Controlling defects and interfaces in composite absorbers can effectively regulate electromagnetic (EM) parameters and enhance the electromagnetic wave (EMW) absorption ability, but the mechanism still needs to be further elucidated. In this study, ZnFe2O4/ZnO/C composite was synthesized via the hydrothermal method followed by post-annealing in different atmospheres. Defects and interfaces were characterized by Raman, PL spectroscopy, XPS and TEM, and their relationship with dielectric loss and EMW absorption performance was discussed in detail. Results show that the N2-annealed ZnFe2O4/ZnO/C composite with abundant defects and interfaces as well as an optimized composition exhibits excellent EMW dissipation ability, with a RLmin value of −17.4 dB and an fe of 3.85 GHz at a thickness of 2.28 mm. The excellent EMW absorption performance originates from suitable impedance matching, significant conduction loss and strong dielectric loss (interfacial polarization, diploe polarization and defect polarization) dominated by lattice defects and interfaces. This study provides a view into the relationship between defects, interfaces, EM parameters and EMW absorption ability, and also suggests an effective way to promote EMW dissipation ability of the absorbers by controlling defects and interfaces.

Interfacial polarization is generally a major cause of dielectric loss, but its exact contribution to the electromagnetic wave (EMW) absorption capacity of absorbers remains to be elucidated. In this work, SnO2@rGO composite (S2) with tight interfaces formed by chemical bonds and SnO2/rGO mixture (S3) were synthesized by a simple chemical route followed by further calcined in argon, respectively. Compared with pure SnO2 (S1) and S3, S2 exhibits much better EMW-dissipation ability, with a smaller minimum reflection loss (RLmin) value of −20.5 dB at a matched thickness of 5 mm and a larger effective absorption bandwidth (fe) value of 5.8 GHz (from 11 GHz to 16.8 GHz) at 3.2 mm. By comprehensively comparing the defects, dipoles, and interfaces in S2 and S3, it is concluded that the excellent EMW absorption capacity of S2 is mainly caused by strong dielectric loss dominated by interfacial polarization as well as suitable impedance matching. This study provides an insight into the exact contribution of interfacial polarization to the EMW-dissipation ability of absorbers, showing that the EMW absorption of graphene-based composites can be effectively promoted by constructing well-connected interfaces between graphene and absorbers.

Benefiting from a high quantum efficiency, low thermal emittance, and large absorption coefficient, InxGa1−xAs is an excellent group III–V compound for negative electron affinity (NEA) photocathodes. As the emission layer, InxGa1−xAs, where x = 0.15, has the optimal performance for detection in the near-infrared (NIR) region. Herein, an NEA In0.15Ga0.85As photocathode with Al0.63Ga0.37As as the buffer layer is designed in the form of a transmission mode module. The electronic band structures and optical properties of In0.15Ga0.85As and Al0.63Ga0.37As are calculated based on density functional theory. The time response characteristics of the In0.15Ga0.85As photocathode have been fully investigated by changing the photoelectron diffusion coefficient, the interface recombination velocity, and the thickness of the emission layer. Our results demonstrate that the response time of the In0.15Ga0.85As photocathode can be reduced to 6.1 ps with an incident wavelength of 1064 nm. The quantum efficiency of the In0.15Ga0.85As photocathode is simulated by taking into account multilayer optical thin film theory. The results indicate that a high quantum efficiency can be obtained by parameter optimization of the emission layer. This paper provides significant theoretical support for the applications of semiconductor photocathodes in the near-infrared region, especially for the study of ultrafast responses in the photoemission process.