MgO is a kind of high secondary electron yield (SEY) material with important applications in electron multipliers. MgO coatings can be used as the electron emission layer for multiplier dynode to improve the electron gain significantly. However, the SEY investigation on ultrathin MgO coatings is not complete and needed to be supplemented urgently. In this work, a series of MgO coatings with increasing thickness were prepared by atomic layer deposition. SEY properties and energy spectra were characterized, and the effect of coating thickness on SEY was systematically analyzed. Experimental results show that SEY of MgO/Si samples rises as the coating thickness increases. Merely, SEY almost does not change with the coating thickness when the thickness exceeds 30 nm. Then, a SEY semi-empirical theory was employed to interpret the SEY regularities of MgO coatings by regarding the coating samples as ideal double-layer structures. Theoretical calculation quantitatively explained the SEY variation observed during the experiments, and further quantified the SEY contribution level of top coating and bottom substrate for the 1 nm and 20 nm MgO coatings. The work is of great significance for comprehending the SEY of ultrathin MgO coatings and expanding the applications of nanoscale coatings with high SEY.

In this study, the effects of variations in the height ($h$) and bottom radius ($r$) of black silicon microstructures on their absorptance and photoelectric response efficiency were analyzed. By using the relation $\cot {\displaystyle \frac{\theta }{2}}={\displaystyle \frac{h}{r}}$ to combine the parameters, it was found that changes in morphology affected the absorptance of black silicon microstructures, with $h$ being directly proportional to the absorptance, while $r$ was inversely proportional. A positive correlation was observed between $\cot {\displaystyle \frac{\theta }{2}}$ and absorptance. However, the correlation between $\cot {\displaystyle \frac{\theta }{2}}$ and photoelectric response efficiency was not significant. Through Raman spectroscopy analysis of the samples, it was concluded that as the laser ablation energy density increased, more lattice defects were introduced, weakening the charge carrier transport efficiency. This study further elucidated the mechanism by which microstructural changes impacted the absorptance and energy density of black silicon, providing valuable insights for optimizing its energy density.