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Structure-dependent mechanical properties of ultrathin zinc oxide nanowires.

Lee WJ, Chang JG, Ju SP, Weng MH, Lee CH - Nanoscale Res Lett (2011)

Bottom Line: As the width of the nanowire decreases, Young's modulus, stress-strain behavior, and yielding stress all increase.In addition, the yielding strength and Young's modulus of Type III are much lower than the other two types, because Type I and II have prominent edges on the cross-section of the nanowire.These results indicate that the ultrathin nanowire possesses very high malleability.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical and Electro-Mechanical Engineering, Center for Nanoscience and Nanotechnology, National Sun Yat-sen University Kaohsiung, 804, Taiwan. jushin-pon@mail.nsysu.edu.tw.

ABSTRACT
Mechanical properties of ultrathin zinc oxide (ZnO) nanowires of about 0.7-1.1 nm width and in the unbuckled wurtzite (WZ) phase have been carried out by molecular dynamics simulation. As the width of the nanowire decreases, Young's modulus, stress-strain behavior, and yielding stress all increase. In addition, the yielding strength and Young's modulus of Type III are much lower than the other two types, because Type I and II have prominent edges on the cross-section of the nanowire. Due to the flexibility of the Zn-O bond, the phase transformation from an unbuckled WZ phase to a buckled WZ is observed under the tensile process, and this behavior is reversible. Moreover, one- and two-atom-wide chains can be observed before the ZnO nanowires rupture. These results indicate that the ultrathin nanowire possesses very high malleability.

No MeSH data available.


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Stress-strain relationship for Type I, II, and III.
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Figure 3: Stress-strain relationship for Type I, II, and III.

Mentions: For clearly discussing the detail of the deformation behavior, a central region and prominent edge are defined for Type I and II in Figure 2. The corresponding stress-strain profiles for the tensile process of different types of nanowires are shown in Figure 3. It is observed that as the wire width decreases, the maximum stress and the slope of stress-strain curve increase. Clearly, the both are much larger for Type I and II than for Type III. In the first stage, the stress increases linearly with slight fluctuation until the yielding occurs at yielding strain. The Young's modulus can be determined from the results of tensile test for the strain of 2%, using linear regression. The calculated results of Young's modulus for three types of nanowires are listed in Table 2, which corresponding to Wang et al.'s work [25] as listed in Table 2. This shows that the smaller the area of the cross-section, the greater the increase in the Young's modulus and the yielding stress. The variation tendency of the mechanical property as a function of width of ZnO nanowires has been verified by Kulkarni et al. [44] and Wang et al. [25]. At strain larger than the yielding strain, as shown in Figure 3, it is observed that the tendency of Type II and III are similar, both possessing two different stages II and III. At stage II, the stress-strain curve shows zigzag fluctuation from the yielding strain to the strain of approximately 35%. This phenomenon in Type II and III represents the local phase transformation, which is illustrated in Figure 4, which shows the side view of the Type II ZnO nanowire under the elongation process at different stages. It is observed that as the strain increases, the necking region of the HX structure gradually grows as shown in Figure 4a,b, because some of the ZnO bond parallel to the axis is broken, and the local HX structure becomes a buckled structure at the prominent edge of the cross-section of Type II. Here, we note that the structure is clearly buckled at the prominent edge of the cross-section of the nanowire, while it is slightly buckled at the central region. In addition, the phase transformation is generated symmetrically along the axis of nanowire, as can be seen by the rectangles in Figure 4b. The phase transformation of the ZnO nanowire has been observed in a loading and unloading process [24]. At stage III, the stress increases significantly with slight fluctuation, and is even higher than the yielding stress at the first stage. The slight fluctuation is due to the phase transformation near both ends, and the significant increase in stress is caused by the new phase as shown in Figure 4c. After the strain passes the maximum stress, the Zn-O bond is broken by a yielding stress of 80 GPa, as shown in Figure 3, and the corresponding snapshot is shown in Figure 4d. With a continuing increase in strain, the necking deformation gradually induces the nanowire to become a two-atom-wide chain in the middle region as shown in Figure 4e,f. After the strain of 108.18%, the two-atom-wide chain is fractured as shown in Figure 4g.


Structure-dependent mechanical properties of ultrathin zinc oxide nanowires.

Lee WJ, Chang JG, Ju SP, Weng MH, Lee CH - Nanoscale Res Lett (2011)

Stress-strain relationship for Type I, II, and III.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211442&req=5

Figure 3: Stress-strain relationship for Type I, II, and III.
Mentions: For clearly discussing the detail of the deformation behavior, a central region and prominent edge are defined for Type I and II in Figure 2. The corresponding stress-strain profiles for the tensile process of different types of nanowires are shown in Figure 3. It is observed that as the wire width decreases, the maximum stress and the slope of stress-strain curve increase. Clearly, the both are much larger for Type I and II than for Type III. In the first stage, the stress increases linearly with slight fluctuation until the yielding occurs at yielding strain. The Young's modulus can be determined from the results of tensile test for the strain of 2%, using linear regression. The calculated results of Young's modulus for three types of nanowires are listed in Table 2, which corresponding to Wang et al.'s work [25] as listed in Table 2. This shows that the smaller the area of the cross-section, the greater the increase in the Young's modulus and the yielding stress. The variation tendency of the mechanical property as a function of width of ZnO nanowires has been verified by Kulkarni et al. [44] and Wang et al. [25]. At strain larger than the yielding strain, as shown in Figure 3, it is observed that the tendency of Type II and III are similar, both possessing two different stages II and III. At stage II, the stress-strain curve shows zigzag fluctuation from the yielding strain to the strain of approximately 35%. This phenomenon in Type II and III represents the local phase transformation, which is illustrated in Figure 4, which shows the side view of the Type II ZnO nanowire under the elongation process at different stages. It is observed that as the strain increases, the necking region of the HX structure gradually grows as shown in Figure 4a,b, because some of the ZnO bond parallel to the axis is broken, and the local HX structure becomes a buckled structure at the prominent edge of the cross-section of Type II. Here, we note that the structure is clearly buckled at the prominent edge of the cross-section of the nanowire, while it is slightly buckled at the central region. In addition, the phase transformation is generated symmetrically along the axis of nanowire, as can be seen by the rectangles in Figure 4b. The phase transformation of the ZnO nanowire has been observed in a loading and unloading process [24]. At stage III, the stress increases significantly with slight fluctuation, and is even higher than the yielding stress at the first stage. The slight fluctuation is due to the phase transformation near both ends, and the significant increase in stress is caused by the new phase as shown in Figure 4c. After the strain passes the maximum stress, the Zn-O bond is broken by a yielding stress of 80 GPa, as shown in Figure 3, and the corresponding snapshot is shown in Figure 4d. With a continuing increase in strain, the necking deformation gradually induces the nanowire to become a two-atom-wide chain in the middle region as shown in Figure 4e,f. After the strain of 108.18%, the two-atom-wide chain is fractured as shown in Figure 4g.

Bottom Line: As the width of the nanowire decreases, Young's modulus, stress-strain behavior, and yielding stress all increase.In addition, the yielding strength and Young's modulus of Type III are much lower than the other two types, because Type I and II have prominent edges on the cross-section of the nanowire.These results indicate that the ultrathin nanowire possesses very high malleability.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical and Electro-Mechanical Engineering, Center for Nanoscience and Nanotechnology, National Sun Yat-sen University Kaohsiung, 804, Taiwan. jushin-pon@mail.nsysu.edu.tw.

ABSTRACT
Mechanical properties of ultrathin zinc oxide (ZnO) nanowires of about 0.7-1.1 nm width and in the unbuckled wurtzite (WZ) phase have been carried out by molecular dynamics simulation. As the width of the nanowire decreases, Young's modulus, stress-strain behavior, and yielding stress all increase. In addition, the yielding strength and Young's modulus of Type III are much lower than the other two types, because Type I and II have prominent edges on the cross-section of the nanowire. Due to the flexibility of the Zn-O bond, the phase transformation from an unbuckled WZ phase to a buckled WZ is observed under the tensile process, and this behavior is reversible. Moreover, one- and two-atom-wide chains can be observed before the ZnO nanowires rupture. These results indicate that the ultrathin nanowire possesses very high malleability.

No MeSH data available.


Related in: MedlinePlus