The realm of two-dimensional (2D) materials has witnessed transformative developments since the inception of graphene in 2004. The excitement surrounding these materials stems from their unique properties and potential applications across various technological domains. Researchers have theoretically predicted the existence of nearly 2,000 distinct 2D materials, with numerous entities synthesized in laboratories. Despite this prolific exploration, the majority of these materials are confined to van der Waals (vdW) layered structures, often limiting the diversity and functionality that could be achieved in advancing nano-scale engineering.
Efforts have been ongoing to create atomically thin 2D metals, representing a pivotal branch of research aimed at expanding the scope of 2D materials beyond the confines of vdW layers. The significance of these ultrathin metals is multifaceted, presenting opportunities to unveil novel physical phenomena and innovative device configurations. However, previous attempts have mostly faltered in presenting large-scale, pristine 2D metals at the desired atomically thin threshold. The challenges predominantly involve achieving precise structural integrity while maintaining the intrinsic properties vital for practical applications.
In a groundbreaking advancement, a group of researchers from the Institute of Physics (IOP) under the Chinese Academy of Sciences has unveiled a remarkable manufacturing technique referred to as vdW squeezing. This methodology represents a paradigm shift, allowing for the synthesis of 2D metals at an unprecedented angstrom-level thickness. The findings of this study were published in the prestigious journal Nature, signaling a key milestone in the field.
At the core of the vdW squeezing technique is an ingenious process whereby pure metals are subjected to high pressure and subsequently melted between two rigid vdW anvils. This innovative approach allows researchers to realize a diverse range of atomically thin 2D metals. Among the notable outputs of this method are bismuth (Bi) at an approximate thickness of 6.3 Å, tin (Sn) at around 5.8 Å, lead (Pb) measuring about 7.5 Å, indium (In) at 8.4 Å, and gallium (Ga) at a thickness of approximately 9.2 Å. The ability to generate such a variety of materials is instrumental in providing a comprehensive platform for further exploration.
The anvils themselves play a crucial role in facilitating the successful production of these 2D metals. Comprising two single-crystalline monolayers of MoS₂ that are epitaxially grown on sapphire, the attributes of the anvils ensure that the 2D metal produced possesses uniform thickness over significant areas, addressing a common issue faced in traditional synthesis techniques. Furthermore, the exceptional Young’s modulus of both sapphire and MoS₂, which is greater than 300 GPa, enables them to withstand extreme pressures. This physical endurance is pivotal in allowing the resultant 2D metals to achieve their angstrom-scale thickness, a characteristic essential for their future applications.
The innovative 2D metals fabricated via the vdW squeezing method are further stabilized by a complete encapsulation between the two MoS₂ monolayers. This encapsulation not only enhances environmental stability but also ensures that the interfaces remain non-bonded. Such a structural design is advantageous for device fabrication processes, as it opens up access to the intrinsic transport properties of these materials, properties that were previously unattainable due to stability and synthesis constraints.
The electrical and spectroscopic evaluations of monolayer bismuth exemplify the impressive physical characteristics exhibited by the synthesized 2D metals. These measurements have showcased significant enhancements in electrical conductivity, a pronounced field effect that aligns with p-type behavior, a notably large nonlinear Hall conductivity, and the emergence of new phonon modes—essential features for future applications in electronic devices and quantum systems.
One of the standout features of the vdW squeezing technique is its versatility. The method empowers researchers to not only synthesize an array of 2D metals but also to exercise atomic precision control over their thickness. By simply adjusting the squeezing pressure utilized during the manufacturing process, the synthesis can yield monolayers, bilayers, or trilayers of 2D metals. This capability permits the exploration of layer-dependent properties that previously evaded scientific inquiry, paving the way for new discoveries in material sciences.
Prof. ZHANG Guangyu, an esteemed author from IOP and a pivotal contributor to the research, has emphasized the implications of the vdW squeezing technique for the future landscape of material synthesis. According to Prof. Zhang, this technique offers an effective atomic-level method not just for creating 2D metal alloys but also for exploring amorphous and other non-vdW 2D compounds. His insights suggest a horizon brimming with possibilities for innovation in quantum, electronic, and photonic device fields.
With considerable potential for future investigation and application, the introduction of the vdW squeezing technique heralds a new chapter in the study of 2D materials. The ability to control the synthesis of these materials with acute precision opens avenues for researchers to tap into the unique properties of newly created 2D metals, driving forward both fundamental research and technological advancements. The explorations into these materials hold promise, potentially leading to a myriad of applications in next-generation electronic devices and beyond.
As the world plunges deeper into the age of nanotechnology, the advancements in the synthesis of 2D metals not only represent a scientific achievement but also illuminate the collective aspirations of innovation. With promising applications waiting at the threshold, the future of 2D materials shines brightly, supported by initiatives such as vdW squeezing that stretch our understanding of physics and materials science. Researchers and technologists alike will undoubtedly watch closely as this domain evolves and possibly reshapes our understanding of material capabilities and their uses in the real world.
The rapid pace at which science is uncovering the potential within 2D materials reflects a broader narrative of human curiosity and ingenuity. As multiple sides of scientific inquiry converge—fundamental physics, materials science, and practical engineering—the journey towards fully understanding and harnessing the power of these materials becomes not merely a goal but a shared ambition that encapsulates the essence of exploration and innovation.
Through meticulous research and the application of novel methodologies, the academic community is not merely observing a trend but rather participating in the evolution of a new scientific frontier, one that promises to unveil the mysteries of materials at the atomic scale and heralds a future filled with technological advancements and breakthroughs.
Subject of Research: 2D metals production using vdW squeezing technique
Article Title: Realization of 2D metals at the ångström thickness limit
News Publication Date: 12-Mar-2025
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