Nano-Cr2O3 films on Al2O3 ceramics with low SEEY and excellent vacuum withstand voltage performance prepared by evaporation-induced self-assembly

In this work, high-continuity nano-Cr 2 O 3 films were fabricated on the Al 2 O 3 ceramic substrate surface via the evaporation-induced self-assembly (EIA) method, aiming at decreasing the secondary electron emission yield (SEEY) and increasing the vacuum withstand voltage performance of Al 2 O 3 ceramic for application in electric vacuum devices. The effects of ethylene glycol monomethyl ether (MOE) addition and calcination temperature on the composition, structure, and various properties of the nano-Cr 2 O 3 films were investigated, and the related mechanisms were discussed. Employing MOE and increasing its addition significantly mitigated internal stress during the liquid film formation and crack-free nano-Cr 2 O 3 films were achieved at 15% addition. With the calcination temperature increasing from 300 °C to 1000 °C, the crystallinity, uniformity, and compactness of the film were improved, while the defect states decreased, resulting in an increase in bandgap, surface resistivity, and decrease in SEEY, presenting the particularity of Cr 2 O 3 . When calcined at above 1000 °C, the Cr 2 O 3 film gradually dissolved into the Al 2 O 3 substrate, which led to the increase in bandgap, surface resistivity and SEEY, approaching the intrinsic characteristics of Al 2 O 3 at 1500 °C. The nano-Cr 2 O 3 film calcined at 1000 °C exhibits optimized comprehensive structure characteristics, moderate surface resistivity (1.30×10 16 Ω/□), the lowest SEEY (2.27), and presenting a much improved and impressive vacuum flashover voltage strength of 65 kV/cm.