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Structure and properties of Co-doped ZnO films prepared by thermal oxidization under a high magnetic field.

Li G, Wang H, Wang Q, Zhao Y, Wang Z, Du J, Ma Y - Nanoscale Res Lett (2015)

Bottom Line: The results show that the high magnetic field obviously changed the structure and properties of the Co-doped ZnO films.As a result, ZnO nanowires were formed without a magnetic field, whereas polyhedral particles formed under a 6 T magnetic field.The changes of oxygen vacancy concentration and Co state caused by the application of the high magnetic field also increase the ferromagnetism of the film at room temperature.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, No 3-11, Wenhua road, Heping district Shenyang, 110819 China.

ABSTRACT
The effect of a high magnetic field applied during oxidation on the structure, optical transmittance, resistivity, and magnetism of cobalt (Co)-doped zinc oxide (ZnO) thin films prepared by oxidizing evaporated Zn/Co bilayer thin films in open air was studied. The relationship between the structure and properties of films oxidized with and without an applied magnetic field was analyzed. The results show that the high magnetic field obviously changed the structure and properties of the Co-doped ZnO films. The Lorentz force of the high magnetic field suppressed the oxidation growth on nanowhiskers. As a result, ZnO nanowires were formed without a magnetic field, whereas polyhedral particles formed under a 6 T magnetic field. This morphology variation from dendrite to polyhedron caused the transmittance below 1,200 nm of the film oxidized under a magnetic field of 6 T to be much lower than that of the film oxidized without a magnetic field. X-ray photoemission spectroscopy indicated that the high magnetic field suppressed Co substitution in the ZnO lattice, increased the concentration of oxygen vacancies, and changed the chemical state of Co. The increased concentration of oxygen vacancies affected the temperature dependence of the resistivity of the film oxidized under a magnetic field of 6 T compared with that of the film oxidized without a magnetic field. The changes of oxygen vacancy concentration and Co state caused by the application of the high magnetic field also increase the ferromagnetism of the film at room temperature. All of these results indicate that a high magnetic field is an effective tool to modify the structure and properties of ZnO thin films.

No MeSH data available.


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XRD patterns of the samples oxidized with and without an applied magnetic field.
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Fig5: XRD patterns of the samples oxidized with and without an applied magnetic field.

Mentions: XRD was used to investigate the crystal structures of the films (Figure 5). The crystal structure of the as-deposited Zn film was hexagonal with (002) preferred orientation. When the Zn particles were oxidized to ZnO, their peaks changed considerably. The (101), (002), and (100) peaks of ZnO appeared in the diffraction patterns of the particles oxidized under applied magnetic fields of both 0 and 6 T. Several peaks of Zn still remained, but they differed between the oxidized samples. For the ZnO formed without an applied magnetic field, only the (101) peak of Zn obviously remained. Meanwhile, for ZnO oxidized under an applied magnetic field of 6 T, the (100), (101), (102), and (103) peaks of Zn were still visible. This means that the oxidation of Zn was not complete under a 6 T magnetic field, which is because a Lorentz force from the high magnetic field acted on the oxygen ions. As a result, a high magnetic field suppresses the oxidation of Zn. Additionally, the preferred orientations of ZnO particles are also different. ZnO formed without an applied magnetic field has (002) preferred orientation, while those for the sample oxidized under a magnetic field of 6 T are (101) for ZnO and (101) for Zn. In contrast, the Co-doped ZnO films did not contain Zn peaks in their XRD patterns, and the peak positions were consistent with hexagonal wurtzite crystal structure. Furthermore, the preferred orientations for both films were (101). Because the Co content of the film was slightly increased under the high magnetic field, the peak position shifted to higher angle, which decreased the lattice parameter c. The Co-doped ZnO films oxidized under magnetic fields of 0 and 6 T exhibited c of 0.5195 and 0.5180 nm, respectively. Additionally, the full width at half-maximum (FWHM) of the three strongest peaks for the films oxidized under magnetic fields of 0 and 6 T were 0.73 ± 0.06° and 0.76 ± 0.03°, respectively. The grain sizes in these films were then calculated from their FWHM to be 11.84 ± 0.9 and 11.42 ± 0.7 nm for the films oxidized under magnetic fields of 0 and 6 T, respectively. This suggests that the grain sizes of both films are similar, even though AFM indicated that the surface particle size of the film oxidized under a magnetic field of 6 T was larger than that of the film oxidized without an applied magnetic field.Figure 5


Structure and properties of Co-doped ZnO films prepared by thermal oxidization under a high magnetic field.

Li G, Wang H, Wang Q, Zhao Y, Wang Z, Du J, Ma Y - Nanoscale Res Lett (2015)

XRD patterns of the samples oxidized with and without an applied magnetic field.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4385247&req=5

Fig5: XRD patterns of the samples oxidized with and without an applied magnetic field.
Mentions: XRD was used to investigate the crystal structures of the films (Figure 5). The crystal structure of the as-deposited Zn film was hexagonal with (002) preferred orientation. When the Zn particles were oxidized to ZnO, their peaks changed considerably. The (101), (002), and (100) peaks of ZnO appeared in the diffraction patterns of the particles oxidized under applied magnetic fields of both 0 and 6 T. Several peaks of Zn still remained, but they differed between the oxidized samples. For the ZnO formed without an applied magnetic field, only the (101) peak of Zn obviously remained. Meanwhile, for ZnO oxidized under an applied magnetic field of 6 T, the (100), (101), (102), and (103) peaks of Zn were still visible. This means that the oxidation of Zn was not complete under a 6 T magnetic field, which is because a Lorentz force from the high magnetic field acted on the oxygen ions. As a result, a high magnetic field suppresses the oxidation of Zn. Additionally, the preferred orientations of ZnO particles are also different. ZnO formed without an applied magnetic field has (002) preferred orientation, while those for the sample oxidized under a magnetic field of 6 T are (101) for ZnO and (101) for Zn. In contrast, the Co-doped ZnO films did not contain Zn peaks in their XRD patterns, and the peak positions were consistent with hexagonal wurtzite crystal structure. Furthermore, the preferred orientations for both films were (101). Because the Co content of the film was slightly increased under the high magnetic field, the peak position shifted to higher angle, which decreased the lattice parameter c. The Co-doped ZnO films oxidized under magnetic fields of 0 and 6 T exhibited c of 0.5195 and 0.5180 nm, respectively. Additionally, the full width at half-maximum (FWHM) of the three strongest peaks for the films oxidized under magnetic fields of 0 and 6 T were 0.73 ± 0.06° and 0.76 ± 0.03°, respectively. The grain sizes in these films were then calculated from their FWHM to be 11.84 ± 0.9 and 11.42 ± 0.7 nm for the films oxidized under magnetic fields of 0 and 6 T, respectively. This suggests that the grain sizes of both films are similar, even though AFM indicated that the surface particle size of the film oxidized under a magnetic field of 6 T was larger than that of the film oxidized without an applied magnetic field.Figure 5

Bottom Line: The results show that the high magnetic field obviously changed the structure and properties of the Co-doped ZnO films.As a result, ZnO nanowires were formed without a magnetic field, whereas polyhedral particles formed under a 6 T magnetic field.The changes of oxygen vacancy concentration and Co state caused by the application of the high magnetic field also increase the ferromagnetism of the film at room temperature.

View Article: PubMed Central - PubMed

Affiliation: Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, No 3-11, Wenhua road, Heping district Shenyang, 110819 China.

ABSTRACT
The effect of a high magnetic field applied during oxidation on the structure, optical transmittance, resistivity, and magnetism of cobalt (Co)-doped zinc oxide (ZnO) thin films prepared by oxidizing evaporated Zn/Co bilayer thin films in open air was studied. The relationship between the structure and properties of films oxidized with and without an applied magnetic field was analyzed. The results show that the high magnetic field obviously changed the structure and properties of the Co-doped ZnO films. The Lorentz force of the high magnetic field suppressed the oxidation growth on nanowhiskers. As a result, ZnO nanowires were formed without a magnetic field, whereas polyhedral particles formed under a 6 T magnetic field. This morphology variation from dendrite to polyhedron caused the transmittance below 1,200 nm of the film oxidized under a magnetic field of 6 T to be much lower than that of the film oxidized without a magnetic field. X-ray photoemission spectroscopy indicated that the high magnetic field suppressed Co substitution in the ZnO lattice, increased the concentration of oxygen vacancies, and changed the chemical state of Co. The increased concentration of oxygen vacancies affected the temperature dependence of the resistivity of the film oxidized under a magnetic field of 6 T compared with that of the film oxidized without a magnetic field. The changes of oxygen vacancy concentration and Co state caused by the application of the high magnetic field also increase the ferromagnetism of the film at room temperature. All of these results indicate that a high magnetic field is an effective tool to modify the structure and properties of ZnO thin films.

No MeSH data available.


Related in: MedlinePlus