Advancements in Plasma-Enhanced Chemical Vapor Deposition for Producing Vertical Graphene Nanowalls.

In recent years, vertical graphene nanowalls (VGNWs) have gained significant attention due to their exceptional properties, including their high specific surface area, excellent electrical conductivity, scalability, and compatibility with transition metal compounds. These attributes position VGNWs as a compelling choice for various applications, such as energy storage, catalysis, and sensing, driving interest in their integration into next-generation commercial graphene-based devices. Among the diverse graphene synthesis methods, plasma-enhanced chemical vapor deposition (PECVD) stands out for its ability to create large-scale graphene films and VGNWs on diverse substrates. However, despite progress in optimizing the growth conditions to achieve micrometer-sized graphene nanowalls, a comprehensive understanding of the underlying physicochemical mechanisms that govern nanostructure formation remains elusive. Specifically, a deeper exploration of nanometric-level phenomena like nucleation, carbon precursor adsorption, and adatom surface diffusion is crucial for gaining precise control over the growth process. Hydrogen's dual role as a co-catalyst and etchant in VGNW growth requires further investigation. This review aims to fill the knowledge gaps by investigating VGNW nucleation and growth using PECVD, with a focus on the impact of the temperature on the growth ratio and nucleation density across a broad temperature range. By providing insights into the PECVD process, this review aims to optimize the growth conditions for tailoring VGNW properties, facilitating applications in the fields of energy storage, catalysis, and sensing.

Back-End-of-Line Compatible Large-Area Molybdenum Disulfide Grown on Flexible Substrate: Enabling High-Performance Low-Power Memristor Applications.

Transition-metal dichalcogenides (TMDs) in flexible technology can offer large-area scalability and high-density integration with a low power consumption. However, incorporating large-area TMDs in a flexible platform is lacking in state-of-the-art data storage technology owing to the high process temperature of TMDs. Low-temperature growth of TMDs can bridge mass production in flexible technology and reduce the complexity of the transferring process. Here, we introduce a crossbar memory array enabled by low-temperature (250 °C) plasma-assisted chemical vapor deposited MoS2 directly grown on a flexible substrate. The low-temperature sulfurization induces nanograins of MoS2 with multiple grain boundaries, allowing the path for charge particles, which leads to the formation of conducting filaments. The back-end-of-line compatible MoS2-based crossbar memristors exhibit robust resistance switching (RS) behavior with a high on/off current ratio of approximately ∼105, excellent endurance (>350 cycles), retention (>200000 s), and low operating voltage (∼±0.5 V). Furthermore, the MoS2 synthesized at low temperature on a flexible substrate facilitates RS characteristics demonstrated under strain states and exhibits excellent RS performance. Thus, the use of direct-grown MoS2 on a polyimide (PI) substrate for high-performance cross-bar memristors can transform emerging flexible electronics.

Large-Scale Plasma-Polymerized Hexamethyldisiloxane Thin Films: Role of Interelectrode Distance and Excellent Corrosion Resistance.

In comparison to the more traditional anticorrosion thin film coatings, the plasma polymerization approach offered a more efficient, dry, and straightforward procedure that made it possible to create dense films of several hundred nanometers in thickness, which has potential applications in metallic implant materials. In this paper, large-scale plasma polymerized hexamethyldisiloxane (ppHMDSO) thin film coatings were deposited on stainless steel substrates at different electrode distances to improve their corrosion resistance. The physicochemical properties and corrosion resistance of the ppHMDSO thin films as prepared at different electrode distances were characterized and gauged utilizing various characterization means. The results indicate that decreasing electrode distance accelerates monomer fragmentation and increases the oxidation process. The deposition rate and roughness of the ppHMDSO films both decreased as the electrode distance increased, while the carbonaceous group and hydrophobicity of the films enhanced. The ppHMDSO film prepared at an electrode distance of 40 mm obtained excellent elastic recovery and wear resistance and had an improved corrosion resistance, resulting in a reduction of 75% of the original corrosion behavior against the corrosion in Hank's solution. The resulting large-scale ppHMDSO thin film coatings can be further employed in implants for tissue engineering and biomaterials.

Enhancement of Room Temperature Ethanol Sensing by Optimizing the Density of Vertically Aligned Carbon Nanofibers Decorated with Gold Nanoparticles.

An ethanol gas sensor based on carbon nanofibers (CNFs) with various densities and nanoparticle functionalization was investigated. The CNFs were grown by means of a Plasma-Enhanced Chemical Vapor Deposition (PECVD), and the synthesis conditions were varied to obtain different number of fibers per unit area. The devices with a larger density of CNFs lead to higher responses, with a maximal responsivity of 10%. Furthermore, to simultaneously improve the sensitivity and selectivity, CNFs were decorated with gold nanoparticles by an impaction printing method. After metal decoration, the devices showed a response 300% higher than pristine devices toward 5 ppm of ethanol gas. The morphology and structure of the different samples deposited on a silicon substrate were characterized by TEM, EDX, SEM, and Raman spectroscopy, and the results confirmed the presence of CNF decorated with gold. The influence of operating temperature (OT) and humidity were studied on the sensing devices. In the case of decorated samples with a high density of nanofibers, a less-strong cross-sensitivity was observed toward a variation in humidity and temperature.

Low-Temperature and Large-Scale Production of a Transition Metal Sulfide Vertical Heterostructure and Its Application for Photodetectors.

The conventional synthesis of two-dimensional (2D) transition metal dichalcogenide (TMDC) heterostructures is low yielding and lack the heterojunction interface quality. The chemical vapor deposition (CVD) techniques have achieved high-quality heterostructure interfaces but require a high synthesis temperature (>600 °C) and have a low yield of heterostructures. Therefore, the large scale and high interface quality of TMDC heterojunctions using low-temperature synthesis methods are in demand. Here, high-quality, wafer-scale MoS2 and WS2 heterostructures with 2D interfaces were prepared by a one-step sulfurization of the molybdenum (Mo) and tungsten (W) precursors via plasma-enhanced CVD at a relatively low temperature (150 °C). The 4 inch wafer-scale synthesis of the MoS2-WS2 heterostructures was validated using various spectroscopic and microscopic techniques. Further, the photocurrent generation and photoswitching phenomenon of the so-obtained MoS2-WS2 heterostructures were studied. The photodevice prepared by the MoS2-WS2 heterostructures at 150 °C showed a photoresponsivity of 83.75 mA/W. The excellent photoresponse and faster photoswitching highlight the advantage of MoS2-WS2 heterostructures toward advanced photodetectors.

Low-Temperature Synthesis of Wafer-Scale MoS2-WS2 Vertical Heterostructures by Single-Step Penetrative Plasma Sulfurization.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted considerable attention owing to their synergetic effects with other 2D materials, such as graphene and hexagonal boron nitride, in TMD-based heterostructures. Therefore, it is important to understand the physical properties of TMD-TMD vertical heterostructures for their applications in next-generation electronic devices. However, the conventional synthesis process of TMD-TMD heterostructures has some critical limitations, such as nonreproducibility and low yield. In this paper, we synthesize wafer-scale MoS2-WS2 vertical heterostructures (MWVHs) using plasma-enhanced chemical vapor deposition (PE-CVD) via penetrative single-step sulfurization discovered by time-dependent analysis. This method is available for fabricating uniform large-area vertical heterostructures (4 in.) at a low temperature (300 °C). MWVHs were characterized using various spectroscopic and microscopic techniques, which revealed their uniform nanoscale polycrystallinity and the presence of vertical layers of MoS2 and WS2. In addition, wafer-scale MWVHs diodes were fabricated and demonstrated uniform performance by current mapping. Furthermore, mode I fracture tests were performed using large double cantilever beam specimens to confirm the separation of the MWVHs from the SiO2/Si substrate. Therefore, this study proposes a synthesis mechanism for TMD-TMD heterostructures and provides a fundamental understanding of the interfacial properties of TMD-TMD vertical heterostructures.

One-step synthesis of carbon-supported electrocatalysts.

Cost-efficiency, durability, and reliability of catalysts, as well as their operational lifetime, are the main challenges in chemical energy conversion. Here, we present a novel, one-step approach for the synthesis of Pt/C hybrid material by plasma-enhanced chemical vapor deposition (PE-CVD). The platinum loading, degree of oxidation, and the very narrow particle size distribution are precisely adjusted in the Pt/C hybrid material due to the simultaneous deposition of platinum and carbon during the process. The as-synthesized Pt/C hybrid materials are promising electrocatalysts for use in fuel cell applications as they show significantly improved electrochemical long-term stability compared to the industrial standard HiSPEC 4000. The PE-CVD process is furthermore expected to be extendable to the general deposition of metal-containing carbon materials from other commercially available metal acetylacetonate precursors.

Deposition Kinetics of Thin Silica-Like Coatings in a Large Plasma Reactor.

An industrial size plasma reactor of 5 m3 volume was used to study the deposition of silica-like coatings by the plasma-enhanced chemical vapor deposition (PECVD) method. The plasma was sustained by an asymmetrical capacitively coupled radio-frequency discharge at a frequency of 40 kHz and power up to 7 kW. Hexamethyldisilioxane (HMDSO) was introduced continuously at different flows of up to 200 sccm upon pumping with a combination of roots and rotary pumps at an effective pumping speed between 25 and 70 L/s to enable suitable gas residence time in the plasma reactor. The deposition rate and ion density were measured continuously during the plasma process. Both parameters were almost perfectly constant with time, and the deposition rate increased linearly in the range of HMDSO flows from 25 to 160 sccm. The plasma density was of the order of 1014 m-3, indicating an extremely low ionization fraction which decreased with increasing flow from approximately 2 × 10-7 to 6 × 10-8. The correlations between the processing parameters and the properties of deposited films are drawn and discussed.

Highly Efficient Nanocarbon Coating Layer on the Nanostructured Copper Sulfide-Metal Organic Framework Derived Carbon for Advanced Sodium-Ion Battery Anode.

High theoretical capacity and low-cost copper sulfide (CuxS)-based anodes have gained great attention for advanced sodium-ion batteries (SIBs). However, their practical application may be hindered due to their unstable cycling performance and problems with the dissolution of sodium sulfides (NaxS) into electrolyte. Here, we employed metal organic framework (MOF-199) as a sacrificial template to fabricate nanoporous CuxS with a large surface area embedded in the MOF-derived carbon network (CuxS-C) through a two-step process of sulfurization and carbonization via H2S gas-assisted plasma-enhanced chemical vapor deposition (PECVD) processing. Subsequently, we uniformly coated a nanocarbon layer on the Cu1.8S-C through hydrothermal and subsequent annealing processes. The physico-chemical properties of the nanocarbon layer were revealed by the analytical techniques of high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). We acquired a higher SIB performance (capacity retention (~93%) with a specific capacity of 372 mAh/g over 110 cycles) of the nanoporous Cu1.8S-C/C core/shell anode materials than that of pure Cu1.8S-C. This encouraging SIB performance is attributed to the key roles of a nanocarbon layer coated on the Cu1.8S-C to accommodate the volume variation of the Cu1.8S-C anode structure during cycling, enhance electrical conductivity and prevent the dissolution of NaxS into the electrolyte. With these physico-chemical and electrochemical properties, we ensure that the Cu1.8S-C/C structure will be a promising anode material for large-scale and advanced SIBs.

Synthetic anionic surfaces can replace microparticles in stimulating burst coagulation of blood plasma.

Biomaterials are frequently evaluated for pro-coagulant activity but usually in the presence of microparticles (MPs), cell-derived vesicles in blood plasma whose phospholipid surfaces allow coagulation factors to set up as functional assemblies. We tested the hypothesis that synthetic anionic surfaces can catalyze burst thrombin activation in human blood plasma in the absence of MPs. In a thromboelastography (TEG) assay with plastic sample cups and pins, recalcified human citrated platelet-poor plasma spontaneously burst-coagulated but with an unpredictable clotting time whereas plasma depleted of MPs by ultracentrifugation failed to coagulate. Coagulation of MP-depleted plasma was restored in a dose-dependent manner by glass microbeads, hydroxyapatite nanoparticles (HA NPs), and carboxylic acid-containing anionic nanocoatings of TEG cups and pins (coated by glow-discharge plasma-polymerized ethylene containing oxygen, L-PPE:O with 4.4 and 6.8 atomic % [COOH]). Glass beads lost their pro-coagulant activity in MP-depleted plasma after their surfaces were nanocoated with hydrophobic plasma-polymerized hexamethyl disiloxane (PP-HMDSO). In FXII-depleted MP-depleted plasma, glass microbeads failed to induce coagulation, however, FXIa was sufficient to induce coagulation in a dose-dependent manner, with no effect of glass beads. These data suggest that anionic surfaces of crystalline, organic, and amorphous solid synthetic materials catalyze explosive thrombin generation in MP-depleted plasma by activating the FXII-dependent intrinsic contact pathway. The data also show that microparticles are pro-coagulant surfaces whose activity has been largely overlooked in many coagulation studies to-date. These results suggest a possible mechanism by which anionic biomaterial surfaces induce bone healing by contact osteogenesis, through fibrin clot formation in the absence of platelet activation.

In Situ Synthesis of Vertical Standing Nanosized NiO Encapsulated in Graphene as Electrodes for High-Performance Supercapacitors.

NiO is a promising electrode material for supercapacitors. Herein, the novel vertically standing nanosized NiO encapsulated in graphene layers (G@NiO) are rationally designed and synthesized as nanosheet arrays. This unique vertical standing structure of G@NiO nanosheet arrays can enlarge the accessible surface area with electrolytes, and has the benefits of short ion diffusion path and good charge transport. Further, an interconnected graphene conductive network acts as binder to encapsulate the nanosized NiO particles as core-shell structure, which can promote the charge transport and maintain the structural stability. Consequently, the optimized G@NiO hybrid electrodes exhibit a remarkably enhanced specific capacity up to 1073 C g-1 and excellent cycling stability. This study provides a facial strategy to design and construct high-performance metal oxides for energy storage.

Fabrication of SiNx Thin Film of Micro Dielectric Barrier Discharge Reactor for Maskless Nanoscale Etching.

The prevention of glow-to-arc transition exhibited by micro dielectric barrier discharge (MDBD), as well as its long lifetime, has generated much excitement across a variety of applications. Silicon nitride (SiNx) is often used as a dielectric barrier layer in DBD due to its excellent chemical inertness and high electrical permittivity. However, during fabrication of the MDBD devices with multilayer films for maskless nano etching, the residual stress-induced deformation may bring cracks or wrinkles of the devices after depositing SiNx by plasma enhanced chemical vapor deposition (PECVD). Considering that the residual stress of SiNx can be tailored from compressive stress to tensile stress under different PECVD deposition parameters, in order to minimize the stress-induced deformation and avoid cracks or wrinkles of the MDBD device, we experimentally measured stress in each thin film of a MDBD device, then used numerical simulation to analyze and obtain the minimum deformation of multilayer films when the intrinsic stress of SiNx is -200 MPa compressive stress. The stress of SiNx can be tailored to the desired value by tuning the deposition parameters of the SiNx film, such as the silane (SiH4)⁻ammonia (NH3) flow ratio, radio frequency (RF) power, chamber pressure, and deposition temperature. Finally, we used the optimum PECVD process parameters to successfully fabricate a MDBD device with good quality.

Low-Temperature Synthesis of Large-Scale Molybdenum Disulfide Thin Films Directly on a Plastic Substrate Using Plasma-Enhanced Chemical Vapor Deposition.

By plasma-enhanced chemical vapor deposition, a molybdenum disulfide (MoS2 ) thin film is synthesized directly on a wafer-scale plastic substrate at below 300 °C. The carrier mobility of the films is 3.74 cm(2) V(-1) s(-1) . Also, humidity is successfully detected with MoS2 -based sensors fabricated on the flexible substrate, which reveals its potential for flexible sensing devices.

Osteoblasts Interaction with PLGA Membranes Functionalized with Titanium Film Nanolayer by PECVD. In vitro Assessment of Surface Influence on Cell Adhesion during Initial Cell to Material Interaction.

New biomaterials for Guided Bone Regeneration (GBR), both resorbable and non-resorbable, are being developed to stimulate bone tissue formation. Thus, the in vitro study of cell behavior towards material surface properties turns a prerequisite to assess both biocompatibility and bioactivity of any material intended to be used for clinical purposes. For this purpose, we have developed in vitro studies on normal human osteoblasts (HOB®) HOB® osteoblasts grown on a resorbable Poly (lactide-co-glycolide) (PLGA) membrane foil functionalized by a very thin film (around 15 nm) of TiO2 (i.e., TiO2/PLGA membranes), designed to be used as barrier membrane. To avoid any alteration of the membranes, the titanium films were deposited at room temperature in one step by plasma enhanced chemical vapour deposition. Characterization of the functionalized membranes proved that the thin titanium layer completely covers the PLGA foils that remains practically unmodified in their interior after the deposition process and stands the standard sterilization protocols. Both morphological changes and cytoskeletal reorganization, together with the focal adhesion development observed in HOB osteoblasts, significantly related to TiO2 treated PLGA in which the Ti deposition method described has revealed to be a valuable tool to increase bioactivity of PLGA membranes, by combining cell nanotopography cues with the incorporation of bioactive factors.