Conventional Chemical Vapor Deposition Method Research Articles

Direct growth Bi2O2Se nanosheets on SiO2/Si substrate for high-performance and broadband photodetector

Bi2O2Se, a newly emerging two-dimensional (2D) material, has attracted significant attention as a promising candidate for optoelectronics applications due to its exceptional air stability and high mobility. Generally, mica and SrTiO3 substrates with lattice matching are commonly used for the growth of high-quality 2D Bi2O2Se. Although 2D Bi2O2Se grown on these insulating substrates can be transferred onto Si substrate to ensure compatibility with silicon-based semiconductor processes, this inevitably introduces defects and surface states that significantly compromise the performance of optoelectronic devices. Herein we employ Bi2Se3 as the evaporation source and oxygen reaction to directly grow Bi2O2Se nanosheets on Si substrate through a conventional chemical vapor deposition method. The photodetector based on the Bi2O2Se nanosheets on Si substrate demonstrates outstanding optoelectronics performance with a responsivity of 379 A W−1, detectivity of 2.9 × 1010 Jones, and rapid response time of 0.28 ms, respectively, with 532 nm illumination. Moreover, it also exhibits a broadband photodetection capability across the visible to near-infrared range (532–1300 nm). These results suggest that the promising potential of Bi2O2Se nanosheets for high-performance and broadband photodetector applications.

Monolayer WS2 Nanosheets Passivated with HfO2 for Enhanced Photodetectors

Two-dimensional transition metal dichalcogenides (TMDCs) are widely used in electronic and optoelectronic devices. However, the conventional chemical vapor deposition (CVD) method is difficult to synthesize large-area monolayer WS2 nanosheets stably, which limits the application of WS2 in the field of photoelectric detection. In this work, we propose an innovative NaCl-assisted CVD method that allows freely adjustable substrate positions for synthesizing monolayer WS2 nanosheets. The obtained maximum grain size of the monolayer WS2 nanosheets is up to 30 μm. Subsequently, we investigated the effect of the HfO2 passivation layer on the performance of the metal–semiconductor–metal (MSM) WS2-based photodetectors. The HfO2 passivation layer brought an overall improvement to the performance of the fabricated photodetectors, exhibiting a high responsivity of 1093.1 AW–1, a high specific detectivity of 2.6 × 1012 Jones, and a high external quantum efficiency of 2.1 × 105%. Furthermore, the physical mechanism of the fabricated photodetectors has been discussed to explain how the HfO2 passivation layer takes effect in the improvement of the WS2-based photodetectors. This result can accelerate the development of optoelectronic devices based on TMDCs.

Growth of Low-Defect Nitrogen-Doped Graphene Film Using Condensation-Assisted Chemical Vapor Deposition Method.

It is significantly important to modulate the electrical properties of graphene films through doping for building desired electronic devices. One of the effective doping methods is the chemical vapor deposition (CVD) of graphene films with heteroatom doping during the process, but this usually results in nitrogen-doped graphene with low doping levels, high defect density, and low carrier mobility. In this work, we developed a novel condensation-assisted CVD method for the synthesis of high-quality nitrogen-doped graphene (NG) films at low temperatures of 400 °C using solid 3,4,5-trichloropyridine as a carbon and nitrogen source. The condensation system was employed to reduce the volatilization of the solid source during the non-growth stage, which leads to a great improvement of quality of as-prepared NG films. Compared to the one synthesized using conventional CVD methods, the NG films synthesized using condensation-assisted CVD present extremely low defects with a ratio of from D- to G-peak intensity (ID/IG) in the Raman spectrum lower than 0.35. The corresponding total N content, graphitic nitrogen/total nitrogen ratio, and carrier mobility reach 3.2 at%, 67%, and 727 cm2V-1S-1, respectively. This improved condensation-assisted CVD method provides a facile and well-controlled approach for fabricating high-quality NG films, which would be very useful for building electronic devices with high electrical performance.

Facilely Fabricated Bright Lead‐Free Perovskite Cs3Cu2I5 Scintillator Film for High‐Definition X‐Ray Imaging

Scintillator is a critical component to detect high‐energy particles or rays, which is widely used in deep space exploration, security inspection, and nondestructive testing and medical diagnosis, such as X‐ray imaging and computed tomography (CT). However, the wider application of traditional inorganic and organic scintillators is limited by the complex operation process or poor adaptability to changeable environment, and there remains a demand to develop green and stable scintillators with high sensitivity and low detection limit. Herein, the one‐step preparation of lead‐free perovskite Cs3Cu2I5 scintillator film for high‐definition X‐ray imaging by conventional chemical vapor deposition method is reported. Cs3Cu2I5 demonstrates good stability and bright‐blue emission at 445 nm and superhigh photoluminescence quantum yield (85.14%). Importantly, upon X‐ray irradiation, the Cs3Cu2I5 perovskite film exhibits light yield (≈39 251 photons MeV−1) as high as two times of the commercially available Ce:LuAG single‐crystal scintillator (≈22 000 photons MeV−1). Furthermore, the practical demonstration for a bamboo stick and insect specimens illustrates sensitive scintillation response to X‐ray signals with superior linearity and high‐quality images in X‐ray photography and CT. Overall, Cs3Cu2I5 film provides nontoxicity, high radioluminescence intensity, and good stability, it can be regarded as a competitive material for X‐ray imaging.

Low-defect-density WS2 by hydroxide vapor phase deposition

Two-dimensional (2D) semiconducting monolayers such as transition metal dichalcogenides (TMDs) are promising channel materials to extend Moore’s Law in advanced electronics. Synthetic TMD layers from chemical vapor deposition (CVD) are scalable for fabrication but notorious for their high defect densities. Therefore, innovative endeavors on growth reaction to enhance their quality are urgently needed. Here, we report that the hydroxide W species, an extremely pure vapor phase metal precursor form, is very efficient for sulfurization, leading to about one order of magnitude lower defect density compared to those from conventional CVD methods. The field-effect transistor (FET) devices based on the proposed growth reach a peak electron mobility ~200 cm2/Vs (~800 cm2/Vs) at room temperature (15 K), comparable to those from exfoliated flakes. The FET device with a channel length of 100 nm displays a high on-state current of ~400 µA/µm, encouraging the industrialization of 2D materials.

Modulated Photoluminescence of Single‐Layer MoS2 via Nanostructured SrTiO3 Surface

AbstractThe structure and morphology of the substrate surface play critical roles in tuning the properties of the supported two‐dimension materials (2DM). In this work, a simple strategy to engineer the SrTiO3 single crystal into a trenched structure which is composed of atomically flat terraces and high steps of several nanometers is developed. Through the conventional chemical vapor deposition method, high quality single‐layered MoS2 nanosheets are successfully fabricated directly on the trenched SrTiO3 (Tr‐STO) substrate, which thus result in a heterostructure with well‐defined interface and controllable corrugated morphology. The corrugated MoS2/Tr‐STO sample displays a drastically suppressed photoluminescence as compared to those grown on atomically flat substrates. Detailed scanning probe microscopy in combination with optical spectroscopy measurements demonstrates that the photoluminescence quenching occurs exclusively in the MoS2 area carpeting the high SrTiO3 steps, which can be attributed to the significantly reduced bandgaps hence massively enriched free charges in these regions. This work not only provides a new strategy to tailor the 2DM properties by simply engineering the substrate surface corrugations, but also brings deep insights into the dependence of properties of the hybridized system on the interface morphologies.

Advances in Microwave‐Enhanced Chemical Vapor Deposition for Graphene Synthesis

AbstractGraphene has received intensive research interest in various areas due to its outstanding mechanical, electrical properties, high specific surface area and 2D flexible structure. Mechanical exfoliation generates defect‐free graphene, but suffers from ultra‐low yield. This drawback can be partially overcome by chemical vapor deposition method (CVD). However, conventional CVD imposes high temperature. In recent years, microwave plasma‐enhanced CVD (MPCVD) has been widely investigated as a viable strategy toward large‐area graphene synthesis. In this review, important issues during the process are summarized. Firstly, various MPCVD devices that have been explored for graphene synthesis are presented. Secondly, effect of carbon sources, nitrogen‐containing gases, and CO2 in the precursors are discussed. Thirdly, MPCVD enabled direct synthesis of graphene on metal substrates and non‐metal sustrates is discussed. Finally, the advances of MPCVD in lowering the graphene synthesis temperature are demonstrated.

Grafting thin N-doped carbon nanotubes on hollow N-doped carbon nanoplates encapsulated with ultrasmall cobalt particles for microwave absorption

It is desirable but challenging to integrate 0D, 1D and 2D materials into 3D nanostructures for the microwave absorption. Herein, short and thin N-doped carbon nanotubes (NCNTs) encapsulated with sub-2-nm magnetic Co particles grafted on hollow nanoplates (HCNP) are fabricated after ZIF-67 nanoplates were annealed at a lower temperature relative to conventional chemical vapor deposition methods. The as-fabricated HCNP/NCNT assembled with 0D, 1D and 2D nanostructures features 3D interconnected open structure, endowing them with abundant interfaces and defects that facilitate its microwave absorption. The minimum reflection loss (RLmin) of −41.08 dB with a thickness of 2 mm and effective absorption bandwidth (EAB) of 4.26 GHz with a thickness of 1.8 mm were achieved by the HCNP/NCNT, superior to the counterparts without NCNTs. Besides its unique structural feature, density functional theory (DFT) calculations demonstrate that the increased microwave absorbability of the HCNP/NCNT is also relevant to the additional dipole polarization and interfacial polarization caused by the NCNTs. Based on the computer simulation technology (CST) results, the HCNP/NCNT can attenuate microwave energy under the actual conditions. The proposed controllable synthesis method may open a new avenue for the reasonable design of high-performance microwave absorbers.

A Novel Carbon-Assisted Chemical Vapor Deposition Growth of Large-Area Uniform Monolayer MoS2 and WS2

Monolayer MoS2 can be used for various applications such as flexible optoelectronics and electronics due to its exceptional optical and electronic properties. For these applications, large-area synthesis of high-quality monolayer MoS2 is highly desirable. However, the conventional chemical vapor deposition (CVD) method using MoO3 and S powder has shown limitations in synthesizing high-quality monolayer MoS2 over a large area on a substrate. In this study, we present a novel carbon cloth-assisted CVD method for large-area uniform synthesis of high-quality monolayer MoS2. While the conventional CVD method produces thick MoS2 films in the center of the substrate and forms MoS2 monolayers at the edge of the thick MoS2 films, our carbon cloth-assisted CVD method uniformly grows high-quality monolayer MoS2 in the center of the substrate. The as-synthesized monolayer MoS2 was characterized in detail by Raman/photoluminescence spectroscopy, atomic force microscopy, and transmission electron microscopy. We reveal the growth process of monolayer MoS2 initiated from MoS2 seeds by synthesizing monolayer MoS2 with varying reaction times. In addition, we show that the CVD method employing carbon powder also produces uniform monolayer MoS2 without forming thick MoS2 films in the center of the substrate. This confirms that the large-area growth of monolayer MoS2 using the carbon cloth-assisted CVD method is mainly due to reducing properties of the carbon material, rather than the effect of covering the carbon cloth. Furthermore, we demonstrate that our carbon cloth-assisted CVD method is generally applicable to large-area uniform synthesis of other monolayer transition metal dichalcogenides, including monolayer WS2.

ALD-Based Synthesis of Wafer-Scale Transition Metal Dichalcogenides Towards Nanoelectronics and Optoelectronics Applications

Two-dimensional (2D) transition metal dichalcogenides (TMDs), such as MoS2 and WS2 have been widely studied due to their unique physical and electronic properties even at one atomic layer thickness. Since the first report on the MoS2 field-effect transistor (FET) device [1], great efforts have been made in the past decade to extend the intriguing features of TMDs to practical applications. However, such integration has been severely bottlenecked by the lack of effective approaches to achieve wafer-scale, uniform, crystalline and stoichiometric TMD films.Till now, it is still prevalent to fabricate TMD-based electronic devices using mechanical exfoliation methods. Although single-crystal flakes with least defects can be obtained, the size, thickness and location of the exfoliated TMD flakes are largely uncontrollable, making it unsuitable for large-scale device integration and massive production. So far, various synthetic approaches have been proposed to grow large-area TMD thin films. Chemical vapor deposition (CVD)-based method is one of the major routines to synthesize high-quality monolayer and few-layer TMD flakes [2-4]. For example, in typical CVD processes to grow MoS2, the films can be achieved either by the reduction reaction between the S and MoO3 source powders or by sulfurizing the Mo (or MoOx) films pre-deposited by using physical vapor deposition. However, the nucleation sites in the CVD process are uncontrollable which may lead to the vertical stacking of the MoS2 flakes in triangle shape deteriorating the crystalline properties of the film. On the other hand, the pre-deposited Mo or MoOx film by using e-beam evaporation or sputtering usually suffer from rough surface morphology and unsatisfactory film uniformity which further limit the homogeneity of the large-scale film and device integration.Atomic layer deposition (ALD) is a surface-controlled film fabrication and can provide a possible route towards the synthesis of TMD thin films since the ALD approach follows the layer-by-layer deposition mechanism [5,6]. As compared to the conventional CVD method, ALD can enable precise thickness control on atomic scale and excellent film uniformity as well as good stoichiometry and crystallinity with proper annealing steps. In this work, we employed the ALD-based synthesis method to grow wafer-scale MoS2 and WS2 thin films. Non-toxic MoCl5, WCl5 and hexamethyldisilathiane (HMDST) precursors have been used which are different and superior to those used in previous work. Film characterizations have confirmed the wafer-level uniformity, crystallinity and stoichiometry of the synthesized films. Homogeneous electrical behaviors have also been obtained from the fabricated FET device arrays. In addition, optoelectronic devices such as photodetectors and simple logic gates such as n-type inverter arrays have been demonstrated using the wafer-scale MoS2 FET arrays. Furthermore, we have used the substitutional doping in the ALD process to achieve controllable p-type doping of MoS2 films, which can provide solid basis for the complimentary metal-oxide-semiconductor (CMOS) integrated circuit applications. This work shows that the ALD-based synthesis of the 2D TMD thin films is an attractive approach and has provided a promising platform to further push forward the circuit and system level applications of the TMD materials.

Horizontal Single-Walled Carbon Nanotube Arrays: Controlled Synthesis, Characterizations, and Applications.

Single-walled carbon nanotubes (SWNTs) emerge as a promising material to advance carbon nanoelectronics. However, synthesizing or assembling pure metallic/semiconducting SWNTs required for interconnects/integrated circuits, respectively, by a conventional chemical vapor deposition method or by an assembly technique remains challenging. Recent studies have shown significant scientific breakthroughs in controlled SWNT synthesis/assembly and applications in scaled field effect transistors, which are a critical component in functional nanodevices, thereby rendering the horizontal SWNT array an important candidate for innovating nanotechnology. This review provides a comprehensive analysis of the controlled synthesis, surface assembly, characterization techniques, and potential applications of horizontally aligned SWNT arrays. This review begins with the discussion of synthesis of horizontally aligned SWNTs with regulated direction, density, structure, and theoretical models applied to understand the growth results. Several traditional procedures applied for assembling SWNTs on target surface are also briefly discussed. It then discusses the techniques adopted to characterize SWNTs, ranging from electron/probe microscopy to various optical spectroscopy methods. Prototype applications based on the horizontally aligned SWNTs, such as interconnects, field effect transistors, integrated circuits, and even computers, are subsequently described. Finally, this review concludes with challenges and a brief outlook of the future development in this research field.

Oxide Inhibitor-Assisted Growth of Single-Layer Molybdenum Dichalcogenides (MoX2, X = S, Se, Te) with Controllable Molybdenum Release.

Though chemical vapor deposition (CVD) methods have been widely used in the growth of two-dimensional transition-metal dichalcogenides (2D TMDCs), the controllable fabrication of 2D TMDCs is yet hard to achieve because of the great challenge of concisely controlling the release of precursors vapor, one of the most critical growth kinetic factors. To solve this important issue, here we report the utilization of oxide inhibitors covering Mo source during CVD reactions to manipulate the release of Mo vapor. In contrast to the lack of capability of conventional CVD methods, 2D molybdenum dichalcogenide (MoX2, X = S, Se, Te) monolayers were successfully fabricated through the proposed CVD protocol with the oxide-inhibitor-assisted growth (OIAG) strategy. In this way, despite the fact that only separated MoTe2 flakes were prepared, both MoS2 (continuous and clean) and MoSe2 (continuous but dotted) monolayer films at the scale of centimeter were obtained. The presented OIAG method enables a comprehensive understanding and precise control of the reaction kinetics for improved growth of 2D MoX2.

Scanning tunneling microscopic investigations for studying conformational change of underlying Cu(111) and Ni(111) during graphene growth

Demonstration of graphene growth on metal substrates using chemical vapor deposition method (CVD) facilitated the large-area synthesis of graphene, which extended the graphene research from the fundamental investigation with a small graphene flake to the various practical applications. Spectroscopic studies using 13C-labeled carbon precursor first suggested two different growth mechanisms of graphene on Ni and Cu substrates during the conventional CVD process, ‘segregation growth’ and ‘surface growth’ for Ni and Cu substrates, respectively. However, the growth mechanism of graphene is not simply understood. For example, the surface science studies have suggested the Ni2C conversion mechanism or the direct surface growth even on Ni surface. Herein, the conformational changes of underlying metal substrate during graphene growth on Ni(111) and Cu(111) are presented, which are highly affected by the different types of growth mechanisms. We believe that our results may widen the knowledge to understand the graphene growth mechanisms on Ni and Cu. Also, the influence of graphene-metal interaction on the electronic structures has been elucidated for graphene grown on Ni and Cu substrates by scanning tunneling spectroscopic studies combined with the theoretical calculation.

Direct Growth of Graphene on a SiGe Alloy Surface by Chemical Vapor Deposition

Integration of graphene with Si-based semiconductor materials, which are core-materials in complementary metal oxide semiconductor (CMOS) technology, is desirable. To date, the synergistic effects of various graphene-semiconductor hybrid systems have been shown to overcome various physical limitations of graphene and semiconductors. However, the graphene utilized in most previous studies was synthesized over a metal catalyst and required additional transfer processes that could generate irreversible physical defects and chemical contamination. Although direct synthesis of graphene on Si or Ge has been developed, research into graphene growth using silicon-germanium (SiGe) as a catalyst remains in its infancy. This is despite expectations that this method would be highly applicable to next-generation CMOS applications. Herein, we demonstrate the direct growth of graphene on a SiGe surface using a conventional chemical vapor deposition method. Optical microscopy, electron microscopy, and Raman spectroscopy were used to confirmed that the graphene was uniformly synthesized over the entire substrate. The advantages of CMOS-compatible graphene growth and high crystallinity of the synthesized graphene will provide opportunities for novel graphene-SiGe hybrid system development and next-generation CMOS technology.

Structural investigation of Al2O3 coatings by PECVD with a high deposition rate

AbstractThe deposition of alumina on thermal barrier coatings can effectively avoid hot corrosion and increase durability. Al2O3 coatings were prepared on an yttria‐stabilized zirconia (YSZ) substrate by plasma chemical vapor deposition (CVD). The effects of microwave power (PM) and total pressure (Ptot) on the crystalline phase and microstructure of Al2O3 coatings were investigated, and the effect of the mechanism on the deposition rate was also analyzed. The α‐Al2O3 coatings with a needle‐like microstructure were formed at a higher PM and Ptot, whereas the γ‐phase coatings exhibited a cauliflower‐like microstructure at a lower PM and Ptot. A maximum deposition rate (Rdep) of 58 μmh−1 was obtained, which is significantly higher than those of conventional CVD methods.

General Growth of Carbon Nanotubes for Cerium Redox Reactions in High-Efficiency Redox Flow Batteries.

Carbon nanotubes (CNTs) possess remarkable mechanical, electrical, thermal, and optical properties that predestine them for numerous potential applications. The conventional chemical vapor deposition (CVD) route for the production of CNTs, however, suffers from costly and complex issues. Herein, we demonstrate a general and high-yield strategy to grow nitrogen-doped CNTs (NCNTs) on three-dimensional (3D) graphite felt (GF) substrates, through a direct thermal pyrolysis process simply using a common tube furnace, instead of the costly and complex CVD method. Specifically, the NCNTs-decorated GF (NCNT-GF) electrode possesses enhanced electrocatalytic performance towards cerium redox reactions, mainly due to the catalytic effect of N atoms doped into NCNTs, and ingenious and hierarchical 3D architecture of the NCNT-GF. As a result, the cell with the NCNT-GF serving as a positive electrode shows the improved energy efficiency with increases of about 53.4% and 43.8% over the pristine GF and the acidly treated GF at a high charge/discharge rate of 30 mA cm−2, respectively. Moreover, the as-prepared NCNT catalyst-enhanced electrode is found to be highly robust and should enable a long-term cycle without detectable efficiency loss after 500 cycles. The viable synthetic strategy reported in this study will contribute to the further development of more active heteroatom-doped CNTs for redox flow batteries.

A unified materials approach to mitigating optical nonlinearities in optical fiber. III. Canonical examples and materials road map

AbstractThis paper, Part III in the Trilogy (Ballato, Cavillon, Dragic, 2018; Dragic, Cavillon, Ballato, et al., 2018a,b), provides a road map for the development of simple core/clad optical fibers whose enhanced performance—in particular, marked reductions in optical nonlinearities—is achieved materially and not through the more conventional present routes of geometrically complex fiber design. More specifically, the material properties that give rise to Brillouin, Raman and Rayleigh scattering, transverse mode instabilities (TMI), and n2‐mediated nonlinear effects are compiled and results on a wide range of optical fibers are discussed with a focus on trends in performance with glass composition. Furthermore, optical power scaling estimations as well as binary and ternary property diagrams associated with Rayleigh scattering, the Brillouin gain coefficient (BGC) and the thermo‐optic coefficient (dn/dT) are developed and employed to graphically represent general trends with composition along with compositional targets for a single intrinsically low nonlinearity, silica‐based optical fiber that can achieve the power scaling goals of future high energy fiber laser applications. A foundational finding of this work is that the high‐silica content optical fibers fabricated using conventional chemical vapor deposition methods will not suffice to meet the power scaling demands of future high‐power and high‐energy fiber lasers.

Templated and Catalytic Fabrication of N-Doped Hierarchical Porous Carbon-Carbon Nanotube Hybrids as Host for Lithium-Sulfur Batteries.

Nitrogen-doped hierarchical porous carbon and carbon nanotube hybrids (N-HPC-CNTs) are fabricated by simple pyrolysis of the N-rich raw material melamine-formaldehyde (MF) resin in the presence of nano-CaCO3 and a bimetallic combination of Fe-Co catalyst. During carbonization, nano-CaCO3 acts as a template for creating a hierarchical porous carbon, and the N atoms originated from MF resin are in situ doped into the carbon matrix simultaneously. Meanwhile, volatile gases generated by the thermal decomposition of MF resin could serve as carbon and nitrogen sources to grow nitrogen-doped CNTs on HPC. The growth mechanism is the same as that for conventional chemical vapor deposition (CVD) growth of CNTs on the metal catalysts, but the technological requirements are obviously not as harsh as those for the CVD method. Low-cost raw materials and simple equipment are sufficient for the growth. Moreover, the density and length of the CNTs are tunable, which can be simply adjusted via applying different amounts of Fe-Co catalysts. Such an N-doped hybrid structured carbon with mesopores can not only effectively prompt the physical and chemical adsorption of polysulfides but also ensures a fast electron transfer because of the incorporation of CNTs, which provides sufficient conducting pathways and effective connections between the CNTs and HPC. Furthermore, CNTs grown on HPC can act as physical barriers to block the large pores on HPC, thereby reducing the polysulfide loss. Benefiting from the advantages, the N-HPC-CNT hybrids are a desirable host prospect for Li-S batteries.

Ultrasensitive label-free detection of DNA hybridization by sapphire-based graphene field-effect transistor biosensor

Abstract Graphene has attracted much attention in biosensing applications for its unique properties. Because of one-atom layer structure, every atom of graphene is exposed to the environment, making the electronic properties of graphene are very sensitive to charged analytes. Therefore, graphene is an ideal material for transistors in high-performance sensors. Chemical vapor deposition (CVD) method has been demonstrated the most successful method for fabricating large area graphene. However, the conventional CVD methods can only grow graphene on metallic substrate and the graphene has to be transferred to the insulating substrate for further device fabrication. The transfer process creates wrinkles, cracks, or tears on the graphene, which severely degrade electrical properties of graphene. These factors severely degrade the sensing performance of graphene. Here, we directly fabricated graphene on sapphire substrate by high temperature CVD without the use of metal catalysts. The sapphire-based graphene was patterned and make into a DNA biosensor in the configuration of field-effect transistor. The sensors show high performance and achieve the DNA detection sensitivity as low as 100 fM (10 −13 M), which is at least 10 times lower than prior transferred CVD G-FET DNA sensors. The use of the sapphire-based G-FETs suggests a promising future for biosensing applications.

Suppressing Nucleation in Metal–Organic Chemical Vapor Deposition of MoS2 Monolayers by Alkali Metal Halides

Toward the large-area deposition of MoS2 layers, we employ metal-organic precursors of Mo and S for a facile and reproducible van der Waals epitaxy on c-plane sapphire. Exposing c-sapphire substrates to alkali metal halide salts such as KI or NaCl together with the Mo precursor prior to the start of the growth process results in increasing the lateral dimensions of single crystalline domains by more than 2 orders of magnitude. The MoS2 grown this way exhibits high crystallinity and optoelectronic quality comparable to single-crystal MoS2 produced by conventional chemical vapor deposition methods. The presence of alkali metal halides suppresses the nucleation and enhances enlargement of domains while resulting in chemically pure MoS2 after transfer. Field-effect measurements in polymer electrolyte-gated devices result in promising electron mobility values close to 100 cm2 V-1 s-1 at cryogenic temperatures.