In order to study the microstructure of MAO coatings, the focused ion beam(Ultra-high resolution SEM-FIB, GAIA3) was utilized to prepare the ultra-thin specimens, and the position of prepared specimens was depicted in Fig.1. The position 1(P1) was randomly selected on the surface of MAO coatings (outer layer), and position 2(P2) was also discretionarily chosen in the inner layer of MAO-4W(Supporting Information, Fig.S1). The microstructure and composition of the outward-inward MAO layers were investigated by transmission electron microscopy(FE-TEM, Talos F200X, America) equipped with energy dispersive spectroscopy(EDS) and selected area electron diffraction (SAED).
The cross section of MAO coatings was mechanically polished with 0.5 um diamond spray and ultrasonically cleaned in acetone andethanol. Then, outward-inward potential of the cross section was measured by Kelvin probe force microscopy(KPFM) on a Bio-FastScan AFM system(FastScan Bio, America).
The photoluminescence(PL) spectra are related to the transfer behavior of the photo-induced electrons and holes so that it can reflect the separation and recombination of photo-induced charge carriers, thus it is often used to evaluate the intrinsic electron storage capability of semiconductors. And PL spectra of the MAO coatings were obtained at 300 nm excitation light using a FluoroMax-4 Spectrofluo-rometer(FluoroMax-4-L TCSPC, Horiba, America).
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