Multi-Scale Statistical Correlation between Morphological Anisotropy and Optical Response in Chemically Deposited AZO Nanorods

This work presents a multiscale statistical framework that quantitatively correlates the anisotropic morphology of solution-grown aluminum-doped zinc oxide (AZO) nanorods with their optical response. AZO nanorods were synthesized via chemical bath deposition on ZnO nanoflower seed layers and systematically characterized using field-emission scanning electron microscopy (FE-SEM). Advanced image processing combined with circular statistical analysis was employed to extract three complementary morphological descriptors: (i) the log-normal distribution parameters of the nanorod aspect ratio (AR), (ii) a scale-dependent critical exponent γ derived from power-law scaling, and (iii) the orientation concentration parameter κ obtained from the von Mises distribution. The results reveal a pronounced scale-dependent growth regime, with γ increasing from 1.307 at 0.1 μm to 3.881 at 30 μm, indicating a transition from diffusion-limited atomic-scale growth to fractal-like aggregation at larger length scales. The nanorods exhibit strong vertical alignment (mean tilt angle θ ≈ 89.0° ± 3.7°), while significant in-plane orientational disorder is observed, as reflected by a reduction of κ from 1.721 to 1.229 at finer spatial resolutions. Optical characterization shows a blue-shifted absorption edge (∼370 nm) and defect-related photoluminescence, both of which are shown to correlate directly with the quantified morphological anisotropy. By linking multiscale structural statistics (γ, κ, and log-normal AR parameters) to optical functionality, this framework provides physically grounded design guidelines for engineering the optoelectronic performance of AZO nanostructures through controlled morphological tuning.