Cross-sectional shape modulation of physical properties in ZnO and Zn1−xCoxO nanowires

Z Y Wu,Y F Lin,F R Chen,W B Jian,I J Chen,J J Kai,J J Lin,S P Chiu

doi:10.1088/1367-2630/10/3/033017

Z Y Wu, Y F Lin + Show 6 more

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https://doi.org/10.1088/1367-2630/10/3/033017

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Abstract

We have prepared comparable-diameter ZnO and Zn1- xCoxO nanowires with both circular and hexagonal cross-sections. The average diameters are ∼113 and ∼134 nm for cylindrical and hexagonal nanowires, respectively. The as-grown nanowires have been characterized via structure, electrical conductivity and photoluminescence (PL) spectrum measurements. Pure ZnO nanowires were Co-ion implanted to make magnetic Zn1- xCoxO nanowires for magnetization studies. Bumpier edge surfaces on a nanometre scale, higher densities of stacking faults and a bending feature along the growth direction have been found in cylindrical ZnO nanowires. As compared with hexagonal nanowires, we have observed relatively higher conductivities in cylindrical nanowires, which implied large numbers of shallow donors existing in the latter nanowires. The cylindrical ZnO nanowires also displayed intensified green defect emission and considerably more stacking faults in the crystalline structure. In addition, we have found increased magnetization and stronger ferromagnetic ordering in cylindrical than in hexagonal Zn1-xCoxO nanowires, and have experimentally identified that the point defects of either Zn interstitials or O vacancies played governing roles in ferromagnetism. We conclude that the cross-sectional shape effect originating a varied point defect density can profoundly modulate the structural, electrical, optical as well as magnetic properties of ZnO and Zn1-xCoxO nanowires.

Highlights

We have prepared comparable-diameter ZnO and Zn1−x Cox O nanowires with both circular and hexagonal cross-sections
We notice that the surface morphology of those cylindrical ZnO nanowires is usually bumpy on a nanometre scale, as is seen in figure 1(b), where the inset denotes the zone axis in the TEM experimental configuration
In connection with our observations of high conductivities and numerous stacking faults in cylindrical nanowires, we argue that these high levels of point defects must be closely associated with the shallow donors that facilitate electrical transport as well as with the planar defects of stacking faults that are sensitive to highresolution TEM analysis

Summary

Introduction

We have prepared comparable-diameter ZnO and Zn1−x Cox O nanowires with both circular and hexagonal cross-sections. We have in the present work fabricated cylindrical and hexagonal ZnO nanowires with comparable diameters, and carried out extensively electrical, optical and magnetic property measurements and structure analysis of these nanowires to uncover shape effects. A highresolution TEM image of a single crystalline nanowire is shown in figure 1(b) with 0.52 nm spaced (001) planes, the [0001] growth direction, and some planar defects of stacking faults as indicated.

Results

Conclusion