In this paper, diamond-like carbon (DLC) coatings with AlCrSi co-doping were deposited by a reactive high power impulse magnetron sputtering (HiPIMS) with utilizing a gas mixture of Ar and C2H2 as ...the precursor. The doping contents of Al, Cr and Si in the coatings were controlled by adjusting the C2H2 flow fraction in the gas mixture. The influences of the HiPIMS frequency and C2H2 flow on the microstructure, composition, mechanical properties and tribological behaviors of the AlCrSi-DLC coatings were researched carefully by using scanning electron microscope, X-ray photoelectron spectroscopy, nano-indentation and ball-on-plate tribometer, respectively. The results show that the doping AlCrSi contents increased as the C2H2 flow fraction decreased, along with the obvious structural transformation of the coatings from amorphous feature to carbide composites. The high C2H2 flow fraction tends to cause the target poisoning, resulting in the instability of the coating composition and the appearance of macro-droplets on the coating surface. The high pulse repeating frequency can effectively prevent the poisoning of the metal target and avoid the form of the arcing even at high C2H2 fraction, which is conducive to control the doping contents of the metal atoms and improve the surface quality of the AlCrSi-DLC coatings. In addition, the high frequency can facilitate the formation of the carbide, which has been expected to improve the hardness of the coatings. However, the existence of a mass of carbide phase causes serious abrasive wear of the coatings at low C2H2 fraction.
•Diamond-like carbon (DLC) coatings with AlCrSi co-doping were deposited.•Effect of the power frequency and C2H2 fraction on the DLC coatings was studied.•High C2H2 fraction causes the formation of the macro-droplets on the coating surface.•High frequency effectively prevents the poisoning of the metal target.
Area-selective atomic layer deposition (AS-ALD) is a promising bottom-up patterning approach for fabricating conformal thin films. One of the current challenges with respect to AS-ALD is the ...deficiency of the surface inhibitor used for fabricating nanoscale three-dimensional structures. In this study, a vapor-deliverable small inhibitor called ethanethiol (ET) that thermally adsorbs on surfaces was used for the AS-ALD of Al2O3. The inhibitor selectively adsorbed on Co and Cu substrates but not on the SiO2 substrate, allowing for the selective deactivation of Co and Cu substrates in Al2O3 ALD. The use of dimethylaluminum isopropoxide (DMAI) as the Al precursor resulted in better inhibition than the use of trimethylaluminum (TMA). Various experimental and theoretical methods, including water contact angle measurements, spectroscopic ellipsometry, X-ray photoelectron spectroscopy, density functional theory calculations, and Monte Carlo simulations, were used to elucidate the process of AS-ALD using ET. Dimerization of the DMAI precursor is considered to be a governing factor for its high deposition selectivity, while the probability of this phenomenon is very low for the TMA precursor. The current study provides insight into the selectivity of AS-ALD from the perspective of the chemical reaction and an opportunity to improve selectivity via precursor selection.
Pt thin films, using the Pt precursor, dimethyl(N,N-dimethyl-3-butene-1-amine-N)platinum (DDAP, C8H19NPt), were deposited by atomic layer deposition (ALD). The growth characteristics of the Pt thin ...films were systemically investigated. A saturated growth rate was obtained with an increase in precursor and reactant pulse times, revealing the nature of the ALD self-limiting process. The growth rate increased with increasing deposition temperature and finally became saturated above 280 °C, showing a high growth rate of 0.85 Å/cycle. The short incubation time for Pt nucleation promoted the growth characteristics, which can be favorable for catalytic applications. The high reactivity and small adsorbate size produced the relatively high growth rate of the Pt thin films deposited with the DDAP precursor. A very low resistivity, close to the value of bulk Pt, was obtained for all Pt thin films deposited at various temperatures. The low resistivity was due to the similar crystalline structure and very high purity of the Pt thin films at all deposition temperatures explored in this study. In addition, Pt thin films were also deposited on a high-aspect-ratio substrate and showed good uniformity and step coverage, with a constant work function, which can be promising for electrode applications. Synthesis of Pt films by ALD using the DDAP Pt precursor and O2 is a noteworthy approach for obtaining films with a high growth rate and low resistivity.
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•TiN protective layer was prepared by PEALD method on SS316L for bipolar plates of PEMFCs.•PEALD-TiN thin films using TDMAT and TiCl4 were carefully investigated and compared.•The ...corrosion protective property of TiN thin films using TDMAT was better than that using TiCl4.
The stainless steel (SS)-based bipolar plate with high conductivity and corrosion resistance is one of the key components in recent polymer electrolyte membrane fuel cells. Therefore, an excellent corrosion protection and good electrical conductivity in SS316L-based bipolar plates can be achieved through plasma-enhanced atomic layer deposition (PEALD) of ultrathin (25–67 nm) TiN thin films. To this end, two types of TiN protective coatings deposited by PEALD using tetrakis(dimethylamino)titanium (TDMAT) and titanium tetrachloride (TiCl4) precursors were evaluated; the evaluations were conducted under conditions simulating the operating conditions of PEMFCs. Regardless of the precursor type, PEALD-TiN onto SS316L resulted in great improvements in electrical conductivity and corrosion resistance. Notably, the TiN thin films prepared using TDMAT exhibited excellent corrosion resistance (<1 μA/cm2) compared to those produced using TiCl4 as the precursor. Systematically structural, compositional, and electrochemical analysis revealed that a ~5-nm-thick ultrathin amorphous interfacial layer, formed and played a key role in the corrosion protection using TDMAT. Furthermore, the TiN thin films by TDMAT greatly lowered the interfacial contact resistance of SS316L from 35.868 to 15.239 mΩ∙cm2 at a compaction force of 127 N/cm2. Our study presents an interesting opportunity for the development of PEALD protective coating materials for SS-bipolar plates.
Fabrication of semiconductor thin films with uniform and vertically aligned one-dimensional nanostructures is an active area of research. We report the synthesis of vertically aligned nanograss ...(NG)-structured SnO2 thin films on a wide range of substrates with a vapor–solid deposition process. In this process, some chemical and physical parameters, such as chemical composition, deposition height from the precursor mixture, deposition temperature, and substrate roughness, are found to play key roles during the growth of SnO2 nanograsses (SNGs). The effects of density change and cross-sectional dimension (width) of the nanograsses (NGs) on surface area improvement of the thin films have been examined by varying the respective parameters. BiVO4 (BV) solution layers were coated onto SNG, forming core–shell type-II heterojunction thin films (SNG-BV). The thickness of the drop-cast BiVO4 solution layers onto the NGs was controlled by the number density of the NGs per unit area. Light absorption efficiency (ηabs) of the core–shell SNG-BV films has been optimized by controlling quasi-arranged periodicity of the core NGs and accessible shell thickness of BiVO4 layers. The charge separation efficiency (ηsep) of SNG-BV films strongly depends on the thickness of the BiVO4 layers onto NGs. Thin layers of BiVO4 coating along the axial direction of thinner SnO2 NGs (25–50 nm) shows enhanced ηsep but lower ηabs due to poor light absorption. On the other hand, the thicker core NGs (40–200 nm) with low surface area provide thick layers of BiVO4, which drives strong light absorption but suffers from efficient ηsep. However, intermediate layers of BiVO4 onto uniformly arranged SnO2 NGs with 30–70 nm width shows enhanced ηabs as well as efficient ηsep compared to other SNG-BV samples. This result demonstrates that control over the horizontal dimension of the core materials in the core–shell heterojunction (keeping vertical restriction) is a viable approach for optimizing the photoelectrochemical efficiency.
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•PtNi catalyst is synthesized by fluidized bed reactor atomic layer deposition (ALD)•PtNi alloy composition is controlled by ALD super-cycle for the strategic structure.•Pt-rich Pt3Ni ...builds the Pt skin-Pt3Ni NPs due to the ALD growth characteristics.•A uniform alloy NPs is observed leading to an excellent electrochemical property.•It also outperforms the commercial catalysts for durability and PEMFC performance.
Structuring Pt-based alloy catalysts with uniform, dense dispersion, and low loading is a challenging work for efficient and relatively low-cost catalysts to promote oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs). Herein, we present a strategy of active PtNi alloy structure formation with uniform metal alloy nanoparticles (NPs) using fluidized bed reactor atomic layer deposition (FBR-ALD). The compositions of the PtNi alloys were controlled by the ALD super-cycle method, where Pt75+XNi25-X alloy catalysts were successfully synthesized by tuning the super-cycle ratio. The as-deposited alloy catalysts consisted of well-dispersed and dense metal NPs, whose characteristics were maintained even after heat treatment at 700 °C with H2 to produce a well-mixed PtNi alloy. During heat treatment, the Pt-rich Pt3Ni alloy converted into the Pt skin-Pt3Ni alloy structure from the ALD growth mechanism, which is evidenced by spherical aberration (Cs)-corrected transmission electron microscopy (TEM), line profiling, X-ray photoelectron spectroscopy (XPS), and electron energy loss spectroscopy (EELS). The ALD synthesized Pt skin-Pt3Ni alloy structure featured a significantly higher electrochemical surface area (ECSA) as well as ORR activity, durability, and PEMFC performance compared to the commercial Pt and Pt3Ni catalysts due to their excellent uniformity, density, and well dispersity as well as the Pt skin-Pt3Ni structure. This study focuses on an atomic scale strategy for a new alloy architecture and marks a step toward a modern high-performing alloy catalyst for future PEMFC technology.
•Diamond-like carbon coatings (DLC) with Al, Ti and Si multi-doping were deposited.•The AlTiSi-DLC coatings exhibited a compositionally modulated multilayer.•The AlTiSi-DLC coatings showed a ...relatively low compressive stress and high hardness.
Diamond-like carbon (DLC) coatings with AlTiSi multi-doping were prepared by a reactive high power impulse magnetron sputtering with using a gas mixture of Ar and C2H2 as precursor. The composition, microstructure, compressive stress, and mechanical property of the as-deposited DLC coatings were studied systemically by using SEM, XPS, TEM, Raman spectrum, stress-tester, and nanoindentation as a function of the Ar fraction. The results show that the doping concentrations of the Al, Ti and Si atoms increased as the Ar fraction increased. The doped Ti and Si preferred to bond with C while the doped Al mainly existed in oxidation state without bonding with C. As the doping concentrations increased, TiC carbide nanocrystals were formed in the DLC matrix. The microstructure of coatings changed from an amorphous feature dominant AlTiSi-DLC to a carbide nanocomposite AlTiSi-DLC with TiC nanoparticles embedding. In addition, the coatings exhibited the compositionally modulated multilayer consisting of alternate Al-rich layer and Al-poor layer due to the rotation of the substrate holder and the diffusion behavior of the doped Al which tended to separate from C and diffuse towards the DLC matrix surface owing to its weak interactions with C. The periodic Al-rich layer can effectively release the compressive stress of the coatings. On the other hand, the hard TiC nanoparticles were conducive to the hardness of the coatings. Consequently, the DLC coatings with relatively low residual stress and high hardness could be acquired successfully through AlTiSi multi-doping. It is believed that the AlCrSi multi-doping may be a good way for improving the comprehensive properties of the DLC coatings. In addition, we believe that the DLC coatings with Al-rich multilayered structure have a high oxidation resistance, which allows the DLC coatings application in high temperature environment.
In this study, the wear resistance of AISI M2 high-speed tool steel produced using direct energy deposition (DED) was investigated in detail. Wear behavior was studied under different wear loads and ...sliding speeds using ball-on-disk tribology tests with two different counterpart balls (bearing steel and ZrO
2
). The wear test results revealed that there was almost no wear damage in the M2 alloy when a bearing steel counterpart ball was used. When a ZrO
2
ball was used as the counterpart, a measurable, but small, amount of wear weight loss of M2 was observed. It was found that M2 alloy fabricated by DED has excellent wear resistance, greater than fully carburized conventional steel and high wear resistance steel produced by DED. The formation of a lubricious tribo-oxide film on the worn DED M2 surface is likely the reason for its excellent wear performance. The total wear weight losses of only ~1.5 mg was observed for the M2 produced by the DED, both in the as-DEDed and heat treated states against ZrO
2
balls, under the wear loading conditions of 50 N wear load, 100 mm/s sliding speed and total sliding distance of 500 m. In comparison to the other wear-resistance materials, the wear weight loss of the M2 produced by the DED was more than 6 times smaller than the fully carburized structural steel and 1.5–4 times smaller than high wear resistance steel produced by the DED. Thus, DED of the M2 alloy offers a great potential for the production of wear-resistance hard-facing of tribological components.
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•Newly designed and sustainable 0D/2D Sn-Co-S/MXene cathode material is reported for asymmetric supercapacitor.•0D/2D Sn-Co-S/MXene hybrid material contributes a high specific ...capacity value of 305.71 mA h gm−1 at 1 A g−1.•The Sn-Co-S/MXene hybrid material has displayed phenomenal electrochemical performance owing to its highly electroactive and conductive architecture.•The Sn-Co-S/MXene//AC ASC device operated at 1.70 (V) displays a high energy density of 43.55 Wh Kg−1.
The design of electrode materials for improved electrochemical properties and stable geometric configuration is known as effective research in developing the electrochemical capability of supercapacitors (SCs). However, there is a difficulty in designing innovative composite material with excellent electrical conductivity and superior specific capacity by way of low cost and easy synthesis process. Herein, for the first time, a stable Sn-Co-S/MXene hybrid material is fabricated through the electrochemical assembly by combining positively charged ultrafine Sn-Co-S nanoparticles (NPs) and negatively charged 2D Ti3C2Tx (MXene) sheets due to electrostatic interaction. The Sn-Co-S/MXene hybrid material has displayed excellent electrochemical performance with an ultrahigh specific capacity of 305.71 mA h gm−1 at 1 A g−1 and capacity retention of 94.8% after 10, 000 charge–discharge cycles. The Sn-Co-S/MXene hybrid material of high electrochemical performance has improved charge transfer kinetics during the charge–discharge process, due to the synergistic coupling effect between ultrafine Sn-Co-S nanoparticles and MXene sheets. Furthermore, the Sn-Co-S/MXene//activated carbon (AC) asymmetric supercapacitor (ASC) device has been configured with the assistance of Sn-Co-S/MXene as cathode and AC as anode materials. The Sn-Co-S/MXene//AC ASC device exhibits a stable potential window of 1.7 V, a high specific capacitance of 108.50F g−1 at 1 A g−1, and an energy density of 43.55Wh kg−1 at a power density of 0.83 kW kg−1. This study validates the design and application of highly electroactive Sn-Co-S/MXene hybrid electrode material for ultrastable asymmetric supercapacitors.
Because of its excellent charge carrier mobility at the Dirac point, graphene possesses exceptional properties for high-performance devices. Of particular interest is the potential use of graphene ...nanoribbons or graphene nanomesh for field-effect transistors. Herein, highly aligned DNA nanowire arrays were crafted by flow-assisted self-assembly of a drop of DNA aqueous solution on a flat polymer substrate. Subsequently, they were exploited as “ink” and transfer-printed on chemical vapor deposited (CVD)-grown graphene substrate. The oriented DNA nanowires served as the lithographic resist for selective removal of graphene, forming highly aligned graphene nanoribbons. Intriguingly, these graphene nanoribbons can be readily produced over a large area (i.e., millimeter scale) with a high degree of feature-size controllability and a low level of defects, rendering the fabrication of flexible two terminal devices and field-effect transistors.
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