Limits...
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.


Related in: MedlinePlus

Electrical resistivityρagainst temperatureTof Co-doped ZnO films oxidized under magnetic fields of 0 and 6 T.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4385247&req=5

Fig8: Electrical resistivityρagainst temperatureTof Co-doped ZnO films oxidized under magnetic fields of 0 and 6 T.

Mentions: The electrical resistivity of the films was investigated by recording their resistivity ρ at different temperatures T, as shown in Figure 8. The films behave as semiconductors because ρ decreases with increasing T. ρ of the film oxidized with an applied magnetic field of 6 T is higher than that of the film oxidized without an applied magnetic field when the temperature is lower than 318 K. According to a previous study, ρ is related to the concentration of oxygen vacancies and grain size [30]. Usually, a small grain size results in a high ρ, and a lower concentration of oxygen vacancies will result in a low ρ. However, in this study, a high concentration of vacancies leads to a high ρ because the scattering is enhanced by oxygen vacancies [31]. This result in the film formed under a magnetic field of 6 T having a higher ρ than that of the film oxidized without a magnetic field because the former contains more vacancies than the latter. The difference of ρ between the films is larger at lower T. High ρ can result from low carrier concentration and/or mobility [32]. In this study, because both films have no change of carrier concentration, the higher ρ of the films with deceasing T mainly results from lowered mobility. At lower temperature, the mobility of carriers is decreased. Because the concentration of oxygen vacancies is higher in the film formed under a magnetic field of 6 T than that formed under 0 T, more carriers are inactive at lower T. This leads to a large decrease in the mobility of carriers with decreasing T. Therefore, the difference in ρ between the two films increases with decreasing T. At RT, ρ of the film oxidized without a magnetic field is 0.164 Ω · m and that of the film oxidized under a magnetic field of 6 T is 0.813 Ω · m, both of which are much lower than that of an undoped ZnO film (1.429 Ω · m).Figure 8


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)

Electrical resistivityρagainst temperatureTof Co-doped ZnO films oxidized under magnetic fields of 0 and 6 T.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Fig8: Electrical resistivityρagainst temperatureTof Co-doped ZnO films oxidized under magnetic fields of 0 and 6 T.
Mentions: The electrical resistivity of the films was investigated by recording their resistivity ρ at different temperatures T, as shown in Figure 8. The films behave as semiconductors because ρ decreases with increasing T. ρ of the film oxidized with an applied magnetic field of 6 T is higher than that of the film oxidized without an applied magnetic field when the temperature is lower than 318 K. According to a previous study, ρ is related to the concentration of oxygen vacancies and grain size [30]. Usually, a small grain size results in a high ρ, and a lower concentration of oxygen vacancies will result in a low ρ. However, in this study, a high concentration of vacancies leads to a high ρ because the scattering is enhanced by oxygen vacancies [31]. This result in the film formed under a magnetic field of 6 T having a higher ρ than that of the film oxidized without a magnetic field because the former contains more vacancies than the latter. The difference of ρ between the films is larger at lower T. High ρ can result from low carrier concentration and/or mobility [32]. In this study, because both films have no change of carrier concentration, the higher ρ of the films with deceasing T mainly results from lowered mobility. At lower temperature, the mobility of carriers is decreased. Because the concentration of oxygen vacancies is higher in the film formed under a magnetic field of 6 T than that formed under 0 T, more carriers are inactive at lower T. This leads to a large decrease in the mobility of carriers with decreasing T. Therefore, the difference in ρ between the two films increases with decreasing T. At RT, ρ of the film oxidized without a magnetic field is 0.164 Ω · m and that of the film oxidized under a magnetic field of 6 T is 0.813 Ω · m, both of which are much lower than that of an undoped ZnO film (1.429 Ω · m).Figure 8

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