Pressure Chemical Vapor Deposition Research Articles

Room-temperature emitters in wafer-scale few-layer hBN by atmospheric pressure CVD

Hexagonal boron nitride (hBN) is a two-dimensional, wide band gap semiconductor material suitable for several technologies. 2D hBN appeared as a viable platform to produce bright and optically stable single photon emitters (SPEs) at room temperature, which are in demand for quantum technologies. In this context, one main challenge concerns the upscaling of 2D hBN with uniform spatial and spectral distribution of SPE sources. In this work we optimized the atmospheric-pressure chemical vapor deposition (APCVD) growth and obtained large-area 2D hBN with uniform fluorescence emission properties. We characterized the hBN films by a combination of electron microscopy, Raman and X-ray photoelectron spectroscopy techniques. The extensive characterization revealed few-layer, polycrystalline hBN films (∼3 nm thickness) with balanced stoichiometry and uniformity over 2″ wafer scale. We studied the fluorescence emission properties of the hBN films by multidimensional hyperspectral fluorescence microscopy. We measured simultaneously the spatial position, intensity, and spectral properties of the emitters, which were exposed to continuous illumination over minutes. Three main emission peaks (at 538, 582, and 617 nm) were observed, with associated replica peaks red-shifted by ∼53 nm. A surface emitter density of ∼0.1 emitters/μm2 was found. A comparative test with pristine hBN nanosheets produced by liquid-phase exfoliation (LPE) was performed, finding that CVD and LPE hBN possess analogous spectral emitter categories in terms of peak position/intensity and density. Overall, the line-shape and wavelength of the emission peaks, as well as the other measured features, are consistent with single-photon emission from hBN. The results indicate that APCVD hBN might proficiently serve as a SPE platform for quantum technologies.

Monolayer MoS2 of high mobility grown on SiO2 substrate by two-step chemical vapor deposition

We report a novel two-step ambient pressure chemical vapor deposition (CVD) pathway to grow high-quality MoS2 monolayer on the SiO2 substrate with large crystal size up to 110 μm. The large specific surface area of the pre-synthesized MoO3 flakes on the mica substrate compared to MoO3 powder could dramatically reduce the consumption of the Mo source. The electronic information inferred from the four-probe scanning tunneling microscope (4P-STM) image explains the threshold voltage variations and the n-type behavior observed in the two-terminal transport measurements. Furthermore, the direct van der Pauw transport also confirms its relatively high carrier mobility. Our study provides a reliable method to synthesize high-quality MoS2 monolayer, which is confirmed by the direct 4P-STM measurement results. Such methodology is a key step toward the large-scale growth of transition metal dichalcogenides (TMDs) on the SiO2 substrate and is essential to further development of the TMDs-related integrated devices.

Tunable hierarchical hexagonal nickel telluride (Ni3Te2) laminated microsheets as flexible counter electrodes for high-performance fibrous dye-sensitized solar cells: Accelerated electrocatalysis reduction of I3− ions

To develop highly active catalysts as counter electrodes is another promising way for improving the photovoltaic conversion efficiency (PCE) of fibrous dye-sensitized solar cells (FDSSCs). Then considering their applications in wearable electronic system, the designed fibrous counter electrodes (FCEs) should possess a good mechanical flexibility except high catalysis performances. Here in this work, hexagonal nickel telluride (Ni3Te2) microsheets with tunable diameters and thicknesses were in-situ prepared via an atmospheric pressure chemical vapor deposition method on nickel wires. Benefiting from their two-dimensional laminated structure and asymmetric crystalline structure, the Ni3Te2 microsheets show a high catalytic activity for the reduction of I3- → I- during the photoelectrochemical processes in FDSSCs. And cell tests show that the maximum PCE of FDSSCs with Ni3Te2 FCEs reaches 11.81% (with an average value of 10.47%), which is 2.10 times that of the ones with Pt FCEs (5.62%). Furthermore, series of optimization on the microscale morphologies of Ni3Te2 microsheets indicates that the suitable diameter (30 ∼ 40 μm) and thickness (ca. 3.0 μm) are suitable for the diffusion and reduction of I3- ions. Besides, the FDDSCs with Ni3Te2 PCEs show a high cycling stability and an excellent dynamic bending stability (attenuation rate of 0.12‰ per bending cycle). This research would provide some insights into the design of high-performance FCEs for FDSSCs towards wearable electronic devices.

Open-air plasma deposition of polymer-supported silica-based membranes for gas separation

In this study, we developed an open-air atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) as a scalable technique to fabricate polymer-supported silica-based membranes for gas separation. Using the open-air AP-PECVD, we achieved a low-temperature deposition of silica-based molecular sieve membranes onto porous polymeric support in a system that can operate under open-air conditions. We investigated the effect of deposition conditions, such as precursor concentration and deposition temperature, on the membrane structure and permeation property. It was revealed that precursor concentration plays a vital role in determining membrane properties. The membranes prepared with low precursor concentration had an inorganic structure with granular morphology, resulting in poor permselective performance. In contrast, deposition at high precursor concentration led to the formation of a continuous layer with a silicone-like structure. By optimizing the precursor concentration, a membrane having a He permeance of 7.25 × 10−8 mol/(m2 s Pa) with a He/SF6 permeance ratio of 171 can be fabricated at room temperature. The deposition at elevated temperature was also effective in improving the permselective performance. By increasing the deposition temperature to 150 °C, the permselective performance of the membrane was improved to a He permeance of 7.7 × 10−8 mol/(m2 s Pa) and He/SF6 of 434. The resultant membranes also exhibited high selectivity for the separation of industrial relevant gas mixtures such as H2/N2 and H2/CH4 with the permeance ratios of 40 and 38, respectively. The present study demonstrates that open-air AP-PECVD is promising as a scalable technique to fabricate polymer-supported silica-based membranes with high productivity.

Ambient Pressure Chemical Vapor Deposition of Flat and Vertically Aligned MoS2 Nanosheets

Molybdenum disulfide (MoS2) got tremendous attention due to its atomically thin body, rich physics, and high carrier mobility. The controlled synthesis of large area and high crystalline monolayer MoS2 nanosheets on diverse substrates remains a challenge for potential practical applications. Synthesizing different structured MoS2 nanosheets with horizontal and vertical orientations with respect to the substrate surface would bring a configurational versatility with benefit for numerous applications, including nanoelectronics, optoelectronics, and energy technologies. Among the proposed methods, ambient pressure chemical vapor deposition (AP-CVD) is a promising way for developing large-scale MoS2 nanosheets because of its high flexibility and facile approach. Here, we show an effective way for synthesizing large-scale horizontally and vertically aligned MoS2 on different substrates such as flat SiO2/Si, pre-patterned SiO2 and conductive substrates (TaN) benefit various direct TMDs production. In particular, we show precise control of CVD optimization for yielding high-quality MoS2 layers by changing growth zone configuration and the process steps. We demonstrated that the influence of configuration variability by local changes of the S to MoO3 precursor positions in the growth zones inside the CVD reactor is a key factor that results in differently oriented MoS2 formation. Finally, we show the layer quality and physical properties of as-grown MoS2 by means of different characterizations: Raman spectroscopy, scanning electron microscopy (SEM), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS). These experimental findings provide a strong pathway for conformally recasting AP-CVD grown MoS2 in many different configurations (i.e., substrate variability) or motifs (i.e., vertical or planar alignment) with potential for flexible electronics, optoelectronics, memories to energy storage devices.

Growth, Raman Scattering Investigation and Photodetector Properties of 2D SnP.

As an important metal phosphides material, 2D tin phosphides (SnPx 0< x≤3) have been theoretically predicted to have intriguing physicochemical properties and potential applications in electronics, optoelectronics, and energy fields. However, the synthesis of high-quality 2D SnP single crystal has not been reported due to the lack of efficiency and reliable growth method. Here, a facile atmospheric pressure chemical vapor deposition (APCVD) method is developed to realize the growth of high-quality 2D SnP nanosheets, by employing tin (Sn) foil as both liquid metal substrates and reaction precursor. Temperature-dependent and angle-resolved polarization Raman spectra observed Raman peaks located at 142.6, 303.3, and 444.2 cm-1 are concluded to belong to A1g mode, which are consistent with the theoretical calculation results. Moreover, the field-effect transistor (FET) devices based on SnP nanosheets show a typical n-type characteristic with an on/off ratio of 103 at 200 K. SnP nanosheets also demonstrate excellent photoresponse performance under the illumination of 473, 532, and 639nm lasers, which can be tuned by Vgs , Vds , and light power density. It is believed that these findings can provide the first-hand experimental information for the future study of 2D SnP nanosheets.

Unveiling the electrical and photo-physical properties of intrinsic n-type 2D WSe2 for high performance field-effect transistors

Atomically thin semiconducting 2D transition metal dichalcogenides have garnered remarkable attention from the scientific community due to their prodigious contributions in the field of next-generation electronic and optoelectronic devices. In this continuation, we report a facile synthesis protocol of monolayer WSe2 films via the atmospheric-pressure chemical vapor deposition (APCVD) technique using hydrothermally synthesized hexagonal-phase tungsten oxide (h-WO3) nanorods. The as synthesized WSe2 crystal is a monolayer of ∼0.9 nm thickness as confirmed by atomic force microscopy. The confocal Raman and photoluminescence (PL) mapping suggests that the grown monolayer WSe2 triangles have lattice defects at edge sites, with a slight red-shift of ∼2 nm in PL, a blue-shift of ∼2 cm−1 in Raman peak and reduction in both the intensities. Confocal time-resolved PL mapping at edges reveals a fast-decay component of ∼582 ps and a slow-decay component of ∼2.18 ns that also signifies the presence of lattice defects, which serves as localized-states for photon-generated charge excitons. Furthermore, we have also investigated its electrical property by devising field-effect transistors (FETs). The fabricated WSe2 based FET shows intrinsic n-type behavior. WSe2 FET offers an electron mobility (μ) of ∼13.2 cm2 V−1 s−1, current ON/OFF ratio of ∼107 with a subthreshold slope (SS) of ∼397 mV/decade, which is relatable to the other reported works on WSe2 based FETs. In addition, the device exhibits very high on-current of order of ∼150 μA/μm. These results indicate that h-WO3 nanorod assisted APCVD synthesized WSe2 has prospective of being a competitor for next-generation optoelectronic, and valley-tronic devices.

Near‐Infrared Electroluminescent Light‐Emitting Transistors Based on CVD‐Synthesized Ambipolar ReSe2 Nanosheets

AbstractNear‐infrared light‐emitting technology is ideal for noncontact diagnostic medical imaging and high‐speed data communications. High‐quality ReSe2 nanosheets of anisotropic single‐crystal structure with a bandgap of 1.26 eV (≈984 nm) are synthesized with an atmospheric pressure chemical vapor deposition (APCVD) method. The as‐synthesized ReSe2 nanosheets‐fabricated light‐emitting transistors (LETs) exhibit nearly symmetric ambipolar characteristics in electrical transport. Judicious selection of asymmetric platinum (Pt)/chromium (Cr) electrodes, with their work functions matching respectively the conduction‐ and valence‐band edges of ambipolar ReSe2, generates a low turn‐on voltage ReSe2‐LET with the balanced number density and field‐effect mobility of bipolar carriers (i.e., electrons and holes). Room‐temperature near‐infrared electroluminescence (NIR EL) from the frequency‐modulated ReSe2‐LET has been observed unprecedentedly with the assistance of a lock‐in detection system. The NIR EL intensity is tested by varying the bias voltage applied to the ReSe2‐LET devices with different channel lengths. The wavelength of the NIR EL from ReSe2‐LET is differentiated with optical bandpass filters. Room‐temperature angle‐dependent two lobe‐shaped EL pattern manifests the inherent anisotropic in‐plane excitonic polarization of the ReSe2 crystal. The highly stable NIR EL from ReSe2‐LETs provides prospective 2D material‐based ultrathin scalable data communication electronics for future development.

Graphene Growth on Electroformed Copper Substrates by Atmospheric Pressure CVD.

Chemical vapor deposition (CVD) is regarded as the most promising technique for the mass production of graphene. CVD synthesis under vacuum is the most employed process, because the slower kinetics give better control on the graphene quality, but the requirement for high-vacuum equipment heavily affects the overall energy cost. In this work, we explore the possibility of using electroformed Cu substrate as a catalyst for atmospheric-pressure graphene growth. Electrochemical processes can produce high purity, freestanding metallic films, avoiding the surface defects that characterize the rolled foils. It was found that the growth mode of graphene on the electroformed catalyst was related to the surface morphology, which, in turn, was affected by the preliminary treatment of the substrate material. Suitable conditions for growing single layer graphene were identified.

Process–Structure–Properties Relationships of Passivating, Electron‐Selective Contacts Formed by Atmospheric Pressure Chemical Vapor Deposition of Phosphorus‐Doped Polysilicon

Herein, we investigate the process–structure–properties relationships of in situ phosphorus (P)‐doped polycrystalline silicon (poly‐Si) films by atmospheric pressure chemical vapor deposition (APCVD) for fabricating poly‐Si passivating, electron selective contacts. This high‐throughput in‐line APCVD technique enables to achieve a low‐cost, simple manufacturing process for crystalline silicon (c‐Si) solar cells featuring poly‐Si passivating contact by excluding the need for vacuum/plasma environment, and additional post‐deposition doping steps. A thin layer of this P‐doped poly‐Si is deposited on an ultrathin (1.5 nm) silicon oxide (SiO x ) coated c‐Si substrate to fabricate the passivating contact. This is followed by various post‐deposition treatments, including a high‐temperature annealing step and hydrogenation process. The poly‐Si films are characterized to achieve a better understanding of the impacts of deposition process conditions and post‐deposition treatments on the microstructure, electrical conductivity, passivation quality, and carrier selectivity of the contacts which assists to identify the optimal process conditions. In this work, the optimized annealing process with post‐hydrogenation yields passivating contact with a saturation current density (J 0) of 3 fA cm−2 and an implied open‐circuit voltage (iV OC) of 712 mV on planar c‐Si wafer. Junction resistivity values ranging from 50 to 260 mΩ cm2 are realized for the poly‐Si contacts processed in the optimal annealing condition.

Water-assisted controllable growth of atomically thin WTe2 nanoflakes by chemical vapor deposition based on precursor design and substrate engineering strategies

WTe2 nanostructures have intrigued much attention due to their unique properties, such as large non-saturating magnetoresistance, quantum spin Hall effect and topological surface state. However, the controllable growth of large-area atomically thin WTe2 nanostructures remains a significant challenge. In the present work, we demonstrate the controllable synthesis of 1T′ atomically thin WTe2 nanoflakes (NFs) by water-assisted ambient pressure chemical vapor deposition method based on precursor design and substrate engineering strategies. The introduction of water during the growth process can generate a new synthesized route by reacting with WO3 to form intermediate volatile metal oxyhydroxide. Using WO3 foil as the growth precursor can drastically enhance the uniformity of as-prepared large-area 1T′ WTe2 NFs compared to WO3 powders. Moreover, highly oriented WTe2 NFs with distinct orientations can be obtained by using a-plane and c-plane sapphire substrates, respectively. Corresponding precursor design and substrate engineering strategies are expected to be applicable to other low dimensional transition metal dichalcogenides, which are crucial for the design of novel electronic and optoelectronic devices.

In-depth characterization of stacking faults forming during the growth of Transition-Metal Di-Chalcogenides (TMDCs) by ambient pressure-CVD

Transition-metal di-chalcogenides (TMDCs) are van der Waals (vdW) layered materials with unique properties, important for the semiconductor industry. Generally, MX2 (where M = metal and X = chalcogen atoms, such as S, Se, or Te) type TMDCs contain easily exfoliable layers, turning to essentially 2D materials. Planar structural defects, such as stacking faults (SFs), change the atomic arrangement, further improving electronic properties, making these materials useful for various applications (optoelectronic devices, spintronics, gas sensing, catalysis, energy storage, thermoelectrics, etc.) Previous reports on TMDC synthesis with specific SFs highlight the challenge in obtaining them. Even more, for a successful application, these SFs should be stable and consistent under experimental conditions. Our previous work on facile preparation of 2H-WSe2 on W foil in an ambient-pressure chemical vapor deposition (APCVD) exhibited inherent selenium vacancies forming during the synthesis. In current research, we present detailed characterization of SFs forming during this synthesis in various 2H structures: (tungsten di-selenide) WSe2, (molybdenum di-selenide) MoSe2 and (tungsten di-sulfide) WS2. The stability of these defects as a function of post-annealing treatments is also discussed.

Controllable direct growth and patterning of graphene based transparent and conductive films on insulating substrates via Cu nanoparticles assisted-catalysis method

To avoid the complex transfer progress of graphene with the traditional chemical vapor deposition (CVD) method, we have developed a Cu nanoparticles (NPs) assisted-catalysis CVD process to directly deposit graphene on insulating substrates. It allows to controllably grow graphene by atmosphere pressure CVD according to regulating the distribution of Cu NPs. The fundamental growth conditions have been systematically investigated and the obtained graphene has preferable photoelectrical performance. Compared with a whole coated distribution of Cu NPs on the substrate, the transmittance of controllably deposited graphene significantly increases by 8.25% with decreased sheet resistance simultaneously. We further regulated the distribution of Cu NPs on the insulating substrate with a designed mask and directly prepared the patterned graphene with good achievement. This approach provides a facile and cost-effective way to directly prepare high-quality patterned graphene on target substrates and opens up a novel idea for fabricating various functional electronic devices.

CVD-Assisted Synthesis of 2D Layered MoSe2 on Mo Foil and Low Frequency Raman Scattering of Its Exfoliated Few-Layer Nanosheets on CaF2 Substrates.

Transition-metal dichalcogenides (TMDCs) are unique layered materials with exotic properties. So, examining their structures holds tremendous importance. 2H-MoSe2 (analogous to MoS2; Gr. 6 TMDC) is a crucial optoelectronic material studied extensively using Raman spectroscopy. In this regard, low-frequency Raman (LFR) spectroscopy can probe this material’s structure as it reveals distinct vibration modes. Here, we focus on understanding the microstructural evolution of different 2H-MoSe2 morphologies and their layers using LFR scattering. We grew phase-pure 2H-MoSe2 (with variable microstructures) directly on a Mo foil using a two-furnace ambient-pressure chemical vapor deposition (CVD) system by carefully controlling the process parameters. We analyzed the layers of exfoliated flakes after ultrasonication and drop-cast 2H-MoSe2 of different layer thicknesses by choosing different concentrations of 2H-MoSe2 solutions. Further detailed analyses of the respective LFR regions confirm the presence of newly identified Raman signals for the 2H-MoSe2 nanosheets drop-cast on Raman-grade CaF2. Our results show that CaF2 is an appropriate Raman-enhancing substrate compared to Si/SiO2 as it presents new LFR modes of 2H-MoSe2. Therefore, CaF2 substrates are a promising medium to characterize in detail other TMDCs using LFR spectroscopy.

Amorphous Carbon Coated Silicon Wafer as Mold Insert for Precision Glass Molding

Press molding of glass is an emerging research area for micro-optics manufacturing. Despite advancements on coating layers of precision molds for glass molding, challenges still exist towards tailoring non-stick coating to provide consistent replication accuracy in thousands of repetitive molding cycles. In this study, atmospheric pressure chemical vapor deposition (APCVD) is introduced to synthesize nanoscale-thickness amorphous carbon layer on the surface of silicon wafer with liquid benzene as the carbon source and silicone rubber as the silicon oxycarbide (SiOC) source. The micro-morphologies of the coating layers under different conditions are obtained and analyzed. In the press molding, the coating exhibits extraordinary physical properties and can remarkably prevent silicon-glass adhesion under elevated temperature. Typical micro-structures, such as micro-pillar and micro-lens arrays on the amorphous carbon coated silicon wafers, are used as mold inserts in precision glass molding to replicate high-precision optical components. The results indicate that this amorphous carbon coated silicon wafer can replicate intricate micro-structures to glass substrates with high-precision dimensions without macroscopic adhesion. This coating technology will protect the mold materials with low adhesion and improve precision glass molding process.

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

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

A mini-review focusing on ambient-pressure chemical vapor deposition (AP-CVD) based synthesis of layered transition metal selenides for energy storage applications

2D layered transition metal selenides grown in ambient pressure CVD for promising energy storage applications.

Probing the electronic structure of fine and large-grained SnO2 layers by spectroscopic ellipsometry and current-voltage measurements

Small- and large-grained undoped SnO2 films were deposited by atmospheric pressure chemical vapor deposition. The electronic structure of films was studied using spectroscopic ellipsometry measurements at temperatures up to 400 °C and at two thermal cycles, which were analyzed using the Tauc-Lorentz (T-L) and the Drude physical models. The parameters of the physical models have revealed information about details of the electronic structure of these films. It was found that the average energy of optical transitions En and the broadening C, related to the energy distance between valence and conduction band (VB and CB) and to the width of bands respectively, are the crucial parameters that influence the light absorption within the visible range. Small values of C and of the amplitude factor A which is related to the extent of the overlapping of wave-functions, observed for small-grained SnO2 samples, indicate the strong localization of wave-functions in the CB and high effective mass of electrons therein, which lead to a linear-quadratic shape of the I-V curves. Gap states, the extent of which was expressed by the difference between the Tauc and the T-L gaps, were found to act as electron donors similarly to oxygen vacancies. Heating in air caused the decrease of gap states and the oxidation of samples, which in turn caused shifts of the plasma frequency, ωp, whose magnitude and direction also depend on the effective mass of carriers, i.e., on the values of A and C.

Nonlinear Optical Properties of ZnO Thin Film at Low Laser Intensity Using Z-Scan Technique

In this work, a highly sensitive well-known z-scan technique was employed to study the nonlinear optical properties of Zinc Oxide thin films as a function of low laser fluencies. The transmissions of the continues-wave red laser diode with wavelength of (650 nm) were measured from the ZnO thin film sample with thickness of (425 nm). The thin film used in this study was deposited on the glass substrates based on atmospheric pressure chemical vapor deposition (APCVD) technique. The measurements were obtained at low laser powers ranging from (1.9-2.5) mW. The results indicated that the nonlinear absorption coefficient, refractive index and the third-order nonlinear optical susceptibility increase with increasing the laser intensity. The obtained curves of the closed aperture showed a positive sign of the nonlinear refractive index which in turn attributed to the self-defocusing of the material. The optical parameters obtained in this work are relatively comparable with that obtained elsewhere. The results also confirm the reliability of the z-scan approach even at low laser intensities.

Synthesis of nitrogen and sulfur Co-doped carbon with special hollow sphere structure for enhanced catalytic oxidation

• Nano-CaCO 3 is used as template for carbon sphere synthesis by CVD. • The N and S doping percentage of the carbon sphere can be easily regulated. • The N and S co-doping can achieve enhanced activity than single doped carbons. • The incorporation of secondary S atoms could enhance the O 2 •− generation in the PMS activation. In this study, a facile atmospheric pressure chemical vapor deposition (CVD) method is used for the synthesis of nitrogen and sulfur co-doped hollow carbon sphere (NSC). Nano-CaCO 3 is used as template for the formation of hollow and highly hierarchical porous carbon structure. The doped percentages of N and S can be easily regulated by changing the ratio of N and S precursors and the deposition temperature. The obtained NSC is highly active for the catalytic oxidation of organic pollutants with peroxymonosulfate (PMS) as oxidant, and the reaction rate constant is 4.5 and 32.7 times faster than the single N or S doped samples, respectively. The PMS activation mechanism is comprehensively investigated by electron paramagnetic resonance (EPR) and radical quenching tests. Superoxide intermediate (O 2 •− ) and singlet oxygen ( 1 O 2 ) play the dominant role for phenol degradation. Moreover, with the introduction of secondary doped S atoms, more O 2 •− are generated for organics degradation. The excellent catalytic activity of NSC should be resulted from the optimized N and S doping percentages and large specific surface area (SSA). The synthesis strategy in this study provides a facile and low-cost synthetic method for heteroatom doped carbon materials and would expand the application of metal-free materials in the environmental remediation field.