Jiuxiang Dai

Abstract

Light-matter interactions in two-dimensional transition metal dichalcogenides (TMDs) are sensitive to the surrounding dielectric environment. Depending on the interacting strength, weak and strong exciton-photon coupling effects can occur when the exciton energy is resonant with the one of photon. Here we report angle-resolved spectroscopic signatures of monolayer tungsten disulfide (1L-WS₂) in weak and strong exciton-photon coupling environments. Inherent optical response of 1L-WS₂ in the momentum space is uncovered by employing a dielectric mirror as substrate, where the energy dispersion is angle-independent while the amplitudes increase at high detection angles. When 1L-WS₂ sits on top of a dielectric layer on silicon, the resonant trapped photon weakly couples with the exciton, in which the minimum of reflection dip shifts at both sides of the crossing angle while the emitted exciton energy remains unchanged. The unusual shift of reflection dip is attributed to the presence of Fano resonance under white-light illumination. By embedding 1L-WS₂ into a dielectric microcavity, strong exciton-photon coupling results in the formation of lower and upper polariton branches with an appreciable Rabi splitting of 34 meV at room temperature, where the observed blueshift of the lower polariton branch is indicative of the enhanced polariton-polariton scattering. Our findings highlight the effect of dielectric environment on angle-resolved optical response of exciton-photon interactions in a two-dimensional semiconductor, which is helpful to develop practical TMD-based architectures for photonic and polaritonic applications.

This review aims to summarize the nearest developments about the 2D van der Waals heterostructures (vdWHs) and vdW superlattices (vdWSLs) preparation via bottom-up methods (e.g., chemical/physical vapor deposition (C/PVD), ultrahigh vacuum (UHV) growth), related physical phenomenon and (opto)electronic devices. The authors summarize the current challenges and future perspectives in the synthesis and application of vdWHs and vdWSLs.

Abstract

2D van der Waals heterostructures (vdWHs) and superlattices (SLs) with exotic physical properties and applications for new devices have attracted immense interest. Compared to conventionally bonded heterostructures, the dangling-bond-free surface of 2D layered materials allows for the feasible integration of various materials to produce vdWHs without the requirements of lattice matching and processing compatibility. The quality of interfaces in artificially stacked vdWHs/vdWSLs and scalability of production remain among the major challenges in the field of 2D materials. Fortunately, bottom-up methods exhibit relatively high controllability and flexibility. The growth parameters, such as the temperature, precursors, substrate, and carrier gas, can be carefully and comprehensively controlled to produce high-quality interfaces and wafer-scale products of vdWHs/vdWSLs. This review focuses on three types of bottom-up methods for the assembly of vdWHs and vdWSLs with atomically clean and electronically sharp interfaces: chemical/physical vapor deposition, metal-organic chemical vapor deposition, and ultrahigh vacuum growth. These methods can intuitively illustrate the great flexibility and controllability of bottom-up methods for the preparation of vdWHs/vdWSLs. The latest progress in vdWHs and vdWSLs, related physical phenomena, and (opto)electronic devices are summarized. Finally, the authors discuss current challenges and future perspectives in the synthesis and application of vdWHs and vdWSLs.

Nature Communications, Published online: 18 March 2022; doi:10.1038/s41467-022-29182-y

npj 2D Materials and Applications, Published online: 18 March 2022; doi:10.1038/s41699-022-00290-z

This work reports the ratiometric luminescence thermography integrated on micro–nano devices vertically based on 2D van der Waals rare earth material ErOCl. 2D ErOCl endows the thermometer with wide-range temperature probing (300–700 K), high relative sensitivity (2.2% K⁻¹ at 300 K), and high repeatability. This novel approach will shed light on the development of a higher integration of electronics.

Abstract

Remote and real-time thermography integrated on micro–nano devices vertically can promote the integration while estimating their operation, which is hitherto challenging. Here, the ratiometric luminescence thermography integrated on micro–nano devices vertically based on 2D van der Waals (vdW) rare earth (RE) material ErOCl is demonstrated. Ratiometric luminescence intensity varies linearly with temperature deriving from the thermal activation between two thermally coupled levels. Typically, this ratiometric micro–nano thermometer has a wide sensing range (300–700 K), high relative sensitivity (2.2% K⁻¹ at 300 K), and high repeatability. With layered structure and insulated properties, 2D ErOCl can be easily integrated on the target chips vertically without dangling bonds so that a high-density integration can be easily realized. Therefore, 2D ErOCl is employed for thermography of a designed micro–nano device, showing real-time, high-resolution temperature distribution of single device even at electrodes with different morphologies. The feasibility of this temperature sensor is further proved by COMSOL simulation. This novel approach, 2D vdW RE based ratiometric luminescence thermography, provides an excellent platform to the development of high performance eletronics with higher integration.

Graphene with linear energy dispersion and weak electron–phonon interaction is highly anticipated to harvest hot electrons in a broad wavelength range. However, the limited absorption and serious back scattering of hot-electrons result in inadequate quantum yields, especially in the mid-infrared range. Here, the greatly enhanced photo-thermionic effect of wafer-scale macroscopic assembled graphene nanofilm largely extends the photodetection of graphene/silicon Schottky diode from 1.5 to 4 μm.

Abstract

Graphene with linear energy dispersion and weak electron–phonon interaction is highly anticipated to harvest hot electrons in a broad wavelength range. However, the limited absorption and serious backscattering of hot-electrons result in inadequate quantum yields, especially in the mid-infrared range. Here, we report a macroscopic assembled graphene (nMAG) nanofilm/silicon heterojunction for ultrafast mid-infrared photodetection. The assembled Schottky diode works in 1.5–4.0 μm at room temperature with fast response (20–30 ns, rising time, 4 mm² window) and high detectivity (1.6 × 10¹¹ to 1.9 × 10⁹ Jones from 1.5 to 4.0 μm) under the pulsed laser, outperforming single-layer-graphene/silicon photodetectors by 2–8 orders. These performances are attributed to the greatly enhanced photo-thermionic effect of electrons in nMAG due to its high light absorption (~40%), long carrier relaxation time (~20 ps), low work function (4.52 eV), and suppressed carrier number fluctuation. The nMAG provides a long-range platform to understand the hot-carrier dynamics in bulk 2D materials, leading to broadband and ultrafast MIR active imaging devices at room temperature.

Abstract

Maximizing wave function overlap (WFO) within type-II superlattices (T2SL) is demonstrated to be important for improving their photoelectric properties, such as optical transition strength and quantum efficiency, which, however, remains a great challenge for now. Herein, the dual strategy of modulating growth temperature and inserting ultrathin AlAs barrier into the AlSb layers is presented to enhance the WFO in InAs/AlSb T2SL. The charge distributions and strain states indicate that moderate growth temperature of 470 °C promotes the As-Sb exchange at AlSb-on-InAs (AOI) interfaces, which would introduce skew of energy band structure towards InAs-on-AlSb (IOA) interface. Such band structure could drive electrons and holes to the IOA interfaces simultaneously, thus resulting in the enhanced WFO. On this basis, insertion of relatively thick (0.3 nm) AlAs layers is found to squeeze more holes towards adjacent interfaces, boosting the WFO further. The InAs/AlSb superlattices with optimized WFO reveal better optical performance, where the peak intensity shows 50% improvement in the PL spectra than the original one. Moreover, a dual-miniband radiative transition mechanism appears in the InAs/AlSb superlattice with relatively thick AlAs intercalation, which helps broaden the wavelength range of the superlattice.

The chemical vapor deposition-grown hexagonal WS₂ monolayer always exhibits alternating bright and dark photoluminescence domains. The correlation between the patterned photoluminescence emission and the details of defects is explored consistently by experiments and density functional theory calculations. The results indicate that the WS-vacancy is the most likely vacancy that matters.

Abstract

Monolayer transition-metal dichalcogenides grown by chemical vapor deposition (CVD) always contain certain types of defects that dramatically affect their electronic and optical properties. For CVD-grown hexagonal WS₂ monolayer, complex photoluminescence (PL) patterns are commonly observed, but the defect-related optical mechanisms are still not well understood. Here, by combining the optical and structural characterizations and ab initio calculations, the correlation between the patterned PL emission and the details of defects in CVD-grown hexagonal WS₂ monolayer are revealed. The temperature-dependent PL spectra show the correlation between the defect-trapped and band-edge exciton emission. The high-resolution scanning transmission electron microscopy identifies the positive correlation between the density of WS _x -vacancy and PL intensity. In the end, the ab initio calculations and molecule adsorption PL spectra show that the coexistence of p- and n-doping effects, caused by the W and S complex vacancy, weakens the modulation of molecular adsorption on PL intensity. This work gives new insights into the origin of the inhomogeneous PL distribution in WS₂ monolayer, which provides important guidance in the regulation of electronic and optical properties of transition-metal dichalcogenides via defect engineering.

V-NAND flash memory, regarding charge-trap materials (polycrystalline Si vs Si₃N_{4− x} ), cell array architecture (NOR vs NAND), device configuration (2D vs 3D), and multilevel cell technologies is reviewed. Ways to overcome current challenges in materials and process technologies for 3D V-NAND are also suggested.

Abstract

Vertically integrated NAND (V-NAND) flash memory is the main data storage in modern handheld electronic devices, widening its share even in the data centers where installation and operation costs are critical. While the conventional scaling rule has been applied down to the design rule of ≈15 nm (year 2013), the current method of increasing device density is stacking up layers. Currently, 176-layer-stacked V-NAND flash memory is available on the market. Nonetheless, increasing the layers invokes several challenges, such as film stress management and deep contact hole etching. Also, there should be an upper bound for the attainable stacking layers (400–500) due to the total allowable chip thickness, which will be reached within 6–7 years. This review summarizes the current status and critical challenges of charge-trap-based flash memory devices, with a focus on the material (floating-gate vs charge-trap-layer), array-level circuit architecture (NOR vs NAND), physical integration structure (2D vs 3D), and cell-level programming technique (single vs multiple levels). Current efforts to improve fabrication processes and device performances using new materials are also introduced. The review suggests directions for future storage devices based on the ionic mechanism, which may overcome the inherent problems of flash memory devices.

A creation of clean van der Waals contacts is reported. Clean contacts made from 2D metal Cl–SnSe₂ can completely eliminate the Femi-level pinning, permitting ideal Schottky barrier heights and polarity-controllable transistors. With the ability to control the carrier polarity, various functional logic gates and circuits (inverter, NAND, and NOR) are demonstrated by integrating WSe₂ transistors with Cl–SnSe₂ contacts.

Abstract

Precise control over the polarity of transistors is a key necessity for the construction of complementary metal–oxide–semiconductor circuits. However, the polarity control of 2D transistors remains a challenge because of the lack of a high-work-function electrode that completely eliminates Fermi-level pinning at metal–semiconductor interfaces. Here, a creation of clean van der Waals contacts is demonstrated, wherein a metallic 2D material, chlorine-doped SnSe₂ (Cl–SnSe₂), is used as the high-work-function contact, providing an interface that is free of defects and Fermi-level pinning. Such clean contacts made from Cl–SnSe₂ can pose nearly ideal Schottky barrier heights, following the Schottky–Mott limit and thus permitting polarity-controllable transistors. With the integration of Cl–SnSe₂ as contacts, WSe₂ transistors exhibit pronounced p-type characteristics, which are distinctly different from those of the devices with evaporated metal contacts, where n-type transport is observed. Finally, this ability to control the polarity enables the fabrication of functional logic gates and circuits, including inverter, NAND, and NOR.

The universal growth of ultrathin perovskite single crystals is realized by designing an oriented solvent microenvironment induced by the interfacial electric field originated from the charge separation between solid and liquid phases. Such a strategy can fabricate a wide range of high-quality ultrathin perovskite single crystals, from layered to nonlayered, organic to inorganic, and toxic to low-toxic lead-free perovskite. Notably, the realization of high quality and diversity of ultrathin perovskites will facilitate both fundamental studies and optoelectronic applications.

Abstract

Perovskites have engaged significant attention owing to rich species and remarkable physical properties as well as optoelectronic applications. Compared to bulk counterparts, ultrathin perovskites exhibit more available compositions due to the breaking of bulk lattice limitation. Coupled with crystal lattice relaxation and quantum confinement, infinite intriguing properties of ultrathin perovskites deserve to be explored. Developing ultrathin perovskites with alterable composition and structure is a necessity to fully explore this versatile family. Herein, a universal strategy is conceived via constructing oriented solvent microenvironment induced by the interfacial electric field originated from the charge separation between solid and liquid phases, which is conducive to controlling the precursor distribution and makes crystals preferentially nucleate and grow in the preferentially lateral mode. From layered to nonlayered, organic to inorganic, and toxic to low-toxic lead-free perovskite, a full-range synthesis is achieved of ultrathin perovskites. This work opens up opportunities both for ultrathin perovskite exploration through compositional engineering and for device miniaturization in energy conversion applications.

A controllable production approach of wafer-scale high-quality single-crystal nucleus-free graphene-mesh metamaterials with zigzag edges is presented. The isotopic labeling approach and the high-voltage localized-space air-ionization nucleus etching method are used to fabricate graphene-mesh metamaterial films on a Cu(111) substrate without chemical contamination and physical contact. The findings of this study provide insights for producing resist-free high-quality low-dimensional metamaterial films.

Abstract

In addition to conventional monolayer or bilayer graphene films, graphene-mesh metamaterials have attracted considerable research attention within the scientific community owing to their unique physical and optical properties. Currently, most graphene-mesh metamaterials are fabricated using common lithography techniques on exfoliated graphene flakes, which require the deposition and removal of chemicals during fabrication. This process may introduce contamination or doping, thereby limiting their production size and application in nanodevices. Herein, the controlled production of wafer-scale high-quality single-crystal nucleus-free graphene-mesh metamaterial films with zigzag edges is demonstrated. The ¹³C-isotopic labeling graphene-growth approach, large-area Raman mapping techniques, and a uniquely designed high-voltage localized-space air-ionization etching method are utilized to directly remove the graphene nuclei. Subsequently, a hydrogen-assisted anisotropic etching process is employed for transforming irregular edges into zigzag edges within the hexagonal-shaped holes, producing a large-scale single-crystal high-quality graphene-mesh metamaterial film on a Cu(111) substrate. The carrier mobilities of the fabricated field-effect transistors on the as-produced films are measured. The findings of this study enable the large-scale production of high-quality low-dimensional graphene-mesh metamaterials and provide insights for the application of integrated circuits based on graphene and other 2D metamaterials.

Atomically resolved multiple 2D phase transformations (MoS₂ → Mo₄S₆, MoSe₂ → L-, Z-Mo₆Se₆) is observed in monolayer transition metal dichalcogenides under in situ heating with stoichiometry control by electron beam irradiation. Through chalcogen sliding and reconstruction mechanisms, phase transformations are well manipulated to fabricate diphase heterostructures with atomically sharp interfaces, which will pave the way to phase engineered optoelectronics.

Abstract

Phase transformation lies at the heart of materials science because it allows for the control of structural phases of solids with desired properties. It has long been a challenge to manipulate phase transformations in crystals at the nanoscale with designed interfaces and compositions. Here in situ electron microscopy is employed to fabricate novel 2D phases with different stoichiometries in monolayer MoS₂ and MoSe₂. The multiphase transformations: MoS₂ → Mo₄S₆ and MoSe₂ → Mo₆Se₆ which are highly localized with atomically sharp boundaries are observed. Their atomic mechanisms are determined as chalcogen 2H ↔ 1T sliding, cation shift, and commensurate lattice reconstructions, resulting in decreasing direct bandgaps and even a semiconductor–metal transition. These results will be a paradigm for the manipulation of multiphase heterostructures with controlled compositions and sharp interfaces, which will guide the future phase engineered electronics and optoelectronics of metal chalcogenides.

Large-area exfoliation of monolayer MoS₂ is realized using metals such as Pd, Cu, Ni, and Ag which have strong binding energy with MoS₂. The exfoliated flakes are of high quality.

Abstract

Au-mediated exfoliation of 2D transition-metal dichalcogenides (TMDs) has received significant attention due to its ability to produce large-area monolayer (ML) flakes. This process has been attributed to strong TMD/Au binding energy (BE) as well as the uniform strain between the TMDs and Au. However, large-area exfoliation of TMDs with other metals that have even stronger theoretical BE than Au/TMD is not successful, leading to question whether the BE plays any role in the exfoliation process. Here, successful demonstration of large-area ML MoS₂ using Cu, Ni, and Ag with various predicted strain, including Pd with almost no strain, but stronger BE than Au/MoS₂ is demonstrated. Optical micrographs show MoS₂ flakes with 100s of µm in size with a yield of several tens to hundreds of ML flakes per exfoliation. Photoluminescence and Raman spectroscopy confirm the ML nature of the flakes, while electrical transport measurements show mobilities of ≈6 cm² V⁻¹ s⁻¹ with a current on-off ratio ≈10⁸ consistent with high-quality ML MoS₂. Given that MoS₂ can be exfoliated with metals that have strong BE irrespective of their strain values suggests that BE is the primary mechanism in successful exfoliation of large-area ML MoS₂.

A dichromatic polarized reflectance method is demonstrated, which can quickly and accurately resolve the crystal orientation (Re–Re chain) in 2D ReS₂ crystals with different thicknesses. It can further be extended to multi-chromatic schemes to achieve greater measurement capability, and be easily tailored to work for different 2D materials, thus offering a simple and effective approach for studying 2D anisotropy.

Abstract

In-plane anisotropy in 2D rhenium disulfide (ReS₂) offers intriguing opportunities for designing future electronic and optical devices, and toward such applications, it is crucial to identify the crystal orientation in such 2D anisotropic materials. Existing spectroscopy or electron microscopy methods for determining the crystalline orientation often require complicated sample preparing procedures and specialized equipment, which could sometimes limit their application. In this work, a dichromatic polarized reflectance method is demonstrated, which can quickly and accurately resolve the crystal orientation (Re–Re chain) in 2D ReS₂ crystals with different thicknesses. Furthermore, it can be readily extended to multi-chromatic schemes to achieve greater measurement capability and can be easily tailored to work for different 2D materials. The method offers a simple and effective approach for studying anisotropy in 2D materials.

Author(s): Ling-Hui Tong, Qingjun Tong, Li-Zhen Yang, Yue-Ying Zhou, Qilong Wu, Yuan Tian, Li Zhang, Lijie Zhang, Zhihui Qin, and Long-Jing Yin

Flat bands in magic-angle twisted monolayer-bilayer graphene are shown to be delocalized on the bilayer side and localized on the monolayer side.

[Phys. Rev. Lett. 128, 126401] Published Tue Mar 22, 2022

Abstract

Group-VI elemental two-dimensional (2D) materials (e.g., tellurene (Te)) have unique crystalline structures and extraordinarily physical properties. However, it still remains a great challenge to controllably grow 2D Te with good repeatability, uniformity, and highly aligned orientation using vapor growth method. Here, we design a Cu foil-assisted alloy-buffer-controlled growth method to epitaxially grow aligned single-crystalline 2D Te on an insulating mica substrate. The in-situ formation of Cu−Te alloy plays a key role on 2D Te growth, alleviating the spatial and temporal non-uniformity of precursor in conventional vapor deposition process. Through transmission electron microscopy (TEM) analysis combined with theoretical calculations, we unveil that the alignment growth of Te in the [110] direction is along the [600] direction of mica, owing to the small lattice mismatch (0.15%) and strong binding strength. This work presents a method to grow aligned high-quality 2D Te in a controllable manner.

2D field-effect-transistors (FETs) are affected by time-dependent changes in their performance, which must be minimized for industrial-scale applications. In this work, the stability of circuits based on 2D transistors is evaluated. The results suggest that the performance parameters of certain material combinations for 2D FETs are already close to Si technologies. Furthermore, parameter variability criteria are formulated to evaluate the future development of 2D technologies.

Abstract

Within the last decade, considerable efforts have been devoted to fabricating transistors utilizing 2D semiconductors. Also, small circuits consisting of a few transistors have been demonstrated, including inverters, ring oscillators, and static random access memory cells. However, for industrial applications, both time-zero and time-dependent variability in the performance of the transistors appear critical. While time-zero variability is primarily related to immature processing, time-dependent drifts are dominated by charge trapping at defects located at the channel/insulator interface and in the insulator itself, which can substantially degrade the stability of circuits. At the current state of the art, 2D transistors typically exhibit a few orders of magnitude higher trap densities than silicon devices, which considerably increases their time-dependent variability, resulting in stability and yield issues. Here, the stability of currently available 2D electronics is carefully evaluated using circuit simulations to determine the impact of transistor-related issues on the overall circuit performance. The results suggest that while the performance parameters of transistors based on certain material combinations are already getting close to being competitive with Si technologies, a reduction in variability and defect densities is required. Overall, the criteria for parameter variability serve as guidance for evaluating the future development of 2D technologies.

Titania nanosheets can be sectioned into substantially rectangular-shaped fragments when adsorbed on a nonflat surface via a spin-coating method. The scission of the nanosheets is attained by the integrated intermolecular forces large enough to cleave the chemical bonds inside the nanosheets. The resultant crevices within the nanosheets preferentially run along the crystallographic orientation, offering a new processing technique for nanomaterials.

Abstract

Secondary processing of 2D nanosheets is an important technique for fabrication of devices and modulation of properties. However, methods for the secondary processing have not been well developed yet, particularly for the scission along crystallographic orientation. In the present paper, it is reported that titania nanosheets can be orthogonally sectioned into substantially rectangular-shaped fragments when deposited on a nonflat substrate surface via spin-coating their suspension. Such events occur for all the nanosheets on the substrate surface. In the deposition process, nanosheets float and stay flat on top of the solvent surface, and adsorb on the substrate with conforming to the bumpy surface by following the descending solvent level. Because the nanosheet area is smaller than the actual area of the bumpy surface having the same projected area, the nanosheet experiences tensile stress along its lateral direction. The tensile stress originates from the intermolecular forces acting between the nanosheet and the substrate surface upon the adsorption on the substrate. Due to the high 2D anisotropy, the integrated intermolecular forces can be large enough to cleave the chemical bonds, leading to the scission of the nanosheet. This interesting finding may offer a new processing technique for cutting and shaping various 2D materials.

Light: Science & Applications, Published online: 24 March 2022; doi:10.1038/s41377-022-00753-4

With a chloroform-assisted method, a record growth rate of 11.5 µm h⁻¹ was achieved and vertical graphene arrays with a height of 100 µm was successfully synthesized. Vertical graphene together with polydimethylsiloxane were used to construct a free-standing thermal interface material, which yielded a high vertical thermal conductivity of 34.2 W m⁻¹ K⁻¹ and excellent cooling effect in light emitting diode.

Abstract

With the continuous progress in electronic devices, thermal interface materials (TIMs) are urgently needed for the fabrication of integrated circuits with high reliability and performance. Graphene as a wonderful additive is often added into polymer to build composite TIMs. However, owing to the lack of a specific design of the graphene skeleton, thermal conductivity of graphene-based composite TIMs is not significantly improved. Here a chloroform-assisted method for rapid growth of vertical graphene (VG) arrays in electric field-assisted plasma enhanced chemical vapor deposition (PECVD) system is reported. Under the optimum intensity and direction of electric field and by introducing the highly electronegative chlorine into the reactor, the record growth rate of 11.5 µm h⁻¹ is achieved and VG with a height of 100 µm is successfully synthesized. The theoretical study for the first time reveals that the introduction of chlorine accelerates the decomposition of methanol and thus promotes the VG growth in PECVD. Finally, as an excellent filler framework in polymer matrix, VG arrays are used to construct a free-standing composite TIM, which yields a high vertical thermal conductivity of 34.2 W m⁻¹ K⁻¹ at the graphene loading of 8.6 wt% and shows excellent cooling effect in interfacial thermal dissipation of light emitting diode.

Broadband Photodetectors

In article number 2103429, Xiangang Luo and co-workers report a broadband photodetector utilizing GaTe after breaking through its bandgap limitation by self-driven O₂ intercalation in air and further reveal its anisotropic nature of both intrinsic and extrinsic photoconductivity. This provides design strategies of 2D materials-based high performance broadband photodetectors for the exploration of the polarized state information.

Several new cleaning methods such as ozone cleaning, annealing, and acetone treatment are found to be ineffective for the complete removal of poly(methyl methacrylate) (PMMA) residues from wet-transferred monolayer MoS₂. In this context, a simple yet effective chemical treatment, 96 h of hot ethanol cleaning, is found to remove the PMMA residues completely. The ultraclean monolayer MoS₂ has shown improved field-effect transistor performance.

Abstract

The transfer of monolayer molybdenum disulfide (1L-MoS₂) onto any target substrates is inevitable for the next generation of optoelectronic devices such as flexible electronics. However, the existing post-transfer treatments are ineffective for the complete removal of poly(methyl methacrylate) (PMMA) polymer, which is usually used as carrier polymer in the wet-transfer method. The presence of PMMA residues seriously degrades the intrinsic properties of any 2D materials. Several new cleaning methods such as annealing, ozone cleaning, and acetone treatment adopted in this report are found to be ineffective for the complete removal of PMMA residues on the transferred 1L-MoS₂ film. A new chemical route is developed and demonstrated with a PMMA nonsolvent, ethanol, and ultraclean transferred 1L-MoS₂ is obtained after 96 h hot ethanol treatment. An interfacial diffusion model is proposed for the mechanism of PMMA removal from the 1L-MoS₂ surface. To observe the effect of cleaning process on electrical properties, 1L-MoS₂ field-effect transistor (FET) devices are fabricated. An enhancement of 80%–85% in the electron mobility is achieved for ultraclean 1L-MoS₂. One order improvement in the FET parameters such as ON/OFF ratio and the subthreshold slope is also observed. It is believed that this novel method can also be applicable for other 2D materials.