Laser Chemical Vapor Deposition Research Articles

Laser chemical vapor deposition of TiC fibers and tubes

Laser Chemical Vapor Deposition (LCVD) is a process in which fibers are deposited from a gaseous precursor to a solid phase under a traversing laser focal point. Here, we grow titanium carbide (TiC) fibers and tubes dependent upon a hyperbaric hydrogen-rich, hydrogen-balanced, and hydrogen-lean environment referenced to a titanium tetrachloride and ethylene gas mixture under three different laser intensities. X-ray diffraction confirms the deposition of TiC with energy dispersive spectroscopy noting a radial compositional gradient of titanium and carbon in the diameter of the deposit. Depending on the hydrogen concentration, the TiC encased a core carbon-rich fiber or formed a hollow tube, with these formations explained by thermophoresis. Furthermore, depending on the gas mixture and laser intensity, the carbon-rich interior and TiC outer shell exhibited different morphologies that are discussed in terms of growth rate regimes. The collective outcomes demonstrate the complex processing space in forming ceramic materials by LCVD.

The influence of the mass transport regime on laser chemical vapor deposited carbon fibers

Laser Chemical Vapor Deposition (LCVD) is a process through which fibers are additively deposited by the dissociation and deposition of a precursor gas into the solid phase under a translating laser focal point. In the hyperbaric pressure conditions, LCVD has two identified reaction regimes. The first being limited by surface reaction kinetics (SRK) and the second being limited by mass transport (MT). This article examines the effects of mass transport (MT) limitations on carbon fiber growth using either ethane (C2H6) or ethylene (C2H4). Both hydrocarbon precursors reveal a growth rate reduction when transitioning from SRK-to-MT to meet the no-slip condition in fluid dynamics. This transition correlates to a fiber microstructure change from a core shell morphology with a graphitic structure (SRK) to a nodular morphology with an amorphous structure (MT). The fiber fracture stress is generally found to be higher in the MT than SRK regime because of the reduction of easily cleaved graphitic planes in the MT fibers. Collectively, these results demonstrate the importance of the MT limited growth regime and how fiber characteristics can be manipulated when grown in this regime.

Improved Water Collection from Short-Term Fog on a Patterned Surface with Interconnected Microchannels.

Fog harvesting is considered a promising freshwater collection strategy for overcoming water scarcity, because of its environmental friendliness and strong sustainability. Typically, fogging occurs briefly at night and in the early morning in most arid and semiarid regions. However, studies on water collection from short-term fog are scarce. Herein, we developed a patterned surface with highly hydrophilic interconnected microchannels on a superhydrophobic surface to improve droplet convergence driven by the Young-Laplace pressure difference. With a rationally designed surface structure, the optimized water collection rate from mild fog could reach up to 67.31 g m-2 h-1 (6.731 mg cm-2 h-1) in 6 h; this value was over 130% higher than that observed on the pristine surface. The patterned surface with interconnected microchannels significantly shortened the startup time, which was counted from the fog contact to the first droplet falling from the fog-harvesting surface. The patterned surface was also facilely prepared via a controllable strategy combining laser ablation and chemical vapor deposition. The results obtained in outdoor environments indicate that the rationally designed surface has the potential for short-term fog harvesting. This work can be considered as a meaningful attempt to address the practical issues encountered in fog-harvesting research.

Atomic Layer Deposition of NiO Using Different Precursors with Different Oxygen Sources

NiO thin films have attracted tremendous attention owing to their outstanding chemical stability, good magnetic and catalytic properties1. It is also considered an efficient electrocatalyst for water oxidation, and is one of the few p-type semiconductive oxides with optical transparency due to its wide bandgap of 3.6 eV. Furthermore, NiO films can control high and low conductive states under an external electric field, which is very useful for developing resistance-switching random-access memory devices2.NiO films have been prepared by different deposition techniques, including sputtering, sol-gel, pulsed laser deposition, spray pyrolysis, and chemical vapor deposition (CVD), atomic layer deposition (ALD). Among these, ALD is a powerful technique to grow thin conformal films with fine-tuning of both composition and thickness. The commonly used nickel precursors for ALD process are Ni(Cp)2, Ni(MeCp)2, Ni(EtCp)2, Ni(dmamp)2, Ni(dmamb)2, Ni(acac)2, Ni(apo)2, Ni(dmg)2, Ni(thd)2, and Ni(amd)2 in combination with ozone, water, hydrogen peroxide, or oxygen plasma1. However, ALD of NiO is not well developed yet. The major disadvantages associated with these nickel precursors are low volatility, thermal instability, and poor reactivity or narrow ALD window. Some of these precursors are expensive or very difficult to synthesize. The aforementioned situations indicate that developing a new ALD process for the NiO film with new precursors is pertinent.In this work, we explored different Ni-precursors such as Ni ketoiminates, Ni(ipki)2 and Ni(eeki)2 (their synthesis has been proposed earlier3), and Alanis, provided by Air Liquide. These different reactants combined with different oxygen sources (H2O and O3) resulted in high-quality NiO thin films. Surface analyses indicate NiO films are stoichiometric. They are uniform and exhibit a columnar morphology as determined by TEM (Fig.1a). From the growth characteristics, it is found that the Ni precursors have a strong effect on the GPC. Similarly, the oxygen source affects GPC but it also influences the morphology of the layer leading to significant roughness variations (observed by XRR and AFM). The use of H2O can also result in a nucleation delay. Polycrystalline films are observed when the reaction temperature reaches 125°C, and the crystallinity is further enhanced with deposition temperature (Fig.1b). After comprehensive optimization of the ALD process with Alanis precursor, it has been possible to reach one of the highest growth rate of 1.5 Å/cy, which is nearly seven times higher than that obtained with Ni(EtCp)2 based reaction with the same ALD reactor and having a wide temperature window (100 to 175 °C) with ozone. The same precursor also reacted well with water, giving a GPC of 0.9 Å with an initial nucleation delay. With the use of Ni-ketoiminates, the growth rate could be enhanced considerably with a GPC of 0.7 Å in combination with O3 at a higher temperature.The NiO layers were subsequently used as catalysts for water photooxidation in alkaline medium. The electrochemical properties are better when compared to layers grown by PVD. References Y. Zhang, L. Du, X. Liu, and Y. Ding, A high growth rate atomic layer deposition process for nickel oxide film preparation using a combination of nickel (II) diketonate-diamine and ozone, App. Surf. Sci., 2019, 481, 138-143.H.L. Lu, G. Scarel, X.L. Li, M. Fanciulli, Thin MnO and NiO films grown using atomic layer deposition from ethylcyclopentadienyl type of precursors, J. Cryst. Growth, 2008, 310, 5464-5468.3. D. Zywitzki, D.H. Taffa, L. Lamkowski, M. Winter, D. Rogalla, M. Wark, and A. Devi, Tuning coordination geometry of nickel ketoiminates and its influence on thermal characteristics for chemical vapour deposition of nanostructured NiO electrocatalysts, Inorg. Chem., 2020,59, 14, 10059-10070. Figure 1

Laser-textured biomimetic copper leaf with structural-wettability dual gradient for efficient fog harvesting

Water collection has gradually become research hot topic owing to its potential for alleviating water shortages in arid areas. To date, numerous artificial materials with hierarchical structure have been fabricated to improve water-collecting efficiency. Here, a multi-bioinspired fog-harvesting artificial Cu-Leaf, deriving from Leaf skeletons, Namib desert beetle, and Cactus spines, is fabricated by ultrafast laser selective ablation, chemical etching and chemical vapor deposition, which achieve efficient water-collecting by combining fog capture, droplet growing and directional transportation together. The four-level wedge-shaped tracks of Cu-Leaf skeleton and its wetting property were finely adjusted and their correlations with the fog-harvesting capability were systematically studied. Force analysis related to fog capture, droplet growing and the droplet directional transportation on the hydrophobic/hydrophilic patterned skeleton surfaces have been highlighted. The optimal biomimetic Cu-Leaf performed superior fog-harvesting property with harvesting rate of 544.03 mg/h cm2, which is 2.5 times that of the original Cu sheet. Moreover, we designed an integrated fog-harvesting device (FHD) that could realize the dynamic fog-harvesting and efficient water storage. Therefore, this work enhances the understanding of the fundamental research and provides valuable strategy for design and preparation of sustainable and efficient fog harvesting systems.

Tribological properties of friction pairs under double composite surface configuration with diamond film and laser texture

A composite model, which combined diamond thin film with surface microstructure, was designed on the surface of silicon carbide by picosecond laser and hot filament chemical vapor deposition. And the multifunctional friction and wear tester was used to study the tribological performance of the friction pair (silicon carbide-graphite) under oil-poor conditions to examine the tribological performance of the friction pair in terms of surface temperature rise and time-varying wear. The results show that the friction coefficient under the composite modeling of surface microstructure and diamond film reaches 0.009, and at the same time, the surface temperature of the composite modeling is only 61.2 ℃, which is 5.1% lower than that of only diamond film and 62.1% lower than that of no surface treatment, which indicates that the high frictional heat has caused a significant graphitization transition in the film. And the surface of the friction sub-surface with the lowest temperature (surface microstructure and diamond thin film composite modeling) kept the carbon content at more than 90% without the formation of Si-C bonding, which guaranteed the complete carbon friction transfer film; At the same time, the ID/IG ratio of the friction surface under the composite modeling of the surface microstructure and diamond film is about 0.06 at the abrasion mark, the ID/IG ratio of the diamond film only is about 0.33, and the ID/IG ratio of the friction surface without any surface treatment is about 1.37. Transient high temperatures lead to abrasion and localized spalling on the surface of friction pairs, causing graphite oxidation to become progressively more severe, thus transforming abrasive wear into adhesive wear. As a result, double composite surface configuration with diamond film and laser texture further reduced the transient temperature rise of the surface and improved the tribological performance of the friction pairs.

Preparation of silicon carbide and tantalum carbonitride composite with high hardness and moderate elastic modulus by laser chemical vapor deposition for anti-erosion protective coatings

Maintaining the harness of silicon carbide (SiC), while reducing Young's modulus of ceramic coatings is crucial for developing highly durable coating systems. This study demonstrated the growth of SiC and tantalum carbonitride (TaCN) composite films with high hardness and low modulus using laser-assisted chemical vapor deposition (CVD) with metal-organic precursors. The effects of deposition temperature on phases, chemical compositions, binding states, microstructures and mechanical properties were investigated. The film prepared at a deposition temperature of 1100 °C were grown at a deposition rate of 81.8 μm h−1, which comprised low-crystallinity SiC and TaCN grains smaller than 10 nm finely mixed and dispersed each other, forming a nanometric mosaic structure. The cross-sectional nanoindentation tests revealed a reduced Young's modulus (E*) of 238.2 GPa and a hardness (H) of 30.4 GPa, corresponding to H/E* and H3/E*2 values of 0.127 and 0.493 GPa, respectively. The SiC–TaCN nanocomposite film exhibited superior durability in erosion tests using a zirconia slurry at 20 kPa, compared with a monolithic SiC film and a silicon nitride substrate.

Research on the Morphology of Lithium Aluminate Films Prepared by Laser Chemical Vapor Deposition

Research on the Morphology of Lithium Aluminate Films Prepared by Laser Chemical Vapor Deposition

Additively manufactured characteristics of carbon fibers deposited from alkane precursors

Laser Chemical Vapor Deposition (LCVD) is an additive processing technique in which freestanding fibers are deposited. This is accomplished by the thermal dissociation of a precursor gas under a translating laser focal point. In this study the relationships between deposited carbon fiber growth regimes based on precursor chemistry, microstructure, mechanical properties, and processing conditions are compared. The precursor gases include gases from the alkane family, i.e., methane (CH4), ethane (C2H6), and propane (C3H8) and the alkene family, i.e., ethylene (C2H4). Each of these gases offer differences in molecular geometry, the amount of carbon and hydrogen present per molecule, and molecular weight. In the hyperbaric growth condition, these variances reveal different abilities to access either the surface-reaction kinetic limited or mass transport limited growth regimes. The deposited fibers morphology revealed either a core shell or nodular structure with each of these morphologies a function of the accessible growth regime. The fracture stress for the different fibers, in each of the accessible growth regimes, are compared revealing a strength dependence that is linked to the extent of graphitization (via Raman spectroscopy characterization). Collectively, these outcomes fundamentally address how precursor chemistry is a critical variable in the manipulation of the processing-structure-property space in LCVD carbon fibers.

High-speed deposition of silicon nitride thick films via halide laser chemical vapor deposition

High-speed deposition of silicon nitride thick films via halide laser chemical vapor deposition

Graphene/SiC composite porous electrodes for high-performance micro-supercapacitors

Micro-supercapacitor (MSC) electrodes prepared by chemical vapor deposition (CVD) possess high potential as on-chip integrated micro-power sources for future microdevices. In this study, porous graphene/SiC composite films are grown using laser CVD. A double-layer specific capacitance up to 219.3 mF/cm2 is achieved at 10 mV/s, which is 26 times higher than those of the electrodes prepared by CVD with the same energy storage mechanism reported in literatures. After 20000 charge-discharge cycles at room temperature (20 °C) and variable temperatures (0–60 °C), the electrode exhibits robust cycling stability with 99.9% and 109.6% capacitance retention, respectively. Subsequently, it is revealed that the abundance of graphene on the SiC porous skeleton plays a key role in promoting the capacitance enhancement. The strong structure of SiC as well as the strong adhesion between graphene and SiC guarantee the excellent cycling stability. Evidently, the preparation of graphene/SiC porous composite films as MSC electrodes is a highly promising route for fabricating high-performance and reliable on-chip power sources for future miniaturized devices.

Nanostructured Vanadium Dioxide Materials for Optical Sensing Applications.

Vanadium dioxide (VO2) is one of the strongly correlated materials exhibiting a reversible insulator-metal phase transition accompanied by a structural transition from a low-temperature monoclinic phase to high-temperature rutile phase near room temperature. Due to the dramatic change in electrical resistance and optical transmittance of VO2, it has attracted considerable attention towards the electronic and optical device applications, such as switching devices, memory devices, memristors, smart windows, sensors, actuators, etc. The present review provides an overview of several methods for the synthesis of nanostructured VO2, such as solution-based chemical approaches (sol-gel process and hydrothermal synthesis) and gas or vapor phase synthesis techniques (pulsed laser deposition, sputtering method, and chemical vapor deposition). This review also presents stoichiometry, strain, and doping engineering as modulation strategies of physical properties for nanostructured VO2. In particular, this review describes ultraviolet-visible-near infrared photodetectors, optical switches, and color modulators as optical sensing applications associated with nanostructured VO2 materials. Finally, current research trends and perspectives are also discussed.

SiC/Graphene Film by Laser CVD as an Implantable Sensor Material for Dopamine Detection.

Implantable electrochemical sensor holds great promise in the real-time monitoring of dopamine (DA) to regulate body function. However, the real application of these sensors is limited by the weak current signal of DA in the human body and the poor compatibility of the on-chip microelectronic devices. In this work, a SiC/graphene composite film was fabricated using laser chemical vapor deposition (LCVD) and employed as a DA sensor. The graphene in the porous nanoforest-like SiC framework offered efficient channels for electronic transmission, leading to an enhanced electron transfer rate and consequently an increased current response for DA detection. The three-dimensional (3D) porous network also facilitated the exposure of more catalytic active sites toward DA oxidation. Besides, the wide distribution of graphene in the nanoforest-like SiC films reduced the interfacial resistance of the charge transfer. The SiC/graphene composite film exhibited excellent electrocatalytic activity toward DA oxidation with a low detection limit of 0.11 μM and a high sensitivity of 0.86 μA·μM-1·cm-2. The film electrode also showed a wide linear response for DA in 0.5-78 μM, along with good selectivity, repeatability, and reproducibility. Furthermore, the cell counting kit-8 (CCK-8) and live-dead assays revealed that the film is also biocompatible for biomedical applications. Therefore, the nanoforest-like SiC/graphene composite film via the CVD process enables a promising candidate for an integrated miniature DA biosensor with high detection performance.

Tio2 and Nickel Coatings on Resistance Welding Electodrs to exetended Life Using Chemical Vapour Desposition Process

TiO2/Ni coating has been deposited onto the electrodes by chemical vapour deposition to improve electrode life during resistance welding of Zn- coated steels. However, welding results revealed that molten Zn penetrates into coating through the cracks and then reacts with substrate copper alloy to form brasses. In the present work, laser treatment was performed on the TiO2/Ni coated electrodes to eliminate cracks formed in the as-deposited TiO2/Ni coating. In addition, a chemical vapour deposition of Ni, TiO2/Ni and Ni has also been carried out to improve coating quality. On the other hand, a Ti coating was also investigated. Those coatings were characterized by electro-microscopy, energy- dispersive X-ray analysis, X-ray diffraction and micro-hardness tests. The results showed that cracks within the as-deposited TiO2/Ni coating could be eliminated with the use of laser treatment and chemical vapour deposition process. However, softening of copper substrate after laser treatment was a problem that restricted welding performance. Welding tests showed that the multi-layer TiO2/Ni coating acted as a better barrier to decrease alloying between the copper alloy and molten Zn as well as pitting (erosion) of electrode. The TiO2 coating demonstrates its potential application on the electrode to further improve the electrode’s life Key Word: Electrode; Molecular; Titanium; Nanotechnology; Nickel.

Laser CVD Growth of Uniquely -oriented β-Ga2 O3 Films on Quartz Substrate with Ultrafast Photoelectric Response.

The oriented growth of β-Ga2 O3 films has triggered extensive interest due to the remarkable and complex anisotropy found in the β-Ga2 O3 bulks. Remarkable properties, including stronger solar-blind ultraviolet (SBUV) absorption, better mobility, and higher thermal conductivity, are usually observed along <010> direction as compared to other low-index axes. So far, <010>-oriented β-Ga2 O3 film growth has been hindered by the lack of suitable substrates and higher surface energy of the (010) crystal plane. Herein, the first growth of uniquely <010>-oriented β-Ga2 O3 films on quartz substrates by laser chemical vapor deposition (LCVD) are reported. By investigating the effects of deposition temperature (Tdep ) and O2 flow rate (RO2 ) on the growth of β-Ga2 O3 films, it is found that the formation of <010> orientation is closely related to the higher stability of oxygen close-packed planes under O-rich condition. As a result, a grain size of up to ≈2µm and a deposition rate of up to ≈ 40µm h-1 are obtained. Metal-semiconductor-metal (MSM) type detector based on <010>-oriented β-Ga2 O3 film exhibits ultra-fast response speed, 1-2 orders of magnitude higher than those of most detectors based on β-Ga2 O3 films with other orientations.

Graphene/SiC-coated textiles with excellent electromagnetic interference shielding, Joule heating, high-temperature resistance, and pressure-sensing performances

Multifunctional, wearable, and durable textiles integrated with smart electronics have attracted tremendous attention. However, it remains a great challenge to balance new functionalities with high temperature stability. Herein, textile-based pressure-sensors with excellent electromagnetic interference (EMI) shielding, Joule heating and high temperature resistance were fabricated by constructing graphene/SiC (G/SiC) heterostructures on carbon cloth via laser chemical vapor deposition (LCVD). The resultant textile exhibited excellent EMI efficiency of 74.2 dB with a thickness of 0.45 mm, Joule heating performance within low working voltage range of 1 to 3 V and fast response time within 20 s. These properties arose from multiple reflections, interfacial polarizations and high conductivity due to the numerous amounts of nanoscale G/SiC heterostructures. More importantly, the G/SiC/CFs demonstrated well high temperature resistance with a <em>T</em>_HRI of 380.16 ^oC owing to the protection of the coating layer on the carbon fibers upon oxidation. Meanwhile, the G/SiC/CFs presented good pressure-sensing performance with a high sensitivity of 52.93 kPa⁻¹, fast response time of 85 ms and wide pressure range up to 186 kPa. These features imply the potential of G/SiC/CFs as an efficient EMI shielding, electrical heater and piezoresistive sensor textiles.

Optimizing Electromagnetic Interference Shielding of Ultrathin Nanoheterostructure Textiles through Interfacial Engineering.

Strong electromagnetic wave reflection loss concomitant with second emission pollution limits the wide applications of electromagnetic interference (EMI) shielding textiles. Decoration of textiles by using various dielectric materials has been found efficient for the development of highly efficient EMI shielding textiles, but it is still a challenge to obtain EMI shielding composites with thin thickness. A route of interfacial engineering may offer a twist to overcome these obstacles. Here, we fabricated a Ni nanoparticle/SiC nanowhisker/carbon cloth nanoheterostructure, where SiC nanowhiskers were deposited by a simple manufacturing method, namely, laser chemical vapor deposition (LCVD), directly grown on carbon cloth. Through directly constructing a Ni/SiC interface, we find that the formation of Schottky contact can influence the interfacial polarization associated with the generation of dipole electric fields, leading to an enhancement of dielectric loss. A striking feature of this interfacial engineering strategy is able to enhance the absorption of the incident electromagnetic wave while suppressing the reflection. As a result, our Ni/SiC/carbon cloth exhibits an excellent EMI shielding effectiveness of 68.6 dB with a thickness of only 0.39 mm, as well as high flexibility and long-term duration stability benefited from the outstanding mechanical properties of SiC nanowiskers, showing potential for EMI shielding applications.

A.C. impedance of γ-LiAlO2 film prepared by laser CVD

(110)-oriented γ-LiAlO₂ film consisting of granular grains was prepared by laser CVD. The complex impedance of polycrystalline γ-LiAlO₂ film showed dispersions due to bulk, grain-boundary and electrode. Temperature dependence of the electrical conductivity for γ-LiAlO₂film, polycrystalline sintered sample and single crystals obeyed Arrhenius behaviour. The electrical conductivity (σT) of the γ-LiAlO₂ film reached 196 S∙m^-1∙K at 1173 K, nearly 5 times higher than the maximum value of γ-LiAlO₂ single crystals and polycrystalline sintered samples.

Status, issues and prospectives of lithium aluminates solid electrolyte including beta alumina in the form of film

Li-Beta alumina exhibited higher ionic conductivity than other lithium aluminate phases of LiAl₅O₈, LiAlO₂ and Li₅AlO₄ because of the special crystal structure having many conduction channels in c-plane. It is usually used as solid electrolyte in Battery. Compared with bulk and powder, Li-Beta alumina film takes advantages of decrease in area specific resistance, reduction of operating temperature, reduction of size/weight for battery and enhancement of battery cycle life. Laser chemical vapour deposition is used to achieve the first synthesis of Li-Beta alumina in form of film, which exhibits a high conductivity of 5.96 S∙m^-1∙K at room temperature. In this process, the remained issue of Li loss is essential to be fixed for large-scale production.

Synthesis of beta alumina films using the process of chemical vapor deposition under lithium-rich atmosphere

This study demonstrates the growth of Li-β-alumina films by laser chemical vapor deposition and investigates the effects of deposition temperature (T_dep), molar ratio of Li/Al (R_Li/Al) and total pressure (P_tot) on the phase formation, microstructure, orientations and deposition rate (R_dep) of the film. Single-phase Li-β-alumina films were deposited at T_dep = 1100 K–1300 K, R_Li/Al = 20–50 and P_tot = 600–1000 Pa. Li-β-alumina films with the hexagonally faceted platelet morphology (flake-like) were deposited at P_tot = 1000 Pa, whereas bulky grains were formed at P_tot=600 Pa. The maximum R_dep of Li-β-alumina films was 30 μm h⁻¹ at Tdep=1225 K, R_Li/Al=30 and P_tot=600 Pa. At room temperature the ionic conductivity of Li-β-alumina film prepared by laser CVD reached 2×10^-4 S/cm, demonstrating superior performance and significant potential in lithium battery.