2, pp. 456-461. DOI: 10.1016/j.snb.2009.01.005.