Two-dimensional Layered Materials Research Articles

Nonlinear saturable properties of indium selenide film fabricated by molecular beam epitaxy method in near infrared region and Q-switched laser performance for Nd:GdYNbO laser

Two-dimensional layered materials have caught considerable attention for their intrinsic value. Much effort has been made to excavate novel 2D materials with more distinctive characteristics as optical modulators. Single-crystal indium selenide (In2Se3) film with few layers fabricated by molecular beam epitaxy method, for the first time, is employed in this study as a saturable absorber for an Nd3+ doped Gd:GdYNbO infrared laser. Our experimental results demonstrate that the high-quality In2Se3 film achieves a desirable modulation depth of 18.4%, but only 5.9% for the LPE one. The shortest pulse duration and maximum single pulse energy of In2Se3 film are both much better than those of MoS2 and WS2 films in the same laser system. It further confirms the distinguishing properties of the MBE-growth In2Se3 film for optical modulation in infrared region.

Epitaxial Growth of GaAs Nanowires on Synthetic Mica by Metal-Organic Chemical Vapor Deposition.

The epitaxial growth of III-V nanowires with excellent optoelectronic properties on low-cost, light-weight, and flexible substrates is a key step for the design and engineering of future optoelectronic devices. In our study, GaAs nanowires were grown on synthetic mica, a two-dimensional layered material, via vapor-liquid-solid growth using metal-organic chemical vapor deposition. The effect of basic epitaxial growth parameters such as temperature and V/III ratio on the vertical yield of the nanowires is investigated. A vertical yield of over 60% is achieved at an optimum growth temperature of 400 °C and a V/III ratio 18. The structural properties of the nanowires are investigated using various techniques including scanning electron microscopy, high-resolution transmission electron microscopy, and high-angle annular dark-field imaging. The vertical nanowires grown at a low temperature and a high V/III ratio are found to have a zincblende phase with a [111] B polarity. The optical properties are investigated by photoluminescence (PL) and time-resolved PL measurements. First-principles electronic structure calculations within the framework of density functional theory elucidate the van der Waals nature of the nanowire/mica interface. Our results also show that these nanowires can be easily lifted off the bulk 2D mica template, providing a pathway for flexible nanowire devices.

Highly Sensitive NO2 Detection by TVS-Grown Multilayer MoS2 Films

Two-dimensional layered materials have been investigated for sensor applications over the last decade due to their very high specific surface area and excellent electrical characteristics. Although grain boundaries are inevitably present in polycrystalline-layered materials used for real applications, few studies have investigated their effects on sensing properties. In this study, we demonstrate the growth of two distinct MoS2 films that differ in grain size by means of chemical vapor deposition (CVD) and thermal vapor sulfurization (TVS) methods. Transistor-based sensors are fabricated using these films, and their NO2 sensing properties are evaluated. The adsorption behavior of NO2 on MoS2 is considered in terms of the Langmuir isotherm, and the experimental results can be well fitted by the equation. The CVD-grown film exhibits electrical properties 1–2 orders of magnitude superior to those of the TVS-grown one, which is attributed to the large grain size of the CVD-grown film. In contrast, the sensitivity to NO2 is unexpectedly found to be higher in the TVS-grown film and is of the same order of a previously reported record value. Transmission electron microscopy observations suggest that the TVS-grown film consists of multiple rotationally oriented grains that are connected by mirror twin grain boundaries. Theoretical calculation results reveal that the adsorption of NO2 on the grain boundary that we modeled is equal to that on the ideal basal plane surface of MoS2. In addition, the porous structure in the TVS-grown film may also contribute to enhancing the sensor response to NO2. This study suggests that a highly sensitive MoS2 sensor can also be fabricated by using a polycrystalline film with small grain size, which can possibly be applied to other two-dimensional materials.

Research progress of neuromorphic devices based on two-dimensional layered materials

In recent years, the development of artificial intelligence has increased the demand for computing and storage. However, the slowing down of Moore’s law and the separation between computing and storage units in traditional von Neumann architectures result in the increase of power consumption and time delays in the transport of abundant data, raising more and more challenges for integrated circuit and chip design. It is urgent for us to develop new computing paradigms to meet this challenge. The neuromorphic devices based on the in-memory computing architecture can overcome the traditional von Neumann architecture by Ohm’s law and Kirchhoff’s current law. By adjusting the resistance value of the memristor, the artificial neural network which can mimic the biological brain will be realized, and complex signal processing such as image recognition, pattern classification and decision determining can be carried out. In order to further reduce the size of device and realize the integration of sensing, memory and computing, two-dimensional materials can provide a potential solution due to their ultrathin thickness and rich physical effects. In this paper, we review the physical effects and memristive properties of neuromorphic devices based on two-dimensional materials, and describe the synaptic plasticity of neuromorphic devices based on leaky integrate and fire model and Hodgkin-Huxley model in detail, including long-term synaptic plasticity, short-term synaptic plasticity, spiking-time-dependent plasticity and spiking-rate-dependent plasticity. Moreover, the potential applications of two-dimensional materials based neuromorphic devices in the fields of vision, audition and tactile are introduced. Finally, we summarize the current issues on two-dimensional materials based neuromorphic computing and give the prospects for their future applications.

A first-principles prediction of novel Janus T'-RuXY (X/Y = S, Se, Te) monolayers: structural properties and electronic structures.

Due to the breaking of the mirror symmetry, two-dimensional layered Janus materials possess many extraordinary mechanical and electronic properties that cannot exist in symmetric structures. In this paper, we propose and investigate the structural and electronic properties of Janus T′-RuXY (X/Y = S, Se, and Te) monolayers using the first-principles simulations. Our calculated results indicate that the T′-RuXY is found to be dynamically and mechanically stable through the phonon dispersion analysis and examination of elastic properties. The T′-RuXY exhibits high anisotropic elastic characteristics due to its in-plane anisotropic atomic structure. Besides, the vertical asymmetry of T′-RuXY leads to the appearance of a difference in the vacuum level between its two different surfaces. At the ground state, all three structures of the Janus T′-RuXY are semiconductors with indirect bandgaps. The bandgaps of T′-RuXY can be modulated by a biaxial strain. Particularly, the semiconductor-to-metal phase transitions are observed in all studied structures at a large compressive strain. Our calculation results not only provide important structural and electronic features of the Janus T′-RuXY monolayers but also show the prospect of their application in nanoelectromechanical devices.

Application of two-dimensional layered materials in surface-enhanced Raman spectroscopy (SERS).

The subject of this perspective is the application of two-dimensional (2D) layered materials in surface-enhanced Raman spectroscopy (SERS). 2D materials are regarded as promising SERS substrates because of their inexpensive and non-toxic characteristics. However, compared with the traditional precious metal substrates, its enhancement factor and detection limit are lower. In this perspective, seven advanced strategies that can improve the SERS properties of 2D materials are highlighted, including layer-dependent strategy, defect engineering, regulation of excitation laser, electric field modulation, phase engineering, arrangement mode and heterostructure design. In addition, the enhancement mechanism, synthesis strategy and application status of typical examples of molybdenum disulfide (MoS2) and MXenes as SERS substrates are discussed in detail. Finally, the prospect of future progress in SERS and possible challenges of 2D layered materials have been put forward.

Effective high-throughput screening of two-dimensional layered materials for potential lithium-ion battery anodes.

Lithium-ion batteries (LIBs) are considered the promising next-generation advanced energy storage devices. It is very important to quickly screen out ideal anode materials for LIBs with excellent performance. In this work, an effective procedure is designed for the high-throughput screening of the three kinds of LIB anode materials from 131 613 inorganic compounds in the Materials Project database. The high throughput screen procedure was not only reliable but was also easily realized. Three ideal anode materials were obtained by considering remarkable thermodynamic stability, Li capacity larger than 372 mA h g-1, band gap smaller than 1.0 eV, and two-dimensional constraint. Furthermore, open-circuit voltage, volume expansion ratio, and the diffusion energy barrier were calculated by the DFT-D corrected density functional method. We believe that our high throughput screen procedure can effectively and accurately search for other kinds of anode materials, which can strongly support the theoretical basis for experimental research.

Positron charge sensing using a double-gated graphene field effect transistor

We utilize a high-mobility double-gated graphene field-effect transistor to measure the accumulated charge created by positron annihilation in its back-gate. The device consists of an exfoliated graphene flake stacked between two hexagonal boron nitride flakes placed on a 1 cm2 substrate of 500 μm thick conducting p-doped Si capped by 285 nm-thick SiO2. The device is placed in close proximity to a 780 kBq 22Na positron source emitting a constant flux of positrons. During the measurement, positrons annihilate within the back-gate, kept floating using a low-capacitance relay. The accumulated positive charge capacitively couples to the graphene device and builds a positive voltage, detectable through a shift in the top-gate dependent graphene resistance characteristic. The shift in the position of the top-gate Dirac peak is then used for extracting the exact voltage buildup and quantitative evaluation of the accumulated charge. Reaching a positron current sensitivity of ∼1.2 fA/Hz, detected over 20min, our results demonstrate the utility of two-dimensional layered materials as probes for charging dynamics of positrons in solids.

Two-dimensional layer materials for highly efficient molecular sensing based on surface-enhanced Raman scattering

Two-dimensional layer materials for highly efficient molecular sensing based on surface-enhanced Raman scattering

Recent Progress on Nanomaterial-Based Membranes for Water Treatment.

Nanomaterials have emerged as the new future generation materials for high-performance water treatment membranes with potential for solving the worldwide water pollution issue. The incorporation of nanomaterials in membranes increases water permeability, mechanical strength, separation efficiency, and reduces fouling of the membrane. Thus, the nanomaterials pave a new pathway for ultra-fast and extremely selective water purification membranes. Membrane enhancements after the inclusion of many nanomaterials, including nanoparticles (NPs), two-dimensional (2-D) layer materials, nanofibers, nanosheets, and other nanocomposite structural materials, are discussed in this review. Furthermore, the applications of these membranes with nanomaterials in water treatment applications, that are vast in number, are highlighted. The goal is to demonstrate the significance of nanomaterials in the membrane industry for water treatment applications. It was found that nanomaterials and nanotechnology offer great potential for the advancement of sustainable water and wastewater treatment.

Manipulation of the SnSe2 gas sensing properties via Au nanoparticles decoration

Gas sensing devices play a key role in safety production, environment protection and human health. Recently, two-dimensional layered materials with large surface area and flexible optoelectronic properties have been widely used for gas sensor design. One of major concern in this field is the sensitivity and selectivity. Here, we show that the sensitivity and selectivity of SnSe2 gas sensor can be manipulated by Au nanoparticles decoration. By choosing NO2 (electron acceptor) and NH3 (electron donor) as target gas, we reveal that the “space charge layer” at the Au-SnSe2 Schottky junction interface plays a critical role in manipulating the sensitivity and selectivity. For NO2, the “space charge layer” hampers the electron transfer from SnSe2 to molecules, thus depressing the sensitivity. While, the electron transfer direction is the opposite when considering NH3, the “space charge layer” would facilitate the electron transfer, thus greatly improving the sensitivity of NH3. Especially, we show that the Au-decorated SnSe2 manifests a sensitivity about -22% toward 80 ppm NH3, which is about three times larger than that measured on pristine SnSe2 under UV illumination. These findings can not only deep our understanding on the mechanism of SnSe2 gas sensing, but also provide an effective strategy to manipulate the sensitivity and selectivity of SnSe2 detector for high performance and low cost gas sensor design.

Synergistic effect of green phosphorus-containing bio-based material and two-dimensional layered material composite on flame-retardant property of polyvinyl alcohol

A novel environment-friendly and efficient flame retardant (phytic acid [PA] - layered double hydroxide [LDH]) has been synthesized to enhance the flame retardancy of PVA. PA-LDH possesses better char formation ability with a high char residue of 68.7 wt% at 600 °C. Peak release rate (pHRR) and heat release capacity (HRC) values of PVA/PA-LDH15% are 180 W/g and 310 J/g-K, with the descent of 69.4% and 31.7%, respectively. The burning rate of PVA/PA-LDH decreased visibly, presented that higher fire retardancy can be obtained for PVA/PA-LDH. It is worth noting that PA-LDH could restrain the melt-dripping of PVA during the combustion process, which is of great significance in fire-spread control. Furthermore, the synergistic flame-retardant mechanism of phosphorus-contained PA and inorganic LDH is proposed based on microscopic analysis on char residues. In addition, PVA/PA-LDH composites exhibit good mechanical properties, the green flame retardant is of considerable significance to the flame-retardant treatment of polymers.

Non-monotonic thickness dependent and anisotropic in-plane thermal transport in layered titanium trisulphide

Due to the potential applications in many fields such as thermoelectric, transistor, and electrode materials, a novel two-dimensional layered material TiS3 has attracted tremendous attention recently. In this article, the thickness dependent and anisotropic in-plane thermal transport behavior is explored by first-principles calculation with Boltzmann transport equation. The calculation results show that when the thickness is smaller than phonon confinement size (PCS), the phonon confinement effect is dominant and the in-plane thermal conductivity has a negative dependence on thickness due to the increase of phonon–phonon scattering; when the thickness is larger than PCS, the confinement effect is weak and the dependence becomes positive due to the decrease of phonon–boundary scattering. Through further analysis, we find this non-monotonic dependence or phonon confinement phenomenon is mainly caused by the low-frequency phonons. The calculation results also show strong thermal anisotropy within the basal plane. The coupling strength, bond length, phonon group velocity, dispersiveness of optical phonon branches, iso-energy surface and iso-surface of electron density distribution are analyzed to explain the anisotropy. Based on the 1D diatomic chain model, a unit cell having similar atomic mass and strong intracell bond can enhance the dispersiveness of optical phonon branches. Those findings here can give physical insights into the thickness dependent and anisotropic in-plane thermal transport in layered materials.

Electrochemical biosensors based on Ti3C2Tx MXene: future perspectives for on-site analysis

MXenes are recently developed two-dimensional layered materials composed of early transition metal carbides and/or nitrides that provide unique characteristics for biosensor applications. This review presents the recent progress made on the usage and applications of MXenes in the field of electrochemical biosensors, including microfluidic biosensors and wearable microfluidic biosensors, and highlights the challenges with possible solutions and future needs. The multilayered configuration and high conductivity make these materials as an immobilization matrix for the biomolecule immobilization with activity retention and to be explored in the fabrication of electrochemical sensors, respectively. First, how the MXene nanocomposite as an electrode modifier affects the sensing performance of the electrochemical biosensors based on enzymes, aptamer/DNA, and immunoassays is well described. Second, recent developments in MXene nanocomposites as wearable biosensing platforms for the biomolecule detection are highlighted. This review pointed out the future concerns and directions for the use of MXene nanocomposites to fabricate advanced electrochemical biosensors with high sensitivity and selectivity. Specifically, possibilities for developing microfluidic electrochemical sensors and wearable electrochemical microfluidic sensors with integrated biomolecule detection are emphasized.

Spin-valley coupling and valley splitting in the MoSi2N4/CrCl3 van der Waals heterostructure

The newly two-dimensional layered materials MA2Z4 (M = Ti/Cr/Mo, A = Si/Ge, Z = N/P/As) possess excellent stability, strong valley-dependent properties, and novel electronic structures. Motivated by recent experimental advances, we have constructed a van der Waals heterostructure consisting of MoSi2N4 and ferromagnetic CrCl3 monolayer and performed first principles calculations to investigate the spin-valley coupling and valley splitting properties. The MoSi2N4/CrCl3 heterostructure is thermally stable at room temperature. Our calculations have shown an enhancement of both valley splitting and valley-contrasting transport properties due to the magnetic proximity effect. Most importantly, the valley-related properties of the MoSi2N4 monolayer are predicated to be rather robust resulting from the protection of the outermost N–Si sublayers. These findings could be helpful to the understanding of the ferromagnetic substrate effect on the valley-dependent properties of MA2Z4-based heterostructures.

Recent Trends in Graphitic Carbon Nitride-Based Binary and Ternary Heterostructured Electrodes for Photoelectrochemical Water Splitting

The graphitic carbon nitride (g-C3N4) is a class of two-dimensional layered material. The ever-growing research on this fascinating material is due to its unique visible light absorption, surface, electrocatalytic, and other physicochemical properties that can be useful to different energy conversion and storage applications. Photoelectrochemical (PEC) water splitting reaction is one of the promising applications of g-C3N4, wherein it acts as a durable catalyst support material. Very recently, the construction of g-C3N4-based binary and ternary heterostructures exhibited superior PEC water splitting performance owing to its reduced reunion of e-/h+ pairs and the fast transfer of charge carriers at the heterostructure interface. This review compiles the recent advances and challenges on g-C3N4-based heterostructured photocatalysts for the PEC water splitting reaction. After an overview of the available literature, we presume that g-C3N4-based photocatalysts showed enhanced PEC water splitting performance. Therefore, it is believed that these materials have tremendous opportunities to act as durable catalyst support for energy-related applications. However, researchers also considered several limitations and challenges for using C3N4 as an efficient catalyst support material that must be addressed. This review article provides an overview of the fundamental principles of PEC water splitting, the current PEC water splitting research trends on g-C3N4-based binary and ternary heterostructured electrodes with respect to different electrolytes, and the other key factors influencing their photoelectrochemical performance. Finally, the future research direction with several recommendations to improve the photocatalytic efficiency of these materials is also provided at the end.

In-Plane Phonon Anisotropy and Anharmonicity in Exfoliated Natural Black Arsenic.

Group-VA two-dimensional layered materials in a puckered honeycomb structure exhibit strong in-plane anisotropy and have emerged as new platforms for novel devices. Here, we report on systematic Raman investigations on exfoliated b-As flakes on the Ag1 and Ag2 polarization dependence on their symmetry, excitation wavelength, and flake thickness. The intensity maximums of both phonons are corrected in the b-As armchair direction under 633 nm excitation regardless of the flake thickness upon considering optical birefringence effects and interference effects. The intensity ratio of Ag1 to Ag2 modes under 532 nm excitation is useful for b-As crystalline orientation identification. Temperature-dependent Raman investigations reveal the linearly anharmonic behaviors of both phonons in the range from 173 to 293 K and a slightly greater first-order temperature coefficient in the zigzag direction. Our findings give deep insight into the in-plane phonon anisotropy and anharmonicity of b-As and provide a step toward future device applications.

Evaluation of Mo(1-x)W x s Alloy Fabricated By Combinatorial Film Deposition

Recently, research on two-dimensional layered materials is progressing rapidly. Transition metal dichalcogenides (TMDs) show bandgap, which is bringing high expectations for a variety of applications such as electronics and optoelectronics. Mo(1-x)W x S2 is an alloy semiconductor of MoS2 and WS2, two of the most representative TMD materials, and it is possible to modulate physical properties such as optical characteristics by changing the W concentration x [1-3]. In this study, we performed a combinatorial film deposition in which the W concentration changes from 0 to 100% within one sample using RF magnetron sputtering method [4]. Since the combinatorial film deposition can form a continuous compositional gradient in the sample, continuous modulation of physical properties is expected. There have been different reports on the fabrication of the alloy with chemical vapor transport followed by exfoliation, or chemical vapor deposition [5]. However, in this study single-step fabrication of the alloy with sputtering was achieved. The physical properties such as the band structure of the fabricated sample were investigated.MoS2 and WS2 targets were used for the fabrication of the alloy. The substrate temperature was 300 °C, Ar pressure was 0.3 Pa, and the RF power applied to the MoS2 and WS2 targets were 80 W and 50 W, respectively. The film thickness was adjusted to approximately 100 nm by controlling the deposition time. Surface oxidized Si was used as the substrate. A schematic diagram of the sample is shown in Fig. 1. Using X-ray photoelectron spectroscopy (XPS) for quantitative analysis of the sample, the W concentration x and the sulfur to metal ratio S / (Mo + W) were calculated by determining the peak area ratios of Mo 3d, W 4f, and S 2p. In addition, spectroscopic ellipsometry analysis was carried out to calculate the bandgap for each concentration region.Figure 2 shows the in-plane composition distribution determined by line measurement with XPS. From Fig. 2, it can be seen that the W concentration changes almost linearly, and the stoichiometric ratio was achieved. The linearly changing composition gradient allowed us to accurately select the composition of the alloy for the other evaluation. The bandgap with respect to W concentration using spectroscopic ellipsometry is shown in Fig. 3. It was confirmed that the band gap can be controlled by changing the W concentration. In addition, the change was accompanied by bowing which is a unique behavior often observed in the alloy materials. Figure 4 shows the band alignment of different W concentration x determined by using XPS and spectroscopic ellipsometry. From this result, it was found that the band structure can be controlled according to the requirements of the devices. We believe that this opens new opportunity for the TMD in electronic device applications.This work was partly supported by JST CREST Number JPMJCR16F4, Japan. This work was also partly supported by JSPS KAKENHI Grant Number 18J22879.REFERENCES Y. Chen, J. Xi, D. O. Dumcenco, Z. Liu, K. Suenaga, D. Wang, Z. Shuai, Y. S. Huang, and L. Xie, ACS Nano 7, 4610 (2013).H. -P. Komsa, and A. V. Krasheninnikov, J. Phys. Chem. Lett. 3, 3652 ( 2012).P. M. Jahani, S. T., H. Beitollahi, S. Mohammadi, and M. R. Aflatoonian, Research on Chemical Intermediates 46, 837(2020).S. Noda, H. Sugime, T. Osawa, Y. Tsuji, S. Chiashi, Y. Murakami, and S. Maruyama. Carbon 44, 8 (2006).Z. Wang, P. Liu, Y. Ito, S. Ning, Y. Tan, T. Fujita, A. Hirata, and M. Chen. Sci. Reports 6, 21536 (2016). Figure 1

Effect of Growth Parameters on MoS2 Film Quality Deposited by Low-Temperature MOCVD Using I-Pr2DADmo(CO)3 and (t-C4H9)2S2

ABSTRACT Molybdenum disulfide (MoS2) is one of the representative two-dimensional layered material that is being actively researched for application in various fields owing to its characteristics such as a moderately wide bandgap (~1.8 eV) and excellent stability. Particularly promising applications include thin film transistors (TFTs) for displays and three-dimensional integrated circuits (3D-ICs). However, applications in these fields require direct deposition of high-quality films at a low temperature in order to meet the conditions such as the softening temperature of the glass for displays (<500-600°C) and the process temperature in the back-end of line of semiconductor device fabrication (<500°C). Low-temperature fabrication of MoS2 thin film using metalorganic chemical vapor deposition (MOCVD) has already been demonstrated in several previous studies [1-3]. However, they include processes such as long deposition times of about 10 hours or more [1,3], the use of highly toxic hydrogen sulfide (H2S) [2,3], and the addition of NaCl as a growth promoter [1,3]. These processes may lead to decrease in productivity and safety problems which would result in cost increase, and decrease in device reliability due to sodium contamination. These problems are considered to be bottlenecks for industrial and practical use. Our previous report examined process strategies that could overcome these challenges [4]. As a molybdenum precursor, we adopted i-Pr2DADMo(CO)3, which shows high adsorption and is expected to improve the throughput and suppress parasitic gas phase reactions. As a sulfur precursor, we used (t-C4H9)2S2, which is non-toxic as opposed to H2S. For the samples in our study, we demonstrated low-temperature (≤500°C) growth of MoS2 thin film without adding NaCl. However, the grain size was very small, about 10 nm, suggesting that it is necessary to improve the film quality for device application. Therefore, the purpose of this study is to investigate the effects of various deposition parameters on film growth and to provide guidelines for process optimization for improvement of film quality.In this study, the growth of MoS2 thin films by MOCVD was carried out in a cold wall type reactor, and the above-mentioned organic compounds were used as Mo and S precursors, and sapphire (0001) was used as the substrate. The samples were evaluated for film morphology by scanning electron microscope (SEM), Atomic Forth Microscopy (AFM) and film composition by X-ray photoelectron spectroscopy (XPS).Figure 1 (a) shows the surface SEM images of each sample with the S precursor supply rate set from 0.2 to 1.5 sccm while keeping the Mo precursor supply rate constant at 4.9 x 10-3 sccm. In addition, Fig. 1 (b) shows the average grain size and nucleation density calculated from 6 points in the sample with respect to the S precursor supply rate. As the S precursor supply rate increased from 0.2 to 0.7 sccm, decrease in nucleation density and increase in grain size up to approximately 110 nm were confirmed. It has been reported that the critical radius of clusters is larger for the clusters with stoichiometric composition than those with higher metal ratio with lacking chalcogen [5]. Therefore, it is considered that nucleation was suppressed by the increase in the critical radius of the cluster induced by the increase in the supply rate of S precursor. On the other hand, when the S precursor supply rate was further increased to 1.5 sccm, the nucleation density increased and the grain size decreased. This suggests that the S precursor supply rate have an optimum value within the range investigated in this study. We also evaluated the effect of temperature, pressure, and so on.This work was partly supported by JST CREST Number JPMJCR16F4, Japan. This work was also partly supported by JSPS KAKENHI Grant Number 18J22879. REFERENCE Kang, S. Xie, L. Huang, Y. Han, P. Y. Huang, K. F. Mak, C.-J. Kim, D. Muller, and J. Park, Nature 520, 656 (2015). Mun, Y. Kim, I.-S. Kang, S. K. Lim, S. J. Lee, J. W. Kim, H. M. Park, T. Kim, and S.-W. Kang, Scientific Reports 6, 21854 (2016). Mun, H. Park, J. Park, D.H. Joung, S.-K. Lee, J. Leem, J.-M. Myoung, J. Park, S.-H. Jeong, W. Chegal, S.W. Nam, and S.-W. Kang, ACS Appl. Electron. Mater. 1 (4), 608 (2019). Yamazaki, Y. Hibino, Y. Oyanagi, Y. Hashimoto, N. Sawamoto, H. Machida, M. Ishikawa, H. Sudo, H. Wakabayashi and A. Ogura, MRS Advances 5, 1643 (2020). Yue, Y. Nie, L. A Walsh, R. Addou, C. Liang, N. Lu, A. T Barton, H. Zhu, Z. Che, D. Barrera, 2D Mater. 4, 045019 (2017). Figure 1

Wafer-scale functional circuits based on two dimensional semiconductors with fabrication optimized by machine learning

Triggered by the pioneering research on graphene, the family of two-dimensional layered materials (2DLMs) has been investigated for more than a decade, and appealing functionalities have been demonstrated. However, there are still challenges inhibiting high-quality growth and circuit-level integration, and results from previous studies are still far from complying with industrial standards. Here, we overcome these challenges by utilizing machine-learning (ML) algorithms to evaluate key process parameters that impact the electrical characteristics of MoS2 top-gated field-effect transistors (FETs). The wafer-scale fabrication processes are then guided by ML combined with grid searching to co-optimize device performance, including mobility, threshold voltage and subthreshold swing. A 62-level SPICE modeling was implemented for MoS2 FETs and further used to construct functional digital, analog, and photodetection circuits. Finally, we present wafer-scale test FET arrays and a 4-bit full adder employing industry-standard design flows and processes. Taken together, these results experimentally validate the application potential of ML-assisted fabrication optimization for beyond-silicon electronic materials.