Study On Microstructure And Wettability Of ZnO Nanorod Arrays Prepared By Cathodic Electrodeposition Method

ZnO is a wide band gap semiconductor with 3.37 eV energy gap.It can be widely used in various fields because of its excellent performance in electronics,photonics,optics and biology.Various manufacturing methods have been developed for the preparation of ZnO with different sizes,crystal structures,crystal forms and particle shapes.In this paper,ZnO nanorod arrays were prepared by cathodic electrodeposition.The effect of deposition time,electrolyte composition and two substrates(ITO/Ti)on their structures,wettability and optical properties were studied in detail,including the X-ray diffraction,scanning electron microscopy,contact angle measuring instrument and Raman spectroscopy.First,ZnO nanorod arrays were prepared on ITO substrates by changing the time of electrochemical deposition.The XRD results illustrate that all of the peaks can be attributed to the hexagonal wurtzite structure.With the increase of electrodeposition time,the crystallinity and the preferential orientation growth in the 002 direction are enhanced.The diameter,surface roughness and thickness of the ZnO array increase with the increase of deposition time.All the samples showed hydrophobicity,and the water contact angle increased to 120° after 120 min of electrodeposition.After 10 min UV irradiation,the surface wettability was converted to hydrophilicity,and the proportions of water contact angle after illumination was compared with that before UV irradiation were 73.5%,63.5%,48.3%and 24.2%,respectively,corresponding to the deposition time 10 min,30 min,60 min and 120 min samples.The results of photoluminescence(PL)show that the peak intensity ratio of the UV emission peak(intrinsic emission peak)of ZnO increases from 2.26%to 63.84%with the increase of the deposition time,and the intensity of visible light emission peak(the emission peak caused by defects)indicates that the intrinsic defects of ZnO nanorod arrays decrease with the deposition time increased from 10min to 120min.The analysis of Raman spectra shows that the ZnO nanorod arrays exhibit 439 cm-1,566 cm-1 and 1097 cm-1 characteristic peaks under these conditions,corresponding to E2 phonon vibrating modes,E1L phonon vibrating modes and E3 vibration mode of ZnO single crystal.Subsequently,keep the other conditions unchanged(Zn2+ concentration unchanged),ZnCl2 solution was doped into Zn(N03)2.The XRD results show that all the peaks are attributed to the hexagonal wurtzite structure,the grain size decreases and the number of crystal nucleus increases with the increase of ZnCl2 concentration,and C-axis(002)direction preferred orientation weakened.The SEM results show that the nanostructures change from rod to taper with the decrease of Zn(NO3)2 concentration.The diameter of ZnO nanorod arrays decreases continuously in addition to the sample of the concentration ratio of 1:1,and the top of nanostructures change from the "annexation" state to away and the gap is increased.PL spectra shows that the UV emission peak of sample A prepared by Zn(NO3)2 electrolyte is relatively strong.With the increase of the concentration of ZnCl2 in the electrolyte,the ratio of UV emission peak is enhanced,the ratio of UV emission peak of sample E prepared by pure ZnCl2 electrolyte is the smallest,defects are the most.With the increase of the chloride ion concentration,a rare emission peak at 350 nm gradually appears.All the samples showed strong hydrophobicity before UV irradiation,and with the increase of ZnCl2 concentration,the water contact angle increased first and then decreased,which may be related to the increase of surface roughness and deterioration of crystallinity.The wettability of the ZnO nanorod array changed from hydrophobicity to hydrophilicity after 15 minutes of UV irradiation,and the light-induced change in water contact angle varied from 45.8 to 12.9%,which may be attritubed to the change with the wetting model,the surface roughness of ZnO structure and the gap.The UV-Vis absorption spectra of the samples showed that the band gap increased to 3.343 close to the standard value of 3.37 eV.Finally,ZnO nanorod arrays were prepared on Ti substrates by changing the deposition time.The results of SEM show that all samples are rod-shaped hexagonal pyramid morphology.With the increase of electrodeposition time,the diameter of nanorods and the gap between rods are reduced.All the samples in the PL spectrum have a narrow UV emission peak and a broad emission region in the visible region.As the electrodeposition time increases,the defect decreases first and then increases,reaching the minimum at 45 min.The deposition time of the sample increased from 15 minutes to 60 minutes,and the water contact angle before the UV irradiation became gradually smaller,which may be related to the smaller surface roughness.The wettability of ZnO nanorod arrays was changed to super-hydrophilicity after 2 hours of UV irradiation,and the light induced change of water contact angle decreases first and then becomes smaller,and reached the maximum at 45 min.which may be related to the change of the wetting model,the surface roughmess of the ZnO nanorod arrays and the number of defects in the film.The curves of band gap width and photocurrent have the same regularity as the PL spectrum,and reached the maximum value at 45 min(UV emission peak intensity,band gap and photo-current size).