Pressure Chemical Vapor Deposition Research Articles

Room-Temperature NO2 Sensing of CVD-Modified WS2–WSe2 Heterojunctions

Two-dimensional (2D) semiconducting heterojunction chemical sensors are in high demand because of their enhanced response, stability, and selectivity. However, fine-tuning heterojunctions using vapor deposition growth still needs further research. Our present study focuses on the ambient pressure chemical vapor deposition (CVD) synthesis of hexagonal tungsten sulfide-tungsten selenide (WS2–WSe2) p–p heterojunctions (as a 2D–2D arrangement). We use the liquid-phase exfoliation method to disperse bulk WS2 and WSe2 and decorate large flakes of WS2 with smaller WSe2 nanosheets in CVD. Electron microscopy and related surface investigations reveal their homogeneity on drop-casting. Two drops from the exfoliated heterojunction dispersion were drop-cast on a transducer to study the NO2 response and related sensing properties. The sensor showed long-term stability (>2 months), even at high humidity levels (40–90%). The gas-sensing properties of this layered p–p heterojunction-based nanocomposite strongly suggest an affinity toward NO2 gas, leading to improved response, high stability, independent of humidity effects, and high selectivity.

Study of morphological evolution and growth mechanism of CVD grown 2D tin disulfide

Fractal patterns formed during non-equilibrium growth processes and are abundant in nature. However, the mechanism of their formation remains unknown. Several growth factors such as relaxation rate, cooling rate, diffusion anisotropy and growth time were identified for regulating the fractal growth. Nevertheless, most articles focused on regular shaped (such as triangles and hexagons) 2D layered metal dichalcogenides (LMDs), whereas fractals have received less attention. Therefore, understanding the controlled synthesis of LMDs materials with unique edge structures is highly desired for various potential applications. Here, we report large fractal growth of tin disulfide (SnS2) by atmospheric pressure chemical vapor deposition technique. The edge length of the atomically thin SnS2 fractals range from 5 to 100 µm. Our study shows the morphological evolution from fractal to triangular-like structure during the CVD growth process. To understand this phenomenon, we anticipated that the early phase of the growth mostly occurs via kinetic regulated pathway resulting fractal like structure. As the domains go through numerous relaxation phases throughout the edge diffusion process, the morphology gets more compact or regular, indicating increased thermodynamic control over the growth process. We have also provided a physical model for the growth mechanism of CVD grown SnS2.

One-Step Synthesis of a Binder-Free, Stable, and High-Performance Electrode; Cu-O|Cu3P Heterostructure for the Electrocatalytic Methanol Oxidation Reaction (MOR).

Although direct methanol fuel cells (DMFCs) have been spotlighted in the past decade, their commercialization has been hampered by the poor efficiency of the methanol oxidation reaction (MOR) due to the unsatisfactory performance of currently available electrocatalysts. Herein, we developed a binder-free, copper-based, self-supported electrode consisting of a heterostructure of Cu3P and mixed copper oxides, i.e., cuprous-cupric oxide (Cu-O), as a high-performance catalyst for the electro-oxidation of methanol. We synthesized a self-supported electrode composed of Cu-O|Cu3P using a two-furnace atmospheric pressure-chemical vapor deposition (AP-CVD) process. High-resolution transmission electron microscopy analysis revealed the formation of 3D nanocrystals with defects and pores. Cu-O|Cu3P outperformed the MOR activity of individual Cu3P and Cu-O owing to the synergistic interaction between them. Cu3P|Cu-O exhibited a highest anodic current density of 232.5 mAcm-2 at the low potential of 0.65 V vs. Hg/HgO, which is impressive and superior to the electrocatalytic activity of its individual counterparts. The formation of defects, 3D morphology, and the synergistic effect between Cu3P and Cu-O play a crucial role in facilitating the electron transport between electrode and electrolyte to obtain the optimal MOR activity. Cu-O|Cu3P shows outstanding MOR stability for about 3600 s with 100% retention of the current density, which proves its robustness alongside CO intermediate.

Continuous Large Area Monolayered Molybdenum Disulfide Growth Using Atmospheric Pressure Chemical Vapor Deposition.

The growth of large crystallite continuous monolayer materials like molybdenum disulfide (MoS2) with the desired morphology via chemical vapor deposition (CVD) remains a challenge. In CVD, the complex interplay of various factors like growth temperatures, precursors, and nature of the substrate decides the crystallinity, crystallite size, and coverage area of the grown MoS2 monolayer. In the present work, we report about the role of weight fraction of molybdenum trioxide (MoO3), sulfur, and carrier gas flow rate toward nucleation and monolayer growth. The concentration of MoO3 weight fraction has been found to govern the self-seeding process and decides the density of nucleation sites affecting the morphology and coverage area. A carrier gas flow of 100 sccm argon results in large crystallite continuous films with a lower coverage area (70%), while a flow rate of 150 sccm results in 92% coverage area with a reduced crystallite size. Through a systematic variation of experimental parameters, we have established the recipe for the growth of large crystallite atomically thin MoS2 suitable for optoelectronic devices.

New insights into APCVD grown monolayer MoS2 using time-domain terahertz spectroscopy

In modern era, wireless communications at ultrafast speed are need of the hour and search for its solution through cutting edge sciences is a new perspective. To address this issue, the data rates in order of terabits per second (TBPS) could be a key step for the realization of emerging sixth generation (6G) networks utilizing terahertz (THz) frequency regime. In this context, new class of transition metal dichalcogenides (TMDs) have been introduced as potential candidates for future generation wireless THz technology. Herein, a strategy has been adopted to synthesize high-quality monolayer of molybdenum di-sulfide (MoS2) using indigenously developed atmospheric pressure chemical vapor deposition (APCVD) set-up. Further, the time-domain transmission and sheet conductivity were studied as well as a plausible mechanism of terahertz response for monolayer MoS2 has been proposed and compared with bulk MoS2. Hence, the obtained results set a stepping stone to employ the monolayer MoS2 as potential quantum materials benefitting the next generation terahertz communication devices.

Formation of Large-Area Twisted Bilayer Graphene on Ni(111) Film via Ambient Pressure Chemical Vapor Deposition

Due to the destruction of the intrinsic symmetry between the layers, twisted bilayer graphene has the advantages of available interlayer coupling, tunable electronic bandgap, and diverse phonon dispersion features, which offers a unique platform for the advanced electronic devices. The segregation growth of large-area twisted bilayer graphene on Ni(111) film by ambient pressure chemical vapor deposition (APCVD) methods is presented in this paper. The growth kinetics include two main aspects of the catalytic reaction of methane on the Ni surface and the carbon segregation from the Ni bulk. The large-area twisted bilayer graphene (TBG) can be fabricated by controlling carbon segregation for the continuous second layer graphene that is rotated relative to the first layer graphene. Low energy electron diffraction (LEED) studies reveal a dominant twist angle of about 22.7°. The analysis shows that the dominant twist angle is closely related to the stable energy structure of TBG with the smallest moiré periodicity. Besides, the other twist angles of TBG are also formed in vicinity of the dominant angle, confirmed by microscopic observations with selected area electron diffraction (SAED). The work in this paper provides a convenient route for the synthesis of TBG on Ni(111) substrate, which can promote the application of twisted graphene in future photoelectric and spintronic devices.

Defect-Induced Efficient Heteroepitaxial Growth of Single-Wall Carbon Nanotubes @ Hexagonal Boron Nitride Films.

Carbon nanotube-based derivatives have attracted considerable research interest due to their unique structure and fascinating physicochemical properties. However, the controlled growth mechanism of these derivatives remains unclear, and the synthesis efficiency is low. Herein, we proposed a defect-induced strategy for the efficient heteroepitaxial growth of single-wall carbon nanotubes (SWCNTs)@hexagonal boron nitride (h-BN) films. Air plasma treatment was first performed to generate defects on the wall of SWCNTs. Then, atmospheric pressure chemical vapor deposition was conducted to grow h-BN on the surface of SWCNTs. Controlled experiments combined with first-principles calculations revealed that the induced defects on the wall of SWCNTs function as nucleation sites for the efficient heteroepitaxial growth of h-BN.

Uniform deposition of ultra-thin TiO2 film on mica substrate by atmospheric pressure chemical vapor deposition: Effect of precursor concentration

The performance of pearlescent pigment significantly affected by the grain size and the roughness of deposited film. The effect of TiCl4 concentration on the initial deposition of TiO2 on mica by atmospheric pressure chemical vapor deposition (APCVD) was investigated. The precursor concentration significantly affected the deposition and morphology of TiO2 grains assembling the film. The deposition time for fully covering the surface of mica decreased from 120 to 10 s as the TiCl4 concentration increased from 0.38% to 2.44%. The grain size increased with the TiCl4 concentration. The AFM and TEM analysis demonstrated that the aggregation of TiO2 clusters at the initial stage finally result to the agglomeration of fine TiO2 grains at high TiCl4 concentrations. Following the results, it was suggested that the nucleation density and size was easy to be adjusted when the TiCl4 concentration is below 0.90%.

Multilayer SnS2/few-layer MoS2 heterojunctions with in-situ floating photogate toward high-performance photodetectors and optical imaging application

Since the successful preparation of the monolayer MoS2 phototransistor, two-dimensional (2D) layered materials (2DLMs) have been regarded as one of the most compelling candidates toward the implementation of the next generation of novel optoelectronic devices and systems. However, most reported 2DLM photodetectors suffer from specific shortcomings, such as low responsivity, large dark current, low specific detectivity, low on/off ratio, and sluggish response rate. Herein, multilayer SnS2/few-layer MoS2 van der Waals heterostructures have been constructed by stacking the MoS2 and SnS2 nanosheets grown by a single atmospheric pressure chemical vapor deposition method. The SnS2/MoS2 heterojunction photodetector demonstrates competitive overall performance with a large on/off ratio of 171, a high responsivity of 28.3 A W−1, and an excellent detectivity of 1.2 × 1013 Jones. In addition, an ultrafast response rate with the response/recovery time down to 1.38 ms/600 is achieved. The excellent properties are associated with the synergy of type-II band alignment of SnS2/MoS2 and the in-situ formed seamless floating photogate, which contribute to separating the photoexcited electron-hole pairs and extending the carrier lifetime. Taking advantage of the excellent photosensitivity, the SnS2/MoS2 device demonstrates proof-of-concept optical imaging application. On the whole, this study provides a distinctive perspective to implement advanced photodetectors with competitive overall performance.

A simplified and masking‐free doping process for interdigitated back contact solar cells using an atmospheric pressure chemical vapor deposition borosilicate glass / phosphosilicate glass layer stack for laser doping followed by a high temperature step

AbstractIn this paper a simplified approach for the generation of laterally p‐ and n‐doped structures applicable for cost‐effective production of interdigitated back contact (IBC) solar cells is presented. We use a stack of doping glasses deposited by atmospheric pressure chemical vapor deposition (APCVD), consisting of borosilicate glass (BSG) and phosphosilicate glass (PSG) on Czochralski‐grown (Cz) silicon substrates. A laser process creates the p‐doped regions by local liquid phase diffusion of boron from the BSG layer into the underlying molten Cz‐Si substrate. Simultaneously, the BSG‐PSG stack is removed by laser ablation. In a subsequent high‐temperature step, phosphorus diffuses from the remaining PSG‐BSG layer into the crystalline silicon substrate under inert gas atmosphere, creating complementary to laser doped areas n+‐doped regions. By the use of APCVD, phosphorus and boron contents of the doping glasses can be adjusted freely to vary the resulting p‐ and n‐doped profiles. A higher boron content in the BSG layer enhances the diffusion of phosphorus through the BSG, especially at lower diffusion temperatures. The resulting doping profiles are characterized using electrochemical capacitance‐voltage measurements and the resulting sheet resistances using the four‐point probe method. The amount of minority dopant contamination in n‐ and p‐doped regions is investigated by secondary ion mass spectrometry. Furthermore, transfer length method (TLM)‐measurements indicate contactability of the generated doped regions.

N-doped carbon nanotubes with high amount of graphitic nitrogen as an excellent electrocatalyst for water splitting in alkaline solution

Nitrogen-doped carbon nanotubes (NCNTs) containing high amounts of graphitic nitrogen (g-N) deposited on nickel foam (NF) are investigated as catalysts for the hydrogen (HER) and oxygen evolution reaction (OER) in alkaline solution. NCNTs with abundant g-N were synthesised on NF at a low temperature (600 °C) via atmospheric pressure chemical vapor deposition over electrodeposited Fe particles. The physicochemical characteristics of NCNTs@NF hybrid electrodes were investigated by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy and compared to those of graphene@NF, ultrathin graphite@NF, and N-doped graphite@NF. The electrochemical activity towards both the HER and OER on all samples was evaluated by linear sweep voltammetry. Experimental results paired with density functional theory (DFT) calculations revealed the contribution of both the metal substrate and the NCNTs to improve the HER performance. DFT results indicate that NCNTs containing high amounts of g-N are a very promising electrocatalyst for water splitting. Furthermore, this study will motivate a direction for reasonable design defects to improve the electrochemical performance of CNTs and consequently meet the targeted requirement of new clean energy devices.

Optimized APCVD method for synthesis of monolayer H-Phase VS2 crystals

Abstract Monolayer transition metal dichalcogenides, specifically H-phase vanadium disulfide (VS2), hold great significance as fundamental components for next-generation low-dimensional spintronic, optoelectronic, and future electronic devices. They also offer an opportunity to explore the intrinsic magnetic properties associated with monolayer H-phase VS2 crystals at room temperature. However, there have been limited experimental studies on synthesizing pure monolayer H-phase VS2 crystals using sodium metavanadate (NaVO3) and sulfur (S) as precursors for vanadium (V) and S, respectively. In this study, we present a facile atmospheric pressure chemical vapor deposition (APCVD) approach for the synthesizing monolayer H-phase VS2 crystals with a thickness of ∼0.7 nm. The lateral dimensions of monolayer VS2 crystals extends up to ∼26 µm. Additionally, we have modulated the growth parameters, such as the temperature of NaVO3 and the Ar gas flow rate, to obtain VS2 flakes with different sizes and morphologies. This significant advancement paves the way for the synthesis of monolayer H-phase VS2 crystals on SiO2/Si substrates using the APCVD technique.

Growth and magnetic properties of two-dimensional vanadium-doped Cr<sub>2</sub>S<sub>3</sub> nanosheets

Two-dimensional magnetic materials are emerging materials developed in recent years and have attracted much attention for their unique magnetic properties and structural features in single or few layers of atomic thickness. Among them, ferromagnetic materials have a wide range of applications such as information memory and processing. Therefore the current research is mainly focused on enriching the two-dimensional ferromagnetic database and developing modification strategies for magnetic modulation. In this paper, two-dimensional vanadium-doped Cr<sub>2</sub>S<sub>3</sub>nanosheets were successfully grown on mica substrates by atmospheric pressure chemical vapour deposition. The thickness and size of the nanosheets can be effectively regulated by changing the temperature and mass of vanadium source VCl<sub>3</sub> powders, with the temperature of 765℃ and the mass of 0.010 g as the most appropriate conditions for the growth of nanosheets. The nanosheets were also characterised by optical microscopy, atomic force microscopy, raman spectroscopy, scanning electron microscopy, X-ray energy spectroscopy, X-ray photoelectron spectroscopy, and the nanosheets were regular in shape, with flat surfaces and controllable thicknesses, and high quality vanadium-doped Cr<sub>2</sub>S<sub>3</sub> nanosheets were prepared. Meanwhile, the magnetic characterisation of the doped samples showed that the Curie transition temperature of the vanadium doped samples changed to 105 K, and the maximum magnetic moment point of 75 K in the M-T curve disappeared after V doping, and from subferromagnetic to ferromagnetic, and the coercivity in the M-H curve also increased significantly, which proved that the vanadium doping could effectively regulate the magnetic properties of Cr<sub>2</sub>S<sub>3</sub> nanosheets. These results are expected to advance the possibility of vanadium-doped Cr<sub>2</sub>S<sub>3</sub> materials toward practical applications and become one of the ideal candidate material for next generation spintronic applications.

Quantum tailoring for polarization-discriminating Bi2S3 nanowire photodetectors and their multiplexing optical communication and imaging applications.

In this study, cost-efficient atmospheric pressure chemical vapor deposition has been successfully developed to produce well-aligned high-quality monocrystalline Bi2S3 nanowires. By virtue of surface strain-induced energy band reconstruction, the Bi2S3 photodetectors demonstrate a broadband photoresponse across 370.6 to 1310 nm. Upon a gate voltage of 30 V, the responsivity, external quantum efficiency, and detectivity reach 23 760 A W-1, 5.55 × 106%, and 3.68 × 1013 Jones, respectively. The outstanding photosensitivity is ascribed to the high-efficiency spacial separation of photocarriers, enabled by synergy of the axial built-in electric field and type-II band alignment, as well as the pronounced photogating effect. Moreover, a polarization-discriminating photoresponse has been unveiled. For the first time, the correlation between quantum confinement and dichroic ratio is systematically explored. The optoelectronic dichroism is established to be negatively correlated with the cross dimension (i.e., width and height) of the channel. Specifically, upon 405 nm illumination, the optimized dichroic ratio reaches 2.4, the highest value among the reported Bi2S3 photodetectors. In the end, proof-of-concept multiplexing optical communications and broadband lensless polarimetric imaging have been implemented by exploiting the Bi2S3 nanowire photodetectors as light-sensing functional units. This study develops a quantum tailoring strategy for tailoring the polarization properties of (quasi-)1D material photodetectors whilst depicting new horizons for the next-generation opto-electronics industry.

Growth and magnetic properties of two-dimensional vanadium-doped Cr<sub>2</sub>S<sub>3</sub> nanosheets

Two-dimensional magnetic materials are emerging materials developed in recent years and have attracted much attention for their unique magnetic properties and structural features in single or few layers of atomic thickness. Among them, ferromagnetic materials have a wide range of applications such as information memory and processing. Therefore the current research is mainly focused on enriching the two-dimensional ferromagnetic database and developing modification strategies for magnetic modulation. In this paper, two-dimensional vanadium-doped Cr<sub>2</sub>S<sub>3</sub>nanosheets were successfully grown on mica substrates by atmospheric pressure chemical vapour deposition. The thickness and size of the nanosheets can be effectively regulated by changing the temperature and mass of vanadium source VCl<sub>3</sub> powders, with the temperature of 765℃ and the mass of 0.010 g as the most appropriate conditions for the growth of nanosheets. The nanosheets were also characterised by optical microscopy, atomic force microscopy, raman spectroscopy, scanning electron microscopy, X-ray energy spectroscopy, X-ray photoelectron spectroscopy, and the nanosheets were regular in shape, with flat surfaces and controllable thicknesses, and high quality vanadium-doped Cr<sub>2</sub>S<sub>3</sub> nanosheets were prepared. Meanwhile, the magnetic characterisation of the doped samples showed that the Curie transition temperature of the vanadium doped samples changed to 105 K, and the maximum magnetic moment point of 75 K in the M-T curve disappeared after V doping, and from subferromagnetic to ferromagnetic, and the coercivity in the M-H curve also increased significantly, which proved that the vanadium doping could effectively regulate the magnetic properties of Cr<sub>2</sub>S<sub>3</sub> nanosheets. These results are expected to advance the possibility of vanadium-doped Cr<sub>2</sub>S<sub>3</sub> materials toward practical applications and become one of the ideal candidate material for next generation spintronic applications.

Direct growth of patterned graphene based on metal proximity catalytic mechanism

In graphene electronics applications, in order to obtain the size and pattern required for the device, it is often necessary to photolithography the graphene after growth, resulting in contamination of graphene by the photoresist which have doping effect. Therefore, in order to avoid this effect, this article focused on directly grown patterned graphene. Based on atmospheric pressure chemical vapour deposition (APCVD) technology, patterned graphene was successfully grown on SiO2/Si by metal proximity catalytic effect. The patterned graphene was characterized by Raman spectroscopy and optical microscope. The effects of parameters such as gas flow, growth temperature, and growth time on the growth of patterned graphene were explored, and the best results were obtained. Metal copper and cobalt thin films were used for assisted catalysis, respectively, and the mechanism of metal proximity catalysis was explored. The experimental results showed that proximity catalysis is a catalytic growth mechanism based on surface diffusion. The growth method avoids using photolithography to make patterns, and can grow patterned graphene on insulating substrates or semiconductors in one step, which is of great significance for making patterned graphene and applying them to semiconductor devices.

Synthesis, Structural and Magnetic Properties of Cobalt-Doped GaN Nanowires on Si by Atmospheric Pressure Chemical Vapor Deposition.

GaN nanowires (NWs) grown on silicon via atmospheric pressure chemical vapor deposition were doped with Cobalt (Co) by ion implantation, with a high dose concentration of 4 × 1016 cm-2, corresponding to an average atomic percentage of ~3.85%, and annealed after the implantation. Co-doped GaN showed optimum structural properties when annealed at 700 °C for 6 min in NH3 ambience. From scanning electron microscopy, X-ray diffraction, high resolution transmission electron microscope, and energy dispersive X-ray spectroscopy measurements and analyses, the single crystalline nature of Co-GaN NWs was identified. Slight expansion in the lattice constant of Co-GaN NWs due to the implantation-induced stress effect was observed, which was recovered by thermal annealing. Co-GaN NWs exhibited ferromagnetism as per the superconducting quantum interference device (SQUID) measurement. Hysteretic curves with Hc (coercivity) of 502.5 Oe at 5 K and 201.3 Oe at 300 K were obtained. Applied with a magnetic field of 100 Oe, the transition point between paramagnetic property and ferromagnetic property was determined at 332 K. Interesting structural and conducive magnetic properties show the potential of Co-doped GaN nanowires for the next optoelectronic, electronic, spintronic, sensing, optical, and related applications.

Role of Hydrogen in Suppressing Secondary Nucleation in Chemical Vapor-Deposited MoS2

We investigate the ability of different carrier gases to control defects and secondary nucleation in atmospheric pressure chemical vapor deposition (APCVD) growth of MoS2 on Si/SiO2 substrates. We observe that a reducing environment using H2 gas is more favorable for achieving uniform two-dimensional (2D) growth. Compared to the growth in an inert environment, secondary nucleation on primary MoS2 domains grown using H2 as the carrier gas (H–MoS2) is drastically reduced. We employ a phase-field model to understand the role of enhanced surface diffusion in H–MoS2, due to passivation of defects and dangling bonds, promoting compact secondary domain formation as opposed to dendritic secondary domains under an inert environment. Using X-ray photoelectron spectroscopy, we show that the Mo(VI) oxidation state (corresponding to MoO3), which is prominent for MoS2 grown under an inert atmosphere, is highly suppressed in H–MoS2, leading to more pristine MoS2. This explains the superior electrical performance of H–MoS2 compared to those grown with other carrier gases. Our results offer a facile route to explore different growth environments to realize large-area true 2D films.

Synthesis of Rhenium-Doped Molybdenum Sulfide by Atmospheric Pressure Chemical Vapor Deposition (CVD) for a High-Performance Photodetector.

Two-dimensional layered materials have attracted tremendous attention as photodetectors due to their fascinating features, including comprehensive coverage of band gaps, high potential in new-generation electronic devices, mechanical flexibility, and sensitive light-mass interaction. Currently, graphene and transition-metal dichalcogenides (TMDCs) are the most attractive active materials for constructing photodetectors. A growing number of emerging TMDCs applied in photodetectors bring up opportunities in the direct band gap independence with thickness. This study demonstrated for the first time a photodetector based on a few-layer Re x Mo1-x S2, which was grown by chemical vapor deposition (CVD) under atmospheric pressure. The detailed material characterizations were performed using Raman spectroscopy, photoluminescence, and X-ray photoelectron spectroscopy (XPS) on an as-grown few-layer Re x Mo1-x S2. The results show that both MoS2 and ReS2 peaks appear in the Re x Mo1-x S2 Raman diagram. Re x Mo1-x S2 is observed to emit light at a wavelength of 716.8 nm. The electronic band structure of the few layers of Re x Mo1-x S2 calculated using the first-principles theory suggests that the band gap of Re x Mo1-x S2 is larger than that of ReS2 and smaller than that of MoS2, which is consistent with the photoluminescence results. The thermal stability of the few layers of Re x Mo1-x S2 was evaluated using Raman temperature measurements. It is found that the thermal stability of Re x Mo1-x S2 is close to those of pure ReS2 and MoS2. The fabricated Re x Mo1-x S2 photodetector shows a high response rate of 7.46 A W-1 under 365 nm illumination, offering a competitive performance to the devices based on TMDCs and graphenes. This study unambiguously distinguishes Re x Mo1-x S2 as a future candidate in electronics and optoelectronics.

Controlled preparation of ultrasmall MoSe2 nanocrytallites and electrocatalytic activity

• Well-defined MoSe 2 nanocrytallites were synthesized by CVD technique. • The MoSe 2 nanocrytallites possess the ultrasmall dimension of ∼20 nm. • The ultrasmall MoSe 2 nanocatalysts were directly grown on carbon cloth substrate. • The ultrasmall MoSe 2 nanocrytallites displayed a good electrocatalytic activity. MoSe 2 is one of the prospective substitutes for electrocatalytic hydrogen evolution due to its particularly two-dimensional layered structure. Different MoSe 2 with fascinating frameworks and wishful dimensions have been synthesized for diversified applications. Well-defined MoSe 2 nanocrytallites were successfully obtained by an atmospheric-pressure chemical vapour deposition (CVD) technique. The MoSe 2 nanocrytallites possess the ultrasmall dimension of ∼20 nm. The products were directly grown on conductive carbon cloth substrate, which can be used as the electrode. Because of the structural advantages, the ultrasmall MoSe 2 nanocrytallites display outstanding hydrogen evolution reaction activity.