% from Cu(NO3)2) showed a minimum lattice strain (Figure 2b). This result suggests that the Cu dopants in sample S4 took proper sites in the ZnO lattice. Generally, the substitution of Zn2+ by Cu2+ would lead to a change in the lattice parameters [18, 27]. However, the pronounced changes in the lattice strain when Cu(NO3)2 is used as the Cu precursor (samples S4 and S5) suggest that the concentration of OH− in the aqueous solution plays an important role in the crystalline quality of the grown nanorods. Figure 2

Crystallite size (a) and lattice strain (b) of undoped and Cu-doped ZnO nanorods. Morphology The morphology of the nanorods was investigated MK-1775 by scanning electron microscopy. The top-view SEM images for the undoped and Cu-doped

ZnO nanorods are shown in Figure 3. The density and diameters of the nanorods showed dependency on Cu precursor and concentration. It can be seen that the average rod diameter increases from approximately 75 nm for undoped nanorods (sample S1) to approximately 210 nm when 1 at.% Cu is added from Cu(CH3COO)2 (sample S2),while when 2 at.% (sample S3) is added from the same precursor, the nanorods aggregated and the structure becomes compact. On the other hand, when 1 at.% of Cu (sample S4) is added from Cu(NO3)2, the average nanorod diameter increases slightly relative to the undoped nanorods. Increasing the Cu content to 2 at.% (sample S5) from Cu(NO3)2, the average nanorod diameter increases to approximately 120 nm. Figure 3 SEM images of the undoped and Cu-doped ZnO nanorods. The variations in the nanorod diameters and densities as functions of Cu concentration and precursors find more are explained in Figure 4a,b. The ZnO unit cell is shown in Figure 4a, where the cations (zinc ions) and the anions (oxygen ions) are arranged alternatively along the c-axis perpendicular to the substrate. Basically,

the nanorod diameter and density are highly affected by the density of the nucleation sites and the pH value of the aqueous solution. Therefore, introducing Cu dopants into the reaction path would increase the nucleation density and hence enhance the growth rate, which in turn, results in a coarsening and lateral Liothyronine Sodium aggregation of the nanorods. Figure 4 Schematics of ZnO unit cell (a) and nanorod growth and aggregation (b). The reason why the nanorods doped with Cu(CH3COO)2 exhibited a larger diameter compared to the nanorods doped with the same concentration of Cu(NO3)2 is that as shown in Equations 2 and 3, both Cu(CH3COO)2 and Cu(NO3)2 release the same concentration of Cu2+. Therefore, the anion concentration is a determinant factor. (2) (3) The two different anions CH 3 COO − and will affect the nanorod growth process in different ways. In the hydrolysis process of CH 3 COO−, more OH− will be released when the amount of OH− in the aqueous solution decreases (Equation 4). Accordingly, both lateral and vertical growth rates will increase with the increase of Cu(CH3COO)2.