In the evolving landscape of two-dimensional materials, the synthesis and characterization of monolayer transition metal dichalcogenides (TMDs) have gained considerable attention. Among these, molybdenum disulfide (MoS₂) stands out due to its remarkable electronic properties that make it suitable for a myriad of applications ranging from transistors to sensors and energy storage devices. In a groundbreaking study, researchers have successfully employed chemical vapor deposition (CVD) to grow monolayer MoS₂, paving the way for potential advancements in nanotechnology and semiconductor applications. This intricate process involves the careful selection of precursors, heating elements, and specific environmental conditions to achieve high-quality material.
The synthesis of monolayer MoS₂ begins with the meticulous preparation of the precursors. In this instance, molybdenum trioxide (MoO₃) and sulfur serve as the primary components, facilitating the growth of MoS₂ during the CVD process. The researchers executed this step by distributing a precisely measured amount of MoO₃ powder within an alumina boat, strategically positioned at the center of a single-zone tube furnace. Complementing this setup was a SiO₂ substrate, which was treated with a sodium hydroxide (NaOH) promoter to enhance the growth process. The controlled environment further included the placement of sulfur powder in a separate alumina boat, carefully positioned 17 centimeters upstream, optimizing the reaction dynamics during synthesis.
Prior to initiating the growth phase, the tube furnace underwent a purging process to remove any impurities or contaminants. Here, nitrogen gas was introduced at a flow rate of 460 standard cubic centimeters per minute (s.c.c.m.) while the furnace was heated to a temperature of 150°C. Once the environment was purged, the nitrogen flow rate was reduced, establishing an ideal backdrop for the growth of MoS₂. The MoO₃ source was subsequently heated to an impressive 720°C, a critical temperature that allows the synthesis reactions to take place efficiently. Meanwhile, sulfur stabilized at a temperature of around 230°C, ensuring that the reaction remained active yet controlled, thus yielding high-quality monolayer MoS₂.
Upon completion of the growth phase, careful attention was paid to cooling the tube back down. To maintain the integrity of the synthesized material, the sulfur source was withdrawn from the heating zone, and the nitrogen gas flow was resumed at 460 s.c.c.m. This cooling protocol was instrumental in preserving the structural characteristics of MoS₂. For the transfer of this material to target substrates, the researchers employed a polydimethylsiloxane (PDMS) dry transfer technique. This method is crucial for ensuring the integrity of the material as it transitions from one substrate to another, marking a significant step in its practical deployment.
In addition to the monolayer MoS₂, the researchers also explored the characteristics of few-layered MoS₂ and tungsten diselenide (WSe₂) samples, which were obtained through mechanical exfoliation from bulk crystals. This process utilized the blue tape method, known for its simplicity and effectiveness in producing high-quality few-layer materials. The substrates designated for these transferred materials mirrored those used for the CVD-grown samples, thereby ensuring consistency across the experimental components.
The substrates themselves played a critical role in the overall study. The research team utilized boron degenerately doped silicon substrates, which were further enhanced with layers of thermally grown SiO₂, atomic-layer-deposition-grown hafnium oxide (HfO₂), and zirconium oxide (ZrO₂). Each of these dielectric materials presented unique electrical and structural properties essential for the successful integration of MoS₂ within electronic devices. Understanding the deposition conditions and characterizations of these dielectrics remains paramount, as they influence the performance and efficiency of the overall devices.
Moreover, to investigate the electronic properties and interface characteristics of the materials, soft and hard X-ray photoelectron spectroscopy (XPS) measurements were conducted. Utilizing the advanced capabilities at beamline I09 at the Diamond Light Source in the UK, the researchers collected detailed spectral information. This data enabled them to determine the elemental composition and electronic states present within the MoS₂ samples. Notably, the high-energy analyzer employed demonstrated precision, capturing spectra that were crucial for confirming the absence of sample charging and beam damage, thereby ensuring the reliability of their results.
The binding energy scale utilized during these measurements was calibrated against the gold 4f core level, lending credibility to the data acquired. A meticulous approach was taken, which included repeated acquisitions to substantiate the findings. This careful consideration of experimental conditions signifies the researchers’ commitment to achieving high-quality results, demonstrating best practices in the synthesis and characterization of 2D materials.
The theoretical framework underpinning this research involved first-principles density functional theory (DFT) calculations. Utilizing the QuantumATK package, researchers applied the hybrid functional of Heyd-Scuseria-Ernzerhof (HSE06) to understand the electronic interactions at the MoS₂/dielectric interfaces. The study focused on various interface models, including those involving HfO₂ and ZrO₂, enabling a comprehensive investigation into their potential as substrates for MoS₂ applications. The DFT calculations supported the experimental findings, corroborating the ideal lattice parameters and structural properties of the materials.
In constructing the interface models, researchers deployed supercell strategies to capture the nuances of the interactions between the 2D TMDs and the dielectric layers. Multiple configurations were tested to optimize the alignment of the lattices, ensuring minimal strain and maximizing the quality of the heterojunctions. The results of these calculations revealed vital insights into the nature of the interactions occurring at the interfaces, highlighting the significance of van der Waals forces in stabilizing the heterostructures.
More practically, the electrical measurements of the synthesized materials were conducted using a Keithley 4200 current-voltage system. The intricate characterization allowed for the assessment of material performance under various conditions, reflecting their potential for real-world applications. Furthermore, photoluminescence (PL) and Raman spectroscopy data collected using a focused laser revealed critical vibrational modes and electronic transitions within the MoS₂ layers, indicating their viability for optoelectronic devices.
In addressing the physical topography of the samples, Atomic Force Microscopy (AFM) data imagery was captured to reveal surface characteristics and layer thicknesses. Employing the Dimension Icon device in peak-force tapping mode provided insights into nanoscale features critical for device engineering. The culmination of these efforts has positioned this research at the forefront of material science, facilitating the design of cutting-edge electronic devices that may redefine industry standards.
Through meticulous research and breakthrough techniques in synthesis and characterization, this work lays the groundwork for understanding and leveraging the attributes of monolayer and few-layer MoS₂ in contemporary technology. The advancement of 2D materials not only emphasizes their unique electronic and optical properties but also enriches the realm of nanoscale engineering, heralding a promising future for advanced electronic devices.
Subject of Research: Synthesis and characterization of monolayer MoS₂ and few-layer TMDs for advanced electronic applications.
Article Title: A clean van der Waals interface between the high-k dielectric zirconium oxide and two-dimensional molybdenum disulfide.
Article References: Yan, H., Wang, Y., Li, Y. et al. A clean van der Waals interface between the high-k dielectric zirconium oxide and two-dimensional molybdenum disulfide.
Nat Electron (2025). https://doi.org/10.1038/s41928-025-01468-1
Image Credits: AI Generated
DOI: 10.1038/s41928-025-01468-1
Keywords: MoS₂, two-dimensional materials, van der Waals interfaces, CVD, XPS, DFT, semiconductor applications.
Tags: chemical vapor deposition techniquescontrolled environment in CVDelectronic properties of MoS₂high-quality material growthmolybdenum trioxide precursormonolayer transition metal dichalcogenidesnanotechnology advancementssemiconductor applications of TMDssodium hydroxide promoter effectssynthesis of MoS₂two-dimensional materials researchZirconium oxide interface
