Light and Matter Interaction in Two-Dimensional Atomically Thin Films

In the last decade, the rise of two-dimensional (2D) materials has attracted a tremendous amount of interest for the entire field of photonics and opto-electronics. The mechanism of light–matter interaction in 2D materials challenges the knowledge of materials physics, which drives the rapid development of materials synthesis and device applications. 2D materials coupled with plasmonic effects show impressive optical characteristics, involving efficient charge transfer, plasmonic hot electrons doping, enhanced light-emitting, and ultrasensitive photodetection. Here, we briefly review the recent remarkable progress of 2D materials, mainly on graphene and transition metal dichalcogenides, focusing on their tunable optical properties and improved opto-electronic devices with plasmonic effects. The mechanism of plasmon enhanced light–matter interaction in 2D materials is elaborated in detail, and the state-of-the-art of device applications is comprehensively described. In the future, the field of 2D materials holds great promise as an important platform for materials science and opto-electronic engineering, enabling an emerging interdisciplinary research field spanning from clean energy to information technology.

A fascinating photonic platform with a small device scale, fast operating speed, as well as low energy consumption is two-dimensional (2D) materials, thanks to their in-plane crystalline structures and out-of-plane quantum confinement. The key to further advancement in this research field is the ability to modify the optical properties of the 2D materials. The modifications typically come from the materials themselves, for example, altering their chemical compositions. This article reviews a comparably less explored but promising means, through engineering the photonic surroundings. Rather than modifying materials themselves, this means manipulates the dielectric and metallic environments, both uniform and nanostructured, that directly interact with the materials. For 2D materials that are only one or a few atoms thick, the interaction with the environment can be remarkably efficient. This review summarizes the three degrees of freedom of this interaction: weak coupling, strong coupling, and multifunctionality. In addition, it reviews a relatively timing concept of engineering that directly applied to the 2D materials by patterning. Benefiting from the burgeoning development of nanophotonics, the engineering of photonic environments provides a versatile and creative methodology of reshaping light–matter interaction in 2D materials.

Two-dimensional (2D) materials such as graphene, transition metal dichalcogenides and phosphorene have emerged as brand new photonic materials with huge potential in a variety of optical applications in recent years, due to their unique properties and multiple functions. Owning to the significantly increased surface to volume ratio in the atomic thin layered structure, the interactions between 2D materials with light become remarkably strong in either elastic or inelastic interactions. Most of previous studies were focused on the inelastic interactions between 2D materials with light, namely Raman and photoluminescence properties. However, we found the elastic interactions between them and light are also very attractive. Based on the properties discovered, we demonstrated several optical applications, such as atomically thin optical lenses and gratings. On the other hand, we found the inelastic interactions with light in the 2D limitation affected a lot by the external environment, which could serve as a unique method to control the working status of the optical devices to meet multiple application needs. Several progresses were demonstrated such as control of excitons and trions in few-layer MoS2 via the co-modulations by both temperature and electric field and the defect engineering by oxygen plasma etching to stimulate new photon emission.

Enhanced optical absorption in two-dimensional (2D) materials has recently moved into the focus of nanophotonics research. In this work, we present a gain-assisted method to achieve critical coupling and demonstrate the maximum absorption in undoped monolayer graphene in the near-infrared. In a two-port system composed of photonic crystal slab loaded with graphene, the gain medium is introduced to adjust the dissipative rate to match the radiation rate for the critical coupling, which is accessible without changing the original structural geometry. The appropriate tuning of the gain coefficient also enables the critical coupling absorption within a wide wavelength regime for different coupling configurations. This work provides a powerful guide to manipulate light–matter interaction in 2D materials and opens up a new path to design ultra-compact and high-performance 2D material optical devices.

Two-dimensional materials have garnered interest from the perspectives of physics, materials, and applied electronics owing to their outstanding physical and chemical properties. Advances in exfoliation and synthesis technologies have enabled preparation and electrical characterization of various atomically thin films of semiconductor transition metal dichalcogenides (TMDs). Their two-dimensional structures and electromagnetic spectra coupled to bandgaps in the visible region indicate their suitability for digital electronics and optoelectronics. To further expand the potential applications of these two-dimensional semiconductor materials, technologies capable of precisely controlling the electrical properties of the material are essential. Doping has been traditionally used to effectively change the electrical and electronic properties of materials through relatively simple processes. To change the electrical properties, substances that can donate or remove electrons are added. Doping of atomically thin two-dimensional semiconductor materials is similar to that used for silicon but has a slightly different mechanism. Three main methods with different characteristics and slightly different principles are generally used. This review presents an overview of various advanced doping techniques based on the substitutional, chemical, and charge transfer molecular doping strategies of graphene and TMDs, which are the representative 2D semiconductor materials.

2D materials (2DMs), due to spin-valley locking degree of freedom, exhibit strongly bound exciton and chiral optical selection rules and become promising material candidates for optoelectronic and spin/valleytronic devices. Over the last decade, the manifesting of 2D materials by circularly polarized lights expedites tremendous fascinating phenomena, such as valley/exciton Hall effect, Moiré exciton, optical Stark effect, circular dichroism, circularly polarized photoluminescence, and spintronic property. In this review, recent advance in the interaction of circularly polarized light with 2D materials covering from graphene, black phosphorous, transition metal dichalcogenides, van der Waals heterostructures as well as small proportion of quasi-2D perovskites and topological materials, is overviewed. The confronted challenges and theoretical and experimental opportunities are also discussed, attempting to accelerate the prosperity of chiral light-2DMs interactions.

With the great success of graphene, two-dimensional (2D) materials, thanks to their fascinating electronic and optoelectronic properties, have aroused extensive attention among the scientific community. Broad research efforts have proven the enormous potential of 2D materials in optoelectronics, electrochemistry, spintronics, energy storage, catalysis, biomedicine, and many other fields. Driven by the promising applications of 2D materials, there has been an emerging trend toward nanofabricating 2D materials with customized parameters, which are essential for tailor-making controllable artificial nanostructures used in building sophisticated 2D material systems. As the most commonly used solid probe lithography technique, atomic force microscopy (AFM) integrates visualization and multi-mode fabrication within one system, demonstrating its superior capability in the nanofabrication of 2D materials. In view of this, in this review article, we offer a brief introduction to how AFM nanofabrication works and the classification of AFM nanofabrication techniques by the tip-sample surface interaction. Following that, we discuss the results of 2D material nanofabrication by mechanical, thermal, electrical, and other AFM techniques in which external stimulations are applied on special AFM probes.

Current understanding and emerging applications of 3D crumpling mediated 2D material-liquid interactions

This talk will present my (biased) perspective on whether two-dimensional (2D) materials could play a role in the semiconductor industry. It is important to recognize that 2D materials are good for applications where their ultrathin nature gives them distinct advantages, such as flexible electronics [1] or light-weight solar cells [2]. They may not be good where conventional materials work sufficiently well, like transistors thicker than a few nanometers. I will focus on 2D materials for 3D heterogeneous integration of electronics, which has major advantages for energy-efficient computing [3]. Here, 2D materials could be monolayer transistors with ultralow leakage [4] (due to larger band gaps than silicon), used to access high-density memory [5]. Recent results from our group [6,7] and others [8] have shown monolayer transistors with good performance, which cannot be achieved with sub-nanometer thin conventional semiconductors, and the 2D performance could be further boosted by strain [9]. I will also describe some unconventional applications, using 2D materials as thermal insulators [10], heat spreaders [11], and thermal transistors [12]. These could enable control of heat in “thermal circuits” analogous with electrical circuits. Combined, these studies reveal fundamental limits and some key applications of 2D materials, which take advantage of their unique properties. Refs: [1] A. Daus et al., Nat. Elec. 4, 495 (2021). [2] K. Nassiri Nazif, et al., Nat. Comm. 12, 7034 (2021). [3] M. Aly et al., Computer 48, 24 (2015). [4] C. Bailey et al., EMC (2019). [5] A. Khan et al. Science 373, 1243 (2021). [6] C. English et al., IEDM, Dec 2016. [7] C. McClellan et al. ACS Nano 15, 1587 (2021). [8] S. Das et al., Nat. Elec. 4, 786 (2021). [9] I. Datye et al., Nano Lett. 22, 8052 (2022). [10] S. Vaziri et al., Science Adv. 5, eaax1325 (2019). [11] C. Koroglu & E. Pop, IEEE Elec. Dev. Lett. 44, 496 (2023). [12] M. Chen et al., 2D Mater. 8, 035055 (2021).

Design of narrowband perfect absorber for enhancing photoluminescence in atomically thin WSe2

The development of two‐dimensional (2D) materials is experiencing a renaissance since the adventure of graphene. 2D materials typically exhibit strong in‐plane covalent bonding and weak out‐of‐plane van der Waals interactions through the interlayer gap. Opening 2D materials is an effective way to alter the physical and chemical properties, such as band gap, conductivity, optical property, thermoelectric property, photovoltaic property and superconductivity. A larger interlayer distance means more accessible active sites for catalysis, an ion‐accessible surface in the interlayer space, which may greatly enhance the performance of 2D materials for energy conversion and storage. Moreover, opening 2D materials by intercalation can change the band filling state and the Fermi level. This review mainly focuses on the opening of 2D materials and their subsequent applications in energy conversion and storage fields, expecting to promote the development of such a new class of materials, namely expanded 2D materials. The exciting progresses of these expanded materials made in both energy conversion and storage devices including solar cells, thermoelectric devices, electrocatalyst, supercapacitors and rechargeable batteries, is presented and discussed in depth. Furthermore, prospects and further developments in these exciting fields of the expanded 2D materials are also commented.

The Moore’s law of scaling of metal oxide semiconductor field effect transistor (MOSFET) had been a driving force toward the unprecedented advancement in development of integrated circuit over the last five decades. As the technology scales down to 7 nm node and below following the Moore’s law, conventional MOSFETs are becoming more vulnerable to extremely high off-state leakage current exhibiting a tremendous amount of standby power dissipation. Moreover, the fundamental physical limit of MOSFET of 60 mV/decade subthreshold slope exacerbates the situation further requiring current transport mechanism other than drift and diffusion for the operation of transistors. One way to limit such unrestrained amount of power dissipation is to explore novel materials with superior thermal and electrical properties compared to traditional bulk materials. On the other hand, energy efficient steep subthreshold slope devices are the other possible alternatives to conventional MOSFET based on emerging novel materials. This dissertation addresses the potential of both advanced materials and devices for development of next generation energy efficient integrated circuits. Among the different steep subthreshold slope devices, tunnel field effect transistor (TFET) has been considered as a promising candidate after MOSFET. A superior gate control on source-channel band-to-band tunneling providing subthreshold slopes well below than 60 mV/decade. With the emergence of atomically thin two-dimensional (2D) materials, interest in the design of TFET based on such novel 2D materials has also grown significantly. Graphene being the first and the most studied among 2D materials with exotic electronic and thermal properties. This dissertation primarily considers current transport modeling of graphene based tunnel devices from transport phenomena to energy efficient integrated circuit design. Three current transport models: semi-classical, semi-quantum and numerical simulations are described for the modeling of graphene nanoribbon tunnel field effect transistor (GNR TFET) where the semi-classical model is in close agreement with the quantum transport simulation. Moreover, the models produced are also extended for integrated circuit design using Verilog-A hardware description language for logic design. In order to overcome the challenges associated with the band gap engineering for making graphene transistor for logic operation, the promise of graphene based interlayer tunneling transistors are discussed along with their existing fundamental physical limitation of subthreshold slope. It has been found that such interlayer tunnel transistor has very poor electrostatic gate control on drain current. It gives subthreshold slope greater than the thermionic limit of 60 mV/decade at room temperature. In order to resolve such limitation of

Structural, electronic and mechanical properties of a novel graphenylene-like structure based on GeC

Atomically thin two-dimensional (2D) materials are ideal host systems for quantum defects as they offer easier characterisation, manipulation and read-out of defect states as compared to bulk defects. Here we introduce the Quantum Point Defect (QPOD) database with more than 1900 defect systems comprising various charge states of 503 intrinsic point defects (vacancies and antisites) in 82 different 2D semiconductors and insulators. The Atomic Simulation Recipes (ASR) workflow framework was used to perform density functional theory (DFT) calculations of defect formation energies, charge transition levels, Fermi level positions, equilibrium defect and carrier concentrations, transition dipole moments, hyperfine coupling, and zero-field splitting. Excited states and photoluminescence spectra were calculated for selected high-spin defects. In this paper we describe the calculations and workflow behind the QPOD database, present an overview of its content, and discuss some general trends and correlations in the data. We analyse the degree of defect tolerance as well as intrinsic dopability of the host materials and identify promising defects for quantum technological applications. The database is freely available and can be browsed via a web-app interlinked with the Computational 2D Materials Database (C2DB).

Symbolic regression for defect interactions in 2D materials