Academic literature on the topic '2D-TMDs materials'

Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) representing the ultimate thickness scaling of channel materials provide a solution to tantalizingly push the limit of technology nodes in the sub-1-nm range. One key challenge with 2D semiconducting TMDs channel materials is the large-scale batch growth on insulating substrates with continuous single crystallinity, spatial homogeneity, and compelling electrical properties. Recent studies have claimed the epitaxy growth of wafer-scale, single-crystal 2D TMDs on C-plane sapphire substrate with deliberately engineered off-cut angles. It has been predominately postulated that exposed step edges break the energy degeneracy of nucleation and thus drive the seamless stitching of mono-oriented flakes. In this talk, I will show that a more dominant factor should be considered. The interaction of 2D TMD grains with the exposed oxygen-aluminum atomic plane establishes an energy-minimized 2D TMD-sapphire configuration. Reconstructing the surfaces of C-plane sapphire substrates to only a single type (symmetry) of atomic planes already guarantees the single-crystal epitaxy of monolayer TMDs without the aid of step edges. Electrical results also evidence the structural uniformity of the monolayers. Our new experimental findings elucidate the long-standing question that curbs the wafer-scale batch epitaxy of 2D TMDs single crystals, an essential step toward using 2D materials for future electronics. Experiments extended to other materials like perovskites also support the argument that the interaction with sapphire atomic surfaces is more dominant than the step edge docking.

The goal of the sensor industry is to develop innovative, energy-efficient, and reliable devices to detect molecules relevant to economically important sectors such as clinical diagnoses, environmental monitoring, food safety, and wearables. The current demand for portable, fast, sensitive, and high-throughput platforms to detect a plethora of new analytes is continuously increasing. The 2D transition metal dichalcogenides (2D-TMDs) are excellent candidates to fully meet the stringent demands in the sensor industry; 2D-TMDs properties, such as atomic thickness, large surface area, and tailored electrical conductivity, match those descriptions of active sensor materials. However, the detection capability of 2D-TMDs is limited by their intrinsic tendency to aggregate and settle, which reduces the surface area available for detection, in addition to the weak interactions that pristine 2D-TMDs normally exhibit with analytes. Chemical functionalization has been proposed as a consensus solution to these limitations. Tailored surface modification of 2D-TMDs, either by covalent functionalization, non-covalent functionalization, or a mixture of both, allows for improved specificity of the surface–analyte interaction while reducing van der Waals forces between 2D-TMDs avoiding agglomeration and precipitation. From this perspective, we review the recent advances in improving the detection of biomolecules, heavy metals, and gases using chemically functionalized 2D-TMDs. Covalent and non-covalent functionalized 2D-TMDs are commonly used for the detection of biomolecules and metals, while 2D-TMDs functionalized with metal nanoparticles are used for gas and Raman sensors. Finally, we describe the limitations and further strategies that might pave the way for miniaturized, flexible, smart, and low-cost sensing devices.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are garnering considerable scientific interest, prompting discussion regarding their prospective applications in the fields of nanoelectronics and spintronics while also fueling groundbreaking discoveries in phenomena such as the fractional quantum anomalous Hall effect (FQAHE) and exciton dynamics. The abundance of binary compound TMDs, such as MX2 (M = Mo, W; X = S, Se, Te), has unlocked myriad avenues of exploration. However, the exploration of ternary compound TMDs remains relatively limited, with notable examples being Ta2NiS5 and Ta2NiSe5. In this study, we report the synthesis of a new 2D ternary compound TMD materials, Ta3VSe8, employing the chemical vapor transport (CVT) method. The as-grown bulk crystal is shiny and can be easily exfoliated. The crystal quality and structure are verified by X-ray diffraction (XRD), while the surface morphology, stoichiometric ratio, and uniformity are determined by scanning electron microscopy (SEM). Although the phonon property is found stable at different temperatures, magneto-resistivity evolves. These findings provide a possible approach for the realization and exploration of ternary compound TMDs.

Abstract This paper gives a detailed description of a high-performance polariton condensate for a quantum mechanical two-level system (TLS). We propose a transition metal dichalcogenides (TMDs) setup and theoretically carry out the spectroscopy of these polariton condensates. Through theoretical and numerical analysis, we obtain many features in two dimensional (2D) multilayer TMDs. We compute the energy of the system and the Landau-Zener-Stückelberg (LZS) quantum tunneling probability under the effect of a sequence of laser light. At certain critical 2D TMDs parameters, the system exhibits a multi-crossing scenario in a privileged position of 2D multilayer TMDs. We predict the consecutive modulations and highlight the conservation of the LZS interference patterns mapped from the 2D TMDs system. At weak coupling regime, a successful conversion of interferometry signals is identified for some values of laser frequency. We explain such a result as a valley sensitive cavity rate model due to coherent exchange and incoherent scattering, meaning that polariton condensate is formed in the valley around the Brillouin zone. The latter is used quantitatively and qualitatively to achieve high-precision measurements beyond that of its elementary constituents. The obtained results confirm that M o S e 2 has the highest sensitivity to radiation field as compared to other 2D multilayer TMDs materials. Therefore, M o S e 2 stands as an appropriate candidate among other 2D TMDs to form polariton condensates.

Abstract Intercalation is basically the process of putting one or multiple guest elements into the van der Waals gaps of a parent crystal in a reversible way. Two-dimensional (2D) materials have shown great promise with intercalant species ranging from organic molecules to ions. Apart from graphene, the most studied 2D materials are the transition metal dichalcogenides (TMDs). Intercalation in TMDs has led to new strategies beyond graphene for 2D structures in materials science, materials engineering, chemistry and physics. This review deals with the possible mechanism of intercalation as well as the window that intercalation can open for compact and ultrathin device technology. Modulation of the physicochemical properties of intercalated TMDs has been thoroughly reviewed. Finally, device performance, especially for energy storage and energy harvesting devices, has been evaluated and specific issues that need attention for future development are highlighted.

Two-dimensional-layered transition metal dichalcogenides (2D-layered TMDs) are a chemically diverse class of compounds having variable band gaps and remarkable electrochemical properties, which make them potential materials for applications in the field of electrochemical energy. To date, 2D-layered TMDs have been wildly used in water-splitting systems, dye-sensitized solar cells, supercapacitors, and some catalysis systems, etc., and the pertinent devices exhibit good performances. However, several reports have also indicated that the active sites for catalytic reaction are mainly located on the edge sites of 2D-layered TMDs, and their basal plane shows poor activity toward catalysis reaction. Accordingly, many studies have reported various approaches, namely active-site engineering, to address this issue, including plasma treatment, edge site formation, heteroatom-doping, nano-sized TMD pieces, highly curved structures, and surface modification via nano-sized catalyst decoration, etc. In this article, we provide a short review for the active-site engineering on 2D-layered TMDs and their applications in electrochemical energy. Finally, the future perspectives for 2D-layered TMD catalysts will also be briefly discussed.

There has been an exponential surge in reports on two-dimensional (2D) materials ever since the discovery of graphene in 2004. Transition metal dichalcogenides (TMDs) are a class of 2D materials where weak van der Waals force binds individual covalently bonded X–M–X layers (where M is the transition metal and X is the chalcogen), making layer-controlled synthesis possible. These individual building blocks (single-layer TMDs) transition from indirect to direct band gaps and have fascinating optical and electronic properties. Layer-dependent opto-electrical properties, along with the existence of finite band gaps, make single-layer TMDs superior to the well-known graphene that paves the way for their applications in many areas. Ultra-fast response, high on/off ratio, planar structure, low operational voltage, wafer scale synthesis capabilities, high surface-to-volume ratio, and compatibility with standard fabrication processes makes TMDs ideal candidates to replace conventional semiconductors, such as silicon, etc., in the new-age electrical, electronic, and opto-electronic devices. Besides, TMDs can be potentially utilized in single molecular sensing for early detection of different biomarkers, gas sensors, photodetector, and catalytic applications. The impact of COVID-19 has given rise to an upsurge in demand for biosensors with real-time detection capabilities. TMDs as active or supporting biosensing elements exhibit potential for real-time detection of single biomarkers and, hence, show promise in the development of point-of-care healthcare devices. In this review, we provide a historical survey of 2D TMD-based biosensors for the detection of bio analytes ranging from bacteria, viruses, and whole cells to molecular biomarkers via optical, electronic, and electrochemical sensing mechanisms. Current approaches and the latest developments in the study of healthcare devices using 2D TMDs are discussed. Additionally, this review presents an overview of the challenges in the area and discusses the future perspective of 2D TMDs in the field of biosensing for healthcare devices.

Abstract Two-dimensional transition metal dichalcogenides (2D-TMDs) are atomically thin semiconductors with a direct bandgap in monolayer thickness, providing ideal platforms for the development of exciton-based optoelectronic devices. Extensive studies on the spectral characteristics of exciton emission have been performed, but spatially resolved optical studies of 2D-TMDs are also critically important because of large variations in the spatial profiles of exciton emissions due to local defects and charge distributions that are intrinsically nonuniform. Because the spatial resolution of conventional optical microscopy and spectroscopy is fundamentally limited by diffraction, near-field optical imaging using apertured or metallic probes has been used to spectrally map the nanoscale profiles of exciton emissions and to study the effects of nanosize local defects and carrier distribution. While these unique approaches have been frequently used, revealing information on the exciton dynamics of 2D-TMDs that is not normally accessible by conventional far-field spectroscopy, a dedicated review of near-field imaging and spectroscopy studies on 2D-TMDs is not available. This review is intended to provide an overview of the current status of near-field optical research on 2D-TMDs and the future direction with regard to developing nanoscale optical imaging and spectroscopy to investigate the exciton characteristics of 2D-TMDs.

This review highlights the advances in Schottky sensors based on 2D TMDs. The preparation methods of 2D TMDs and the vital Schottky sensors such as photodetectors, gas sensors, strain sensors, and biosensors are summarized and discussed.

This thesis describes the fabrication and characterization of two-dimensional transition dichalcogenides (2D TMDs) nanolayers for various applications in electronic and opto-electronic devices applications. In Chapter 1, crystal and optical structure of TMDs materials are introduced. Many TMDs materials reveal three structure polytypes (1T, 2H, and 3R). The important electronic properties are determined by the crystal structure of TMDs; thus, the information of crystal structure is explained. In addition, the detailed information of photon vibration and optical band gap structure from single-layer to bulk TMDs materials are introduced in this chapter. In Chapter 2, detailed information of physical properties and synthesis techniques for molybdenum disulfide (MoS2), tungsten disulfide (WS2), and molybdenum ditelluride (MoTe2) nanolayers are explained. The three representative crystal structures are trigonal prismatic (hexagonal, H), octahedral (tetragonal, T), and distorted structure (Tʹ). At room temperature, the stable structure of MoS2 and WS2 is semiconducting 2H phase, and MoTe2 can reveal both 2H (semiconducting phase) and 1Tʹ (semi-metallic phase) phases determined by the existence of strains. In addition, the pros and cons of the synthesis techniques for nanolayers are discussed. In Chapter 3, the topic of synthesized large-scale MoS2, WS2, and MoTe2 films is considered. For MoS2 and WS2 films, the layer thickness is modulated from single-layer to multi-layers. The few-layer MoTe2 film is synthesized with two different phases (2H or 1Tʹ). The all TMDs films are fabricated using two-step chemical vapor deposition (CVD) method. The analyses of atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and Raman spectroscopy confirm that the synthesis of high crystalline MoS2, WS2, and MoTe2 films are successful. The electronic properties of both MoS2 and WS2 exhibit a p-type conduction with relatively high field effect mobility and current on/off ratio. In Chapter 4, vertically-stacked few-layer MoS2/WS2 heterostructures on SiO2/Si and flexible polyethylene terephthalate (PET) substrates is presented. Detailed structural characterizations by Raman spectroscopy and high-resolution/scanning transmission electron microscopy (HRTEM/STEM) show the structural integrity of two distinct 2D TMD layers with atomically sharp van der Waals (vdW) heterointerfaces. Electrical transport measurements of the MoS2/WS2 heterostructure reveal diode-like behavior with current on/off ratio of ~ 104. In Chapter 5, optically uniform and scalable single-layer Mo1-xWxS2 alloys are synthesized by a two-step CVD method followed by a laser thinning. Post laser treatment is presented for etching of few-layer Mo1-xWxS2 alloys down to single-layer alloys. The optical band gap is controlled from 1.871 to 1.971 eV with the variation in the tungsten (W) content, x = 0 to 1. PL and Raman mapping analyses confirm that the laser-thinning of the Mo1-xWxS2 alloys is a self-limiting process caused via heat dissipation to SiO2/Si substrate, resulting in fabrication of spatially uniform single-layer Mo1-xWxS2 alloy films.

La miniaturisation des MOSFET a permis une forte diminution des transistors et des puces, ainsi qu’une augmentation exponentielle des capacités de calcul. Cette miniaturisation ne peut néanmoins continuer ainsi: de nos jours, un microprocesseur peut contenir des dizaines de milliards de transistors et la chaleur dégagée par ces composants peut fortement détériorer ses performances. De plus, du fait de leur principe même de fonctionnement, la tension d’alimentation des MOSFET ne peut être réduite sans en impacter les performances. De nouvelles architectures telles que le TFET -basé sur l’effet tunnel bande-à-bande et pouvant fonctionner à des tensions d’alimentation très basses- ainsi que de nouveaux matériaux pourraient donc apporter une alternative au MOSFET silicium. Les monocouches de dichalcogènures de métaux de transitions (TMDs) -des semiconducteurs à bande interdite directe d’environ 1 à 2 eV- possèdent un fort potentiel pour l’électronique et la photonique. De plus, dans le cas de contraintes appropriées, ils peuvent conduire un alignement de bandes présentant un broken-gap; cette configuration permet de surpasser les limites habituelles du TFETs, à savoir de faibles courants dus à l’effet tunnel sur lequel ces dispositifs reposent. Dans ce travail de thèse, des hétérojonctions planaires de TMD sont modélisées via une approche atomistique de liaisons fortes, et une configuration broken-gap est observée dans deux d’entre elles (MoTe2/MoS2 et WTe2/MoS2). Leur potentiel dans le cadre de transistors à effet tunnel (TFETs) est évalué au moyen de simulations de transport quantique basées sur un modèle TB atomistique ainsi que la théorie des fonctions de Green hors-équilibre. Des TFETs type-p et type-n basés sur ces hétérojonctions sont simulés et présentent des courants ON élevés (ION > 103 µA/µm) ainsi que des pentes sous-seuil extrêmement raides (SS < 5 mV/dec) à des tensions d’alimentation très faibles (VDD = 0.3 V). Plusieurs architectures novatrices basées sur ces TFETs et découlant de la nature 2D des matériaux utilisés sont également présentées, et permettent d’atteindre des performances encore plus élevées
Nowadays, microprocessors can contain tens of billions of transistors and as a result, heat dissipation and its impact on device performance has increasingly become a hindrance to further scaling. Due to their working mechanism, the power supply of MOSFETs cannot be reduced without deteriorating overall performance, and Si-MOSFETs scaling therefore seems to be reaching its end. New architectures such as the TFET, which can perform at low supply voltages thanks to its reliance on band-to-band tunneling, and new materials could solve this issue. Transition metal dichalcogenide monolayers (TMDs) are 2D semiconductors with direct band gaps ranging from 1 to 2 eV, and therefore hold potential in electronics and photonics. Moreover, when under appropriate strains, their band alignment can result in broken-gap configurations which can circumvent the traditionally low currents observed in TFETs due to the tunneling mechanism they rely upon. In this work, in-plane TMD heterojunctions are investigated using an atomistic tight-binding approach, two of which lead to a broken-gap configuration (MoTe2/MoS2 and WTe2/MoS2). The potential of these heterojunctions for use in tunnel field-effect transistors (TFETs) is evaluated via quantum transport computations based on an atomistic tight-binding model and the non-equilibrium Green’s function theory. Both p-type and n-type TFETs based on these in-plane TMD heterojunctions are shownto yield high ON currents (ION > 103 µA/µm) and extremely low subthreshold swings (SS < 5 mV/dec) at low supply voltages (VDD = 0.3 V). Innovative device architectures allowed by the 2D nature of these materials are also proposed, and shown to enhance performance even further

Le sujet de cette thèse s'inscrit dans la thématique des matériaux bidimensionnels (2D) d'épaisseur atomique. L'étude des propriétés optiques et électroniques des hétérostructures hybrides à base de dichalcogénures de métaux de transition (TMD) MX₂ (M = Mo, W ; X = S, Se, Te) est aujourd'hui considérée avec attention en raison de futures applications et d'études plus fondamentales. Plus que leurs propriétés physiques intrinsèques, en configuration multicouche, ces matériaux offrent des phénomènes physiques prometteurs tels que la modulation de la valeur de la bande interdite, la ferroélectricité pour des configurations cristallines spécifiques, etc. En particulier, ce travail se consacre aux hétérostructures hybrides à base de diséléniure de tungstène (WSe₂) sur des substrats de graphène et de phosphate de gallium (GaP). En mettant en œuvre des techniques de microscopie et de spectroscopie telles que la spectroscopie Raman et la spectroscopie de photoémission résolue en angle (ARPES), une étude des propriétés électroniques, optiques et structurelles d'hétérostructures composées de plusieurs matériaux 2D a été réalisée afin de fournir une meilleure compréhension de ces systèmes émergents. Par conséquent, les premières mesures directes de la structure de bande électronique de la phase rhomboédrique de la structure bicouche de WSe₂ déposée sur un substrat 2D de graphène sont présentées dans ce manuscrit. La croissance directe de ce matériau 2D sur un substrat 3D de GaP a été étudiée pour plusieurs épaisseurs. Ces travaux ont permis d'identifier l'effet de la nature de la phase cristalline ainsi que la méthode de croissance sur les structures de bandes électroniques, ce qui permet une meilleure compréhension de ces systèmes émergents
The subject of this thesis is two-dimensional (2D) materials of atomic thickness. The study of the optical and electronic properties of hybrid heterostructures based on MX₂ transition metal dichalcogenides (TMDs) (M = Mo, W; X = S, Se, Te) is now being carefully considered with a view to future applications and more fundamental studies. Beyond their intrinsic physical properties, in multilayer configurations, these materials offer promising physical phenomena such as modulation of bandgap values, ferroelectricity for specific crystal configurations, and so on. In particular, this work focuses on hybrid heterostructures based on tungsten diselenide (WSe₂) on graphene and gallium phosphate (GaP) substrates. Using microscopy and spectroscopy techniques such as Raman spectroscopy and angle-resolved photoemission spectroscopy (ARPES), we investigated the electronic, optical, and structural properties of heterostructures composed of several 2D materials to better understand these emerging systems. Accordingly, the first direct measurements of the electronic band structure of the rhombohedral phase of the WSe₂ bilayer structure deposited on a 2D graphene substrate are presented in this manuscript. The direct growth of this 2D material on a 3D GaP substrate has been studied for several thicknesses. This work has enabled us to identify the effect of the nature of the crystalline phase and the growth method on the electronic band structures, providing a better understanding of these emerging systems

Face aux enjeux environnementaux et liés à la santé publique, les capteurs de gaz toxiques et/ou polluants sont au cœur d’une recherche intensive et de moteurs d’innovation. Leur développement est d'une importance capitale et un enjeu majeur pour la société. Les capteurs à base d’oxyde métallique sont les plus étudiés et présentent beaucoup d’avantages tels que leur faible coût, une grande sensibilité et une intégration facile dans un système portable miniaturisé. Cependant, leurs températures de fonctionnement élevées limitent leur mise en œuvre dans les appareils portables et flexibles. Les matériaux 2D sont une classe émergente de matériaux, fonctionnant à température ambiante, ils suscitent un vif intérêt pour le développement de capteurs de gaz résistifs en raison de leurs excellentes flexibilités mécaniques, de leurs grandes surfaces spécifiques et actives, ainsi que leur haute sensibilité aux gaz. Dans cette famille, les chalcogénures de métaux de transition (TMDs), tels que le MoS2, présentent des propriétés exceptionnelles grâce à une bande interdite ajustable. Ils représentent des candidats prometteurs pour la détection des gaz toxiques à température ambiante.Dans ce contexte, l'objectif de cette thèse est de fabriquer et optimiser des capteurs résistifs de gaz toxiques à base du matériau 2D MoS2, par voie liquide, pour la détection de NO2. La première étape de ce travail a consisté au développement et à l’optimisation d’un procédé d’exfoliation en phase liquide afin de produire des suspensions colloïdales de nano-feuillets de MoS2 en grande quantité. En parallèle, nous avons évalué différents modes de dépôts permettant d’obtenir des films minces à partir de nano-feuillets individuels : la filtration sous vide et l'auto-assemblage à l'interface liquide/liquide. Différents types de caractérisations microscopiques et spectroscopiques, couplée avec des mesures électriques, ont été utilisées pour déterminer les conditions d’exfoliation optimales d'obtention de nano-feuillets de MoS2, ainsi que les propriétés structurales et électriques des couches minces fabriquées par les deux modes de dépôts différents. Une deuxième partie de ce travail a porté sur la conception et la réalisation de capteurs interdigités résistifs basées sur les couches minces fabriquées avec les nano-feuillets de MoS2. Ces capteurs montrent, à température ambiante, une bonne sensibilité à une faible concentration de NO2 de 1 ppm. Toutefois, la récupération complète après la détection du NO2 n’est pas systématique, dû en particulier à la génération de lacunes atomiques dans les nano-feuillets de MoS2 lors de l'exfoliation en phase liquide. Pour résoudre ce problème, nous passivions ces lacunes avec des nanoparticules d’or. La fonctionnalisation des nano-feuillets de MoS2 par des nanoparticules d’or augmentent la sensibilité vers le NO2 et réduit le temps de récupération par rapport au capteur de MoS2 seul
In response to environmental and public health issues, sensors for toxic and/or polluting gases are at the core of extensive research and innovation. Therefore, their development is important and also a major challenge for society. Up to date for gas sensing applications, metal oxide chemiresistive sensors are the most widely investigated devices thanks to their ease in fabrication, simplicity of operation, and facile integration in miniaturization. However, their high working temperature restricts their implementation in the wearable, flexible devices. Two-dimensional (2D) materials possess great potential in serving as a gas-sensing layer in wearable gas sensors due to their excellent mechanical flexibility, large specific surface areas, strong surface activities with a high gas sensitivity. Among this family, transition metal chalcogenides (TMDs), such as molybdenum disulfides (MoS2), exhibit outstanding properties thanks to its tunable band gap, and are also promising candidates for the detection of toxic gas at room temperature.This thesis aims to fabricate and optimize nitrogen dioxide (NO2) chemiresistive gas sensors based on solution-processed 2D MoS2. The first step in the work involved the development and the optimization of liquid phase exfoliation process to produce colloidal suspensions of MoS2 nanosheets on a large scale. In parallel, we assessed vacuum-assisted filtration and liquid/liquid interfacial self-assembly as two thin film fabrication techniques from individual nanosheets. Besides 2D MoS2 dispersion production and thin film processing, a multiscale physicochemical characterization of the produced MoS2 through microscopic and spectroscopic techniques, coupled with electrical measurements was conducted to determine the optimal exfoliation conditions to obtain MoS2 nanosheets and the morphologies of thin films produced by two distinct deposition processes. Then, MoS2 thin film fabricated by vacuum-assisted filtration with gold interdigitated electrodes on top were assessed for NO2 gas sensing, which exhibited a moderate sensitivity to a low NO2 concentration down to 1 ppm at room temperature. However, full recovery of NO2 sensing cannot always be achieved due to the MoS2 NSs atom vacancies generated during liquid shear exfoliation. To solve this issue, we passivated these vacancies on MoS2 nanosheets with gold nanoparticles (Au NPs). The functionalization of MoS2 nanosheets with Au NPs improved the sensitivity towards NO2 and lowered the recovery time compared to bare MoS2 sensor

The transistor scaling is witness to many extraordinary inventions during its consecutive miniaturization. The journey began from Dennard’s classical constant field scaling, crossing through the milestones like strain engineering, high ‘k’ gate dielectric, ultrathin body transistor (UTB), silicon on insulator (SOI), and multi-gate 3D architectures, and continues in the form of advanced FinFET technology. However, further downscaling is sensing a dead-end because of the various challenges due to fundamental limitations of silicon, the building material of the transistor. Among these, two significant challenges are mobility degradation due to boundary scattering by surface dangling bonds and loss of gate control due to quantum confinement. To keep downscaling alive, the research community is looking for an alternate material that can mitigate these issues and consist of better fundamental properties from silicon like intrinsic mobility, thermal conductivity, optical response, and mechanical strength. Two-dimension material (2D material) shows great potential for next-generation electronic material and provides multiple avenues for further exploration. The material is one or a few atomic-layer 2D thin sheets of covalently bonded atoms stacked using weak van der Walls (vdW) forces in the third dimension. The lack of surface dangling bond and atomic-scale thickness mitigates the significant challenges of low mobility and inadequate gate control of the silicon material, respectively. Presently, more than 150 materials exist in the 2D material family. Graphene, Transition Metal Dichalcogenides (TMDs), and Phosphorene are well ahead of other family members due to their extraordinary properties, thereby plenty of investigations. Despite these properties, the materials have several roadblocks to their technological application. Opening bandgap and minimizing contact resistance are significant challenges in graphene, and reducing contact resistance and mature growth and reliability are big concerns for the TMDs. Phosphorene, which has hybrid properties of graphene and TMDs, is relatively less explored due to its spontaneous degradation in the ambient environment. Understanding and mitigating its spontaneous ambient degradation is still an open challenge for the electronics and material research communities across the globe. Keeping in mind these limitations, we explore the problems one by one and find their reasonable solutions. Based on DFT investigations, the discussion begins with a proposal for a reliable direct bandgap opening technique in graphene. Graphene possesses zero bandgap due to its highly symmetric hexagonal structures, which touch its π and π* orbitals’ energy states near the Fermi level, known as the Dirac point. Breaking this symmetry by carbon vacancy or Stone-Wales (SW) defects opens the bandgap at the Dirac point. However, the carbon vacancy creates unwanted mid-gap (trap) states, attributed to unbound orbitals of the nearest unsaturated carbon atoms at the vacant site. Moreover, the unsaturated carbon atoms react with ambient gases like oxygen, making graphene unstable. Interestingly, hydrogenation or fluorination of the unsaturated carbon atoms near the vacant site helps prevent the trap states while contributing to promising direct band gaps in graphene. The opened bandgap is tunable in the infrared regime and persists for different sizes and densities of hydrogenated or fluorinated patterns. The proposed approach is thermodynamically favorable as well as stable. The next work demonstrates the contact resistance reduction of graphene with palladium (Pd) by carbon vacancy engineering. The discussion begins with fundamental insights into the Pd-graphene interface and carbon vacancy-assisted contact resistance reduction using Density Functional Theory (DFT), followed by its experimental validation by various processes. Our study reveals significant interaction of Pd with graphene. Their orbitals overlap leads to potential barrier lowering at the interface, which can be reduced further by bringing graphene closer to the bulk Pd using carbon vacancy engineering at the contacts. Thus, the carbon vacancy-assisted barrier modulation reduces contact resistance by increasing carrier transmission probabilities at the interface. The theoretical findings have been emulated experimentally by carbon vacancy engineering at the graphene Field Effect Transistors (FETs). Different contact engineered graphene devices with Pd contacts shows significant contact resistance reduction, measuring as low as ~78 Ω-µm at room temperature. The contact resistance shows a ‘V’ shape curve as a function of defect density. The optimum contact resistance achieved is significantly lower than their pristine counterpart, as predicted by the theoretical estimates. Subsequently, the journey turns towards an atomic level investigation of phosphorene ambient degradation using the first-principles Molecular Dynamics (MD) simulations in the following work. The study reveals that the oxygen molecule dissociates spontaneously over pristine phosphorene in the ambient environment resulting in an exothermic reaction, which is boosted further by increasing partial pressure, temperature, and the presence of oxygen free radicals. The surface reaction is mainly due to lone pair electrons of phosphorous atoms, making the degradation directional and spontaneous under oxygen atoms. Furthermore, water molecules play a vital role in the degradation process by changing the reaction dynamics path of phosphorene-oxygen interaction and reducing activation energy and reaction energy due to its catalyzing action. In addition, phosphorous vacancy acts as an epicenter for oxidation. The oxygen attacks directly over the vacant site and reacts faster than its pristine counterpart. As a result, phosphorene edges resembling extended vacancy are prominent reaction sites that oxidize anisotropically due to different bond angle strains. The edge initiated spontaneous degradation, and rapid oxidation under the free radicals are validated using consistent probing under an optical microscope and Transmission Electron microscope (TEM), respectively. After material exploration, the next work reveals a unique reliability issue in the Phosphorene FETs. Here, we investigate the role of channel excess holes (due to inversion) in phosphorene degradation using the first-principles MD computations and electrical and Raman characterization. The results show that phosphorene degrades faster under negative gate bias (excess hole) than in pristine conditions (unbiased). The rapid degradation is mainly due to the enhanced chemical interaction of oxygen with the available hole in the channel. The computational findings are experimentally verified over phosphorene FETs. Compared to the unbiased condition, the devices show a faster change in drain current and fast decay of all primary Raman peaks in the ambient environment under negative gate bias. At the risk of ambient degradation, phosphorene thin flakes are to be identified quickly using a non-destructive technique like Raman to make their FETs for further exploration. The next work shows that the Raman signature of a low-frequency interlayer out-of-plane phonon mode, known as breathing mode, helps in identifying the thin flake quickly. Further, the work talks about thermal evolution and estimates the first-order temperature coefficient of different breathing modes. All the captured modes show a negative temperature coefficient around -0.002-0.003 cm-1/K across different flake thicknesses. Moreover, a closer look at the thermal evolution reflects that the modes follow three-phonon and four-phonon process dominant scattering phenomena at low and high-temperature ranges. The three-phonon process scattering is dominant below ~100 K, shifting to four-phonon process dominant scattering beyond ~150 K. Besides, the work discusses pristine instrumental error in the Raman shift characterization and suggests a mitigation method using Stokes and Anti-stokes scattering lines. Finally, the last work discusses the interactions of different metals (Au, Cr, Ni, and Pd) with TMDs (MoS2, MoSe2, WS2, and WSe2). The work reflects that Au has a weak interaction with all the TMDs. Thus, it stays more than 2 Å away from the TMDs surfaces. However, other metals show strong chemistry with TMDs. Due to weak interaction, Au offers very few metal-induced gap states (MIGS) in all the TMDs. On the other hand, metals like Cr, Ni, and Pd flood many MIGS in the bandgap region of the TMDs. During interactions, all the metals offer n-type doping to TMDs. Chalcogen vacancy enhances the interaction of the metals with all the TMDs. The vacancy leaves the unbounded orbitals, which bond strongly with the approaching metals. The bonding enhancement reduces the metal-TMDs distances that can be used in contact resistance engineering in their bulk counterparts. Chalcogen interstitial impurity also enhances the bond strength of some metal-TMDs interfaces. Our journey helps in overall technological advancement in the leading 2D materials. The work digs into the leading roadblocks like contact resistance reduction and method of bandgap opening in graphene, understanding the degradation issue of phosphorene at the material and device level, and exploring metal-TMDs interactions for their contact resistance engineering.

Discovery of grapheme has paved way for experimental realization of many physical phenomena such as massless Dirac fermions, quantum hall effect and zero-field conductivity. Search for other two dimensional (2D) materials led to the discovery of boron nitride, transition metal dichalcogenides(TMDs),transition metal oxides(MO2)and silicene. All of these materials exhibit different electronic and transport properties and are very promising for nanodevices such as nano-electromechanical-systems(NEMS), field effect transistors(FETs),sensors, hydrogen storage, nano photonics and many more. For practical utility of these materials in electronic and photonic applications, varying the band gap is very essential. Tuning of band gap has been achieved by doping, functionalization, lateral confinement, formation of hybrid structures and application of electric field. However, most of these techniques have limitations in practical applications. While, there is a lack of effective method of doping or functionalization in a controlled fashion, growth of specific sized nanostructures (e.g., nanoribbons and quantum dots),freestanding or embedded is yet to be achieved experimentally. The requirement of high electric field as well as the need for an extra electrode is another disadvantage in electric field induced tuning of band gap in low dimensional materials. Development of simpler yet effective methods is thus necessary to achieve this goal experimentally for potential application of these materials in various nano-devices. In this thesis, novel methods for tuning band gap of few 2D materials, based on strain and stacking, have been proposed theoretically using first principles based density functional theory(DFT) calculations. Electronic properties of few layered nanomaterials are studied subjected to mechanical and chemical strain of various kinds along with the effect of stacking pattern. These methods offer promising ways for controlled tuning of band gap in low dimensional materials. Detailed methodology of these proposed methods and their effect on electronic, structural or vibrational properties have also been studied. The thesis has been organized as follows: Chapter1 provides a general introduction to the low dimensional materials: their importance and potential application. An overview of the systems studied here is also given along with the traditional methods followed in the literature to tune their electronic properties. The motivation of the current research work has also been highlighted in this chapter. Chapter 2 describes the theoretical methodology adopted in this work. It gives brief understanding of first principles based Density Functional Theory(DFT) and various exchange and correlation energy functionals used here to obtain electronic, structural, vibrational and magnetic properties of the concerned materials. Chapter 3 deals with finding the origin of a novel experimental phenomenon, where electromechanical oscillations were observed on an array of buckled multiwalled carbon nanotubes (MWCNTs)subjected to axial compression. The effect of structural changes in CNTs in terms of buckling on electronic properties was studied. Contribution from intra-as well as inter-wall interactions was investigated separately by using single-and double-walled CNTs. Chapter 4 presents a method to manipulate electronic and transport properties of graphene bilayer by sliding one of the layers. Sliding caused breaking of symmetry in the graphene bilayer, which resulted in change in dispersion in the low energy bands. A transition from linear dispersion in AA stacking to parabolic dispersion in AB stacking is discussed in details. This shows a possibility to use these slid bilayers to tailor graphene based devices. Chapter 5 develops a method to tune band gap of bilayers of semiconducting transition metal dichalcogenides(TMDs) by the application of normal compressive strain. A reversible semiconductor to metal(S-M) transition was reported in this chapter for bilayers of TMDs. Chapter 6 shows the evolution of S-M transition from few layers to the bulk MoS2 under various in-plane and out of plane strains. S-M transition as a function of layer number has been studied for different strain types. A comparison between the in-plan and normal strain on modifying electronic properties is also presented. Chapter 7 discusses the electronic phase transition of bulk MoS2 under hydrostatic pressure. A hydrostatic pressure includes a combined effect of both in-plane and normal strain on the structure. The origin of metallic transition under pressure has been studied here in terms of electronic structure, density of states and charge analysis. Chapter 8 studies the chemical strain present in boron nitride nanoribbons and its effect on structural, electronic and magnetic properties of these ribbons. Properties of two achiral (armchair and zig-zag) edges have been analyzed in terms of edge energy and edge stress to predict stability of the edges. Chapter9 summarizes and concludes the work presented in this thesis.

Discovery of grapheme has paved way for experimental realization of many physical phenomena such as massless Dirac fermions, quantum hall effect and zero-field conductivity. Search for other two dimensional (2D) materials led to the discovery of boron nitride, transition metal dichalcogenides(TMDs),transition metal oxides(MO2)and silicene. All of these materials exhibit different electronic and transport properties and are very promising for nanodevices such as nano-electromechanical-systems(NEMS), field effect transistors(FETs),sensors, hydrogen storage, nano photonics and many more. For practical utility of these materials in electronic and photonic applications, varying the band gap is very essential. Tuning of band gap has been achieved by doping, functionalization, lateral confinement, formation of hybrid structures and application of electric field. However, most of these techniques have limitations in practical applications. While, there is a lack of effective method of doping or functionalization in a controlled fashion, growth of specific sized nanostructures (e.g., nanoribbons and quantum dots),freestanding or embedded is yet to be achieved experimentally. The requirement of high electric field as well as the need for an extra electrode is another disadvantage in electric field induced tuning of band gap in low dimensional materials. Development of simpler yet effective methods is thus necessary to achieve this goal experimentally for potential application of these materials in various nano-devices. In this thesis, novel methods for tuning band gap of few 2D materials, based on strain and stacking, have been proposed theoretically using first principles based density functional theory(DFT) calculations. Electronic properties of few layered nanomaterials are studied subjected to mechanical and chemical strain of various kinds along with the effect of stacking pattern. These methods offer promising ways for controlled tuning of band gap in low dimensional materials. Detailed methodology of these proposed methods and their effect on electronic, structural or vibrational properties have also been studied. The thesis has been organized as follows: Chapter1 provides a general introduction to the low dimensional materials: their importance and potential application. An overview of the systems studied here is also given along with the traditional methods followed in the literature to tune their electronic properties. The motivation of the current research work has also been highlighted in this chapter. Chapter 2 describes the theoretical methodology adopted in this work. It gives brief understanding of first principles based Density Functional Theory(DFT) and various exchange and correlation energy functionals used here to obtain electronic, structural, vibrational and magnetic properties of the concerned materials. Chapter 3 deals with finding the origin of a novel experimental phenomenon, where electromechanical oscillations were observed on an array of buckled multiwalled carbon nanotubes (MWCNTs)subjected to axial compression. The effect of structural changes in CNTs in terms of buckling on electronic properties was studied. Contribution from intra-as well as inter-wall interactions was investigated separately by using single-and double-walled CNTs. Chapter 4 presents a method to manipulate electronic and transport properties of graphene bilayer by sliding one of the layers. Sliding caused breaking of symmetry in the graphene bilayer, which resulted in change in dispersion in the low energy bands. A transition from linear dispersion in AA stacking to parabolic dispersion in AB stacking is discussed in details. This shows a possibility to use these slid bilayers to tailor graphene based devices. Chapter 5 develops a method to tune band gap of bilayers of semiconducting transition metal dichalcogenides(TMDs) by the application of normal compressive strain. A reversible semiconductor to metal(S-M) transition was reported in this chapter for bilayers of TMDs. Chapter 6 shows the evolution of S-M transition from few layers to the bulk MoS2 under various in-plane and out of plane strains. S-M transition as a function of layer number has been studied for different strain types. A comparison between the in-plan and normal strain on modifying electronic properties is also presented. Chapter 7 discusses the electronic phase transition of bulk MoS2 under hydrostatic pressure. A hydrostatic pressure includes a combined effect of both in-plane and normal strain on the structure. The origin of metallic transition under pressure has been studied here in terms of electronic structure, density of states and charge analysis. Chapter 8 studies the chemical strain present in boron nitride nanoribbons and its effect on structural, electronic and magnetic properties of these ribbons. Properties of two achiral (armchair and zig-zag) edges have been analyzed in terms of edge energy and edge stress to predict stability of the edges. Chapter9 summarizes and concludes the work presented in this thesis.

AbstractThe recent emergence of two-dimensional (2D) materials such as graphene and transition metal dichalcogenides (TMDs) of the family (Mo, W)(S, Se)2 has attracted interest from a broad range of engineering applications, including advanced sensing and energy harvesting and conservation, because of their distinctive properties. However, it is critical important to achieve intact delamination and transfer of these atomically thin materials, as well as to understand the effects of the target substrates on their optical and electronic properties. Therefore, we developed and compared techniques for transferring as-grown WS2 crystals to arbitrary substrates. Polystyrene-assisted wet transfer can realize improved preservation of monolayer WS2 crystals than the commonly used poly(methyl methacrylate) (PMMA)-assisted wet transfer method, due to minimal chemical etching involved in the 2D material delamination process. The intercalation of alkali ions in the PMMA-based transfer method induces chemical doping over the transferred 2D crystals, leading to the formation of trions. Moreover, the edges of the crystals on hydrophilic substrates, such as sapphire or SiO2/Si, are subject to ambient water intercalation, which locally affects the photoluminescence behavior of the monolayer WS2 by doping and changing of the dielectric environment. This non-uniform optical behavior is absent when the crystal is transferred onto a hydrophobic substrate through which ambient water cannot penetrate. These results have important implications for the choice of target substrate and transfer method adopted for 2D TMD-based applications such as next-generation strain sensing, photodetectors, gas sensing, bio sensing, solar energy harvesting and radiative cooling in which uniform behavior of the channel material is required.

Owing to their unique features such as high surface area, rich electroactive sites, ultrathin thickness, excellent flexibility and mechanical stability and multiple surface functionalities enables outstanding electrochemical response which provides high energy and power density supercapacitors based on them. Also, the Van der Waals gap between layered 2D materials encourages the fast ion transport with shorter ion diffusion path. 2D materials such as MXenes, graphene, TMDs, and 2D metal–organic frame work, TMOs/TMHs materials, have been described with regard to their electrochemical properties for MSCs. We have summarized the recent progress in MSC based on well-developed 2D materials-based electrodes and its potential outcomes with different architectures including interdigitated pattern, stacked MSC and 3D geometries for on-chip electronics. This chapter provides a brief overview of the recent developments in the field of 2D material based all-solid-state microsupercapacitors (MSCs). A brief note on the MSC device configuration and microfabrication methods for the microelectrodes have been discussed. Taking advantage of certain 2D materials such as 2D MXenes, TMDs, TMOs/TMHs that provide good surface chemistry, tunable chemical and physical properties, intercalation, surface modification (functionalization), heterostructures, phase transformations, defect engineering etc. are beneficial for enhancement in pseudocapacitance as it promotes the redox activity.

2D materials have been widely used in various applications due to their remarkable and distinct electronic, optical, mechanical and thermal properties. Memristive effect has been found in several 2D systems. This chapter focuses on the memristors based on 2D materials, e. g. monolayer transition metal dichalcogenides (TMDs) and hexagonal boron nitride (h-BN), as the active layer in vertical MIM (metal–insulator–metal) configuration. Resistive switching behavior under normal DC and pulse waveforms, and current-sweep and constant stress testing methods have been investigated. Unlike the filament model in conventional bulk oxide-based memristors, a new switching mechanism has been proposed with the assistance of metal ion diffusion, featuring conductive-point random access memory (CPRAM) characteristics. The use of 2D material devices in applications such as flexible non-volatile memory (NVM) and emerging zero-power radio frequency (RF) switch will be discussed.

Two-dimensional (2D) materials such as graphene, chalcogenides, topological insulators, black phosphorus, and MXenes have of late become the focus of intense research efforts due to the excellent and unique optoelectrical properties these materials possess. This is due to the unique properties these materials possess, such as tunable bandgaps, high mobility in the energy bandgap, third-order nonlinearity, and nonlinear absorption that can be tailored to suit the specific needs of different optical applications. These properties have allowed for the development of fiber optic-based pulsed laser systems with better integration and flexibility capabilities as well as improved performance as compared to their bulk counterparts. In this chapter, the development of optical fiber pulsed lasers that incorporate selected 2D materials, particularly 2D chalcogenides that encompass metal monochalcogenides (MMs), and traditional metal dichalcogenides (TMDs) and MXenes is reviewed. This chapter will cover the fundamental aspects of the aforementioned materials, the operating principles of Q-switching and mode-locking, and the configuration of these 2D materials as saturable absorbers (SAs). The main section of this chapter will focus on the current status of the development of Q-switched and mode-locked optical fiber laser systems using 2D material-based SAs. Finally, the chapter will explore the perspectives and challenges on the future of the potential applications of these 2D materials in pulsed optical systems.

A better understanding comes from the AFM surface investigation of irradiated silicon for application as corrosion inhibitors. A Si-surface coated with 2D materials like MoS2, graphene, MXene, MnS, SnxSy family, 2D-transition metal dichalcogenides (2D-TMDs), transition metal chalcogenides (TMCs) and 2D-layered double hydroxides (2D-LDH) nanomaterials can be used for surface protection in modern Industry 4.0 where humidity and corrosive gas pollutants plays a significant role. The role of hydrated molecule complex or ion detection sensors due to their electronic transport phenomenon and high oxygen affinity at the interfaces nearby surface is also a supportive escort. Irradiated surfaces which are coated with complex 2D metal oxide-based nanomaterials show super inhibiting properties. Ar-ion beam induced low energy irradiaton effect on silicon or metal surface holds a firm layer protection of metals underneath and has a longer life compared to general treatments. This review elaborate the interaction of atoms and ripples on Si-substrate for harmful corrosions through AFM micrographs.

Two-dimensional materials arouse ever greater interest in the scientific community due to their electronic and optical properties. Among these 2D materials, the 2D family of transition metal dichalcogenides (TMDs) offers great potential for applications in optoelectronics and nanotechnology. Of these TMD nanomaterials, platinum diselenide PtSe2 has been extensively studied since the successful synthesis of a PtSe2 monolayer in 2015. In this chapter, the multilayer PtSe2 is investigated with first-principle calculations. In order to calculate the optical properties of the system, we first determine its dielectric function. From this, we can extract other optical functions, such as refractive index, extinction coefficient, absorption coefficient, and reflectivity. A good description of these properties can be enhanced by a detailed study of the material’s band structure.

Inorganic crystalline silicon solar cells account for more than 90% of the market despite a recent surge in research efforts to develop new architectures and materials such as organics and perovskites. The reason why most commercial solar cells are using crystalline silicon as the absorber layer include long-term stability, the abundance of silicone, relatively low manufacturing costs, ability for doping by other elements, and native oxide passivation layer. However, the indirect band gap nature of crystalline silicon makes it a poor light emitter, limiting its solar conversion efficiency. For instance, compared to the extraordinary high light absorption coefficient of perovskites, silicon requires 1000 times more material to absorb the same amount of sunlight. In order to reduce the cost per watt and improve watt per gram utilization of future generations of solar cells, reducing the active absorber thickness is a key design requirement. This is where novel two-dimensional (2d) materials like graphene, MoS2 come into play because they could lead to thinner, lightweight and flexible solar cells. In this chapter, we aim to follow up on the most important and novel developments that have been recently reported on solar cells. Section-2 is devoted to the properties, synthesis techniques of different 2d materials like graphene, TMDs, and perovskites. In the next section-3, various types of photovoltaic cells, 2d Schottky, 2d homojunction, and 2d heterojunction have been described. Systematic development to enhance the PCE with recent techniques has been discussed in section-4. Also, 2d Ruddlesden-Popper perovskite explained briefly. New developments in the field of the solar cell via upconversion and downconversion processes are illustrated and described in section-5. The next section is dedicated to the recent developments and challenges in the fabrication of 2d photovoltaic cells, additionally with various applications. Finally, we will also address future directions yet to be explored for enhancing the performance of solar cells.

Commonly, metallic materials are used in practical ways to increase the shielding effectiveness (SE) through an appropriately designed assembly process. Unfortunately, the high density of devices that require it and the poor environmental stability of metals have impeded their massive use. In addition, for applications in the automotive, aerospace, and electronics industries, materials with light weight and good chemical stability are also required. The purpose of this chapter is to describe the impact that two-dimensional materials (or 2D materials) are having on the development of materials used for electromagnetic interference shielding, particularly the impulse of materials such as graphene, MXenes, transition metal dichalcogenides (TMDs), and phosphorene. The advances in the last decade are analyzed and alternatives are proposed that will come in the next decades. The shielding mechanisms presented by the two-dimensional materials are analyzed in detail and the specific applications in which these materials can be used are presented.

Transition metal dichalcogenides (TMDs) are class of materials with general formula MX2, where M is transition metal element from group IV, V, and VI (Mo, W, etc.); while X is chalcogen (S, Se, or Te). As the thickness of TMD decreases from bulk to monolayer, 2D TMDs exhibits a series of specific properties. Among all TMDs, molybdenum disulfide (MoS2) is one of the few with a natural layered structure, indicating that MoS2 can be stripped easily using scotch tape, to obtain high-quality MoS2 monolayer, without complicated chemical synthesis. MoS2 monolayer is an emergent semiconductor having a direct bandgap of 2.4 eV, and has potential applications in nanoelectronics, optoelectronics, and flexible electronics, etc.1)

The recent discovery of many-body physics such as strongly correlated electrons, superconductivity and magnetism in precisely twist angle-controlled bilayer graphene at a magic angle revived enormous interest on moiré lattice system. Many-body physics in bilayer moiré system is not limited to graphene, but rather robustly appears in 2D semiconductor materials such as transition metal dichalcogenides (TMDs). Monolayer semiconductor TMDs have conduction and valence bands with relatively large effective mass which enhances the influence of Coulomb interactions, also resulting in formation of strongly bound excitons with optical excitations. In twisted bilayer semiconductor TMDs, the superlattice effect due to the formation of moiré lattice further enhances the influence of Coulomb interaction for electrons and expected to show many-body electronic phases.

We demonstrate the strong electro-refractive response of CuCrP2S6 (CCPS)-integrated SiPh microring resonators in the near-infrared wavelength. Results show significant refractive index tuning of 2.8 x10-3 RIU with low optical losses and high modulation efficiency, outperforming earlier TMDs-based phase shifters.

Extensive attention has been paid on moiré superlattice, which is composed of two different atomically thin monolayer 2D transition metal dichalcogenides (TMDs) semiconducting materials (MX2:M=Mo, W, X=S, Se).

In this work, we predict the existence of hyperbolic-exciton-polaritons (HEPs) in 2D semiconductors of transition-metal-dichalcogenides (TMDs) at visible frequencies. We show that hyperbolicity can be induced in the layered material owing to the behavior of the excitons supported by the TMD, therefore leading to the existence of HEPs. We derive the HEPs dispersion relation, analyzing their confinement and loss properties and finding the HEPs’ wavelengths are about two orders of magnitude smaller than the corresponding free-space wavelength. Furthermore, we show that the existing HEPs are coupled to the valley degree-of-freedom, leading to a hyperbolic spin-valley hall effect.