MoS2 Crystals Research Articles

Surface-Bound and Volatile Mo Oxides Produced During Oxidation of Single MoS2 Crystals in Air and High Relative Humidity.

We report on the MoO3 oxides and their derivatives on microscopic 2H MoS2 flakes oxidized in air and high relative humidity at a moderate temperature range below 410 °C. We combine XPS and AFM measurements such as topography, friction, creation of nanoscale ripples and scratches on the MoS2 flakes deposited on Si substrates. We detect MoO3 oxides mostly by measuring selected nanomechanical properties of the MoO3 layer, such as its compressive mechanical stress at the plastic yield. We discuss basal surface coverage of the single MoS2 flakes by the MoO3 oxides. We discuss conditions for appearance of all possible MoO3 oxide derivatives, such as molybdenum(VI) hydroxyoxides and MoO3 hydrates. Our findings agree with an expected mechanistic switch in thermal oxidation in water vapors vs. air.

Visualization of Crystallographic Orientation and Twist Angles in Two-Dimensional Crystals with an Optical Microscope.

Recently, twisted two-dimensional (2D) bilayers have attracted intense interest due to the emergence of exotic physics in moiré superlattices arising from strong interactions between electrons in the two misaligned lattices. Accurate determination and control of crystallographic orientation is vital to construct twisted 2D bilayers. Here, we demonstrate a very simple method to visualize crystallographic orientation in various 2D crystals by directly imaging n-tritriacontane crystallites epitaxially grown on 2D crystals using an ordinary optical microscope. The specific orientation of the molecular assembly allows the lattice orientation of the underlying 2D crystals to be determined with a high precision using an optical microscope. When tested on a 2D bilayer comprising staggered stacked MoS2 crystals, the twist angle can also be determined accurately. Our findings offer a nondestructive method for determining the lattice structure of 2D crystals and their bilayers and can also be a metrology tool for establishing large-area surface crystalline order.

Variations of paramagnetic defects and dopants in geo-MoS2 from diverse localities probed by ESR.

Exfoliated flakes from molybdenite crystals often still serve as benchmark substrates for two-dimensional MoS2 fundamental and device-oriented research. In this article, results are reported of a multi-frequency electron paramagnetic resonance (EPR) study on a series of natural 2H MoS2 crystals taken from various (seven) geological sites with the intent to explore the variations in quality and properties in terms of occurring paramagnetic point defects, with particular focus on the assessment of the predominant type of impurity dopant. The sample set covers three types of overall doping regimes, i.e., p-type, n-type, and mixed (n-type and p-type parts in one sample). The doping type appears primarily governed by substitutional impurities as evidenced by the observed As and N acceptor (both substituting for S) and Re donor (substituting for Mo) signals. For all p-type specimens, doping is found to be ruled by As where, however, a strong variation is revealed in doping uniformity, which appears not directly correlated with the As dopant density. Without specific precautions taken, surface contamination related EPR signals are observed in virtually all As-excavated geo-MoS2 specimens. While several of these signals are of unassigned origin, two prominent ones are identified, one as concerning oxo-Mo5+ compounds and the other Mn2+ centers. The geo-MoS2 sample with the foremost n-type doping shows, besides the prime Re donor EPR signal, an intense powder-pattern signal, tentatively typified by g∥ = 2.076, g⊥ = 2.253, which is suggested to originate from intercalation-related defects. The results bear out the necessity of rigorous surface cleaning, even including invasive removal of surface layers, to obtain pristine MoS2 parent crystals suitable for enabling exfoliation of high quality flakes.

Ultrafast nucleation and growth of high-quality monolayer MoSe2 crystals via vapor-liquid-solid mechanism

The controlled production of two-dimensional atomically thin transition metal dichalcogenides (TMDs) is fundamentally important for their device applications. However, the synthesis of large-area and high-quality TMD monolayers remains a challenge due to the lack of sufficient understanding of growth mechanisms, especially for the chemical vapor deposition (CVD). Here we report molten-salt assisted CVD growth of highly crystalline MoSe2 monolayers via a novel vapor-liquid-solid (VLS) mechanism. Our results show that the growth rate of the VLS-grown monolayer MoSe2 is about 40 times faster than that of MoSe2 grown via the vapor-solid (VS) mechanism, which makes the fabrication of 100 μm domains for ∼2 min and a uniform monolayer film within 5 min. The ultrafast growth of monolayer MoSe2 crystals benefits from the synergic effect of one-dimensional VLS growth and two-dimensional VS edge expansion. Moreover, these MoSe2 monolayers exhibit high crystal quality and enhanced photoluminescence due to efficient Se-vacancy repairing by the doping of halogen atoms. These findings provide a new understanding of MoSe2 growth and open up an opportunity for the rapid synthesis of high-quality TMD monolayers and heterostructures.

The influence of crystal thickness and interlayer interactions on the properties of heavy ion irradiated MoS2

Ion irradiation is a versatile tool to introduce controlled defects into two-dimensional (2D) MoS2 on account of its unique spatial resolution and plethora of ion types and energies available. In order to fully realise the potential of this technique, a holistic understanding of ion-induced defect production in 2D MoS2 crystals of different thicknesses is mandatory. X-ray photoelectron spectroscopy, electron diffraction and Raman spectroscopy show that thinner MoS2 crystals are more susceptible to radiation damage caused by 225 keV Xe+ ions. However, the rate of defect production in quadrilayer and bulk crystals is not significantly different under our experimental conditions. The rate at which S atoms are sputtered as a function of radiation exposure is considerably higher for monolayer MoS2, compared to bulk crystals, leading to MoO3 formation. P-doping of MoS2 is observed and attributed to the acceptor states introduced by vacancies and charge transfer interactions with adsorbed species. Moreover, the out-of-plane vibrational properties of irradiated MoS2 crystals are shown to be strongly thickness-dependent: in mono- and bilayer MoS2, the confinement of phonons by defects results in a blueshift of the mode. Whereas, a redshift is observed in bulk crystals due to attenuation of the effective restoring forces acting on S atoms caused by vacancies in adjacent MoS2 layers. Consequently, the frequency of tri- and quadrilayer crystals is statistically invariant on account oft competition between phonon confinement effects and interlayer interactions. The linewidth is observed to decrease in bi- and trilayer crystals after low dose irradiation and is attributed to layer decoupling. This work shows that there is a complex interplay between defect production, crystal thickness and interlayer interactions in MoS2. Our results demonstrate that ion irradiation is an effective tool to modulate the electronic, vibrational and structural properties of MoS2, which may prove beneficial for practical applications.

Thin-Film Transistor (TFT) Gas Sensor Based on Quantum Dots-Sensitized Molybdenum Disulfide

Introduction NO2 primarily gets in the air from the burning of fuel. Exposure to NO2 may potentially increase susceptibility to respiratory infections, and a 5 min emergency exposure limit of 35 ppm NO2 exposure has been proposed by the American Industrial Hygiene Association [1]. There is an increasing demand to develop large-scale networking of gas sensors for achieving online NO2 monitoring with low power consumption. Semiconductor gas sensors employing high-temperature ceramics technology have attracted intense research and industry interests because of their high sensitivity and low cost. However, the high operating temperature of these sensors still sets a limit to their compatibility with CMOS technology, making it challenging to achieve gas sensor array with large-scale manufacture and application level. On the other hand, electronic gas sensors based on TFTs have shown promising results, because of the control over gate voltage can modulate the carrier concentration in the semiconductor channel by orders of magnitude, which allows the TFT gas sensors to be more sensitive and selective. 2D transition metal dichalcogenides (TMDs), typically molybdenum disulfide (MoS2) nanoflakes, are popular channel materials used for TFT-based gas sensors [2, 3], due to their unique electronic properties and large specific surface area. However, MoS2 TFT gas sensors always suffer the sluggish and weak response as well as incomplete recovery during operated at room temperature, significantly limiting their practical applications.Herein, we proposed to construct MoS2 TFT gas sensor by sensitizing with PbS quantum dots (QDs), a highly tunable 0D nanomaterials with size-dependent bandgap and excellent solution processability [4], aiming to improve the room-temperature response and recovery kinetics. The huge amount of surface dangling bonds of QDs make them sensitive receptors for gas molecules. The hybrid PbS/MoS2 architecture benefited from excellent adsorption of the NO2 molecules to the highly active surface of PbS QDs, combined with the high mobility MoS2 nanoflakes-based TFT, thereby achieve the optimal NO2-sensing performance at room temperature. Experimental details Fabrication of MoS2 TFT sensors. The few-layer MoS2 nanoflakes were mechanically exfoliated from bulk crystal MoS2 onto the Si substrates covered by a 300 nm thick SiO2 layer. The substrates with interdigitated 5 nm Cr/100 nm Au as source-drain electrodes were pre-patterned by photolithography, followed by electron beam evaporation and the lift-off process. Alternatively, high quality MoS2 monolayer can be also synthesized on the above SiO2/Si substrates in a tube furnace by high purity sulfur powder and MoO3 powder, as S and Mo precursor, respectively, and then obtained MoS2 TFT with a bottom-gate bottom-contact configuration. Sensitization of MoS2 channel with PbS QDs. Organo-hot injection method were typically employed for the synthesis of PbS QDs. Ascribe to the excellent solution processability and stable dispersibility of QDs, we use programmable electrohydrodynamic jet printing technologies as well as spin-coating methods to directly deposit QDs on the surface of MoS2 nanoflakes. Finally, we successfully fabricated the TFT sensors based on 0D PbS/2D MoS2. Gas sensing experiments. As-fabricated PbS/MoS2 TFT sensors were measured using probe station connected with semiconductor parameter analyzer (Model B1500A, Keysight) to monitor the real-time current change, and electrical properties including current-voltage, transfer and output characteristics. All the electrical and gas sensing characterizations had been carried out in an ambient air atmosphere or inert atmosphere of N2 at room temperature (25°C). The concentration of NO2 was controlled by a mixture of NO2 (50 ppm in N2) and N2 (99.99%) flow measured by the mass flow controller. Results and Conclusions In conclusion, we have proposed a novel strategy to construct PbS/MoS2 TFT gas sensors for room temperature NO2 detection. Compared to the pristine MoS2 TFT sensors, the PbS/MoS2 TFT sensors exhibited higher sensitivity with fast response/recovery kinetics toward NO2. The sensing mechanism was attributed to the synergistic effect by the favorable 0D-2D interface, making combined efforts for excellent access of gas molecules to highly active PbS QDs, as well as the superb charge transport in MoS2 nanoflakes that made a great enhancement of the gas-sensing performance. The 0D-QDs with tunable bandgaps will further promote progress in the engineering of the band alignment at the 0D-2D heterojunction interface, paving a promising way to develop gas-sensing performance of 2D layered materials.

Enabling room temperature ferromagnetism in monolayer MoS2 via in situ iron-doping

Two-dimensional semiconductors, including transition metal dichalcogenides, are of interest in electronics and photonics but remain nonmagnetic in their intrinsic form. Previous efforts to form two-dimensional dilute magnetic semiconductors utilized extrinsic doping techniques or bulk crystal growth, detrimentally affecting uniformity, scalability, or Curie temperature. Here, we demonstrate an in situ substitutional doping of Fe atoms into MoS2 monolayers in the chemical vapor deposition growth. The iron atoms substitute molybdenum sites in MoS2 crystals, as confirmed by transmission electron microscopy and Raman signatures. We uncover an Fe-related spectral transition of Fe:MoS2 monolayers that appears at 2.28 eV above the pristine bandgap and displays pronounced ferromagnetic hysteresis. The microscopic origin is further corroborated by density functional theory calculations of dipole-allowed transitions in Fe:MoS2. Using spatially integrating magnetization measurements and spatially resolving nitrogen-vacancy center magnetometry, we show that Fe:MoS2 monolayers remain magnetized even at ambient conditions, manifesting ferromagnetism at room temperature.

Laser processing of thin film sputtered MoS2: Thinning, oxidation, and crystallization

The interest in thin film 2D materials has brought renewed attention to the compound molybdenum disulfide (MoS2). As a 2D material, MoS2 can exhibit high transport mobility and transitions to a direct-gap semiconductor when thinned down to a few atomic layers. Consequently, it has both electronic and photonic device applications. The bulk of research on crystalline MoS2 is via exfoliated and chemical vapor deposited material. In this work, we present a laser processing approach that offers flexibility in the types of composite materials that can be produced. We demonstrate laser crystallization of sputter-deposited amorphous MoS2 (∼10 nm) and subsequent thinning down to a few atomic layers that result in direct bandgap emission. With further laser processing under inert gas purge (argon) and low vacuum air, we fabricate composite nano-materials comprised of metallic and molybdenum oxides. Material characterization is done by optical interferometry, atomic force microscopy, SEM, Auger, and Raman diagnostics, but the ongoing physics of the laser thinning process is elucidated by XPS measurements.

Investigating the Redox Properties of Two-Dimensional MoS2 Using Photoluminescence Spectroelectrochemistry and Scanning Electrochemical Cell Microscopy.

Control over photophysical and chemical properties of two-dimensional (2D) transition metal dichalcogenides (TMDs) is the key to advance their applications in next-generation optoelectronics. Although chemical doping and surface modification with plasmonic metals have been reported to tune the photophysical and catalytic properties of 2D TMDs, there have been few reports of tuning optical properties using dynamic electrochemical control of electrode potential. Herein, we report (1) the photoluminescence (PL) enhancement and red-shift in the PL spectrum of 2D MoS2, synthesized by chemical vapor deposition and subsequent transfer onto an indium tin oxide electrode, upon electrochemical anodization and (2) spatial heterogeneities in its photoelectrochemical (PEC) activities. Spectroelectrochemistry shows that positive electrochemical bias causes an initial ten-fold increase in the PL intensity followed by a quick decrease in the enhancement. The PL enhancement and spectrum red-shift are associated with the decrease in nonradiative decay rates of excitons formed upon electrochemical anodization of 2D MoS2. Additionally, scanning electrochemical cell microscopy (SECCM) study shows that the 2D MoS2 crystal is spatially sensitive to PEC oxidation at positive potentials. SECCM also shows a photocurrent increase caused by spatially heterogeneous edge-type defect sites of the crystal.

Room-Temperature Patterning of Nanoscale MoS2 under an Electron Beam.

Molybdenum disulfide (MoS2) is traditionally grown at a high temperature and subsequently patterned to study its electronic properties or make devices. This method imposes severe limitations on the shape and size of MoS2 crystals that can be patterned precisely at required positions. Here, we describe a method of direct nanoscale patterning of MoS2 at room temperature by exposing a molybdenum thiocubane single-source precursor to a beam of electrons. Molybdenum thiocubanes with various alkylxanthate moieties [Mo4S4(ROCS2)6, where R = alkyl] were prepared using a "self-assembly" approach. Micro-Raman and micro-FTIR spectroscopic studies suggest that exposure to a relatively smaller dose of electrons results in the breakdown of xanthate moieties, leading to the formation of MoS2. High-resolution transmission electron micrographs suggest that the growth of MoS2 most likely happens along (100) planes. An electron-beam-induced chemical transformation of a molybdenum thiocubane resist was exploited to fabricate sub-10 nm MoS2 lines and dense dots as small as 13 nm with a pitch of 33 nm. Since this technique does not require the liftoff and etching steps, patterning of MoS2 with interesting shapes, sizes, and thicknesses potentially leading to tunable band gap is possible.

Controllable Growth of Bilayer MoS2 Crystals by Reverse-Flow Chemical Vapor Deposition

Molybdenum disulfide (MoS2) is a two-dimensional (2D) semiconductor, which shows potential applications in catalysis, optoelectronics and electronics. The stacking order in layered materials induces different performances in interlayer couplings and electronic devices. Therefore, controlling the stacking orientations is necessary but remains a significant challenge. Here uniform and high-quality bilayer MoS2 flakes (AA/AB) have been synthesized by reverse-flow chemical vapor deposition (CVD), through controlling growth temperatures. 770 °C is suitable for the growth of AA stacking and AB stacking prefers higher temperature at 820 °C. The reverse-flow helps to generate bilayer MoS2 with few nucleation points and the general method for the synthesis of bilayer MoS2 in different stacking orientations paves a way for development of 2D semiconductor applications.

Extended 1D defect induced magnetism in 2D MoS2 crystal

Exploring two dimensional (2D) magnetic materials is important for both fundamental research and practical applications in nanoscale spintronics. Although dispersive doping of atoms in 2D nonmagnetic transition-metal dichalcogenides (TMD) has been broadly studied in recent years, the regular linear substitution inside 2D nonmagnetic TMD is rarely explored. Herein, based on first-principles calculations, we report a series of hybrid magnetic structures formed by linear atomic doping in MoS2 monolayer. We demonstrate that F and Fe atoms linear-doped MoS2 are ferromagnetic semi-metals while Mn and Co atoms linear-doped MoS2 are ferromagnetic semiconductors in their ground states. Except for F dopant, the magnetic ground states of Mn, Fe, or Co atom linear-doped MoS2 are independent of the width of linear defect. The thermal and lattice dynamical stabilities of linear-doped MoS2 monolayer are confirmed with the molecular dynamics simulations and phonon spectra. A ferromagnetic semi-metal or semiconductor to half-metallic ferromagnet transition in doped MoS2 monolayer is revealed with applying strain. Further, atomically thin magnetic zones with different shapes can also be achieved by arranging the dopants. The induced magnetic properties render linear-doped MoS2 a promising material for spintronics in the nanoscale.

Bandgap tuning of two-dimensional materials by sphere diameter engineering.

Developing a precise and reproducible bandgap tuning method that enables tailored design of materials is of crucial importance for optoelectronic devices. Towards this end, we report a sphere diameter engineering (SDE) technique to manipulate the bandgap of two-dimensional (2D) materials. A one-to-one correspondence with an ideal linear working curve is established between the bandgap of MoS2 and the sphere diameter in a continuous range as large as 360 meV. Fully uniform bandgap tuning of all the as-grown MoS2 crystals is realized due to the isotropic characteristic of the sphere. More intriguingly, both a decrease and an increase of the bandgap can be achieved by constructing a positive or negative curvature. By fusing individual spheres in the melted state, post-synthesis bandgap adjustment of the supported 2D materials can be realized. This SDE technique, showing good precision, uniformity and reproducibility with high efficiency, may further accelerate the potential applications of 2D materials.

Formation of MoS2 from elemental Mo and S using reactive molecular dynamics simulations

Mo- and S-based lubricant additives reduce friction in boundary lubrication through the formation of molybdenum disulfide (MoS2) during operation. However, the fundamental mechanisms of MoS2 formation are still not fully understood, in part because direct experimental measurement is challenging during the crystallization process. Previously, reactive molecular dynamics simulations were used to model the formation of crystalline MoS2 by compressing and heating amorphous material consisting of Mo and S. Here, the authors test the robustness of these models to capture the crystallization process under different simulation conditions and with different reactive force fields. Lastly, a reactive force field that contains parameters for Mo, S, and O was modified to enable it to capture MoS2 crystallization in the presence of oxygen.

Comparative Study of DC and RF Sputtered MoSe2 Coatings Containing Carbon—An Approach to Optimize Stoichiometry, Microstructure, Crystallinity and Hardness

Low stoichiometry, low crystallinity, low hardness and incongruencies involving the reported microstructure have limited the applicability of TMD-C (Transition metal dichalcogenides with carbon) solid-lubricant coatings. In this work, optimized Mo–Se–C coatings were deposited using confocal plasma magnetron sputtering to overcome the above-mentioned issues. Two different approaches were used; MoSe2 target powered by DC (direct current) or RF (radio frequency) magnetron sputtering. Carbon was always added by DC magnetron sputtering. Wavelength dispersive spectroscopy displayed Se/Mo stoichiometry of ~2, values higher than the literature. The Se/Mo ratio for RF-deposited coatings was lower than for their DC counterparts. Scanning electron microscopy showed that irrespective of the low carbon additions, the Mo–Se–C coatings were highly compact with no vestiges of columnar growth due to optimal bombardment of sputtered species. Application of substrate bias further improved compactness at the expense of lower Se/Mo ratio. X-ray diffraction, transmission electron microscopy, and Raman spectroscopy confirmed the presence of MoSe2 crystals, and (002) basal planes. Even very low carbon additions led to an improvement of the hardness of the coatings. The work reports a comparison between RF and DC sputtering of MoSe2 coatings with carbon and provides a guideline to optimize the composition, morphology, structure, and mechanical properties.

Effect of reaction temperature and reaction time on the structure and properties of MoS2 synthesized by hydrothermal method

AbstractIn this study, molybdenum disulfide (MoS2) nanostructures were synthesized by a facile hydrothermal process, using ammonium heptamolybdate tetrahydrate ((NH4)6Mo7O24.4H2O) and thiourea (CH4N2S) as the reactants. The effects of experimental parameters including reaction temperatures and reaction times on the structure and morphology of MoS2 have primarily been investigated. The morphology, microstructure, chemical composition and optical properties of as‐synthesized MoS2 were characterized using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), energy dispersive X‐ray spectroscopy (EDS), X‐ray diffraction (XRD), Raman and Photoluminescence spectroscopy. The FESEM and TEM results indicate that depending on the reaction temperature, the three types of morphologies of MoS2 crystals could be obtained. Morphologies of MoS2 changed gradually from aggregated particles to flake‐like structure, then finally to nanosheet morphology with increasing reaction temperature from 160 to 220 oC. However, it was found that the reaction time contributed significantly to the restacking and refinement of MoS2 crystal structure, rather than affecting the morphology of the investigated samples. Both XRD and Raman investigations reveal that the as‐synthesized MoS2 has a hexagonal phase structure (2H‐MoS2). Interestingly, the as‐prepared MoS2 nanosheets exhibit photoluminescence in the visible range with the emitted photon energy of ~1.81 and ~1.95 eV, these properties make MoS2 a promising candidate as the material of choice for next‐generation optoelectronic and photonic devices.

Photocatalytic Properties of Copper Nitride/Molybdenum Disulfide Composite Films Prepared by Magnetron Sputtering

Cu3N/MoS2 composite films were prepared by magnetron sputtering under different preparation parameter, and their photocatalytic properties were investigated. Results showed that the composite films surface was uniform and had no evident cracks. When the sputtering power of MoS2 increased from 2 W to 8 W, the photocatalytic performance of the composite films showed a trend of increasing first and then decreasing. Among these films, the composite films with MoS2 sputtering power of 4 W showed the best photocatalytic degradation performance. The photocatalytic degradation rate of methyl orange at 30 min was 98.3%, because the MoS2 crystal in the films preferentially grew over the Cu3N crystal, thereby affecting the growth of the Cu3N crystal. The crystallinity of the copper nitride also increased. During photocatalytic degradation, the proper amount of MoS2 reduced the band gap of Cu3N, and the photogenerated electron hole pairs were easily separated. Thus, the films produces additional photogenerated electrons and promotes the degradation reaction of the composite films on methyl orange solution.

Photocarrier-Induced Active Control of Second-Order Optical Nonlinearity in Monolayer MoS2.

Atomically thin transition metal dichalcogenides (TMDs) in their excited states can serve as exceptionally small building blocks for active optical platforms. In this scheme, optical excitation provides a practical approach to control light-TMD interactions via the photocarrier generation, in an ultrafast manner. Here, it is demonstrated that via a controlled generation of photocarriers the second-harmonic generation (SHG) from a monolayer MoS2 crystal can be substantially modulated up to ≈55% within a timeframe of ≈250 fs, a set of performance characteristics that showcases the promise of low-dimensional materials for all-optical nonlinear data processing. The combined experimental and theoretical study suggests that the large SHG modulation stems from the correlation between the second-order dielectric susceptibility χ(2) and the density of photoexcited carriers in MoS2 . Indeed, the depopulation of the conduction band electrons, at the vicinity of the high-symmetry K/K' points of MoS2 , suppresses the contribution of interband electronic transitions in the effective χ(2) of the monolayer crystal, enabling the all-optical modulation of the SHG signal. The strong dependence of the second-order optical response on the density of photocarriers reveals the promise of time-resolved nonlinear characterization as an alternative route to monitoring carrier dynamics in excited states of TMDs.

Realization of 2D crystalline metal nitrides via selective atomic substitution.

Two-dimensional (2D) transition metal nitrides (TMNs) are new members in the 2D materials family with a wide range of applications. Particularly, highly crystalline and large area thin films of TMNs are desirable for applications in electronic and optoelectronic devices; however, the synthesis of these TMNs has not yet been achieved. Here, we report the synthesis of few-nanometer thin Mo5N6 crystals with large area and high quality via in situ chemical conversion of layered MoS2 crystals. The versatility of this general approach is demonstrated by expanding the method to synthesize W5N6 and TiN. Our strategy offers a new direction for preparing 2D TMNs with desirable characteristics, opening a door for studying fundamental physics and facilitating the development of next-generation electronics.

MoS2-on-paper optoelectronics: drawing photodetectors with van der Waals semiconductors beyond graphite.

We fabricate paper-supported semiconducting devices by rubbing a layered molybdenum disulfide (MoS2) crystal onto a piece of paper, similar to the action of drawing/writing with a pencil on paper. We show that the abrasion between the MoS2 crystal and the paper substrate efficiently exfoliates the crystals, breaking the weak van der Waals interlayer bonds and leading to the deposition of a film of interconnected MoS2 platelets. Employing this simple method, which can be easily extended to other 2D materials, we fabricate MoS2-on-paper broadband photodetectors with spectral sensitivity from the ultraviolet (UV) to the near-infrared (NIR) range. We also used these paper-based photodetectors to acquire pictures of objects by mounting the photodetectors in a homebuilt single-pixel camera setup.