The Effect of Microstructural Changes Produced by Heat Treatment on the Electromagnetic Interference Shielding Properties of Ti-Based MXenes

Abstract

Ti-based MXenes such as Ti₃C₂T_X and Ti₂CT_X have attracted considerable attention because of their superior electromagnetic interference (EMI) shielding effectiveness compared to other EMI shielding materials, especially for high electromagnetic (EM) wave absorption. In this study, we investigated the microstructural changes produced by heat treatment and their effect on the EMI shielding properties of Ti-based MXenes. Ti₃C₂T_X and Ti₂CT_X films were prepared using vacuum filtration and annealed at temperatures up to 300 °C. The microstructures and chemical bonding properties of these heat-treated Ti₃C₂T_X and Ti₂CT_X films were analyzed, and the EMI shielding effectiveness was measured in the X-band and THz frequency range. The porous Ti₃C₂T_X film showed higher EM absorption than that calculated using the transfer matrix method. On the other hand, the Ti₂CT_X films had a more densely stacked structure and lower EM absorption. As the heat treatment temperature increased, Ti₃C₂T_X developed a more porous structure without significant changes in its chemical bonding. Its EM absorption per unit of thickness increased up to 6 dB/μm, while the reflectance remained constant at less than 1 dB/μm after heat treatment. This suggested that the heat treatment of Ti-based MXenes can increase the porosity of the film by removing residual organics without changing the chemical bonds, thereby increasing electromagnetic shielding through absorption.

Keywords: EM absorption; EMI shielding effectiveness; Ti-based MXene; heat treatment; porous structure.

Figure 1

(a) Schematic showing the synthesis process of Ti-based MXene; (b) XRD spectra of Ti₃C₂T_X and Ti₂CT_X, compared with the MAX phases of Ti₃AlC₂ and Ti₂AlC, respectively. SEM images of the synthesized (c) Ti₃C₂T_X and (d) Ti₂CT_X flakes, where the inset in (d) shows a magnified SEM image of Ti₂CT_X with nanoparticles on the surface.

Figure 2

XRD spectra of Ti₃C₂T_X and Ti₂CT_X heat-treated at different temperatures.

Figure 3

Cross-sectional SEM images of as-prepared (a) Ti₃C₂T_X, (e) Ti₂CT_X films, (b–d) Ti₃C₂T_X and (f–h) Ti₂CT_X films heat-treated at 100, 200, and 300 °C, respectively (from left to right). The scale bar is 1 μm.

Figure 4

(a,b) Plots of thickness and sheet resistance values of Ti₃C₂T_X and Ti₂CT_X films heat-treated at different temperatures, respectively. (c,d) Conductivities of Ti₃C₂T_X and Ti₂CT_X films calculated using the thickness and sheet resistivity values in (a) and (b), respectively.

Figure 5

(a) XPS survey spectra of Ti₃C₂T_X and Ti₂CT_X. (b,c) High-resolution XPS spectra scanned over Ti 2p, C 1s, and O 1s of Ti₃C₂T_X and Ti₂CT_X films, respectively, before heat treatment.

Figure 6

Histograms showing the percentage changes in the (a) Ti, (b) C, and (c) O bonding states in the Ti₃C₂T_X and Ti₂CT_X films as the heat treatment temperature increased.

Figure 7

(a,b) Measured EMI SE_T, SE_A, and SE_R values for Ti₃C₂T_X and Ti₂CT_X films, compared to values calculated using transfer matrix method. (c) Power coefficients, R, A, and T, of Ti₃C₂T_X and Ti₂CT_X films. (d) Schematic illustrating the multiple reflections of electromagnetic waves with and without pores inside a material.

Figure 8

EMI SE values normalized to thickness: (a) SE_T/t, (b) SE_R/t, and (c) SE_A/t of Ti₃C₂T_X films heat-treated at different temperatures.

Figure 9

Total EMI SE values of (a) Ti₃C₂T_X and (b) Ti₂CT_X films heat-treated at different temperatures in THz frequency range.