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Through selective plasma doping, the in situ construction of homogeneous lateral WSe2 P–N junctions within a single WSe2 flake is achieved. Our device shows an external quantum efficiency of ∼228% and a high photoresponsivity of ∼7.1 × 104 mA W−1.

X-ray imaging and computed tomography (CT) technology, as the important non-destructive measurements, can observe internal structures without destroying the detected sample, which are always used in biological diagnosis to detect tumors, pathologies, and bone damages. It is always a challenge to find materials with a low detection limit, a short exposure time, and high resolution to reduce X-ray damage and acquire high-contrast images. Here, we described a low-cost and high-efficient method to prepare centimeter-sized anthracene crystals, which exhibited intense X-ray radioluminescence with a detection limit of ∼0.108 μGy s

Artificial synapses in neuromorphic computing systems hold potential to emulate biological synaptic plasticity to achieve brain-like computation and autonomous learning behaviors in non-von-Neumann systems. 2D materials, such as graphene, graphene oxide, hexagonal boron nitride, transition metal dichalcogenides, transition metal oxides, 2D perovskite, and black phosphorous, have been explored to achieve many functionalities of biological synapses due to their unique electronic, optoelectronic, electrochemical, and mechanical properties that are lacking in bulk materials. This review features the current development in the state-of-the-art artificial synaptic electronic devices based on 2D materials. The structures of these devices are first discussed according to their number of terminals (two-, three-, four-, and multi-terminals) and geometric layouts (vertical, horizontal, hybrid). Since different 2D materials have been utilized to fabricate these devices, their underlying physical mechanisms and principles are further discussed, and their artificial neuron synaptic functionalities and performances are analyzed and contrasted. Finally, a summary of the current research status and major achievements is concluded, and the outlooks and perspectives for this emerging and vibrant field and the potential applications of these devices for neuromorphic computing are presented.

Mid-infrared (MIR) photonics has attracted tremendous interest because of its broad applications at atmospheric windows. In this work, we report high-performance MIR photonics based on large-scale and good-quality monolayer molybdenum disulfide (MoS2). The open-aperture Z-scan measurement on the nonlinear saturable absorption features shows that the as-grown monolayer MoS2 possesses a modulation depth of 26% and a low saturable intensity of 271 kW/cm2, enabling its application as an excellent saturable absorber for the MIR pulse generation. This is further evident by the measured high effective nonlinear absorption coefficient β eff (−16 cm/MW). In addition, the two-photon absorption coefficient and the nonlinear refractive index of monolayer MoS2 are also determined by the closed-aperture Z-scan technology. As an application, we demonstrate a passively Q-switched Tm,Ho:CaLu0.1Gd0.9AlO4 (Tm,Ho:CLGA) disordered crystal laser at 2.1 μm by using the monolayer MoS2 as the saturable absorber for the first time, producing a minimum pulse width of 765 ns and a pulse repetition rate of 36 kHz. Our results demonstrate that large-scale monolayer MoS2 is a promising candidate for the MIR photonic applications.

Two-dimensional (2D) semiconductors could potentially replace silicon in future electronic devices. However, the low carrier mobility in 2D semiconductors at room temperature, caused by strong phonon scattering, remains a critical challenge. Here we show that lattice distortions can reduce electron–phonon scattering in 2D materials and thus improve the charge carrier mobility. We introduce lattice distortions into 2D molybdenum disulfide (MoS2) using bulged substrates, which create ripples in the 2D material leading to a change in the dielectric constant and a suppressed phonon scattering. A two orders of magnitude enhancement in room-temperature mobility is observed in rippled MoS2, reaching ∼900 cm2 V−1 s−1, which exceeds the predicted phonon-limited mobility of flat MoS2 of 200–410 cm2 V−1 s−1. We show that our approach can be used to create high-performance room-temperature field-effect transistors and thermoelectric devices. Agency for Science, Technology and Research (A*STAR) National Research Foundation (NRF) Submitted/Accepted version J.W. acknowledges the SERC Central Research Fund (CRF KIMR211001kSERCRF) and Advanced Manufacturing and Engineering Young Individual Research Grant (AME YIRG grant no. A2084c170). D.C. and J.W. acknowledge National Research Foundation Competitive Research Programs (NRFCRP24-2020-0002). M.Y. acknowledges funding support (project IDs 1-BE47, ZE0C, ZE2F and ZE2X) from The Hong Kong Polytechnic University. K.H. acknowledges funding from the Accelerated Materials Development for Manufacturing Program at the Agency for Science, Technology and Research (A*STAR) via the AME Programmatic Fund under grant no. A1898b0043. D.X. and T.L. acknowledge the Young Scientist project of the MOE Innovation platform. D.X. acknowledges the National Natural Science Foundation (NSF) of China (grant no. 62104041) and Shanghai Sailing Program (grant no. 21YF1402600). T.L. acknowledges the NSF of Shanghai (grant no. 22ZR1405700).

Hybrid materials of π-conjugated molecular semiconductors combined with 2D materials exhibit significant potential for novel (opto)electronics. The overall characteristics of molecular growth, such...

Local impurity states arising from atomic vacancies in two-dimensional (2D) nanosheets are predicted to have a profound effect on charge transport due to resonant scattering and can be used to manipulate thermoelectric properties. However, the effects of these impurities are often masked by external fluctuations and turbostratic interfaces; therefore, it is challenging to probe the correlation between vacancy impurities and thermoelectric parameters experimentally. In this work, we demonstrate that n-type molybdenum disulfide (MoS2) supported on hexagonal boron nitride (h-BN) substrate reveals a large anomalous positive Seebeck coefficient with strong band hybridization. The presence of vacancies on MoS2 with a large conduction subband splitting of 50.0 ± 5.0 meV may contribute to Kondo insulator-like properties. Furthermore, by tuning the chemical potential, the thermoelectric power factor can be enhanced by up to two orders of magnitude to 50 mW m-1 K-2 Our work shows that defect engineering in 2D materials provides an effective strategy for controlling band structure and tuning thermoelectric transport.

Recently, layered two-dimensional (2D) palladium diselenide (PdSe2), with a unique low- symmetry puckered pentagon atomic morphology, has emerged as a promising candidate for next-generation nanoelectronics and optoelectronics because of its chemical stability and extraordinary electrical properties. Moreover, PdSe2 possesses a strong thickness-dependent bandgap that varies from 0 eV for bulk to 1.3 eV for monolayer, which can further render its potential applications in optoelectronics. However, the layer-dependent optoelectronic properties of PdSe2 are still lacking up to date. Herein, we studied the optoelectronics transport characteristics of high-quality PdSe2-based photodetectors with different thicknesses. We demonstrated an enhancement of PdSe2 photodetector performance owing to the band engineering via a thickness reduction. The highest responsivity of 5.35 A/W can be achieved with an external quantum efficiency of 1250% at the wavelength of 532 nm. We attribute such high performance in photoresponsivity to the high valley convergence in the conduction band of layered PdSe2, in agreement with first-principles calculation. Our results offer new insight into the layer-dependent optoelectronic properties of PdSe2 and open new avenues in engineering next-generation 2D-based electronics and optoelectronics.

Controllable synthesis of MoS2 with desired grain morphology via chemical vapor deposition (CVD) or physical vapor deposition (PVD) remains a challenge. Hence, it is important to understand polycry...

Heterostructures comprising van der Waals (vdW) stacked transition metal dichalcogenide (TMDC) monolayers are a fascinating class of two-dimensional (2D) materials. The presence of interlayer excitons, where the electron and the hole remain spatially separated in the two layers due to ultrafast charge transfer, is an intriguing feature of these heterostructures. The optoelectronic functionality of 2D heterostructure devices is critically dependent on the relative rotation angle of the layers. However, the role of the relative rotation angle of the constituent layers on intralayer absorption is not clear yet. Here, we investigate MoS2/WSe2 vdW heterostructures using monochromated low-loss electron energy loss (EEL) spectroscopy combined with aberration-corrected scanning transmission electron microscopy and report that momentum conservation is a critical factor in the intralayer absorption of TMDC vdW heterostructures. The evolution of the intralayer excitonic low-loss EEL spectroscopy peak broadenings as a function of the rotation angle reveals that the interlayer charge transfer rate can be about an order of magnitude faster in the aligned (or anti-aligned) case than in the misaligned cases. These results provide a deeper insight into the role of momentum conservation, one of the fundamental principles governing charge transfer dynamics in 2D vdW heterostructures.

The control of the density and type of line defects on two-dimensional (2D) materials enable the development of new methods to tailor their physical and chemical properties. In particular, mirror twin boundaries (MTBs) on transition metal dichacogenides have attracted much interest due to their metallic state with charge density wave transition and spin-charge separation property. In this work, we demonstrate the self-assembly of 2,3-diaminophenazine (DAP) molecule porous structure with alternate L-type and T-type aggregated configurations on the MoSe2 hexagonal wagon-wheel pattern surface. This site-specific molecular self-assembly is attributed to the more chemically reactive metallic MTBs compared to the pristine semiconducting MoSe2 domains. First-principles calculations reveal that the active MTBs couple with amino groups in the DAP molecules facilitating the DAP assembly. Our results demonstrate the site-dependent electronic and chemical properties of MoSe2 monolayers, which can be exploited as a natural template to create ordered nanostructures., Mirror twin boundaries (MTBs) have been observed as metallic line defects in 2D transition metal dichalcogenides, but their chemical properties are not well understood. Here, the authors show that MTB defect networks on MoSe2 are more chemically reactive to organic molecules than pristine domains, and can template the self-assembly of hexagonal organic porous structures.

Growth of the large-sized and high-quality MoS2 single crystals for high-performance low-power electronic applications is an important step to pursue. Despite the significant improvement made in minimizing extrinsic MoS2 contact resistance based on interfacial engineering of the devices, the electron mobility of field-effect transistors (FETs) made of a synthetic monolayer MoS2 is yet far below the expected theoretical values, implying that the MoS2 crystal quality needs to be further improved. Here, we demonstrate the high-performance two-terminal MoS2 FETs with room-temperature electron mobility up to ∼90 cm2 V-1 s-1 based on the sulfurization growth of the bifunctional precursor, sodium molybdate dihydrate. This unique transition-metal precursor, serving as both the crystalline Mo source and seed promotor (sodium), could facilitate the lateral growth of the highly crystalline monolayer MoS2 crystals (edge length up to ∼260 μm). Substrate surface treatment with oxygen plasma prior to the deposition of the Mo precursor is fundamental to increase the wettability between the Mo source and the substrate, promoting the thinning and coalescence of the source clusters during the growth of large-sized MoS2 single crystals. The control of growth temperature is also an essential step to grow a strictly monolayer MoS2 crystal. A proof-of-concept for thermoelectric device integration utilizing monolayer MoS2 sheds light on its potential in low-voltage and self-powered electronics.

The observation of regular (h0l) planar defects in α-MoO3 crystals can be traced back to over 60 years ago. Two mechanisms have been proposed to interpret the formation of the planar defects. One is related to the diffusion of oxygen vacancies because of thermal-driven release of oxygen atoms in vacuum and the consequent crystallographic shear of α-MoO3. The other is associated with redox reactions of moisture and/or hydrocarbons that give rise to HxMoO3 precipitates. Here, we report that regularly spaced (302) planar defects can be introduced into α-MoO3 belt crystals by heating in liquid sulfur at 300 °C. These defects are undetectable by both atomic force microscopy and scanning electron microscopy at the crystal surface. Raman scattering enhancement and weakening have been observed for different phonon modes of α-MoO3 at the (302) planar defects as probed from the (010) surface. Their comparisons with the Raman scattering enhancements at the edges and the argon-plasma-induced Raman spectral evolutions...

The introduction of patterned sapphire substrates (PSS) has been regarded as an effective method to improve the photoelectric performance of 2D layered materials in recent years. Molybdenum disulfide (MoS

Two-terminal resistive switching devices are commonly plagued with longstanding scientific issues including interdevice variability and sneak current that lead to computational errors and high-power consumption. This necessitates the integration of a separate selector in a one-transistor-one-RRAM (1T-1R) configuration to mitigate crosstalk issue, which compromises circuit footprint. Here, we demonstrate a multi-terminal memtransistor crossbar array with increased parallelism in programming

Atomically thin Bi

Local impurity states arising from atomic vacancies in two-dimensional (2D) nanosheets are predicted to have a profound effect on charge transport due to resonant scattering and can be used to manipulate thermoelectric properties. However, the effects of these impurities are often masked by external fluctuations and turbostratic interfaces; therefore, it is challenging to probe the correlation between vacancy impurities and thermoelectric parameters experimentally. In this work, we demonstrate that n-type molybdenum disulfide (MoS

The quasimetallic 1T′ phase 2D transition‐metal dichalcogenides (TMDs) consist of 1D zigzag metal chains stacked periodically along a single axis. This gives rise to its prominent physical properties which promises the onset of novel physical phenomena and applications. Here, the in‐plane electronic correlations are explored, and new mid‐infrared plasmon excitations in 1T′ phase monolayer WSe2 and MoS2 are observed using optical spectroscopies. Based on an extensive first‐principles study which analyzes the charge dynamics across multiple axes of the atomic‐layered systems, the collective charge excitations are found to disperse only along the direction perpendicular to the chains. Further analysis reveals that the interchain long‐range coupling is responsible for the coherent 1D charge dynamics and the spin–orbit coupling affects the plasmon frequency. Detailed investigation of these charge collective modes in 2D‐chained systems offers opportunities for novel device applications and has implications for the underlying mechanism that governs superconductivity in 2D TMD systems., New 1D mid‐infrared anisotropic plasmons are observed in the quasimetallic phase of WSe2 and MoS2 monolayers. In‐depth analysis reveals that the long‐range inter‐chain coupling is responsible for this 1D charge dynamics, and the plasmon energy is dictated by the effects of spin–orbit coupling. This study establishes an inextricable link between the 1D‐chain structure and charge dynamics in quasimetallic phase 2D transition‐metal dichalcogenides.

Resistive random-access memories (ReRAMs) based on transition metal dichalcogenide layers are promising physical sources for random number generation (RNG). However, most ReRAM devices undergo performance degradation from cycle to cycle, which makes preserving a normal probability distribution during operation a challenging task. Here, ReRAM devices with excellent stability are reported by using a MoS

In this chapter, we review the recent literature on scanning tunneling microscopy/scanning tunneling spectroscopy (STM/STS) and angle-resolved photoemission spectroscopy (ARPES) characterization of 2D semiconductor materials, focusing on 2D transition metal dichalcogenides (TMDCs) and mono-elemental 2D materials. After the introduction, we provide a brief description of the working principles of the STM and ARPES techniques, highlighting some of their advantages and limitations. We next discuss the fundamental atomic and electronic properties of 2D TMDCs (e.g., MoS2, MoSe2, and WSe2) characterized by STM/STS and ARPES/spin-resolved ARPES, to elucidate their exotic layer-dependent properties. In addition, we highlight some recent progress achieved on 2D mono-elemental materials, including silicene, black phosphorus, antimonene. We conclude this chapter with a forward-looking perspective on the future scientific challenges and developments in this field.

Controllable synthesis of MoS

The intricate features of many-body interactions and spin-orbit coupling play a significant role in numerous physical phenomena. Particularly in two-dimensional transition metal dichalcogenides (2D-TMDs), excitonic dynamics are a key phenomenon that promises opportunities for diverse range of device applications. Here, we report the direct observation of a visible-range three-dimensional resonant exciton and its associated charged exciton in monolayer tungsten diselenide, as compared to monolayer molybdenum disulfide. A comprehensive experimental study that includes high-resolution TEM, Raman, high-resolution spectroscopic ellipsometry over a wide temperature range down to 4 K, high-energy temperature, and excitation power-dependent photoluminescence spectroscopy has been conducted. It is supported by first-principles calculations to unravel the influence of spin-orbit coupling in the formation of the resonant exciton and to identify its in-plane and out-of-plane features. Furthermore, we study the impact of temperature and thickness on the spin-orbit coupling strength in 2D-TMDs. This work is crucial in creating a platform in the fundamental understanding of high-energy resonant exciton in layered two-dimensional systems and that such high-energy optoelectronic features make them an increasingly attractive candidate for novel electronic and optoelectronic applications particularly in the aspects of solar cells and light-emitting diodes via the manipulation of excitonic states.

Recent theoretical studies suggest none or minor changes in the band gap of two-dimensional (2D) α-MoO3 nanosheets as compared with that of the bulk because of the weak interlayer electronic interactions. Unfortunately, this suggestion is lacking positive support in the literature. Herein, we report experimental observations of huge blue shifts in the absorption edge of layered α-MoO3 as its thickness t is reduced approaching atomic layers. When t > 10 nm, every order of magnitude of thickness reduction gives rise to a blue shift of ∼0.29 eV without causing any Raman mode shifts. This blue shift, in terms of finite difference time domain calculations, is attributable to optical interferences at the crystal surfaces. However, when t is further reduced below ∼10 nm, an even larger blue shift, accompanied by a mode softening of the most strengthened Mo–O–Mo stretching phonon (Ag), has been observed. This observation is consistent with those of 2D α-MoO3 nanosheets produced by aqueous exfoliations and, based ...

We present a method for substitutional p-type doping in monolayer (1L) and few-layer (FL) WS2 using highly reactive nitrogen atoms. We demonstrate that the nitrogen-induced lattice distortion in atomically thin WS2 is negligible due to its low kinetic energy. The electrical characteristics of 1L/FL WS2 field-effect transistors (FETs) clearly show an n-channel to p-channel conversion with nitrogen incorporation. We investigate the defect formation energy and the origin of p-type conduction using first-principles calculations. We reveal that a defect state appears near the Fermi level, leading to a shallow acceptor level at 0.24 eV above the valence band maximum in nitrogen-doped 1L/FL WS2. This doping strategy enables a substitutional p-type doping in intrinsically n-type 1L/FL transition metal dichalcogenides (TMDCs) with tunable control of dopants, offering a method for realizing complementary metal-oxide-semiconductor FETs and optoelectronic devices on 1L/FL TMDCs by overcoming one of the major limits o...

Crystalline α-MoO3 belts consisting of nanosheets stacked along their [010] axes were synthesized via thermal vapor transport of MoO3 powders at elevated temperatures. The MoO3 belts were millimeters in length along their [001] axes and tens to hundreds of micrometers in width along their [100] axes. Mechanical and aqueous exfoliations of the belts to form two-dimensional (2D) nanosheets were processed via the scotch-tape and bovine serum albumin (BSA) assisted methods, respectively. Upon scotch-tape exfoliation, the Raman features of MoO3 exhibited monotonic decreases in intensity as the thickness was gradually fell to approach that of a 2D nanosheet. Most Raman features eventually disappeared when a monolayer nanosheet was produced, except for the Mo–O–Mo stretching mode (Ag) at ~818 cm−1, which was accompanied by mode-softening of up to 5 cm−1. This mode softening, hitherto not reported for 2D α-MoO3 nanosheets, can be attributed to lattice relaxations that are validated here via theoretical density functional perturbation theory calculations. The BSA-assisted exfoliation products exhibited a blueshift in the α-MoO3 nanosheet absorption edge; they also revealed an absorption peak at 3.98 eV that can be attributed to their intrinsic exciton absorptions. These observations, together with the facile synthesis of high-purity α-MoO3 crystals, illuminate the possibility of further 2D α-MoO3 nanosheet production and lattice dynamic studies.

Single-layer molybdenum disulfide (MoS2) has attracted significant attention due to its electronic and physical properties, with much effort invested toward obtaining large-area high-quality monolayer MoS2 films. In this work, we demonstrate a reactive-barrier-based approach to achieve growth of highly homogeneous single-layer MoS2 on sapphire by the use of a nickel oxide foam barrier during chemical vapor deposition. Due to the reactivity of the NiO barrier with MoO3, the concentration of precursors reaching the substrate and thus nucleation density is effectively reduced, allowing grain sizes of up to 170 μm and continuous monolayers on the centimeter length scale being obtained. The quality of the monolayer is further revealed by angle-resolved photoemission spectroscopy measurement by observation of a very well resolved electronic band structure and spin–orbit splitting of the bands at room temperature with only two major domain orientations, indicating the successful growth of a highly crystalline an...

We present an analysis of the electronic properties of an MoS2 monolayer (ML) and bilayer (BL) as-grown on a highly ordered pyrolytic graphite (HOPG) substrate by physical vapour deposition (PVD), using lab-based angle-resolved photoemission spectroscopy (ARPES) supported by scanning tunnelling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) for morphology and elemental assessments, respectively. Despite the presence of multiple domains (causing in-plane rotational disorder) and structural defects, electronic band dispersions were clearly observed, reflecting the high density of electronic states along the high symmetry directions of MoS2 single crystal domains. In particular, the thickness dependent direct-to-indirect band gap transition previously reported only for MoS2 layers obtained by exfoliation or via epitaxial growth processes, was found to be also accessible in our PVD grown MoS2 samples. At the same time, electronic gap states were detected, and attributed mainly to structural defects in the 2D layers. Finally, we discuss and clarify the role of the electronic gap states and the interlayer coupling in controlling the energy level alignment at the MoS2/substrate interface.

Since the first isolation of graphene, new classes of two-dimensional (2D) materials have offered fascinating platforms for fundamental science and technology explorations at the nanometer scale. In particular, 2D transition metal dichalcogenides (TMD) such as MoS2 and WSe2 have been intensely investigated due to their unique electronic and optical properties, including tunable optical bandgaps, direct-indirect bandgap crossover, strong spin-orbit coupling, etc., for next-generation flexible nanoelectronics and nanophotonics applications. On the other hand, organics have always been excellent materials for flexible electronics. A plethora of organic molecules, including donors, acceptors, and photosensitive molecules, can be synthesized using low cost and scalable procedures. Marrying the fields of organics and 2D TMDs will bring benefits that are not present in either material alone, enabling even better, multifunctional flexible devices. Central to the realization of such devices is a fundamental understanding of the organic-2D TMD interface. Here, we review the organic-2D TMD interface from both chemical and physical perspectives. We discuss the current understanding of the interfacial interactions between the organic layers and the TMDs, as well as the energy level alignment at the interface, focusing in particular on surface charge transfer and electronic screening effects. Applications from the literature are discussed, especially in optoelectronics and p-n hetero- and homo-junctions. We conclude with an outlook on future scientific and device developments based on organic-2D TMD heterointerfaces.

The understanding of the interlayer interactions in vertical heterostructures of two-dimensional (2D) transition metal dichalcogenides (TMDCs) is essential to exploit their advanced functions for next-generation optoelectronics and electronics. Here we demonstrate a monolithic stacking of TMDC heterostructures with 2D MoS2 and WS2 layers via in situ physical vapor deposition. We find that the kinetically sputtered atoms are able to overcome the interlayer van der Waals forces between the vertical layers, leading to a substantial number of randomly oriented stacks with various twist angles. Our X-ray photoelectron spectroscopy results reveal a type II heterojunction for 2D WS2/MoS2, showing a band alignment with a conduction band offset of 0.41 eV and a valence band offset of 0.25 eV. In particular, we observed a remarkable interlayer coupling and associated exciton relaxation at the hetero-interface due to the misoriented stacks. By analyzing the band structures and charge densities of the vertical stacks using first-principles calculations, we reveal that the interlayer coupling is a function of the interlayer distance and is relatively insensitive to the angle of misorientation.

Memristor crossbar with programmable conductance could overcome the energy consumption and speed limitations of neural networks when executing core computing tasks in image processing. However, the implementation of crossbar array (CBA) based on ultrathin 2D materials is hindered by challenges associated with large-scale material synthesis and device integration. Here, a memristor CBA is demonstrated using wafer-scale (2-inch) polycrystalline hafnium diselenide (HfSe2 ) grown by molecular beam epitaxy, and a metal-assisted van der Waals transfer technique. The memristor exhibits small switching voltage (0.6 V), low switching energy (0.82 pJ), and simultaneously achieves emulation of synaptic weight plasticity. Furthermore, the CBA enables artificial neural network with a high recognition accuracy of 93.34%. Hardware multiply-and-accumulate (MAC) operation with a narrow error distribution of 0.29% is also demonstrated, and a high power efficiency of greater than 8-trillion operations per second per Watt is achieved. Based on the MAC results, hardware convolution image processing can be performed using programmable kernels (i.e., soft, horizontal, and vertical edge enhancement), which constitutes a vital function for neural network hardware.

The introduction of patterned sapphire substrates (PSS) has been regarded as an effective method to improve the photoelectric performance of 2D layered materials in recent years. Molybdenum disulfide (MoS2 ), an intriguing transition metal 2D materials with splendid photoresponse owing to a direct-indirect bandgap transition at monolayer, shows promising optoelectronics applications. Here, a large-scale, continuous multilayer MoS2 film is prepared on a SiO2 /Si substrate and transferred to flat sapphire substrate and PSS, respectively. An enhanced dynamic distribution of local electric field and concentrated photon excitons across the interface between MoS2 and patterned sapphire substrates are revealed by the finite-difference time-domain simulation. The photoelectric performance of the MoS2 /PSS photodetector is improved under the three lasers of 365, 460, and 660 nm. Under the 365 nm laser, the photocurrent increased by 3 times, noise equivalent power (NEP) decreases to 1.77 × 10-14 W/Hz1/2 and specific detectivity (D*) increases to 1.2 × 1010 Jones. Meanwhile, the responsivity is increased by 7 times at 460 nm, and the response time of the MoS2 /PSS photodetector is also shortened under three wavelengths. The work demonstrates an effective method for enhancing the optical properties of photodetectors and enabling simultaneous detection of broad-spectrum emissions.

Carbon nanotubes showing tensile strength up to 20 GPa and stiffness up to 1000 GPa, are the strongest fibers known to mankind, which has been proved to be an extraordinary filler for light metals such as aluminium and titanium metals and alloys. However, the efficiency of its reinforcement to hard metallic materials such as Nickel-based superalloys are still unknown and under developed in the current powder metallurgy research. This study focuses on the sintering and mechanical properties of carbon nanotube reinforced Inconel 625 superalloy. The carbon nanotube modified Inconel 625 powder was pressed with a polymer binder and sintered to achieve high density. The mechanical properties are measured and compared with non-reinforced counterparts to verify the efficiency of carbon nanotube reinforcement. The mechanism of such reinforcement will be discussed based on the optical image and nano-indentation analysis.

Selective laser melting (SLM) was used for additive manufacturing multi-wall carbon nanotube (MWCNT) reinforced Inconel 625 composites. The MWCNTs were coated on Inconel 625 powder through molecular-level mixing. Compared to the SLM fabricated Inconel 625 sample, the composite sample showed significant improvement in ultimate tensile and yield strength with less elongation. Heat-treatment on the composite sample recovered its elongation to the level of pure Inconel 625 while maintaining its ultimate tensile strength but reducing its yield strength. The microstructures of the composite sample had a slightly faster cooling rate than the pure metallic sample during SLM fabrication. The electron backscatter diffraction graphs revealed the grain refinement induced by MWCNTS in the alloy matrix. The Raman spectra and TEM micrographs revealed the presence of MWCNT in the metal matrix after SLM fabrication. Keywords: Selective laser melting, Inconel 625, Carbon nanotube, Metal matrix composite, Heat treatment

Earth abundant materials based photoelectrochemical cells (PECs) are designed using aluminium alloyed iron silicide (FeSi(Al)) as auxiliary electrode, tungsten oxide (WO3) and iron-oxide (Fe2O3) as working electrodes for solar driven hydrogen (SH) production. Low temperature grown metallic α-phase and semiconducting β-phase FeSi(Al) are introduced as auxiliary electrode and hydrogen evolution performance is compared with commercially available platinum electrode. The β-phase FeSi(Al) electrode yields similar hydrogen evolution compared with platinum electrode and are highly stable in electrolyte solution. This study shows that the earth-abundant iron-silicide and cheap metal oxides based PEC cells provide great potential toward Pt-free devices for the development of sustainable and low cost PECs for large scale solar hydrogen production.

With the advent of the Internet of Things (IoT), applications such as flexible electronics, optoelectronics, self and low power electronics, and neuromorphic electronics are emerging rapidly, two dimensional (2D) layered materials such as molybdenum disulfide (MoS 2 ) have shown great potential and are called to have a major role in these areas. However, low cost and high yield synthesis of 2D materials is critical towards their commercial implementation. Here, we present a chemical vapor deposition (CVD) process for the synthesis of MoS 2 films using novel precursors with low sublimations point, which enables a fast and low temperature growth of crystalline 2D MoS 2 films greatly reducing the process cost. Raman spectroscopy, photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS), scanning tunneling microscope (STM) and electrical transport are used to determine the crystallinity and elucidate the compositional, optical and electrical characteristics of the CVD grown MoS 2 for its use in future electronic applications.

Growth of highly crystalline MoS 2 single crystals with large edge length of ~260 μm was demonstrated via the sulfurization process. The high quality of the MoS 2 atomic layer, exemplified by its optical property and electrical performance, presents a significant step towards scalable preparation of this material. The back–gated FETs based on as–grown, single-layer MoS 2 exhibited the extraordinary high electron mobility value (~90 cm2V-1s-1) which is the largest reported to date for as-grown, monolayer MoS 2 in a 2-terminal device configuration.

The observation of regular ( h0 l) planar defects in α-MoO