Nondestructive characterization of nanoporous alumina films using terahertz scattering imaging

Ordered nanoporous (NP) alumina (Al2O3) films were grown on Al substrates through a two-step electrochemical anodization process. The morphology as well the roughness are characterized by terahertz (THz) reflectometry and scattering imaging. In particular, we show that before second anodization, irregular surface of NP Al2O3 leads to significant THz scattering, whereas far more homogeneous following less scattering. regularity is not readily ascertained using visible-light optical microscopy. results corroborated field-emission scanning electron microscopy (SEM) atomic-force (AFM), both which time-consuming, easy operate, can only provide local characterization substrate. THz-based techniques allow for nondestructive entire 10–100 μm length scale important range applications while providing information over macroscopic scan areas, obviate need sample preparation required other common surface-morphology techniques.