Nano-engineering and nano-manufacturing in 2D materials: marvels of nanotechnology

Bridging Nanomanufacturing and Artificial Intelligence-A Comprehensive Review

Nanomanufacturing and digital manufacturing (DM) are defining the forefront of the fourth industrial revolution-Industry 4.0-as enabling technologies for the processing of materials spanning several length scales. This review delineates the evolution of nanomaterials and nanomanufacturing in the digital age for applications in medicine, robotics, sensory technology, semiconductors, and consumer electronics. The incorporation of artificial intelligence (AI) tools to explore nanomaterial synthesis, optimize nanomanufacturing processes, and aid high-fidelity nanoscale characterization is discussed. This paper elaborates on different machine-learning and deep-learning algorithms for analyzing nanoscale images, designing nanomaterials, and nano quality assurance. The challenges associated with the application of machine- and deep-learning models to achieve robust and accurate predictions are outlined. The prospects of incorporating sophisticated AI algorithms such as reinforced learning, explainable artificial intelligence (XAI), big data analytics for material synthesis, manufacturing process innovation, and nanosystem integration are discussed.

Twisted van der Waals Quantum Materials: Fundamentals, Tunability, and Applications

Twisted van der Waals (vdW) quantum materials have emerged as a rapidly developing field of two-dimensional (2D) semiconductors. These materials establish a new central research area and provide a promising platform for studying quantum phenomena and investigating the engineering of novel optoelectronic properties such as single photon emission, nonlinear optical response, magnon physics, and topological superconductivity. These captivating electronic and optical properties result from, and can be tailored by, the interlayer coupling using moiré patterns formed by vertically stacking atomic layers with controlled angle misorientation or lattice mismatch. Their outstanding properties and the high degree of tunability position them as compelling building blocks for both compact quantum-enabled devices and classical optoelectronics. This paper offers a comprehensive review of recent advancements in the understanding and manipulation of twisted van der Waals structures and presents a survey of the state-of-the-art research on moiré superlattices, encompassing interdisciplinary interests. It delves into fundamental theories, synthesis and fabrication, and visualization techniques, and the wide range of novel physical phenomena exhibited by these structures, with a focus on their potential for practical device integration in applications ranging from quantum information to biosensors, and including classical optoelectronics such as modulators, light emitting diodes, lasers, and photodetectors. It highlights the unique ability of moiré superlattices to connect multiple disciplines, covering chemistry, electronics, optics, photonics, magnetism, topological and quantum physics. This comprehensive review provides a valuable resource for researchers interested in moiré superlattices, shedding light on their fundamental characteristics and their potential for transformative applications in various fields.

Advancing piezoelectric 2D nanomaterials for applications in drug delivery systems and therapeutic approaches

Precision drug delivery and multimodal synergistic therapy are crucial in treating diverse ailments, such as cancer, tissue damage, and degenerative diseases. Electrodes that emit electric pulses have proven effective in enhancing molecule release and permeability in drug delivery systems. Moreover, the physiological electrical microenvironment plays a vital role in regulating biological functions and triggering action potentials in neural and muscular tissues. Due to their unique noncentrosymmetric structures, many 2D materials exhibit outstanding piezoelectric performance, generating positive and negative charges under mechanical forces. This ability facilitates precise drug targeting and ensures high stimulus responsiveness, thereby controlling cellular destinies. Additionally, the abundant active sites within piezoelectric 2D materials facilitate efficient catalysis through piezochemical coupling, offering multimodal synergistic therapeutic strategies. However, the full potential of piezoelectric 2D nanomaterials in drug delivery system design remains underexplored due to research gaps. In this context, the current applications of piezoelectric 2D materials in disease management are summarized in this review, and the development of drug delivery systems influenced by these materials is forecast.

MXene and Xene: promising frontier beyond graphene in tissue engineering and regenerative medicine

The emergence of 2D nanomaterials (2D NMs), which was initiated by the isolation of graphene (G) in 2004, revolutionized various biomedical applications, including bioimaging and -sensing, drug delivery, and tissue engineering, owing to their unique physicochemical and biological properties. Building on the success of G, a novel class of monoelemental 2D NMs, known as Xenes, has recently emerged, offering distinct advantages in the fields of tissue engineering and regenerative medicine. In this review, we focus on the comparison of G and Xene materials for use in fabricating tissue engineering scaffolds. After a brief introduction to the basic physicochemical properties of these materials, recent representative studies are classified in terms of the engineered tissue, i.e., bone, cartilage, neural, muscle, and skin tissues. We analyze several methods of improving the clinical potential of Xene-laden scaffolds using state-of-the-art fabrication technologies and innovative biomaterials. Despite the considerable advantages of Xene materials, critical concerns, such as biocompatibility, biodistribution and regulatory challenges, should be considered. This review and collaborative efforts should advance the field of Xene-based tissue engineering and enable innovative, effective solutions for use in future tissue regeneration.

Enhanced interactions of excitonic complexes in free-standing WS2

Excitonic complexes, bound states of electrons and holes, provide a promising platform in monolayer transition-metal dichalcogenide (TMDC) semiconductors for investigating diverse many-body interaction phenomena. The surrounding dielectric environment has been found to strongly influence the excitonic properties of the TMDC monolayers. While the impact of different dielectric surroundings on two-dimensional semiconductor materials and their strong correlations have been well studied, the effects on exciton formation and its properties resulting from a further reduction in dielectric screening remain elusive. In this study, we examined free-standing tungsten disulfide (WS2) monolayers, where the efficient generation of higher-order correlated excitonic complexes is readily observed. This phenomenon arises from the effective mutual interactions among excitons and internal carriers, attributed to the modulated exciton dynamics generated by the further reduced dielectric screening effect in the freestanding structure. The formation efficiency of excitonic complexes is enhanced and the multiple biexciton species (five particles such as charged biexcitons and acceptor/donor-bound biexcitons) are successfully induced under low excitation intensity and moderate temperature conditions. Our findings offer valuable insights into the influence of the dielectric environment on exciton interactions and enable a productive avenue for exploring fundamental many-body interactions, providing new possibilities for dielectric engineering of atomic thin semiconductors.

Laser-Synthesized 2D-MoS2 Nanostructured Photoconductors

The direct laser synthesis of periodically nanostructured 2D transition metal dichalcogenide (2D-TMD) films, from single source precursors, is presented here. Laser synthesis of MoS₂ and WS₂ tracks is achieved by localized thermal dissociation of Mo and W thiosalts, caused by the strong absorption of continuous wave (c.w.) visible laser radiation by the precursor film. Moreover, within a range of irradiation conditions we have observed occurrence of 1D and 2D spontaneous periodic modulation in the thickness of the laser-synthesized TMD films, which in some cases is so extreme that it results in the formation of isolated nanoribbons with a width of ~200 nm and a length of several micrometers. The formation of these nanostructures is attributed to the effect that is known as laser-induced periodic surface structures (LIPSS), which is caused by self-organized modulation of the incident laser intensity distribution due to optical feedback from surface roughness. We have fabricated two terminal photoconductive detectors based on nanostructured and continuous films and we show that the nanostructured TMD films exhibit enhanced photo-response, with photocurrent yield increased by three orders of magnitude as compared to their continuous counterparts.

Extraordinary Phonon Displacement and Giant Resonance Raman Enhancement in WSe2/WS2 Moiré Heterostructures

Twisted van der Waals heterostructures are known to induce surprisingly diverse and intriguing phenomena, such as correlated electronic phase and unconventional optical properties. This can be realized by controlled rotation of adjacent atomic planes, which provides an uncommon way to manipulate inelastic light-matter interactions. Here, we discover an extraordinary blue shift of 5-6 wavenumbers for high-frequency phonon modes in WS₂/WSe₂ twisted heterobilayers, captured meticulously using Raman spectroscopy. Phonon spectra displace rapidly over a subtle change in interlayer twist angle owing to heterostrain and atomic reconstruction from the Moiré pattern. First-order linear coefficients of the phonon modes in twisted heterostructures are further found to increase largely compared to their monolayer counterpart and vary immensely with the twist angle. Exceptional and extravagant enhancement of up to 50-fold is observed in the Raman vibrational intensity at a specific twist angle; this is largely influenced by the resonance process derived from a simple critical twist angle model. In addition, we depict how the resonance can be modulated by changing the thermal conditions and also the stacking angle. Therefore, our work further highlights the twist-driven phonon dynamics in pristine two-dimensional heterostructures, adding vital insight into Moiré physics and promoting comprehensive understanding of structural and optical properties in Moiré superlattices.

Extraordinary Nonlinear Optical Interaction from Strained Nanostructures in van der Waals CuInP2S6

Local strain engineering and structural modification of 2D materials furnish benevolent control over their optoelectronic properties and provide an exciting approach to tune light-matter interaction in layered materials. Application of strain at the nanoscale is typically obtained through permanently deformed nanostructures such as nanowrinkles, which yield large band gap modulation, photoluminescence enhancement, and surface potential. Ultrathin transition metal dichalcogenides (TMDs) have been greatly analyzed for such purposes. Herein, we extend strain-induced nanoengineering to an emerging 2D material, CuInP₂S₆ (CIPS), and visualize extraordinary control over nonlinear light-matter interaction. Wrinkle nanostructures exhibit ∼160-fold enhancement in second harmonic generation (SHG) compared to unstrained regions, which is additionally influenced by a change in the dielectric environment. The SHG enhancement was significantly modulated by the percentage of applied strain which was numerically estimated. Furthermore, polarization-dependent SHG revealed quenching and enhancement in the parallel and perpendicular directions, respectively, due to the direction of the compressive vector. Our work provides an important advancement in controlling optoelectronic properties beyond TMDs for imminent applications in flexible electronics.