Laser-forged transformation and encapsulation of nanoalloys: pioneering robust wideband electromagnetic wave absorption and shielding from GHz to THz

The emergence of the internet of things has promoted wireless communication’s evolution towards multi-band and multi-area utilization. Notably, forthcoming sixth-generation (6G) communication standards, incorporating terahertz (THz) frequencies alongside existing gigahertz (GHz) modes, drive the need for a versatile multi-band electromagnetic wave (EMW) absorbing and shielding material. This study introduces a pivotal advance via a new strategy, called ultrafast laser-induced thermal-chemical transformation and encapsulation of nanoalloys (LITENs). Employing multivariate metal-organic frameworks, this approach tailors a porous, multifunctional graphene-encased magnetic nanoalloy (GEMN). By fine-tuning pulse laser parameters and material components, the resulting GEMN excels in low-frequency absorption and THz shielding. GEMN achieves a breakthrough of minimum reflection loss of −50.6 dB in the optimal C-band (around 4.98 GHz). Computational evidence reinforces GEMN’s efficacy in reducing radar cross sections. Additionally, GEMN demonstrates superior electromagnetic interference shielding, reaching 98.92 dB under THz band (0.1–2 THz), with the mean value result of 55.47 dB. These accomplishments underscore GEMN’s potential for 6G signal shielding. In summary, LITEN yields the remarkable EMW controlling performance, holding promise in both GHz and THz frequency domains. This contribution heralds a paradigm shift in EM absorption and shielding materials, establishing a universally applicable framework with profound implications for future pursuits.

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Introduction
In recent decades, there has been an unprecedented surge in wireless communication technology, leading to significant societal changes across various domains [1,2].Within this wireless communication landscape, the deployment of electromagnetic waves (EMWs) across various frequency bands is tailored to specific applications, collectively shaping the fabric of the network of wireless communication [3,4].The evolution is exemplified by the ongoing development of sixth-generation (6G) communication standards following the commercial realization of 5G standardization.Anticipated to exhibit data transfer rates 100 times those of prevailing standards [5,6], 6G technology represents a notable shift, marked by the incorporation of terahertz (THz) wavesthose exceeding 100 GHz frequency-proffering boundless prospects for high precision and ultrafast internet of things applications [4,[6][7][8].However, existing communication systems, such as satellite communications, frequently employ low-frequency EMWs (S-band and C-band) due to their wide signal coverage and robust penetration capabilities.Thus, it can be implied that the convergence of gigahertz (GHz) and THz will be future wireless communication trend [9,10].Accordingly, the imperative arises for versatile electromagnetic materials simultaneously effective in both GHz and THz domains [11,12].Notwithstanding, prevailing challenges necessitate meticulous consideration prior to their practical realization.
A central challenge lies in achieving high magnetic component dispersion in wave-absorbing materials within conventional preparation procedures, often resulting in suboptimal low-frequency EMW absorption [9,13,14].Similarly, the realm of THz EMW shielding remains limited, hampering the establishment of mass-processable materials exhibiting remarkable shielding performance [15].These limitations of material and processing technique greatly limit the application of future communication mode.Consequently, the development of materials proficient in low-frequency EMW absorption and THz shielding, coupled with a universally applicable processing technique, emerges as a critical endeavor.
As new types of multifunctional materials, metal-organic frameworks (MOFs) are synthesized via coordination bonding between metallic ions and organic ligands, exhibiting some unique physical attributes [16][17][18].These attributes have underpinned their extensive utilization in catalysis, gas separation, and beyond [19].Within the domain of EMW absorption, MOFs have paved the way for the development of porous carbon-based derivatives [16,17,20], endowed with benefits including reduced density, elevated mechanical strength, and robust stability-qualities conducive to absorber density reduction [21].Moreover, carbon-based MOF derivatives manifest high electron conductivity, fostering pronounced resistance loss and effective electromagnetic shielding within the THz band [22,23].By leveraging the transition of metal ions within MOFs to their reduced counterparts-metal oxides or nanoparticles-via multivariate MOFs (MTV-MOFs), the resulting carbonized MTV-MOFs derivatives effectively mitigate the limitations associated with single-component material loss mechanisms, thereby optimizing absorber impedance matching conditions [24,25].
Present MOF carbonization processes, involving hightemperature calcination or solvent-based methods, are characterized by intricate procedures, substantial energy and solvent consumption.For instance, Wu et al synthesized a binary MOF-based hybrid nanoflowers via magnetic stirring reaction for 18 h with high temperature [26].Liu et al introduced Mn-Based MOFs-derived composites using solvothermal method with 105 • C for 20 h [27].Similarly, Ouyang et al reported the carbonizing MOF-74 derivatives by solvothermal method with 120 • C for 24 h [28].In the same way, Yi et al prepared the Co-based PBA with a long reaction under 500 • C-900 • C [29].By contrast, laser-based processing presents advantages of rapidity, convenience, and simplicity, offering potential for large-scale preparation.For instance, in comparison to lengthy high-temperature tubular furnace reactions, lasers enable swift high-temperature reactions.Laser parameters can be adeptly adjusted to regulate the degree of graphitization, influencing conductive loss, while also precisely modulating thermalchemical reduced nanoalloy particle sizes, achieving nanoscale preparation with favorable dispersity.Consequently, the laser chemical inducing method excels in dispersing nanoalloys into carbon matrices, enhancing extensive interfacial loss and optimizing the magnetic and dielectric loss within lowfrequency regimes matching [30].
Within this context, this paper represents significant strides towards the realization of high-performance EMW absorbers and shields via laser-induced thermal-chemical transformation and encapsulation of nanoalloys (LITENs).A highefficiency method to mass-produce graphene-encased magnetic nanoalloys (GEMNs) via LITEN has been introduced, offering simplicity, stability, and parameter adjustability that holds promise for broader absorber applications.Moreover, the electromagnetic response characteristics of GEMN have been systematically analyzed, encompassing low-frequency microwave absorption, THz shielding, and radar cross-section (RCS) reduction.Under laser-customized impedance matching, the GEMN(Fe/Co/Ni) synergistically exhibited exceptional EMW absorption.Remarkably, the Fe/Co/Ni nanocomposites attained a minimum reflection loss (RL min ) of −50.6 dB at a remarkably low frequency of 4.98 GHz.In the THz domain, GEMN's electromagnetic interference (EMI) shielding excelled, yielding values of up to 98.92 dB, with an average shielding of 55.47 dB spanning 0.1-2 THz.These findings unequivocally demonstrate GEMN's efficacy as an electromagnetic coupling trap, paving the way for high potential in the forthcoming era of wireless communication.

Result and discussion
Figure 1(a) provides an illustrative representation of the LITEN process underlying the laser thermal-chemical transformation of graphene encased magnetic nanoalloys.This procedure involves the application of pulse laser-induced thermal chemical transformation, which instantaneously pyrolyzes Fe/Co/Ni MTV-MOF crystals, culminating in the creation of a porous graphene foam encapsulating magnetic nanoalloys.The native MTV-MOF crystals encompass terephthalic acid as the linker and Ni 2+ /Co 2+ /Fe 2+ as central nodes (figure 1(c)).Following laser treatment, the terephthalic acid transforms into a porous graphene structure, concurrently facilitating the conversion of ions into their respective nanoalloy forms, encased within the graphene matrix to thwart oxidation.Specifically, the detailed LITEN process can be broken down into several processes.With the laser energy absorbed by the MTV-MOF, it forms high temperature and high pressure at localized position within one pulse inside the slide.Upon this extreme manufacturing situation, the isolated MOF crystals were instantly pyrolyzed by thermochemical pyrolysis.The organic species were reorganized to form a 3D graphene skeleton while laser forged, while the reduced Fe/Co/Ni atoms gathered to form nanoalloy and buried in the graphene skeleton.In addition, the plasma produced by laser ablation propels the precursor in GEMN, which achieves an even and homogeneous reaction.Ultimately, the organic linkers undergo complete pyrolysis, resulting in the formation of a porous graphene foam housing embedded magnetic constituents.Capitalizing on its robust electrical conductivity and magnetic coupling properties, GEMN functions as an EMW trap (figure 1(b)), poised to excel in GHz absorption and THz electromagnetic shielding and absorption applications.
The discussion engendered by this fabrication process underscores its potential significance in various technological applications.The utilization of LITEN for the synthesis of GEMNs presents a novel avenue in material engineering.This method's precision in controlling the conversion of MOF components into tailored nanoalloys while concurrently generating a graphene foam structure offers unique advantages.By preventing metal oxidation and effectively integrating the magnetic constituents within the graphene matrix, the resulting GEMN possesses an optimal structure for EMW manipulation.Moreover, the introduced reductive atmosphere during the process contributes to enhancing the stability and performance of the resultant material.Furthermore, the adaptability of the LITEN renders it amenable to scalability and mass production.Compared to conventional techniques with prolonged reaction times and energy-intensive steps, this method's rapid and controlled thermal event is advantageous for large-scale material preparation.The ensuing GEMN's robust potential as an EMW trap, capable of simultaneous GHz absorption and THz electromagnetic shielding and absorption, holds implications for a wide spectrum of technological fields including wireless communication, sensing, and electronic warfare.
The meticulously delineated fabrication process through LITEN represents a significant advancement in material synthesis.This process harnesses the unique properties of MOFs, graphene, and nanoalloys to yield a multifunctional material with remarkable potential for transformative applications.The interplay between reductive environments, precise thermal control, and structural integration elucidates the promise of this method for shaping the future of EMW manipulation technologies.In this study, we employed (Ni 2 Co 1 ) 1 -xFex-MOF-NF [31] as a representative example for the facile and costeffective preparation of GEMN via LITEN, exemplifying the adaptability and potential of this method.The modularity of the metal ion ligands in terms of elements and content ratios offers a customizable framework, thereby enabling optimization of the absorber's impedance matching.The MTV-MOF was further scrutinized by scanning electron microscopy (SEM), revealing a 3D foam-like architecture composed of interconnected nanofibers (figures 1(d) and S1).Subsequent laser treatment led to the complete pyrolysis of the foam-like MOF into a porous 3D graphene foam (figure 1(e)).With the laser power of 4.56 W, the penetration depth of the MOF can be 30 µm (figure S2).According to the SEM image in figure S3, it can be figured out that the organic ligands are more easily carbonized, meanwhile the metal ions are also easily reduced to larger nanoparticles.Hence, by controlling the laser parameter, the dielectric constant and permeability of the absorbing material can be effectively matched.This carbonaceous material displayed pronounced resistance loss characteristics, accompanied by the observation of cavities within GEMN, which assume the role of EMW traps, thereby enhancing wave refraction and absorption.
The magnetic nanoalloys, generated via thermal reduction, became embedded within the porous graphene matrix (figure S4), functioning as magnetic loss agents akin to bamboo thorns in the EMW trap.Notably, the Fe/Co/Ni nanoalloy, driven by the ferromagnetically enhanced Kirkendall diffusion effect, exhibited confinement within a core-shell structure, effectively thwarting magnetic agglomeration.Consequently, magnetic nanoalloys, ranging around 100 nm, were clearly discernible within the foam-like architecture [14,32].Additionally, a substantial population of sub-10 nm alloy particles was found to be distributed upon the graphene layer (figure 1(f)).
Transmission electron microscopy (TEM) analysis of GEMN has provided valuable insights into the material's structural characteristics and the uniformity of its magnetic nanoalloy nanoparticles, as illustrated in figure 1(g).This examination following laser-induced thermal-chemical processes revealed the successful generation of uniformly  dispersed nanoparticles.The utilization of pulse laser-induced thermionic reduction contributed to the enhanced uniformity in particle distribution.Statistical data from the analysis demonstrated that the synthesized magnetic nanoalloy particles exhibited a normal particle distribution ranging from 3 nm to 19 nm, with an average value of approximately 6.2 nm (figure 1(i)).Furthermore, the selected area electron diffraction (SAED) image presented in figure 1(j) exhibited the distinct electron diffraction pattern, providing clear evidence that the graphene-encased Fe/Co/Ni ternary alloys consisted of multiple crystalline nanoparticles.This crystallinity underscores the robustness and stability of the synthesized nanomaterial, further supporting its suitability for various applications.
Moreover, energy dispersive x-ray spectroscopy (EDS) mappings (figures 1(k) and S5) conducted on the graphene surface displayed a consistent and uniform distribution of all metallic elements.This distribution aligns with the findings from EDS spectra observed via SEM (figure S6).The uniform elemental distribution is crucial as it ensures the homogeneity of the material's electromagnetic properties, particularly its ability to interact with EMWs.This analysis not only confirms the uniformity and metallic nature of the magnetic nanoalloy nanoparticles within GEMN but also provides a structural basis for its excellent electromagnetic properties.The uniform distribution and crystalline nature of the nanoparticles are key factors contributing to GEMN's performance in electromagnetic applications.
In figure 2(a), the XRD pattern of a GEMN (Fe/Co/Ni) is presented.There is a distinct peak at 26.36 • corresponding to the (002) crystal plane of graphene [33], while the features of 44.193 • , 51.441 • , and 75.759 • arise from (111), (200), and (220) crystallographic planes of Fe/Co/Ni with a face-centered cubic structure, indicative of alloy formation [34].This observation underscores the successful incorporation of Fe/Co/Ni alloy within the trimetallic samples.The morphological analysis reveals the encasement of nanoalloys within the graphene layer.Graphene formation is further confirmed by the Raman spectra at 1339 cm −1 , 1583 cm −1 , and 2688 cm −1 (figure 2(b)), which corresponds to the D/G/2D peaks [24].This outcome remains consistent when employing femtosecond laser irradiation (figure S7).The relative peak intensity (ID/IG) ratio in the Raman spectrum suggests graphene formation under distinct laser pulse widths.Notably, TEM images of the graphene shell indicate predominantly 3-7 layers of graphene (figure S8).With nanosecond lasers yielding heightened thermal effects, an increase in defect generation is observed.The GEMN exhibits significant electrical conductivity facilitated by its graphene-based conductive network.Electrical conductivity measurements under varying laser powers (figure S9) reveal optimal results at 4.56 W, indicative of the material's substantial potential for conductivityrelated EMW absorption.
Furthermore, Fourier-Transform Infrared (FTIR) analysis of GEMN and corresponding Fe/Co/Ni MOF samples (figures 2(c) and S10) provides insights into chemical changes of post-laser processing.The appearance of characteristics at 3420 cm −1 , 1575 cm −1 , 1394 cm −1 , and 751 cm −1 come down to the tensile vibration of O-H, the vibration of COOH, and the bending vibration of the carbon hydrogen bond in the benzene ring, respectively.The vanish of the sharp characterization of 3606 cm −1 post-laser treatment signifies the breakdown of metal ion coordination and the formation of the nanoalloy.
Surface element analysis and the assessment of their valence states within GEMN(Fe/Co/Ni) were conducted using x-ray photoelectron spectroscopy (XPS).The comprehensive XPS spectrum (figure S11) revealed the Fe, Co, Ni, C, and O elements within in GEMN sample.The emergence of oxygen (O) can be ascribed to defects within the graphene structure, and the formation of oxygen-containing groups inside of the sample.A more particular examination of the valence states of Fe, Co, and Ni was carried out through Fe 2p, Co 2p, and Ni 2p XPS spectra, as depicted in figures 2(d)-(f), respectively.In the Ni 2p spectrum, it can be observed that two prominent peaks located 853.6 eV and 870.9 eV unequivocally confirm the metallic state of Ni atoms.Additionally, the peaks located at 861.6 and 879.7 eV indicate the presence of Ni 2+ within the Fe/Co/Ni alloys, with an evident satellite peak located at 858.2 eV.A similar analysis of the Co 2p spectrum reveals a prominent peak at 779.2 eV, affirming the metallic state of Co.Furthermore, the binding energies at 780.9 eV and 787.2 eV signify the presence of Co 2+ , accompanied by a satellite peak at 783.1 eV and another at 794.1 eV.Regarding the Fe element, a peak at 705.6 eV confirms its metallic state, while characteristic peaks at 707.9 eV and 713.5 eV correspond to Fe 2+ and Fe 3+ .Collectively, these results provide compelling evidence for the successful formation of distinct Fe/Co/Ni alloy phases within the GEMN structure.This detailed surface analysis underscores the precise control achieved in fabricating the desired alloy compositions, which is of paramount importance in tailoring the electromagnetic properties of the material for specific applications.
Nitrogen sorption tests were conducted to assess the properties of both GEMN and Fe/Co/Ni MTV-MOF, with the corresponding results presented in figure 2(g).Furthermore, the distribution of pore size was determined through the BJH method, as depicted in figure S12.Notably, the Fe/Co/Ni MTV-MOF exhibited a substantial Brunauer-Emmett-Teller (BET) surface area of 86.218 cm 3 •g −1 .However, following laser treatment, the BET surface area notably decreased to 33.257 cm 3 •g −1 .The distinction in BET surface area can be further elucidated by analyzing the pore size distribution.The MOF material inherently comprises a distributed array of micropores, which, under the influence of laser treatment, undergo carbonization and crosslinking processes.Consequently, it can be observed that the BET surface area of GEMN is diminished when compared to the original MOF material.
For an in-depth evaluation of the GEMN samples, VSM hysteresis loops further recorded the magnetic properties of the sample.According to the result of figure 2(h), both GEMN samples, encompassing Fe/Co/Ni, Fe/Ni, and Co/Ni nanocomposites, demonstrated saturation magnetization (M s ) values of approximately 39.33 emu•g −1 , 24.65 emu•g −1 and 20.26 emu•g −1 , respectively.Furthermore, an additional magnetic property is revealed in the inset of figure 3(i), where coercivity (H c ) values were determined to be approximately 199.96 Oe for Fe/Co/Ni, 159.61 Oe for Fe/Ni, and 100.07 Oe for Co/Ni nanocomposites, respectively.The variation in H c results arises from the difference of components in GEMN, and the distribution of defects induced by laser treatment.According to the principles of ferromagnetic resonance theory, it is discerned that larger H c values contribute to an enhanced EMW absorption performance, particularly at high frequencies.
In EMW absorption research, it is widely recognized that an RL value below −10 dB corresponds to the effective absorption of EMWs, thereby defining this effective absorption bandwidth (EAB).In the context of this study, the RL values of GEMN with varying elements were assessed at 25 wt% loadings (figures 3(a)-(c)).The intricate contour maps of 3D-RL curves across frequency and thickness variations are displayed in figures 3(a)-(c).A notable observation is the remarkable EMW absorption performance exhibited by GEMN(Fe/Co/Ni), which outperforms other samples.Specifically, the RL min value of −50.6 dB is attained at 4.98 GHz frequency, resulting in an EAB spanning 3.92 GHz.Conversely, under the same loading ratio, the bicomponent samples (Ni/Fe and Ni/Co) demonstrate inferior absorption performance due to inadequate impedance matching.
The quarter wavelength (1/4 λ) matching model has been widely used to evaluate the result between the frequency of RL max and the matched thickness (t m ) of an air-absorber can be expressed as: which λ denotes the wavelength of EMW and c denotes the speed of light.In line with the experimental results presented  in figures 3(d)-(f), the experimentally determined t m (corresponding to RL min ) exhibits commendable consistency with the simulated values.These findings substantiate the agreement of GEMN's absorption curve with the λ/4 destructive interference model.Furthermore, impedance matching is a pivotal determinant of air-absorber performance.For the traditional impedance matching theory, a value of normalized characteristic impedance modulus ((Z = |Z in /Z 0 |) approaching 1 signifies better impedance matching [35].Correspondingly, as shown in figures 3(g)-(i), the RL min of GEMN tends to align with Z values near 1, which represents the well impedance matching under this frequency/thickness.Combining EMW loss mechanism with impedance matching theory, the GEMN realized a better frequency matching [36].The C-band EMW is characterized by attributes such as extensive propagation distance, strong penetration, robust antiinterference capabilities, and heightened accuracy and resolution (figure 3(j)).Nevertheless, common absorbers often present optimal matching bands in high-frequency ranges, limiting effective electromagnetic absorption within the Cband.Consequently, employing the thermal-chemical inducing strategy, GEMN achieves superior dispersion of magnetic components (figure 3(k)), thereby demonstrating excellent low-frequency band matching and absorption performance, which holds potential significance for C-band applications.
The electromagnetic parameters of GEMN are elucidated in figure 4. The real part (ε ′ , µ ′ ) and the imaginary part (ε ′′ , µ ′′ ) of these parameters correspond to the storage and dissipation mechanisms of EMWs, respectively.Within the low-frequency range, both real part (ε ′ ) and imaginary part (ε ′′ ) exhibit comparable descending trends.This behavior is evident from figure 4 ).Notably, the consistent alteration tendencies in real part (ε ′ ) and imaginary part (ε ′′ ) across all samples suggest a shared dielectric loss mechanism (figures 4(a) and (b)).Furthermore, the presence of multiple evident fluctuation peaks in ε ′′ curves indicates the occurrence of polarization relaxation behavior.This phenomenon effectively augments the EMW absorption performance.
The tanδε = ε ′′ /ε ′ , denoting the actual dielectric loss capability, is depicted in figure 4(c).It becomes evident that GEMN(Fe/Co/Ni) showcases a stable loss performance across 2-18 GHz.In comparison to the binary alloy counterparts, the Fe/Co/Ni sample yields the highest tan δε value across this scope.The complex permeability of GEMN samples is delineated in figures 4(d) and (e), revealing a serpentineshaped decrease in response to increasing frequency.This serpentine pattern signifies the multiple resonances of dielectric loss occurring within the absorber's interior.Due to the small particle size and high dispersion of GEMN, µ ′′ exhibits a high value in the low-frequency band.As a result, these samples exhibit multiple magnetic loss mechanism [36,37].The variation trends of tanδµ (tan δµ = µ ′′ /µ ′ ) portray that GEMN (Fe/Co/Ni) and GEMN (Fe/Ni) exhibit the highest tan δµ (0.19-0.26) and the lowest tanδµ (0.05-0.12), respectively.By comparing the tanδε (figure 4(c)) and tan δµ (figure 4(f)) curves of these samples, the tan δµ and tan δε are nearly matching under low frequency band, and tan δµ < tanδε in the high frequency region.These findings collectively underline GEMN's capacity to harbor multiple magnetic/dielectric loss mechanisms for effective dissipation.
The attenuation coefficients (α) displayed in figure 4(g) demonstrate similar trends among all samples across a broad frequency range.Carbon-based components bestow excellent attenuation capabilities, with observed differences attributed to previously analyzed impedance matching variations.In contrast to the distinct components, while the attenuation coefficients of GEMN remain akin, GEMN(Fe/Co/Ni) surpasses the other bicomponent samples.Magnetic losses can be specifically divided into hysteresis losses, eddy current losses, and multi-source resonance losses.The C 0 value is commonly employed to study the loss mechanism, and a consistent C 0 value suggests eddy current loss as primary magnetic loss way.However, as figure 4(h) illustrates, with the C 0 value fluctuating, it can be referenced the eddy current loss is not the principal contributor.Consequently, GEMN samples exhibit not only eddy current loss but also capabilities for natural resonance and exchange resonance losses.
The Cole-Cole semicircle (figure 4(i)) corresponds to Debye dipole relaxation process, while the extension curve corresponds to conductive loss.In this context, distorted semicircles observed in GEMN samples suggest the multiple loss mechanism of GEMN.The interfacial polarization relaxation arises from uneven charge distribution at defects and interfaces between nanoalloys and graphene, while the dipolar relaxation is attributed to functional groups like C=O and C-O.The high carbon content in both samples results in straight-line behavior, indicating high conductive loss.
Figure 5 encapsulates and elucidates the intricate EMW absorption mechanisms underpinning the GEMN.To elucidate further, the laser-induced graphene's porous conductive framework was pivotal in establishing a heightened capacity for conductive loss within the nanocomposites.The internal porous structure of GEMN enhances the multiple scattering of EMWs within the material, thereby enhancing the electromagnetic absorption of the material.Moreover, the profusion of interfaces between graphene, Ni, Fe and Co potentiated augmented interfacial polarization.Meanwhile, the defects in the GEMN present within the structure also facilitated dipole polarization effects.
Additionally, the introduction of magnetic nanoalloys introduced the dimension of natural resonance, thereby further amplifying the EMW attenuation prowess.Finally, by adeptly tailoring the impedance match between the graphene and the magnetic alloy nanoparticles, the composite GEMN proficiently permitted the efficient penetration of EMWs.To conclude, an insightful arrangement of component composition and microstructural design within laser-induced MOFderived nanocomposites coalesced to yield a superlative EMW absorption performance.This intricate comprehension highlights the fusion of various mechanisms that contribute to the exceptional absorptive attributes demonstrated by the GEMN structure.
In the domain of microwave absorption materials, the RCS assumes a pivotal role as a direct assessment metric within practical stealth technology scenarios.Specifically, RCS quantifies the intensity of the echo generated by a target when subjected to radar wave irradiation.It represents the effective area of the target and is symbolized by the projected area of an equivalent reflector that possesses uniformity in all directions.Consequently, lower values signify enhanced absorption performance.In this context, we conducted RCS simulations for the GEMN absorber using CST simulation software.The simulation model, as depicted in figure 6(a), entailed the placement of the absorber atop a perfectly electrically conducting (PEC) layer.The incident wave approached from the negative direction of the absorber plane, with θ representing the angle of incidence in the simulation setup.Comparative visualizations of the PEC sample and GEMN under varying thetas are showcased in figure 6(b).Clearly discernible is the diminished signal strength of the GEMN/PEC absorber in contrast to the PEC sample, with all RCS values for GEMN/PEC registering lower than −10 dB•m −2 .Further insight into the twodimensional RCS values of the PEC and GEMN/PEC, across distinct incident angles, is presented in figures 6(c) and (d).These values correspond substantively with the exceptional microwave absorption performance previously discussed.A contrast of the radar maps post-absorption, as illustrated in figure 6(e), underscores the GEMN's capacity for reducing the scattering and reflection of EMWs emanating.
THz waves have attracted great attention due to the immense potential in the realm of 6G wireless communication.However, the development of THz waves caused a surge   in THz pollution, giving rise to concerns related to physical health and information security [38].The demand for efficient THz protective materials has consequently become imperative to address the requirements across diverse frequency bands [23].The evaluation of THz shielding in this study is predicated on the utilization of both transmission and reflection modes within the framework under the conventional THz time-domain spectroscopy (THz-TDS) system.The reflection mode THz-TDS spectra for the air reference and GEMN(Fe/Co/Ni) samples are presented in figure 7(a).Notably, the reference group exhibits a stronger THz reflection signal due to the complete reflection of THz waves by the aluminum plate.Conversely, the GEMN samples display notably weaker signals, indicating significant penetration of THz waves into the material.In the context of the transmissionmode THz-TDS spectra depicted in figure 7(b), the reference sample allows for the complete passage of THz waves, while the GEMN shows minimal signals, signifying effective THz wave shielding.
According to the A-R-T coefficients of the GEMN under THz band (figure 7(c)), it can be observed that the GEMN exhibits great absorbed performance during the EMW shielding process.Combined with the electromagnetic properties of GEMN, it can be inferred that this behavior arises from the conversion of the highly conductive network into electrical current and heat, thereby dissipating THz energy, and from the intricate porous structure within the film that promotes internal reflection and scattering of THz waves.Figure 7(d) examines the shielding property of GEMN under several thicknesses, which reveals its exceptional THz shielding capability.
The peak shielding value reaches 98.92 dB under 0.886 µm, and the average shielding result of approximately 55.47 dB is included in the frequency of 0.1-2 THz.This performance vastly outperforms that of other EMI shielding materials, which was detailedly illustrated in figure 7(e).Consequently, owing to its remarkable THz EMI shielding efficacy, GEMN holds immense promise for applications in the realm of 6G technology, as depicted in figure 7(f).

Conclusion
In summary, LITEN has been established as a robust approach for the transformation of MTV-MOF into a series of GEMNs, thereby enabling wideband EMW absorption and shielding across GHz and THz ranges.In contrast to alternative carbonization techniques employed in carbon-based MOF derivatization, laser thermal-chemical inducing offers distinct advantages in terms of its rapid, convenient, and straightforward process, thereby demonstrating potential for large-scale production.This methodology facilitates the generation of reduced nanoparticles as small as 3 nm, intricately enclosed within graphene shells.Concurrently, the laser-induced formation of heterojunction microstructures engenders abundant heterointerfaces that potentiate heightened dielectric loss capabilities.Furthermore, the adjustability of the degree of graphitization afforded by this technique enables precise modulation of impedance matching, ultimately contributing to enhanced absorption property.In the microwave range, the synergistic integration of graphene and magnetic nanoalloys, coupled with high-density magnetic-carbon unit interactions, enables effective impedance matching within the C-band.This configuration yields a noteworthy RL min with −50.6 dB at 4.98 GHz.This exceptional performance stems from optimized impedance matching under laser parameter control.Expanding into the THz regime, the GEMN exhibits an extraordinary RL max result of 98.92 dB, accompanied by an extensive frequency scope of 0.1-2 THz.This remarkable THz shielding proficiency emanates from the harmonious interplay between excellent electrical conductivity and a porous microstructure.Given its remarkable EMW absorption and shielding prowess across a broad frequency spectrum, the GEMN material, along with its associated preparatory techniques, holds substantial potential for catalyzing advancements in the forthcoming era of wireless communication technologies.

Experimental section
) and p-phthalicacid (1, 4-BDC) were purchased from Sigma Aldrich Corporation.N, N-Dimethylformamide (DMF) was purchased from Shanghai Sinopharm Chemical Reagent.And all reagents were used as received without treatment.

Synthesis of GEMN
The synthesized method of Fe/Co/Ni MTV-MOF was referenced from Qian et al [31].Take the synthesis of (Ni 2 Co 1 )0.9Fe 0.1 -MOF as an example, 0.6 mmol of Ni(CH3COO) 2 • 4H 2 O, 0.3 mmol of Co(CH 3 COO) 2 • 4H 2 O, and 0.1 mmol Fe(CH 3 COO) 2 • 4H 2 O were dissolved in 10 ml DMF.And 1 mmol of 1, 4-dicarboxybenzene was dissolved with 5 ml DMF.Then, solution A was quickly poured into the solution B under magnetic stirring and maintained for 1 h at room temperature.Finally, the products ((Ni 2 Co 1 ) 0.925 Fe 0.075 -MOF) were obtained by centrifugation, washing with DMF and ethanol for several times, and drying at 60 • C for 12 h in electric oven before being used for laser treatment.
Under the laser thermal-chemical inducing, the nanosecond laser system was used for laser source, with 80 ns pulse duration and 1064 nm wavelength at 20 kHz.Here, to obtain the GEMN, the laser power adjusted to 4.56 W with the velocity of 100 mm•s −1 , and the scan interval is 12 µm.
The chemical state of the sample was determined using XPS (Thermo Fisher Scientific).The XRD (XPert Pro) patterns were recorded in the range of 10 • -80 • with 2 • •min 1 .FTIR (Thermo Nicolet 5700) spectra of the samples have been further measured.The BET surface area was measured by (Micromeritics, ASAP2460).And the VSM was measured by the LakeShore7404.The Raman spectra were tested by a 532 nm laser excitation (Raman spectrometer, in Via Reflex).

Electromagnetic parameters measurement
The electromagnetic parameters were tested by vector network analyzer (Agilent E5071C).The ring-like samples (outer/inner diameters of 7.0 mm/3.04 mm) in this study were formed using the transmission/reflection coaxial line method.The GEMN composite was present in the mixture at a weight ratio of 25%, relative to the total mixture.This composition was utilized in the fabrication of the ring-like samples for further analysis or experimentation.

Microwave absorption calculation
Based on the electromagnetic parameters measured above, the microwave absorption performance was deduced from following equations through the transmission line theory, RL (dB) = 20 log z in − z 0 z in + Z 0 (2) where Z in represents the input characteristic impendence; Z 0 represents the free space impendence; u r and e r are the complex permeability and permittivity; d represents the sample thickness; c represents the velocity of microwave; and f represents the frequency of the corresponding band.

THz shielding and absorption measurements
Analysis of GEMN shielding performance in THz band was using THz-TDS system.The testing frequency scope is 0.1-2 THz, and the EMI shielding performance can be inferred by these equations: E s and E a represent the amplitudes of THz pulses for the samples and the air cavity, respectively.In addition, the RL values of the sample can be inferred from this equation: E i and E r represent the amplitudes of reflection THz pulses for the samples and the reference Al plate, respectively.

Figure 1 .
Figure 1.LITEN induced graphene-encased magnetic nanoalloys (GEMNs).(a) Schematic of the LITEN for preparing GEMNs.(b) The application schematic of GEMN 'trap' in low-frequency band electromagnetic wave absorption and terahertz electromagnetic shielding.(c) Schematic illustrations of the process of preparing GEMN.(d) SEM image of the Fe/Co/Ni MTV-MOF.(e) SEM image of the GEMN.(f) The high magnifications SEM image of magnetic nanoalloy on graphene layer.(g) TEM image revealed that the magnetic nanoalloy was distributed on graphene layer.(h) Local magnification image of the GEMN.(i) The particle size distribution of magnetic nanoalloy nanoparticles.(j) The SAED pattern of GEMN.(k) Elemental distribution mapping of C/Fe/Co/Ni nanocomposites.

Figure 2 .
Figure 2. The characterization of the GEMNs.(a) XRD of GEMN.(b) Raman spectra of GEMNs under nanosecond laser.(c) The FTIR of the GEMN.The XPS analysis of (d) Ni 2p, (e) Co 2p, and (f) Fe 2p spectrums of the GEMN.(g) The BET of the GEMN and the corresponding MTV-MOF.(h) Room temperature magnetic hysteresis loops of GEMN under different compositions.

Figure 6 .
Figure 6.The CST simulation model of RCS with GEMN absorber.(a) The schematic diagram of RCS model.(b) Simulated RCS results of PEC and GEMN(Fe/Co/Ni) covered PEC.3D RCS plots for (c) PEC and (d) covered with GEMN(Fe/Co/Ni).(e) RCS values of samples at different angles.

Figure 7 .
Figure 7. Terahertz absorption performance of the GEMN.The THz testing of the GEMN(Fe/Co/Ni) with air reference (a) reflection consequence and (b) transmission consequence.(c) A-R-T coefficients of the GEMN under THz band.(d) THz shielding performance of GEMN under different thicknesses.(e) The terahertz shielding performance of GEMN and the other class of materials.(f) Schematic of THz-band application in wireless communication.