Controlled Surface Oxidation Research Articles

Controlled surface oxidation of mesoporous silicon microparticles to achieve a stable Si/SiOx anode for lithium-ion batteries

Silicon (Si) is the most promising next-generation anode material for lithium-ion batteries. However, it often suffers from a fast capacity fading due to the large volume changes during the lithiation/delithiation resulting in electrical contact loss between different components of the anode and eventually in battery fading. Mesoporous structure of silicon is a potential material to overcome the issue as the pores could accommodate the volume change during the battery cycling. However, its high surface area can cause continuous parasitic electrolyte decomposition reactions, causing low initial coulombic efficiency (ICE), capacity fading, and battery safety issue. In this study, the surface passivation of mesoporous Si microparticles produced with electrochemical etching and milling was realized through thermal oxidation. The silicon oxide (SiOx) layer generated acted as a protective layer to stabilize the Si surface, thus improving Si electrode performance. Electrochemical characterization showed that the electrode performance of Si/SiOx was strongly correlated with the oxygen content. The Si/SiOx anode delivered a discharge capacity of over 2000 mAh g−1 when the oxygen content was less than 34 wt%, but a much lower capacity when there was higher oxygen content. The best sample (oxidation at 700 °C) showed ICE of 78% and a stable cycling performance for over 180 cycles with a limited capacity of 800 mAh g−1. The results indicate that the appropriate oxidation of mesoporous Si surface to get optimized surface/oxygen content enhances the electrochemical performance of Si anodes essentially.

Gate‐Deterministic Remote Doping Enables Highly Retentive Graphene‐MXene Hybrid Memory Devices on Plastic

AbstractIn this work, a highly retentive and synaptic‐functional transistor memory device architecture based on the gate‐deterministic remote doping of graphene via surface‐oxidized Ti3C2TX MXene nano‐floating‐gates (NFG) is presented. By using solution‐phase size‐sorting followed by controlled surface oxidation process, a regulated distribution of MXene nanoflakes comprising metallic Ti3C2TX as the core surrounded by TiO2‐a high dielectric constant insulator‐as the shell is achieved. The size‐sorted core/shell‐like MXene nanoflakes show a self‐sustainable charge trapping/detrapping behavior, which is highly feasible for realizing non‐embed NFGs for transistor memory devices. Interestingly, unlike the conventional NFG‐embedded architecture, the introduction of core/shell‐like MXene under an electrolyte‐gated graphene field‐effect transistor (GFET) architecture induces a cooperative evolution of the hysteresis loop associated with ionic motion in the electrolyte gates and charge trapping/detrapping in the nanoflakes, resulting in a deterministic remote doping of the graphene layer. The resulting device exhibited a highly retentive memory behavior, which can be optimized by the nanoflake size distribution. In addition, synaptic functions having mechanical flexibility can be successfully emulated using MXene‐based GFETs fabricated on a flexible polyethylene naphthalate substrate.

P=O Functionalized Black Phosphorus/1T-WS2 Nanocomposite High Efficiency Hybrid Photocatalyst for Air/Water Pollutant Degradation.

Research on layered two-dimensional (2D) materials is at the forefront of material science. Because 2D materialshave variousplate shapes, there is a great deal of research on the layer-by-layer-type junction structure. In this study, we designed a composite catalyst with a dimension lower than two dimensions and with catalysts that canbe combined so that the band structures can be designed to suit various applications and cover for each other’s disadvantages. Among transition metal dichalcogenides, 1T-WS2 can be a promising catalytic material because of its unique electrical properties. Black phosphorus with properly controlled surface oxidation can act as a redox functional group. We synthesized black phosphorus that was properly surface oxidized by oxygen plasma treatment and made a catalyst for water quality improvement through composite with 1T-WS2. This photocatalytic activity was highly efficient such that the reaction rate constant k was 10.31 × 10−2 min−1. In addition, a high-concentration methylene blue solution (20 ppm) was rapidly decomposed after more than 10 cycles and showed photo stability. Designing and fabricating bandgap energy-matching nanocomposite photocatalysts could provide a fundamental direction in solving the future’s clean energy problem.

Controlled oxidation of mild steel by potassium permanganate solution to enhance protective functioning of silane coatings

The influence of potassium permanganate in the surface treatment solution on the protection of subsequent silane film was assessed using surface analysis and electrochemical methods. In order to formulate the treatment solutions, several concentrations of KMnO4 up to 200 ppm were added to a diluted sulfuric acid solution. The scanning electron microscopy (SEM/EDS), atomic force microscopy (AFM), water contact angle, grazing X-ray diffractometry (GXRD), electrochemical impedance spectroscopy (EIS) and polarization measurements were employed to obtain the optimal content of KMnO4 in sulfuric acid solution. It was shown that controlled surface oxidation of mild steel at the optimal concentration of KMnO4, 100 ppm, increased the subsequent organosilane layer protective functioning against corrosion attacks.

Controlled surface oxidation of HfSe2 via oxygen-plasma treatment

Growing uniform surface oxides is vital for fabricating 2D materials based electronic and optoelectronic devices. However, the surface transition metal oxides (TMOs) of air-exposure transitional metal dichalcogenides (TMDs), such as HfOx on HfSe2, are island-type, with poor TMOs/TMDs interface quality. Here, we report a controlled surface oxidation of atomically thin HfSe2 flakes via oxygen-plasma treatment, where a dense atomically flat HfOx film is produced. This HfOx film is found to be a good surface passivation layer to prevent the inner part from further oxidation in air, which is also promising as a high-K dielectric in HfSe2-based devices.

High-Performance Oxygen Evolution Anode from Stainless Steel via Controlled Surface Oxidation and Cr Removal

Improving the water oxidation performance of abundantly available materials, such as stainless steel (SS), with notable intrinsic electrocatalytic oxygen evolution reaction (OER) activity due to the presence of Ni and Fe is highly anticipated in water splitting. A new method for promoting the corrosion of stainless steel (304) was found which assisted the uniform formation of oxygen evolution reaction (OER) enhancing NiO incorporated Fe2O3 nanocrystals with the simultaneous reduction in the surface distribution of OER inactive Cr. An equimolar combination of KOH and hypochlorite was used as the corroding agent at 180 °C. The effect of corrosion time on the OER activity was studied and found that better water oxidation performance was observed when the corrosion time was 12 h (SS-12). The SS-12 showed an abnormal enhancement in OER activity compared to the untreated SS and other optimized versions of the same by requiring very low overpotentials of 260, 302, and 340 mV at the current densities of 10, 100, ...

Dual-scale micro/nanostructures for high-efficiency water collection

We describe a simple method of synthesizing dual-scale dome-like micro/nanostructures on copper using temperature controlled surface oxidation. The produced surfaces show two conflicting attributes, large contact angles and large droplet departure radii. Together, these two attributes promote water collection from air. A range of 80%-100% collection rate enhancements was observed for copper surfaces with a number of different wettability characteristics. Theoretical results showed that large departure droplets introduce strong disturbances in the diffusion boundary layer, which may be responsible for decreasing the vapor mass transfer resistance and enhancing the rate of water collection through moisture condensation.

Oxidation fabrication and enhanced soft magnetic properties for core-shell FeCo/CoFe2O4 micron-nano composites

FeCo/CoFe2O4 micron-nano composites have been fabricated by controllably oxidizing micron-sized FeCo particles. High-purity 60-nm-thick CoFe2O4 layers can be formed in situ on the surface of the unoxidized FeCo particles to form a dense FeCo/CoFe2O4 core-shell structure. The good intrinsic magnetic properties, including a high saturation magnetization of 210A·m2·kg−1 and a low coercivity of 11.7Oe, are obtained in these FeCo/CoFe2O4 composites due to the nanoscale thickness of the ferrimagnetic CoFe2O4 layers. For traditional soft magnetic composites, low core loss can only be obtained by seriously sacrificing their magnetic induction. In this work, balanced soft magnetic properties with low core loss and high magnetic induction are obtained in the fully compacted FeCo/CoFe2O4 composites, which promise great potential applications in high-power and high-frequency magnetic devices. This controlled surface oxidation may also provide an effective surface treatment for metal-based soft magnets to improve their overall performance.

Uranium binding by biochar fibres derived from Luffa cylindrica after controlled surface oxidation

Controlled surface modification of biochar fibres derived from Luffa cylindrica sponges has been carried out by nitric acid and the degree of oxidation could be controlled by changing the acid concentration or the reaction time. The extent of surface oxidation has been quantified by acid–base titration and FTIR-spectroscopy. Furthermore, uranium binding has been studied as a function of various parameters and the experimental results show that even under strong acidic conditions the relative sorption is above 80 % and the sorption capacity of the biochar fibres for U(VI) at pH 3 is qmax = 92 g kg−1.

Controlled surface oxidation of multi-layered graphene anode to increase hole injection efficiency in organic electronic devices

Ultraviolet ozone (UVO) surface treatment of graphene changes its sp2-hybridized carbons to sp3-bonded carbons, and introduces oxygen-containing components. Oxidized graphene has a finite energy band gap, so UVO modification of the surface of a four-layered graphene anode increases its surface ionization potential up to ∼5.2 eV and improves the hole injection efficiency (η) in organic electronic devices by reducing the energy barrier between the graphene anode and overlying organic layers. By controlling the conditions of the UVO treatment, the electrical properties of the graphene can be tuned to improve η. This controlled surface modification of the graphene will provide a way to achieve efficient and stable flexible displays and solid-state lighting.

Influence of controlled surface oxidation on the magnetic anisotropy of Co ultrathin films

We studied the influence of controlled surface-limited oxidation of electrodeposited epitaxial Co(0001)/Au(111) films on their magnetic anisotropy energy using real time in situ magneto optical Kerr effect and density functional theory (DFT) calculations. We investigated the Co first electrochemical oxidation step which we demonstrate to be completely reversible and determined the structure of this oxide layer. We show that the interface magnetic anisotropy of the Co film increases by 0.36 erg/cm2 upon Co surface oxidation. We performed DFT calculations to determine the different surface structures in a wide potential range as well as the charge transfer at the Co surface. Our results suggest that the magnetic anisotropy change is correlated with a positive charge increase of 0.54 e− for the Co surface atom upon oxidation.

Optimum conditions for fabricating superhydrophobic surface on copper plates via controlled surface oxidation and dehydration processes

The superhydrophobic surfaces on copper substrate were fabricated by direct oxidation and dehydration processes, and the reaction and modification conditions were optimized. Firstly, the oxidation conditions including the concentrations of K2S2O8 and NaOH, the oxidation time were studied. It is found that the superhydrophobicity would be better if the copper plates were oxidized in 0.06MK2S2O8 and 3.0M NaOH solution at 65°C for 35min. Then, the modification conditions including modifier concentration and modification time were investigated. The results showed that 5wt% lauric acid and 1h modification time were suitable modification conditions for preparing copper-based superhydrophobic surfaces. The surface fabricated under optimized conditions displayed excellent superhydrophobicity of high water contact angle of 161.1° and a low contact angle hysteresis of 2.5°. The surface microstructure and composition of the superhydrophobic surfaces were also characterized by SEM and FT-IR. It is found that the highly concentrated micro/nanostructured sheets and the low surface energy materials on the surface should be responsible for the high superhydrophobicity.

Fundamental Studies of Electrochemically Controlled Surface Oxidation and Hydrophobicity of Natural Enargite

The surface oxidation and hydrophobicity of natural enargite (Cu(3)AsS(4)) and the formation of oxidation species at the mineral surface have been examined by a novel experimental approach that combines electrochemical techniques and atomic force microscopy (AFM). This approach allows for in-situ, synchronized electrochemical control and examination of the oxidative surface morphology of enargite. Combined with ex-situ cryo X-ray photoelectron spectroscopy surface analysis, the surface speciation of enargite surface oxidation has been obtained, comparing the newly fractured natural enargite surface with those that have been electrochemically oxidized at pHs 4 and 10. At pH 4, surface layer formations consisting of metal-deficient sulfide and elemental sulfur were identified, associated with a limited increase in root-mean-square (rms) roughness (1.228 to 3.143 nm) and apparent heterogeneous distribution of surface products as demonstrated by AFM imaging. A mechanism of initial rapid dissolution of Cu followed by diffusion-limited surface layer deposition was identified. At pH 10, a similar mechanism was identified although the differences between the initial and diffusion-limited phases were less definitive. Surface species were identified as copper sulfate and copper hydroxide. A significant increase in surface roughness was found as rms roughness increased from 0.795 to 9.723 nm. Dynamic (receding) contact angle measurements were obtained by a droplet evaporation method. No significant difference in the contact angle on a surface oxidized at pH 10 and the freshly polished surface was found. A significant difference was found between the polished surface and that oxidized at pH 4, with an increase in contact angle of about 13° (46° to 59°) after oxidation. Competing effects of hydrophilic (copper oxides and hydroxides) and hydrophobic (elemental sulfur) species on the mineral surface under oxidizing conditions at pH 4 and the change in surface roughness at pH 10 may contribute to the observed effects of electrochemically controlled oxidation on enargite hydrophobicity.

Rapid Synthesis of Wettability Gradient on Copper for Improved Drop‐Wise Condensation

AbstractWe describe a simple method of making wettability gradients for the first time on copper using temperature controlled surface oxidation. The temperatures of the sample copper sheet are controlled to change from 330 to 620 K for a distance of 36 mm, with the presence of oxygen (air). Cone‐like Cu2O nanostructures are grown on the sample surface due to surface oxidation. Since the rate of oxidation varies with temperatures, the heights of the produced nanocones increase gradually from the cold end to the hot end, which create a wettability gradient in between, with water contact angles changing from 88° (the cold end) to 18° (the hot end). The same method can also be used for copper wires and tubes. Due to the extensive use of metal materials in industry, the technique presented here may have great importance for practical applications. The produced wettability gradient on copper, as an example, is demonstrated to be able to enhance water condensation rate up to 30%, depending on the direction of the gradient relative to gravity.

Dependence of the quality of adhesion between poly(dimethylsiloxane) and glass surfaces on the composition of the oxidizing plasma

Controlled surface oxidation of polydimethylsiloxane (PDMS) is essential for permanent adhesion between device components composed of this elastomer. The permanent adhesion between such microdevice components results from covalent crosslinking across the interfaces between PDMS and other silica-based materials, such as glass, quartz, and PDMS. Optimal duration and conditions of oxidation, attained via treatments with oxygen-containing plasma, are crucial for microfabrication procedures with quantitative yields. While insufficient PDMS oxidation does not provide high enough surface density of siloxyl groups for cross-interface linking, overoxidation of PDMS yields rough silica surface layers that prevent the adhesion between flat substrates. Ideally, for a set of plasma conditions, the range of treatment durations producing permanent adhesion should be as broad as possible: i.e., the surface oxidation of PDMS sufficient for irreversible binding has to complete significantly before the effects of overoxidation become apparent. Such a requirement assures that relatively small fluctuations in the treatment conditions will not result in over- or under-oxidation and, hence, will not compromise the yields of the fabrication procedures. We examined the dependence of the quality of adhesion (QA) between plasma-treated PDMS and glass substrates on the composition of the oxygen-containing plasma and on the radio frequency (RF) of the plasma generator. We observed that plasma generated at megahertz RF provided superior conditions than kilohertz RF. Concurrently, an increase in the oxygen content of binary gas mixtures, used for the plasma, broadened the treatment durations that afford superior QA.

Laser surface micro-engineering for industrial applications in Singapore

Some recent research in laser-induced surface ripple structures, surface ablation, surface colouration, and their potential industrial applications are discussed in this article. Both wavelength and sub-wavelength periodic surface structures were observed on semiconductors such as InP and GaN/sapphire surfaces after irradiation of femtosecond laser pulses. The orientation of the periodic structures was dependant on the laser beam polarization, and the period was dependent on the incident laser fluence. Such surface periodic structures may find applications in controlling surface hydrophobic and hydrophilic properties. Excimer laser ablation of epoxy compounds from wafer level chip size packages was found to be a feasible method to expose the micron-size Au bumps for solder reflow, which is a critical process in manufacturing portable electronic products. Studies on controlled surface oxidation by laser pulses showed that a range of colours can be achieved on a stainless steel surface. Selective Cr oxidation and iron oxides were detected. The appearance of colour is the result of the light constructive interference of the transparent oxide layer and is determined by the oxide thickness and the refractive index. The potential industrial applications of the techniques are discussed.

Analysis of oxide formation induced by UV laser coloration of stainless steel

Laser-induced coloration on metal surfaces has important applications in product identification, enhancing styles and aesthetics. The color generation is the result of controlled surface oxidation during laser beam interaction with the metal surfaces. In this study, we aim to obtain in-depth understanding of the oxide formation process when an UV laser beam interacts with stainless steel in air. The oxide layer is analysed by means of optical microscopy, scanning electron microscopy (SEM) and time-of-flight secondary ion mass spectrometer (TOF-SIMS). TOF-SIMS results clearly show the formation of duplex oxide structures. The duplex structure includes an inner layer of Cr oxide solution and an outer layer of Fe oxide solution. The oxide layer thickness increased as the results of Fe diffusion to surface during multiple laser scanning passes.

Super-hydrophobic CuO Nanoflowers by Controlled Surface Oxidation on Copper

A CuO nanoflower film was fabricated on copper by controlled surface oxidation in KOH aqueous solutions with an oxidant K2S2O8 and subsequent heat treatment in air. Results show that the nanoflower is formed by self-assembly of tens of CuO nanosheets. The nanosheet is about 2μm in length, 120nm in width, and 12nm in thickness. After fluorination treating, the nanoflower film exhibits super-hydrophobic properties, with a water contact angle of about 158? The possible mechanism was proposed on the growth of the CuO nanoflowers. Also, the wettability of the CuO films was discussed on the basis of Cassie theories.

Surface Characterizations of Carbon Multiwall Nanotubes: Comparison between Surface Active Sites and Raman Spectroscopy

In carbon nanotubes and nanofilaments, the surface properties play a fundamental role for any use or application. It is therefore necessary to know and to control their surface characteristics, which are dependent on the fabrication process and surface treatments. In this work, two selected series of multiwalled nanotubes on which a thermal treatment and/or a controlled surface oxidation, using nitric acid solutions, have been carried out. The structural changes of the nanotubes due to these treatments have been followed by means of two different approaches: first, a solid-state chemistry approach with the determination of chemical surface properties of the carbon characterized by the active surface area (ASA) concept and, second, a more physical approach with Raman microspectroscopy. With this track, it was possible to quantify the surface/morphology ratio in nanotubes, especially in relation with their wettability and adhesion. Hence, we have established a general relationship between physical and chem...

Nucleation controlled surface oxidation epitaxy of thermally grown NiO on (0 0 1) Ni for coated conductor applications assisted by Mo or Mn microalloying

High temperature oxidation of cube textured (1 0 0)Ni and (1 0 0)Ni–0.1wt%(Mo or Mn) was carried out in a wide temperature regime between 900 and 1400 °C in air. Special attention was paid to avoid pre-oxidation at lower temperatures, thus favouring nucleation controlled surface oxidation epitaxy (SOE) as opposed to SOE achieved by competitive grain growth. Consequently, cube textured epitaxial NiO layers, under 1 μm in thickness, have been grown on pure Ni in a much wider working window than previously published. Furthermore, thin cube textured NiO layers have been grown on Ni–0.1%Mo tape in a still wider working window of ∼200 °C between 1150 and 1350 °C. Preliminary results on Ni–0.1wt%Mn show a similar trend. An in-plane orientation of <5° and out of plane orientation approaching 2° was obtained. Single crystal like transparent NiO films were grown under optimal conditions.