Heterodimensional Structure Switching Multispectral Stealth and Multimedia Interaction Devices

Abstract Lightweight and flexible electronic materials with high energy attenuation hold an unassailable position in electromagnetic stealth and intelligent devices. Among them, emerging heterodimensional structure draws intensive attention in the frontiers of materials, chemistry, and electronics, owing to the unique electronic, magnetic, thermal, and optical properties. Herein, an intrinsic heterodimensional structure consisting of alternating assembly of 0D magnetic clusters and 2D conductive layers is developed, and its macroscopic electromagnetic properties are flexibly designed by customizing the number of oxidative molecular layer deposition (oMLD) cycles. This unique heterodimensional structure features highly ordered spatial distribution, with an achievement of electron‐dipole and magnetic–dielectric double synergies, which exhibits the high attenuation of electromagnetic energy (160) and substantial improvement of dielectric loss tangent (≈200%). It can respond to electromagnetic waves of different bands to achieve multispectral stealth, covering visible light, infrared radiation, and gigahertz wave. Importantly, two kinds of ingenious information interaction devices are constructed with heterodimensional structure. The hierarchical antennas allow precise targeting of operating bands (S‐ to Ku‐ bands) by oMLD cycles. The strain imaging device with high sensitivity opens a new horizon for visual interaction. This work provides a creative insight for developing advanced micro–nano materials and intelligent devices.


Fabrication of PP-MG Heterodimensional Structure
Graphene oxide (GO) nanosheets were prepared by a modified Hummers' method. [1]Magnetic graphene (MG) was prepared by a facile hydrothermal method.Typically, 0.058 g of Ni(NO3)2•6H2O and 0.162 g of Fe(NO3)3•9H2O were dispersed evenly into GO suspension (0.7 mg•mL -1 ).NH3•H2O was used to adjust the pH value to 10.The obtained solution was transferred to 50 mL of Teflon-lined autoclave and maintained at 180 ℃ (24 h).Finally, the black magnetic powder was obtained by washing, drying, and grinding.PP-MG heterodimensional structure was fabricated by oxidative molecular layer deposition (oMLD), which was realized in a homemade atomic layer deposition (ALD) reactor.Typically, the MG nanosheets dispersed into ethanol were dropped on a quartz substrate.After being dried in air, the quartz substrate was transferred to ALD reactor.The PEDOT was deposited by sequential exposure of EDOT monomers and MoCl5 oxidants at 115 ℃.A complete cycle includes an exposure of EDOT monomer (7 s) followed by a N2 purge (60 s) and an exposure of MoCl5 oxidant (10 s) followed by a N2 purge (60 s).The PEDOT cycles were repeated 20, 40, 60, 80 times, and the resulting products were denoted as 20 PP-MG, 40 PP-MG, 60 PP-MG, and 80 PP-MG, respectively.

Characterization and Simulation
The microstructure and elemental composition of the resultant PP-MG heterodimensional structure were recorded by transmission electron microscopy (TEM) and energy-dispersive X-Ray spectroscopy (EDX).The cross section of PP-MG structure was imaged by atomic force microscopy (AFM) (Bruker, Dimension FastScan).Raman spectra was obtained by Raman spectrometer (Renishaw, inVia, 514 nm).The complex permittivity and complex permeability (2-18 GHz) were measured by vector network analyzer (Anritsu, 37269D).The first principles calculation was performed by DMol3 module.The electromagnetic field response characteristic was investigated by CST Microwave Studio and High Frequency Structure Simulator.

Calculation of εc", εp", wr, ws, wd, wc, wp, wm, and σRCS
The contribution of conduction (εc") and relaxation (εp") to dielectric loss are defined as follow, where σ is the leakage conductivity.ε0 is the vacuum permittivity.ω is the angular frequency (ω = 2πf).τ is the relaxation time.εs and ε∞ represent the static permittivity and the relative dielectric permittivity at high frequency limit (optical permittivity), respectively.
The magnetic eddy current coefficient is estimated by, where μ0 is the vacuum permeability.
The ratio of converted electromagnetic energy to stored electromagnetic energy (wr) is calculated based on complex permittivity (ε' and ε'') and complex permeability (μ' and μ''), The electromagnetic energy storage efficiency (ws) and conversion efficiency (wd), (5) where E0 and H0 represent the electric field intensity amplitude and the magnetic field intensity amplitude of EM wave, respectively.
Attenuation and conversion of electromagnetic energy driven by charge transport (wc), dipole polarization (wp), and magnetic response (wm), The radar cross section value is defined as, where S and λ represent the area of the simulation model and wavelength of incident wave, respectively.ES and Ei are the electric field intensity of scattered wave and incident wave, respectively.

Figure S1 .
Figure S1.Schematic diagram of experimental set-up.

Figure S5 .
Figure S5.Atomic-scale insight into rGO nanosheets and first-principles calculations.a) Formation of intrinsic defects and foreign adatoms.b) Raman spectrum of GO nanosheets.c) Atomic-scale phase of Stone-Wales defect, double vacancies, and C-OH.Scale bars are 0.5 nm.d) Calculated Raman spectra of double vacancies and C-OH.e) Electron densities of intrinsic defects and C-OH.f) Density of states of intrinsic defects and C-OH.

Figure
Figure S6.a) Reconstruction of conductive network.Raman spectra of (b) MG nanosheets and (c) PP-MG heterodimensional structure.The ID/IG value of PP-MG heterodimensional structure cannot be accurately evaluated due to the interference of PEDOT peaks.d) Microstructure of MG nanosheets and PP-MG heterodimensional structure.

Figure S7 .
Figure S7.a) 3D plots of complex permittivity versus frequency and oMLD cycle.3D plots of (b) real permeability and (c) imaginary permeability versus frequency and oMLD cycle.d) 2D plots of attenuation constant (α) versus PEDOT cycle at different frequencies.e) Electromagnetic response of heterodimensional structure, including charge transport, dipole relaxation, magnetic eddy current, and magnetic-dielectric synergy.Inset is equivalent circuit model.f) The ratio of converted electromagnetic energy to stored electromagnetic energy inside PP-MG heterodimensional structure (wr).g) The electromagnetic energy storage efficiency inside PP-MG heterodimensional structure (ws).h) The electromagnetic energy conversion efficiency inside PP-MG heterodimensional structure (wd).

Figure S9 .
Figure S9.a) RCS simulation model.b) Visual application of PP-MG heterodimensional structure as stealth coating.3D radar wave scattering signals of (c) 40 PP-MG and (d) PEC at 14 GHz (Ku-band).3D radar wave scattering signals of (e) 60 PP-MG and (f) PEC at 11 GHz (X-band).3D radar wave scattering signals of (g) 80 PP-MG and (h) PEC at 3.5 GHz (S-band).

Figure S10 .
Figure S10.Geometries and dimensions of artificial magnetic conductor-backed antennas.