One-step Chemical Vapor Deposition Method Research Articles

Lead-free CsCu2I3 thin films prepared by one-step chemical vapor deposition method for ultraviolet photodetector

Lead-free CsCu2I3 thin films prepared by one-step chemical vapor deposition method for ultraviolet photodetector

Band Gap Engineering of MoxW1-xS2 Alloy Monolayers with Wafer-Scale Uniformity.

Modulating the band gap of two-dimensional (2D) transition metal dichalcogenide (TMDC) semiconductors is critical for their application in a wider spectral range. Alloying has been demonstrated as an effective method for regulating the band gap of 2D TMDC semiconductors. The fabrication of large-area 2D TMDC alloy films with centimeter-scale uniformity is fundamental to the application of integrated devices. Herein, we report a liquid-phase precursor one-step chemical vapor deposition (CVD) method for fabricating a MoxW1-xS2 alloy monolayer with a large size and an adjustable band gap. Good crystalline quality and high uniformity on a wafer scale enable the continuous adjustment of its band gap in the range of 1.8-2.0 eV. Density functional theory calculations provided a deep understanding of the Raman-active vibration modes of the MoxW1-xS2 alloy monolayer and the change in the conductivity of the alloy with photon energy. The synthesis of large-area MoxW1-xS2 alloy monolayers is a critical step toward the application of 2D layered semiconductors in practical optoelectronic devices.

Controllable Synthesis of Transferable Ultrathin Bi2Ge(Si)O5 Dielectric Alloys with Composition-Tunable High-κ Properties.

Two-dimensional (2D) alloys hold great promise to serve as important components of 2D transistors, since their properties allow continuous regulation by varying their compositions. However, previous studies are mainly limited to the metallic/semiconducting ones as contact/channel materials, but very few are related to the insulating dielectrics. Here, we use a facile one-step chemical vapor deposition (CVD) method to synthesize ultrathin Bi2SixGe1-xO5 dielectric alloys, whose composition is tunable over the full range of x just by changing the relative ratios of the GeO2/SiO2 precursors. Moreover, their dielectric properties are highly composition-tunable, showing a record-high dielectric constant of >40 among CVD-grown 2D insulators. The vertically grown nature of Bi2GeO5 and Bi2SixGe1-xO5 enables polymer-free transfer and subsequent clean van der Waals integration as the high-κ encapsulation layer to enhance the mobility of 2D semiconductors. Besides, the MoS2 transistors using Bi2SixGe1-xO5 alloy as gate dielectrics exhibit a large Ion/Ioff (>108), ideal subthreshold swing of ∼61 mV/decade, and a small gate hysteresis (∼5 mV). Our work not only gives very few examples on controlled CVD growth of insulating dielectric alloys but also expands the family of 2D single-crystalline high-κ dielectrics.

Compositional design of C-coated multi-elemental alloy nanoparticles for superior microwave absorption

Exploring improved electromagnetic wave absorption performance in magnetic components involves capitalizing on dual dielectric relaxation and multiple magnetic resonances, ultimately giving rise to a dielectric-magnetic matching effect. Herein, a one-step Metal-organic Chemical Vapor Deposition (MOCVD) method has been utilized to fabricate C-coated ternary and quaternary alloy nanoparticles (FeCoNi, FeCoNiCu, FeCoNiMg, and FeCoNiMn) with tunable magnetization. The results affirm that the capabilities of impedance matching and electromagnetic wave attenuation can be significantly regulated by compositing nanoparticles with different elements. The optimized C-coated FeCoNiMg nanoparticles demonstrate an exceptional capacity for electromagnetic wave attenuation, achieving a reflection loss value of −51.8 dB at a matched thickness of 2.9 mm. Moreover, the absorption bandwidth significantly broadens to 7.60 GHz (10.4 – 18.0 GHz) with a thickness of 2.7 mm. The exceptional performance in electromagnetic attenuation is credited to the dielectric loss and improved impedance matching characteristics induced by the C-coated FeCoNiMg nanoparticles. The findings from this study will be beneficial in the development of lightweight and highly effective electromagnetic wave absorbers using magnetic alloy nanoparticles.

Thermal transport and optical anisotropy in CVD grown large area few-layer MoS2 over an FTO substrate

Atomically thin MoS2 is a promising candidate for its integration into devices due to its strikingly unique electronic, optical, and thermal properties. Here, we report the fabrication of a few-layer MoS2 thin film over a conducting fluorine-doped tin oxide-coated glass substrate via a one-step chemical vapor deposition method. We have quantitatively analyzed the nonlinear temperature-dependent Raman shift using a physical model that includes thermal expansion and three- and four-phonon anharmonic effects, which exhibits that the main origin of nonlinearity in both the phonon modes primarily arises from the three-phonon anharmonic process. We have also measured the interfacial thermal conductance (g) and thermal conductivity (ks) of the synthesized film using the optothermal Raman spectroscopy technique. The obtained values of g and ks are ∼7.218 ± 0.023 MW m−2 K−1 and ∼40 ± 2 W m−1 K−1, respectively, suggesting the suitability of thermal dissipation in MoS2 based electronic and optoelectronic devices. Furthermore, we performed a polarization study using the angle resolved polarized Raman spectroscopy technique under non-resonance and resonance excitations to reveal the electron–photon–phonon interaction in the prepared MoS2, based on the semi-classical theory that includes deformation potential and Fröhlich interaction. Our study provides much needed experimental information about thermal conductivity and polarization response in a few-layer MoS2 grown over the conducting substrate, which is relevant for applications in low power thermoelectric and optoelectronic devices.

Room-Temperature Ferromagnetism in Layered Mn-Substituted MoS2

Intrinsically two-dimensional (2D) ferromagnetic materials normally exhibit a low transition temperature, above which they would lose their magnetic properties. This makes it difficult to develop them for practical applications. Substituting transition metal atoms into 2D systems provides a straightforward way for achieving room-temperature ferromagnetism. Here, we propose a one-step chemical vapor deposition method to prepare Mn-substituted MoS2 monolayers, which exhibit robust magnetism, as confirmed by a combined study of physical property measurement systems and magneto-optical measurements. High-resolution transmission electron microscopy, Raman signals, and X-ray photoelectron spectroscopy analysis have all shown that the manganese atoms in MoS2 act as a substitute for the molybdenum sites. The microscopic origin of magnetism in Mn-MoS2 is further revealed on the basis of first-principles calculations, which corroborate the experimental results obtained. Our study demonstrates a simple route to creating 2D ferroelectric materials with broad prospects in spintronic devices and next-generation memory components.

Versatile graphene-alumina nanofibers for microwave absorption and EMI shielding

Carbon-based hybrid nanostructures have shown to be promising candidates as cost-efficient and effective fillers for electromagnetic interference shielding and RF absorption. In this work, hybrids of graphene-augmented inorganic (alumina) nanofibers (GAIN) have been incorporated in epoxy resin to fabricate a multilayer structure with tunable absorption. Highly aligned graphene augmented alumina nanofibers of 10 ± 2 nm in diameter were produced with the help of a hot wall one-step catalyst-free chemical vapor deposition method at 1000 °C. Effective medium approximation has been used to calculate the intrinsic dielectric properties of GAIN nanofibers. The highest loss tangent of 0.4 has been achieved in a 5 mm thick composite containing 1 vol% of randomly oriented nanofibers. Furthermore, aligned graphene augmented nanofibers were embedded in an epoxy resin matrix to examine the effect of fiber alignment on the dielectric properties of the composite. Based on the obtained dielectric data, a superposed three-layer structure has been fabricated, offering an absorption of >90% in the entire X-band and an absorption peak of −25 dB at ∼11 GHz. Several multilayer designs based on finite element method coupled with Monte Carlo simulations have been proposed to tune the absorption characteristics. This work demonstrates the potential of the hybrid nanofibers with a dual loss function for versatile design options in the area of RF absorption.

Continuous Growth of Carbon Nanotubes on Carbon Fiber Surface by Chemical Vapor Deposition Catalyzed by Cobalt with Thiourea

The continuous preparation of carbon nanotubes (CNTs)/carbon fiber (CF) multiscale reinforcements was realized via one-step chemical vapor deposition (CVD) method. In order to alleviate the damage of CF caused by catalyst etching at high temperature, catalytic promoter was adopted to improve the activity of the catalyst, thus reducing the CVD temperature. By adjusting the cobalt-based catalyst system, the effects of thiourea concentration on the morphology, microstructure and tensile strength of CNTs/CF samples were systematically investigated. It was found that the length and quantity of CNTs were added as the thiourea concentration increased, and the graphitization degree of the sample increased at first because of the well-grown CNTs, and then decreased due to the formation of amorphous carbon. Moreover, the tensile strength of CNTs/CF multiscale reinforcements was improved, which derived from the enhanced defect repair function of synthesized CNTs. Remarkably, CNTs/CF-0.02 exhibited a high single-filament tensile strength value (up to 4.51 GPa), which was about 6.6% higher than that of Desized cf Besides, the crystal structure and composition of reduced catalysts were analyzed, confirming the successful sulfur doping into cobalt particles. Therefore, the work offers a facile, economical, and efficient route for manufacturing CNTs/CF multi-scale reinforcements at comparatively low temperature.

Al Foil-Supported Carbon Nanosheets as Self-Supporting Electrodes for High Areal Capacitance Supercapacitors.

Self-supporting electrode materials with the advantages of a simple operation process and the avoidance of the use any binders are promising candidates for supercapacitors. In this work, carbon-based self-supporting electrode materials with nanosheets grown on Al foil were prepared by combining hydrothermal reaction and the one-step chemical vapor deposition method. The effect of the concentration of the reaction solution on the structures as well as the electrochemical performance of the prepared samples were studied. With the increase in concentration, the nanosheets of the samples became dense and compact. The CNS-120 obtained from a 120 mmol zinc nitrate aqueous solution exhibited excellent electrochemical performance. The CNS-120 displayed the highest areal capacitance of 6.82 mF cm-2 at the current density of 0.01 mA cm-2. Moreover, the CNS-120 exhibited outstanding rate performance with an areal capacitance of 3.07 mF cm-2 at 2 mA cm-2 and good cyclic stability with a capacitance retention of 96.35% after 5000 cycles. Besides, the CNS-120 possessed an energy density of 5.9 μWh cm-2 at a power density of 25 μW cm-2 and still achieved 0.3 μWh cm-2 at 4204 μW cm-2. This work provides simple methods to prepared carbon-based self-supporting materials with low-cost Al foil and demonstrates their potential for realistic application of supercapacitors.

Gallium doping-assisted giant photoluminescence enhancement of monolayer MoS2 grown by chemical vapor deposition

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted enormous research interest owing to their unique photo-physics and excellent optoelectronic properties. However, the ubiquitous defects in 2D TMDCs greatly affect the optoelectronic properties of them. For example, the prototype molybdenum disulfide (MoS2) exhibits very poor photoluminescence (PL) due to the high defect density. Here, we report a defect repair strategy based on a facile one-step chemical vapor deposition method that achieves two orders of magnitude enhancement in photoluminescence (PL) and one order of magnitude prolonging in carrier lifetime. Interestingly, we can controllably synthesize Ga-doped samples with different morphologies by adjusting the ratio of precursors, and the PL intensities at the central and edge regions are quite different. Combined with scanning transmission electron microscopy characterization, we systematically elucidate this growth behavior and obtain a more precise defect repair strategy. This strategy of selectively repairing the defects of monolayer MoS2 by gallium doping to achieve significant enhancement of photoluminescence may provide a facile and feasible method for the regulation of optoelectronic properties of 2D materials.

Synthesis and characterization of large-sized monolayer MoS2 nanoflakes by sulfurization of exfoliated MoO3 powder

We demonstrate a novel approach based on sulfurization of MoO3 powder pre-exfoliated on the SiO2/Si substrate to synthesize high crystalline quality and large-sized monolayer MoS2 films uniformly covering the whole substrate. The surface morphology, thickness, crystalline quality, and luminescence mechanism of the MoS2 films were characterized by the optical microscopy, Raman spectroscopy, and photoluminescence spectroscopy. The results reveal that MoS2 films directly synthesized on the bare SiO2/Si substrate by our method have high surface coverage superior over those of one-step chemical vapor deposition (CVD) method and exhibit uniform monolayer with larger lateral length up to ∼120 µm compared to those of the traditional two-step CVD method. Our proposed growth strategy opens up new pathways for CVD synthesis of high crystalline quality and large-sized uniform monolayer MoS2 films and can also be utilized for synthesizing other two-dimensional materials.

Production of MFe2O4 (M = Zn, Ni, Cu, Co and Mn) multiple cavities microspheres with salt template to assemble a high-performance acetone gas sensor

In this study, a one-step chemical vapor deposition (CVD) method was used, utilizing template NaCl and dextrin as the porogen and structural support. The synthesized spinel MFe2O4 (M = Zn, Ni, Cu, Co and Mn) microspheres with multiple cavities structure were applied to the acetone gas sensor detection. Through the characterization of the sensitive materials, the average pore diameter of the microspheres was about 60 nm. Compare with other metal cations, when M = Zn or Ni, the MFe2O4 samples revealed the super gas sensitivity at working temperatures of 250 °C and 175 °C, and the response values to 100 ppm acetone were 25 and 24.3, respectively. In addition, they also exhibited excellent selectivity and long-term stability to acetone. The excellent gas sensitivity of ZnFe2O4 and NiFe2O4 could be attributed to the replacement of Fe with Zn and Ni ions to obtain a higher Fe3+/Fe2+ atomic ratio, thereby increasing the content of adsorbed oxygen. In summary, the gas sensing performance of spinel MFe2O4 oxide had been systematically studied by replacing Fe with other transition metals. The iron-containing spinel oxides are expected to be promising sensing material for gas sensors due to their rich elements and excellent activity.

Ultra-high response acetone gas sensor based on ZnFe2O4 pleated hollow microspheres prepared by green NaCl template

In this study, ZnFe2O4 pleated hollow microspheres were synthesized by a one-step chemical vapor deposition (CVD) method using NaCl as a green salt template, and successfully used for the detection of acetone gas. NaCl as a green non-polluting and easy-to-remove structural template effectively modulate the morphology and structure of ZnFe2O4. The prepared sensitive materials were observed by SEM and TEM to have dense solid, hollow, pleated hollow and nanosheet structures, respectively. Among them, ZnFe2O4 pleated hollow microspheres exhibited a large specific surface area (185.24 m2/g) and the best sensing performance. Compared with other materials, ZnFe2O4 pleated hollow microspheres presented a response of up to 95.0 for 100 ppm acetone at the optimal working temperature of 200 °C. The large specific surface area and superior surface permeability exhibited by the pleated hollow structure effectively increased the reaction sites and overall utilization of the sensitive material both internally and externally, which resulted in ultra-high response properties to acetone. The ZnFe2O4 pleated hollow microspheres prepared using NaCl green template had excellent acetone molecular sensitivity properties, which is expected to be a promising sensitive material for acetone gas sensors.

Controllable p-type doping of monolayer MoS2with tantalum by one-step chemical vapor deposition

The synthesis of controllable pure and p-typein situTa-doped monolayer MoS2with different doping concentrationsviaa one-step salt-assisted chemical vapor deposition (CVD) method with systematic characterization studies is reported.

Epitaxial Growth of Step-Like Cr2 S3 Lateral Homojunctions Towards Versatile Conduction Polarities and Enhanced Transistor Performances.

For expanding the applications of 2D transition metal dichalcogenides (TMDCs), integrating functional devices with diverse conduction polarities in the same parent material is a very promising direction. Improving the contact issue at the metal-semiconductor interface also holds fundamental significance. To achieve these concurrently, step-like Cr2 S3 vertical stacks with varied thicknesses are achieved via a one-step chemical vapor deposition (CVD) method route. Various types of 2D Cr2 S3 lateral homojunctions are thus naturally evolved, that is, pm -ambipolar/n, p/ambipolar, ambipolar/n, and nm -ambipolar/n junctions, allowing the integration of diverse conduction polarities in single Cr2 S3 homojunctions. Significantly, on-state current density and field-effect mobility of the thinner 2D Cr2 S3 flakes stacked below are detected to be ≈5 and ≈6 times increased in the lateral homojunctions, respectively. This work should hereby provide insights for designing 2D functional devices with simpler structures, for example, multipolar field-effect transistors, photodetectors, and inverters, and provide fundamental references for optimizing the electrical performances of 2D materials related devices.

Facile synthesis of two-dimensional MoS2/WS2 lateral heterostructures with controllable core/shell size ratio by a one-step chemical vapor deposition method

Facile synthesis of two-dimensional MoS2/WS2 lateral heterostructures with controllable core/shell size ratio by a one-step chemical vapor deposition method

Visible light photocatalytic properties of one-step SnO2-templated grown SnO2/SnS2 heterostructure and SnS2 nanoflakes

The nanoflakes of SnS2/SnO2 heterostructure and SnS2 were synthesized by a one-step SnO2-templated chemical vapor deposition method. The metal oxide-assisted growth mechanism of SnS2/SnO2 heterostructure and SnS2 nanoflakes were realized through investigating serial microstructures of products with varied growth time. Furthermore, the photocatalytic activity for MB dyes degradation of varied growth time products was used to explore the effect of product microstructure under the visible light irradiation. The SnO2/SnS2 heterostructure and the oxide vacancies of nanoflakes demonstrated an improved visible light photocatalytic performance for MB degradation, which was around twice of the pure SnS2 nanoflakes and better than P25. The results of different scavengers on the degradation efficiency for MB indicate the·O2 −, and ·OH are the main active species in the photodegradation reaction. The one-step growth mechanism of SnS2/SnO2 could prove a facile process to grow metal oxide-metal sulfide heterostructure.

Revealing the many-body interactions and valley-polarization behavior in Re-doped MoS2 monolayers

Substitutional doping has proved to be one of the most important approaches to tune and improve the opto-electronic performance of traditional semiconductors. Similarly, controllable substitution of cations in two-dimensional layered materials can effectively modify and manipulate the band structures, which help to explore sciences and broaden the related applications. In this paper, the salt-assisted one-step chemical vapor deposition method was used to achieve Re substitution in MoS2 monolayers. High-resolution scanning transmission electron microscopy confirms the substitution of Re atoms in Mo sites. X-ray photoelectron spectroscopy and micro-photoluminescence (PL) characterization studies suggest that the Re substitution introduces typical n-type doping in MoS2 monolayers, resulting in the distinct many-body interactions in the doped sample with a higher trion ratio than in the pristine sample in the wide temperature window. The result is further confirmed by the shorter recombination lifetime observed in the Re-doped sample acquired by time-resolved PL measurements. More intriguingly, the circularly polarized PL characterization studies demonstrate that Re doping can improve the valley polarization of the MoS2 monolayer. Our work provides a deep understanding of the optical properties and the associated many-body interactions in the Re-doped MoS2 system and offers a potential way to enhance the valley polarization for spin-/valley-photonic applications.

One-step in-situ fabrication of carbon nanotube/stainless steel mesh membrane with excellent anti-fouling properties for effective gravity-driven filtration of oil-in-water emulsions

The occurrence of membrane fouling has resulted in limited wastewater treatment applications. The development of superhydrophilic-underwater superoleophobic materials has received significant attention owing to their good anti-fouling properties. However, to fabricate such materials need costly regents and tedious steps. Thus, developing a one-step process to prepare a low-cost material for oil/water separation is still desired. In this study, bio-inspired from an arachnid, inorganic carbon nanotube stainless steel meshes (CNT@SSMs) having superhydrophilic-underwater superoleophobic and excellent anti-fouling properties and a unique fiber structure were fabricated via a one-step thermal chemical vapor deposition method. The CNT@SSMs had a small pore size enabling a high water flux of 10,639 L m−2h−1 and the separation of oily wastewater, including various emulsions, at a high rejection ratio of >98.89%. As a result of its excellent chemical stability under high temperatures, a broad pH range, and saline environments, the CNT@SSM has the potential to be used in extreme conditions. In summary, these CNT@SSMs are easy to fabricate and are low-cost as a result of inexpensive reagents involved. Moreover, these novel superwetting membranes are promising candidates for treatment of hazardous oily wastewater.

SnO2/ZnSnO3 double-shelled hollow microspheres based high-performance acetone gas sensor

In this study, the preparation process and the sensing performance toward acetone of SnO2/ZnSnO3 composite microspheres with the double-shelled hollow structure were reported. It was synthesized by one-step chemical vapor deposition (CVD) method using sucrose as solid precursor pyrolysis carbon template. In addition, the internal structure of the composite microspheres can be effectively controlled by changing the sucrose concentration. The perfect double-shelled hollow structure (average diameter of about 500 nm) of the prepared sensitive materials was observed through SEM and TEM. It is noteworthy that the double-shelled hollow structure had a large specific surface area (188.60 m2/g), which can both increase the internal and external reactive sites of the sensitive material effectively. Compared with other obtained composite microspheres, the SnO2/ZnSnO3 sample with double-shelled hollow structure presented the best sensing performance, and the response to 100 ppm acetone reached 30 at 290 °C. Furthermore, it also presented excellent selectivity and long-term stability to acetone. The excellent performance was attributed to the synergistic effect of the double-shelled hollow structure with large specific surface area and the n-n heterojunction at the interface of the SnO2/ZnSnO3 composite. The sensing mechanisms of the double-shelled hollow SnO2/ZnSnO3 composite material were discussed in detail.