Fabricating and examining nanocomposite of P₃HT- Graphene- MoS₂ by laser ablation method

Abstract

This study presents the first successful synthesis of a nanocomposite comprising Poly (3-hexylthiophene) (P₃HT), graphene (G), and molybdenum disulfide (MoS₂) via laser ablation, using a Q-switch Nd-YAG laser with a repetition rate of 1 (Hz) and different laser pulses of 200, 500, and 800 for both graphene and MoS₂, the morphological and optical properties of the samples was thoroughly investigated by various analytical techniques including Transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR), and spectrophotometer UV-Vis. Transmission electron microscopy showed that the graphene and molybdenum nanoparticles were semispherical or ball-shaped, with diameters ranging from 6.7 to 61.7 nm. The UV-Vis findings show that the absorbance and absorption coefficient increase with the number of pulses due to the increased concentration of nanoparticles. The FTIR results confirm strong bonding between the P₃HT-G_800P/MoS_{2 800P} nanocomposite bonds. The indirect energy gap of the Nanocomposite is estimated to be 1.99 (eV), making it attractive for optoelectronic applications.

Introduction

Nanotechnology has rapidly advanced, particularly in developing nanoscale fibers, tubes, rods, wires, and particles, garnered significant attention. To facilitate the manufacturing of these nanomaterials, research is necessary in related areas of molecular compounds. Nanoparticle technology aims to create products with unique physical and chemical properties primarily due to their nanometer scale. Due to its potential use in a number of fields, including catalysis, magnetic recording media, microelectronics, medicine, environmental pollution removal, sterilization, and viral suppression, metal oxide nanoparticles have attracted the attention of researchers [1].

The most intensively studied and developed nanocomposites at the moment are made of polymer-based nanomaterials. They offer numerous advantages due to their film-forming ability, activated functionalities, and dimensional variability, making them highly desirable materials [2].

Depending on whether they contain polymeric material, nanocomposite materials can be divided into different categories. Nonpolymer-based nanocomposites, also known as inorganic nanocomposites, are those in which the composition does not contain any polymers or components generated from polymers. Metal-based, ceramic-based, and ceramic-ceramic-based nanocomposites are further categories for nanocomposites. [3]. In our study, a nanocomposite material was produced using Poly(3-hexylthiophene) (P₃HT), graphene, and MoS₂.P₃HT is commonly used as a p-type donor material, but it has limitations, including a large energy band gap of 2.0 (eV) and a relatively higher HOMO energy level of 5.0 (eV). The properties of P₃HT, such as its large energy band gap and relatively higher HOMO energy level, limit its ability to efficiently absorb most solar radiation, particularly in the red and infrared regions. This is a significant factor contributing to the (P₃HT) lower efficiency in solar cells. The peak flux density of the solar spectrum occurs at approximately 700 (nm), which is equivalent to an energy of 1.7 (eV) [4].

The P₃HT with a molecular weight of 16 000 (g/mol) strikes a valuable balance between performance and processability for organic electronics applications due to its high regioregularity that promotes efficient charge transport and exciton dissociation. Chloroform, a common solvent for P3HT, allows for solution preparation for techniques like spin-coating and blending, facilitating the formation of uniform and well-organized P₃HT films upon solvent evaporation [5].

MoS₂ is a member of the family of layered transition-metal dichalcogenides (TMDCs) and is classified as a semiconductor. In recent years, MoS₂ has attracted considerable attention due to its exceptional physical and chemical properties [5]. This substance exhibits a high capacity for light absorption and is abundant, relatively inexpensive, and has an adjustable band gap. MoS₂ has a direct band gap of 1.8 (eV) [6], in single-layered form, compared to 1.2 (eV) [7, 8], in its bulk form, where it is an indirect semiconductor. Switchable transistors and photodetectors can be made thanks to this characteristic. The 2D layered structure of MoS₂ has unique optical electronic features that differ significantly from those in the bulk form [9, 10].

On the other hand, the Nanocomposite was prepared by laser ablation, as the laser ablation of solids in the liquid opened up unique perspectives for manufacturing top-down approach nanoparticles. The technique of rapid reactive quenching of ablated species at the plasma-liquid interface was first introduced by Fojtik et al. in 1993 and is a relatively new method. This promising technique allows for the controlled fabrication of nano-materials by producing high-quality nanoparticles without chemical reagents. The process involves the rapid quenching of ablated species at the interface between the plasma and a liquid, resulting in nanoparticles that are free from contaminants. The laser ablation process means using laser beam energy to remove part of the sample. Three major phases can be distinguished, as shown in Fig. 1. Evaporation, lighted plasma, and finally the creation of nanoparticles (NPs) are the results of laser ablation. A section of the target’s surface will fragment into electrons, ions, and molecules when a laser beam is focused on it [11]. A number of significant and important factors, such as the laser wavelength, pulse duration, and the interaction of individual nanoparticles (NPs) with the laser beam inside the liquid, affect how nanoparticles (NPs) behave [12]. During the initial stages of the nano-material creation process, a plasma is generated, and the liquid’s absorption and nonlinear effects are considered, especially in the case of femtosecond pulses or slightly absorbing liquids [13]. Nonetheless, introducing a liquid complicates the procedure in various ways. First, the liquid confines the plasma produced by the laser, significantly restricting its expansion. Secondly, the plasma’s rapid expansion and the liquid’s superheating can cause the formation of a shock wave and a bubble, which then serve as a medium for the plasma to expand into [14].

Materials and methods

Materials

The acquisition of high-quality materials is essential for any successful scientific research. We procured Graphite and Molybdenum Disulfide (MoS₂) targets of 99.99% purity, boasting a diameter of 2(cm) and a thickness of 4(mm), from the esteemed Shenzhen Rearth Technology Co. Limited in China. Additionally, we obtained P₃HT polymer powder with a molecular weight of 16 000 (g/mol) from the same reliable source. The Chloroform alcohol used in our experiments, which has a molecular weight of 119 (g/mol), was also procured from a trusted laboratory reagent in India and used without further purification. Our research is carried out with the highest degree of accuracy and reliability thanks to such thorough attention to detail. As a result, we can definitely claim that our findings are accurate and reliable. These findings will undoubtedly have a big impact on the development of science.

Synthesis of P₃HT—G/MoS₂ nanocomposite

The experimental procedure involved the synthesis of Nanocomposite using a meticulous and well-planned approach. Initially, 0.5 (mg) of Poly(3-hexylthiophene) (P₃HT) was dissolved in 40 ml of chloroform and using a magnetic stirrer for 30 min to obtain a polymer solution. Next, the Graphite and Molybdenum Disulfide (MoS₂) targets were washed with ethanol to ensure cleanliness.

Subsequently, a clean glass beaker was used to hold the graphite target, to which 5 (ml) of the P₃HT solution was added. Nd: YAG laser beam of wavelength 1064 (nm) and the energy per pulse (200 mJ), pulse duration 10 (ns), with several pulses at pulse repetition rate (PRR) of 1(Hz) was used to ablate the target. This resulted in the formation of a Nano solution colloidal of graphene particles. The MoS₂ target was then immersed in the colloidal graphene Nano solution and ablated using a laser beam with different pulses (500 and 800). The resulting nanocomposite were labeled as P₃HT—G_200P/MoS_{2 500P} and P₃HT—G_200P/MoS_{2 800P}.

The above process was repeated with the same parameters for graphite (500 and 800) pulse, and the MoS₂ target was placed in each sample of the colloidal nano-solution of graphene. The ablation was performed with an energy of 200 (mJ) and several pulses of 200 (pulse) for each sample, yielding the colloidal nanocomposites labeled as P₃HT—G_500P/MoS_{2 200P} and P₃HT—G_800P/MoS_{2 200P}. Moreover, the same approach was employed to prepare Nanocomposite with an equal number of pulses (200 and 800) pulse for graphite and MoS₂. The resulting colloidal nanocomposites were labeled P₃HT—G _200P/MoS_{2 200P} and P₃HT—G_800P/MoS_2800P. Overall, this study’s carefully designed experimental approach successfully synthesizes various colloidal nanocomposites with different laser ablation parameters, offering a significant contribution to Nanoscience and nanotechnology.

Characterization techniques

The nanocomposite thin films’ optical measurements are obtained using a spectrophotometer by Phillips (Japanese company) ‘Shimadzu UV-1650 PC’, in which the wavelength ranges between 200–900 nm. The optical properties are calculated from these optical measurements; FTIR spectroscopy of the Nanocomposite was tested with the Fourier Transform Infrared Spectrophotometer (Shimazdu, IRAffinity-1, Japan) in the 450–4000 (cm⁻¹) wave number range. Use the atomic force microscope (Model: TT-2) supplied by Angstrom. To determine the particle morphology of the prepared NPs and their statistical distribution.

Energy gap and absorption coefficient calculation

hν = the laser photon energy,

A = a constant,

N = band transition type constant.

Where A is the absorbance and t is the thickness.

Results and discussion

FTIR measurement

FTIR spectra of synthesized P₃HT-G/MoS₂ NP_S at different Laser pulses are illustrated in Fig. 2. The ablation of both the graphite target and MoS₂ was performed in chloroform solution at room temperature using an energy of 200 (mJ) and a wavelength of 1064 (nm) with several pulses of 800 (pulse). In the P₃HT spectrum, the C-H stretching is represented by peaks at 772, 1807, and 3394.80 (cm⁻¹) [20]. The MoS₂ spectrum shows bands at 667.90 and 772.29 (cm⁻¹) attributed to Mo–S stretching and S stretching, respectively [21]. The spectrum of G peaks at 1649.34 and 1695.42 (cm⁻¹), corresponding to C = C stretching [22]. In addition, the peaks at 232.97, 2852.44, and 2919.14 (cm⁻¹) in the MoS₂ and G spectra represent C-H stretching as show in Fig. 2a [23].

Figure 2b indicates that increasing the number of pulses of MoS₂ results in a stronger bond between (S) atoms due to the increase in force constant (K) and, thus, an increase in wavenumber. Furthermore, Fig. 2c shows a clear peak for the (C = C) bond, indicating increased graphene concentration in the composite material, specifically in P₃HT-G_200P/MoS_{2 500P}. In Fig. 2d, we observe characteristic peaks of all the bonds in P₃HT-G_800P/MoS_{2 800P} nanocomposite, indicating strong bonding and an increase in nanoparticle concentration for both MoS₂ and G. Overall, all the prepared nanocomposite exhibit characteristic peaks of P₃HT, MoS₂, and G in their spectra.

Atomic force microscopy measurements

The atomic force microscopy (AFM) technique was utilized to investigate the surface topography of (P₃HT—G/MoS₂) Nanocomposite fabricated on a p-type silicon wafer. The average pore diameter, roughness average (Ra), and root mean square (RMS) values were estimated and tabulated in Table 1. It is noteworthy from the table that the highest Ra, RMS, and average particle size were observed for the (P₃HT—G_800P/MoS_{2 800P}) sample, with values of 25.27, 20.98, and 100.7(nm), respectively. Conversely, the lowest values were recorded for the (P₃HT—G_200P/MoS_{2 200P}) sample, with values of 5.54, 4.116, and 52.77(nm) for Ra, RMS, and average particle size, respectively. Figure 3 illustrates 2D images of (P₃HT—G/MoS₂) samples prepared with varying laser pulses for graphite and MoS₂ are presented. The results indicate a significant change in the surface topography of the samples, which is attributed to an increase in the number of pulses for both graphite and MoS₂.

Transmission electron microscopy characteristics

The Fig. 4 presents transmission electron microscopy (TEM) images of the P₃HT-G/MoS₂ nanocomposite, revealing various regions with diameters ranging from 6.7 to 61.7 nm. The images indicate that the G and MoS₂ nanoparticles have a semispherical or ball shape, which is consistent with the findings of reference [24].

Some TEM images show that the nanoparticles coalesce to form a larger spherical particle. This phenomenon may result from several factors, including the small size of the particles and their interactions with the electron beam. When a sample is exposed to an electron beam in TEM, the electrons can interact with the atoms in the sample, causing changes in the morphology and structure of the sample. Furthermore, the projection of three-dimensional nanoparticles onto a two-dimensional image plane can cause nanoparticles that are very close to each other to appear as a single particle, even if they are not physically connected. On the other hand, some TEM images clearly exhibit the core-shell effect in the P₃HT-G/MoS₂ nanocomposite. These findings provide valuable insights into the morphological characteristics of the nanocomposite and can aid in the development of new nanocomposite materials with tailored properties.

Optical properties

Absorbance (A) and absorption coefficient (α)

The absorption the absorption edge of MoS₂ as in the Fig. 5 at (520) nm, and also notice the weak peak at (636) nm which same as report [25]. The absorption spectrum of the (P₃HT—G/MoS₂) nanocomposite has been studied for all samples prepared. Figure 6a, b, and c show that the absorbance peaks increase with an increase in the number of pulses for both graphite and MoS₂ targets, indicating an increase in the concentration of nanoparticles The highest absorption peak is 0.92 at the wavelength 303 nm for the sample P₃HT—G_800P/MoS_{2 800P}, and the lowest peak is 0.74 at the wavelength 277 nm for the sample P₃HT—G_200P/MoS_{2 200P}. Additionally, the AFM results confirmed a shift in both the absorption peaks of G NPs and MoS₂ NPs towards longer wavelengths, indicating an increase in particle size due to the quantum confinement effect, supported by previous research [26]. Table 2 displays the absorbance values and absorption coefficient for all prepared samples. The absorption coefficient spectra (α) for all the prepared films were determined using Equation (5). Notably, the absorption coefficient (α) value for all samples is less than 10⁴ (cm⁻¹), indicating an indirect energy gap.

Energy gap calculation

The photon energy (E_g) was calculated for MoS₂ nanoparticles as a function of (αhv)² as shown in Fig. 6a, where they were in the form of a colloidal suspension in chloroform solution. The energy band gap of the P₃HT—G/MoS₂ nanocomposite has been estimated through the use of Equation (3), where of (αhυ)² versus (hυ) was plotted. Figure 7b displays the energy gap values for all prepared samples. The indirect energy gap ranges from 2.2 (eV) for the sample P₃HT—G_200P/MoS_{2 200P} to 1.99 (eV) for the sample P₃HT—G_800P/MoS_{2 800P}, depending on the number of laser pulses used. On the other hand, as the number of pulses increases, the energy gap decreases due to displacement towards longer wavelengths. This is consistent with the results of the absorbance, which is attributed to an increase in the concentration of both G and MoS₂.

Conclusions

This study successfully prepared a ternary compound of P₃HT, G, and MoS₂ using the laser ablation method for the first time. Investigations were done into how the quantity of laser pulses affected the compound’s structural, morphological, and optical characteristics. The UV-Vis data showed that when the number of laser pulses increased, there was an increase in absorbance because of the higher concentration of nanoparticles and a shift towards longer wavelengths (redshift) because of the bigger nanoparticle size. The AFM result supported these findings. Moreover, the FT-IR results indicated a strong bonding between the bonds of the (P₃HT-G_800P/MoS_{2 800P}) nanocomposite, and the energy gap was estimated to be approximately 1.99 eV. This number is encouraging for optoelectronic applications since the molybdenum and graphene nanoparticles’ two-dimensional bonding provides excellent porosity and a good surface area for light absorption. Overall, this research advances our knowledge of the characteristics of P₃HT, G, and MoS₂ ternary compounds, which may find use in optoelectronics. The results obtained from this study provide valuable insights into the structural and optical properties of P₃HT-G/MoS₂ nanocomposite. The surface topography of the nanocomposite changed dramatically with an increase in the number of laser pulses, according to the AFM data. This was due to an increase in nanoparticle concentration. Overall, the findings of this study indicate that by varying the number of laser pulses utilized during production, it is possible to tailor the structural and optical characteristics of P₃HT-G/MoS₂ nanocomposite. The design and improvement of nanocomposite materials for use in a variety of applications, such as photovoltaics, sensing, and optoelectronics, may be affected by these discoveries. In order to maximize these materials’ qualities and explore their potential for use in real-world applications, more study is necessary.

Data availability

The data underlying this article will be shared on reasonable request to the corresponding author.

Authors’ contributions

Nagham M. Obaid (Investigation [equal], Resources [equal], Writing—original draft [equal], Amer Al-Nafiey (Investigation [equal], Supervision [equal], Writing—review & editing [equal]), Hassan A. Majeed (Formal analysis [equal]), and Ghaleb Ali Al-Dahash (Project administration [equal])

Conflict of interest statement: The authors declare no conflict of interest.

Funding

The authors have no competing financial interests to declare. This research was funded entirely by personal resources.

References