Chemical Deposition Research Articles

Controlled Growth of Ultrathin Graphitic Carbon Nitride Films by Chemical Vapor Deposition

Controlled Growth of Ultrathin Graphitic Carbon Nitride Films by Chemical Vapor Deposition

Unveiling the Correlation between Defects and High Mobility in MoS2 Monolayers.

Defects in semiconductors play a crucial role in modifying their electronic structure and transport properties. In transition metal dichalcogenides, atomic chalcogen vacancies are a primary source of intrinsic defects. While the impact of these vacancies on electrical transport has been widely studied, their exact role remains not fully understood. In this work, we correlate optical spectroscopy, low-temperature electrical transport measurements, scanning tunneling microscopy (STM), and first-principles density functional theory (DFT) calculations to explore the effect of chalcogen vacancies in MoS2 monolayers grown by chemical vapor deposition. We specifically highlight the role of disulfur vacancies in modulating electrical properties, showing that these defects increase the density of shallow donor states near the conduction band, which facilitates electron hopping conduction, as evidenced by low-temperature transport and STM measurements. These findings are further supported by DFT calculations, which reveal that the electronic states associated with these defects are relatively delocalized, promoting hopping conduction and inducing n-type doping. This mechanism accounts for the observed high field-effect mobility (>100 cm2 V-1s-1) in the samples. These findings highlight the potential for defect engineering as a universal approach to customizing the properties of 2D materials for various applications.

Recent Progress in Chemical Vapor Deposition of 2D Magnetic Materials

AbstractMagnetic 2D materials have gotten significant attention due to their unique low‐dimensional magnetism and potential applications in advanced spintronics, providing an perfect platform for investigating magnetic properties at the 2D limit. The chemical vapor deposition (CVD), known for its simplicity and strong controllability, has become a key technique for fabricating ultrathin magnetic nanosheets. This article systematically reviews recent advancements in CVD‐grown magnetic 2D materials, focusing on the effects of growth parameters on material morphologies and properties, and analyzing the construction of heterostructures and their role in magnetic regulation. In addition, various magnetic characterization methods are introduced, and potential applications of these materials in spintronic devices are discussed. By summarizing current challenges, the article provides insights into future research directions, emphasizing the need to improve material stability, Curie temperature, and scalable synthesis to enable practical applications of 2D magnetic materials.

Characterizing the magnetic noise power spectrum of dark spins in diamond

Abstract The coherence times of solid-state spin qubits are often limited by the presence of a spin bath. Characterizing the spectrum of the local magnetic field fluctuations of the bath is key to understanding spin qubit decoherence. Here we use pulsed electron paramagnetic resonance (pEPR) based noise spectroscopy to measure the magnetic noise power spectra for ensembles of P1 (substitutional nitrogen) centers in diamond that typically form the bath for NV (nitrogen-vacancy) centers. The Carr-Purcell-Meiboom-Gill (CPMG) dynamical decoupling experiments on the P1 centers were performed on a low [N] CVD (chemical vapor deposition) sample and a high [N] HPHT (high-temperature, high-pressure) sample at 89 mT. We characterize the NV centers of the latter sample using the same 2.5 GHz pEPR spectrometer. All power spectra show two distinct features, a broad component that is observed to scale as approximately 1/ω^{0.7-1.0}, and a prominent peak at the 13C Larmor frequency. The behavior of the broad component is consistent with an inhomogeneous distribution of Lorentzian spectra due to clustering of P1 centers, which has recently been shown to be prevalent in HPHT diamond. We develop techniques utilizing harmonics of the CPMG filter function to improve characterization of high-frequency signals, which we demonstrate on the 13C nuclear Larmor frequency. At 190 mT this is 2.04 MHz, 5.7 times higher than the CPMG modulation frequency (<357 kHz, hardware-limited). Understanding the properties of the bath allow us to either exploit it as a quantum resource or optimize decoupling performance, while also informing sample fabrication technologies. The techniques are applicable to ac magnetometry for nanoscale nuclear magnetic resonance and chemical sensing.

Exploring SiC CVD growth parameters compatible with remote epitaxy

Remote epitaxy (RE) is a promising technique where monolayers of van der Waals-bonded (i.e., 2D) material act as a release layer for epitaxial film removal and substrate reuse. Epitaxial graphene (EG) grown in situ on SiC(0001) is an ideal RE substrate as it avoids damage or contamination associated with 2D material transfer. However, standard high-temperature, hydrogen-based SiC chemical vapor deposition (CVD) is not compatible with graphene and alternative growth parameters are required for SiC RE. This study investigates reduced-H2 CVD growth of SiC/C/SiC(0001) and the effects on the in situ-grown EG release layer. This study achieved smooth, single-crystalline SiC(0001) epilayers on EG substrates using predominantly Ar carrier gas (2% H2), but no EG was detected at the growth interface after this deposition. Growth modifications, including a pregrowth propane dose, longer precursor ramp steps with high starting C/Si ratios, and reduced SiC growth temperatures, were explored to further mitigate graphene damage. With these changes, isolated patches of 5–10 nm thick graphitic carbon layers remained after SiC RE. Thermodynamic simulations suggest that lower temperatures and increased C/Si ratios will improve C stability. Through this study, optimal SiC RE growth conditions are proposed for a balance of graphene survivability and SiC morphology.

Fractal Scaling in the Gas-Phase Agglomeration of Nanowires.

Assembling1D nanoparticles (nanowires (NW) or nanotubes) as networks enables bridging multiple scales to form macroscopic materials such as fibers, sheets and electrodes. This can be done directly in the gas phase from 1D nanoparticle aerosols grown by floating catalyst chemical vapor deposition (FCCVD). In FCCVD nanowires/nanotubes grow to high aspect ratios (102-106) floating in a gas stream and can agglomerate to form an aerogel. This work studies the agglomeration of Si nanowires by scanning electron microscopy of samples taken from the gas downstream of the reaction zone, and through simulations with a Brownian collision algorithm to form agglomerate models. In the experimental analysis of over 312 samples no individualized NWs are found, only agglomerates. This is consistent with the fast binary collision rates of 0.24 s estimated. The agglomerates show "fractal" scaling, with a fractional dimension Df of 1.8 and agglomerate size increasing with the number of nanowires to the power of 1/Df, consistent with a diffusion limited cluster aggregation process. Formation of a nanowire aerogel involves percolation of agglomerates, therefore occurring at much lower volume fraction than for individualized particles considering excluded volume theory. Compared to FCCVD carbon nanotubes of higher aspect ratio, these SiNWs require longer residence time for gelation.

Study on elementary gas-phase reaction kinetics and chemical vapor deposition modeling from methyltrichlorosilane

Through modeling with computational fluid dynamics (CFD), it is possible to thoroughly and effectively explore the impact of different growth conditions on the chemical vapor deposition (CVD) process. Conducting CFD simulations for the CVD process must couple with reaction kinetics. Currently, research on the reaction kinetics and simulations of the CVD process using methyltrichlorosilane (MTS) as a precursor is still limited. In this study, at first, density functional theory was employed to investigate the reaction paths of MTS and the related gaseous species in its gas-phase system at various temperatures ranging from 1000 to 1800 K, providing a theoretical basis for improving the gas-phase reaction kinetics in CVD models used to analyze the distribution of gaseous species. Based on the modification and improvement of the gas-phase reaction kinetics for MTS pyrolysis, this study proposes a new gas-phase reaction kinetics model suitable for CVD simulation modeling. Then, CFD simulations of CVD by employing finite element theory have been conducted using the reaction kinetics model proposed in this study. The effects of temperature, initial MTS composition ratio, and the residence time on the distribution of gas-phase species have been studied.

Study of evolution for 3D structured surface with nano-balls and walls-like features with thickness variation for WO3 thin films made by spray deposition

The present work regards a unique yet study of 3D structured surface evolution of nano-balls and walls-like features with thickness variation, for tungsten oxide (WO3) thin films made by spray deposition. Since in most optoelectronic applications the surface morphology and structure play a crucial role and WO3 is one of the most studied and used metal oxide semiconductors in a significant variety of optoelectronic applications, a detailed study of recently observed and reported unique 3D complex architecture of WO3 coatings fabricated by spray pyrolysis (starting from different precursors) is of great importance for further development of thin film coatings and devices. In this scope, two different series of WO3 of 11 samples with different thicknesses each, starting from two tungsten peroxide precursor concentrations (0.05 M and 0.1 M) were fabricated by spray pyrolysis and thoroughly characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction and Raman spectroscopy. Results suggest that, for the mentioned concentrations, the main structural differences affect mostly the surface morphology and slightly the surface texturing. These observations prove the reliability of fabrication of coatings with such surface morphology by spray pyrolysis method and open new perspectives for better sensors, electrochromic or photochromic devices, and more.

Wafer‐Scale Synthesis of Topological Insulator Sb2Te3 Thin Films

AbstractRecently, metal‐organic chemical vapor deposition (MOCVD) has been proven successful to grow topological insulators such as antimony telluride (Sb2Te3), with their use as efficient spin‐charge converters at room temperature also being reported. On the other hand, a wafer‐scale synthesis of Sb2Te3 thin films showing clear‐cut electrical conduction driven by topologically protected surface states is still missing. Within this work, the growth of Sb2Te3 thin films with variable thicknesses over 4‐inch (4″) wafer‐scale Si(111) substrates as conducted via MOCVD is reported. By performing magnetoconductance measurements, weak antilocalization phenomena are detected over the whole 4″ area, thus proving the possibility to produce wafer‐scale Sb2Te3 topological insulator thin films. Furthermore, comprehensive information on the variability of the functional properties of Sb2Te3 thin films with their morphological, chemical, and structural properties, as probed by scanning electron microscopy, X‐ray diffraction/reflectivity, atomic force microscopy, Raman spectroscopy, time‐of‐flight secondary ion mass spectrometry, and energy‐dispersive X‐ray analyses is reported. This work provides a breakthrough for the technology scale‐up of these novel materials to be employed in future spintronic devices as well as applications in nanoelectronics, thermoelectrics, and quantum computing.

Direct observations of nucleation and early-stage growth of Au-catalyzed GaAs nanowires on Si(111)

Developing a reliable procedure for the growth of III-V nanowires (NW) on silicon (Si) substrates remains a significant challenge, as current methods rely on trial-and-error approaches with varying interpretations of critical process steps such as sample preparation, Au-Si alloy formation in the growth reactor, and NW alignment. Addressing these challenges is essential for enabling high-performance electronic and optoelectronic devices that combine the superior properties of III-V NW semiconductors with the well-established Si-based technology. Combining conventional scalable growth methods, such as metalorganic chemical vapor deposition (MOCVD) within situcharacterization using environmental transmission electron microscopy (ETEM-MOCVD) enables a deeper understanding of the growth dynamics, if that knowledge is transferable to the scalable processes. We report on successful epitaxial growth of Au-catalyzed GaAs NWs on Si(111) substrates using micro-electromechanical system chips with monocrystalline Si-cantilevers in both conventional MOCVD and ETEM-MOCVD systems. The conventional MOCVD provided a framework for initial parameter tuning, while ETEM-MOCVD offered valuable insights into early nucleation and catalyst-substrate interactions. Our findings show that nucleation is significantly influenced by the removal of native oxide layers and the initial formation of the Au-Si alloy. Ourin situstudies revealed different NW-substrate interfaces, essential for optimizing the epitaxial growth process. We identified three typical configurations of NW 'roots', each impacted by growth conditions and preparation steps, affecting the structural and potentially the optical properties of the NWs. Similarly, doping from the Si-substrate may affect both optical and electrical properties; however, compositional analysis revealed no traces of Si in NWs post-nucleation and a small amount in the catalytic droplet. Our research highlights the importance ofin situstudies for a comprehensive understanding of nucleation mechanisms, paving the way for optimizing III-V NW growth on Si substrates and developing high-performance III-V/Si devices.

Enhanced multifunctionality of SnO2 and W-doped SnO2 thin films synthesized via ultrasonic spray pyrolysis: applications in UV photodetectors, photocatalysis, and tunable surface hydrophilicity

Enhanced multifunctionality of SnO2 and W-doped SnO2 thin films synthesized via ultrasonic spray pyrolysis: applications in UV photodetectors, photocatalysis, and tunable surface hydrophilicity

High-Dielectric-Constant MgZrO3 by Spray Pyrolysis for Thin-Fim Transistors in Low-Power Electronics

High-Dielectric-Constant MgZrO₃ by Spray Pyrolysis for Thin-Fim Transistors in Low-Power Electronics

The effect of cobalt doping on the structure and properties of copper oxide thin films: Evolution in surface morphology, p- to n-type carrier transition and enhancement optoelectronic behavior

This paper reports the preparation of CuO and cobalt (Co)-doped CuO (Co:CuO) thin films (TFs) by a convenient spray pyrolysis reactor. Co concentration (conc.) was varied in CuO TFs from 2 to 8[Formula: see text]at.% at the step of 2[Formula: see text]at.%. In the FESEM images of undoped films, aggregations of nanoparticles were found. The surface morphology of CuO turned into porous and spongy nanostructures for 6[Formula: see text]at.% Co-doping. In XRD analysis, CuO film showed a monoclinic crystal structure with ([Formula: see text]11) peak occurrence. The crystallite size of the films was found to be between 5[Formula: see text]nm and 12[Formula: see text]nm. In UV–vis spectroscopy, the optical transmittance of Co:CuO films increased in the visible region and then saturated in the NIR light region. The highest transmittance of about 96% was found for the 6 at.% Co:CuO film. The band gap of Co:CuO increased with Co doping. Urbach energy, refractive index, dielectric constants and dispersion energy parameters were estimated. Electrical resistivity and carrier concentration were found in the order of [Formula: see text]-cm and [Formula: see text] [Formula: see text]cm[Formula: see text], respectively. CuO films showed n-type conductivity for 4, 6 and 8[Formula: see text]at.% Co-doping. The figure of merit increased significantly with Co-doping up to 6[Formula: see text]at.%, indicating the enhancement in optoelectronic behavior.

Catalytic oxidation potential of graphene encapsulated iron-based nanocatalysts synthesized via chemical vapor deposition

Abstract In recent years, conventional treatment methods have been reported as insufficient for effectively removing organic substances from water, emphasizing the potential of advanced oxidation processes as a promising solution. Therefore, the aim of this research was to evaluate the catalytic oxidation potential of graphene-encapsulated iron-based nanocatalysts synthesized from iron-containing salts using chemical vapor deposition combined with persulfate/UV-C for the degradation of total organic carbon in surface water. The microstructural and magnetic properties of the synthesized nanocatalysts were determined prior to their use as catalysts for advanced oxidation processes. The analysis results showed a significant total organic carbon removal ability, resulting in a reduction of up to 1.76 mg/L from an initial concentration of 4.55 mg/L under the conditions of pHo = 8.0, T = 25 °C, PS = 0.5 mM, and t = 60 min. Moreover, a decrease in UV254 during all experiments indicated that the organic matter present in the raw water, especially those with aromatic structures, underwent significant transformations during the catalytic processes.

Controllable Syntheses, Structure Identifications, and Property Explorations of Self-Intercalated 2D Transition Metal Chalcogenides.

2D transition metal dichalcogenides (2D TMDCs) have attracted intensive interest in physics and materials science-related fields, due to their exotic properties (e.g., superconductivity, charge density wave (CDW) phase transition, magnetism, electrocatalytic property). Intercalation of native metal atoms in the layered 2D TMDCs (e.g., from VS2 to V5S8 by V intercalation) can afford new stoichiometric ratios, phase states, and thus rich properties. This review hereby summarizes the recent progress in the controllable syntheses, structure characterizations, and property explorations of self-intercalated 2D transition metal chalcogenides (TMCs), with the metal elements focusing on group-V, VI, and VIII metals. The self-intercalation-related synthetic strategies will be introduced via chemical vapor deposition (CVD) and molecule beam epitaxy (MBE), especially by tuning the chemical potentials of intercalated metal elements, growth promoters, substrates, etc. Additionally, the structure/phase identifications of the self-intercalated 2D TMCs through various characterization techniques will be overviewed. More significantly, the intriguing properties in such 2D TMCs will be thoroughly discussed, such as the thickness- or composition-dependent magnetism, CDW phase transition, electrocatalytic property, etc. Finally, challenges and prospects are proposed for developing new self-intercalated 2D materials and their heterostructures and exploring their unique properties and applications.

Surface Nanostructure Fabrication by Initiated Chemical Vapor Deposition and Its Combined Technologies.

Initiated chemical vapor deposition (iCVD) is a versatile technique that enables the direct growth of nanostructures and surface modification of such structures. Unlike traditional CVD methods, iCVD operates under mild conditions, allowing for damage-free processing of delicate substrates. It can produce highly uniform polymer layers, with thicknesses ranging from over 15 μm to sub-10 nm, conformally coating intricate geometries. The broad range of polymer compositions achievable with iCVD offers precise control of surface chemistry. In this Viewpoint, we present iCVD's mechanisms and the principles for controlling the composition and morphology of deposited layers. We summarize various surface nanostructures including nanodomes, nanocones, nanowrinkles, nanoparticles, and nanoporous structures that are directly fabricated using iCVD. We also demonstrate the integration of iCVD with other advanced methods, such as photo, soft, and nanoimprint lithography; template-assisted growth; and thermal CVD, to leverage the advantages of multiple methods and overcome individual limitations in nanofabrication. Through these combined strategies, we show the iCVD's potential for creating multifunctional nanostructures with broad applications across engineering and biomedical fields.

In Situ Preparation of Thin-Film Q-Switches Based on Vanadium Dioxide for Pulsed Fiber Lasers

In the presented work, erbium fiber lasers operating in the pulsed mode with a nonlinear element containing a vanadium oxide saturable absorber are demonstrated. The structure of the saturable absorber is based on a segment of thinned silica fiber coated with a thin-film vanadium oxide by the method of metalorganic chemical vapor deposition. A fiber laser scheme is demonstrated that allows controlling the transmission of the internal cavity of the resonator during laser generation and deposition of a thin film. We have demonstrated a method for obtaining and annealing nanocoatings with laser generation control. We controlled the laser output parameters directly during the synthesis of the saturable absorber material. Vanadium oxides obtained in the work demonstrated the Mott–Paierls phase transition practically at room temperature. In this work, the optical characteristics of the output radiation of a fiber laser with a saturable absorber were measured. At temperatures above 70 °C, the coatings demonstrate a passive Q-switch with a repetition rate of 38 kHz and a pulse duration of 3.8 μs. At temperatures below the phase transition, a short-term mode-locking mode occurs. The transmission jump at a wavelength of about 1350 nm during structural rearrangement was 24%. For comparison, VO2 nanopowder in a polydimethylsiloxane elastomer matrix was used as a saturable absorber material. The nanopowder modulator made it possible to obtain pulses with a frequency of 27 kHz and a duration of about 7.2 μs.

Effects of Red Mud on Microstructures and Heat Resistance of ZL109 Aluminum Alloy

The effects of red mud on the microstructures and high-temperature tensile properties of the ZL109 aluminum alloy have been investigated. Red mud/ZL109-based composite materials with added red mud (a major byproduct of the aluminum industry), which has been coated with nickel by chemical deposition, have been prepared through gravity casting. The results show that the addition of red mud promotes the alloy’s microstructure and helps to uniformly distribute the eutectic silicon. It also increases the content of heat-resistant phases, such as the Q-Al5Cu2Mg8Si6 and γ-Al7Cu4Ni phases. These changes significantly enhance the alloy’s high-temperature tensile properties. The alloy with 1% (wt.%) red mud exhibits the best tensile strength at both room temperature and 350 °C, reaching 295.4 MPa and 143.3 MPa, respectively. The alloy with 1.5% (wt.%) red mud demonstrates excellent performance at 400 °C, achieving a tensile strength of 86.2 MPa through the cut-through method and Orowan mechanism. As a reinforcing material, red mud not only improves the high-temperature resistance of the aluminum alloy but also provides a way to recycle industrial waste. This study offers a new way to address the red mud waste problem and helps develop high-performance, heat-resistant aluminum alloys. It shows the potential of these alloys in high-temperature applications.

WxMo1‐xO2 Nanocrystals Synthesized by WSe2‐Assisted Chemical Vapor Deposition Method

Transition metal oxide alloys, with tunable stoichiometric ratio, have garnered significant attention due to their unique electronic structure and diverse chemical properties. However, synthesis of micron‐scale, single‐crystalline transition metal oxide alloys remains a challenge due to their unique alloy structure and stringent synthesis conditions. Herein, a WSe2‐assisted chemical vapor deposition method is reported for synthesizing WxMo1‐xO2 nanocrystals with various dimensions: nanorods, nanoplates, and nanodots. The microscopic (optical microscope, atomic force microscope, and scanning electron microscope) images reveal that the nanocrystals have well‐defined non‐layered polyhedral structures. The elemental composition is confirmed by Raman spectroscopy and energy dispersion spectroscopy. The change in phonon symmetry in nanorods and the blue shift of Raman peaks in nanocrystals demonstrate the significant role of the quantum confinement effect. The spatial distribution of the various dimensional nanocrystals provides insights into the possible growth mechanism and the key role of the WSe2 in growth. The WSe2‐assisted growth strategy for alloyed nanocrystals can expand the transition metal oxide alloy material library and offer a platform for exploring additional properties of transition metal oxide alloys.

Experimental study of CuBi2O4 photocathode synthesized by spray pyrolysis and electrochemical deposition methods for visible light harvesting in photoelectrochemical cells

This research examined methods that are suitable, easy to fabricate, and low-cost for producing CuBi2O4 photocathodes for application in photoelectrochemical cells. Both spray pyrolysis and electrochemical deposition techniques were used to produce thin films for various types of semiconductor electrodes. The CuBi2O4 thin film was coated on fluorinedoped tin oxide (FTO) using spray pyrolysis and electrochemical deposition, followed by annealing in an oxygen atmosphere. X-ray diffraction (XRD) characterized the crystal structures, confirming them as Kusachiite. Scanning electron microscopy (SEM) analysis revealed that CuBi2O4 fabricated by electrochemical deposition exhibited smaller particles, while the spray pyrolysis method produced a plate-like structure. The optical properties were investigated using UV-visible reflection, and the energy bandgaps of the products were estimated using Tauc plots, showing slight differences. Chopped light voltammetry (CLV) was used to evaluate the photon conversion efficiency of the synthesized photocathodes. Results indicated that the photocathode made by electrochemical deposition responded better to light compared to the one made by spray pyrolysis. With 0.5 M Na2SO3 as a sacrificial agent, the highest photocurrent density obtained was 0.2 mA/cm², while with 0.5 M NaHCO3, the highest photocurrent was 0.5 µA/cm², indicating poorer performance.