Conventional Chemical Vapor Deposition Research Articles

Controllable optical emission wavelength in all-inorganic halide perovskite alloy microplates grown by two-step chemical vapor deposition

All-inorganic halide perovskites (IHP), CsPbX3 (X = Cl, Br, I) exhibiting efficient optical emissions within the spectral range of 410 to 730 nm are potential candidates for many optoelectronic devices. Anion alloying of these IHPs is expected to achieve tunable emission wavelength covering the entire visible spectrum. Here, we developed a two-step chemical vapor deposition (CVD) process for growing quaternary IHP CsPbX3 (X = Cl/Br and Br/I) alloys. By exploiting the fast diffusion of halide anions in IHPs, the alloy composition can be precisely controlled by the growth time of the respective layers once the growth of the individual ternary IHP is optimized. Hence complexities in the multi-parameter optimization in the conventional CVD growth of quaternary alloys can be mitigated. Using this process, we synthesized single crystalline, homogeneous and thermally stable CsPbCl3(1−X)Br3x and CsPbBr3(1−X)I3x perovskites alloy microplates and demonstrated continuously tunable emission covering the spectrum from 428 to 715 nm by varying the halide compositions in the alloys. These alloy microplates also exhibit room temperature amplified spontaneous emissions (ASE) along with strong photonic discharges from the microplate’s edges and hence are potentially useful as a gain medium as well as optical cavities for emissions with wavelengths covering the visible spectrum.

On-Wafer Fast Evaluation of Failure Mechanism of 0.25-μm AlGaN/GaN HEMTs: Evidence of Sidewall Indiffusion

In this article, we present the results of on-wafer short-term (24 h) stress tests carried out on 0.25-μm AlGaN/GaN HEMTs. Devices on-wafer were submitted to 24-h dc tests, at various gate and drain voltage values corresponding to dissipated power densities PD up to 40 W/mm, with estimated channel temperature ~=375 °C. GEN1 devices adopted a Ni/Pt/Au gate metallization and conventional plasma-enhanced chemical vapor deposition (PE-CVD) SiN passivation; in GEN2 devices, a modified gate metallization and a two-layer SiN passivation were adopted. When tested at P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> > 25 W/mm, a substantial decrease of drain current ID and transconductance gm was measured in GEN1 HEMTs, without any significant shift of threshold voltage. Failure analysis revealed that Au and O interdiffusion took place from the sidewalls; Au gradually substituted Ni as a Schottky contact, while O, in the presence of high electric field, high temperature, and high current, promoted (Al)GaN oxidation and pitting. On the contrary, negligible degradation was found after high temperature storage of GEN1 devices without applied bias, up to 450 °C. In GEN2, process modification was effective in reducing the impact of this failure mechanism, resulting in only 5% gm decrease after 24 h at a junction temperature of 375 °C with P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> = 38 W/mm. Results demonstrate the effectiveness of the adopted on-wafer screening methodology in identifying potentially dangerous failure mechanisms.

Direct synthesis of single-layer graphene films on quartz substrate by a nanoparticle-assisted method

Matching graphene to semiconducting or insulating substrates is necessary for wide-ranging applications. Although synthesis of high-quality graphene on metal surfaces has gained great success, the transfer process of graphene is quite complicated and may cause defects and contamination. Therefore, the growth of graphene on insulating substrates is very important. Here, a direct synthesis method of single-layer graphene films on quartz substrate via a Cu-nanoparticle-assisted method was reported (N-CVD). The growth rate and quality of graphene on quartz showed a remarkable improvement compared with the conventional CVD process. Localized catalyzation made it possible for large-scale and continuous growth. Furthermore, the graphene glass fabricated by this method showed great performances on electrical, optical and thermal properties, and was proved to be hydrophobic. We designed a 2 cm × 2 cm single-layer graphene defogger, which can remove the fog completely within 10 s with a 30 V input voltage. Briefly, this work aims to present a low-cost, uniform and scalable method for graphene synthesis on insulating substrates.

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.

A review of graphene synthesisatlow temperatures by CVD methods

Chemical vapor deposition (CVD) is the most effective method for the synthesis of large-scale and high-quality graphene. However, the growth temperature of graphene is high, about 1000 °C, using conventional CVD, meaning that it is expensiveand thus limits the use of the material. The synthesis of CVD graphene at low temperatures(<600°C) is therefore the focus of many researchers. Recent research on the production of CVD graphene at low temperaturesis reviewed. Comprehensive comparison, analysis and discussion of quality, number of layers, domain size and the uses of graphenesynthesized at low temperatures using different precursors (gas, liquid and solids) and substrates (metals, metal alloys and dielectric materials) are given for different CVD methods (atmospheric pressure CVD, plasma enhanced CVD, catalyst-enhanced CVD, surface wave plasma CVD, microwave plasma CVD, radio frequency plasma enhanced CVD and electron cyclotron resonance CVD). The future prospects and challenges of preparing graphene at low temperatures are discussed.

3D few-layered MoS2/graphene hybrid aerogels on carbon fiber papers: A free-standing electrode for high-performance lithium/sodium-ion batteries

In this work, we developed a drop coating-freeze drying-thermal reduction method to prepare ultrathin MoS2 nanosheets/graphene hybrid aerogels on a carbon fiber paper substrate (MoS2/GS-A), which is simpler, more efficient and easier to amplify than conventional hydrothermal or chemical vapor deposition (CVD) methods. More importantly, the preparation of aerogels and electrode is completed simultaneously, which not only greatly simplifies the traditional electrode preparation but also avoids the damage of aerogel structure caused by grinding, so as to construct a long-range three-dimensional connected conductive network and porous structure at the electrode level. Benefitting from the superb electronic and ionic transport kinetics across the whole electrode, the electrode delivered an ultra large capacity of 1709 mAh g−1 at 0.2 A g−1 and remarkable rate capability of 1384 and 865 mAh g−1 at current densities of 0.6 and 1.0 A g−1 in lithium-ion batteries. Moreover, the electrode also exhibited outstanding sodium-ion storage capacity, and a stable charge capacity of 850 mAh g−1 was retained after 100 cycles under 0.1 A g−1.

Sustainable production of value-added carbon nanomaterials from biomass pyrolysis

The production of renewable energy and chemicals from biomass can be performed sustainably using pyrolysis, but the production costs associated with biomass pyrolysis hinder its wider application. The use of renewable precursors and waste heat to fabricate high-quality functional carbon nanomaterials can considerably improve the sustainability and economic viability of this process. Here, we propose a method to maximize the economic benefits and the sustainability of biomass pyrolysis by utilizing waste pyrolysis gases and waste heat to prepare high-quality three-dimensional graphene foams (3DGFs). The resulting 3DGFs exhibit excellent performance in environmental and energy-storage applications. On the basis of a life-cycle assessment, the overall life-cycle impacts of the present synthetic route on human health, ecosystems and resources are less than those of the conventional chemical vapour deposition (CVD) process. Overall, incorporating the pyrolytic route for fabricating functional carbonaceous materials into the biomass pyrolysis process improves the sustainability and economic viability of the process and can support wider commercial application of biomass pyrolysis. Biomass pyrolysis for renewable energy and chemicals offers sustainability advantages but is expensive. This study shows a route to improve both the sustainability and economic viability of biomass pyrolysis by using pyrolytic gases and waste heat to fabricate high-quality carbon nanomaterials.

Ion‐Selective Sensors Based on Laser‐Induced Graphene for Evaluating Human Hydration Levels Using Urine Samples

AbstractComplex graphene electrode fabrication protocols including conventional chemical vapor deposition and graphene transfer techniques as well as more recent solution‐phase printing and postprint annealing methods have hindered the wide‐scale implementation of electrochemical devices including solid‐state ion‐selective electrodes (ISEs). Herein, a facile graphene ISE fabrication technique that utilizes laser induced graphene (LIG), formed by converting polyimide into graphene by a CO2 laser and functionalization with ammonium ion (NH4+) and potassium ion (K+) ion‐selective membranes, is demonstrated. The electrochemical LIG ISEs exhibit a wide sensing range (0.1 × 10−3–150 × 10−3 m for NH4+ and 0.3 × 10−3–150 × 10−3 m for K+) with high stability (minimal drop in signal after 3 months of storage) across a wide pH range (3.5–9.0). The LIG ISEs are also able to monitor the concentrations of NH4+ and K+ in urine samples (29–51% and 17–61% increase for the younger and older patient; respectively, after dehydration induction), which correlate well with conventional hydration status measurements. Hence, these results demonstrate a facile method to perform in‐field ion sensing and are the first steps in creating a protocol for quantifying hydration levels through urine testing in human subjects.

Characterization of Europium Doped Silicon Oxide, Silicon Oxynitride, and Silicon Nitride Films Prepared By Integrated Ecr-PECVD and Magnetron Sputtering

The compatibility of Si-based light sources with mainstream metal-oxide semiconductor technology has become very interesting over the past decades due to their potential in integrated optoelectronics circuits of monolithic Si [1]. A very promising approach to improve the light emission from silicon-based materials is doping silicon with rare earth elements, and numerous research is involved in this field [1]. However, there are only a few works on europium (Eu) doped silicon-based matrix. In this work, Eu doped silicon oxide, silicon oxynitride, and silicon nitride thin films were deposited on P (100) Si substrates using integrated electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR-PECVD) and magnetron sputtering. Silane (SiH4), oxygen (O2), and Nitrogen(N2) gases were used as precursors and solid Eu as the sputtering target. The integrated ECR-PECVD and sputtering system allows tunable and highly consistent Eu doping concentration, better control of the layer stoichiometry along with less hydrogen incorporation in the deposited film compared to conventional CVD systems [2]. Several thin films were investigated using room temperature photoluminescence (PL) and X-ray diffraction (XRD). A detailed investigation of the effect of annealing on the PL was performed. The annealing temperature was varied from 500 OC to 1200 OC in nitrogen and a mixture of nitrogen and hydrogen atmospheres. It was observed that the intensity of the PL spectra increased with increasing annealing temperature. Besides, the hydrogen passivation effect has been studied in this work, which shows that hydrogen passivation increases the intensity of the peak. Based on the XRD measurements, we have found that the amorphous silicon oxide structure changes to a crystalline structure by adding nitrogen in the film. Interestingly silicon oxynitride and silicon nitride films do not show any luminescence at room temperature. The influence of the precursors' gases in the atomic percentage of the thin films was analyzed by Rutherford Backscattering spectrometry (RBS). In addition to it, the thickness and the index of refraction were characterized by variable angle spectroscopic ellipsometry (VASE).Reference: 1. Lin, Z., Huang, R., Wang, H., Wang, Y., Zhang, Y., Guo, Y., ... & Li, H. (2017). Dense nanosized europium silicate clusters induced light emission enhancement in Eu-doped silicon oxycarbide films. Journal of Alloys and Compounds, 694, 946-951.2. Miller, J. W., Khatami, Z., Wojcik, J., Bradley, J. D. B., & Mascher, P. (2018). Integrated ECR-PECVD and magnetron sputtering system for rare-earth-doped Si-based materials. Surface and Coatings Technology, 336, 99-105.

(Invited) Quantum Multi-Body Interactions in Semiconducting WSe2 and C60-Graphene Hybrids for High-Performance Photodetectors

In this work we will discuss the use of halide-assisted low-pressure chemical vapour deposition (HA-LPCVD) with NaCl to help facilitate the growth of monolayer WSe2 at low growth temperatures of ~ 750oC, which is lower than the typical temperatures needed with conventional CVD for realizing 1L WSe2. Moreover, we experimentally probed the quantum multi-body interactions in 1L WSe2 ascribed to excitons, trions and other localized states by analyzing the temperature-dependent photoluminescence spectra. A 1L WSe2 based photodetector was fabricated using Al contacts, which shows a high photoresponsivity, and the interface state trap density of the Al/WSe2 junction was computed to be extremely low. Hybrids of two-dimensional (2D) graphene with fullerene (C60) molecules were also fabricated using electrophoretic deposition, where the C60 clusters are electrically charged upon the application of an external bias in a polar solvent. A low energy shift in the Fermi level EF ~ 140 meV was calculated for the hybrids. When the hybrid devices were irradiated with a broadband white light source and a tunable laser source (with wavelength λ ranging from ~ 400-1100 nm), a strong photoresponse was evident, in contrast to the bare graphene devices which appeared unresponsive. We will discuss the strong photo-response of the C60-graphene hybrids reported here which we attribute to the doping enhancement arising in the graphene upon the adsorption of C60.

(Invited) Quantum Multi-Body Interactions in Semiconducting WSe2 and C60-Graphene Hybrids for High-Performance Photodetectors

In this work we will discuss the use of a halide-assisted low-pressure chemical vapor deposition (HA-LPCVD) with NaCl to help facilitate the growth of monolayer WSe2 at low growth temperatures of ~ 750oC, which is lower than the typical temperatures needed with conventional CVD for realizing monolayer (1L) WSe2. Moreover, we experimentally probed the quantum multi-body interactions in 1L WSe2 ascribed to excitons, trions and other localized states by analyzing the temperature-dependent photoluminescence spectra. A 1L WSe2 based photodetector was fabricated using Al contacts, which shows a high photoresponsivity, and the interface state trap density (Dit) of the Al/WSe2 junction was computed to be extremely low. Hybrids of two-dimensional (2D) graphene with fullerene (C60) molecules were also fabricated using electrophoretic deposition, where the C60 clusters are electrically charged upon the application of an external bias in a polar solvent. A low energy shift in the Fermi level EF ~ 140 meV was calculated for the hybrids. When the hybrid devices were irradiated with a broadband white light source and a tunable laser source (with wavelength λ ranging from ~ 400-1100 nm), a strong photoresponse was evident, in contrast to the bare graphene devices which appeared unresponsive. We will discuss the strong photo-response of the C60-graphene hybrids reported here which we attribute to the doping enhancement arising in the graphene upon the adsorption of C60.

(INVITED) Hybrid glass optical fibers-novel fiber materials for optoelectronic application

Hybrid glass optical fibers incorporated with optoelectronic materials and functionalities are highly anticipated for potential applications in optical communication, remote sensing, biomedicine, and nonlinear optics. However, the design and construction of hybrid glass fibers present significant challenges due to restrictions on the composition of fiber fabricated using conventional chemical vapor deposition (CVD) methods and the difficulty in maintaining the optoelectronic performance stably of fiber prepared by common rod-in-tube fiber-drawing technique. In this review, a versatile fiber-drawing approach which is called “melt-in-tube” (MIT) or “molten core” is presented to produce hybrid glass optical fibers. During the fiber-drawing process, the core is melted whereas the cladding is only just softened. The recent advances of the hybrid glass fibers including glass core-glass cladding fiber, crystal core-glass cladding fiber, and semiconductor core-glass cladding fiber are reported. In addition, the extensive applications of the hybrid glass fibers in the fields of fiber laser, fiber sensing, frequency conversion, photodetection and thermoelectric conversion are also discussed. These breakthroughs and advances in novel fiber materials and applications offer new opportunities for the research and development of optoelectronic devices.

Palladium nanoparticles supported by three-dimensional freestanding electrodes for high-performance methanol electro-oxidation

Palladium (Pd) nanoparticles (NPs) prepared by gas phase cluster deposition demonstrated excellent electrocatalytic activity. Herein, a series of Pd NPs modified freestanding electrodes with a super clean surface and easy repeating process for methanol oxidation reaction is reported. Pd NPs with different coverage were deposited on Ni foams and three-dimensional graphene-Ni foams, respectively. Owning to the special three-dimensional structure of Ni foam, the Pd NPs-Ni foam composite exhibited remarkable activity and unusually long-term stability for methanol electro-oxidation. The introduced three-dimensional graphene prepared by conventional chemical vapour deposition improved the electrocatalytic performance. The results can be attributed to the Pd NPs with high electrochemical activity and unique properties for three-dimensional supports.

Impacts of Mo Promotion on Nickel-Based Catalysts for the Synthesis of High Quality Carbon Nanotubes Using CO₂ as the Carbon Source.

In recent years, the primary greenhouse gas (carbon dioxide) has caused a series of severe issues, such as global warming, climate change, etc. Therefore, CCU, CCS and CCUS technologies have been employed to reduce CO₂ emissions. Through our developed "chemical vapor deposition integrated process (CVD-IP)" using carbon dioxide as the carbon source, CO₂ could be catalytically activated and converted to high-value carbon nanotubes. In this work, methane and carbon dioxide has been applied to synthesize CNTs respectively to compare the difference between conventional CH4 CVD and CO₂ CVD-IP technology using Ni-Mo bimetallic catalysts. In the conventional CH4 CVD technology, the carbon productivity and the thermal stability of CNTs could be improved by changing the Mo content of the catalyst, the better catalytic performance 4% Mo catalyst is selected as model catalyst to apply to CO₂ CVD-IP technology. Moreover, when the weak oxidant CO₂ is the only carbon source in the CVD-IP technology, the carbon yield is 22% and the carbon productivity is 1.98 g/gcat. TG curves and Raman spectroscopy display that the CNTs with better thermal stability and higher degree of graphitization are achieved. TEM confirms that the fewer wall numbers and defects of CNTs are obtained. These characterizations suggest that the high quality CNTs could be achieved by CO₂ CVD-IP technology.

Electrochemical properties of vertically aligned graphenes: tailoring heterogeneous electron transfer through manipulation of the carbon microstructure.

The electrochemical response of different morphologies (microstructures) of vertically aligned graphene (VG) configurations is reported. Electrochemical properties are analysed using the outer-sphere redox probes Ru(NH3)62+/3+ (RuHex) and N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), with performances de-convoluted via accompanying physicochemical characterisation (Raman, TEM, SEM, AFM and XPS). The VG electrodes are fabricated using an electron cyclotron resonance chemical vapour deposition (ECR-CVD) methodology, creating vertical graphene with a range of differing heights, spacing and edge plane like-sites/defects (supported upon underlying SiO2/Si). We correlate the electrochemical reactivity/response of these novel VG configurations with the level of edge plane sites (%-edge) comprising their structure and calculate corresponding heterogeneous electron transfer (HET) rates, k0. Taller VG structures with more condensed layer stacking (hence a larger global coverage of exposed edge plane sites) are shown to exhibit improved HET kinetics, supporting the claims that edge plane sites are the predominant source of electron transfer in carbon materials. A measured k0eff of ca. 4.00 × 10−3 cm s−1 (corresponding to an exposed surface coverage of active edge plane like-sites/defects (% θedge) of 1.00%) was evident for the tallest and most closely stacked VG sample, with the inverse case true, where a VG electrode possessing large inter-aligned-graphene spacing and small flake heights exhibited only 0.08% of % θedge and a k0eff value one order of magnitude slower at ca. 3.05 × 10−4 cm s−1. Control experiments are provided with conventional CVD (horizontal) grown graphene and the edge plane of highly ordered pyrolytic graphite (EPPG of HOPG), demonstrating that the novel VG electrodes exhibit ca. 3× faster k0 than horizontal CVD graphene. EPPG exhibited the fastest HET kinetics, exhibiting ca. 2× larger k0 than the best VG. These results are of significance to those working in the field of 2D-carbon electrochemistry and materials scientists, providing evidence that the macroscale electrochemical response of carbon-based electrodes is dependent on the edge plane content and showing that a range of structural configurations can be employed for tailored properties and applications.

Direct transfer of CVD-grown graphene onto eco-friendly cellulose film for highly sensitive gas sensor

In this study, cellulose flexible film was used as a supporting substrate for the development of an eco-friendly graphene gas sensor. The flexible cellulose substrate was fabricated by the method reported in the previous study. Graphene was grown on Cu foil using a conventional CVD method and directly transferred onto the cellulose substrate via a wet-transfer method. The results of conductivity, Raman spectroscopy, and SEM images confirmed that graphene was well-transferred onto the cellulose substrate without noticeable cracks. The performance of graphene gas sensors was measured by monitoring the current change according to the periodic injection of NO2 target and N2 purging gases. The graphene gas sensor built on cellulose film exhibited superior sensing performance compared to graphene on SiO2, mainly due to the functional groups in cellulose film. In addition, the incorporation of halloysite nanotube into cellulose film enhanced the sensitivity of the graphene sensor much more because the surface area of the transferred graphene became larger. This study demonstrates that the highly sensitive graphene gas sensor could be fabricated by the use of ecofriendly cellulose film as a supporting substrate.

Gas-Source CVD Growth of Atomic Layered WS2 from WF6 and H2S Precursors with High Grain Size Uniformity

Two-dimensional (2D) transition-metal dichalcogenides have attracted a considerable amount of attention because of their potential for post-silicon device applications, as well as for exploring fundamental physics in an ideal 2D system. We tested the chemical vapour deposition (CVD) of WS2 using the gaseous precursors WF6 and H2S, augmented by the Na-assistance method. When Na was present during growth, the process created triangle-shaped WS2 crystals that were 10 μm in size and exhibited semiconducting characteristics. By contrast, the Na-free growth of WS2 resulted in a continuous film with metallic behaviour. These results clearly demonstrate that alkali-metal assistance is valid even in applications of gas-source CVD without oxygen-containing species, where intermediates comprising Na, W, and S can play an important role. We observed that the WS2 crystals grown by gas-source CVD exhibited a narrow size distribution when compared with crystals grown by conventional solid-source CVD, indicating that the crystal nucleation occurred almost simultaneously across the substrate, and that uniform lateral growth was dominant afterwards. This phenomenon was attributed to the suppression of inhomogeneous nucleation through the fast and uniform diffusion of the gas-phase precursors, supported by the Na-assisted suppression of the fast reactions between WF6 and H2S.

Fe2Ti interlayer for improved adhesion strength and corrosion resistance of TiN coating on stainless steel 316L

Hard TiN coating (with a Vickers hardness higher than 1300 HV) on soft steel (smaller than 200 HV) has a great tendency to mechanical failure due to the significant mismatch in hardness. To tackle this issue, a Fe2Ti metallurgically bonding interlayer was designed and fabricated in between TiN coating and stainless steel 316L substrate. Results reveal that thickness of the Fe2Ti interlayer is tunable and plays an important role in adhesion strength and corrosion resistance of the resulting coating system. Fe2Ti interlayer with 5.0 μm in thickness significantly enhanced adhesion strength (50 N) and decreased corrosion rate (8.128 × 10−4 mm/yr), and the corrosion rate is one-tenth of the monolayer TiN coating fabricated by conventional CVD or PVD methods.

Reduced dislocation density and residual tension in AlN grown on SiC by metalorganic chemical vapor deposition

Crack-free AlN films with threading dislocation density (TDD) below 109 cm−2 are needed for deep-UV optoelectronics. This is typically achieved using pulsed lateral overgrowth or very thick buffer layers (&amp;gt;10 μm), a costly and time-consuming approach. A method for conventional metalorganic chemical vapor deposition growth of AlN/SiC films below 3 μm with greatly improved quality is presented. Focusing on substrate pretreatment before growth, we reduce average film stress from 0.9 GPa (tension) to −1.1 GPa (compression) and eliminate cracking. Next, with optimized growth conditions during initial deposition, AlN films with x-ray rocking curve widths of 123 arc-sec (0002) and 304 arc-sec (202¯1) are developed, and TDD is confirmed via plan view transmission electron microscopy (TEM) to be 2 × 108 cm−2. Film stress measurements including x-ray 2θ-ω, reciprocal space mapping, and curvature depict compressively stressed growth of AlN on 4H-SiC due to lattice mismatch. The thermal expansion coefficient mismatch between AlN and SiC is measured to be Δα=αAlN−αSiC=1.13×10−6 °C−1 and is found to be constant between room temperature and 1400 °C. TEM confirms the existence of dense misfit dislocation (MD) networks consistent with MD formation near SiC step edges and low MD density regions attributed to nearly coherent AlN growth on SiC terraces. These low-TDD, crack-free AlN/SiC buffers provide a platform for deep-UV optoelectronics and ultrawide bandgap electronics.

Synthesis of Carbon Nanotubes by Plasma-Enhanced Chemical Vapor Deposition Using Fe1−xMnxO Nanoparticles as Catalysts: How Does the Catalytic Activity of Graphitization Affect the Yields and Morphology?

The choice of a catalyst for carbon nanotube (CNT) growth is critical to controlling the morphology and chirality of the final product. Plasma-enhanced chemical vapor deposition (PECVD) can alleviate the requirements of the catalyst, i.e., they must be active for both the decomposition of the source gas and graphitization in the conventional thermal CVD. However, it is still not well understood how the catalytic activity of the graphitization affects the yield and quality of CNTs. In this paper, we systematically investigated the influence of the catalytic activity of graphitization by tuning the composition of Fe1−xMnxO (x = 0–1) nanoparticles as catalysts. As the Mn component increased, the number of CNTs decreased because Mn has no catalytic function of the graphitization. The quality of CNTs also affected by the inclusion of the Mn component. Our study may provide useful information to develop a new catalyst for CNT growth in PECVD.