Ultrathin Coatings Research Articles

Ultra-thin conversion coatings on AMg3 aluminum alloy. Part II. Modification of coating for its application as primer for powder paint

Ultra-thin conversion coatings on AMg3 aluminum alloy. Part II. Modification of coating for its application as primer for powder paint

Ultrathin Surface Coating of Nitrogen-Doped Graphene Enables Stable Zinc Anodes for Aqueous Zinc-Ion Batteries.

Owing to the high volumetric capacity and low redox potential, zinc (Zn) metal is considered to be a remarkably prospective anode for aqueous Zn-ion batteries (AZIBs). However, dendrite growth severely destabilizes the electrode/electrolyte interface, and accelerates the generation of side reactions, which eventually degrade the electrochemical performance. Here, an artificial interface film of nitrogen (N)-doped graphene oxide (NGO) is one-step synthesized by a Langmuir-Blodgett method to achieve a parallel and ultrathin interface modification layer (≈120nm) on Zn foil. The directional deposition of Zn crystal in the (002) planes is revealed because of the parallel graphene layer and beneficial zincophilic-traits of the N-doped groups. Meanwhile, through the in situ differential electrochemical mass spectrometry and in situ Raman tests, the directional plating morphology of metallic Zn at the interface effectively suppresses the hydrogen evolution reactions and passivation. Consequently, the pouch cells pairing this new anode with LiMn2 O4 cathode maintain exceptional energy density (164Whkg-1 after 178 cycles) at a reasonable depth of discharge, 36%. This work provides an accessible synthesis method and in-depth mechanistic analysis to accelerate the application of high-specific-energy AZIBs.

Conformal Growth of Ultrathin Hydrophilic Coatings on Hydrophobic Surfaces Using Initiated Chemical Vapor Deposition.

Hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) was deposited onto hydrophobic polytetrafluoroethylene (PTFE) surfaces using initiated chemical vapor deposition. By tuning the reactor conditions, the reaction kinetics were varied to achieve a wide range of deposition rates that spanned over 2 orders of magnitude (∼0.1-10 nm/min). Depositions rates at >1 nm/min were successful in overcoming the interfacial energy and wettability barriers between the hydrophobic and hydrophilic polymers and were found to achieve both conformal and ultrathin coatings. PHEMA coatings as thin as ∼10 nm over PTFE were able to transform a hydrophobic surface with a water contact angle of ∼110° to a hydrophilic one with an angle of ∼20°.

The testing methods for anti-icing properties of ultra-thin fluoropolymer coatings

The paper discusses the testing methods of ultra thin film-forming fluorocontained polymer compositions, which form the surface modifying structures, long-life coatings and nanosize films, giving the treated surface anti-icing, tribological and hydrophobic properties.

Controlled Lay-By-Layer Etching of CVD Grown Multilayer h-BN Single Crystal

Being a 2D insulator with alternating sp2 hybridized B and N atoms in a honeycomb structure, Hexagonal Boron Nitride(hBN) not only have uniqure properties like high transparency, large thermal conductivity, high mechanical strength and superior chemical inertness by itself, but also be able to promote other 2D materials’ performance when serving as the ultra-smooth dielectrilayer.[1,2] Since CVD process is established as the most effective way to grow large area hBN materials, it is critical to understand and control the growth process so as to making them ready for the large scale industrial applications. Etching of 2D materials should provide a scalable route for fabrication of highly desired various nanostructures such as nanoribbons with controlled termination providing a simple and direct way for 2D material property design, such as controlling the band gap and optical properties. [3,4] However, it is often easy to initiate the etching, but difficulty the control the location, shape, and size of the etching pattern. Previously reported etching patterns for 2D materials can be generally divided into four different categories: domain, boundary, fractal, and adlayer etching. [3-6] These etching patterns may co-exist in the etching process, but the dominant pattern depends on competition between various factors such as atmosphere, temperature, substrate, time etc. Layer number increase can often be achieved by increase the reaction temperature, time, and precursor concentration.While the layer number reducing after the multilayer hBN growth process remain challenging. Here we use the as-grow multilayer hBN single crystal from CVD process for controllable etching experiment, then both temperature related hydrogen etching and electronic energy related e-beam etching will be used to remove single layer of as-grown multilayer hBN. References Lu, G.; Wu, T; Yuan, Q.; Wang, H.; Wang, H.; Feng Ding, F.; Xie, X.; Jiang, M. Synthesis of large single-crystal hexagonal boron nitride grains on Cu–Ni alloy. Nat. Commun. 2014, 6, 6160.Liu, Z.; Gong, Y.; Zhou, W.; Ma, L.; Yu, J.; Idrobo, J. C.; Jung, J.; MacDonald, A.H.; Vajtai, R.; Lou, J.; Ajayan, P.M. Ultrathin high-temperature oxidation-resistant coatings of hexagonal boron nitride. Nat. Commun. 2013, 4, 2541.Vlassiouk, I.; Regmi, M.; Fulvio, P.; Dai, S.; Datskos, P.; Eres, G.; Smirnov, S. Role of hydrogen in chemical vapor deposition growth of large single-crystal graphene. ACS nano 2011, 5, 6069-6076.Wang, L.; Wu, B.; Jiang, L.; Chen, J.; Li, Y.; Guo, W.; Hu, P.; Liu, Y. Growth and Etching of Monolayer Hexagonal Boron Nitride. Adv. Mater. 2015, 27, 4858–4864.Rong, Y.; He, K.; Pacios, M.; Robertson, A. W.; Bhaskaran, H.; Warner, J. H. Controlled Preferential Oxidation of Grain Boundaries in Monolayer Tungsten Disulfide for Direct Optical Imaging. ACS Nano, 2015, 9, 3695–3703.Stehle, Y.; Sang, X.; Unocic, R.; Voylov, D.; Jackson, R.; Smirnov, S.; Vlassiouk, I., Anisotropic etching of hexagonal boron nitride and graphene: question of edge terminations Nano letters, 2017, 17 (12), 7306-7314

Ultrathin Diamond Nanofilms-Development, Challenges, and Applications.

Diamond is a highly attractive material for ample applications in material science, engineering, chemistry, and biology because of its favorable properties. The advent of conductive diamond coatings and the steady demand for miniaturization in a plethora of economic and scientific fields resulted in the impetus for interdisciplinary research to develop intricate deposition techniques for thin (≤1000nm) and ultra-thin (≤100nm) diamond films on non-diamond substrates. By virtue of the lowered thickness, diamond coatings feature high optical transparency in UV-IR range. Combined with their semi-conductivity and mechanical robustness, they are promising candidates for solar cells, optical devices, transparent electrodes, and photochemical applications. In this review, the difficulty of (ultra-thin) diamond film development and production, introduction of important stepping stones for thin diamond synthesis, and summarization of the main nucleation procedures for diamond film synthesis are elucidated. Thereafter, applications of thin diamond coatings are highlighted with a focus on applications relying on ultrathin diamond coatings, and the excellent properties of the diamond exploited in said applications are discussed, thus guiding the reader and enabling the reader to quickly get acquainted with the research field of ultrathin diamond coatings.

Ultrathin Polydopamine-Graphene Oxide Hybrid Coatings on Polymer Filters with Improved Filtration Performance and Functionalities.

Thin polymer fiber mats, in particular those made of nonwoven polypropylene (PP) fibers, are extensively used for medical and industrial filtration. The recent pandemic has increased the demand for the fabrication of protective masks. The nonwoven PP filter has limitations in filtration efficiency and lacks advanced functionalities. Here, we propose a simple, effective, and low-cost method to functionalize PP filters and endow antimicrobial and photothermal properties. Our approach is based on the deposition of an ultrathin hybrid coating composed of graphene oxide (GO) and polydopamine on the surface of PP filters by spray-coating. The complementary properties and synergic effects of GO and polydopamine in the ultrathin coating improved the filtration efficiency of the PP filter by 20% with little change in pressure drop. Single component coatings did not result in similar improvements in performance. The ultrathin coating also makes the surface of the filter more hydrophilic with negative charges. The photothermal property of GO enables a rapid temperature increase of the surface-coated filter upon light irradiation for easy sterilization. Furthermore, cationic polymer brushes can be grafted to the ultrathin hybrid coating, which adds the highly desired antimicrobial property to the PP filters for their more effective protection against microorganisms.

Evolvement Investigation of Secondary Electron Emission for Ultrathin MgO Coatings Prepared by Atomic Layer Deposition

MgO is a kind of high secondary electron yield (SEY) material with important applications in electron multipliers. MgO coatings can be used as the electron emission layer for multiplier dynode to improve the electron gain significantly. However, the SEY investigation on ultrathin MgO coatings is not complete and needed to be supplemented urgently. In this work, a series of MgO coatings with increasing thickness were prepared by atomic layer deposition. SEY properties and energy spectra were characterized, and the effect of coating thickness on SEY was systematically analyzed. Experimental results show that SEY of MgO/Si samples rises as the coating thickness increases. Merely, SEY almost does not change with the coating thickness when the thickness exceeds 30 nm. Then, a SEY semi-empirical theory was employed to interpret the SEY regularities of MgO coatings by regarding the coating samples as ideal double-layer structures. Theoretical calculation quantitatively explained the SEY variation observed during the experiments, and further quantified the SEY contribution level of top coating and bottom substrate for the 1 nm and 20 nm MgO coatings. The work is of great significance for comprehending the SEY of ultrathin MgO coatings and expanding the applications of nanoscale coatings with high SEY.

Ultra-thin conversion coatings on AMg3 aluminum alloy. Part I. Optimization of coating deposition process

Ultra-thin conversion coatings on AMg3 aluminum alloy. Part I. Optimization of coating deposition process

Enhancing the stability of polymer nanostructures via ultrathin oxide coatings for nano-optical device applications

Polymer nanostructures have drawn tremendous attention due to their wide applications in nanotechnology. However, the morphology of the polymer nanostructures is fragile under harsh conditions such as high-power irradiation and organic-solution environments during the fabrication or the measurement processes, significantly limiting their potential applications. In this work, we propose and demonstrate a simple approach to improve the stability of polymer nanostructures by coating a conformal ultrathin oxide film via atomic-layer deposition. Due to the refractory and dense coating of the oxide layer, the stability of polymer structures is enhanced by the prohibition of deformation occurrences from thermally induced reflow and organic solution. As a proof of concept, poly(methyl methacrylate) (PMMA) nanostructures coated with a sub-10-nm TiO2 layer are demonstrated, and the structures exhibit high temperature stability at 180 °C and good resistance to soluble damage from organic solutions. Subsequently, the mechanism of the improved thermal stability is analyzed via mechanical simulations. Such an effective approach is proposed to significantly broaden the application of polymer nanostructures as functional elements for optical structures/devices that require excellent thermal and chemical stability.

Sub‐20 nm Bilayer Hydrophilic Poly(Vinyl Pyrrolidone) Coatings for Antifouling Nanofiltration Membranes

AbstractFouling is a major concern in membrane technology. Neutral hydrophilic coatings alleviate fouling on membrane surfaces by passively resisting the adsorption of foulants without altering the properties of membranes. Coatings, however, often result in a trade‐off of reduced water flux. Ultrathin hydrophilic coatings could minimize the influence on water flux, but its fabrication is challenging via traditional methods. Here, fabrication of sub‐20 nm bilayer hydrophilic coating is reported that is grafted onto nanofiltration (NF) membranes via a one‐step initiated chemical vapor deposition (iCVD) method. The iCVD coating is conducted by conformally depositing a crosslinked poly(vinyl pyrrolidone‐co‐ethylene glycol dimethacrylate) bottom layer on pretreated NF membrane, followed by in situ grafting of poly(vinyl pyrrolidone) homopolymer to further improve surface hydrophilicity. Both thickness and crosslinking degree of the bottom coating are systematically tailored to reduce its side effects on permeation rate and salt rejection. The modified NF membranes exhibit 99% lower microbial adhesion compared to the pristine membrane, with minor impact on permeation and salt rejection performance. The coating is also stable against continuous ultrasonication. The reported method is thus expected to shed light on facile novel ways of reducing membrane fouling in desalination and industrial wastewater treatment.

Oxygen Gas and UV Barrier Properties of Nano-ZnO-Coated PET and PHBHHx Materials Fabricated by Ultrasonic Spray-Coating Technique.

Ultrasonic spray-coating (USSC)—a wet chemical deposition method to deposit ultrathin (down to 20 nm) coatings—is being applied as a promising alternative deposition method for functional coatings due to an economical, simple, and precise coating process with easy control over its operating parameters. In this research, zinc oxide nanoparticles (ZnO NPs) were ultrasonically spray-coated on commercial-grade polyethylene terephthalate (PET) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) films. The most suitable parameters for the ink composition, the ultrasonic spray-coating process, and the number of coating passes (up to 50×) were selected on the basis of a series of experiments. The oxygen gas barrier properties in terms of the oxygen transmission rate (OTR) of neat PET, and 3×, 5×, 10×, and 50× ZnO NP-coated PET and PHBHHx substrates were investigated. The OTR values for neat PET, and 3×, 5×, and 10× ZnO NP-coated PET substrates were found to be the same; however, a 5% reduction in OTR for 50× ZnO NP-coated PET substrate was observed compared to the neat PET substrate. No reduction in OTR was found for any above number of coating passes on PHBHHx substrates against the neat PHBHHx substrate. However, the ultraviolet (UV) tests of 3×, 5×, and 10× ZnO NP-coated PET and PHBHH× substrates revealed a significant decrease in percentage transmission for 10× coated PET and PHBHHx substrates as compared to their 3× and 5× ZnO NP-coated substrates, respectively. It was revealed from the study that the 50× ZnO NP coating of the PET substrate created a slight difference in OTR as compared to the reference substrate. However, the ultrasonic spray-coating method created a significant UV barrier effect for 3×, 5×, and 10× ZnO NP-coated PET and PHBHHx substrates, which demonstrates that the optimized coating method cannot be used to create a high oxygen barrier but can certainly be applied for UV barrier applications in food packaging. It is concluded that ultrasonic spray deposition of ZnO NPs on PET and PHBHHx materials has shown promising results for UV barrier properties, demonstrating the advantages of using this method compared to other coating methods with regard to cost-effectiveness, precise coating, and better process control.

Fano-resonant ultrathin film optical coatings.

Optical coatings are integral components of virtually every optical instrument. However, despite being a century-old technology, there are only a handful of optical coating types. Here, we introduce a type of optical coatings that exhibit photonic Fano resonance, or a Fano-resonant optical coating (FROC). We expand the coupled mechanical oscillator description of Fano resonance to thin-film nanocavities. Using FROCs with thicknesses in the order of 300 nm, we experimentally obtained narrowband reflection akin to low-index-contrast dielectric Bragg mirrors and achieved control over the reflection iridescence. We observed that semi-transparent FROCs can transmit and reflect the same colour as a beam splitter filter, a property that cannot be realized through conventional optical coatings. Finally, FROCs can spectrally and spatially separate the thermal and photovoltaic bands of the solar spectrum, presenting a possible solution to the dispatchability problem in photovoltaics, that is, the inability to dispatch solar energy on demand. Our solar thermal device exhibited power generation of up to 50% and low photovoltaic cell temperatures (~30 °C), which could lead to a six-fold increase in the photovoltaic cell lifetime.

Fast Evaporation Enabled Ultrathin Polymer Coatings on Nanoporous Substrates for Highly Permeable Membranes

SummaryThin polymer coatings covering on porous substrates are a common composite structure required in numerous applications, including membrane separation, and there is a strong need to push the coating thicknesses down to the nanometer scale to maximize the performances. However, producing such ultrathin polymer coatings in a facile and efficient way remains a big challenge. Here, uniform ultrathin polymer covering films (UPCFs) are realized by a facile and general approach based on rapid solvent evaporation. By fast evaporating dilute polymer solutions spread on the surface of porous substrates, we obtain ultrathin coatings (down to ∼30 nm) exclusively on the top surface of porous substrates, forming UPCFs with a block copolymer of polystyrene-block-poly(2-vinyl pyridine) at room temperature or a homopolymer of poly(vinyl alcohol) (PVA) at elevated temperatures. Upon selective swelling of the block copolymer and crosslinking of PVA, we obtain highly permeable membranes delivering ∼2–10 times higher permeance in ultrafiltration and pervaporation than state-of-the-art membranes with comparable selectivities. We have invented a very convenient but highly efficient process for the direct preparation of defective-free ultrathin coatings on porous substrates, which is extremely desired in different fields in addition to membrane separation.

Polyhedral oligomeric silsesquioxanes as protective monolayer coatings against the high-temperature corrosion of concentrating solar power absorber surfaces

The third generation of concentrating solar power (CSP) hybrid absorbers with enhanced solar absorptance and low thermal emittance (spectrally selective) is designed to have a high solar-to-thermal energy conversion efficiency, in spite of robust, long-term resistance to environmental loads. In this study, we report on the deposition, testing, and antioxidation properties of ultra-thin (1–3 nm) mono-, di-, and tri-layers of hybrid organic‒inorganic polyhedral oligomeric silsesquioxanes (POSS) on Inconel 617. The latter is a well-known metal alloy, which is used as a CSP absorber material. Ultra-thin POSS layers were prepared by Langmuir‒Blodgett (LB) deposition. After deposition, the detailed signature characteristics of the POSS monolayer were investigated using X-ray photoelectron spectroscopy (XPS), infrared reflection‒absorption spectroscopy (IRRAS), and contact angle measurements. The XPS results with element concentration profiles reveal that the LB method enables the formation of a dense ultra-thin POSS coating on the Inconel surface, which eventually improves the antioxidation properties. To further test the corrosion resistance improvement of the developed coatings, electrochemical impedance spectroscopy (EIS) and potentiodynamic tests were performed in 0.5 M NaCl solution. The as-obtained data were fitted with the corresponding equivalent circuit, which shows an increased charge transfer resistance (Rct) for coated samples. Tafel polarization plots show suppressed cathodic and anodic reaction rates for samples coated with ultra-thin POSS coatings. We envision that such coatings will have significant potential as a primer for spectrally selective absorber coatings for CSP technology.

Recent advances in probing two-dimensional materials confined water by scanning probe microscopy

<p indent=0mm>Interfacial water is ubiquitous in nature and industry, which plays a crucial role in areas such as wetting, corrosion, lubrication and electrochemistry. The structure and dynamic behavior of interfacial water have been proven to be different from those of bulk water. Therefore, to deeply understand the unique properties of interfacial water, structural imaging with atomic resolution is of great importance. Up to now, owing to its high temporal and spatial resolution, scanning probe microscopy (SPM) has been extensively applied to investigate water molecules at solid interfaces. However, most of those SPM investigations are conducted at cryogenic temperature or under ultra-high vacuum, as under ambient conditions the capillary force between SPM tip and water molecules will perturb the structures of interfacial water on solid surface. Thanks to the two-dimensional (2D) materials which can be utilized as ultra-thin coatings owing to its atomic thickness, good flexibility, impermeability and chemical stability. The graphene coating could protect and fix the structures of interfacial water, which enables the structural imaging by SPM. The 2D material confined water expands the scope of SPM research on interfacial water, promoting the development of interface science. The structure and dynamics of 2D material confined water can be influenced by the structure and hydrophilicity of the interface materials, as well as environment factors such as humidity, temperature and pressure. In recent years, a great deal of works have been conducted with SPM to explore the properties of 2D material confined water and remarkable research results have been achieved. In this review, we will introduce recent progress in probing 2D materials confined water by SPM under ambient conditions, including detecting the microscopic structures of 2D confined water, probing the dynamic behaviors of 2D confined water as well as nanomanipulation of 2D confined water. Furthermore, the effects of confined water on the optical, electrical and frictional properties of the 2D material coatings are also discussed. Finally, a perspective on the directions of future SPM studies of 2D material confined water and the challenges faced by this field are presented. We hope that this review will inspire interest in 2D confined water and provide some new ideas for researchers in this field.

Light-Promoted Electrostatic Adsorption of High-Density Lewis Base Monolayers as Passivating Electron-Selective Contacts.

Achieving efficient passivating carrier‐selective contacts (PCSCs) plays a critical role in high‐performance photovoltaic devices. However, it is still challenging to achieve both an efficient carrier selectivity and high‐level passivation in a sole interlayer due to the thickness dependence of contact resistivity and passivation quality. Herein, a light‐promoted adsorption method is demonstrated to establish high‐density Lewis base polyethylenimine (PEI) monolayers as promising PCSCs. The promoted adsorption is attributed to the enhanced electrostatic interaction between PEI and semiconductor induced by the photo‐generated carriers. The derived angstrom‐scale PEI monolayer is demonstrated to simultaneously provide a low‐resistance electrical contact for electrons, a high‐level field‐effect passivation to semiconductor surface and an enhanced interfacial dipole formation at contact interface. By implementing this light‐promoted adsorbed PEI as a single‐layered PCSC for n‐type silicon solar cell, an efficiency of 19.5% with an open‐circuit voltage of 0.641 V and a high fill factor of 80.7% is achieved, which is one of the best results for devices with solution‐processed electron‐selective contacts. This work not only demonstrates a generic method to develop efficient PCSCs for solar cells but also provides a convenient strategy for the deposition of highly uniform, dense, and ultra‐thin coatings for diverse applications.

Functional relationship of tribological and anti-adhesive, non-stick properties of ultra-thin (nanosized) fluorinated coatings

In the general concept of ultra-thin tribology coatings, main attention is paid to the relationships of antifriction and antiadhesive (anti-sticking) nano-containing compositions, for example epila...

Non-linear dynamics and self-similarity in the rupture of ultra-thin viscoelastic liquid coatings

The influence of viscoelasticity on the dewetting of ultrathin polymer films is unraveled by means of theory and numerical simulations in the inertialess limit. Three viscoelastic models are employed to analyse the dynamics of the film, namely the Oldroyd-B, Giesekus, and FENE-P models. We revisit the linear stability analysis first derived by [Tomar et al., Eur. Phys. J. E., 2006, 20, 185-200] for a Jeffrey's film to conclude that all three models formally share the same dispersion relation. For times close to the rupture singularity, the self-similar regime recently discovered [Moreno-Boza et al., Phys. Rev. Fluids, 2020, 5, 014002], where the dimensionless minimum film thickness scales with the dimensionless time until rupture as hmin = 0.665τ1/3, is asymptotically established independently of the rheological model. The spatial structure of the flow is characterised by a Newtonian core and a thin viscoelastic boundary layer at the free surface, where polymeric stresses become singular as τ → 0. The Deborah number and the solvent-to-total viscosity ratio affect the rupture time but not the length scale of the resulting dewetting pattern and asymptotic flow structure close to rupture, which is thus shown to be universal. Our three-dimensional simulations lead us to conclude that bulk viscoelasticity alone does not explain the experimental observations of dewetting of polymeric films near the glass transition.

Ultrathin clay-containing layer-by-layer separator coating enhances performance of lithium-sulfur batteries

Dissolution of polysulfides upon cycling of the sulfur cathode and their diffusion through the separator membrane ‒ the shuttle effect ‒ is a major factor which deteriorates performance and safety of lithium-sulfur (Li-S) batteries. Here, ultrathin, light-weight polyelectrolyte-clay layer-by-layer assemblies have been developed as versatile nanocoatings on the polypropylene (PP) separator to suppress the shuttle effect. The use of weak polyelectrolytes (polyethyleneimine, PEI, and polyacrylic acid, PAA) and montmorillonite (MMT) or halloysite (Hal) clay nanoparticles enabled full control over mass and charge balance of polyelectrolyte/clay film components, which was critical for achieving ion selectivity and reduction of the polysulfide diffusion. The differences in the geometry and structure of MMT and Hal (nanoplatelets vs. nanotubes), as well as in the pH-controlled charge density of PEI and PAA greatly affected the thickness, morphology, and the ultimate performance of the nanocoatings. In particular, deposition of 450 nm MMT-based coatings at pH 3 and 6 lead to an increase in electrolyte uptake, delayed the lithium dendrite growth and enhanced the discharge capacity of the cell from 300 mAh g−1 for bare to 690 mAh g−1 for coated PP separator over 200 charge-discharge cycles 0.5 C. At the same time, 250 nm-thick Hal-based coatings deposited at pH 3 resulted in an increase in the Coulombic efficiency from 50% for the bare PP separator to ~99% for the coated one, showing an outstanding performance. Additionally, the polyelectrolyte-clay nanocoatings significantly improve thermal and dimensional stability of the PP separator. The results demonstrate that ultrathin LbL clay-containing coatings on the PP separator membrane can drastically improve the cyclability of the Li-S cells.