Study Of Structureand Pysical Properties In Fe And C Ion Co-Implanted ZnO Thin Films

ZnO thin films of thickness about 300 nm were deposited on microscopic glass substrates at room temperature by means of radio frequency (rf) magnetron sputtering. The ZnO thin films were first implanted with 120 keV Fe ions at a dose of 5.0?1016 cm^-2, and then subjected to 20 keV C ion implantation at different doses of 1.0?10¹⁵, 3?10¹⁵ and 5.0?10¹⁵ cm^-2, respectively. After implantation, some of the samples were annealed at 350℃in a flow of oxygen gas for 2 hrs. Techniques, such as scanning electron microscopy (SEM), x-ray diffraction spectroscopy (XRD), x-ray photoelectron spectroscopy (XPS), ultraviolet-visible optical spectroscopy (UV-Vis), photoluminescence (PL) and physics property measurement system (PPMS), have been used to characterize the morphology, structure, composition, optical and magnetic properties of Fe and C co-implanted and/or annealed ZnO thin films. Through the research, the following results have been obtained.(i) SEM observations and EDX measurements reveal that Fe and/or C ion implantation leads to rough surface of ZnO films. The subsequent annealing could cause growth of ZnO grains. Meanwhile, the contents of main elements involved in ZnO films were found to decrease during Fe and/or C ion implantation and subsequent annealing. (ii) XRD results show that there exist two diffraction peaks in the as-deposited ZnO film, i.e. ZnO (002) and (004) peaks, which are located at 2?=34.6o and 72o, respectively. Fe ion implantation induces a new weak diffraction peak at about 44.4o, which corresponds to theα-Fe(110), indicating formation of Fe nanoparticles. Additional C ion implantation not only gives rise to intensity decrease of theα-Fe(110) peak, but also the clear transformation of Fe nanoparticles into Fe oxide nanoparticles, which is confirmed by the occurrence of new diffraction peak at about 63°. Moreover, the structures of ZnO film under Fe and C co-implantation have also been studied in detail by consideration of modifications in ZnO (002) peak. The results show that lattice damage was created in Fe and C ion co-implanted ZnO films accompanied by clear growth of ZnO grains. The ZnO (002) peak was also found to shift to larger diffraction angle as the C ion dose increases. (iii) XPS measurements indicate that the chemical states of the implanted Fe atoms are mainly zero-valence state and compound-valence state, respectively. Carbon substitutes for oxygen and bonds with Zn, leading to formation of Zn-C bonds in the co-implanted ZnO films. (iv) UV-Vis measurements reveal that there only exists a strong absorption peak at wavelength of 380 nm in the as-deposited ZnO film. Fe ion implantation gives rise to decrease in the optical band gap of the ZnO film. However, it has been found that the optical band gap becomes larger in the Fe and C ion co-implanted ZnO samples. PL measurements demonstrate that in the Fe ion singly implanted ZnO, the PL property has been largely improved. Nevertheless, additional C ion implantation leads to sharp decrease of the luminescence. Moreover, with increasing C content, the slight red shift of PL peak has also been observed. The luminescence of the virgin ZnO could be divided into three peaks, which are located at 360, 400 and 450 nm, respectively. The PL peak at 360 nm could be attributed to the intrinsic luminescence of ZnO. The other two peaks should be mainly related to O vacancies and to Zn interstitials, respectively. Generally, the intensities of PL peaks related to defects increase with increasing the defect concentration. However, the luminescence disappeared if the concentration of defects was far over optimal concentration. (v) The results from PPMS measurements show that only a weak magnetism has been found in the Fe only implanted ZnO. The additional C implantation could increase the magnetism of the film. The subsequent annealing has been found to reduce the magnetism in both Fe singly implanted and Fe and C co-implanted ZnO film. Based on the results from the analyses of structures, the modifications in physical properties of ZnO under Fe and/or C ion implantation have been discussed.