Copper-based Surfaces Research Articles

Strategic approaches to enhance efficiency and commercial feasibility of copper-based surface plasmon resonance sensing

Despite enormous progress in the field of surface plasmon resonance (SPR) imaging sensor technology in the past three decades, noble metals like Au and Ag, despite their drawbacks, continue to be the metals of choice for plasmonic sensing layers. The conventional architecture of the SPR sensor based on gold/silver and glass prism hinders scaling, portability, and industrial manufacturing. In this contribution, we present a novel architecture of SPR sensor using copper on polycarbonate prism as a cost-effective, scalable, and mass-producible alternative. Various optimization techniques, such as interface layer, protective encapsulation, and 2D affinity layer are explored to address the challenges related to the practical application of copper in a plasmonic sensor. Our results show that optimized architectures of SPR sensor based on copper has a sensitivity of 235.01°/RIU. From a quantitative analysis of the interrelationships among various performance parameters, we have derived a comprehensive sensing parameter that integrates signal quality and sensitivity. The proposed architecture of the copper based SPR sensor can lead to inexpensive, compact, and handy probes that do not sacrifice accuracy or reliability.

Dual BaTiO3 layer-cavity assisted enhancement of copper-based surface plasmon resonance biosensor

Studies have shown that the two-dimensional transition metal dichalcogenides, graphene and MXene (Ti3C2Tx), and other materials not only can effectively improve the sensitivity of the surface plasmon resonance (SPR) biosensor but also reduce the detection accuracy. A SPR sensor based on dual barium titanate (BaTiO3) layers forming Fabry-Pérot (F-P) cavity was proposed to achieve this goal. Specifically, we employed a copper/nickel (Cu/Ni) bimetal as the plasmonic metal, two layers of BaTiO3 wrapped Cu/Ni bimetal to form a F-P cavity structure, and PMMA as the sensing layer. By optimizing the thickness of each film layer, the sensitivity reached 554.6 º/RIU, 6.2% higher than Cu/Ni/PMMA structure, and the corresponding full width at half maximum (FWHM) decreased by 15.4%. In addition, we used seven two-dimensional materials to replace PMMA but keeping other parameters unchanged, the obtained FWHM of the reflection spectrum was also reduced. These findings may benefit the application of the Fabry-Pérot cavity in biosensors and spectral modulation.

Molecular dynamics investigation of argon evaporation on copper surfaces covered with graphene and carbon nanotubes

The recent advancements in nanoscience have led to a significant improvement in surface characteristics, which play a critical role in heat transfer. In this study, the heat transfer of modified copper-based surfaces covered with graphene sheets and carbon nanotubes (CNTs) is investigated using molecular dynamics method, and compared with the heat transfer of a simple copper surface. To modify the surfaces, various numbers of carbon nanotubes with different heights are used. Investigations are conducted on the dynamics of liquid argon clusters, the distribution of argon density, temperature changes, and the phase transition from liquid to the gas. In comparison to the pre-defined reference surface, heat transfer shows an improvement for the copper-based surface coated with graphene platelets. Similarly, simulation results indicate that the increase in both the quantity and height of carbon nanotubes leads to the enhancement of the heat transfer of the surface. Additionally, it is found that, when CNTs are inserted on a surface, a shorter time is required for liquid argon to reach the temperature of solid surface.

Artistic and Laboratory Patinas on Copper and Bronze Surfaces

The study of characterisation and production of artificial patinas plays a key role in the field of cultural heritage. In particular, artistic patinas should be considered as an integral part of the artworks, as they are deliberately produced by artists and metalworkers as a part of their artistic design. Therefore, it is important to achieve a good knowledge of their composition and corrosion behaviour in order to setup and perform optimal conservation strategies for their preservation. In addition, the possibility of realising laboratory patinas that are as representative as possible of natural corrosion layers is important for the realisation of laboratory specimens which can be used as reliable model systems (mock-ups) for the study of degradation mechanisms and conservative treatments. For this work, both artistic and laboratory patinas have been considered and investigated. In particular, six different artistic patinas produced by Fonderia Artistica Battaglia were characterised. Moreover, a series of laboratory patinas was produced according to chemical procedures adapted from those already reported in the literature. The patina morphology was evaluated by stereomicroscopy observations, their composition was analysed by means of FTIR and XRD analysis and their corrosion behaviour was evaluated by LPR and EIS measurements. Finally, the LPR and EIS analysis have pointed out the low protection provided by the corrosion layers of artistic patinas. In regard to laboratory patinas, the optimized procedures of production were found to be effective for the realization of the main corrosion products of copper-based surfaces. From an electrochemical point of view in particular, quite different electrochemical behaviours were observed on artificial corrosion layers with the same chemical composition.

Influence of topography on electrical contact resistance of copper-based materials

The design of an electrical contact is crucial to ensure optimal performance, reliability, and efficiency of connectors. One key aspect is the surface quality of the contacting bodies—among other factors such as material selection, contact geometry, etc. In this work, we evaluated the influence on electrical contact resistance (ECR) of a smooth copper-based surface (brass, bronze, and tin-plated copper) when contacted against surfaces with different degrees of roughness. Furthermore, a carbon nanotube (CNT) coating was proposed with the goal of mitigating the topography-induced influence of the textured counter electrodes. The electrodes and counter electrodes were thoroughly characterized to understand the contacting mechanisms through numerical modeling,—namely, Greenwood-Williamson and Jackson-Green models—as well as using a practical-oriented slope analysis. Load-dependent ECR measurements were carried out to quantify the effect of roughness on contact resistance. When contacting against brass and bronze, a clear correlation between roughness and ECR can be established, with higher roughness equating to lower ECR In tin-plated copper, on the other hand, this hierarchy is not as well defined due to the ease with which the tin plating deforms, thus enabling the penetration of outstanding asperities and consequently establishing a better electrical contact. CNT-coated counter electrodes showed promising results, partially confirming the hypothesis proposed. However, unforeseen topography-related interactions with the CNT coating produced exceptions in the ECR measurements. Nonetheless, for most cases studied the coating did mitigate the influence of roughness.

Research proposal on architectural copper-based antimicrobic solutions in high traffic spaces

This contribution investigates research opportunities in the field of architecture and design management focusing on user health in high traffic spaces. The field of application is Airport Passenger Terminals. Looking at the COVID-19 pandemic and anticipating the possibility of events of the same magnitude, it is necessary to approach the problem of the safety in public spaces. Based on the State of the Art about antimicrobial material studies, Science of Architecture could propose innovative solutions that are compliant with health safety and prevention for high-use surfaces. These solutions will combine antimicrobial materials with a digital solution that could manage data about surfaces, allowing the maintenance team to valuate and optimize operations. After few hours the hygiene level of copper-based surfaces is higher than any other material. Copper-based furniture could be paired with sensors that send data to management software. Combining the use of scientifically demonstrated antibacterial surfaces with high-performance management tools could be the best option to achieve health safety and contribute to social sustainability. Airport terminals are the ideal high-traffic buildings to use as test model because they have all the characteristics that could be analysed concerning the safety and the perception of safety of architectural spaces by users.

Copper-based surface plasmon coupled emission steering for biosensor applications

Surface plasmon coupled emission (PCE) was demonstrated using Copper (Cu) as metal film and Rhodamine B (RhB) dye doped Poly Vinyl Alcohol (PVA) as dielectric layer coupled to a hemicylindrical prism in Reverse Kretschmann (RK) configuration. Emission directionality was observed due to PCE and the dielectric layer thicknesses highly influence PCE emission steering. A correlation of emission directionality and the dielectric layer thickness was achieved. For dielectric with higher thicknesses, PCE tuning was also observed apart from emission steering. Emission steering and a promising PCE tuning in Cu could pave the way for a cost effective PCE based bio-chemical sensor.

Controlling Morphology and Wettability of Intrinsically Superhydrophobic Copper-Based Surfaces by Electrodeposition

Electrodeposition is an effective and scalable method to grow desired structures on solid surfaces, for example, to impart superhydrophobicity. Specifically, copper microcrystals can be grown using electrodeposition by controlling deposition parameters such as the electrolyte and its acidity, the bath temperature, and the potential modulation. The aim of the present work is the fabrication of superhydrophobic copper-based surfaces by electrodeposition, investigating both surface properties and assessing durability under conditions relevant to real applications. Accordingly, copper-based layers were fabricated on Au/Si(100) from Cu(BF4)2 precursor by electrodeposition, using cyclic voltammetry and square-pulse voltage approaches. By increasing the bath temperature from 22 °C to 60 °C, the growth of various structures, including micrometric polyhedral crystals and hierarchical structures, ranging from small grains to pine-needle-like dendrite leaves, has been demonstrated. Without any further physical and/or chemical modification, samples fabricated with square-pulse voltage at 60 °C are superhydrophobic, with a contact angle of 160° and a sliding angle of 15°. In addition, samples fabricated from fluoroborate precursor are carefully compared to those fabricated from sulphate precursor to compare chemical composition, surface morphology, wetting properties, and durability under UV exposure and hard abrasion. Results show that although electrodeposition from fluoroborate precursor can provide dendritic microstructures with good superhydrophobicity properties, surfaces possess lower durability and stability compared to those fabricated from the sulphate precursor. Hence, from an application point of view, fabrication of copper superhydrophobic surfaces from sulphate precursor is more recommended.

Comment on "High-Resolution Microscopical Studies of Contact Killing Mechanisms on Copper-Based Surfaces".

In the original paper, Chang and co-workers describe the contact killing of Bacillus subtilis, a Gram-positive bacterium, on copper-containing substrates and offer a mechanism for its accomplishment. The present Comment offers support for that mechanism and adds a necessary initial step, the degradation of the overlying peptidoglycan lattice. Degradation is necessary because the lattice is too thick, and its pores too small, for substrate-membrane contact without it. A suggestion is offered as to how degradation is accomplished.

High-Resolution Microscopical Studies of Contact Killing Mechanisms on Copper-Based Surfaces.

The mechanisms of bacterial contact killing induced by Cu surfaces were explored through high-resolution studies based on combinations of the focused ion beam (FIB), scanning transmission electron microscopy (STEM), high-resolution TEM, and nanoscale Fourier transform infrared spectroscopy (nano-FTIR) microscopy of individual bacterial cells of Gram-positive Bacillus subtilis in direct contact with Cu metal and Cu5Zn5Al1Sn surfaces after high-touch corrosion conditions. This approach permitted subcellular information to be extracted from the bioinorganic interface between a single bacterium and Cu/Cu5Zn5Al1Sn surfaces after complete contact killing. Early stages of interaction between individual bacteria and the metal/alloy surfaces include cell leakage of extracellular polymeric substances (EPSs) from the bacterium and changes in the metal/alloy surface composition upon adherence of bacteria. Three key observations responsible for Cu-induced contact killing include cell membrane damage, formation of nanosized copper-containing particles within the bacteria cell, and intracellular copper redox reactions. Direct evidence of cell membrane damage was observed upon contact with both Cu metal and Cu5Zn5Al1Sn surfaces. Cell membrane damage permits copper to enter into the cell interior through two possible routes, as small fragmentized Cu2O particles from the corrosion product layer and/or as released copper ions. This results in the presence of intracellular copper oxide nanoparticles inside the cell. The nanosized particles consist primarily of CuO with smaller amounts of Cu2O. The existence of two oxidation states of copper suggests that intracellular redox reactions play an important role. The nanoparticle formation can be regarded as a detoxification process of copper, which immobilizes copper ions via transformation processes within the bacteria into poorly soluble or even insoluble nanosized Cu structures. Similarly, the formation of primarily Cu(II) oxide nanoparticles could be a possible way for the bacteria to deactivate the toxic effects induced by copper ions via conversion of Cu(I) to Cu(II).

Machine Learning and Statistical Approach to Predict and Analyze Wear Rates in Copper Surface Composites

This research demonstrates the application of machine learning models and statistics methods in predicting and analyzing dry sliding wear rates on novel copper-based surface composites. Boron nitride particles of varying fractions was deposited experimentally over the copper surface through friction stir processing. Experimental and statistical analysis proved that the presence of BN particles can reduce wear rate considerably. Analysis of worn-out surface revealed a mild adhesive wear during low load condition and an abrasive mode of wear during higher load conditions. Artificial neural network based feed forward back propagation model with topology 4-7-1 was modeled and prediction profiles displayed good agreement with experimental outcomes.

Investigation of the Corrosion Behavior of Atomic Layer Deposited Al₂O₃/TiO₂ Nanolaminate Thin Films on Copper in 0.1 M NaCl.

Fifty nanometers of Al2O3 and TiO2 nanolaminate thin films deposited by atomic layer deposition (ALD) were investigated for protection of copper in 0.1 M NaCl using electrochemical techniques. Coated samples showed increases in polarization resistance over uncoated copper, up to 12 MΩ-cm2, as measured by impedance spectroscopy. Over a 72-h immersion period, impedance of the titania-heavy films was found to be the most stable, as the alumina films experienced degradation after less than 24 h, regardless of the presence of dissolved oxygen. A film comprised of alternating Al2O3 and TiO2 layers of 5 nm each (referenced as ATx5), was determined to be the best corrosion barrier of the films tested based on impedance spectroscopy measurements over 72 h and equivalent circuit modeling. Dissolved oxygen had a minimal effect on ALD film stability, and increasing the deposition temperature from 150 °C to 250 °C, although useful for increasing film quality, was found to be counterproductive for long-term corrosion protection. Implications of ALD film aging and copper-based surface film formation during immersion and testing are also discussed briefly. The results presented here demonstrate the potential for ultra-thin corrosion barrier coatings, especially for high aspect ratios and component interiors, for which ALD is uniquely suited.

Facile fabrication and hydrophobic properties of Cu2O nanowire films on Cu substrates

Abstract Cu2O nanowires have been grown on Cu substrates by electrochemical etching followed with dehydration annealing. The as resulted films show excellent hydrophobic performance without organic surface modification. The contact angles (and slide angles) of the as-resulted Cu2O nanowire films grown on Cu mesh, Cu foam, and Cu foil are 168.3 ± 0.09° (slide angle 19°), 171.7 ± 0.28° (slide angle 22°), and 172.8 ± 0.96° (slide angle 2°), respectively. The Cu2O nanowire films on Cu foil represent the best hydrophobic activity for copper-based surfaces without any organic modification and additives. The special configurations of the Cu2O nanowire films on the Cu substrates and their surface energies both have impacts on the excellent hydrophobic performance. The growth mechanism and the performance-structure relationship of the Cu2O nanowire films are also discussed. This study suggests a low-cost and environment friendly method for the preparation of hydrophobic coating material.

Interfacing a Potential Purely Organic Molecular Quantum Bit with a Real-Life Surface.

By using a multidisciplinary and multitechnique approach, we have addressed the issue of attaching a molecular quantum bit to a real surface. First, we demonstrate that an organic derivative of the pyrene-Blatter radical is a potential molecular quantum bit. Our study of the interface of the pyrene-Blatter radical with a copper-based surface reveals that the spin of the interface layer is not canceled by the interaction with the surface and that the Blatter radical is resistant in presence of molecular water. Although the measured pyrene-Blatter derivative quantum coherence time is not the highest value known, this molecule is known as a "super stable" radical. Conversely, other potential qubits show poor thin film stability upon air exposure. Therefore, we discuss strategies to make molecular systems candidates as qubits competitive, bridging the gap between potential and real applications.

Low-Voltage Reversibly Switchable Wettability through Electrochemical Manipulation of Oxidation State

Various biological organisms in nature exhibit unique surface wettability in order to adapt to their living environment. Diverse range of wettability can be observed, ranging from the low-adhesion superhydrophobic lotus leaf with self-cleaning property, high-adhesion superhydrophobic gecko foot, to the in-air superhydrophilic and underwater superoleophobic fish scale. Inspired by these natural systems with superwetting/antiwetting properties, significant efforts have been devoted to fabricate artificial surfaces with different wettabilities by engineering the surface morphology and chemical composition. Of particular interest is the stimuli-responsive surface which integrates two extreme wetting states of water-attracting and water-repelling properties. External stimuli such as temperature, light, pH, and electrical potential could induce reversible changes in the wetting behavior of the smart surface through transformation in the topological structure and/or surface chemistry. Here we present a novel approach for reversible wettability cycling on dendritic core-shell copper nanostructure surface through electrochemical modulation of the oxidation state. Application of low voltage in the range of regular alkaline battery (<1.5 V) converts the as-prepared copper-based surface from roll-off superhydrophobic, to sticky superhydrophobic, and superhydrophilic wetting state. Precise control over the rate and extent of the wetting switching is achieved by tuning the magnitude and period of the applied voltage. Air drying at room temperature for 1 hour or mild heat drying at 100°C for 30 min reverses the wettability transition to initial superhydrophobic state with low adhesion easy roll-off property. We describe the underlying mechanism for the reversible adhesion and wettability switching from the physical and electrochemical perspectives, as well as practical applicability of this method with specific demonstration for on-demand oil-water separation. The in-situ adhesion and wettability control reported in this work provide a platform for design of oxidation state-mediated wetting transition on different metal oxides for application in remote water filtration, atmospheric water harvesting, droplet manipulation, and microfluidic lab-on-a-chip application.

Optimizing the Tribological Behavior of Hybrid Copper Surface Composites Using Statistical and Machine Learning Techniques

Copper-based surface composite dispersed with varying fractions of hybrid reinforcement was fabricated through friction stir processing (FSP). Hybrid reinforcement particles were prepared from aluminum nitride (AIN) and boron nitride (BN) particles of equal weight proportion. Based on design of experiments, wear characteristics of the developed copper surface composites were estimated using pin-on-disk tribometer. Experimental parameters include volumetric fraction of hybrid reinforcement particles (5, 10, and 15 vol %), load (10, 20, 30 N), sliding velocity (1, 1.5, and 2 m/s), and sliding distance (500, 1000, and 1500 m). Microstructural characterization demonstrated uniform dispersion of hybrid reinforcement particles onto the copper surface along with good bonding. Hardness of the developed surface composites increased with respect to increase in hybrid particle dispersion when compared with copper substrate while a reduction in density values was revealed. Analysis on wear rate values proved that wear rate decreased with increase in hybrid particle dispersion and increased with increase in load, sliding velocity, and distance. Analysis of variance (ANOVA) specified load as the most significant factor over wear rate values followed by volume fractions of particle dispersion, sliding velocity, and distance. Regression model constructed was found efficient in predicting wear rate values. Analysis of worn out surfaces through scanning electron microscopy (SEM) revealed the transition of severe to mild wear with respect to increase in hybrid reinforcement particle dispersion. A feed forward back propagation algorithm-based artificial neural network (ANN) model with topology 4-7-1 was developed to predict wear rate of copper surface composites based on its control factors.

Tailoring gas-phase CO2 electroreduction selectivity to hydrocarbons at Cu nanoparticles

Copper-based surfaces appear as the most active catalysts for CO2 electroreduction to hydrocarbons, even though formation rates and efficiencies still need to be improved. The aim of the present work is to evaluate the continuous gas-phase CO2 electroreduction to hydrocarbons (i.e. ethylene and methane) at copper nanoparticulated-based surfaces, paying attention to particle size influence (ranging from 25–80 nm) on reaction productivity, selectivity, and Faraday efficiency (FE) for CO2 conversion. The effect of the current density and the presence of a microporous layer within the working electrode are then evaluated. Copper-based gas diffusion electrodes are prepared by airbrushing the catalytic ink onto carbon supports, which are then coupled to a cation exchange membrane (Nafion) in a membrane electrode assembly. The results show that the use of smaller copper nanoparticles (25 nm) leads to a higher ethylene production (1148 μmol m−2 s−1) with a remarkable high FE (92.8%), at the same time, diminishing the competitive hydrogen evolution reaction in terms of FE. This work demonstrates the importance of nanoparticle size on reaction selectivity, which may be of help to design enhanced electrocatalytic materials for CO2 valorization to hydrocarbons.