Ultrathin Protective Layer Research Articles

Ultrathin Protection Layer via Rapid Sputtering Strategy for Stable Aqueous Zinc Ion Batteries

AbstractSurface side reactions and time‐consuming modification methods hinder the practical application of zinc‐ion batteries. This study introduces an ultrathin protection layer for the Zn anode via a rapid sputtering method. The dopants on the CN10@Zn anode create surface dipoles and local variations in charge distribution, facilitating zinc ion migration to pyrrolic nitrogen dopant sites with reduced adsorption barriers. Additionally, hydroxyl oxygen dopants enhance the hydrophilicity of the sputtering layer, forming a strong adhesion with the zinc anode and improving ion accessibility. This results in dense nucleation sites for uniform zinc deposition. Consequently, the sputtered layer achieves a Coulombic efficiency of 99.8% over 2,700 cycles in Cu||Zn cells and a lifespan of up to 2,100 h in zinc symmetric cells. When paired with Na0.65Mn2O4 cathodes, the sputtered layer retains 89% capacity over 1,000 cycles at 1 A g−1. This study presents a promising method for rapidly fabricating ultrathin electrode materials.

Patterning functional oxides: Some failures and solutions in fabricating a Hall bar

Functional oxides exhibit diverse useful properties, opening attractive prospects for electronic, magnetic, and optoelectronic devices. However, the chemical instability of these oxides with some microfabrication processes, especially when dealing with thin films (<40 nm) or micrometer-scale lateral dimensions, can pose a considerable challenge. Here, we describe the fabrication process of a Hall bar device used as a test structure for thin functional oxide films. This process employs photolithography and dry etching, utilizing standard clean-room materials and methods. The device layout and fabrication process are described in detail, including conclusions and lessons gained from several failed attempts during process development. A key lesson is the advantage of employing an ultrathin protective layer to protect the oxide film surface. In addition, we encountered two additional fabrication challenges: photoresist hardening during dry etching and edge accumulation of photoresist during spin-coating. Effective solutions to these issues are described. We hope that our lessons and conclusions, not limited to functional oxides, will help to shorten the process development for other materials and devices.

Sulfonate Functionalized Turbostratic Carbon Derived from Borassus flabellifer Flower: A Ultrathin Protective Layer to Mitigate the Dendrite Formation on the Metallic Lithium Anode

Sulfonate Functionalized Turbostratic Carbon Derived from <i>Borassus flabellifer</i> Flower: A Ultrathin Protective Layer to Mitigate the Dendrite Formation on the Metallic Lithium Anode

A synergy establishment by metal-organic framework and carbon quantum dots to enhance electrochemical water oxidation

Available online Integrating transition metal centered MOFs with conductive materials is a feasible route to enhance electron transfer efficiency of materials. Herein, a composite porous structure CQDs10@NiFe-MOF-A was fabricated via introducing carbon quantum dots (CQDs) into porous NiFe-MOF. The CQDs would make partial loss of lattice in MOF during its growth, leading to the composite building block with the coexistance of crystalline region and amorphous region. The calcining treatment would produce an ultrathin protective layer as well as some lattice collapse. The synergy effect between NiFe ions effectively regulated electronic structure of metal active sites, and successful grafting of CQDs to NiFe-MOF significantly improved electrical conductivity. As expected, the catalyst exhibited outstanding OER performances with high mass activity of 91.6 A/g at overpotential of 300 mV and robust durability of 10,000 cycles in 1 mol/L KOH, which outperformed that of noble catalyst IrO2 of 25.2 A/g. The strategy paves a feasible and effective avenue for the non-noble metal catalysts.

Phosphine-Based Porous Organic Polymer/rGO Composite Anode and α-MnO2 Nanowire Cathode Cooperatively Enabling High-Voltage Aqueous Asymmetric Supercapacitors

Aqueous supercapacitors often yield a restricted cell voltage, resulting in a low specific energy, due to unwanted water electrolysis and a narrow electrode potential range. Herein, a novel hierarchical nanostructured phosphine based porous organic polymer (PP)/reduced graphene oxide (rGO) aerogel composite anode is fabricated. Benefitting from the excellent electrical conductivity and ultra-thin protection layer of rGO aerogel, PP/rGO could extend the potential window to -1.0-0 V, exhibiting significantly enhanced specific capacitance (380.2 F/g@2 A/g) and good rate capability (165.0 F/g@4 A/g). To complement the wide potential window, α-MnO2 nanowire is employed as cathode due to its large and stable potential window (0 to 0.8 V). Remarkably, a 2 V aqueous PP/rGO//α-MnO2 asymmetric supercapacitor (ASC) is successfully fabricated, exhibiting a high specific energy of 39 Wh/kg with extraordinary cycling stability and rate capability (96% retention after 10000 cycles), outperforming most of the previously reported rGO based ASCs. Furthermore, a coin-type PP/rGO//α-MnO2 ASC device is further fabricated that can illuminate a red LED for 3 mins, demonstrating its great potential for practical application. The knowledge gained in this study using in situ formed hetero-nanostructure to expand the voltage window will open up new possibilities for electrode design targeting a widen potential window and high energy ASCs.

Self-Induced Passive Nonreciprocal Transmission by Nonlinear Bifacial Dielectric Metasurfaces

The breaking of Lorentz reciprocity law is a non-trivial task, since it usually requires bulky magnets or complicated time-modulation dynamic techniques to be accomplished. In this work, we present a simple and compact design of a nonlinear bifacial dielectric metasurface to achieve strong self-induced passive nonreciprocal transmission without the use of external biases. The proposed design is ideal for free space optics applications, can operate under both incident polarizations, and require very low input excitation power to reach the nonreciprocal regime. It is composed of two passive silicon-based metasurfaces exhibiting Fano and Lorentzian resonances embedded in an ultrathin glass substrate. Highly asymmetric field enhancement is achieved with the proposed design that leads to strong nonreciprocity at low excitation intensities due to the large Kerr nonlinearity of silicon. Moreover, cascade designs are presented to further improve the insertion loss, broaden the nonreciprocal intensity range, and increase the isolation ratio by enhancing the transmission contrast. Finally, it is demonstrated that the proposed nonlinear metasurface is robust to fabrication imperfections and can achieve large isolation for a relative broad input power range even in the case of two incident waves impinging at the same time from both directions. The current work is expected to lead to new compact nonreciprocal nanophotonic devices, such as all-optical diodes, isolators, circulators, and ultrathin protective layers for sensitive optical components.

General Nondestructive Passivation by 4-Fluoroaniline for Perovskite Solar Cells with Improved Performance and Stability.

Hybrid perovskite thin films are prone to producing surface vacancies during the film formation, which degrade the stability and photovoltaic performance. Passivation via post-treatment can heal these defects, but present methods are slightly destructive to the bulk of 3D perovskite due to the solvent effect, which hinders fabrication reproducibility. Herein, nondestructive surface/interface passivation using 4-fluoroaniline (FAL) is established. FAL is not only an effective antisolvent candidate for surface modification, but also a large dipole molecule (2.84 Debye) with directional field for charge separation. Density functional theory calculation reveals that the nondestructive properties are attributed to both the conjugated amine in aromatic ring and the para-fluoro-substituent. A hot vapor assisted colloidal process is employed for the post-treatment. The molecular passivation yields an ultrathin protection layer with a hydrophobic fluoro-substituent tail and thus enhances the stability and optoelectronic properties. FAL post-treated perovskite solar cell (PSC) delivers a 20.48% power conversion efficiency under ambient conditions. Micro-photoluminescence reveals that passivation activates the dark defective state at the surface and interface, delivering the impact picture of boundary on the local carriers. This work demonstrates a generic nondestructive chemical approach for improving the performance and stability of PSCs.

Investigation of (Leaky) ALD TiO2 Protection Layers for Water-Splitting Photoelectrodes.

Protective overlayers for light absorbers in photoelectrochemical water-splitting devices have gained considerable attention in recent years. They stabilize light absorbers which would normally be prone to chemical side reactions leading to degradation of the absorber. Atomic layer deposition (ALD) enables conformal and reproducible ultrathin protective layer growth even on highly structured substrates. One of the most widely investigated protective layers is amorphous TiO2, deposited by ALD at a relatively low temperature (120-150 °C). We have deposited protective layers from tetrakis(dimethylamido)titanium(IV) at two different temperatures and investigated their chemical composition as well as optical and electrochemical properties. Our main findings reveal a change in the flat band potential with thickness, reaching a stable value of about -50 to -100 mV versus reversible hydrogen electrode for films >30 nm, with doping densities of ∼1020 cm3. Practical thicknesses to achieve pinhole-free films are evaluated and discussed.

Tribological characteristics of micro-ball bearing with V-shaped grooves coated with ultra-thin protective layers

Abstract The tribological characteristics of micro-ball bearing comprising Si substrate with V-shaped grooves applied with various types of thin films were investigated. Self-assembled monolayers and metallic thin films were deposited on the Si substrate to enhance the tribological characteristics. Experiments were conducted for 100 and 2000 cycles to estimate initial frictional behavior and durability of micro-ball bearing, respectively. It was demonstrated that both metallic thin films and self-assembled monolayers effectively reduced the friction coefficient and extended the lifetime of the micro-ball bearing. Particularly, self-assembled monolayer exhibited more stable frictional characteristics and longer lifetime compared to metallic thin films.

Durable graphene-coated bipolar plates for polymer electrolyte fuel cells

In this paper, we investigate the role of a graphene layer for polymer electrolyte fuel cells (PEFCs) which require an ultrathin protective layer for copper bipolar plates. The graphene layer was deposited by chemical vapor deposition using CH4 at 830 °C. We examined the deposited graphene layer to characterize microstructural properties using a Raman spectroscopy microscope and a secondary electron microscope. During the electrochemical tests, the current–voltage–power (I–V–P) performance of the single cell using the copper bipolar plate with the graphene layer was highly stable for 5 h, while the I–V–P performance of the single cell using the pure copper bipolar plate (without the graphene layer) was much lower. We conclude that the graphene layer acts as a very thin passivation layer on the copper bipolar plate of a PEFC.

Role of hexagonal boron nitride in protecting ferromagnetic nanostructures from oxidation

Ferromagnetic contacts are widely used to inject spin polarized currents into non-magnetic materials such as semiconductors or 2-dimensional materials like graphene. In these systems, oxidation of the ferromagnetic materials poses an intrinsic limitation on device performance. Here we investigate the role of ex situ transferred chemical vapour deposited hexagonal boron nitride (hBN) as an oxidation barrier for nanostructured cobalt and permalloy electrodes. The chemical state of the ferromagnets was investigated using x-ray photoemission electron microscopy because of its high sensitivity and lateral resolution. We have compared the oxide thickness formed on ferromagnetic nanostructures covered by hBN to uncovered reference structures. Our results show that hBN reduces the oxidation rate of ferromagnetic nanostructures suggesting that it could be used as an ultra-thin protection layer in future spintronic devices.

Observation of a carbon-based protective layer on the sidewalls of boron doped ultrananocrystalline diamond-based MEMS during in situ tribotests

We have fabricated dedicated MEMS tribotesters made from boron doped ultrananocrystalline diamond (B-UNCD) as the structural material, and carried out comprehensive nano-tribological measurements when two B-UNCD sidewall surfaces underwent sliding interaction in a micro-electromechanical systems (MEMS) in a humid and dry atmosphere. We have investigated the evolution of tribological contacts during sliding interactions and corresponding surface modification under repeated cyclic sliding conditions, while measuring displacement and lateral force with 4 nm and 64 nN resolution, respectively. We have observed the formation of carbon-based ultra-thin protective layer at the sliding interface as characterized by Raman spectroscopy and scanning electron microscopy. Interestingly, the formation of this protective layer occurs in both a dry and wet atmosphere, albeit at different rates when the energy dissipated due to friction reaches a plateau, starting from 200 000 and 400 000 cycles, respectively. Once this layer is formed, we do not observe any measurable wear indicating stable operation for an extended time period. Our results demonstrate that B-UNCD is a very promising material to overcome the wear-related reliability problems in MEMS.

Electrochemical behavior of Mx−1Ox (M = Ti, Ce and Co) ultra-thin protective layers for MCFC cathode

In the world of alternative energy sources, the Molten Carbonate Fuel Cell (MCFC) is one of the promising technologies for the efficient conversion of hydrogen or hydrocarbons to power and heat. One of the main issues for optimizing this device is the control of the dissolution of the state-of-the-art porous nickel oxide cathode. A protective coating by more stable metal oxides seems to be one of the best solutions. In this paper, ultra-thin layers of TiO2 (50 nm), Co3O4 (50 nm) and CeO2 (20 nm) were deposited on porous nickel substrates, by a sequential CVD technique, known as Atomic Layer Deposition (ALD), producing high quality, homogeneous and conformal layers. The electrochemical behavior and morphological features of the three coated samples were compared in a Li2CO3–K2CO3 (62–38 mol%) eutectic melt under a standard cathode atmosphere (CO2/air 30:70 vol%) for 230 h. Finally, the respective advantages and drawbacks of Co3O4, TiO2 and CeO2 coatings are pointed out.

Nanoscale Thermomechanics of Wear-Resilient Polymeric Bilayer Systems

We explore the effect of an ultrathin elastic coating to optimize the mechanical stability of an underlying polymer film for nanoscale applications. The coating consists of a several nanometer thin plasma-polymerized norbornene layer. Scanning probes are used to characterize the system in terms of shear-force-induced wear and thermally assisted indentation. The layer transforms a weakly performing polystyrene film into a highly wear-resistive system, ideal for high-density and low-power data storage applications. The result can be understood from the indentation characteristics with a hot and sharp indenter tip. The latter gives rise to a deformation mode in the fully plastic regime, enabling a simple interpretation of the results. The softening transition and the yield stress of the system on a microsecond time scale and a nanometer size scale were obtained. We show that the plastic deformation is governed by yielding in the polystyrene sublayer, which renders the overall system soft for plastic deformation. The ultrathin protection layer contributes as an elastic skin, which shields part of the temperature and pressure and enables the high wear resistance against lateral forces. Moreover, the method of probing polymers at microsecond and nanometer size scales opens up new opportunities for studying polymer physics in a largely unexplored regime. Thus, we find softening temperatures of more than 100 °C above the polystyrene glass transition, which implies that for the short interaction time scales the glassy state of the polymer is preserved up to this temperature.

Physicochemical aspects of the protection of metals from corrosion with the use of nano-and microsize coatings

The formation of thin protective layers at metals, which could be successfully used for corrosion control, has long been the focus of attention for physical chemists. Those layers are formed either during the adsorption of corrosion inhibitors (CTs) or in reactions of the cations of the metal to be protected with some components of the medium. The latter case involves not only nanosized layers formed by CIs but also thick conversion (oxide, phosphate, etc.) coatings. Let us restrict our consideration to conversion coatings (CCs) with a thickness δ of ≤5 μm. Apparently, it is methods designed to form thin and ultrathin protective layers that will be in the best demand by the technologies of the XXI century. We will consider only a few important problems that physical chemists face with when studying the possibilities of the protection of metals from corrosion.

Methyl-terminated Si(1 1 1) surface as the ultra thin protection layer to fabricate position-controlled alkyl SAMs by using atomic force microscope anodic oxidation

Methyl-terminated Si(1 1 1) (Me–Si(1 1 1)) and bilayer-GaSe terminated Si (BGS) surfaces were investigated to explore their usefulness as the protection layer in the fabrication process of nanometer-scale self-assembled monolayers (SAMs). BGS was not stable in the reagent involved in the alkyl SAM formation, whereas Me–Si(1 1 1) was suitable for the protection layer. Anodization using atomic force microscope (AFM) and following HF and hexadecene treatments were performed to form nano-scale alkyl SAM lines on the Me–Si(1 1 1) surface. It was found from AFM observation and frictional force measurement that only the patterned areas were selectively covered with hexadecyl SAMs.

Inelastic light scattering: a multiscale characterization approach to vibrational, structural and thermo-mechanical properties of nanostructured materials

Inelastic light scattering is a powerful technique for the characterization of nanostructured materials, at different length scales. Raman scattering is a well established tool for materials characterization (structure, bonding and composition), through the measurement of vibrational properties. Due to phonon confinement, the Raman spectra of nanoparticles and nanostructured materials are substantially different from the spectra of the corresponding bulk, and provide useful information relative to the size and the dynamical behavior of the building blocks. In situ measurements permit the investigation of phenomena such as cluster deposition, film growth, thermal and chemical stability of nanostructures. Brillouin spectroscopy measures acoustic phonons and elastic properties of thin films and bulk materials at a mesocopic scale (hundreds of nanometers). The observation of acoustic damping and localization in nanostructured materials gives access to information such as interaction between nanoscale constituents, phase transitions, self-similar properties and meso-structure dynamical behavior. We provide a wide range of examples: characterization of the elastic properties of cluster-assembled films and ultrathin protective layers; in situ Raman spectroscopy of metastable linear carbon aggregates (carbynes) produced by cluster beams; measurement of acoustic modes in carbon nanotubes; detection of surface melting of metallic nanoparticles, by detection of confined vibrational modes.