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Secondary electron (SE) emission (SEE) from material surfaces is a frequent phenomenon in space and vacuum environments. SEE modulation is important since it governs the performance of some devices such as electronic multipliers or induces some detrimental effects such as multipactors. Surface coating has been reported to modulate SEE effectively, whereas SEE behaviors of coating structures are not clearly understood yet, and the appropriate theory to describe SEE characteristics quantitatively for coating structures is less developed so far. Here, we have prepared four alumina coatings possessing various thicknesses to research the SEE characteristics of coating structures and have shown how the coating thickness affects the SEE behaviors. Besides, by considering coating/substrate as an ideal double-layer structure, we have derived several equations to describe the producing, transmitting, and escaping processes of excited inner SEs and finally constructed a unidimensional SEE model for double-layer structures. The model is applicable to reveal the dependence of true SE yield (TSEY) on the top and bottom layers’ physical properties and estimate TSEY proportions contributed by the top and bottom layers at random energy points. By employing the concept, SEE characteristics of Al2O3/Si, MgO/Si, and TiO2/Si double-layer structures have been quantitatively interpreted. Moreover, the abnormal SEY curve with a double-hump shape, which is induced by the peak position distinction of SiO2/Si structures, can also be explained. This work is of great significance to comprehend TSEY modulating regularities of various double-layer structures applied in surface engineering.

Alumina ceramics used in microwave systems are susceptible to the multiplication of secondary electron emission on the surface due to the influence of resonation between electrons and RF electrical field, and the detrimental effect of multipactor may be therefore triggered. For the alumina-loaded microwave components, low secondary electron yield (SEY) is urgent to be achieved on the inserted alumina surfaces for mitigating multipactor. In this work, for achieving an ultralow SEY surface of alumina, two recognized low-SEY treatments are combined. For the primary SEY suppression, a series of microstructures were fabricated on the alumina surfaces with various porosity and aspect ratio at hundred-micron scales by infrared laser etching. The microstructure with 52.14% porosity and 1.78 aspect ratio showed an excellent low-SEY property, which could suppress the SEY peak value (δm) of alumina from 2.46 to 1.00. For the secondary SEY suppression, the SEY dependence of TiN coating on sputtering parameters was studied, and the lowest δm of 1.19 was achieved when the gas flow ratio of Ar:N2 was 15:7.5. Whereafter, by depositing TiN ceramic coating onto the laser-etched porous samples, an ultralow SEY, δm equaled 0.69, was achieved on the alumina surfaces. The simulation work revealed the impact of dielectric surface charge on electron multiplication and uncovered the mechanism of using low SEY surfaces to inhibit multipactor. Some coaxial filters with alumina filled were fabricated for verification, the results revealed that the multipactor threshold increased from 125 W to 425 W after applying the TiN-coated porous alumina, and to 650 W after treating another multipactor sensitive area with the same low-SEY process. This work developed an advisable method to sharply reduce SEY, which is of great significance for the multipactor mitigation of the alumina-loaded microwave components.