Two-dimensional SnO/SnO2 heterojunctions for electromagnetic wave absorption

[Display omitted] •Homojunction and heterojunction achieved for the 2D SnO/SnO2 systems.•Visualized differences in charge distribution at interfaces via electron holography.•Work function correlated to charge separation and interfacial polarization.•Enhanced electromagnetic wave absorption resulted from SnO/SnO2 heterojunctions. Interfacial polarization is critical in electromagnetic (EM) wave absorption for dielectric materials. The underlying mechanisms and related factors of the interfacial polarization, however remain veiled, refraining the advance of dielectric absorbers with enhanced attenuation. Herein, two-dimensional (2D) SnO nanosheets have been used as a template, whose dominating interface evolves from SnO-(001)/SnO-(110) to SnO-(110)/SnO2-(101) and SnO2-(101)/SnO2-(211) via controllable oxidation. Combined off-axis electron holography and first-principle calculations indicate that larger difference in the work function of the SnO-(110)/SnO2-(101) (1.986 eV) compared with those of the SnO-(001)/SnO-(110) and SnO2-(101)/SnO2-(211) (0.338 eV and 0.534 eV, respectively) gives rise to distinctive charge density distribution. As such enhanced interfacial polarization can be achieved for favorable electromagnetic wave absorption of the SnO/SnO2 heterojunctions. This study not only provide a versatile method to fabricate 2D heterojunctions with tuned interfaces, correlations among work function, charge separation and interfacial polarization are also established, which is instructive for electric polarity manipulation for various applications.