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[la-2023-029297.R1 by authors.pdf](https://mdr.nims.go.jp/filesets/50ba8902-5a8b-465c-b496-77c58c3153f5/download)

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[Pragati A. Shinde](https://orcid.org/0000-0003-1730-2374), [Katsuhiko Ariga](https://orcid.org/0000-0002-2445-2955)

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This document is the Accepted Manuscript version of a Published Work that appeared in final form in Langmuir, copyright © 2023 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.langmuir.3c02929[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

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[Two-dimensional Nanoarchitectonics for Two-Dimensional Materials: Interfacial Engineering of Transition Metal Dichalcogenides](https://mdr.nims.go.jp/datasets/1106689d-77b1-4e6e-991c-64bbd2344e72)

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1Two-dimensional Nanoarchitectonics for Two-Dimensional Materials: Interfacial Engineering of Transition Metal DichalcogenidesPragati A. Shindea and Katsuhiko Arigaa,baResearch Center for Materials Nanoarchitectonics, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, JAPANbGraduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, JAPANAbstract: Transition metal dichalcogenides (TMDs) have been attracted increasingly attention in fundamental studies and technological applications owing to their atomically thin thickness, Page 1 of 52ACS Paragon Plus EnvironmentLangmuir1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859602expanded interlayer distance, motif bandgap, and phase transition ability. Even though TMDs own a wide variety of material assets from semiconductor to semimetallic to metallic, the materials with fixed features may not show excellence for precise application. As a result of exclusive crystalline polymorphs, physical and chemical assets of TMDs can be efficiently modified via various approaches of interface nanoarchitectonics, including heteroatom doping, heterostructure, phase engineering, reducing size, alloying, and hybridization. With the modifying properties, TMDs become interesting materials in diverse fields, including catalysis, energy, electronics, transistors, and optoelectronics. 1 IntroductionSince the successful preparation of graphene, two-dimensional (2D) materials having exclusive physical and chemical assets attracted much interest for potential applications in catalysis, energy, electronics, transistors and optoelectronics1-4. From the library of 2D materials, TMDs have recently attracted the attention of scientific research and industries owing to their exclusive crystal structures and different material properties5-7. TMDs are generally denoted as MX2, where M represents transition metal squeezed in two chalcogen X (X: S, Se, and Te) atoms in a single cell8. Metals from groups 4 to 10 have different numbers of electrons in their d orbital and filling, Page 2 of 52ACS Paragon Plus EnvironmentLangmuir1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859603resulting in diverse electronic assets such as insulator, semiconducting, semimetallic, metallic and superconductors9-11. The comprehensive series of electronic properties not only lift the progress of TMDs in electronics and optoelectronics but also enable promising bids in catalysis and energy 12-15. Furthermore, different TMDs atomic arrangements are vital in defining material properties16. In monolayer TMDs, the metal-chalcogen bond is covalent, whereas after several TMD layers stacked, it forms bulk TMD material17. Here, weak van der Waals forces hold the neighboring layers together7, 18. The weak interactions between layers are overwhelmed via the exfoliation process to get thin sheets19-20. Additionally, variations in chemical bonding and crystal structure of metal atoms lead to diverse crystalline phases of TMDs. Furthermore, the fiery popularity of TMDs relies not only on their inherent properties but also on tunable electrical and electrocatalytic performance21-22. Because of the high anisotropy and exclusive structural polymorphs, features of TMDs are efficiently modified through different strategies of interface engineering, including heteroatom doping, heterostructure, phase engineering, reducing size, alloying, and hybridization17, 23-24. For example, through phase engineering, 2H semiconducting TMDs can be converted into 1T metallic TMDs, leading to high electronic conductivity25. The alternative instance is via the incorporation of heteroatoms or Page 3 of 52ACS Paragon Plus EnvironmentLangmuir1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859604doping, charge carrier in TMDs can be modified. Recent technologies as well as devices need an inclusive collection of fine material properties, which can barely be found in a solitary material deprived of tuning. Thus, the 2D TMDs offer a giant platform for modifying the material properties to anticipate functionality, further appealing to excessive courtesy and inaugural prospects for diverse applications. This review summarizes current advancements in interface nanoarchitectonics of TMDs, mostly converging assets at the interface. 2 Crystal Structures of Transition Metal Dichalcogenides (TMDs)In a post-graphene decade, TMDs are the furthermost prevalent family of 2D layered materials because of their fascinating electronic assets and broad utilization in various arenas. For TMDs, one unit cell is three atoms thick where transition metal in each monolayer squeezed in two chalcogens, forming stoichiometric (MX2)26. The interlayer bonds in TMDs are covalent, whereas the interlayer bonds between two MX2 are generally van der Waals27. TMDs have diverse atomic arrangements, and their novel electrical properties in different polymorphs are mostly interrelated to their performance28. TMDs exist in different phases depending on the coordination of M and X atoms ((Figure 1a-e)23 , including the thermodynamically stable 2H phase with trigonal prismatic synchronization of metal atoms in each layer, where the multiple layers are stacked in the AB order Page 4 of 52ACS Paragon Plus EnvironmentLangmuir123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960529. The analogous atomic arrangements like 2H phase form 3R TMDs, but the location of M and X atoms shifted, leading to a diverse stacking order of ABC in unit cell18, 30. In disparity, 1T phase TMDs own octahedral coordination of M atoms with AA stacking order 19. The 1T TMDs can be simply changed to distorted octahedral 1T'. Because of the difference in electronic structure, 2H polymorph is semiconducting with bandgap of 1.2 – 1.9 eV, while the 1T/T' polymorph is metallic31. As the number of electrons in outer orbitals changes, total electron energy also changes, resulting in phase transition from 2H to 1T and 1T', respectively32. Thus, the electron number in d orbital and atomic arrangement of metal determines the phase, which significantly determines the assets of TMDs8. Page 5 of 52ACS Paragon Plus EnvironmentLangmuir1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606Figure 1. Atomic structures of different polymorphs of TMDs a) 1H-MX2, b) 1T-MX2, c) distorted 1T-MX2, d) 2H-MX2 and 3R-MX2. Reprinted with permission from. Ref.23. Copyright 2015 Royal Society of Chemistry.  d) top and side sights of 2H MoS2 and 1T MoS2 monolayer. Reprinted rom ref.33. Copyright 2015 American Chemical Society.The 2H polymorphs in TMDs is semiconducting and stable, whereas the 1T/T' polymorphs is metastable with high electrical conductivity34. Nevertheless, 1T/T' polymorphs undergo a phase Page 6 of 52ACS Paragon Plus EnvironmentLangmuir1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859607conversion from 1T/T' to 2H phase due to the surface atoms reordering, and reverse progression is recognized as exciting with a high alteration barrier; hence, TMDs are naturally found in 2H phase35. Experimental and theoretical studies confirm that the in 2H TMDs edge sites are electrochemically active for electrochemical reactions, whereas basal planes are chemically inactive21, 36. In contrast, basal planes are more functional for 1T/T' TMDs, as edge and in-plan atoms are energetic in 1T/T' polymorphs rather than only edges in 2H TMDs37. In MoS2, the individual unit cell comprises Mo atoms squeezed in two S atoms. Based on atomic arrangement (S-Mo-S), MoS2 is commonly observed in two crystalline phases, 1T and 2H. As seen in Figure 1d, a single Mo was bounded by six S atoms in both polymorphs. In 2H MoS2, Mo atoms are prismatically synchronized to S atoms in top and bottom planes, whereas in 1T phase MoS2, Mo atoms coordinated octahedrally with S layers and S atoms in top and bottom planes are balanced33.3 Engineering Strategies of InterfacesIn recent years, TMDs have offered a huge platform for scientific research and their practical applications in electronics, catalysis, and energy storage fields38. Various efficient methods have been developed to fully exploit their potential to produce TMDs with desired phase structure, mixed phase, and defects. Distinct from bulk materials, 2D TMDs are interface-type materials, and Page 7 of 52ACS Paragon Plus EnvironmentLangmuir1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859608their performance for particular applications is structured and revealed by the interface. The TMDs crystal deepened with inherent defects like vacancies, grain boundaries, and substitutional impurities. The presence of such defects indicates a noteworthy influence on the electrical conductivity and performance activity of TMDs based devices. Therefore, is necessary to develop different strategies of defect and interface engineering to accomplish materials with unique features and high performance. The interface nanoarchitectonics enables carrier transport, persuades successful doping, and amends the band structure and phase modulation in TMDs; based on which multifunctional heterostructures can be constructed. With this, understanding the role of the interface and developing efficient interface engineering strategies is of great influence for further developments of TMDs-based electronics, optoelectronics, transistors, catalyst and energy storage devices. The investigation of actual approaches to tune basal planes of TMDs is significantly vital for the imminent progress of such an auspicious library of compounds. Figure 2 shows a schematic illustration for different strategies of interface nanoarchitectonics in TMDs.Page 8 of 52ACS Paragon Plus EnvironmentLangmuir1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859609Figure 2. Schematic design for the different approaches of interface nanoarchitectonics in TMDs.3.1 Doping with HeteroatomsDoping is an active technique to skill the properties of TMDs via incorporating impurities. TMDs have different properties extending from insulating to semiconducting to metallic. Doping in TMDs is a capable method to alter the structure and electrical, optical, magnetic, and electrochemical properties of TMDs via altering band alignment39. In TMDs, dopant atoms are introduced in layers or change the structure to form a different phase. Substitution of dopant atoms can be a direct substitution in lattice or interstitial regions in existing atoms in a lattice of TMDs40. For catalysis and energy applications, doping increases electroactive sites by altering the surface architecture to interpret formation of additional active sites e.g., basal plane of TMDs, thus enhancing the catalytic and energy storage performance41-42. MoS2 is a promising material for Page 9 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596010catalysis and storage applications; however, boundaries associated with its low electrical conductivity and few surface-active sites restrict its performance43. Among the numerous approaches employed to improve the activity of MoS2, one effective strategy is heteroatom metal doping in MoS2 lattice to improve the number of active sites. Until now, different metal intercalated MoS2 has been stated, including Co-doped MoS244, Ni-doped MoS245, Pd-doped MoS246 and P-doped MoS247. Li and coworkers doped Pt in MoS2 and achieved fractional phase transition of MoS2 from 2H to 1T phase, leading to enhanced HER performance48. The metal doping into MoS2 gives phase transition, enhances electrical conductivity, and decreases charge-transfer resistance49-51. The flower-like MoS2 was seen in the TEM image (Figure 3a). The STEM showed two crystallographic phases in Pt-doped MoS2, 2H and 1T MoS2 (Figure 3b). The downshifts in S 2p and Mo 3d spectra demonstrated successful 2H to 1T phase transition (Figure 3c, d). Such a phase transition after doping might be caused by an electron donated from the Pt atom after doping into MoS2 lattice. DFT optimized structures showed three possible Pt doping sites in MoS2 (Figure 3e-g). DFT analysis again revealed that S species next to Pt in MoS2 acted as furthermost active regions for HER (Figure 3h-j). Even though most of the reports showed that doping into TMDs increases the performance of materials with great improvement in conductivity Page 10 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596011of TMDs, however heavily doped electronegative dopants such as phosphorus cause low conductivity owing to the delocalized electrons in metal52. Song et al.52 in their recent work, demonstrated that during phosphorus doping, reaction time, temperature and percentage of phosphorus was essential to achieve more benefits as P doping into MoS2 at low temperature retain the morphology. On the other hand, Yacaman et al.53 utilized red phosphorus for P doping into MoS2 lattice at 900 ºC, that caused ruin of MoS2 morphology. Furthermore, Li et al.54 reported fabrication of 1T@2H MoS2 homojunction and achieved high activity for supercapacitors. Te thermal treatment of MoS2 led to formation of 1T@2H MoS2 (Figure 3k). Authors verified that Te intercalation in MoS2 lattice triggered the interlayer expansion, offered high conductivity, and facilitated charge transportation and ion diffusion. 1T@2H MoS2 showed 6-10 layers with increased interlayer distance of 0.64 nm than the bare 2H MoS2 (0.615 nm) with two distinct lattice regions corresponding to 1T MoS2 and 2H MoS2, respectively (Figure 3l). Some crystalline phase deformation and defects were observed after Te doping, which helps to enhance electrochemical performance (Figure 3m). Liu and coworkers55 designed P intercalation into MoS2 nanosheets to incorporate electroactive sites on the basal plane, increase interlayer spacing, and utilized P-doped MoS2 for electrocatalysis. The excellent HER activity was achieved with a Tafel slope of 34 Page 11 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596012mV/dec and a small overpotential of 43 mV. Similarly, Shi et al.56 developed Co-doped tungsten oxide first and then converted oxide into sulfide by sulfurization. The obtained Co-doped WS2 showed excellent HER activity with an overpotential of 210 mV at 10 mA cm-2.The thermal stability of TMDs is lower than that of conventional semiconductors such as Si. Therefore, the thermal diffusion at high temperatures for doping in TMDs is inappropriate. Substitutional metal/non-metal doping during the growth process of TMDs is more favorable, which moderates the carrier density through the growth process. Numerous endeavors have done to obtain selective doping for a wide-scale synthesis process. The dopant can be selectively injected into the TMDs lattice, creating defective sites. The post-annealing after-growth process is sometimes required to activate the dopant and reconstruct the crystal structure. Generally, doping introduces impurity atoms into the TMDs structure. However, most of the time, impurity atoms are matchless to the TMDs creative lattice structure, which does not replace the original atoms of TMDs. In such a case, impurity atoms are doped into the inner region of TMDs, and many such impurity atoms disrupt the lattice structure. As previously reported by Zhang and coworkers57 when the doping concentration of Mn in MoS2 is higher than 2%, the lattice structure of MoS2 gets degraded. The different metals and non-metals can be selected as dopants for TMDs; however, the Page 12 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596013doping concentration should be optimized. Further studies are needed to investigate systematically doping into the TMDs and its associated challenges.Figure 3. a, b) TEM and STEM for Pt@MoS2, c, d) XPS spectra of S 2p, and Mo 3d of MoS2 and Pt@MoS2, e-g) DFT structures for Pt doping sites and equivalent formation energy. h) Free energy plots of HER at the equilibrium potential. i) Top and side view of the structure of H atom absorbed on the S atom of Pt@MoS2. j) Probable p-orbital DOS of S. Reprinted with permission from ref.48. Page 13 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596014Copyright 2021 Elsevier. k) Schematic protocol for fabrication procedure of Te-doped 1T@2H MoS2. l and m) atomic prearrangement of 1T (red circles) and 2H (green circles) phases and a Fourier transform image. Reprinted with permission from ref.54. Copyright 2019 Royal Society of Chemistry.3.2 Surface Phase Modulation/Phase EngineeringPage 14 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596015Figure 4. a) Schematic protocol for the partial phase conversion in MoS2, b) SEM image of 1T-2H MoS2, c) HRTEM image showing atomic arrangement for 2H and 1T phase, d) XRD pattern and XPS spectra of e) Mo 3d and f) S 2s of T-2H MoS2. Reprinted with permission from ref.58. Copyright 2018 Wiley-VCH, g) plot of formation energies of 2H MoS2 with S vacancies, O atoms and mixture of both. Reprinted from ref.59. Copyright 2018 American Chemical Society, h) Atomic model presenting the hydrogen-triggered synthesis of WS2-ReS2 and i) high-resolution ADF-STEM of heterojunction. Reprinted with permission from ref.60. Copyright 2020 Wiley-VCH.Interface nanoarchitectonics through surface phase modulation is an efficient method to regulate the performance of TMDs. As discussed in the above section, TMDs are found in both metallic and semiconducting phases, namely, 1T, 2H, and 3R, based on the arrangement of M and X atoms. The phase transition in TMDs from naturally occurring 2H to 1T phase can be triggered by several routes, including chemical exfoliation, alkali metal ion intercalation, plasma treatment, electron beam irradiation, hot electron injection, etc23. The phase modulation in single-layer TMDs mainly depends on the number of electrons in d-orbital of metal. Modification in the filling of d-orbitals permits phase transition. Until now, there are several reports on the phase transition of group 6 TMDs including MoS2, MoSe2, WS2, and Page 15 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596016WSe261-63. The phase conversion in MoS2 was first attained via alkali ion intercalation, which now became a common strategy for triggering phase conversion in other TMDs64. The conversion 2H to 1T phase was prompted by electron transfer from the s-orbital of alkali metal to the d-orbital of transition metal27. For example, Li-intercalation in 2H MoS2 led to the construction of 1T phase MoS265. The inverse scenario of 1T to 2H phase conversion was seen in TaS2 after Li-intercalation66. Kumar and coworkers67 adopted the Li-ion exfoliation technique for 2H to 1T phase conversion in MoS2 and got 78.6% 1T phase in the final product. The obtained material showed good catalytic activity with a Tafel slope of 53 mV/dec and an overpotential of 262 mV.Recent studies from Wang et al.58 demonstrated 1T-2H MoS2 heterostructures via annealing of 2H MoS2 in phosphorus vapors and Ar gas. Here, phosphorus was embedded into the interior of MoS2 and inhabited the interspace in bulk MoS2, inducing expansion of MoS2 and, at the same time, fractional phase transfer from 2H to 1T phase. The obtained 1T-2H MoS2 heterostructures showed a good electronic conductivity of 8620 S m-1, 500 times larger than bulk 2H MoS2 (16.1 S m-1). Figure 4a demonstrates a typical procedure for the fabrication of 1T-2H MoS2, where 2H MoS2 was treated at high temperature in red P vapor in an Ar atmosphere. The numerous nanosheets of 2H MoS2 having lateral sizes of 500 nm to 5 µm were formed (Figure 4b). TEM image revealed two different lattice regions in plane consistent to Page 16 of 52ACS Paragon Plus EnvironmentLangmuir123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960172H MoS2 and 1T MoS2, individually (Figure 4c). The most substantial diffraction peak in 2H MoS2 corresponding to (002) was observed at 14.5 º, which shifted to 14.1 º in 1T-2H MoS2, indicating increased interlayer distance (Figure 4d). Analogous results were observed in XPS spectra of Mo 3d (Figure 4e) and S 2s (Figure 4f), where peaks corresponding to 1T MoS2 appeared on decreased binding energies. Gan and coworkers59 performed another exciting study on phase engineering of MoS2. Here, phase conversion in MoS2 was achieved without intercalation of guest species. This study triggered phase conversion via cyclic voltammetry by electrochemical integration of S vacancies and O intercalation into the S-Mo-S. DFT analysis revealed that the S vacancies and O doping were responsible for decreasing the band gap of MoS2, forming 1T phase, and enhancing material conductivity. The band structures of 2H-MoS2 (Figure 4g) were constructed because phase transition, integration of S vacancies and O-doping happened mostly on the basal plane of 2H-MoS2. The figures showed that to form 3.7% S vacancies in 2H-MoS2, more energy than 3.7% O atoms was required. O intercalation caused development of S vacancies as S vacancies become electronegative with the upsurge of O atoms. The authors showed that the 1T/2H MoS2 showed much improved electrocatalytic performance compared to bare MoS2 due to tuning of both structural and electronic properties. Furthermore, MoS2 with 1T/2H interface exhibits excellent performance owing to metallic 1T MoS2 in direct contact Page 17 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596018with 2H MoS2, thus avoiding the van der Waals gap barriers68. In a 2H to 1T phase transfer process, MoS2 initially converted into a transitional 1T' state and later 1T phase. Thermodynamically, 2H MoS2 was more stable than the other MoS2 polymorphs. Similarly, fluorine intercalation in WS2 persuades phase conversion from 2H phase to 1T phase69. Fluorination improves stability of 1T WS2, making it more stable than the 2H WS2.Usually, phase conversion in exfoliated TMDs is incomplete, showing a fraction of 2H and 1T phases forming the 2H-1T hybrid phase70. 1T MoS2 and 1T WS2 show metallic characteristics, whereas the 1H-1T hybrid interfaces signify new electronic heterojunctions transversely layered structures, promising for electronic devices. Moreover, 2H to 1T phase conversion in MoTe2 via laser irradiation was studied by Tan et al.71 The Te vacancies created due to the laser irradiation offer a driving force for such phase transition. One of the most remarkable recent studies was conducted by Liu and Xu60. In this study, authors engineered 2H-1T′ WS2-ReS2 heterophase having a strident interface through hydrogen-incorporated chemical vapor deposition (Figure 4h). The heterophase structure was obtained by altering the carrier gas concentration in hydrogen. The authors showed that the growth of monolayer ReS2 was possible using argon gas, whereas a mixture of argon and hydrogen gas formed monolayer WS2. The sharp 2H-1T heterophase interface for WS2-ReS2 heterojunction Page 18 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596019shown in Figure 4i differentiates WS2, ReS2, and interface sites. The electrical transport measurements across such heterophase junctions disclose solid refinement structures and polarization-sensitive photodiode properties.  In our recent study, we developed 1T-2H WS2 heterostructures through nanoarchitectonics of phosphorus mediated 2H to 1T phase transition. The obtained dual-phase 1T-2H WS2 showed 2D transformable phase structure, enlarged interlayers and electrochemically active sites. From the theoretical analysis it was proved that the 1T WS2 phase obtained after phosphorus doping exhibited semimetallic nature with improved electronic conductivity. Here, edge-enriched metallic phase and enhanced interlayer distance of 1T-2H WS2 heterostructures authenticate high Na+ ion intercalation efficiency for hybrid supercapacitor.72 Another remarkable phase engineering study was reported by Zhai and coworkers, where reversible phase transition in WS2 occurred73. The earlier reported literature on the phase transition of TMDs is mostly irreversible. The proton intercalation-deintercalation into semimetallic 1T'-WS2 leads to reversible phase transition and distorted octahedral 1T'd – WS2 formation. After proton deintercalation, the newly formed 1T'd – WS2 completely transformed to the original 1T'-WS2. The reversible phase transition phenomenon in TMDs is advantageous for transistors and memory devices. Page 19 of 52ACS Paragon Plus EnvironmentLangmuir123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960203.3 Interface Engineering Between TMDs and Carbon-Based MaterialsCarbon-based materials are widely employed as a backbone to improve the performance of TMDs, and each possesses unique characteristics and properties74. WS2 monolayer has been reported as a direct semiconductor with a wide band gap of 1.98 eV75, which is poor conductive for electron transfer. Zhang et al.76 developed a graphene/WS2 heterostructure to advance charge transfer features of monolayer WS2. The electronic band structures of graphene and WS2 were presented in Figure 5a and b. Graphene demonstrated complete metallic features with zero band gap, whereas monolayer WS2 revealed a wide band gap. Figure 5c showed that graphene/WS2 heterostructure demonstrated a band gap of ~1 eV, much smaller than monolayer WS2. In heterostructure, band structure of WS2 drifts downside, which minimizes the wide band gap of WS2 (Figure 5d). The graphene in heterostructure efficiently improves the conductivity and donates the metallic characteristic to heterostructure, thus improving graphene/WS2 heterostructure performance. Furthermore, Wang et al.77 developed electronic structures of twisted bilayers of graphene/MoS2. Authors showed that there is significant difference in band structures of twisted bilayers of graphene/MoS2 and non-twisted one. Figure 5e and f demonstrated the structural arrangements of graphene/MoS2 with different interlayer rotation angle. The band structure obtained for two Page 20 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596021different rotation angles (Figure 5g) showed that the E-k dispersion relations are almost same for these two angles with negligible difference of 0.02 eV shift in MoS2 energy states. Figure 5. The electronic band structures of a) graphene, b) monolayer WS2, c) and d) graphene/WS2 heterostructure. Reprinted with permission from ref.76. Copyright 2012 Elsevier. Geometric structures of graphene/MoS2 with different interlayer rotation angle e) θ= 3º, f) θ= Page 21 of 52ACS Paragon Plus EnvironmentLangmuir1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859602224.8º and g) corresponding band structures and PDOS. Reprinted from ref.77. Copyright 2015 American Chemical Society.Furthermore, numerous attempts have been made to explore the geometric and electrical properties of TMDs combined with other 2D materials. Different studies on TMDs/graphene specify that such heterostructure can persuade hetero-interfacial charge transfer and improve thermodynamic stability78. Yu and coworkers reported another interesting structural feature of MoS2/graphene heterostructure79. The synthesis procedure for self-assembled MoS2/graphene through electrostatic attraction was shown in Figure 6a. The thermal treatment of MoS42–/PEI/GO layers removes redundant PET and converts MoS42– to Mos2 and graphene oxide to graphene with stacked architecture. The low angle diffraction peaks at 7.99° and 16.98° in the XRD pattern showed extended interlayer spacings of MoS2 and distance between MoS2 and graphene (Figure 6b). Analogous results were obtained for Raman spectra of MoS2/graphene (Figure 6c). The interface of MoS2 and graphene with exclusive structural features led to edge-active sites and defects in the heterostructure, which improved electronic conductivity. Ratha et al.80 prepared WS2/reduced graphene oxide (RGO) through a hydrothermal route for supercapacitor. TEM and HRTEM images (Figure 6d, e) for WS2/RGO demonstrated the even dispersal of WS2 on RGO. Due to the Page 22 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596023multiple chemical states of W atoms from +2 to +6, excellent energy storage performance was achieved in 1M Na2SO4 electrolyte. Zhang et al.81 reported single-layer mesoporous MoS2/carbon using SBA-15-P123 duel-template. The template avoids the addition of carbon and the use of sulfur source. The MoS2/carbon revealed good sodium storage with a 310 mA h/g capacity at 5 A/g. Recently, bimetallic chalcogenide-tagged nitrogen-doped carbon (NbMo6S8/NC) nanosheets were demonstrated for aqueous Zn-ion capacitors. Here nitrogen doping in carbon avoided NbMo6 S8 nanoflower aggregation, increased interlayer spacing and made disordered structure. The obtained NbMo6S8/NC electrode illustrated excellent electrochemical performance with a specific capacity of 167.89 mA h g−1 at 0.25 A g−1.82 So far, CuxS/carbon composite83, WS2/carbon84, Co9S8/carbon, NiSx/porous carbon85, etc., has been developed, showing significant performance improvement through the interface approach.Page 23 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596024Figure 6. a) synthesis procedure for MoS2/graphene, b) XRD pattern and Raman spectra for  MoS2/graphene. Reprinted from ref.79. Copyright 2020 American Chemical Society, d and e) TEM Page 24 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596025and HRTEM images of WS2/RGO hybrid. Reprinted from ref.80. Copyright 2013 American Chemical Society.3.4 Interface Engineering between TMDs and Metal OxidesUnlike individual 2D TMDs approaches, combining 2D and 1D materials with precise dimensions and diverse properties is expected to give multiple compensations when used in a device. Various approaches have been developed to advance the activity of TMDs, which mainly include performance improvement through electronic conductivity engineering and active site engineering. As discussed in the above section, electronic conductivity can be increased through heteroatom doping and phase transition, enabling interfacial charge transport. The active sites can be increased through surface medication. Recently, researchers enhanced the activity of 2D TMDs by developing metal sulfide/oxide heterojunction to improve the materials' performance through hybridization synergistic effect. For example, Hu et al.86 developed high-performance MoS2/metal oxide heterostructures through modulating interface electronic structure. The electronic structures of MoS2/Ni2O3H, MoS2/Co3O4, and MoS2/Fe2O3 were attained from the density functional theory Page 25 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596026(DFT) calculations (Figure 7a-c). The electron distribution was mainly observed on the interface near the Fermi level (Ef) for MoS2/Ni2O3H. The apparent strain was observed near the interface, leading to structure distortion, and the most electroactive sites were transition metals near the interface. Figure 7d-g demonstrated that high electrochemically active sites were at the TMDs/metal oxide interface region, suitable for the hydrogen evolution activity. From the sensitivity of 3d-band in different transition oxides, Ni-3d of Ni2O3H towards the interface is highly stimulated to accomplish fast electron transfer. Wang and coworkers87 prepared WS2 nanotubes by sulfurization of WO3 nanowires. The HRTEM images in Figure 7h and i demonstrated three-layer walled and six-layer walled WS2 nanotubes, respectively, with the same outer diameter of 10 nm. It was clearly seen that a longer sulfurization time increased the number of WS2 layers. Thus, WO3/WS2 interface structure was easily obtained by controlling the preparation conditions. Page 26 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596027Figure 7. The contour plots for bonding and anti-bonding orbitals near the fermi level for a) MoS2/Ni2O3H, b) MoS2/Co3O4, and c) MoS2/Fe2O3. d) PDOSs of 3d bands of MoS2/Ni2O3H, MoS2/Co3O4, and MoS2/Fe2O3. e) Site-dependent 3d-band of Ni in MoS2/Ni2O3H. f) Site-dependent 3d-band of Co in MoS2/Co3O4. g) Site-dependent 3d-band of Fe in MoS2/Fe2O3. Reprinted with permission from ref.86. Copyright 2020 Wiley-VCH. HRTEM images for h) three-layer and i) six-layer WS2 nanotubes and inside WO3 core. Reprinted with permission from ref.87. Page 27 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596028Copyright 2016 Springer-Nature. j) Gibbs free energy diagram for hydrogen evolution of 2H MoS2, 1T MoS2 and V doped 1T MoS2 and k) Gibbs free energy of V doped 1T MoS2 in a pH range of 0 to 13. Reprinted with permission from ref.88. Copyright 2021 Elsevier.Li and co-workers88 developed vanadium doped 1T MoS2 nanosheets directly on a carbon paper. Here, the direct growth of material on current collector empowers good integration and decreases the resistance. The hydrazine molecules form precursors intercalated into MoS2 and acted as Lewis base, provided additional electron to maintained 1T phase of MoS2. Theoretical calculations proved that the vanadium doped 1T MoS2 offered nearly zero Gibbs free energy, which achieved best hydrogen adsorption. Figure 7j showed the calculated Gibbs free energy diagram for hydrogen evolution activity of 2H MoS2, 1T MoS2 and vanadium doped 1T MoS2, which proved that vanadium doped 1T MoS2 had lowest ∆GH value of 0.03 eV and better performance. The Gibbs free energy of vanadium doped 1T MoS2 in full pH range was shown in Figure 7k. Jung and Choudhari89 developed a 1D/2D WO3/WS2 core-shell interface structure directly on the W foil substrate through an unprompted oxidation/sulfurization process. Similarly, WS2@NiCo2O490, Co3O4/MoS291 TMDs/metal oxide heterostructures have been developed with exciting interface properties. Thus, the overall results indicate that composites of TMDs with metal oxides enhance Page 28 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596029the conductivity of material, facilitating rapid charge carrier transport, which may be further employed for potential applications.4 ConclusionsThe recent advancement in interface and phase engineering of 2D TMDs for tuning their properties to achieve high electronic conductivity and superior interfacial characteristics has been reviewed. Different types of interfaces in TMDs-based materials arising from intercalation of guest ions, phase modulation, TMDs/carbon, and TMDs/metal oxide contact, which can be adequately engineered through interface engineering strategies. The phase transition via surface charge doping at the TMDs interface has been considered an efficient way to modify the charge carrier density, which deliberately impacts the electronic properties and performance of device. The TMDs/metal interface obtained via heteroatom doping i.e., intrinsic impurity atoms present at TMDs interface, enables charge carrier transport in TMDs. Furthermore, partial phase conversion in TMDs from naturally occurring 2H semiconducting to 1T metallic phase showed superior structural advantages, improved electrical conductivity, and highly exposed basal and edge active sites that are advantageous for catalysis and energy applications. For energy storage devices such as supercapacitors and rechargeable batteries, interface engineering improves the charge storage Page 29 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596030efficiency through their expanded interlayers. As an HER electrocatalysis, this strategy lowers the Gibbs free energy, enables fast proton/electron adsorption and hydrogen release, beneficial for good HER activity. Moreover, interface nanoarchitectonics analyses92 different defects present in the lattice structure of TMCs, including intercalated impurities, grain boundaries, vacancies, and phase conversion and their consequences on the electronic features of TMCs. Proper interface engineering can remarkably enable charge carrier density, creating active heteroatom intercalation and dropping the contact resistance in electronic devices. Furthermore, implementation of electronic as well as energy storage and conversion devices based on 2D TMDs necessitates controlled interface engineering to further improve their charge carrier density and device performance. This strategy can be further prolonged to produce TMDs with dual-phase structures, interfaces, and defects and sheds light on the expansion of future 2D TMDs. Even though there has been much advances in the development of phase modulated and interlayer expanded TMDs and their wide applications in various fields, still there are many challenges. It is tough to synthesize TMDs in a single step with controlled size, layer number, interlayer distance phase composition, number of guest species to obtained optimal material and Page 30 of 52ACS Paragon Plus EnvironmentLangmuir12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758596031performance are yet to be industrialized. The relation between quantities, type of guess ions and interlayer distance and their device performance are not yet well-known. The intercalation sites of guest dopants and their intercalation with TMDs need to be understood. Author InformationCorresponding Author* Prof. Katsuhiko Ariga - Research Center for Materials Nanoarchitectonics, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Japan; Email: ARIGA.katsuhiko@nims.go.jp. *Dr. Pragati A. Shinde - Research Center for Materials Nanoarchitectonics, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba 305-0044, Japan; Email: SHINDE.PragatiAnkush@nims.go.jp. NotesThe authors declare no competing financial interest.AcknowledgmentPage 31 of 52ACS Paragon Plus EnvironmentLangmuir123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960mailto:SHINDE.PragatiAnkush@nims.go.jp32This work is supported by the Japan Society for the Promotion of Science (JSPS) KAKENHI Grant Number JP22F22368.References1. Luo, B.; Liu, G.; Wang, L., Recent advances in 2D materials for photocatalysis. Nanoscale 2016, 8 (13), 6904-6920.2. Schaibley, J. R.; Yu, H.; Clark, G.; Rivera, P.; Ross, J. S.; Seyler, K. L.; Yao, W.; Xu, X., Valleytronics in 2D materials. Nature Reviews Materials 2016, 1 (11), 1-15.3. Wang, F.; Wang, Z.; Yin, L.; Cheng, R.; Wang, J.; Wen, Y.; Shifa, T. A.; Wang, F.; Zhang, Y.; Zhan, X.; He, J., 2D library beyond graphene and transition metal dichalcogenides: a focus on photodetection. Chemical Society Reviews 2018, 47 (16), 6296-6341.4. Shinde, P. A.; Olabi, A. G.; Chodankar, N. R.; Patil, S. 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