Allying nanophotonic structures with two-dimensional van der Waals materials

Photonic platforms with excellent nonlinear optical characteristics are very important to improve the devices' performance parameters such as integration, modulation speeds and working bandwidths for all-optical signal processing. The traditional processing technology of photonic platforms based on silicon, silicon nitride and silicon oxide is mature, but the nonlinear function of these optical platforms is limited due to the characteristics of materials; Although two-dimensional (2D) materials possess excellent nonlinear optical properties, their nonlinear potentials cannot be fully utilized because of their atomic layer thickness. Integrating 2D materials with mature photonic platforms can significantly improve the interaction between light and matter, give full play to the potentials of 2D materials in the field of nonlinear optics, and improve the nonlinear optical performances of the integrated platforms on the basis of fully utilizing the mature processing technology of the photonic platforms. Based on the above ideas, starting from the basic principle of nonlinear optics (Section 2), this review combs the research progress of various nonlinear photonic platforms (resonators, metasurfaces, optical fibers, on-chip waveguides, etc.) heterogeneously integrated with 2D materials, realized by traditional transfer methods (Section 3) and emerging direct-growth methods (Section 4) in recent years, and the introduction is divided into second-order and third-order nonlinearity. Comparing with the transfer methods, the advantages of using direct-growth methods to realize the heterogeneous integration of 2D materials and photonic platforms for the study of nonlinear optics are expounded, and the technical difficulties to be overcome in preparing the actual devices are also pointed. In the future, we can try to grow 2D materials directly onto the surfaces of various cavities to study the enhancement of second-order nonlinearity; we can also try to grow 2D materials directly onto the on-chip waveguides or microrings to study the enhancement of third-order nonlinearity. Generally speaking, the research on integrated nonlinearity by directly growing 2D materials onto various photonic structures has aroused great interest of researchers in this field. As time goes on, breakthrough progress will be made in this field, and technical problems such as continuous growth of high-quality 2D materials onto photonic structures and wafer-level large-scale preparation will be broken through, further improving the performance parameters of chips and laying a good foundation for optical communication, signal processing, optical sensing, all-optical computing, quantum technology and so on.

This chapter describes the prospects of integration of Two-dimensional (2D) materials with photonic nanostructures to enable future active nanophotonic devices. It focuses on development of controlling light emission from transition metal dichalcogenides (TMD) by nanophotonic integration. The monolayer form demonstrates a range of novel optical effects, including strong excitonic effects, photo-luminescence , valley polarisation, single-photon emission and second-harmonic generation, which show great potential for fabricating novel “flat” active nanophotonic devices in the future. Integration with photonic nanostructures is a solution to such challenges, since photonic nanostructures such as plasmonic nanoparticles show great capability to manipulate light–matter interaction at the nanoscale. A greater understanding of the coupling between photonic nanostructures and 2D materials is required, thus potentially better controlling the properties of these materials. For example, non-linear coupling between 2D materials, especially second-order non-linearity, has attracted intense interest. Dielectric nanostructures, such as photonic crystal cavities, have also been proposed for enhancing the emission from TMD monolayers.

Two-dimensional (2D) materials exhibit a number of improved mechanical, optical, and electronic properties compared to their bulk counterparts. The absence of dangling bonds in the cleaved surfaces of these materials allows combining different 2D materials into van der Waals heterostructures to fabricate p-n junctions, photodetectors, and 2D-2D ohmic contacts that show unexpected performances. These intriguing results are regularly summarized in comprehensive reviews. A strategy to tailor their properties even further and to observe novel quantum phenomena consists in the fabrication of superlattices whose unit cell is formed either by two dissimilar 2D materials or by a 2D material subjected to a periodic perturbation, each component contributing with different characteristics. Furthermore, in a 2D material-based superlattice, the interlayer interaction between the layers mediated by van der Waals forces constitutes a key parameter to tune the global properties of the superlattice. The above-mentioned factors reflect the potential to devise countless combinations of van der Waals 2D material-based superlattices. In the present feature article, we explain in detail the state-of-the-art of 2D material-based superlattices and describe the different methods to fabricate them, classified as vertical stacking, intercalation with atoms or molecules, moiré patterning, strain engineering and lithographic design. We also aim to highlight some of the specific applications of each type of superlattices.

Most optoelectronic characteristics of two-dimensional (2D) materials are associated with excitonic effects. Excitonic effects in 2D material have been intensively investigated, and various efforts to engineer exciton behavior in 2D materials have been reported for advanced nanophotonic and optoelectronic applications. Excitons in 2D semiconductors can be controlled by external stimuli, including mechanical, electrical, thermal, and magnetic stimuli. Mechanical stimuli applied to a 2D material can generate uniform or non-uniform deformation and strain gradient in the 2D lattice, which creates a strain-induced bandgap energy gradient in the 2D material. In an inhomogeneous bandgap energy gradient generated by a non-uniform strain gradient, excitons drift across the energy gradient. Exciton engineering in deformed 2D materials aims to control exciton movement by mechanical strain. In this snapshot review, we focus on exciton engineering in a mechanically deformed 2D material and their potential towards advanced optoelectronic and photonic applications.

The isolation of graphene has sparked an unprecedented world wide research activity on the topic of two-dimensional (2D) materials. However, even though graphene has a high potential for various applications, its metallic character is a significant limitation for a large variety of electron devices, starting with the conventional field effect transistor. This limitation could be overcome in the near future by the use of layered van der Waals crystals such as black phosphorus (i.e., phosphorene, which is one to few layers of black phosphorus) and also by other semiconducting 2D materials such as transition metal dichalcogenides (TMDCs) of general formula MX2, where M is the metal and X the chalcogen (S, Se and Te). For instance, phosphorene exhibits a direct band gap varying between ~ 0.3 eV for bulk crystals to ~ 2 eV for a monolayer. In layered TMDC structures, each layer typically comprises 3 atomic planes (corresponding to a thickness below 8 Å), and consists of an hexagonally-organized atomic layer of metal atoms sandwiched between two planes of chalcogen atoms, also in hexagonal configurations. M–X bonds inside each layer are covalent; however, the sandwiching chalcogen layers are linked by weak van der Waals bonds, so that a bulk crystal is easy to cleave along the chalcogen planes. As with phosphorene, most semiconducting TMDC materials also see their band gap increasing as thickness decreases and they switch from indirect to direct band gap for a monolayer. To date, the most studied semiconductor TMDCs are MoS2 and WS2. Because they are atomically thin, 2D materials are particularly well suited for flexible electronics applications. After a brief description of the major features of phosphorene and TMDCs (crystal structures, relevant electronic properties as a function of thickness …), the talk will highlight recent results concerning field effect transistor characteristics. In particular, carrier mobility values as high as 5000 cm2/Vs have been measured in phosphorene films. Since local substitutional-type doping cannot be used in 2D materials, there is a general contacting problem (Schottky barrier formation), which is of paramount importance for device applications. In particular, two types of contacts can be formed: the top contact and the edge contact, which behave differently. Generally speaking, the semiconductor thickness is much smaller than the depletion length at the contact, which is an intriguing and novel situation. In the second part of the talk, various synthesis methods will be presented and discussed, particularly in view of their possible use in the field of large area electronics. For most devices fabricated so far, the 2D layers were obtained by exfoliation of bulk crystals. However, recent progress in synthesis include molecular beam epitaxy, controlled chemical vapour deposition and vapour phase transport. Those various approaches will be discussed, as well as the newly-introduced atomic layer deposition (ALD) process. As most 2D materials are grown on a separate substrate, the transfer problem will be highlighted, particularly concerning phosphorene which is highly hygroscopic, and sensitive to the presence of light. The presentation will be concluded by some perspectives concerning the industrialization of 2D materials.

Abstract: Next-Gen Semiconductors: Quantum Dots, 2D Materials, and Spintronics for AI, 5G and Beyond offers a unified framework linking quantum‐scale phenomena to manufacturable devices and system performance. The book integrates three pillars—colloidal quantum dots for photonics and imaging, van der Waals (2D) materials for RF/logic/sensing, and spintronics/magnonics for non-volatile and wave-based compute—into heterogeneous packages that meet the latency, energy, and reliability targets of AI accelerators and 5G/6G front ends. We translate materials descriptors (bandgap, spin Hall angle, dielectric screening) into device metrics (PLQY, TMR, contact resistivity) and system KPIs (pJ/MAC, EVM/ACLR, J/bit, gCO₂e/GB). Beyond performance, the text embeds security (measured boot, PUFs, PQC agility), safety (reliability and failure containment), and sustainability (circular materials, repairability) as first-class requirements. Methods chapters specify metrology, ML-assisted TCAD, benchmark suites, and accreditation gates from pilot line to qualification. Case studies across Asia, Europe, the Americas, and Africa demonstrate repeatable paths from discovery to deployment. The result is a rigorous, end-to-end playbook for researchers, practitioners, and policymakers seeking to convert nanoscale innovation into trusted, low-carbon infrastructure for intelligent sensing, connectivity, and computation. Keywords: quantum dots, perovskite QDs, 2D materials, graphene, TMDCs, spintronics, SOT-MRAM, magnonics, van der Waals heterostructures, Si photonics, co-packaged optics, antenna-in-package, AI accelerators, 5G/6G RF, energy efficiency, reliability, hardware security, post-quantum cryptography, sustainability, circular electronics, ML-assisted TCAD

Layered two-dimensional (2D) materials interact primarily via van der Waals (vdW) bonding, which has created opportunities for heterostructures that are not constrained by epitaxial lattice matching [1]. However, since any passivated surface interacts with another via non-covalent forces, vdW heterostructures are not limited to 2D materials alone. In particular, 2D materials can be integrated with a diverse range of other materials, including those of different dimensionality, to form mixed-dimensional vdW heterostructures [2]. Furthermore, chemical functionalization allows tailoring of the properties of 2D materials and the degree of coupling across heterointerfaces [3]. In this talk, the prospects of mixed-dimensional heterostructures for quantum photonic science and technology will be discussed with a focus on how chemical functionalization can manipulate and enhance single-photon emission in strained 2D transition metal dichalcogenides [4]. In addition to technological implications, this talk will explore fundamental issues including band alignment, doping, trap states, and charge/energy transfer across heterointerfaces.[1] D. Lam, et al., ACS Nano, 16, 7144 (2022).[2] M. I. B. Utama, et al., MRS Bulletin, 48, 905 (2023).[3] S. H. Amsterdam, et al., J. Am. Chem. Soc., 143, 17153 (2021).[4] M. I. B. Utama, et al., Nature Communications, 14, 2193 (2023).

The rapid development and unique properties of two-dimensional (2D) materials, such as graphene, phosphorene and transition metal dichalcogenides enable them to become intriguing candidates for future optoelectronic applications. To maximize the potential of 2D material-based optoelectronics, various photonic structures are integrated to form photonic structure/2D material hybrid systems so that the device performance can be manipulated in controllable ways. Here, we first introduce the photocurrent-generation mechanisms of 2D material-based optoelectronics and their performance. We then offer an overview and evaluation of the state-of-the-art of hybrid systems, where 2D material optoelectronics are integrated with photonic structures, especially plasmonic nanostructures, photonic waveguides and crystals. By combining with those photonic structures, the performance of 2D material optoelectronics can be further enhanced, and on the other side, a high-performance modulator can be achieved by electrostatically tuning 2D materials. Finally, 2D material-based photodetector can also become an efficient probe to learn the light-matter interactions of photonic structures. Those hybrid systems combine the advantages of 2D materials and photonic structures, providing further capacity for high-performance optoelectronics.

Exploring the extraordinary optoelectronic properties of two‐dimensional (2D) materials to construct advanced optoelectronic devices is a major goal for academic researchers and industrialists. Emerging 2D Janus materials are the innovative class of 2D materials in which two sides are either asymmetrical functionalized or exposed to different environments. Distinctive features of Janus 2D materials such as tunable bandgaps, electronic structures, the presence of Rashba effects, excitonic effects, piezoelectric effects etc. make its magnificent candidates for optoelectronic devices. The van der Waals (vdWs) heterostructure with novel properties assembled by Janus 2D materials and low dimensional materials provides new opportunities and promising applications. This review aims to offer the recent advances in the Janus 2D materials and inside mechanism in 2D Janus vdWs heterostructure from an optoelectronics point of view. Here, the latest progress in the Janus 2D materials including their vdWs heterostructures from the perspective of theoretical prediction, and synthesis techniques is presented. The investigation of their physical optoelectronics properties and optoelectronic device applications is summarized. Finally, the future directions, challenges, and opportunities regarding the research process of Janus 2D materials and their vdWs heterostructure are discussed for designing promising optoelectronic devices.

Two-dimensional (2D) ferroelectric and magnetic van der Waals materials are emerging platforms for the discovery of novel cooperative quantum phenomena and development of energy-efficient logic and memory applications as well as neuromorphic and topological computing. This review presents a comprehensive survey of the rapidly growing 2D ferroic family from the synthesis perspective, including brief introductions to the top-down and bottom-up approaches for fabricating 2D ferroic flakes, thin films, and heterostructures as well as the important characterization techniques for assessing the sample properties. We also discuss the key challenges and future directions in the field, including scalable growth, property control, sample stability, and integration with other functional materials.

We investigate the interfacial transport of water and hydrophobic solutes on van der Waals bilayers and heterostructures formed by stacking graphene, hBN, and MoS2 using extensive ab initio molecular dynamics simulations. We compute water slippage and the diffusio-osmotic transport coefficient of hydrophobic particles at the interface by combining hydrodynamics and the theory of the hydrophobic effect. We find that slippage is dominated by the layer that is in direct contact with water and only marginally altered by the second layer, leading to a so-called "slip opacity". The screening of the lateral forces, where the liquid does not feel the forces coming from the second nearest layer, is one of the factors leading to the "slip opacity" in our systems. The diffusio-osmotic transport of small hydrophobes (with a radius below 2.5 Å) is also affected by the slip opacity, being dramatically enhanced by slippage. Furthermore, the direction of diffusio-osmotic flow is controlled by the solute size, with the flow in the opposite direction of the concentration gradient for smaller hydrophobes, and vice versa for larger ones. We connect our findings to the wetting properties of two-dimensional materials, and we propose that slippage and wetting can be controlled separately: whereas the slippage is mostly determined by the layer in closer proximity to water, wetting can be finely tuned by stacking different two-dimensional materials. Our study advances the computational design of two-dimensional materials and van der Waals heterostructures, enabling precise control over wetting and slippage properties for applications in coatings and water purification membranes.

The van der Waals gap of two-dimensional (2D) materials provides natural ion diffusion channels for lithium. However, individual 2D materials (such as graphene, ${\mathrm{MoS}}_{2}$, and MXene) cannot offer all the properties needed to maximize the performance for energy storage. Heterostructures, by stacking different 2D materials, are promising for combining the advantages and eliminating the disadvantages of individual 2D materials. ${\mathrm{MoS}}_{2}$-based heterostructures have been prepared for lithium storage, while intercalation and diffusion mechanisms have yet to be elucidated. In the current work, the heterointerface effects on lithium intercalation and diffusion of seven $H$- and distorted $T$ $(\mathit{dT})$-${\mathrm{MoS}}_{2}$-based heterostructures are systematically studied by density functional theory calculations, and highlight the atomistic origin of differences between $H$$(\mathit{dT})$-${\mathrm{MoS}}_{2}$/graphene, $H$$(\mathit{dT})$-${\mathrm{MoS}}_{2}/H$$(\mathit{dT})$-${\mathrm{MoS}}_{2}$, and $H$$(\mathit{dT})$-${\mathrm{MoS}}_{2}$/MXene hetero- and homostructures. From the energetic point of view, the heterointerface makes for an easier phase transition of ${\mathrm{MoS}}_{2}$ to the $\mathit{dT}$ phase in the ${\mathrm{MoS}}_{2}$/graphene heterostructure. Then we discuss the general idea of a rational design of the van der Waals gap for efficient lithium storage and diffusion. Our work opens a new avenue for optimizing the ion diffusion properties of 2D material heterostructures by designing the van der Waals channel for ion diffusion.

Precision and chip contamination-free placement of two-dimensional (2D) materials is expected to accelerate both the study of fundamental properties and novel device functionality. Current transfer methods of 2D materials onto an arbitrary substrate deploy wet chemistry and viscoelastic stamping. However, these methods produce a) significant cross contamination of the substrate due to the lack of spatial selectivity b) may not be compatible with chemically sensitive device structures, and c) are challenged with respect to spatial alignment. Here, we demonstrate a novel method of transferring 2D materials resembling the functionality known from printing; utilizing a combination of a sharp micro-stamper and viscoelastic polymer, we show precise placement of individual 2D materials resulting in vanishing cross contamination to the substrate. Our 2D printer-method results in an aerial cross contamination improvement of two to three orders of magnitude relative to state-of-the-art dry and direct transfer methods. Moreover, we find that the 2D material quality is preserved in this transfer method. Testing this 2D material printer on taped-out integrated Silicon photonic chips, we find that the micro-stamper stamping transfer does not physically harm the underneath Silicon nanophotonic structures such as waveguides or micro-ring resonators receiving the 2D material. Such accurate and substrate-benign transfer method for 2D materials could be industrialized for rapid device prototyping due to its high time-reduction, accuracy, and contamination-free process.

Two-dimensional (2D) materials have brought a spectacular revolution in fundamental research and industrial applications due to their unique physical properties of atomically thin thickness, strong light-matter interaction, unity valley polarization and enhanced many-body interactions. To fully explore their exotic physical properties and facilitate potential applications in electronics and optoelectronics, an effective and versatile characterization method is highly demanded. Among the many methods of characterization, optical second harmonic generation (SHG) has attracted broad attention because of its sensitivity, versatility and simplicity. The SHG technique is sufficiently sensitive at the atomic scale and therefore suitable for studies on 2D materials. More importantly, it has the capacity to acquire abundant information ranging from crystallographic, and electronic, to magnetic properties in various 2D materials due to its sensitivity to both spatial-inversion symmetry and time-reversal symmetry. These advantages accompanied by its characteristics of non-invasion and high throughput make SHG a powerful tool for 2D materials. This review summarizes recent experimental developments of SHG applications in 2D materials and also provides an outlook of potential prospects based on SHG.

Two-dimensional (2D) Van der Waals materials have emerged as a very attractive class of optoelectronic material due to the unprecedented strength in its interaction with light. In this talk I will discuss approaches to enhance and control this interaction by integrating these 2D materials with microcavities, and metamaterials. I will first discuss the formation of strongly coupled half-light half-matter quasiparticles (microcavity excitonpolaritons) [1], their spin-optic [2], and electrical control/excitation (Fig. 1) [3], in the 2D transition metal dichalcogenide (TMD) systems. Prospects for enhanced nonlinear optical interaction using Rydberg states in TMDs will be discussed. Use of photonic hypercrystals and hyperbolic media to enhance the spontaneous emission from the TMDs will also be presented. Following this, I will discuss the routing of valley excitons in 2D TMDs using chiral metasurfaces (Fig. 2) [4]. Finally, time permitting, I will briefly talk about developing deterministic quantum emitters at room temperature using defects in hexagonal boron nitride [5] and prospects of coupling these emitters to high Q resonators.