Broadband ultrafast photoresponse CuS / MXene composite nonlinear optical material and preparation method and application thereof

Abstract

The invention belongs to the field of nonlinear optical materials, and discloses a broadband photoresponse CuS / MXene composite nonlinear optical material and a preparation method and application thereof. According to the preparation method, few-layer Mo2TiC2 MXene, copper chloride and sodium sulfide are used as reaction raw materials, an aqueous solution containing cetyltrimethylammonium chloride is used as a reaction solution, and the catalyst is prepared through a coprecipitation method. The obtained CuS / MXene composite nonlinear optical material is of a zero-dimensional / two-dimensional heterostructure and comprises few layers of Mo2TiC2 MXene and CuS nanoparticles loaded on the surface of the Mo2TiC2 MXene. The CuS / MXene composite material has the properties of stable structure, broadband optical absorption and ultrafast carrier response, shows an excellent broadband optical nonlinear effect, can be designed into an ultrahigh-speed, high-parallelism and low-loss broadband nonlinear photonic device, and has a wide application prospect in all-optical communication, photon calculation, quantum optics and the like.

Description

Technical Field

[0001] This invention belongs to the field of nonlinear optical composite materials and broadband photonic devices, specifically relating to a broadband optically responsive CuS / MXene composite nonlinear optical material, its preparation method, and its applications. Background Technology

[0002] Traditional optics relies on optical lenses to passively alter the propagation path of light fields. To achieve active and multifunctional manipulation of light fields, the optical nonlinear effects generated by the interaction of strong lasers with the medium offer an effective means. By avoiding inefficient photoelectric conversion, all-optical signals based on nonlinear optics can provide processing speeds far exceeding those of electronic devices, opening up new application areas such as optical communication, supercontinuum light sources, high-resolution optical microscopy, all-optical AC, quantum optics, and quantum information processing. In fact, high-performance and highly stable photonics applications depend on excellent nonlinear optical materials. However, existing nonlinear optical materials suffer from drawbacks such as low optical damage threshold, poor laser resistance, poor integration, and complex fabrication processes. Therefore, designing novel nonlinear optical materials is crucial for achieving high efficiency, high performance, and low cost in devices.

[0003] Two-dimensional materials, due to their controllable atomic thickness and layered structure, have been extensively studied, such as graphene, black phosphorus, transition metal dichalcogenides, hexagonal boron nitride, and MXene. The general formula for MXene is M... n+1 X n T x In this model, M represents a transition metal, X represents carbon, and T represents a surface terminating group. Due to their diverse composition, researchers have theoretically predicted over 100 types of MXenes and demonstrated their excellent physicochemical properties and material performance, such as broadband light absorption, high photothermal conversion efficiency, high electrical conductivity, ultrafast optics, and hydrophilicity. These properties hold promise as platform-type functional materials with unique advantages in multiple fields, including electronics, chemistry, and mechanics. Reports show that MXene films can achieve ultrafast carrier dynamics response and large light absorption capacity over a wide wavelength range, which is crucial for improving the efficiency of optical devices and designing photonic devices with broadband parallel and high-speed processing capabilities. Furthermore, the terminating groups (-OH, -O, -F, etc.) on the MXene surface can directly modulate the work function, band gap, hydrophilicity / hydrophobicity, and electrochemical activity of MXenes, clearly indicating that MXenes are ideal optical functional materials. In recent years, MXene materials (such as Ti3C2T) have been increasingly recognized for their potential applications. xMXenes have been widely studied and applied in electrochemical energy storage (such as lithium-ion batteries and supercapacitors) and photocatalysis (such as water splitting and CO2 reduction). However, exploration of their nonlinear optical properties (such as two-photon absorption, nonlinear refraction, and optical limiting effect) is relatively scarce, with few published reports and patents. Meanwhile, to further expand the performance and application range of MXenes, introducing functional molecules with different properties into the MXene system has become a key strategy. This strategy can synergistically utilize multiple functions, paving the way for the design and preparation of novel functional MXene-based nonlinear optical materials. Therefore, the development of functionalized MXene composite materials is very promising. Summary of the Invention The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a broadband optically responsive CuS / MXene composite nonlinear optical material, its preparation method and application.

[0004] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows: In a first aspect, the present invention provides a method for preparing a CuS / MXene composite nonlinear optical material, comprising the following steps: (1) Using Mo2TiAlC2 as raw material, hydrofluoric acid solution was added to carry out an intercalation reaction to remove the Al layer, resulting in Mo2TiC2T with the Al layer removed. x MXene (T) x (representing functional groups such as -OH and -F), and then exfoliated using tetrabutylammonium hydroxide to obtain few-layer Mo2TiC2MXene nanosheets; (2) Co-precipitation reaction of copper chloride, sodium sulfide and the Mo2TiC2MXene nanosheets was carried out in an aqueous solution containing hexadecyltrimethylammonium chloride. The sample after reaction was freeze-dried to obtain CuS / MXene composite powder. (3) The CuS / MXene composite powder is dispersed in a water-organic solvent mixture to form a dispersion, and a CuS / MXene composite film is formed by interfacial film formation method to obtain the CuS / MXene composite nonlinear optical material.

[0005] In the above preparation method, further, in step (1), the particle size of Mo2TiAlC2 is 400 mesh, the mass fraction of the hydrofluoric acid solution is >40%, and the ratio of the amount of Mo2TiAlC2, hydrofluoric acid solution and tetrabutylammonium hydroxide is 1.5~2.5 g∶18~22 mL∶28~32 mL.

[0006] Furthermore, in step (1), the intercalation reaction is carried out at 50~60℃ for 45~50 h; during the exfoliation process, the product of the intercalation reaction is first poured into an aqueous solution containing hexadecyltrimethylammonium chloride and stirred, then washed with ethanol 2~4 times, the lower precipitate is then added to deionized water, sonicated and centrifuged, and the upper suspension is collected to obtain a few layers of Mo2TiC2MXene nanosheets; the aqueous solution containing hexadecyltrimethylammonium chloride is obtained by mixing hexadecyltrimethylammonium chloride with a concentration of 25 wt% and deionized water at a volume ratio of 45~55 μL: 38~42 mL.

[0007] Furthermore, in step (2), the molar ratio of copper chloride to sodium sulfide is 1:1; the aqueous solution containing hexadecyltrimethylammonium chloride is obtained by mixing hexadecyltrimethylammonium chloride with a concentration of 25 wt% and deionized water at a volume ratio of 45~55 μL: 38~42 mL.

[0008] Furthermore, in step (2), the coprecipitation reaction is carried out in a water bath at 85~95℃ for 12~18 min. After the reaction, the mixture is cooled in ice water and then freeze-dried to obtain CuS / MXene composite powder.

[0009] Furthermore, in step (3), the organic solvent is toluene; in the water-organic solvent mixture, the volume ratio of water to organic solvent is 400:4~6.

[0010] Furthermore, in step (3), the specific operation of the interfacial film-forming method includes: pouring the dispersion into water, letting it stand, and after film formation, taking it out, drying it at room temperature to obtain a CuS / MXene composite film.

[0011] Existing MXenes (such as TiC2MXene) are typically limited by a single transition metal layer and a relatively fixed structure. Introducing a second metal (such as Mo) can directly alter the material's electronic density of states and Fermi level position, thus facilitating the tuning of material properties. Therefore, the core of this invention is: firstly, using a bimetallic Mo2TiC2MXene as the matrix, its ordered Mo / Ti atomic arrangement provides more easily customizable electronic structures and photoelectric properties. Simultaneously, existing composites of MXene with dopants such as sulfides (such as WS2, MoS2, SnS2, ZnS, and MnS) fail to provide an effective near-infrared optical window. This invention creatively proposes a composite scheme embedding MXene with a narrow-bandgap semiconductor CuS, which exhibits strong localized surface plasmon resonance. Through the synergistic effect of the two and effective interface charge transfer, broadband light absorption from the visible to near-infrared range is achieved. Therefore, this invention utilizes CuS / MXene composite materials to directionally enhance broadband third-order nonlinear optical performance, providing a technical foundation for constructing efficient, stable, and solution-processable MXene-based broadband nonlinear optical functional devices.

[0012] Secondly, this invention provides a broadband ultrafast optical response CuS / MXene composite nonlinear optical material. The CuS / MXene composite nonlinear optical material is a zero-dimensional / two-dimensional heterostructure comprising a few layers of Mo2TiC2MXene and CuS nanoparticles loaded on the two-dimensional surface of the Mo2TiC2MXene. This CuS / MXene composite nonlinear optical material constructs a zero-dimensional / two-dimensional heterostructure with significant interfacial interactions by combining near-infrared optically responsive copper sulfide nanoparticles (CuS) with Mo2TiC2MXene. This structure effectively modulates the electronic structure and optical properties of the material, thereby obtaining enhanced and tunable broadband ultrafast optical nonlinear characteristics. Based on this excellent property, the CuS / MXene composite material can be used to construct functional photonic devices and realize applications in the field of broadband optical information processing.

[0013] In the aforementioned CuS / MXene composite nonlinear optical material, the CuS nanoparticles have a particle size of 3.6 nm and are uniformly dispersed on the surface of Mo2TiC2MXene; the few-layered Mo2TiC2MXene has 4 to 5 atomic layers.

[0014] Thirdly, the present invention provides an application of CuS / MXene composite nonlinear optical material, which is used to fabricate broadband photonic devices.

[0015] The above-described application is characterized in that the operating wavelength of the broadband photonic device covers 400~1600 nm.

[0016] This material, through the composite of CuS with broadband optical response and Mo2TiC2MXene, constructs a zero-dimensional / two-dimensional heterostructure with significant interfacial interactions. This structure effectively modulates the electronic structure and optical properties of the material, thereby achieving enhanced and tunable broadband ultrafast optical nonlinear characteristics. Based on this superior property, the CuS / MXene composite material can be used to construct functional photonic devices, enabling applications in broadband optical information processing.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The CuS / MXene composite nonlinear optical material of the present invention constructs a heterostructure of CuS nanoparticles (zero-dimensional) and Mo2TiC2MXene (two-dimensional), and utilizes interfacial interactions to effectively control the electronic structure and optical properties of the material, enabling the composite material to exhibit excellent optical nonlinear response in a wide wavelength range of 400~1600 nm. This performance effectively solves the core defects of traditional nonlinear optical materials, such as narrow bandwidth, slow response and weak nonlinear effect, and can meet the dual requirements of broadband optical information processing for wide spectral coverage and ultrafast response.

[0018] 2. Compared to single Mo2TiC2MXene (which exhibits nonlinearity only in specific wavelength bands and is difficult to control due to its intrinsic electronic structure), this invention loads CuS nanoparticles onto the surface of Mo2TiC2MXene via co-precipitation, forming a heterostructure with strong interfacial interactions. The CuS / MXene composite material exhibits broadband light absorption from the visible to near-infrared bands. Simultaneously, the charge transfer between heterojunctions (XPS shows a negative shift of the Mo 3d peak and a positive shift of the S 2p peak) and the ultrafast carrier dynamics across the entire 440–700 nm wavelength band verify the ultrafast and broadband nonlinear optical response. This design overcomes the research limitations of Mo2TiC2MXene relying solely on intrinsic properties, providing a feasible path for the development of functionalized MXene-based nonlinear optical materials.

[0019] 3. The preparation methods of the present invention all use conventional laboratory equipment and do not require harsh conditions such as high vacuum, high temperature and high pressure.

[0020] 4. The CuS / MXene composite nonlinear optical material prepared by this invention has uniform film thickness and stable bonding with the substrate, and can be directly used for the fabrication and packaging of photonic devices. Compared with powdered nonlinear materials (which require additional molding processes and are prone to introducing defects), this film morphology can be integrated into optical routing systems without secondary processing and is compatible with the structures of existing optical communication, supercontinuum light sources and other devices. At the same time, the material's stable optical nonlinear response over a wide wavelength range (400~1600 nm) can cover the needs of multiple fields such as optical communication, biological imaging, and quantum optics, providing core material support for the development of multifunctional photonic devices (such as broadband optical switches and all-optical modulators). Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The images show scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the Mo2TiC2MXene, CuS, and CuS / MXene composite materials prepared in this invention. Figure a shows the SEM image of Mo2TiAlC2, and Figure b shows the SEM image of Mo2TiC2T... x SEM images, Figure c shows the stripped few-layer Mo2TiC2T x The SEM images are shown in Figure 1, with the inset showing the sheet thickness obtained by atomic force microscopy (AFM). Figure d shows the TEM image and particle size distribution of CuS nanoparticles, Figure e shows the TEM image of CuS / MXene, and Figure f shows the elemental mapping of CuS / MXene. Figure 2 XRD patterns of Mo2TiC2MXene, CuS, and CuS / MXene composite materials prepared in this invention; Figure 3 The UV-Vis absorption spectra of Mo2TiC2MXene, CuS, and CuS / MXene prepared in this invention are shown. Figure 4 The photoelectron spectra of the Mo2TiC2MXene and CuS / MXene composite materials prepared in this invention are shown in Figure a, where Figure a is the fine Mo 3d spectrum of CuS and CuS / MXene, and Figure b is the fine S 2s spectrum of CuS and CuS / MXene. Figure 5The images show the ultrafast transient absorption spectra of the Mo2TiC2MXene and CuS / MXene composite materials prepared in this invention. Figure a is a two-dimensional color-coded transient absorption spectrum of Mo2TiC2, Figure b is the transient absorption spectrum of Mo2TiC2, Figure c is the time-resolved spectrum of Mo2TiC2, Figure d is a two-dimensional color-coded transient absorption spectrum of CuS / MXene, Figure e is the transient absorption spectrum of CuS / MXene, and Figure f is the time-resolved spectrum of CuS / MXene. Figure 6 The figure shows the third-order optical nonlinear properties of the Mo2TiC2MXene composite material prepared in this invention. Figure ad shows the Z-scan test results of Mo2TiC2 and CuS / MXene at 400 nm, 532 nm, 800 nm and 1064 nm, respectively, and the solid line is the fitting result. Figure 7 The figure shows the third-order optical nonlinear properties of the CuS / MXene composite material prepared in this invention. Figure ad shows the closed-pore Z-scan test results of Mo2TiC2 and CuS / MXene at 400 nm, 532 nm, 800 nm and 1064 nm, respectively, and the solid line is the fitting result.

[0023] In all the attached figures, Mo2TiC2 is Mo2TiC2MXene, and Mo2TiC2-CuS is CuS / MXene. Detailed Implementation

[0024] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0025] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0026] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0027] The ultrafast nonlinear Z-scan test optical route consists of a femtosecond laser, a beam splitter, a focusing lens, an electrically driven displacement platform, and an optical power meter. The light source is a Chameleon Ti:sapphire femtosecond laser with an integrated optical parametric oscillator (OPO), covering a wavelength range of 340–1600 nm, a repetition rate of 80 MHz, a pulse width of 100 fs, a single-pulse energy of 12.5 nJ, and an average power of approximately 1 W. The femtosecond laser, with its tunable pulsed laser output from the additional OPO, enables the testing of broadband ultrafast optical nonlinear properties of CuS / MXene composite thin films.

[0028] The focal length of the focusing lens is 150 mm.

[0029] The electric displacement platform has a range of 100 mm and a minimum displacement distance of 2.5 μm. The sample is placed on the electric displacement platform and can move along the -Z to +Z direction. Its Z=0 position coincides with the focal point of the focusing lens.

[0030] The aforementioned optical power meter can record optical power in real time during the Z-scan process and has the following characteristics: a sampling rate of up to 250 kHz, a measurement resolution of up to 0.0004%, an accuracy controlled within ±0.2%, and supports a wide bandwidth measurement from 1 Hz to 250 kHz. Its detection wavelength covers the spectral range of 200–1800 nm, the probe can detect power in the range of 20 pW to 2 W, the photosensitive surface diameter is 8 mm, and the maximum energy measurement limit is 5 μJ.

[0031] The movement of the displacement platform and the data acquisition of the optical power probe are programmed in LabVIEW control software to achieve automated operation and recording.

[0032] Tetrabutylammonium hydroxide, molecular formula: C 16 H 37 NO, CAS No.: 2052-49-5.

[0033] Example: A broadband optically responsive CuS / MXene composite nonlinear optical material is disclosed, which is a zero-dimensional / two-dimensional heterostructure comprising a few layers of Mo2TiC2MXene and CuS nanoparticles supported on the two-dimensional surface of Mo2TiC2MXene. The CuS nanoparticles have a particle size of 3.6 nm and are uniformly dispersed on the surface of Mo2TiC2MXene; the few layers of Mo2TiC2MXene have 4 to 5 atomic layers.

[0034] The preparation method of this CuS / MXene composite nonlinear optical material includes the following steps: (1) Preparation of few-layer Mo2TiC2MXene nanosheets Pour 20 mL of hydrofluoric acid into the liner and place it in an oil bath. Secure the liner with clamps, start stirring, and minimize the noise of the magnetic stir bar rotation. Heat to a constant temperature of 55 °C. Weigh 2 g of 400-mesh molybdenum-titanium-aluminum carbide raw material and slowly add it to the liner. Continue heating for 48 h. After stopping heating, take 40 mL of deionized water using a graduated cylinder, pour 20 mL into the liner, and add the sample to two centrifuge tubes. You can use the remaining 20 mL to rinse the sample again and transfer it to the centrifuge tubes. During this process, you can see some white liner waste. Gently stir and remove it with a plastic spoon. Add deionized water to the sample solution in the centrifuge tube to 35 mL. After balancing, first shake the sample solution evenly with a shaker, centrifuge at 3500 rpm for 2 min, and repeat three times. This process is used to remove hydrofluoric acid. The precipitate is waste sample that has not been completely etched. The suspension is collected in a container, sealed with plastic wrap, and placed in a refrigerator for refrigeration. After it is completely frozen, it is then air-dried. 0.5 g of the cooled sample was poured into a glass bottle containing 30 mL of tetrabutylammonium hydroxide solution and stirred on a magnetic stirrer for 24 h. After stirring, the solution was washed three times with ethanol. The supernatant was the excess tetrabutylammonium hydroxide solution. The lower precipitate was added to deionized water and sonicated. The ultrasonic speed was set to 3500 rpm / h, and the ultrasonicated sample was centrifuged. After 1 h, the supernatant suspension was collected, which was a few layers of Mo2TiC2 nanosheets. The precipitate could be subjected to the above ultrasonic and centrifugation operations repeatedly for 3 times. The collected sample was purged with nitrogen for 10 min, then sealed and stored in a refrigerator for later use.

[0035] (2) Preparation of CuS nanoparticles and CuS / MXene composite powder Add 8.5 mg of copper chloride to 40 mL of water, then add 50 μL of hexadecyltrimethylammonium chloride; stir the mixture at room temperature for 30 min until all solids dissolve; add 12.1 mg of sodium sulfide and stir for 5 min; then add 5 mL of Mo2TiC2 nanosheet solution and transfer to a 90 ℃ water bath; after reacting for 15 min, rapidly cool in ice water to form green CuS nanoparticles; collect the obtained CuS solution and freeze-dry at -50 ℃, the resulting powder is used for the next step; the step of adding Mo2TiC2 nanosheet solution is removed to prepare individual CuS nanoparticles.

[0036] (3) Preparation of CuS / MXene composite thin films Dissolve 0.5 g of CuS / MXene mixed powder in 2 mL of deionized water. While stirring continuously, add 4-6 mL of toluene to the vial and stir vigorously for 20 min. Pour approximately 400 mL of deionized water into a 500 mL glass beaker. While vigorously stirring the deionized water, pour the well-stirred dispersion into the glass beaker. Fix the hydrophilically treated silica glass onto a glass rod and place it at the bottom of the glass beaker beforehand. Wait 20 min to allow the emulsion to separate and form an interfacial film. After the CuS / MXene composite is formed at the water-toluene interface, slowly lift the substrate to the top of the beaker while keeping its surface direction parallel to the interface. When the glass passes through the water-organic solvent interface, the CuS / MXene composite covers the glass. Separate the coated silica glass from the glass rod and dry it in air for 12 h to obtain the final product, the CuS / MXene composite film.

[0037] (4) Product characterization and performance testing Figure 1 The microstructure characterization results of each sample are presented. Figure 1 a and Figure 1 The images of the Mo2TiAlC2MAX phase and the multilayered MXene structure shown in Figure b confirm the transformation of both materials from bulk to two-dimensional phases. Because the etching process strips away Al atomic layers from the bulk material, the surface morphology becomes rougher and a preliminary layered structure forms, which can be observed in the SEM. Figure 1 As can be seen in c, the structure exhibits a transparent lamellar structure, indicating that the intercalating agent effectively transformed multilayered Mo2TiC2 into few-layered Mo2TiC2. CuS nanoparticles are shown... Figure 1 In image d, the CuS nanoparticles are uniformly distributed, with a particle size of approximately 3.6 nm. Figure 1 e and Figure 1 f represents the elemental mapping of the CuS / MXene composite material. The original image overlaps with the image containing Mo, Ti, Cu, and S elements, indicating that Mo2TiC2 and CuS are uniformly dispersed in the CuS / MXene composite material and that CuS is successfully bonded to the MXene surface.

[0038] Figure 2XRD results for Mo2TiC2, CuS, and CuS / MXene composites are presented. The XRD patterns of the original Mo2TiAlC2MAX phase show that 9.4°, 19.0°, 28.6°, and 61.8° correspond to the (002), (004), (006), and (110) diffraction peaks, respectively. On the one hand, after exfoliation, MXene changes from a bulk material structure to a layered structure, and the corresponding two-dimensional layered diffraction peaks are reflected in the enhancement of the low-angle diffraction peaks in the XRD, i.e., the (002) peak broadens and shifts to a lower angle (2θ from 9.8° to 6.1°). On the other hand, the strongest peak (104) of the MAX phase at 39.7° is significantly reduced, confirming the removal of Al atomic layers in the MAX phase. The fewer-layered Mo2TiC2 exhibits a more pronounced low-angle shift in the two-dimensional diffraction peaks compared to the multilayered Mo2TiC2, indicating that the layered properties of the intercalated Mo2TiC2 are more pronounced. The diffraction peaks of CuS are located at 2θ at 29.2, 31.7, 47.9, and 59.3°, corresponding to the (102), (103), (110), and (116) planes of the CuS standard card (JCPDS 06-0464). The XRD characteristic peaks of Mo2TiC2 and CuS appear in the CuS / MXene composite material, indicating the presence of CuS and Mo2TiC2 in the composite material. In addition, the (002) peak of MXene has a large shift angle (2θ changes from 5.9° for Mo2TiC2 to 6.9° for CuS / MXene), indicating a slight shrinkage in the interlayer spacing of the composite material.

[0039] Figure 3 The absorption spectra of Mo2TiC2, CuS, and CuS / MXene are shown. The CuS absorption spectrum exhibits a bimodal characteristic, with absorption peaks located in the visible short-wavelength region before 600 nm and in the visible long-wavelength to near-infrared transition region after 700 nm. This can be attributed to the electronic structure of the semiconductor CuS nanoparticles and the vibrational absorption of atoms in the crystal structure. The absorption in the visible light range originates from the band gap absorption of CuS. The vibrational absorption of atoms in the crystal lattice also contributes to the absorption spectrum, especially in the near-infrared band, where lattice vibrational absorption is significantly enhanced. In the 800 nm to near-infrared range, the absorption of CuS increases sharply with increasing wavelength, while the absorption of Mo2TiC2 decreases. CuS enhances the absorption of Mo2TiC2 from the visible to the near-infrared region, leading to increased absorption of the CuS / MXene composite material over a wide range (800-1300 nm).

[0040] Figure 4 Showing fine spectra of Mo2TiC2MXene, CuS, and CuS / MXene. Figure 4The characteristic peaks of Mo 3d spectral density of Mo2TiC2MXene in a were 229.4, 232.6, and 235.7 eV, respectively, which were attributed to the Mo-C bond (Mo... 4+ ) and Mo-O bond (Mo 5+ / Mo 6 + This may be due to partial oxidation of the material surface during preparation or testing. Compared with the XPS results of Mo2TiC2MXene, the Mo 3d peak of the CuS / MXene composite shifts towards a lower binding energy, indicating a chemical interaction and charge transfer between Mo2TiC2 and CuS in the composite, forming a heterojunction. In this heterostructure, electrons from Mo atoms in Mo2TiC2 transfer to CuS, resulting in a reduction in the effective positive charge of Mo and a lower electron binding energy, ultimately manifested as a negative shift of the Mo 3d peak. Furthermore, an additional peak at 226.7 eV appears in the CuS / MXene composite, which is attributed to CuS. The high-resolution XPS spectrum of S is shown below. Figure 4 As shown in b. The test results show 168.5 and 161.5 (S 2p). 3 / 2 ) and 162.6 eV (S 2p 1 / 2 The peak value of ) is attributed to the S of CuS, which is respectively. 4+ S 2 Binding energies at the two sites. XPS spectroscopy reveals a high-energy shift in the S 2p binding energy of the CuS / MXene composite compared to Mo2TiC2. This result also indicates a strong electronic interaction between S and Mo elements.

[0041] Figure 5 The ultrafast transient absorption spectra were used to investigate the ultrafast carrier dynamics of Mo2TiC2MXene and CuS / MXene composite films. A 343 nm laser pulse was selected as the pump light in the experiment to provide sufficient energy to excite ground-state particles to transfer to excited states. Figure 5 As shown in Figures a and 5d, the color two-dimensional plots of the ultrafast transient absorption spectra reveal time- and spectrally resolved transient absorption signals for both samples. The Mo2TiC2MXene spectrum of the Mo2TiC2MXene sample shows stimulated emission characteristics in the 440-530 nm range, while longer wavelengths exhibit excited-state absorption characteristics. However, the CuS / MXene composite film exhibits excited-state absorption behavior across the entire probe spectrum from 440-700 nm, with stimulated emission at shorter wavelengths suppressed by the doped CuS. Furthermore, the excited-state absorption signal in the transient absorption spectrum of the CuS / MXene composite material shows a symmetrical distribution, and its sidebands decrease more rapidly. Figure 5b and 5e recorded the transient absorption spectra at 1, 5, 10, 20, 50, and 100 ps. It can be clearly seen that the transient absorption spectra of both samples simultaneously show that the spectral results first increase and then decrease with increasing delay time, corresponding to the carrier excitation and relaxation processes. For example... Figure 5 As shown in c and 5f, the dynamic curves (450, 500, 550, 600, and 700 nm) of the two samples demonstrate a rapid carrier relaxation process. The results for the CuS / MXene composite material show a difference in spectral characteristics from Mo2TiC2 at 550 nm, exhibiting a broadband excited-state absorption signal. The suppression of excited-state absorption may be attributed to an energy transfer pathway between CuS and Mo2TiC2. When the probe wavelength is 530 nm, the appearance of stimulated emission features originates from energy transfer from Mo2TiC2 to CuS. Furthermore, a double exponential decay fit was performed on the broadband transient absorption spectra containing both excited-state absorption and stimulated emission features, revealing a fast response time of approximately 10 ps and a slow response time of approximately 100 ps for both samples.

[0042] Figure 6 Broadband open-aperture Z-scan measurements of Mo2TiC2MXene and CuS / MXene composite films are presented. The Z-scan optical path system was constructed using a femtosecond pulsed laser with an 800 nm fundamental frequency incident light, a single pulse energy of 12.5 nJ, a pulse bandwidth of 100 fs, and a repetition rate of 80 MHz. Integrating an optical parametric oscillator module into the laser extended the wavelength range to 340-1600 nm. The dots in the figure represent the experimental data, and the solid line represents the fitting results. The corresponding incident excitation intensities at four wavelengths (400, 532, 800, and 1064 nm) were 37, 56, 91, and 114 GW / cm², respectively. 2 Under laser intensities of 400 and 532 nm, the Mo2TiC2MXene sample exhibited symmetrical peak shapes. Figure 6 (a, 6b) This means that the sample exhibits typical saturated absorption characteristics under the test conditions; while showing symmetrical valley shapes at 800 and 1064 nm ( Figure 6 c, 6d), exhibiting typical anti-saturation absorption characteristics. This is because the Mo2TiC2MXene sample shows significant absorption before 800 nm, but the absorption weakens after 800 nm. Conversely, the CuS / MXene composite film exhibits consistent saturation absorption characteristics across a wide wavelength range, and the peak height or valley depth is more pronounced than that of the Mo2TiC2MXene sample. This also proves that there is an interaction between the two, which changes the original absorption properties and electronic states. Furthermore, based on beam propagation theory and approximate analysis of thin samples, the third-order optical nonlinear absorption coefficient of the CuS / MXene composite film is derived. βThe nonlinear absorption coefficients measured at wavelengths of 400, 532, 800, and 1064 nm were respectively 2.8×10 9 , 4.3×10 9 , 3.5×10 9 and 2.1×10 9 cm / W. Figure 7 The optical nonlinear refractive response of Mo₂TiC₂MXene and CuS / MXene composite films was characterized using a closed-aperture Z-scan method. The results show that both the Mo₂TiC₂MXene sample and the CuS / MXene composite film exhibit a valley-to-peak shape in the broadband Z-scan trajectory, indicating that both exhibit a self-focusing effect, i.e., positive nonlinear refractive index. In the curves obtained under the same incident intensity, the CuS / MXene composite film shows a larger peak-valley difference, indicating that the CuS / MXene composite film has a better optical nonlinear refractive response than the Mo₂TiC₂MXene sample. Furthermore, coefficient fitting was performed on the closed-aperture Z-scan results of the CuS / MXene composite film, and the fitting results for the nonlinear refractive index coefficients at wavelengths of 400, 532, 800, and 1064 nm are as follows: 1.9×10 8 , 3.4×10 8 , 4.3×10 8 and 2.7×10 8 m 2 / W.

[0043] In summary, the two-dimensional CuS / MXene composite thin film synthesized using this invention exhibits good crystallinity, structural stability, broadband optical absorption, and ultrafast carrier response. It demonstrates excellent broadband optical nonlinear effects and can be designed as a nonlinear photonic device with ultra-high speed, high parallelism, and low loss characteristics, showing broad application prospects in all-optical communication, photonic computing, and quantum optics.

Claims

1. A method for preparing a CuS / MXene composite nonlinear optical material, characterized in that, Includes the following steps: (1) Using Mo2TiAlC2 as raw material, hydrofluoric acid solution was added to carry out intercalation reaction to remove the Al layer, and then tetrabutylammonium hydroxide was used for exfoliation treatment to obtain Mo2TiC2 MXene nanosheets with few layers. (2) Co-precipitation reaction of copper chloride, sodium sulfide and the Mo2TiC2 MXene nanosheets was carried out in an aqueous solution containing hexadecyltrimethylammonium chloride. The sample after reaction was freeze-dried to obtain CuS / MXene composite powder. (3) The CuS / MXene composite powder is dispersed in a water-organic solvent mixture to form a dispersion, and a CuS / MXene composite film is formed by interfacial film formation method to obtain the CuS / MXene composite nonlinear optical material.

2. The preparation method according to claim 1, characterized in that, In step (1), the particle size of Mo2TiAlC2 is 400 mesh, the mass fraction of the hydrofluoric acid solution is >40%, and the ratio of the amount of Mo2TiAlC2, hydrofluoric acid solution and tetrabutylammonium hydroxide is 1.5~2.5 g∶18~22 mL∶28~32 mL.

3. The preparation method according to claim 1, characterized in that, In step (1), the intercalation reaction is carried out at 50~60℃ for 45~50 h; during the exfoliation process, the product of the intercalation reaction is first poured into an aqueous solution containing hexadecyltrimethylammonium chloride and stirred, then washed with ethanol 2~4 times, the lower precipitate is then added to deionized water, sonicated and centrifuged, and the upper suspension is collected to obtain a few layers of Mo2TiC2 MXene nanosheets; the aqueous solution containing hexadecyltrimethylammonium chloride is obtained by mixing hexadecyltrimethylammonium chloride with a concentration of 25 wt% and deionized water at a volume ratio of 45~55 μL: 38~42 mL.

4. The preparation method according to claim 1, characterized in that, In step (2), the molar ratio of copper chloride to sodium sulfide is 1:1; the aqueous solution containing hexadecyltrimethylammonium chloride is obtained by mixing hexadecyltrimethylammonium chloride with a concentration of 25 wt% and deionized water at a volume ratio of 45~55 μL: 38~42 mL.

5. The preparation method according to claim 1, characterized in that, In step (2), the coprecipitation reaction is carried out in a water bath at 85~95℃ for 12~18 min. After the reaction, the mixture is cooled in ice water and then freeze-dried to obtain CuS / MXene composite powder.

6. The preparation method according to claim 1, characterized in that, In step (3), the organic solvent is toluene; in the water-organic solvent mixture, the volume ratio of water to organic solvent is 400:4~6.

7. The preparation method according to claim 1, characterized in that, In step (3), the specific operation of the interfacial film formation method includes: pouring the dispersion into water, letting it stand, and after the film is formed, taking it out, drying it at room temperature, and obtaining a CuS / MXene composite film.

8. A broadband ultrafast optical response CuS / MXene composite nonlinear optical material obtained by the preparation method according to any one of claims 1 to 7, characterized in that, The CuS / MXene composite nonlinear optical material is a zero-dimensional / two-dimensional heterostructure containing a few layers of Mo2TiC2 MXene and CuS nanoparticles loaded on the two-dimensional surface of the Mo2TiC2 MXene.

9. The CuS / MXene composite nonlinear optical material according to claim 8, characterized in that, The CuS nanoparticles have a particle size of 3-4 nm and are uniformly dispersed on the surface of Mo2TiC2 MXene; the few-layered Mo2TiC2 MXene has 4-5 atomic layers.

10. An application of a CuS / MXene composite nonlinear optical material obtained by the preparation method according to any one of claims 1 to 7, or the CuS / MXene composite nonlinear optical material according to any one of claims 8 to 9, characterized in that, Broadband photonic devices were fabricated using the CuS / MXene composite nonlinear optical material described above.

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