Is Molybdenum Disulfide (MoS2) a Serious Rival to Graphene?

Two-dimensional (2D) materials such as molybdenum disulfide (MoS₂) and graphene have become prominent in materials science due to their unique properties and potential applications, particularly in the semiconductor and energy sectors. These materials are increasingly considered alternatives to conventional substances in various industries.

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The appeal of 2D materials lies in their high surface area, notable photocatalytic properties, and ability to conduct electricity, which makes them suitable for applications in nano-electronics and optoelectronics. In addition to graphene and MoS₂, the family of 2D materials includes transition metal dichalcogenides (TMDs) like tungsten disulfide (WS₂), tungsten diselenide (WSe₂), and molybdenum diselenide (MoSe₂), which offer useful mechanical, optical, and electrical characteristics.¹

Other materials are also being explored. Borophene, a monolayer boron allotrope, is being studied for its superconducting, thermal, and elastic properties, while phosphorene, derived from black phosphorus, has shown promise in applications such as sensors, supercapacitors, and biomedical devices.^2,3 These materials are also being evaluated for their role in energy storage systems, including lithium-ion batteries.

As research progresses, graphene and MoS₂ remain central to the development of 2D materials, each offering distinct advantages. This article examines how MoS₂ compares to graphene, exploring whether it should be viewed as a rival or a complementary material and considering the broader developments in the field of 2D materials.

Applications of MoS₂

Nanoelectronics

Due to its semiconducting properties and tunable band gap, MoS₂ has demonstrated significant potential in nanoelectronics, sensors, and biomedical fields.

For example, MoS₂ monolayers have exhibited strong performance in 5 nm electronic devices. These applications include 2D MoS₂-based field-effect transistors, which are used to develop operational amplifiers with an open-loop gain of approximately 36 dB at low frequencies. Additionally, modern MoS₂ photodetectors exhibit high efficiency, eliminating the need for complex fabrication methods.⁴

Flexible Electronics

MoS₂ has become a key material for flexible electronics thanks to its mechanical properties and electronic versatility. Historically, the growth of MoS₂ in rigid substrates posed challenges for its use in flexible applications.

However, recent advancements have enabled the development of high-quality MoS₂ monolayers on ultrathin, flexible glass substrates with thicknesses below 40 µm. Chemical vapor deposition is now a preferred method for synthesizing MoS₂ for these applications, achieving optimized mobility of 9.1 cm² V⁻¹ s⁻¹.⁵

These developments have reduced energy consumption and improved the performance of flexible devices, making MoS₂ suitable for applications in flexible superconductors and electronics.

Energy Storage

MoS₂ has transformed the energy storage landscape, offering innovative solutions alongside graphene. For example, MoS₂-based core-shell structures optimize energy performance by combining a functional core with a protective shell. These structures enhance the electrochemical and catalytic properties of MoS₂, making it a viable material for lithium-ion batteries, supercapacitors, and hydrogen evolution reactions.

Additionally, MoS₂ nanocomposites paired with carbon and transition metal oxides are gaining traction for energy storage and conversion technologies.⁶

Biomedical Applications

MoS₂ has shown potential in the biomedical field due to its biocompatibility and strong binding energy with biomolecules. MoS₂-based nanostructures have been investigated for their ability to enhance drug delivery, refine bio-imaging techniques, support the development of sensitive biosensors, and enable advancements in photo-thermal therapy.⁷

The Direct Band Gap Advantage of MoS₂

Graphene has long been celebrated for its electrical conductivity and mechanical strength, but its lack of a natural band gap limits its use in optoelectronics and low-power digital devices. In contrast, MoS₂ offers a distinct advantage due to its direct band gap of 1.8 eV in its monolayer form, compared to its bulk indirect band gap of 1.2 eV. This feature allows MoS₂ to efficiently absorb and emit light, making it a superior material for photodetectors, LEDs, and solar cells.

Researchers have shown that varying the size of MoS₂ nanoparticles can adjust their electrical properties for applications such as optical sensors. The synthesis of heterojunction layer structures that combine MoS₂ with HfO₂ has demonstrated its applicability in nanoscale field-effect transistors. Additionally, strain engineering in monolayer MoS₂ enables controlled modification of band gaps and photoluminescence, making it suitable for use in solar cell technologies.⁸

Integrating MoS₂ and Graphene: Hybrid Systems

Rather than replacing graphene, MoS₂ often complements it in hybrid systems, combining the strengths of both materials for improved performance in various applications.

A notable example is the use of direct ink writing (DIW) to fabricate 3D catalytic electrodes. Hybrid MoS₂-graphene aerogels demonstrate a superior active surface area and sustain electric current over a range of 100 mA in acidic mediums. Additionally, these aerogels exhibit lower degradation of active surface area with repeated use compared to traditional materials.⁹

MoS₂ nanoparticles integrated with 2D graphene sheets have been utilized to develop highly sensitive and efficient sensors. For instance, hybrid sensors for LPG gas detection achieve a sensitivity of 12.2 % and a response time of 12 seconds.¹⁰

Similarly, humidity sensors based on MoS₂ and graphene perform reliably across a relative humidity range of 20–95 %, achieving a recovery time of 6.6 seconds. These sensors are also highly stable and exhibit repeatability under variable conditions.¹¹

In biomedical applications, MoS₂-graphene hybrids are employed in biosensors for glucose detection, demonstrating the versatility of these composites for diverse applications.

The Commercialization of MoS₂

The commercial viability of MoS₂ continues to grow, particularly in the semiconductor industry. Researchers at the Korea Advanced Institute of Science and Technology (KAIST) have developed a sub-nanometer chip using ambipolar MoS₂. This material efficiently transports both positive and negative charges, enabling it to function as both a transistor and a photodetector.

Companies like Samsung Electronics and Taiwan Semiconductor Manufacturing Corporation are incorporating MoS₂ into next-generation 3 nm chips for optoelectronics.¹²

MoS₂ has also been investigated for its potential in in-memory computing, particularly in addressing the need for high-density, low-power computation in on-device AI-memory processing.

Conventional chip manufacturing methods face challenges in meeting these requirements, but researchers have proposed a concept integrating a multilevel, high gate-coupling ratio memory device with a MoS₂ channel. This design enables high-density 3D NAND Flash-based in-memory computing.¹³

The MoS₂ channel in these devices has demonstrated a reliable memory window of approximately 8 V. Simulations involving these MoS₂-based memory devices in AI systems have shown an accuracy of 95.8 % during testing.¹³ These findings indicate that MoS₂ could support advancements in in-memory computing and contribute to the development of more efficient AI-integrated systems.

Conclusion: Rival or Complement?

The question of whether MoS₂ is a serious rival to graphene depends on the context. While MoS₂ surpasses graphene in optoelectronic applications due to its direct band gap and excels in energy storage and flexible electronics, graphene remains unparalleled in electrical conductivity and thermal management. Rather than viewing them as competitors, their strengths often complement each other, as demonstrated by the success of hybrid MoS₂-graphene systems.

MoS₂ continues to face challenges such as scalability and stability under extreme conditions. However, recent advancements in synthesis methods and material integration are helping to address these issues. In the future, MoS₂ will likely play a vital role alongside graphene in modern electronics, energy solutions, and biomedical technologies.

References and Further Reading

1. Alam, S., et. al. (2021). Synthesis of emerging two-dimensional (2D) materials–Advances, challenges and prospects, FlatChem. https://doi.org/10.1016/j.flatc.2021.100305
2. Bhavyashree, M., et. al. (2022). Exploring the emerging applications of the advanced 2-dimensional material borophene with its unique properties. RSC advances. https://doi.org/10.1039/D2RA00677D
3. Idumah, C., et. al. (2023). Novel trends in phosphorene and phosphorene@polymeric nanoarchitectures and applications. emergent mater. https://doi.org/10.1007/s42247-023-00507-x
4. Samy, O., et. al. (2022). A Review on MoS2 Properties, Synthesis, Sensing Applications and Challenges. Crystals. https://doi.org/10.3390/cryst11040355
5. Hoang, A., et al. (2023). Low-temperature growth of MoS2 on polymer and thin glass substrates for flexible electronics. Nat. Nanotechnol. Available at: https://doi.org/10.1038/s41565-023-01460-w
6. Kour, P., et. al. (2023). MoS2-based core-shell nanostructures: Highly efficient materials for energy storage and conversion applications. Journal of Energy Storage. https://doi.org/10.1016/j.est.2023.107393
7. Bharti, S., et. al. (2024). Recent progress in MoS2 nanostructures for biomedical applications: Experimental and computational approach. Analytical Biochemistry. https://doi.org/10.1016/j.ab.2023.115404
8. Rai, D., et. al. (2021). Promising optoelectronic response of 2D monolayer MoS2: A first principles study. Chemical Physics. https://doi.org/10.1016/j.chemphys.2020.110824
9. Chandrasekaran, S., et. al. (2022). Three-dimensional printed MoS2/graphene aerogel electrodes for hydrogen evolution reactions. ACS Materials Au. https://doi.org/10.1021/acsmaterialsau.2c00014
10. Munusami, V., et. al. (2022). High sensitivity LPG and H2 gas sensing behavior of MoS2/graphene hybrid sensors prepared by facile hydrothermal method. Ceramics International. https://doi.org/10.1016/j.ceramint.2022.05.334
11. Li, X., et. al. (2022). A high-sensitivity MoS2/graphene oxide nanocomposite humidity sensor based on surface acoustic wave. Sensors and Actuators A: Physical. https://doi.org/10.1016/j.sna.2022.113573
12. Kyong, K., et. al. (2024). Korean scientists develop tech for sub-nanometer chip. [Online] UPI. Available at: https://www.upi.com/Science_News/2024/02/02/Korea-sub-nanometer-semiconductor-chip/2131706882192/ [Accessed on November 18, 2024].
13. Kim, Y., et. al. (2024). Low‐Power Charge Trap Flash Memory with MoS2 Channel for High‐Density In‐Memory Computing. Advanced Functional Materials. https://doi.org/10.1002/adfm.202405670

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