Chemical Vapor Deposition Process Research Articles

Morphology and Structure of TiO2 Nanotube/Carbon Nanostructure Coatings on Titanium Surfaces for Potential Biomedical Application.

Titanium is the most used material for implant production. To increase its biocompatibility, continuous research on new coatings has been performed by the scientific community. The aim of the present paper is to prepare new coatings on the surfaces of the pure Ti Grade 2 and the Ti6Al4V alloy. Three types of coatings were achieved by applying anodization and chemical vapor deposition (CVD) methods: TiO2 nanotubes (TNTs) were formed by anodization, carbon nanotubes (CNTs) were obtained through a metal-catalyst-free CVD process, and a bilayer coating (TiO2 nanotubes/carbon nanostructures) was prepared via successive anodization and CVD processes. The morphology and structure of the newly developed coatings were characterized using SEM, EDX, AFM, XRD, and Raman spectroscopy. It was found that after anodization, the morphology of the TiO2 layer on pure Ti consisted of a "sponge-like" structure, nanotubes, and nano-rods, while the TNTs layer on the Ti alloy comprised mainly nanotubes. The bilayer coatings on both materials demonstrated different morphologies: the pure Ti metal was covered by a layer of nanotubular and nano-rod TiO2 structures, followed by a dense carbon layer decorated with carbon nanoflakes, and on the Ti alloy, first, a TNTs layer was formed, and then carbon nano-rods were deposited using the CVD method.

Improvement of warpage and leakage for 3D NAND flash memory

GLS (Gate line split) filling is a very important process in 3D NAND flash memory (3D NAND) fabrication. Filling materials in the GLS should have threefold properties, such as warpage tunability, leakage-free and low resistance. In this paper, the effects of different GLS filling materials (SiO2, W, amorphous silicon: A-Si) on F-attack, warpage and resistance were studied. GLS filled with A-Si shows best performance on warpage and F-attack. For 3D NAND, the number of stacked layers is predicted as a function of the wafer warpage, and the wafer warpage difference between GLS filled with A-Si and W was compared. With the same number of stacking layers, the wafer warpage post GLS filled with A-Si is smaller than that filled with W. Meanwhile, A-Si is produced by the decomposition of SiH4 by low pressure chemical vapor deposition (LPCVD) process, F-related by-product in the GLS filling material and consequent ACS (array common source) to WL (Word line) leakage by F-attack are avoided. A-Si is the best choice for GLS filling. This work provides an efficient method to solve the warpage and leakage problem in 3D NAND flash memory fabrication.

Guiding Principles for the Design of a Chemical Vapor Deposition Process for Highly Crystalline Transition Metal Dichalcogenides

2D transition metal dichalcogenides (TMDs) for advanced logic transistor technologies are deposited by various modifications of the chemical vapor deposition (CVD) method using a wide variety of precursors. Being a major electrical performance limiter, the TMD crystal grain size strongly differs between the various CVD precursor chemistries from nano‐ to millimeter‐sized crystals. However, it remains unclear how the CVD precursor chemistry affects the nucleation density and resulting TMD crystal grain size. This work postulates guiding principles to design a CVD process for highly crystalline TMD deposition using a quantitative analytical model benchmarked against the literature. The TMD nucleation density reduces favorably under low supersaturation conditions where the metal precursor sorption on the starting surface is reversible and the corresponding metal precursor desorption rate exceeds the overall deposition rate. Such reversible precursor adsorption guarantees efficient long‐range gas‐phase lateral diffusion of precursor species in addition to short‐range surface diffusion, which vitally increases crystal grain size. The proposed model explains the large spread in experimentally observed TMD nucleation densities and crystal grain sizes for state‐of‐the‐art CVD chemistries. Ultimately, it empowers the reader to interpret and modulate precursor adsorption and diffusion reactions through designing CVD precursor chemistries.

The investigation of initial decomposition paths of methyltrichlorosilane on (0001) and (000[formula omitted]) surfaces of 4H-SiC: A DFT study

Methyltrichlorosilane (CH3SiCl3, MTS), a favored precursor for chemical vapor deposition (CVD) process of silicon carbide (SiC) epitaxial layer fabrication in a wide variety of temperatures, has been investigated prevalently. In this work, the investigation focused on the initial decomposition paths of MTS with active surface sites on 4H-SiC surfaces. The surfaces employed in this study include both (0001) face and (0001¯) face, which represent Si face and C face, respectively. The decomposition pathways of MTS decomposed with the active surface sites of 4H-SiC surfaces were researched theoretically with employment of transition state theory (TST). The barriers of Gibbs free energies and the estimated reaction rate constants were acquired to discuss the decomposition reactivity of MTS with the active sites on 4H-SiC surfaces. This work shows that MTS has tendency to decompose on both (0001) face and (0001¯) face of 4H-SiC, the H and Cl atoms can be abstracted by active surface sites on (0001) face and (0001¯) face, and impingement of MTS to active surface sites on (0001) and (0001¯) surfaces can yield C-containing and Si-containing surface species.

Heavily boron-doped polycrystalline diamond films: Microstructure, chemical composition investigation and plasma in-situ diagnostics

The introduction of boron brings excellent electrical conductivity to diamond films, but also induces uncontrollability of the doping process. Therefore, it is crucial to the monitor of the growth and doping processes. In this work, to establish the correlation between the gas-phase chemical reactions and the microstructure characteristics of heavily boron-doped diamond (BDD) films, the plasma reactions in the chemical vapor deposition (CVD) process of BDD films were in-situ diagnosed and monitored using optical emission spectroscopy (OES), and the effect of different B/C ratios (from 10,000 to 60,000 ppm) on the microstructure, chemical composition were investigated comprehensively. As the B/C ratio increases, the insufficient gas-phase excitation and the “hydrogen abstraction” reaction of BH species lead to a massive loss of H species in the gas-phase of plasma, which is unfavorable for the diamond growth, weakens the etching on sp2 carbon, induces the development of defects and seriously damages the diamond films quality. The in-situ diagnostics and monitoring of the plasma state can realize the optimization of the growth and doping process for heavily doped polycrystalline BDD films, which is highly significant for its preparation and application.

Two‐Dimensional Ultrathin C2N Nanosheets for High‐Performance Sodium‐Ion Storage

AbstractIn this study, we have created and investigated ultrathin, large‐size two‐dimensional C2N nanosheets, which serve as promising anode materials for sodium ion batteries. Those ultrathin C2N nanosheets were produced through a chemical vapor deposition process, involving the polymerization of the precursor molecule HAT‐CN on sodium chloride templates. Notably, these nanosheets inherit an abundance of nitrogen sites from the precursor molecules, which are highly advantageous for sodium ion storage. In addition, the ultrathin nature of these nanosheets leads to significantly shorter ion transport pathways, enhancing their capacity for rapid ion storage compared to C2N particles. As a result, the anode constructed using C2N nanosheets demonstrates a notably higher capacity of 335.1 mAh g−1 at 0.5 A g−1, outperforming the 211.5 mAh g−1 of C2N particles. Furthermore, it exhibits outstanding rate performance, achieving 255.4 mAh g−1 at a current density of 2.0 A g−1, along with excellent cycle stability, maintaining a reversible capacity retention of 92.9 % over 1500 cycles at 2.0 A g−1. This research introduces a novel approach to developing high‐capacity anode materials for sodium storage by utilizing carbon nitride materials.

Recent Advances in Spin-coating Precursor Mediated Chemical Vapor Deposition of Two-Dimensional Transition Metal Dichalcogenides.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have garnered widespread interest in the scientific community and industry for their exceptional physical and chemistry properties, and great potential for applications in diverse fields including (opto)electronics, electrocatalysis, and energy storage. Chemical vapor deposition (CVD) is one of the most compelling growth methods for the scalable growth of high-quality 2D TMDs. However, the conventional CVD process for synthesis of 2D TMDs still encounters significant challenges, primarily attributed to the high melting point of precursor powders, and achieving a uniform distribution of precursor atmosphere on the substrate to obtain controllable smaple domains is difficult. The spin-coating precursor mediated chemical vapor deposition (SCVD) strategy provides refinement over traditional methods by eliminating the use of solid precursors and ensuring a more clean and uniform distribution of the growth material on the substrate. Additionally, the SCVD process allows fine-tuning of material thickness and purity by manipulating solution composition, concentration, and the spin coating process. This Review presents a comprehensive summary of recent advances in controllable growth of 2D TMDs with a SCVD strategy. First, a series of various liquid precursors, additives, source supply methods, and substrate engineering strategies for preparing atomically thin TMDs by SCVD are introduced. Then, 2D TMDs heterostructures and novel doped TMDs fabricated through the SCVD method are discussed. Finally, the current challenges and perspectives to synthesize 2D TMDs using SCVD are discussed.

Synthesis and functionalization of carbon nanostructures in a single‐step CVD process through the implementation of a recycled precursor

AbstractBackgroundRecycled materials are a major research topics of the new era to relieve pressure on raw material extraction from our planet and reduce its pollution levels. This has helped us to reinvent our relationship with nature, and to commit ourselves to a sustainable economic and social reconstruction. An excellent option to add value to waste while protecting the environment is the synthesis of carbon nanostructures (CNSs) using a recycled material as a precursor. In this research, the synthesis and functionalization of CNSss in a single‐step chemical vapour deposition (CVD) process was carried out using a recycled precursor. The methanol fraction is waste from the distillation process in the production of alcoholic beverages. The synthesis temperatures were 750, 800 and 850 °C.ResultsAs a result, carbon nanotubes, carbon nanoribbons and carbon nanobeads with diameters <100 nm and widths <500 nm were obtained. The crystal size of CNSs decreased with increasing synthesis temperature, from 20 to 12 nm. RAMAN spectra revealed the high degree of graphitization and the presence of different types of nanostructures. Carbonyl (CO) and hydroxide (‐OH) stretching of the carboxylic acid were present in all samples.ConclusionThe results obtained shown that the CNSs synthetized are functionalized in a single‐step CVD process using the methanolic fraction as a precursor. © 2024 Society of Chemical Industry (SCI).

Gas-Phase Synthesis of Iron Silicide Nanostructures Using a Single-Source Precursor: Comparing Direct-Write Processing and Thermal Conversion.

The investigation of precursor classes for the fabrication of nanostructures is of specific interest for maskless fabrication and direct nanoprinting. In this study, the differences in material composition depending on the employed process are illustrated for focused-ion-beam- and focused-electron-beam-induced deposition (FIBID/FEBID) and compared to the thermal decomposition in chemical vapor deposition (CVD). This article reports on specific differences in the deposit composition and microstructure when the (H3Si)2Fe(CO)4 precursor is converted into an inorganic material. Maximum metal/metalloid contents of up to 90 at. % are obtained in FIBID deposits and higher than 90 at. % in CVD films, while FEBID with the same precursor provides material containing less than 45 at. % total metal/metalloid content. Moreover, the Fe:Si ratio is retained well in FEBID and CVD processes, but FIBID using Ga+ ions liberates more than 50% of the initial Si provided by the precursor. This suggests that precursors for FIBID processes targeting binary materials should include multiple bonding such as bridging positions for nonmetals. In addition, an in situ method for investigations of supporting thermal effects of precursor fragmentation during the direct-writing processes is presented, and the applicability of the precursor for nanoscale 3D FEBID writing is demonstrated.

Epitaxial Growth of Two-Dimensional Nonlayered AuCrS2 Materials via Au-Assisted Chemical Vapor Deposition.

Two-dimensional (2D) nonlayered transition metal dichalcogenide (TMD) materials are emergent platforms for various applications from catalysis to quantum devices. However, their limited availability and nonstraightforward synthesis methods hinder our understanding of these materials. Here, we present a novel technique for synthesizing 2D nonlayered AuCrS2 via Au-assisted chemical vapor deposition (CVD). Our detailed structural analysis reveals the layer-by-layer growth of [AuCrS2] units atop an initial CrS2 monolayer, with Au binding to the adjacent monolayer of CrS2, which is in stark contrast with the well-known metal intercalation mechanism in the synthesis of many other 2D nonlayered materials. Theoretical calculations further back the crucial role of Cr in increasing the mobility of Au species and strengthening the adsorption energy of Au on CrS2, thereby aiding the growth throughout the CVD process. Additionally, the resulting free-standing nanoporous AuCrS2 (NP-AuCrS2) exhibits exceptional electrocatalytic properties for the hydrogen evolution reaction.

Preparing iron oxide clusters surface modified Co3O4 nanoboxes by chemical vapor deposition as an efficient electrocatalyst for oxygen evolution reaction

Interface engineering is an effective way for optimizing the electronic configuration of Co3O4 to enhance the intrinsic activity of oxygen evolution reaction (OER). However, how to enrich accessible activity sites at the interface is still a challenge. Herein, Co3O4 hollow nanoboxes modified by iron oxide nanoclusters (FeOx NCs) (Fe-Co3O4 NBs) as OER electrocatalysts are prepared by a chemical vapor deposition process. Benefiting from high exposed surface area and utilization of atoms, FeOx NCs incorporation can not only regulates the spin state of Co sites, but also exposes more accessible sites for OER. Therefore, Fe-Co3O4 NBs shows excellent OER performance, manifested by the lower overpotential (η) of 265 mV at 10 mA cm−2 and smaller Tafel slope of 54.2 mV dec−1 compared to Co3O4 NBs, and many reported Co based OER electrocatalyst. Further density functional theory analysis reveals that FeOx NCs can downshift the d center of Co sites, which decreases the energy barrier of potential-determining step (PDS) for OER (*OH → *O + H+ + e−) to enhance the electroactivity. This work provides guidance for further designing high-performance OER electrocatalysts.

Effect of Thickness and Thermal Treatment on the Electrical Performance of 2D MoS2 Monolayer and Multilayer Field-Effect Transistors

We deposited high-quality molybdenum disulfide (MoS2) monolayer and multilayer crystals on SiO2/Si substrates, by means of a chemical vapor deposition (CVD) process at atmospheric pressure. Notably, NaCl salt was used as component of the precursors to assist the growth of MoS2 crystals, which were intended for use as the active channel layer in the fabrication of field-effect transistors (FETs). The resulting MoS2 crystals from this CVD process were analyzed by optical, scanning electron, and atomic force microscopies, and by Raman and photoluminescence spectroscopies. The optical images and the micrographs obtained by SEM revealed the formation of dispersed MoS2 crystals with a triangular shape all over the SiO2 surface. The thickness of the MoS2 crystals, analyzed by atomic force microscopy, showed minimum values of around 0.7 nm, confirming the formation of monolayers. Additionally, multilayers with larger thickness were also identified. The Raman and photoluminescence spectra of the MoS2 crystals corroborated the formation of single and multiple layers. The fabrication of the FET back-SiO2 -gate configuration was made by depositing patterned source and drain Ti contacts on the dispersed MoS2 crystals to achieve the Ti/MoS2/SiO2/Si layer stacks. MoS2-based FETs with one and three layers were assembled and their electrical response analyzed by I–V output and transfer curves showing the typical characteristics of an n-type semiconductor channel operating in depletion mode. The electrical performance parameters of the devices, such as mobility and threshold voltage, were also determined from this analysis. Finally, to enhance their electrical response, the MoS2-based devices were thermally annealed at 200 °C for 30 min in Ar atmosphere. The increase in the mobility of the device was 176% compared to the device before the treatment.

Combined Experimental and Computational Insight into the Role of Substrate in the Synthesis of Two-Dimensional WSe2.

Synthesis of large-area transition-metal dichalcogenides (TMDs) with controlled orientation is a significant challenge to their industrial applications. Substrate plays a vital role in determining the final quality of monolayer materials grown via the chemical vapor deposition process by controlling their orientation, crystal structure, and grain boundary. This study determined the binding energy and equilibrium distance for tungsten diselenide (WSe2) monolayers on crystalline and amorphous silicon dioxide and aluminum dioxide substrates. Differently oriented WSe2 monolayers are considered to investigate the role of the substrate in the orientation, binding strength, and equilibrium distance. This study can pave the way to synthesizing high-quality two-dimensional (2D) materials for electronic and chemical applications.

Nano- and micro-crystalline diamond film structuring with electron beam lithography mask

Direct current plasma enhanced chemical vapor deposition (CVD) was employed to create polycrystalline diamond films from CH4/H2 gaseous mixture at 98 mbar pressure and various substrate temperatures between 720 °C and 960 °C. The Si chips with patterns of periodic masked and open seeded zones were used as substrates. The mask free seeded areas evolved into polycrystalline diamond films after CVD process. The diamond crystallites of the films featured single crystal ordering individually with distinct cubic (100) or octahedral (111) facets on the film surfaces. Notably, specific growth conditions were determined for obtaining diamond films composed of the crystallites of nanometre and micrometre scale. These conditions are differing from those observed for non-pattern-prepared Si substrates. The nano-crystalline diamonds emerged within the 4.5–5 A current range, with growth conditions involving 3% CH4/H2 mixture at 98 mbar. The micro-crystalline diamonds (MCDs) predominantly characterized by well-developed rectangular (100) crystal faces on the film surface were successfully grown with current settings of 5.5–6 A, under 3% CH4/H2 mixture at 98 mbar. Furthermore, MCDs characterized by entirely crystalline (111) diamond faces forming CVD film surface were attained within a growth parameter range of 4.5–5.8 A, employing 3% CH4/H2 mixture for certain samples, or alternatively, utilizing 5 A with a 1.5% CH4/H2 mixture for others. Upon thorough evaluation, it was established that SiO2, TiO2, and Cr masks are well-suited materials for the planar patterning of both nano- and micro-crystalline diamond films, and the bottom-up approach can pave the way for the production of diamond planar structures through CVD, facilitated by electron beam lithography (EBL).

Controllable preparation of novel homogenous reinforcement poly(p-phenylene terephthamide) hollow fiber nanofiltration membrane with nanoscale ordered structures for organic solvent nanofiltration

Organic solvent nanofiltration (OSN) is a green, energy-saving, and highly efficient emerging membrane separation technology, and there is an urgent need for robust, easy-to-process OSN membranes with high permeance and small solute selectivity for industrial applications. Herein, we propose a new strategy for accurately designing novel OSN membranes. Specifically, a polyamide (PA) interlayer was synthesized in-situ on the surface of homogeneous reinforced poly(p-phenylene terephthamide) (PPTA) hollow fiber membrane by interfacial polymerization (IP) using both ultra-low concentrations piperazine (PIP, 0.05 wt%) and trimesoyl chloride (TMC, 0.005 wt%), and then a defect-free and dense PPy layer was deposited on top of the hydrophilic PA interlayer by chemical vapor deposition (CVD) process to prepare PA/PPy composite membranes with spherical cluster or strip cluster “Turing-like” structure. The resulting PA/PPy composite membranes presented an excellent high selective permeability, the dimethylacetamide (DMAc) permeability was 21.1 L·m−2·h−1·MPa−1, and the molecular weight cut-off (MWCO) was as low as 185 Da. A 30-hour OSN test at elevated temperatures (80 °C) and in organic solvent (DMAc), as well as a one-month immersion test in ethanol and DMAc at room temperature, demonstrated superior separation performance and structural stability of the membranes, indicating their application potential in harsh solvent systems. Our novel method for developing nanoscale ordered structured PA/PPy composite membranes offers great potential for the development of multilevel structural designs in the preparation of high-performance OSN membranes with potential industrial applications.

Improved heteroepitaxy of κ-Ga2O3 on c-plane sapphire by initial mist flow stabilization during mist chemical vapor deposition

Kappa-phase gallium oxide (κ-Ga2O3) is a metastable gallium oxide polymorph and an ultrawide bandgap semiconductor with potential applications in various electronic and optoelectronic devices. In this study, we present the effect of mist flow stabilization during the initial stages of mist chemical vapor deposition process on the crystal quality of heteroepitaxial thin films of κ-Ga2O3 grown on c-plane sapphire. Two κ-Ga2O3 films were grown using the same growth parameters with the only differing factor being the stabilization of the initial mist flow. Structural and optical properties of the films were characterized. Both processes resulted in epitaxial growth; however, controlling the initial mist flow leads to an improved Ga2O3/Al2O3 interface and superior crystal quality. The film grown with regulated mist flow exhibited an optical bandgap of 4.93 eV, a smooth surface with a root mean square roughness of 1.56 nm and a rocking curve full-width half-maximum value of 0.17°. Also, Ti/Au deposition on κ-Ga2O3 resulted in an interface resembling that of β-Ga2O3 and Ti/Au, explaining previous reports of ohmic behavior between κ-Ga2O3 and Ti/Au contacts.

Morphology-Controlled ZnO@ZnWO4 Hetero-Nanostructures for Efficient Photooxidation of Water in Near-Neutral pH.

One-dimensional ZnO nanorods (NRs) have been extensively studied as photoanodes because of their unique optical properties, high electron mobility, and suitable band positions for water oxidation. However, their practical efficiency is often compromised by chemical instability during water oxidation and high carrier recombination rates. To overcome this issue, precise morphological control of ZnO@ZnWO4 core-shell structured photoanodes, featuring a ZnO core and a ZnWO4 shell was used. This was accomplished by depositing WO3 onto hydrothermally grown ZnO NRs using the thermal chemical vapor deposition process. The photoelectrochemical performance of ZnO@ZnWO4 with an optimized morphology outperforms that of pristine ZnO NRs. Systematic optical and electrochemical analyses of ZnO@ZnWO4 demonstrated that the enhancement is attributed to the enhanced charge transfer efficiency facilitated by the optimized ZnWO4 shells.

Effect of BN interfacial layer on the mechanical behavior of SiC fiber reinforced SiC ceramic matrix composites

AbstractBoron nitride (BN) interfacial layer with controlled thickness and structure was prepared on the surface of near stoichiometric ratio SiC fiber preforms by a chemical vapor deposition process, and the SiC/SiC composites were obtained by polymer precursor infiltration and pyrolysis process. The microstructure of the BN interfacial layer and SiC/SiC composites was tested by scanning electron microscopy, and the mechanical behavior of SiC/SiC composites was characterized by a mechanical properties test. Results showed that BN interfacial layer was evenly distributed in the fiber preforms with excellent thickness consistency. As the thickness of the BN interfacial layer increased, the deflection path of the crack increased gradually, resulting in the flexural strength first increasing and then decreasing. The mechanical behavior mentioned above was mainly attributed to the dual effects of load transfer and crack propagation of the BN interfacial layer; that was, the crack propagation of ceramic matrix under external load lengthened the path of load transfer and formed a large number of fibers bridging and pulling out successively, which contributed to the energy dissipation mechanism.

Analysis of Influencing Factors on Silicon Epitaxial Growth in Horizontal Single‐Wafer Reactor through Orthogonal Test

AbstractSilicon epitaxy is a crucial process used in semiconductor manufacturing to deposit high‐quality films of silicon. This technique is widely used in the production of integrated circuits, as it enables the fabrication of intricate electronic structures with enhanced performance characteristics. This study conducts numerical simulations on a chemical vapor deposition (CVD) reactor to explore the impact of process parameters on the growth rate and non‐uniformity of silicon. The investigation encompasses both the gas and surface reactions of the trichlorosilane‐hydrogen (TCS‐H2) system. The distributions of gas flow velocity, temperature, and main components are systematically studied by varying the process parameters, including susceptor temperature, inlet gas velocity, susceptor rotating speed, inlet gas temperature, upper wall temperature, and TCS mole fraction. Furthermore, the orthogonal test method is introduced to assess the effect of all parameters on the growth non‐uniformity. The results reveal that the inlet gas velocity and susceptor temperature have a significant influence on the growth rate and non‐uniformity. The silicon growth rate is primarily influenced by the TCS mole fraction, whereas the rotation speed of the substrate primarily influences the growth non‐uniformity of growth. Finally, the optimal scheme is proposed as valuable guidance for enhancing silicon chemical vapor deposition processes in industrial applications.

High bismuth-doped germanosilicate fiber for efficient E + S-band amplification.

Bismuth-doped germanosilicate fiber (BGSF), the active media of fiber amplifiers, has attracted widespread attention. Here, we report a BGSF with a high bismuth concentration of 0.075 wt. % and achieve high-efficiency E + S-band amplification, which was prepared by the modified chemical vapor deposition (MCVD) process. The small signal absorption (SSA) and unsaturated loss (UL) of BGSF at 1310 nm are 1.32 and 0.11 dB/m, respectively. The results show a record with only 45 m BGSF was created, to the best of our knowledge, which provides a maximum gain of 39.24 dB with an NF of 6.2 dB at 1430 nm under -20 dBm input signal power.