Fig. 1. Preparation flowchart of aluminum-based electromagnetic absorber（a） Silicon substrate，（b） Silicon substrate/aluminum film，（c） Silicon substrate/aluminum/alumina film，（d） Silicon substrate/aluminum/alumina/aluminum film

Fig. 2. An absorber with a three-layer film stack structure（a） Schematic structure，（b） SEM cross-sectional view

Fig. 3. Reflectance spectrum curves of the absorber（a） The experimental reflection spectrum curve of samples with alumina thickness of 63 nm， 73 nm， 81 nm， and 90 nm，（b） The simulation of samples with alumina thickness of 63 nm， 73 nm， 81 nm， and 90 nm. Reflection spectrum curve，（c） The experimental reflection spectrum curve of samples with alumina thickness of 105 nm， 117 nm， 136 nm and 146 nm，（d） The simulated reflection spectrum curve of samples with alumina thickness of 105 nm， 117 nm， 136 nm and 146 nm

Fig. 4. Schematic diagram of absorber structure

Fig. 5. Optical parameters of each layer of 100 nm Al/63 nm Al₂O₃/5 nm Al（a） 100 nm aluminum，（b） 63 nm Alumina，（c） 5 nm aluminum. The black curve is the refractive index n， and the red curve is the extinction coefficient k

Fig. 6. Line chart of the thickness relationship between the superabsorber cavity and the position of the absorption peak

Fig. 7. Variable angle reflection spectra of the device under different polarization states. Experimental（a-c） and calculated（d-f） reflectance spectra as a function of incidence angles under different polarization conditions

Fig. 8. The electric and magnetic field distribution at the resonant wavelength of the sample at 8° incidence（a） The electric field distribution at the xz longitudinal section（y=0 nm），（b） The magnetic field distribution at the xz longitudinal section（y=0 nm）

Fig. 9. （a） Diagram of the experimental setup of the electromagnetic absorber for light heating，（b） The heating curve of the sample under 240 mW laser power，（c） The heating curve of the sample under 300 mW laser power，（d） The heating curve of the sample under 440 mW laser power， in which the black curve is the room temperature change curve， and the red curve is the sample temperature change curve

Table 1. The relationship between the thickness of alumina and the peak position, bandwidth and range of the devices’ superabsorption