The increasing miniaturization of smart communication terminals leads to significant crosstalk between adjacent signal ports. Current metal-based electromagnetic interference (EMI) shielding films rely on reflection, which becomes less effective with denser integration. Furthermore, these films are susceptible to damage from repeated folding or harsh conditions, causing signal leakage. To address this, thin EMI shielding films with strong electromagnetic wave absorption capabilities are needed. Graphene, carbon nanotubes, MXenes, and other low-dimensional materials are promising candidates due to their excellent electrical conductivity, porous structures, and potential for high absorption rates. Compounding these with magnetic nanometallic oxides further enhances EMI shielding and absorption. Previous methods, such as in-situ growth or physical mixing, have shown promise but lack universality and struggle to achieve high conductivity, low thickness, and high EMI shielding effectiveness simultaneously. High temperatures or strong reducing agents needed for high conductivity in graphene-based materials can cause agglomeration and degradation of magnetic oxides. This research aims to overcome these limitations by developing a novel laser-based compounding method.

Existing research on EMI shielding materials highlights the advantages of graphene, carbon nanotubes, and MXenes as conductive and porous scaffolds. Studies have explored compounding these with magnetic nanometallic oxides like NiFe₂O₄ and SrFe₁₂O₁₉ to enhance EMI shielding effectiveness and absorption. For instance, Kumara et al. fabricated NiFe₂O₄/rGO nanocomposite films achieving 38.2 dB shielding, while Huang et al. prepared MXene/MWCNTs/SrFe₁₂O₁₉ films with 62.9 dB shielding, but with reduced conductivity. These studies demonstrate the potential of these composites but also highlight challenges in achieving uniform nanoparticle distribution and maintaining high conductivity during fabrication. Laser processing offers advantages in materials synthesis and structuring but can cause damage to conductive networks due to the blast effect and heat accumulation. Previous laser-based approaches have struggled to create integrated films with uniformly distributed nanoparticles without compromising conductivity. This research seeks to address these limitations by introducing a novel method for controlled laser processing.

This study introduces a "popcorn-making-mimic" strategy for preparing rGO/LIG@NiFe₂O₄ composite films. The method utilizes a laser-assisted instantaneous compounding method in ambient conditions. A layer of graphene oxide (GO) acts as a protective lid on top of the laser-induced graphene (LIG) substrate before the introduction of NiFe₂O₄ precursor salts. This GO lid converts the transient laser pulse energy into uniformly distributed heat, preventing mass loss and structural damage caused by heat accumulation and bursting. The process involves: (1) Laser writing of LIG on a polyimide (PI) substrate; (2) application of NiCl₂·6H₂O and Fe(NO₃)₃·9H₂O precursor solutions; (3) application of GO solution; (4) laser processing of the composite film in ambient conditions. The resulting rGO/LIG@NiFe₂O₄ composite films were characterized using various techniques, including SEM, XRD, Raman spectroscopy, XPS, BET, four-probe resistance measurements, VSM, and vector network analysis to measure EMI shielding effectiveness. Finite element analysis was used to model the heat and stress distributions during laser processing with and without the GO lid.

The "popcorn-making-mimic" strategy successfully created highly integrated rGO/LIG@NiFe₂O₄ composite films with uniformly distributed NiFe₂O₄ nanoparticles (3.63 ± 0.98 nm). The GO lid effectively prevented structural damage and mass loss during laser treatment. The composite films exhibited significantly improved EMI shielding effectiveness compared to LIG alone. A single-sided film (70 µm) achieved a total EMI shielding effectiveness (SEₜ) of 36 dB, with 75% absorption, while a double-sided film (166 µm) reached 51 dB with 73% absorption. The absolute shielding effectiveness (SSE/t) was 20906 dB cm²/g. The improved performance was attributed to the synergistic effect of the highly conductive LIG and the uniformly distributed NiFe₂O₄ nanoparticles. The composite films also showed excellent mechanical flexibility and high temperature/humidity aging reliability, with minimal changes in square resistance after 10,000 bending cycles and 500 h of aging at 85 °C and 85% relative humidity. Finite element analysis confirmed the crucial role of the GO lid in regulating heat distribution and reducing stress within the rGO layers, leading to the formation of uniformly sized nanoparticles and preventing cracking. Compared to LIG@NiFe₂O₄ films made without the GO lid, the rGO/LIG@NiFe₂O₄ films demonstrated a substantial improvement in both EMI shielding effectiveness and absorption.

The findings demonstrate the effectiveness of the "popcorn-making-mimic" strategy in overcoming the challenges of creating high-performance EMI shielding films. The uniform distribution of NiFe₂O₄ nanoparticles within the highly conductive and porous LIG structure is crucial for achieving high EMI shielding effectiveness and absorption. The GO lid plays a vital role in regulating the heat distribution during laser processing, preventing damage to the conductive network and enabling the formation of uniformly sized nanoparticles. The excellent mechanical flexibility and aging reliability of the composite films are significant advantages for practical applications. The results represent a significant advance in EMI shielding technology, providing a versatile and scalable method for producing high-performance materials suitable for various electronic devices.

This study successfully developed a novel "popcorn-making-mimic" strategy for fabricating high-performance graphene@NiFe₂O₄ flexible films for EMI shielding. The method uses a GO lid to control heat distribution during laser processing, leading to uniformly distributed nanoparticles and enhanced material properties. The resulting films exhibit superior EMI shielding, absorption, flexibility, and reliability. This approach offers a promising pathway for developing advanced composite materials for various applications. Future research could explore different magnetic nanoparticles and carbon-based materials, optimization of laser processing parameters, and integration into real-world electronic devices.

While this study demonstrates the effectiveness of the "popcorn-making-mimic" strategy, further investigation is needed to fully optimize the process parameters for different applications. The long-term stability and performance under extreme conditions require further evaluation. The scalability of this method for large-scale industrial production also needs to be explored. The current study focused on the X-band frequency range; broader frequency range testing is desirable for complete characterization. The finite element analysis simplified the model; incorporating more detailed material properties could improve simulation accuracy.