Design of Multilayered 2D Nanomaterial Composite Structures for EMI Shielding Analysis.

It is still very challenging to effectively design nanocomposite microstructures with significantly improved electromagnetic interference shielding effectiveness (EMI SE). Herein, we developed a facile method for fabrication of molybdenum disulfide/graphene nanoplatelets (MoS2/GNPs) nanocomposites, in which GNPs are utilized as highly effective electrical transport materials, while MoS2 resolves the agglomeration problem of GNPs. GNPs also serve as an efficient cluster of electrical transport systems and dampen the incoming electromagnetic wave. Two types of samples are synthesized and compared in context of EMI SE values: physically mixed composite and layered samples. The sandwiched MoS2 between GNP layers showed an EMI SE of ∼24 dB, which was an almost 14% improvement relative to MoS2/GNPs nanocomposites exhibiting an EMI SE value of ∼21 dB, both containing 0.5 wt % GNPs. This work provides a new strategy for the design of multifunctional nanocomposites using the simple low-cost vacuum filtration method for EMI shielding for future applications.

Introduction

Electronics are everywhere, from autonomous vehicles to space technology in recent times. As a result, a new type of pollution known as electromagnetic (EM) pollution has emerged.[1,2] Electromagnetic interference (EMI) in electrical devices is a common problem that, if not properly addressed, can cause system damage. Medical gadgets suffer from EMI, which can cause injury to the user and prevent the device from achieving the desired outcomes.[3] EMI can momentarily disable a piece of technology and, if left unprotected for a long period of time, can cause irreparable damage. As a result, it is critical to ensure that all electronic devices are appropriately protected from interference. To resolve this issue of EMI, new materials and designs that can effectively absorb these EM waves must be developed.

Metal shielding is the most typical approach for EMI protection. Metals have the capability of absorbing and reflecting waves, removing all emissions, and providing electronic shielding. However, experiments are being conducted to see whether lightweight materials like carbon nanotubes, graphite microfibers, and metal oxides such as ZnO, CuS, MnO, Fe3O4, NiO/SiC, and Fe3O4@TiO2[4−9] could be used to replace the metals. Molybdenum disulfide is a transition metal chalcogenide, with a layered structure comparable to that of graphite, that has gained a lot of consideration because of its semiconducting properties.[10]

For EMI shielding, graphene-based nanocomposites have been widely studied. Stretched graphene nanosheets (GNSs) generating obstacle walls in melamine sponge were investigated by Guo et al.[11] for excellent EMI shielding. By using a fluid-assisted technique, the GO nanosheets covered with melamine sponge pores were utilized, followed by freeze-drying and reduction procedures. The composite foam had a density of 0.011 g/cm3, an EMI SE of 37.2 dB, and a specific EMI SE of 845.5 dB·cm2/g with a graphene loading of 0.1 vol %. Song et al.[12] investigated the EM shielding properties of flexible multilayer graphene sheets with high conductivity and found the effective EM shield equal to 27 dB. Guo et al.[13] reported the biomass-derived carbon and iron oxide with good EM wave absorption characteristics.

Composites of MoS2/GNPs have found potential applications within the region of energy, capacity, and transformation. The dielectric properties and electromagnetic wave assimilation execution of the MoS2/GNPs composite have never been detailed. In this aspect, the composites of MoS2/GNPs were arranged and their predominant electromagnetic wave retention properties were proved.[14] Moreover, the shape of nanomaterials also affects the ultimate electrical properties such as electrical conductivity and electromagnetic interference shielding efficacy and dielectric properties.[15,16]

The strategy for effective EMI shielding is to increase the real part of the complex permittivity, ε″, which is associated with the absorption of EM waves. The increase in ε″ comes from multiple polarization mechanisms such as electronic, ionic, dipolar, and space charge polarizations.[17−20] Since ionic and electronic contributions dominate at low frequency regimes, therefore, key to the enhancement of ε″ at high EM wave frequencies will be to enhance interface and dipolar polarizations. Various interface design strategies have been adopted to increase space charge polarization, which are usually complex.[17−19] In this study, we have adopted a simple strategy where void-free compact-layered structures of 2D GNPs and MoS2 nanosheets were fabricated by the simple and cost-effective vacuum filtration method. Two design strategies were adopted to fabricate these layered structures. One strategy involved a single layer of physically mixed composite materials of GNPs and MoS2 with varying loadings, and the other one considered the bi- and trilayer structures of these materials where each layer was composed of a single type of 2D material. The sandwich construction, i.e., trilayer structures, showed enhanced EMI shielding effectiveness due to more space charge polarization losses along with other types of losses because of multiple interfaces. These layered constructions could be used in many fields, such as flexible electronics, automobile industry, and space technologies.

Experimental Section

Materials

Bulk MoS2 and graphite powder were purchased from Jiangsu XFNANO Materials Tech Co., Ltd., China. N-Methyl-2-pyrrolidone (NMP) and nylon filter papers with a pore size of 0.45 μm were obtained from Sigma-Aldrich.

Synthesis of 2D Materials

First, 2D materials of MoS2 and graphene were prepared from bulk materials by exfoliation in NMP. For the synthesis of 2D nanosheets of MoS2, 0.2 g of MoS2 was mixed in 100 mL of NMP and dispersed by magnetic stirring for 45 min. After that, the dispersion was probe-sonicated for 64 h using 40% amplitude at 0.3 cycle. This 100 mL dispersion was equally distributed in six centrifuge tubes, which were centrifuged at 1500 rpm for 45 min to exfoliate MoS2. The sediments were stuck to the walls of these tubes, and the supernatants were transferred to another set of six tubes, which were further centrifuged at 1000 rpm for 45 min. Subsequently, the exfoliated dispersions were poured into the vacuum filtration assembly. After filtration through 0.45 μm nylon filter paper, the filtered cake was removed from the filtration assembly and dried overnight in a vacuum oven at the temperature of 60 °C. Once dried, MoS2 was scratched from the nylon filter paper and was used for layered structure fabrication and further testing.

A similar procedure was used to prepare graphene nanoplatelets by exfoliation of bulk graphene powder in NMP.

Layered Structure Fabrication by Vacuum Filtration

Vacuum filtration was used to fabricate layered structures of synthesized 2D materials. Two design strategies were adopted: the first strategy involved a single-layer structure containing physically mixed nanocomposites of 2D materials, and the second one dealt with the bi- and trilayer structures where, instead of nanocomposites, each layer was composed of a single 2D material. The overall loading of 2D materials in all layered structures, single-, bi-, and trilayer ones, was kept constant, i.e., 6 mg. The required amount of 2D materials, for each layer, was dispersed in 12 mL of 1:1 ethanol–water solution in an ultrasonic bath for 30 min and then filtered through the nylon paper by vacuum suction. The loading and sequence of layers are given in Table . The single-layer structures were fabricated by physically mixing 0, 50, 75, and 100% MoS2 nanosheets with graphene platelets in ethanol–water solution and then filtering each dispersion through the nylon filter paper by suction. The filtered cakes were dried in an oven at 60 °C for 1 h. The process schematic is shown in Figure .

Table 1

Sample Designation for Single-, Bi-, and Trilayer Structures

structure	composition and sequence of layers in a structure	sample/structure designation
single layer	6 mg of graphene	6G
	3 mg of MoS2 and 3 mg of graphene	3MS-3G
	4 mg of MoS2 and 2 mg of graphene	4MS-2G
	6 mg of MoS2	6MS
bilayer	3 mg of MoS2/3 mg of graphene	3MS/3G
trilayer	2 mg of MoS2/2 mg of graphene/2 mg of MoS2	2MS/2G/2MS
	2 mg of graphene/2 mg of MoS2/2 mg of graphene	2G/2MS/2G

Figure 1

Schematic of single- and multilayer structure fabrication processes as well as EMI mechanisms.

In bilayer structures, the first layer was fabricated by dispersing 3 mg of MoS2 in ethanol–water solution followed by vacuum suction through nylon filter paper. The filtered cake was dried in an oven at 60 °C for 1 h. Subsequently, this dried cake was again loaded into the vacuum filtration assembly and a dispersion containing 3 mg of graphene platelets was filtered through it to fabricate the second layer. The filtered cake was again dried in an oven at 60 °C. A similar procedure was adopted for the fabrication of trilayer structures where 25% of each 2D material was sandwiched between the two layers of the other material (Table ).

Characterizations

The surface morphologies of synthesized samples were analyzed using scanning electron microscopy (SEM) (JEOL-JSM-6490LA). The crystal structure of the prepared powder materials was probed using X-ray diffraction (XRD, STOE Siemens D5005) with CuKα radiation (λ = 1.54 Å) operating at a voltage of 40 kV and a working current of 40 mA. The samples were subjected to a step scan of 0.04° and a scan rate of 1.00 s.

EMI shielding is primarily determined by the electrical conductivity and magnetic permeability of materials, as well as the frequency of radiation has also the major role. The effectiveness of the shielding material is the ratio of incident power (PI) to transmitted power (PT) through the shield, as given by eq :

EMI testing of prepared samples was carried out at a PNA Model E8364B. The data was obtained as scattering parameters, which were a combination of reflection responses (eq ) and transmission (eq ). These scattering parameters are called S-parameters, which are S11, S12, S21, and S22.

The sum of the contributions from shielding effect reflection (SER), shielding effect absorption (SEA), and various internal reflections makes up the total EMI SE (SET) (SEM). Because the re-reflected waves are dissipated as heat in the shielding material at higher EMI SE values and with a multilayer EMI shield, contribution from numerous internal reflections is integrated in the absorption. The total EMI SE (SET) is the sum of the contributions from reflection (SER), absorption (SEA), and multiple internal reflections (SEM) (eq ):where both SER (eq ) and SEA (eq ) are as follows,When an impedance mismatch exists between the shielding material’s surface and the incoming radiation, microwave reflection occurs. However, absorption occurs when incoming electromagnetic wave energy is attenuated, and the internal inhomogeneity of the shielding material causes repeated reflections. It is worth noting that an SEA of less than 10 dB is adequate to eliminate multiple reflection contributions. The total shielding effectiveness (SET) is the total shielding contribution owing to the above-mentioned components, and the specifics tying it to the various scattering characteristics have been described elsewhere.

The complex permittivity properties of the synthesized materials including dielectric constant and dielectric loss were measured with a vector network analyzer (VNA, N5242A PNA-X, Agilent) at room temperature in the frequency range of 1 to 8 GHz. For finding the real factor of resistivity, the following relation (eq ) was usedHere, ε′ is the dielectric constant, C is the capacitance, d is the distance between the plates, and ε0 is the permittivity of free space.

For finding the imaginary factor of resistivity, the following equation (eq ) was used, where tan δ is the dissipation factor

Results and Discussion

Morphological and Structural Analyses

The morphologies of synthesized 2D materials of GNPs and MoS2 are shown in Figure . SEM images of synthesized GNPs revealed triangular and rectangular forms (Figure A,B) with layered sheets of sizes varying between 1 and 5 μm and thickness in the 2–10 nm range (Figure ). A broad variety of layered agglomerates of varying shapes and numbers of layers were observed. There were no single- or few-layer sheets of graphene found. The flake-like structures with stacking of few layers were evident from the morphological analysis of synthesized MoS2 (Figure C,D). The MoS2 sheets were composed of clusters of various thicknesses. As reported in the literature, the mechanical strength between the layers of bulk MoS2 was weakened during probe sonication[21] and nanosheets of sizes ranging from 1 to 5 μm were obtained.

Figure 2

SEM images of (A, B) GNPs and (C, D) MoS2.

The elemental maps of single-layer composite structures along with their corresponding SEM images are shown in Figure . The SEM images revealed the dominance of morphologies in composite structures similar to the ones observed for pristine graphite nanosheets (Figure A,B) when the concentration of GNPs was increased in the composite materials (Figure E,F). Meanwhile, the morphologies of composites having higher concentrations of MoS2 were similar to that of pristine MoS2. The sulfur and molybdenum contents decreased with increasing content of graphene in a physically mixed composite layer (Figure A–F). The dispersion of both phases was mostly uniform in the composite layer. The large interfacial contact between MoS2 and GNP 2D materials was evident for 3MS-3G composition (Figure C,D) compared to the other compositions ( Figure A,B,E,F).

Figure 3

Elemental mapping of (A, B) 4MS-2G, (C, D) 3MS-3G, and (E, F) 2MS-4G.

To find the thickness and lateral length of nanosheets, the 2D materials were analyzed by atomic force microscopy (AFM), and results are shown in Figure . The length of GNPs was around 0.2 μm, and the height was ∼5.2 nm. Also, areal roughness parameters, Ra and Rz, were 2.69 and 20.8 nm, respectively, for GNPs. MoS2 flakes were ∼0.5 μm in length, and their thickness was ∼10.2 nm. Similarly, for MoS2, Ra and Rz were 1.62 and 31.62 nm, respectively.

Figure 4

AFM topography of (A) GNPs and (B) MoS2.

Figure shows the XRD patterns of graphene nanoplatelets (GNPs). The characteristic peaks of graphene are evident in Figure A. A high intensity peak at a 2θ value of 26° was associated with the (002) plane of graphite. Also, two less intense peaks at 44° and 54° are evident in Figure A, which belonged to (100) and (004) planes of graphene, respectively. These characteristic peaks of GNPs match well with PDF card #00-02-0212 given in Figure B and conform to the reported literature.[22]

Figure 5

XRD patterns of (A) GNPs and (B) reference PDF card #00-02-0212.

Figure A shows the XRD pattern of MoS2. The diffraction peaks at 14.37°, 32.67°, 35.86°, 39.53°, 44.16°, 49.76°, 58.32°, and 60.12° belonged to (002), (100), (102), (103), (104), (105), (110), and (112) planes, respectively. The observed XRD peaks of MoS2 matched well with reference PDF card #01-077-1716 shown in Figure B and with a previous report.[23]

Figure 6

XRD patterns of (A) MoS2 and (B) reference PDF card #01-077-1716.

Raman spectroscopy is a quick way to get a direct look at electron–phonon interactions, which means that it is very sensitive to electronic and crystallographic structures.[24,25]Figure A illustrates the Raman spectrum of GNPs where the main band for GNPs was observed at around 1600 cm–1. The Raman spectra of carbon compounds have three primary bands between 1200 and 2800 cm–1. The D and G bands at 1360 and 1600 cm–1, respectively, are caused by sp2 sites, while the T band at 1060 cm–1 is due to sp3 contributions.[24] There was no D band observed for synthesized GNPs (Figure ). Some literature reports suggest that the Raman spectrum would be redshifted when graphene is subjected to strain because of the stretch of the carbon–carbon bond.[26,27]

Figure 7

Raman scan of 2D materials: (A) GNPs and (B) MoS2.

In Figure B, first-order E2g1 at around 289 cm–1 corresponding to MoS2 was observed when the incident energy was considered nonresonant. MoS2 showed aberrant resonance Raman characteristics as reported in ref (28). The resonant activation of exciton states mediated by acoustic phonon scattering causes the central peak.[28] Furthermore, due to resonance with exciton or exciton–polariton state characteristics, several second-order Raman peaks were observed.

Electromagnetic Shielding Performances of Multilayer Structure Films

The effectiveness of EMI shielding with single-layer physically mixed composite structures is shown in Figure . The EM absorption capacities of both pristine 2D materials, i.e., MoS2 and GNPs, were lower compared to those of their composites (Figure A). However, pristine GNPs illustrated greater EM reflection behavior compared to pristine MoS2, which may be attributed to higher electrical conductivities of GNPs compared to those of MoS2 nanosheets. The addition of MoS2 into GNPs or vice versa led to enhanced EM wave absorption characteristics of the resultant composite (Figure A). The maximum EMI SE was established at 50% content of each phase, i.e., 3MS-3G, where it reached a value of −20.8 dB at a lower frequency of 2 GHz. A drop in EMI SE was observed for all compositions at frequencies higher than 5 GHz (Figure C).

Figure 8

EMI SE characteristics of various single-layer composite structures. (A) Absorption, (B) reflection, and (C) total EMI shielding effectiveness.

As has previously been established,[29] multiple polarizations such as interfacial, dipolar, ionic, and electronic polarizations[19,30] and relaxation mechanisms can explain the absorption of EM waves impinging on the hybrid structures of various compositions. The electronic and atomic dipoles have a quick reaction to the alternating EM field in the GHz region and synchronize with the EM wave, resulting in no EM wave energy loss.[30] The contributions from ionic and electronic polarizations usually occur at lower frequencies, i.e., UV or IR; therefore, interfacial and dipole polarization effects may dominate in increased EMI SE at higher frequency ranges.[19]

It has been observed that the additions of GNPs in MoS2 resulted in enhanced EMI SE (Figure ), and the large interface contact due to these graphene additions may have provided the platform for the polarization. Also, with high electrical conductivity, graphene sheets with a high aspect ratio tend to raise the percolation network.[31] The charge carriers get accumulated at the interface heterostructures, causing space charge polarization, and since these charges find themselves unable to respond in accordance with the incident EM field, they lead to the energy loss of EM radiation.[32] Hence, the maximum EMI SE was obtained for the single-layer 3MS-3G composite.

The EMI SE of the bi- and trilayer structures was better compared to that of the single-layered composite structures (Figure ). The bilayer structure, i.e., 3MS/3G, showed poor EM wave absorption and overall EM shielding characteristics compared to the trilayer ones (Figure ). In trilayer structures, the EMI SE was the maximum, i.e., −24.4 dB, when the MoS2 layer was sandwiched between GNP layers (2G/2MS/2G; Figure ) and was relatively lower (−23.7 dB) when the GNP layer was sandwiched between MoS2 layers (2MS/2G/2MS; Figure C). Also, the EMI SE of 2G/2MS/2G was constant for the entire frequency region (Figure ).

Figure 9

EMI shielding effectiveness of bi- and trilayer structures. (A) Absorption, (B) reflection, and (C) total EMI shielding effectiveness.

The better EM wave shielding properties of bi- or trilayer samples were due to multiple interfaces that might lead to space charge polarization and, hence, dissipation of wave energy as explained earlier. The highest EMI SE of 2G/2MS/2G can be attributed to the fact that the more conductive facing layers of the sandwich structures will allow more EM waves to enter the layered structures and, hence, higher absorption of ME waves due to conductive losses. Also, the difference in electrical conductivities between GNPs and MoS2 will result in higher charge accumulation at these heterostructure interfaces and, hence, further energy losses due to space charge polarization. Therefore, sandwiching the insulator layer of MoS2 in the conducting layer of GNPs was a better design strategy for EMI shielding, probably due to the less reflection and, hence, higher absorption and attenuation of EM waves.

Table provides a comparison of the shielding effectiveness of materials and strategies used in this study and that of the already reported ones. The results of this study are better than those of many of the recently reported literature. For example, Zhang et al.[33] reported sulfonated reduced less defect graphene oxide (S-rLGO) combined with P(St-BA) latex through blending and casting processes and reported an overall shielding effectiveness of 16 dB. Khan et al.[34] found an EMI effectiveness of 18 dB with graphene- and MoS2-based materials. The EMI shielding of the MoS2-rGO/Fe3O4 nanostructure was assessed in the 8–12 GHz range by Prasad et al.[35] and was 8.27 dB. Also, the MoS2-rGO composite showed an inadequate shielding capacity (SET = 3.81 dB) across the entire spectrum of EM studied. According to the study, interfacial polarization played a vital role in dielectric losses along with other loss mechanisms. Guo et al.[36] studied the rGO@barium titanate (BT)/poly(vinylidene fluoride) (PVDF) composite and concluded that this composite can exhibit an EMI SER (reflection) of 23 dB with a filler loading of 25 wt %.

Table 2

EMI Shielding Effectiveness Data

sr. no.	author	material	year	fabrication/synthesis method	dB ranges	reference
1	Ding et al.	rGO-MoS2-Fe3O4	2021	hydrothermal technique	–48 dB (reflection)	(37)
2	Prasad et al.	Co@MoS2/rGO	2020	autoclave	29–46 dB	(38)
3	Zahid et al.	RGO/TPU	2020	solution casting technique	53 dB	(39)
4	Shakir et al.	PS/PANI blends	2020	solution casting method	45 dB	(40)
5	Zhang et al.	S-rLGO/P(St-BA) latex	2020	blending and casting	16 dB	(33)
6	Khan et al.	graphene and MoS2	2020	blending and filtration	18 dB	(34)
7	Prasad et al.	MoS2-rGO and MoS2-rGO/Fe3O4 nanostructure	2018	hydrothermal method	3.81 dB (MoS2-rGO) and 8.27 dB (MoS2-rGO/Fe3O4)	(35)
8	Guo et al.	GO nanosheets covered with melamine sponge	2019	fluid-assisted method	37 dB	(11)
9	Shakir et al.	PVC/PANI/TRGO	2019	hydrothermal technique and solution casting methods	56 dB	(41)
10	Zhang et al.	graphene/PMMA nanocomposite	2011	foaming with subcritical CO2	13–19 dB	(42)
11	Guo et al.	rGO@BT/poly(vinylidene fluoride) (PVDF)	2017	physical mixing and drop casting	22 dB	(36)
12	Guo et al.	rGO@MoS2/PVDF	2016	blending and hot molding	28 dB	(43)
13	Liang et al.	15% functionalized graphene/epoxy resin	2009	in situ functionalization	21 dB	(44)
14	Sajid et al.	single-layer composite 3MS-3G		vacuum filtration	21 dB	this study
15	Sajid et al.	trilayer structure 2G/2MS/2G		vacuum filtration	24 dB	this study

Dielectric Properties

The dielectric data of complex permittivity of the fabricated single-layer composite structures of MoS2 and GNPs is given in Figure . This data showed the typical frequency-dependent behavior and can be explained based on the Debye theory (eq ),where the dielectric constant (ε′) is the ability of a material to store electric charge in the electric field. The imaginary part (ε″), usually referred to as the loss factor, is a material’s ability to absorb or dissipate energy through conversion of electric energy into heat.[19]

Figure 10

(A, B) Real part of the dielectric permittivity of various single-layer composite structures as a function of EM waves’ frequency and (C) tangent loss curves of these structures.

Figure A shows the data for the real part of the complex permittivity, ε′, for single-layer composite structures. At low frequencies, all the materials showed high values of dielectric constant and the values of dielectric constant dropped with increasing frequencies. This behavior can be explained based on Koop’s theory, according to which dielectric structures are the inhomogeneous Maxwell Wagner type.[45] The materials are composed of conducting grains separated by nonconducting boundaries. The hopping of electrons at the interface because of grain boundaries in the composite interface facilitates the higher permittivities. GNPs had a dielectric constant of 20, additions of MoS2 in GNPs resulted in an increase in dielectric constant, and it reached a value of around 120 for the 3MS-3G composite structure (Figure A). Primarily, the addition of GNPs into MoS2 was beneficial for the creation of multiple interfaces, facilitating the interfacial polarization of the composites and higher dielectric permittivity.[14−16] The larger surface area of MoS2/GNPs structures resulted in greater dipole polarization, which increased the dielectric constant. The charge on the surface of the MoS2/GNPs heterostructure can drive the migration and redistribution of atoms or dipoles within the material.

The increasing concentrations of MoS2 in GNPs led to an increase in complex permittivity, ε″, and maximum values of the complex permittivity, ε″, at all frequencies were observed for 3MS-3G structures (Figure B). Since the contributions to the complex permittivity, ε″, due to electronic and ionic polarizations mostly dominate in IR or visible regions of the EM spectrum, the observed enhancement of the complex permittivity, ε″, would come from dipolar and interface polarization mechanisms. The peaks in complex permittivity, ε″, versus frequency graphs (see arrows in Figure B) at high frequencies are usually indicative of contributions from the interface polarization effect.[17−19] Therefore, heterostructure interfaces in the 3MS-3G single-layer composite structure resulted in higher complex permittivity, ε″, as was evident by the peaks at higher frequencies (Figure B).

The tangent loss behavior of single-layer composite structures is shown in Figure C. The dielectric loss was comparatively large in the lower frequency region due to the charge mobility in the composite materials, whereas the dielectric loss was decreased in the higher frequency region due to the dipolar and interfacial polarization losses. Furthermore, in the high frequency range, a steady increase can be seen, it is because of dynamic relaxation of segmental motions in the amorphous phase, and it is called the dielectric relaxation peak of dielectric loss. These dielectric loss results were consistent with the imaginary part and real part of dielectric constants (Table ).

Table 3

Dielectric Properties of Different Samples at 2 GHz

sample	ε′	ε″	tan δ
6MS	70.9	600.10	0.68
6G	18.5	100	0.95
3MS-3G	112.0	1100	0.52
2MS-4G	16.3	150	0.10
4MS-2G	79.7	700	0.15

Conclusions

This study successfully exploited the simple low-cost vacuum filtration method for the fabrication of layered heterostructure interfaces of 2D materials of graphene and MoS2 to mitigate the electromagnetic interference. Various layered structures were established by varying the concentrations of 2D materials in a single layer or by changing the order of each 2D material in bi- or trilayer structures. The heterostructures of bi- or trilayers exhibited better EMI SE with dB values reaching 24 compared to the single-layer composite structures, which could be due to the multiple interfaces present in these structures because of interface polarization effects. The sandwiching of MoS2 in GNP layers was a better strategy compared to the physical mixing of these materials into a single composite layer with the same loading of each 2D material.