English

• The new generation of communication technologies, especially the rapid development of 5G is facilitating people's daily life, but also brings serious electromagnetic wave (EMW) pollution [1–4]. As a critical component of electromagnetic protection, EMW absorption materials have garnered increasing attention in recent years due to their capability to efficiently dissipate EMW energy [5,6]. Interfacial polarization, a primary mechanism driving EMW energy loss, is crucial for enhancing the absorption performance of such materials, while designing specialized interfacial barriers has proven to be a key strategy for optimizing interfacial polarization [7–9]. Despite these advances, most interface engineering strategies focus on heterogeneous interface polarization, leaving work function design largely unexplored as a pathway for optimizing EMW absorbers.

  Two-dimensional (2D) materials are ideal for constructing interfacial polarization on account of their large specific surface area. Transition metal dichalcogenides (TMDs), as representative 2D materials, possess unique properties such as tunable electromagnetic response, multiphase structure and adaptability for composite formation, making them promising for EMW absorption applications [10–13]. TMDs of the VIB group, such as MoS₂ and WS₂, have been extensively used for EMW absorption, but the restricted active sites of their edge platforms lead to a relatively narrow EAB [14,15]. The VS₂ of the VB group has excellent carrier mobility and abundant active sites, exhibiting excellent potential for EMW absorption [16,17]. However, VS₂ is extremely susceptible to oxidation, transitioning from V⁴⁺ (in VS₂) to V⁵⁺, and the floral lamellae are easily fragmented under typical composite preparation conditions. Existing VS₂ EMW absorbers therefore use a post-synthesis strategy [18,19]. While this approach mitigates some of these issues, it also restricts the broader application potential of VS₂-based EMW absorbers.

  As a classic conductive polymer, polypyrrole (PPy) exhibits exceptional chemical stability, lightweight nature, and tunable dielectric properties. It offers significant advantages over other conductive polymers in terms of synthesis cost, processing convenience, high mass density and flexibility [20–22]. To overcome the limitations of VS₂ in EMW absorber composites, we have introduced a novel strategy that involves encapsulating it with a PPy conductive polymer. The PPy coating not only preserves the valence state and structural morphology of VS₂ during subsequent compositing processes but also enhances stability. Moreover, the conductive polymer layer, with its moderate work function and smooth interface, serves to construct protective interface structures that effectively balance the high dielectric properties of VS₂. However, the addition of PPy unavoidably impacts the impedance matching of the absorber. To address this, we incorporated layered 1T/2H-MoS₂ using a straightforward hydrothermal process, which not only enhances the interface loss within the composite but also optimizes impedance matching, thus improving the EMW absorption capabilities of the material.

  In this study, we skillfully crafted an EMW absorber using a straightforward two-step hydrothermal method. The device comprises a layered structure with a 1T/2H-MoS₂ impedance matching layer, a PPy protective layer, and VS₂, which serves as the core material. This composite not only stabilizes the valence state and morphological structure of VS₂ but also incorporates a multi-gradient work function interface to significantly enhance interface polarization. Our investigation into the EMW loss mechanisms within these multi-gradient interfaces was validated through both RCS simulation and experimental data. The results demonstrate that constructing a multi-gradient work function interface effectively balances the dielectric properties with impedance matching, significantly enhancing the composite material's absorption capacity. This study underscores the importance of interface engineering in EMW attenuation and provides new insights and potential research directions for future research into enhancing microwave attenuation mechanisms by exploring multi-interface carrier dynamics.

  As depicted in Fig. 1 and Fig. S1 (Supporting information), a flower-like 1T/2H-MoS₂/PPy/VS₂ absorber with a multi-gradient work function interface was fabricated using a simple two-step hydrothermal method. Initially, flower-shaped VS₂ nanoplates were synthesized through hydrothermal treatment. Subsequently, at room temperature, a layer of conductive polymer PPy was applied to the VS₂ surface. The introduction of PPy not only stabilized the valence state of VS₂ but also provided a smooth interface, serving as an ideal growth site for 1T/2H-MoS₂. Notably, during the in-situ formation of MoS₂, the reaction released a significant amount of ammonia. These ammonia molecules would penetrate through the PPy layer into the interlayers of VS₂ without affecting its valence stability.

  Figure 1

  

  Figure 1.  Schematic diagram of the interfacial structure and gradient work function interface polarization of 1T/2H-MoS₂/PPy/VS₂. The 1T/2H-MoS₂/PPy/VS₂ composite enhances EMW absorption by facilitating carrier migration and aggregation at interfaces, driven by multi-gradient work function differences.

  DownLoad: Full-Size Img PowerPoint

  The structural modifications introduced during the synthesis process directly influence the material's electromagnetic wave (EMW) absorption properties (Fig. 1). The high conductivity of pure VS₂ causes poor impedance matching with free space, which limits the penetration of incident EMW into the material's interior, reducing its absorption efficiency. With the introduction of PPy and 1T/2H-MoS₂, the heterogeneous interfaces are increased, thereby optimizing impedance matching and enhancing absorption performance. According to the interfacial polarization theory, the difference in the work function between heterogeneous interfaces is the main motive force for interfacial polarization. Under the influence of an alternating electromagnetic field, carriers will flow from the interface of low work function materials to the interface of high work function materials, triggering polarization and relaxation phenomena [5,23,24]. It was reported that the work function of lamellar MoS₂ ranged from 4.04 eV to 4.4 eV, the exact value of which was affected by the number of sulfur vacancies or adsorbed gases; the conductive polymer PPy had a work function range from 4.6 eV to 5.2 eV; compared to VS₂, which had the highest work function of about 5.5 eV [25–27]. This multi-layered heterostructure forms a gradient work function distribution, which facilitates the directional migration of carriers and significantly enhances the separation, migration and aggregation efficiency of carriers, thereby enhancing the EMW absorption performance of the material [28]. Additionally, the conductive network constructed by multiple elemental components enhanced the conductive loss, and the sulfur vacancies and carbon defects in the PPy layer enhanced the dipole polarization, further improving the EMW absorption.

  The XRD analysis of the samples (Fig. S2a in Supporting information) revealed that the synthesized VS₂ and PPy/VS₂ both exhibit typical diffraction peaks of VS₂ at 15.38°, 35.74°, 45.24°, 57.12°, 58.3°, and 59.56°. These characteristic peaks correspond respectively to the (001), (011), (012), (110), (103), and (111) crystal planes (PDF #89–1640) [17,18]. No impurity peaks were detected, highlighting the exceptional purity of the products. Diffraction peaks located around 8.9° and 14° can be observed for simple MoS₂, which indicates that MoS₂ is a mixed phase of 1T/2H, and the creation of the hybrid phase reinforced the interfacial polarization in favor of EMW absorption [29]. The ammonia produced with the in-situ growth of 1T/2H-MoS₂ (Fig. S2a) enters into the interlayers of VS₂, which results in a shift of the diffraction peaks of VS₂ (PDF #41–0642) [30]. The annealing treatment of 1T/2H-MoS₂/PPy/VS₂ (Fig. S2b in Supporting information) shows a shift in diffraction peaks to higher angles, likely attributed to the escape of NH₃ molecules from the VS₂ interlayer at elevated temperatures. The results of the above analysis show that there is no valorization of V⁴⁺ in VS₂ and that no other substances are generated. The Raman spectra of all samples (Fig. S3 in Supporting information) shows that the Raman peaks of VS₂ are located at 280 and 405 cm^-1, which correspond to E_1g (displacement and shear of V and S atoms in the plane) and A_1g (displacement and compression of S atoms symmetrically along the c-axis), respectively [31,32]. With the introduction of MoS₂, the Raman characteristic peak corresponding to E_2g¹ (displacement and shear of Mo and S atoms in the plane) can be observed in Fig. S3. According to our previous study, as E_2g¹ is smaller than the A_1g Raman characteristic peak, this indicates that the sample has more edge than platform structures, which facilitate the electron leaps and easily generate dissipative currents in MoS₂ [33]. Carbon defects can generate dipole polarization under an external electromagnetic field, significantly contributing to the EMW attenuation process [34–36]. The values of I_D/I_G for PPy/VS₂ and 1T/2H-MoS₂/PPy/VS₂ are 0.95 and 0.93, respectively, which indicates that the composite MoS₂ has no effect on the value of I_D/I_G. The carbon defects are not the primary cause of the performance differences of the absorber.

  To further understand the factors affecting the performance of 1T/2H-MoS₂/PPy/VS₂, the surface elemental composition and chemical states were analyzed (Fig. S4 in Supporting information). The characteristic peaks of Mo, V, S, C, and N are distinctly observed in Fig. S4a. For the Mo element in the composite, four peaks are fitted (Fig. S4b): The peaks at 232.95 and 229.81 eV correspond to 2H-MoS₂, while those at 232.12 and 228.98 eV correspond to 1T-MoS₂ [29,31,32]. The XPS energy spectra analysis of the Mo element reveals that 1T-MoS₂ and 2H-MoS₂ account for 57.7% and 42.3% of the total MoS₂, respectively. This suggests the existence of a massive phase interface in 1T/2H-MoS₂, and the distorted grain boundaries between this interface introduce significant interfacial polarization. As shown in Fig. S4c, the V element for the composite can be fitted into two peaks, with the two diffraction peaks of 524.42 and 516.85 eV corresponding to V⁴⁺ 2p_1/2 and V⁴⁺ 2p_3/2, respectively, and no other diffraction peaks were fitted, indicating that there was no valorization of VS₂ during the composite process [14].

  The peaks at 163.13 and 161.88 eV correspond to S 2p_1/2 and S 2p_3/2, respectively (Fig. S4d), with the low-coordinated S 2p_1/2 being associated with sulfur vacancies [10,37]. The integrated area analysis of the XPS spectra for elemental S shows that S 2p_1/2 constitutes 37.2% of the composite, suggesting a significant presence of sulfur vacancies. These vacancies disrupt charge distribution balance, leading to the formation of defects that enhance dielectric polarization through induced polarization. As shown in Fig. S4e, the fitted analysis of the C 1s spectra of the samples resulted in three fitted peaks, 284.99 eV (C_α), 283.93 eV (C_β), and 286.47 eV (-C=N-), which belong to the typical C elemental diffraction peaks in PPy [38,39]. While the N 1s spectrum consists of five diffraction peaks at 401.7, 400.31, 399.03, 396.71, and 394.9 eV, which corresponds to the five fitted peaks consisting of -N⁺-, -NH-, -C=N-, nitride, and -C-N⁺, respectively (Fig. S4f), where the diffraction peak of the nitride may be caused by the interaction of NH₃ into the interlayer of VS₂ [38,40].

  The samples' morphology and structural characteristics were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) (Fig. 2 and Fig. S5 in Supporting information). From Fig. 2a, it is evident that VS₂ has a flower-like lamellar structure with a lamellar thickness of about 10 nm. The surface of VS₂ becomes rougher after coating PPy can be observed in Fig. 2b, at the same time, the intact flower-like structure is still preserved, which proves that PPy/VS₂ has a high structural stability. A typical flower-like structure of 1T/2H-MoS₂ is shown in Fig. 2c. A complete flower-like lamellar structure of 1T/2H-MoS₂/PPy/VS₂ can be distinctly visualized in Fig. 2d and Fig. S5, which demonstrate that the PPy layer successfully protects the structural integrity of VS₂ during the composite process. The EDS image of 1T/2H-MoS₂/PPy/VS₂ was shown in Fig. S5, and the uniform distribution of the elements V, Mo, S, C, and N proved the homogeneity of the synthesized product.

  Figure 2

  

  Figure 2.  Microscopic morphology and interfacial structural composition of composites. (a-d) SEM, (e-h) TEM, and (i-l) HRTEM images of VS₂, PPy/VS₂, 1T/2H-MoS₂ and 1T/2H-MoS₂/PPy/VS₂.

  DownLoad: Full-Size Img PowerPoint

  TEM and HRTEM were employed to investigate the internal structure and lattice dimensions of the composites (Figs. 2e-l). It can be observed in Figs. 2e and i that VS₂ has a distinct lamellar structure, and that lattice spacings of 0.57 and 0.25 nm can be observed in the HRTEM images, which correspond to the (001) and (011) crystalline surfaces of VS₂, respectively [17,27,30]. Meanwhile, it can be observed in Figs. 2f and j that the PPy coating is uniformly coated on the surface of VS₂, with the thickness of PPy being about 15 nm approximately. The synthetic MoS₂ can be observed in Figs. 2g and k which consists of both 1T and 2H phases, among which the 1T phase has metallic properties (triangular lattice) and the 2H phase has semiconducting properties (honeycomb lattice), with distorted grain boundaries between the two phases, and the interfacial polarization generated between such interfaces contributes to the depletion of the EMW [29]. The three-layer dielectric structure of 1T/2H-MoS₂/PPy/VS₂ can be recognized in Figs. 2h and l and exhibits a gradient work function distribution. Some corresponding high-resolution images are shown in Fig. S6 (Supporting information). The designed interfaces undergo charge redistribution and accumulate charges at the interface, leading to interfacial polarization. This is driven by differences in the dielectric properties and conductivity of the components under an external electric field. The lattice spacing represented by the crystalline surfaces in the corresponding electron diffraction diagrams indicates the successful synthesis of the material (Fig. S7 in Supporting information).

  The EMW absorption performance of the absorbers was measured (with a loading rate of 50%). The EMW absorption properties and impedance matching of the samples were calculated by the following equations (Eqs. 1–3) [10,41–44]. The 3D patterns of the RL values of the absorbers are shown in Figs. 3a-d, and the calculated 2D patterns of the loss capacity concerning the impedance matching Z are shown in Figs. 3e-h.

  $ R L(\mathrm{dB})=20 \text{log} \left|\frac{Z_{\text {in }}-Z_0}{Z_{\text {in }}+Z_0}\right| $

  (1)

  $ Z_{\text {in }}=Z_0 \sqrt{\frac{\mu_{\mathrm{r}}}{\varepsilon_{\mathrm{r}}}} \tanh \left(j \frac{2 \pi f d}{c} \sqrt{\mu_{\mathrm{r}} \varepsilon_{\mathrm{r}}}\right) $

  (2)

  $ Z=\left|\frac{Z_{\mathrm{in}}}{Z_0}\right|=\sqrt{\frac{\mu_{\mathrm{r}}}{\varepsilon_{\mathrm{r}}}} $

  (3)

  Figure 3

  

  Figure 3.  Electromagnetic wave absorption properties of composites. (a-d) RL values and (e-h) loss capacity profiles of VS₂, PPy/VS₂, 1T/2H-MoS₂ and 1T/2H-MoS₂/PPy/VS₂.

  DownLoad: Full-Size Img PowerPoint

  where Z_in and Z₀ denote the input impedance and free-space characteristic impedance of the standard absorbing material, respectively, f denotes the frequency of the EMW, d denotes the thickness of the sample, and c denotes the speed of the EMW in free-space. ε_r and μ_r represent the complex permittivity and complex permeability of the material, respectively. The result shows that VS₂ has the worst EM wave absorption performance with only −11.18 dB RL_min at 3.5 mm thickness and only 0.64 GHz EAB at 3.3 mm, which indicates that VS₂ has almost no EM wave loss capacity at 50% load. A skinning effect caused by its excessive conductivity is responsible for this (Fig. 3a), and Fig. 3e shows that at present its Z value has an area of 0 in the loss capacity range, indicating that it is very hard for EMW to enter the interior of the material [5,14]. The coated PPy/VS₂ composite optimizes the impedance matching (Fig. 3f), but its inferior EMW loss capability results in undesirable absorption performance. PPy/VS₂ achieves a reflection loss of −33.77 dB, but the matching thickness is up to 9.1 mm. As mentioned previously, although 1T/2H-MoS₂ exhibits some EMW loss performance, with an EAB of 4.8 GHz at a matched thickness of 2.4 mm, its unitary loss capability renders it unsatisfactory for practical applications (Figs. 3c and g). Comparatively, the 1T/2H-MoS₂/PPy/VS₂ exhibits a strong reflection loss and broadband absorption at a relatively thin-matched thickness. Specifically, the composite has an RLmin of −58.59 dB at a matched thickness of 2.3 mm and exhibits a broadband absorption of 7.44 GHz at 2.5 mm. The above results indicate that the 1T/2H-MoS₂/PPy/VS₂ composite designed gradient work function interface has enhanced interfacial polarization and excellent impedance matching, which realizes the practical application requirements of strong absorption and broad bandwidth, which has broad application prospects.

  To further investigate the EMW loss behavior of the composites, we tested and analyzed the electromagnetic parameters (Fig. 4 and Fig. S8 in Supporting information). The complex permittivity (ε_r = ε′ - jε′′) and permeability (μ_r = μ′ - jμ′′) are crucial electromagnetic parameters that dictate the absorber's EMW absorption performance. The real parts (ε′ and μ′) represent the capacity to store EMW, while the imaginary parts (ε′′ and μ′′) reflect the capacity to dissipate EMW [45,46]. MoS₂, PPy, and VS₂ are typical dielectric materials, characterized by μ′ fluctuating around 1 and μ′′ around 0, indicating a negligible contribution from magnetic losses (Fig. S8). The ε_r-f of VS₂, PPy/VS₂, 1T/2H-MoS₂ and 1T/2H-MoS₂/PPy/VS₂ composites as well as the calculated tanδ_ε-f curves are shown in Figs. 4a-c. The dielectric real part ε′ of all samples shows a decreasing trend with increasing frequency (Fig. 4a), which is consistent with the dispersion effect. Meanwhile, pure VS₂ exhibits high ε′ values, resulting in a strong skinning effect, which prevents the incident EMW from entering the interior of the material, leading to a poor impedance match [34,47]. As shown in Fig. 4b, the 1T/2H-MoS₂/PPy/VS₂ composites have the highest ε′′ values except for VS₂, indicating a strong loss capability. 1T/2H-MoS₂/PPy/VS₂ exhibits multiple polarization fluctuation loss peaks, corresponding to various polarization processes: (1) Sulfur vacancies disturb the charge distribution equilibrium, leading to the induction of dipole polarization; (2) Heterogeneous interfaces composed of multi-gradient work functions have enhanced interfacial polarization losses [48,49]. Depending on these abundant loss mechanisms, the 1T/2H-MoS₂/PPy/VS₂ composites exhibit excellent EMW absorption properties. The dielectric loss tangent (tanδ_ε) is employed to assess the dielectric loss capacity of the absorber (Fig. 4c), and the test results show that compared with other materials, 1T/2H-MoS₂/PPy/VS₂ has a larger value of tanδ_ε, which is highly consistent with the test results of the sample's EMW absorption performance. Meanwhile, the larger tanδ_ε value of 1T/2H-MoS₂/PPy/VS₂ composites on this occasion suggests that the dielectric loss dominates in the EMW attenuation process.

  Figure 4

  

  Figure 4.  Electromagnetic parameters of composites and their polarization relaxation phenomena. (a-c) ε′-f, ε′′-f and tanδ_ε-f curves of all samples. (d) Dielectric loss fitting of 1T/2H-MoS₂/PPy/VS₂.

  DownLoad: Full-Size Img PowerPoint

  To further investigate the effect of the interface work function design on the polarization loss, the polarization relaxation process of the sample was explored using the Debye theory. The Debye relaxation Cole-Cole model can be expressed as Eq. 4 [50,51]:

  $ \left(\varepsilon^{\prime}-\frac{\varepsilon_{\mathrm{S}}+\varepsilon_{\infty}}{2}\right)+\left(\varepsilon^{\prime \prime}\right)^2=\left(\frac{\varepsilon_{\mathrm{S}}-\varepsilon_{\infty}}{2}\right)^2 $

  (4)

  here, ε_s and ε_∞ represent the static dielectric constant and the high-frequency limiting dielectric constant, respectively. Each semicircle in the ε′ - ε′′ curve corresponds to a Debye relaxation process. The relaxation processes based on the above equations (Figs. S9a-d in Supporting information) indicate that the 1T/2H-MoS₂/PPy/VS₂ composite has multiple twisted semicircles compared to the other samples, suggesting the presence of more polarization relaxation phenomena. These polarization relaxation processes can be divided into the following key components. On the one hand, sulfur vacancies and carbon defects present in the 1T/2H-MoS₂/PPy/VS₂ and PPy polymer layers, which disturb the charge distribution, resulting in dipole polarization; on the other hand, the interfacial structure between the multiple work function components affects the distribution of electrons and leads to interfacial polarization. In addition, the appearance of long trailing tails is observed in Figs. S9a, c and d, while this phenomenon is not observed in PPy/VS₂ composites, which is related to the excellent conduction loss of 1T-TMDs (with metallic properties) [29,52]. The linear function slopes of ε′ and ε′′/f represent the polarization relaxation time τ. The calculated τ is shown in Figs. S9e-h (Supporting information). ε′ and ε′′/f curves appear linear in both the low and high frequency, which suggests the combined effect of dipolar polarization and interfacial polarization in the 1T/2H-MoS₂/PPy/VS₂ composite during the EMW loss process. By fitting the conductivity loss ε_c′′ and the polarization loss ε_p′′, the contribution of distinguishing the two loss modes to MAMs is explored (Eq. 5) [53,54]:

  $ \varepsilon^{\prime \prime}=\varepsilon_{\mathrm{p}}^{\prime \prime}+\varepsilon_{\mathrm{c}}^{\prime \prime}=\frac{2 \pi f \tau\left(\varepsilon_{\mathrm{S}}-\varepsilon_{\infty}\right)}{1+(2 \pi f)^2 \tau^2}+\frac{\sigma}{2 \pi f \varepsilon_0} $

  (5)

  where σ is the conductivity and ε₀ is the vacuum dielectric constant. The conductivity of the material is fitted using Python least squares method as shown in Fig. 4d, and the fitting results indicate that the dielectric loss process of electromagnetic waves is divided into conduction loss at low frequencies (2–3.3 GHz) and polarization loss at medium and high frequencies. By comparing the contributions of the two, polarization loss is the main loss mechanism of the composite at medium and high frequencies. This indicates that the construction of the gradient work function interface greatly optimizes the electromagnetic wave loss performance of the composites.

  The attenuation constant α (Fig. S10 in Supporting information) is a key parameter for evaluating the EMW absorption performance of the absorber and has been calculated for the samples using the following equation (Eq. 6) [55,56]:

  $ \alpha=\frac{\sqrt{2} \pi f}{c} \sqrt{\left(\mu^{\prime \prime}{ }_{\mathrm{r}} \varepsilon^{\prime \prime}{ }_{\mathrm{r}}-\mu^{\prime}{ }_{\mathrm{r}} \varepsilon^{\prime}{ }_{\mathrm{r}}\right)+\sqrt{\left(\mu^{\prime \prime}{ }_{\mathrm{r}} \varepsilon^{\prime \prime}{ }_{\mathrm{r}}-\mu^{\prime}{ }_{\mathrm{r}} \varepsilon^{\prime}{ }_{\mathrm{r}}\right)^2+\left(\mu^{\prime}{ }_{\mathrm{r}} \varepsilon^{\prime \prime}{ }_{\mathrm{r}}+\mu^{\prime \prime}{ }_{\mathrm{r}} \varepsilon^{\prime}{ }_{\mathrm{r}}\right)^2}} $

  (6)

  The attenuation constant was used as a measurement of the capability strength of the absorber to attenuate the incident EMW. The results show that under the equal loading, the attenuation ability of the composites for electromagnetic waves is in the order of VS₂ > 1T/2H-MoS₂/PPy/VS₂ > 1T/2H-MoS₂ > PPy/VS₂. Except for the poor impedance matching of VS₂ which results in poor absorption performance, the strength of the loss capability of the other samples is generally consistent with the EMW absorption performance of the composites.

  To further evaluate the practical EMW loss capability of composites under far-field conditions, we simulated radar cross-section (RCS) values using CST software [57–59]. As shown in Fig. S11 (Supporting information), the dimensions of the perfect electrical conductor (PEC) are defined to be 100 mm × 100 mm × 2 mm, while the dimensions of the absorber coating are 100 mm × 100 mm × 2.5 mm. The simulated RCS values for incidence angles ranging from −60° to +60° are illustrated in Fig. S12a (Supporting information), which reveals that the RCS values start to increase slowly from ± 60° and fluctuate along with the change in detection angle. Compared to pure PEC, VS₂, PPy/VS₂ and 1T/2H-MoS₂, the PEC model of the 1T/2H-MoS₂/PPy/VS₂ composite coating shows excellent curve stability with less fluctuation in the test range from −60° to 60°, and the scattering signals are essentially lower than −10 dB m² throughout the test range. This demonstrates that the composite has a stable electromagnetic wave attenuation capability, making it optimized for applications in complex EMW angular incidence environments. In addition, the RCS values of this absorber are generally below −20 dB m² except near 0°, which is comparable to the RCS levels of birds and insects [46,60]. It can also be observed in Figs. S12b-f (Supporting information) that 1T/2H-MoS₂/PPy/VS₂ has the weakest radiation scattering structure and color change, which further proves that most of the EMW energy is effectively attenuated. These simulation results demonstrate the great potential of 1T/2H-MoS₂/PPy/VS₂ composites as stealth coatings for civil and military applications.

  In this study, a 1T/2H-MoS₂/PPy/VS₂ EMW absorber with multi-gradient work function has been successfully constructed, and the effect of interfacial polarization on the EMW loss has been thoroughly discussed by combining experiments and simulations. It was found that the combination of heterogeneous interfaces with gradient work function and the construction of multi-interfacial structures significantly enhanced the interfacial polarization of the materials, achieving effective carrier transfer and accumulation between the interfaces. This not only enhances the polarization loss inside the material, but also optimizes the impedance matching, which enables the 1T/2H-MoS₂/PPy/VS₂ composite to achieve an EAB of 7.44 GHz at a thickness of 2.5 mm. Radar cross-section (RCS) simulation results further validate the effectiveness of this multi-gradient work function interface design strategy in practical applications, and the composites show a low radar cross-section of −7.2 dB m² at 0°, which illustrates their excellent EMW loss capability. In conclusion, this study emphasizes the importance of modulating EMW absorption properties through multi-facial design, and establishes a new way to enhance microwave absorption properties through elaborate interfacial engineering.

  Declaration of competing interest

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  CRediT authorship contribution statement

  Jinkun Liu: Writing – original draft, Validation, Investigation, Formal analysis, Data curation, Conceptualization. Xuelian Yang: Validation, Investigation. Wenxuan Chen: Validation, Investigation. Pingan Zhu: Writing – review & editing. Guanglei Wu: Writing – review & editing. Jing Zheng: Writing – review & editing, Supervision, Project administration, Funding acquisition. Xu Hou: Writing – review & editing.

  Acknowledgments

  This work was supported by the National Natural Science Foundation of China (Nos. 22275156, 52025132, 21,621,091, 52300138, 22021001 and 22121001), the Fundamental Research Funds for the Central Universities of China (No. 20720220019), the National Science Foundation of Fujian Province of China (No. 2022J02059), the 111 Project (Nos. B17027, B16029), and the New Cornerstone Science Foundation through the XPLORER PRIZE.

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2025.111293.

  
  
• 1. [1]

     Y. Zhang, L. Zhang, L. Tang, et al., ACS Nano 18 (2024) 8411–8422. doi: 10.1021/acsnano.3c13057

  2. [2]

     X. Zhou, P. Min, Y. Liu, et al., Science 385 (2024) 1205–1210. doi: 10.1126/science.adp6581

  3. [3]

     H. Lv, Y. Yao, S. Li, et al., Nat. Commun. 14 (2023) 1982. doi: 10.1038/s41467-023-37436-6

  4. [4]

     P.A. Rasheed, R.P. Pandey, F. Banat, et al., Matter 5 (2022) 546–572. doi: 10.1016/j.matt.2021.12.021

  5. [5]

     M. Qin, L. Zhang, H. Wu, Adv. Sci. 9 (2022) 2105553. doi: 10.1002/advs.202105553

  6. [6]

     C. Yu, B. Xie, X. Yao, et al., Matter 6 (2023) 4321–4338. doi: 10.1016/j.matt.2023.10.010

  7. [7]

     L. Wang, X. Yu, X. Li, et al., Chem. Eng. J. 383 (2020) 123099. doi: 10.1016/j.cej.2019.123099

  8. [8]

     K. Cao, W. Ye, Y. Zhang, et al., Chem. Eng. J. 492 (2024) 152275. doi: 10.1016/j.cej.2024.152275

  9. [9]

     K. Cao, W. Ye, Y. Zhang, et al., J. Mater. Sci. Technol. 195 (2024) 63–73. doi: 10.1016/j.jmst.2023.12.069

  10. [10]

      J. Liu, Z. Jia, Y. Dong, et al., Mater. Today Phys. 27 (2022) 100801. doi: 10.1016/j.mtphys.2022.100801

  11. [11]

      K. Yang, Y. Cui, Z. Liu, et al., Chem. Eng. J. 426 (2021) 131308. doi: 10.1016/j.cej.2021.131308

  12. [12]

      L. Liu, S. Zhang, F. Yan, et al., ACS Appl. Mater. Interfaces 10 (2018) 14108–14115. doi: 10.1021/acsami.8b00709

  13. [13]

      K. Cao, W. Ye, Y. Zhang, et al., Chem. Eng. J. 489 (2024) 151384. doi: 10.1016/j.cej.2024.151384

  14. [14]

      H. Wang, H. Zhang, J. Cheng, et al., J. Materiomics 9 (2023) 492–501. doi: 10.3390/w15030492

  15. [15]

      D. Zhang, T. Liu, J. Cheng, et al., Nano-Micro Lett. 11 (2019) 38. doi: 10.4018/978-1-5225-7591-7.ch003

  16. [16]

      Z. Zhou, X. Yang, D. Zhang, et al., Adv. Compos. Hybrid Mater. 5 (2022) 2317–2327. doi: 10.1007/s42114-022-00416-3

  17. [17]

      Z. Huang, J. Cheng, H. Zhang, et al., J. Mater. Sci. Technol. 107 (2022) 155–164. doi: 10.1016/j.jmst.2021.08.005

  18. [18]

      J. Cheng, H. Jiang, L. Cai, et al., Chem. Eng. J. 457 (2023) 141208. doi: 10.1016/j.cej.2022.141208

  19. [19]

      K. Cao, W. Ye, Y. Zhang, et al., Chem. Eng. J. 496 (2024) 154184. doi: 10.1016/j.cej.2024.154184

  20. [20]

      Z. Jiao, J. Hu, M. Ma, et al., J. Colloid Interface Sci. 650 (2023) 2014–2023. doi: 10.1016/j.jcis.2023.07.072

  21. [21]

      H. Gu, J. Huang, N. Li, et al., J. Mater. Sci. Technol. 146 (2023) 145–153. doi: 10.1016/j.jmst.2022.11.010

  22. [22]

      Y. Bi, M. Ma, Y. Liu, et al., J. Colloid Interface Sci. 600 (2021) 209–218. doi: 10.1016/j.jcis.2021.04.137

  23. [23]

      Z. Jia, J. Liu, Z. Gao, et al., Adv. Funct. Mater. 35 (2025) 2405523. doi: 10.1002/adfm.202405523

  24. [24]

      Y. Liu, Z. Jia, Q. Zhan, et al., Nano Res. 15 (2022) 5590–5600. doi: 10.1007/s12274-022-4287-5

  25. [25]

      S.Y. Lee, U.J. Kim, J. Chung, et al., ACS Nano 10 (2016) 6100–6107. doi: 10.1021/acsnano.6b01742

  26. [26]

      D.H. Won, J. Chung, S.H. Park, et al., J. Mater. Chem. A 3 (2015) 1089–1095. doi: 10.1039/C4TA05901H

  27. [27]

      W. Zan, W. Geng, H. Liu, et al., J. Alloys Compd. 658 (2016) 152–156. doi: 10.1016/j.jallcom.2015.10.145

  28. [28]

      H. Zhang, X. Zhou, M. Yuan, et al., Adv. Funct. Mater. 34 (2024) 2313829. doi: 10.1002/adfm.202313829

  29. [29]

      M. Ning, P. Jiang, W. Ding, et al., Adv. Funct. Mater. 31 (2021) 2011229. doi: 10.1002/adfm.202011229

  30. [30]

      D. Wu, C. Wang, M. Wu, et al., J. Energy Chem. 43 (2020) 24–32. doi: 10.1016/j.jechem.2019.08.003

  31. [31]

      X. Guo, E. Song, W. Zhao, et al., Nat. Commun. 13 (2022) 5954. doi: 10.1038/s41467-022-33636-8

  32. [32]

      X. Wang, Z. Chen, Y. He, et al., Chem. Eng. J. 451 (2023) 138575. doi: 10.1016/j.cej.2022.138575

  33. [33]

      J. Liu, Z. Jia, W. Zhou, et al., Chem. Eng. J. 429 (2022) 132253. doi: 10.1016/j.cej.2021.132253

  34. [34]

      X. Ma, S. Liu, H. Luo, et al., Adv. Funct. Mater. 34 (2024) 2310126. doi: 10.1002/adfm.202310126

  35. [35]

      G. Yin, J. Wu, L. Ye, et al., Adv. Funct. Mater. 35 (2025) 2314425. doi: 10.1002/adfm.202314425

  36. [36]

      Z. An, Y. Li, X. Luo, et al., Matter 5 (2022) 1937–1952. doi: 10.1016/j.matt.2022.04.011

  37. [37]

      J. Liu, L. Zhang, H. Wu, Adv. Funct. Mater. 32 (2022) 2200544. doi: 10.1002/adfm.202200544

  38. [38]

      H. Huang, X. Xia, J. Yun, et al., Energy Storage Mater. 52 (2022) 473–484. doi: 10.1016/j.ensm.2022.08.016

  39. [39]

      Y. Fang, X.Y. Yu, X.W.D. Lou, Angew. Chem. Int. Ed. 57 (2018) 9859–9863. doi: 10.1002/anie.201805552

  40. [40]

      D. Mao, Z. Zhang, M. Yang, et al., Int. J. Miner. Metall. Mater. 30 (2023) 581–590. doi: 10.1007/s12613-022-2556-7

  41. [41]

      F. Pan, M. Ning, Z. Li, et al., Adv. Funct. Mater. 33 (2023) 2300374. doi: 10.1002/adfm.202300374

  42. [42]

      B. Zhao, Y. Du, H. Lv, et al., Adv. Funct. Mater. 33 (2023) 2302172. doi: 10.1002/adfm.202302172

  43. [43]

      M. Liu, B. Zhao, K. Pei, et al., Small 19 (2023) 2300363. doi: 10.1002/smll.202300363

  44. [44]

      C. Wu, Z. Chen, M. Wang, et al., Small 16 (2020) 2001686. doi: 10.1002/smll.202001686

  45. [45]

      T. Liu, Y. Zhang, C. Wang, et al., Small 20 (2024) 2308378. doi: 10.1002/smll.202308378

  46. [46]

      J. Xiao, B. Zhan, M. He, et al., Adv. Funct. Mater. 35 (2025) 2316722. doi: 10.1002/adfm.202316722

  47. [47]

      X. Wang, F. Pan, L. Cai, et al., Chem. Eng. J. 475 (2023) 146319. doi: 10.1016/j.cej.2023.146319

  48. [48]

      S. Liu, D. Fang, F. Xing, et al., Chem. Eng. J. 479 (2024) 147613. doi: 10.1016/j.cej.2023.147613

  49. [49]

      L. Li, Z. Chen, F. Pan, et al., Chem. Eng. J. 470 (2023) 144236. doi: 10.1016/j.cej.2023.144236

  50. [50]

      L. Cai, H. Jiang, F. Pan, et al., Small 20 (2024) 2306698. doi: 10.1002/smll.202306698

  51. [51]

      Y. Zhu, T. Liu, L. Li, et al., Nano Res. 17 (2024) 1655–1665. doi: 10.1007/s12274-023-6272-z

  52. [52]

      J. Xiao, X. Qi, X. Gong, et al., Nano Res. 15 (2022) 7778–7787. doi: 10.1007/s12274-022-4625-7

  53. [53]

      F. Zhang, N. Li, J.F. Shi, et al., Small 20 (2024) 2312135. doi: 10.1002/smll.202312135

  54. [54]

      Y. Liu, X. Wei, X. He, et al., Adv. Funct. Mater. 33 (2023) 2211352. doi: 10.1002/adfm.202211352

  55. [55]

      X. Xiong, H. Zhang, H. Lv, et al., Carbon 219 (2024) 118834. doi: 10.1016/j.carbon.2024.118834

  56. [56]

      X. Li, R. Hu, Z. Xiong, et al., Nano-Micro Lett. 16 (2024) 42. doi: 10.1007/s40820-023-01255-7

  57. [57]

      H. Liang, G. Chen, D. Liu, et al., Adv. Funct. Mater. 33 (2023) 2212604. doi: 10.1002/adfm.202212604

  58. [58]

      L. Rao, L. Wang, C. Yang, et al., Adv. Funct. Mater. 33 (2023) 2213258. doi: 10.1002/adfm.202213258

  59. [59]

      M. Yuan, H. Lv, H. Cheng, et al., Adv. Funct. Mater. 33 (2023) 2302003. doi: 10.1002/adfm.202302003

  60. [60]

      X. Wang, Y. Yuan, X. Sun, et al., Small 20 (2024) 2311657. doi: 10.1002/smll.202311657

• 

  Figure 1  Schematic diagram of the interfacial structure and gradient work function interface polarization of 1T/2H-MoS₂/PPy/VS₂. The 1T/2H-MoS₂/PPy/VS₂ composite enhances EMW absorption by facilitating carrier migration and aggregation at interfaces, driven by multi-gradient work function differences.

  下载: 全尺寸图片 幻灯片
  

  Figure 2  Microscopic morphology and interfacial structural composition of composites. (a-d) SEM, (e-h) TEM, and (i-l) HRTEM images of VS₂, PPy/VS₂, 1T/2H-MoS₂ and 1T/2H-MoS₂/PPy/VS₂.

  下载: 全尺寸图片 幻灯片
  

  Figure 3  Electromagnetic wave absorption properties of composites. (a-d) RL values and (e-h) loss capacity profiles of VS₂, PPy/VS₂, 1T/2H-MoS₂ and 1T/2H-MoS₂/PPy/VS₂.

  下载: 全尺寸图片 幻灯片
  

  Figure 4  Electromagnetic parameters of composites and their polarization relaxation phenomena. (a-c) ε′-f, ε′′-f and tanδ_ε-f curves of all samples. (d) Dielectric loss fitting of 1T/2H-MoS₂/PPy/VS₂.

  下载: 全尺寸图片 幻灯片
•