Chemical Vapor Deposition Growth Research Articles

First principles investigation of ammonia borane decomposition for understanding h-BN growth on the copper surface

Ammonia borane (AB) is a highly promising precursor for the large-scale growth hexagonal boron nitride (h-BN) via chemical vapor deposition (CVD) methods. However, the unclear decomposition mechanism of precursor molecules on the Cu surface poses a great challenge for understanding the CVD growth process of h-BN. In this work, we addressed this issue by conducting first-principles calculations to investigate the decomposition mechanism of AB on the Cu surface. Our calculations revealed that AB preferentially decomposed into ammonia and borane. Further analysis demonstrates that borane exhibits a higher dehydrogenation rate than ammonia, suggesting a single atom self-assembly growth mode of h-BN under B-rich conditions. Our calculations revealed the formation of BNHx-related byproducts during h-BN growth using AB as a precursor, resulting from the intricate decomposition of AB on the Cu surface under CVD conditions. Our findings have significant implications for comprehending and controlling the growth of h-BN in CVD process.

Self-condensation-assisted chemical vapour deposition growth of atomically two-dimensional MOF single-crystals

Two-dimensional metal-organic frameworks (MOFs) have a wide variety of applications in molecular separation and other emerging technologies, including atomically thin electronics. However, due to the inherent fragility and strong interlayer interactions, high-quality MOF crystals of atomic thickness, especially isolated MOF crystal monolayers, have not been easy to prepare. Here, we report the self-condensation-assisted chemical vapour deposition growth of atomically thin MOF single-crystals, yielding monolayer single-crystals of poly[Fe(benzimidazole)2] up to 62 μm in grain sizes. By using transmission electron microscopy and high-resolution atomic force microscopy, high crystallinity and atomic-scale single-crystal structure are verified in the atomically MOF flakes. Moreover, integrating such MOFs with MoS2 to construct ultrathin van der Waals heterostructures is achieved by direct growth of atomically MOF single-crystals onto monolayer MoS2, and enables a highly selective ammonia sensing. These demonstrations signify the great potential of the method in facilitating the development of the fabrication and application of atomically thin MOF crystals.

Planarization of p-GaN surfaces on MOCVD grown V-defect engineered GaN-based LEDs

The large polarization barriers between the quantum wells and quantum barriers in long-wavelength GaN-based light-emitting diodes (LEDs) inhibit their performance by requiring excess driving voltages to reach standard operating current densities. Lateral injection of carriers directly into quantum wells is required to circumvent this issue. V-defects are naturally occurring inverted hexagonal defects with semipolar 101¯1-plane sidewalls generated on surface depressions from threading dislocations. LEDs engineered to intentionally generate V-defects below the active region of the LED can achieve lateral carrier injection through the V-defect sidewalls and have already been able to demonstrate world record wall-plug efficiencies for LEDs in the green-red wavelengths. V-defects can be enlarged during kinetically limited growth where the growth rate of the c-plane GaN is faster than that of their sidewalls, leaving them unfilled. We report on the metal organic chemical vapor deposition growth conditions required to fill in V-defects with p-GaN during epitaxial growth of the LED post the active region. Circular transmission length measurements of Pd/Au contacts processed on p-GaN surfaces with various amounts of unfilled V-defects showed no significant difference in their sheet resistance and specific contact resistance. J–V measurements of LEDs grown with varying unfilled V-defect densities showed no significant difference in the forward bias regime. However, in the reverse bias regime, catastrophic breakdown occurred at markedly lower voltages for samples with larger unfilled V-defect densities. This suggests that unfilled V-defects may act as hotspots for device failure, and planarizing LED surfaces may help prevent early degradation of LED devices.

Overcoming the Incompatibility Between Electrical Conductivity and Electromagnetic Transmissivity: A Graphene Glass Fiber Fabric Design Strategy.

Conventional conductive materials such as metals are crucial functional components of conductive systems in diverse electronic instruments. However, their severe intrinsic impedance mismatch with air dielectric causes strong reflection of incident electromagnetic waves, and the resulting low electromagnetic transmissivity typically interferes with surrounding electromagnetic signal communications in modern multifunction-integrated instruments. Herein, graphene glass fiber fabric (GGFF) that merges intrinsic electrical and electromagnetic properties of graphene with dielectric attributes and highly porous macrostructure of glass fiber fabric (GFF) is innovatively developed. Using a novel decoupling chemical vapor deposition growth strategy, high-quality and layer-limited graphene is prepared on noncatalytic nonmetallic GFF in a controlled manner; this is pivotal to realizing GGFF with the desired compatibility among high conductivity, low electromagnetic reflectivity, and high electromagnetic transmissivity. At the same sheet resistance over a wide range of values (250-3000 Ω·sq-1), the GGFF exhibits significantly lower electromagnetic reflectivity (by 0.42-0.51) and higher transmissivity (by 0.27-0.62) than those of its metal-based conductive counterpart (CuGFF). The material design strategy reported herein provides a constructive solution to eliminate the incompatibility between electrical conductivity and electromagnetic transmissivity faced by conventional conductive materials, spotlighting the applicability of GGFF in electric heating scenarios in radar, antenna, and stealth systems.

Combination of chemical vapor deposition and thermal growth methods for facile synthesis of tin oxide-doped multiwalled carbon nanotubes

Combination of chemical vapor deposition and thermal growth methods for facile synthesis of tin oxide-doped multiwalled carbon nanotubes

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.

Controlled lattice deformation for high-mobility two-dimensional MoTe2 growth

Two-dimensional (2D) MoTe2 shows great potential for future semiconductor devices, but the lab-to-fab transition is still in its preliminary stage due to the constraints in the crystal growth level. Currently, the chemical vapor deposition growth of 2D MoTe2 primarily relies on the tellurization process of Mo-source precursor (MSP). However, the target product 2H-MoTe2 from Mo precursor suffers from long growth time and suboptimal crystal quality, and MoOx precursor confronts the dilemma of unclear growth mechanism and inconsistent growth products. Here, we developed magnetron-sputtered MoO3 film for fast and high-mobility 2H-MoTe2 growth. The solid-to-solid phase transition growth mechanism of 2D MoTe2 from Mo and MoOx precursor was first experimentally unified, and the effect mechanism of MSPs on 2D MoTe2 growth was systematically elucidated. Compared with Mo and MoO2, the MoO3 precursor has the least Mo-unit lattice deformation and exhibits the optimal crystal quality of growth products. Meanwhile, the lowest Gibbs free energy change of the chemical reaction results in an impressive 2H-MoTe2 growth rate of 8.07 μm/min. The constructed 2H-MoTe2 field-effect transistor array from MoO3 precursor showcases record-high hole mobility of 85 cm2/(V·s), competitive on-off ratio of 3×104, and outstanding uniformity. This scalable method not only offers efficiency but also aligns with industry standards, making it a promising guideline for diverse 2D material preparation towards real-world applications.

Area-Selective Chemical Vapor Deposition of Gold by Electron Beam Seeding.

Chemical vapor deposition (CVD) is an established method for producing high-purity thin films, but it typically necessitates the pre- and post-processing using a mask to produce structures. This study presents a novel maskless patterning technique that enables area-selective CVD of gold. A focused electron beam is used to decompose the metal-organic precursor Au(acac)Me2 locally, thereby creating an autocatalytically active seed layer for subsequent CVD with the same precursor. The procedure can be included in the same CVD process without the need for clean room lithographic processing. Moreover, it operates at low temperatures of 80°C, over 200K lower than standard CVD temperatures for this precursor, reducing thermal load on the specimen. Given that electron beam seeding operates on any even moderately conductive surface, the process does not constrain device design. This is demonstrated by the example of vertical nanostructures with high aspect ratios of ≈40:1 and more. Written using a focused electron beam and the same precursor, these nanopillars exhibit catalytically active nuclei on their surface. Furthermore, by using the onset of the autocatalytic CVD growth, for the first time the local temperature increase caused by the writing of nanostructures with an electron beam can be preciselydetermined.

Numerical investigation on the effect of gas-phase dynamics on graphene growth in chemical vapor deposition

Chemical vapor deposition (CVD) is a crucial technique to prepare high-quality graphene because of its controllability. In the research, we perform a systematic computational fluid dynamics numerical investigation on the effect of gas-phase reaction dynamics on the graphene growth in a horizontal tube CVD reactor. The research results indicate that the gas-phase chemical reactions in the CVD reactor are in a nonequilibrium state, as evidenced by the comparison of species mole fraction distributions during the CVD process and under chemical equilibrium conditions. The effect of gas-phase reaction dynamics on the deposition rate of graphene under different conditions is studied, and our research shows that the main causes of change in graphene growth rates under different conditions are gas-phase reaction dynamics and active species transport. The results of numerical simulation agree well with the experimental phenomena. The research results also indicate that, for methane, the main limiting factor of graphene growth is the surface kinetic reaction rate. Conversely, for active species, the main limiting factor of graphene growth is species transport. Our research suggests that the growth rate of graphene can be regulated from the perspective of the gas reaction mechanism. This method has theoretical guiding significance and can be extended to the preparation of large-area graphene.

Graphene as the anti-oxidation protective layer: How good or bad can it be?

This study investigates the conditional anti-oxidation layer of graphene on Cu and its variation of morphology and strain state, demonstrating that the oxidation process could be divided into two stages. The chemical vapor deposition (CVD) growth and a high-humidity environment were exploited to observe the Cu foil oxidizing with the protection layer of graphene. The observation of optical microscopy (OM) and scanning electron microscopy (SEM) reveals the sequence process of the anti-oxidation layer of graphene on the diverse Cu orientations. Except for the wrinkles on graphene and orientations of Cu, the vacancies in the graphene play a crucial role in anti-oxidation. Furthermore, the oxidation of underlying Cu deteriorates the quality of graphene and reduces the strength of interaction at the graphene/Cu interface. The oxidation of graphene-capped Cu is divided into two stages: (i) The attenuated graphene/Cu interaction due to the Cu oxidation beneath, and (ii) the generation and enlargement of CuO particles damage the adjacent graphene, as clearly observed in the OM and SEM images. The time evolution analysis using angular-resolved photoelectron spectroscopy (ARPES) offers robust evidence to support the worse quality of graphene and the decoupling between graphene and Cu foil after the oxidation process. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy express that the defects are created by the degradation of graphene rather than the generation of external functional groups. Thus, the Cu oxidation simultaneously influences both the substrate (Cu) and the protective layer (graphene), substantially weakening the graphene/Cu interaction.

Investigation on the effect of chemical mechanical polishing sapphire substrate on chemical vapor deposition growth of two-dimensional MoS2

Two-dimensional molybdenum disulfide (2D MoS2), with atomic-level thickness, whose crystal crystallinity and size are easily influenced by the surface morphology of the substrate during growth. This work systematically investigates the impact of chemical mechanical polishing (CMP) sapphire substrate on chemical vapor deposition (CVD) growth of 2D MoS2. A green and highly efficient CMP method for the sapphire substrate is first proposed, whose maximum material removal rate (MRR) of 4.27 µm/h with surface roughness (Ra) of 0.10 nm (AFM, scanning area of 5 × 5 μm2) can be attained. The size and thickness statistics of 2D MoS2 domains grown on different substrates indicate that the CMP sapphire substrate in this work can promote the size and monolayer uniformity of 2D MoS2 during CVD growth. Meanwhile, Raman and photoluminescence (PL) spectra of monolayer MoS2 grown on different substrates also indicates the monolayer MoS2 grown on the CMP sapphire substrate in this work has superior crystalline quality and optical properties. The above findings have provided new insights into the mechanisms underlying 2D MoS2 growth on surfaces in various states and are expected to accelerate the development of large size large-size and high-quality growth of two-dimensional material for further device applications.

Synthesis of N-doped graphene film with tunable graphitic and pyridinic doping content

Nitrogen-doped (N-doped) graphene films with up to a 17.39 at.% doping level were synthesized with the chemical vapor deposition growth method. An extensive range of tunable nitrogen doping levels was achieved by selecting organic molecules as precursors grown at a wide temperature range of 300 to 1000 °C. The benzene rings in the precursor significantly reduced the energy requirements of N-doped graphene. The incorporation of bridgehead nitrogen and amino groups ensured a high nitrogen doping level and offered the tunable modulation of nitrogen dopant concentrations. The influence of temperature on the nitrogen content was investigated, distinguishing the graphitic and pyridinic dopant types, each demonstrating unique trends considering the dopant stability and growth mechanism. Specifically, the proportion of graphitic doping could be modulated from 40 % to 100 %. Notably, the pyrrolic type was absent at lower temperatures and was nearly negligible at elevated temperatures. Therefore, we developed a synthesis method for N-doped graphene growth that allowed for the selective and prioritized tuning of nitrogen dopant types. This method is particularly favorable when specific nitrogen dopants at certain doping levels are required for electrical and chemical catalytic applications.

Effect of sulfur and phosphorous doping on the growth rate of CVD diamond (111)

The purpose with the present study has been to theoretically investigate the effect of P (or S) doping on the chemical vapor deposition (CVD) growth rate of diamond. Density functional theory (DFT) calculations under periodic boundary conditions were then used for the investigation of the highly symmetric H-terminated diamond (111) surface. It was shown that both the thermodynamics and kinetics of P (or S) substitutional doping during diamond (111) growth were severely affected by the dopants (as compared with the non-doped situation).As a result of the thermodynamic calculations, except for P doping in C layer 1, the thermodynamic driving force for the diamond (111) growth was found to be largely improved by positioning P within the upper surface region of the H-terminated diamond (111) surface, while the opposite was true for S-doping. The P doping had a local vertical influence on the H abstraction energies, which was not the situation for the S doping. Also, both P and S doping showed a local lateral influence on the H abstraction energies, which was more pronounced for P doping.As a result of the kinetic calculations, the vertical and lateral P doping showed no local effect on the H abstraction energy barriers. In fact, these energy barriers became zero for P positioned in C layer 2 and downwards and were also zero for longer distances from the H adsorbate. On the other hand, the vertical S doping showed a local effect on the calculated barrier energies, but no lateral effect. The calculated energy barriers were zero for all surface H adsorbates on the H-terminated diamond (111) surface when S was positioned in the 4th atomic C layer. The different results for P doping versus S doping could be explained by the fact that S contains one electron extra and that P has a larger electronegativity value.Consequently, the results showed that P positioned in the upper diamond (111) surface lattice caused an enhancement in the diamond growth rate. The exception was the position in C atomic layer 1, for which both P doping and S doping had no effect on the diamond growth rate. On the other hand, a growth rate improvement was only found for S positioned in the 4th C layer. Due to the much higher (i.e., more positive) theoretical incorporation energies of S dopants versus P dopants in the diamond lattice, it has here been concluded that P doping is more effective than S doping in increasing the growth rate of the H-terminated diamond (111). Especially when considering that the H adsorbates are very mobile on this diamond surface, which has been shown by ab initio MD simulations at experimental CVD temperatures. These observations correlate well with experimental results.

One-dimensional diamond nanostructures: Fabrication, properties and applications

Diamonds exhibit a unique combination of numerous excellent physical and chemical properties, such as the highest hardness, high Young's modulus, wide bandgap, high carrier mobility, negative electron affinity, and high thermal conductivity. Especially, diamond has attracted significant attention in recent years for its outstanding performance in high-frequency and high-power electronic devices and thermal management. Inheriting the intrinsic physical and chemical properties of diamonds, one-dimensional (1D) diamond nanostructures exhibit many additional properties that are unavailable for bulk diamond or thin films, e.g., large specific surface area, ultrahigh elasticity, and some plasticity, tip effect as well as direct transport for photon or photo-induced carriers. These properties make 1D diamond nanostructures an ideal candidate for applications ranging from micro/nano-electromechanical systems (MEMS/NEMS) to field electron emission, optical, electrochemical, and biological areas. This review will first introduce the development of controlled synthesis methods of 1D diamond nanostructure, including bottom-up chemical vapor deposition growth and top-down selective etching of bulk diamond. Subsequently, we will summarize recent advances in the mechanical, electron field emission, optical, and biological properties of 1D diamond nanostructures and their applications in electron and photon emitter, MEMS, sensing, intracellular delivery, etc.

Chemical Vapor Deposition Growth of 2D Ferroelectric Materials for Device Applications

Abstract2D ferroelectric materials have garnered extensive attention for promising applications in next‐generation electronic devices, which provides a platform to explore ferroelectricity without the critical thickness constraint of traditional perovskite oxide‐based ferroelectric materials. Recent studies have shown that chemical vapor deposition (CVD) can synthesis the large‐area 2D ferroelectric materials, making the 2D ferroelectric materials to be compatible with scalable semiconductor devices. In this Review, the CVD‐grown 2D ferroelectric materials are summarized in terms of materials, properties to devices application view. First, the synthesis strategy and recent advances of the CVD growth of 2D ferroelectric materials are highlighted in the aspects of diverse groups of 2D materials. Second, the recent experimental progress of 2D ferroelectric devices is introduced, and the potential applications of 2D ferroelectric devices are discussed. The availability of the CVD‐grown 2D ferroelectrics provides an abundant playground for not only deep studying the ferroelectric properties, but also conceiving various device applications. Lastly, the perspectives are provided to address the current challenges in terms of materials design, physics mechanism, device, and multifunctional application.

Bio-inspired transparent and antibiofouling diamond films via layer-by-layer self-assembly seeding

Bio-inspired diamond nanostructures featuring high transparency and anti-bacterial adhesion were constructed via layer-by-layer (LbL) self-assembly seeding and chemical vapor deposition growth. The topography of the diamond nanofilms was determined by initial nanodiamond seeds distribution, which was adjusted by nanodiamond colloidal stability. With increasing number of LbL bilayers, the bulge size and roughness of the deposited films increased. With increasing number of bilayers from 1 to 5, UV–Vis transmittance slightly decreased from max. 90 %–83 %, while the contact angle increased from 90° to 130°. All the nanostructured diamond films possess very high IR transmittance between 85% and 90%, which is close to the bare quartz (95%). Compared with conventional flat diamond films, nanostructured diamond films repelled most of the bacteria, suggesting excellent anti-biofouling property. With increasing seeding bilayer number, more bacteria were repelled. The highest bacterial reduction was achieved to 99% by diamond film seeded with 5 bilayers. The bio-mimicking nanostructured diamond film represent a potent solution for achieving highly transparent, anti-biofouling and highly durable optical coatings for biomedical and marine optical instrument.

Single-walled carbon nanotube synthesis with RuRhPdIrPt high entropy alloy catalysts

Using high-entropy alloy nanoparticles (HEA NPs) composed of five platinum-group metals (5PGM), Ru, Rh, Pd, Ir, and Pt, as catalysts, we succeeded in growing single-walled carbon nanotubes (SWCNTs) via chemical vapor deposition (CVD). After CVD growth with C2H2 feedstock at 750 ℃ for 10 min, high-density SWCNTs were grown from 5PGM HEA NPs. The diameters of most SWCNTs were in the range of 0.83–1.1 nm, exhibiting the growth of small-diameter SWCNTs. Compared with monometal PGM catalysts, the SWCNT yield with the 5PGM HEA NP catalysts was much higher and was compatible even with those with Fe and Co.

The effect of nickel oxide in the direct growth of MnOx on Ni foam by chemical vapor deposition

Manganese oxide has emerged as a promising material for use as a charge storage electrode material. In this work, we demonstrate the low-pressure chemical vapour deposition (CVD) growth of manganese oxide conformal coatings on Ni-foams utilising an MnCl2 solid source precursor, utilising an oxide formed on the surface of the Ni-foam as an oxygen reservoir for the synthesis of a predominantly MnO x layer. The resulting MnO x layer is highly dependent on sample pre-treatment, owing to modifications in the Ni oxide layer. The phase structure, electronic states, morphology, and electrochemical analysis were determined by x-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning-electron microscopy (FE-SEM), and capacitance–voltage (CV) measurements. The importance of the oxide layer is demonstrated by modifying the thickness of the NiO layer over the Ni foam, with clear changes in the resultant structure, morphology, and areal capacitance, with the highest performance MnO x coating found to be obtained without any oxide removal from the Ni foam substrate.

First-principles investigation of hydrogen-related reactions on (100)–(2 × 1)[formula omitted]H diamond surfaces

Hydrogen radical attacks and subsequent hydrogen migrations are considered to play an important role in the atomic-scale mechanisms of diamond chemical vapour deposition growth. We perform a comprehensive analysis of the reactions involving H-radical and vacancies on H-passivated diamond surfaces exposed to hydrogen radical-rich atmosphere. By means of first principles calculations—density functional theory and climbing image nudged elastic band method—transition states related to these mechanisms are identified and characterised. In addition, accurate reaction rates are computed using variational transition state theory. Together, these methods provide—for a broad range of temperatures and hydrogen radical concentrations—a picture of the relative likelihood of the migration or radical attack processes, along with a statistical description of the hydrogen coverage fraction of the (100) H-passivated surface, refining earlier results via a more thorough analysis of the processes at stake. Additionally, the migration of H-vacancy is shown to be anisotropic, and occurring preferentially across the dimer rows of the reconstructed surface. The approach used in this work can be generalised to other crystallographic orientations of diamond surfaces or other semiconductors.

Toward Controlled Synthesis of 2D Crystals by CVD: Learning from the Real-Time Crystal Morphology Evolutions.

The rich morphology of 2D materials grown through chemical vapor deposition (CVD), is a distinctive feature. However, understanding the complex growth of 2D crystals under practical CVD conditions remains a challenge due to various intertwined factors. Real-time monitoring is crucial to providing essential data and enabling the use of advanced tools like machine learning for unraveling these complexities. In this study, we present a custom-built miniaturized CVD system capable of observing and recording 2D MoS2 crystal growth in real time. Image processing converts the real-time footage into digital data, and machine learning algorithms (ML) unveil the significant factors influencing growth. The machine learning model successfully predicts CVD growth parameters for synthesizing ultralarge monolayer MoS2 crystals. It also demonstrates the potential to reverse engineer CVD growth parameters by analyzing the as-grown 2D crystal morphology. This interdisciplinary approach can be integrated to enhance our understanding of controlled 2D crystal synthesis through CVD.