Polycrystalline Copper Foils Research Articles

Growth of centimeter-scale single-crystal graphene on polycrystalline copper foil for ultrahigh sensitive sweat sensors

The low-cost growth of wafer-scale single-crystal (SC) shows great potential in its practical application. Epitaxial growth of large-area SC graphene on pre-produced SC metal foil with a specific index surface has been reported, which requires a high cost and complexity of operational processes. Here, we demonstrate an easy and low-cost approach for the growth of wafer-scale SC graphene on polycrystalline copper foil, the growth kinetics and the lattice orientation for graphene growth controlled by induced surface steps. Despite graphene domains grown across the Cu grain boundary, the domains have a common crystal orientation at the macroscale induced by the surface steps. This work demonstrates the polycrystalline Cu foil can also grow graphene domains with unidirectional alignment and seamless stitching on the large area. The wearable 2D graphene array sensors have also been developed for the detection of interleukin-6 (IL-6) in sweat, which can locate and detect infection or disease in a non-invasive way. Our growth method and novel application put up a new way of production and utilization of SC two-dimensional (2D) materials.

Nanotwinned Copper Foil for “Zero Excess” Lithium–Metal Batteries

The “zero excess” lithium–metal battery cell concept, in which the pristine negative electrode consists only of the current collector, while all lithium is present only in the positive electrode active material, promises substantial improvements in energy density. However, the achievement of stable cycling for more than just a few cycles requires a careful design and adjustment of all cell components─especially the current collector at the negative electrode. Herein, we provide a comparative investigation of commercial, polycrystalline copper foil, characterized by a rather random [111], [200], and [220] orientation and a high concentration of grain boundaries, and nanotwinned copper foil, which has a solely [111]-oriented grain structure. Remarkably, the plated lithium on the foil with [111] orientation reveals a much more homogeneous morphology independent of the current density applied, while several dendritic lithium deposits are observed on the polycrystalline copper foil. This also translates into higher Coulombic efficiency and stabilized cycling performance of Cu[111]||NMC811 cells, highlighting the important impact of the crystal orientation of the current collector.

Oxygen activated CVD growth of large-area multilayer h-BN on polycrystalline copper foils

The synthesis of large-area multilayer hexagonal boron nitride (h-BN) is a prerequisite for advanced 2D material-based transparent electronics. The formation of large-area h-BN domains limits the possibility of grain boundary leakage current and mechanical ruptures of h-BN layers. In this work, we report the oxygen-activated synthesis of high-quality multilayer h-BN on polycrystalline copper foils, to reduce the nucleation site density and enhance the size of h-BN domains up to ∼180 μm. The oxygen-activated synthesized h-BN domains are at least 20–30 times larger than the domains synthesized by the non-oxygen-based synthesis process.Experimental results demonstrate that the h-BN domain size does not depend on the crystal orientation of the catalyst. X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), Atomic force microscopy (AFM), and Angle-resolved photoemission spectroscopy (μ-ARPES) measurements together with Raman spectroscopy indicate that the synthesized h-BN layers are of high quality.

Front Cover: Benchmarking the Electrochemical CO2 Reduction on Polycrystalline Copper Foils: The Importance of Microstructure Versus Applied Potential (ChemCatChem 21/2022)

The Front Cover shows five polycrystalline copper surfaces, with differing microstructural features, on which the electrochemical CO2 reduction reaction is performed. In their Research Article, R. Kortlever and co-workers benchmark the electrochemical CO2 reduction reaction on five commercial polycrystalline copper foils. A thorough characterization of these foils show that they possess different microstructural features, such as grain sizes, crystallite sizes, micro-strains and crystallographic orientations. However, the study finds that the CO2 reduction performance of these foils is very similar. The obtained results stress the importance of the applied potential as a dominant factor controlling the electrocatalytic performance, outperforming microstructural effects in polycrystalline copper foils. More information can be found in the Research Article by R. Kortlever and co-workers.

Benchmarking the Electrochemical CO2 Reduction on Polycrystalline Copper Foils: The Importance of Microstructure Versus Applied Potential

AbstractCopper is one of the most promising catalysts for the CO2 reduction reaction (CO2RR) due to its unique capability of producing multicarbon products in appreciable quantities. Most of the CO2RR research efforts have been directed towards the development of new electrocatalysts to either increase product selectivities or decrease overpotentials. In contrast, only a few studies have systematically tested or benchmarked CO2RR performances of electrocatalysts. In this paper, for the first time, the performances of five different polycrystalline copper foils purchased from different suppliers are benchmarked for their CO2RR performance. Their differences are characterized in terms of microstructural features and the effect that these microstructural properties have on the electrocatalytic behavior during potentiostatic CO2RR experiments are evaluated. It is shown that the potential applied is the dominant factor controlling CO2RR selectivities, leading to the conclusion that microstructural properties of polycrystalline copper electrodes have a negligible effect on the outcome of CO2RR experiments.

Silica Particle-Mediated Growth of Single Crystal Graphene Ribbons on Cu(111) Foil.

The authors report the growth of micrometer-long single-crystal graphene ribbons (GRs) (tapered when grown above 900°C, but uniform width when grown in the range 850°C to 900°C) using silica particle seeds on single crystal Cu(111) foil. Tapered graphene ribbons grow strictly along the Cu<101> direction on Cu(111) and polycrystalline copper (Cu) foils. Silica particles on both Cu foils form (semi-)molten Cu-Si-O droplets at growth temperatures, then catalyze nucleation and drive the longitudinal growth of graphene ribbons. Longitudinal growth is likely by a vapor-liquid-solid (VLS) mechanism but edge growth (above 900°C) is due to catalytic activation of ethylene (C2 H4 ) and attachment of C atoms or species ("vapor solid" or VS growth) at the edges. It is found, based on the taper angle of the graphene ribbon, that the taper angle is determined by the growth temperature and the growth rates are independent of the particle size. The activation enthalpy (1.73± 0.03eV) for longitudinal ribbon growth on Cu(111) from ethylene is lower than that for VS growth at the edges of the GRs (2.78 ±0.15eV) and for graphene island growth (2.85± 0.07eV) that occurs concurrently.

Microstructural Analysis of Copper Foil Etched and Annealed in ECR Plasma Reactor

Microstructural analysis of commercially available cold-rolled polycrystalline copper foil, etched and annealed in an in-house developed Electron Cyclotron Resonance (ECR) Plasma Enhanced Chemical Vapour Deposition (PE-CVD) reactor, have been carried out using x-ray diffraction (XRD) studies. The annealing experiments were carried out under a vacuum environment, keeping the working pressure of the reactor at 50×10-3 mbar, for three different time spans of 30 mins, 45 mins and 1 hour at 823 K (550 °C) and 923 K (650 °C) respectively in presence of hydrogen plasma. The XRD studies reveal the significance of annealing time at two different temperatures for the determination of physical and microstructural parameters such as the average grain size and micro-strain in copper lattice by Williamson-Hall (W-H) method.

DEVELOPMENT OF PLASTIC DEFORMATION IN TWO-DIMENSIONAL COPPER POLYCRYSTALS WITH DIFFERENT TWIN STRUCTURE

Experimental studies of regularities of occurrence and development of substructural and orientational heterogeneity of polycrystalline copper foils with different twin structure in the process of their deformation in conditions of active tension have been carried out. It is shown that by selecting the regime of thermal treatment of fine-grained copper foil three types of samples with different twin structure can be obtained. The first type is characterized by the presence of twins, which differ in size, shape and type of boundaries. Samples of the second type contain twins with faceted boundaries. Samples of the third type contain parallel twins with rectilinear boundaries. Such a variety of twin structures not only predetermines the difference of mechanical characteristics for samples of different types but also regularities of substructure and orientation changes accompanying the plastic deformation of samples. The use of a highly sensitive imaging method that allows in situ characterization of substructural and orientational heterogeneity during deformation and other methods (optical and raster microscopy, interferometry) allowed us to detect specific features of the course of relaxation processes in samples of different types.

Triethylborane as Single Boron and Carbon Source Toward Stable and Homogeneous Boron‐Doped Graphene

Herein, the synthesis of a stable and homogeneous boron‐doped graphene film using triethylborane as a single source of carbon and boron is reported. The effects of triethylborane amount and growth time on the synthesis of doped graphene are investigated under the same growth conditions on polycrystalline copper foil in a three‐zone chemical vapor deposition (CVD) system, which has not thus far been researched in detail. The findings show that boron‐doped graphene films are successfully synthesized. The results enable the design of a recipe for thin‐film doped graphene grown with optimum optical transmission and sheet resistance via amending TEB molarity and growth time. Such changes suggest that the single‐layer graphene film with high homogeneity can be obtained for the film grown using 0.5 m triethylborane along with 10 min growth time as confirmed by Raman mapping and atomic force microscope (AFM) measurements. It is further revealed that increasing the amount of triethylborane and growth times leads to the formation of thicker graphene films. In addition, X‐ray photoelectron spectrometer (XPS) measurements indicate that boron atoms get into a honeycomb structure, thanks to substitutional doping. The findings of this study have significant implications for the implementation of boron‐doped graphene films in semiconductor‐based technology.

On the growth of copper oxide nanowires by thermal oxidation near the threshold temperature at atmospheric pressure

This study focuses on the growth of copper oxide nanowires networks (CuO NWs) close to the onset temperature, found to be 310 ℃. The NWs were obtained by thermal oxidation in air of polycrystalline copper foils on hot plate. The investigated oxide layers with the NWs network on their surface grown between 200 ℃ and 440 ℃, were characterized by: SEM-EDX, STEM-EDX, XRD, and micro-Raman techniques. The accurate determination of copper content in self-exfoliated oxide sheets is above the stoichiometric concentration. XRD reveals nano-crystallites of 20–40 nm, in Cu2O phase of thick oxide sheets located close to the oxide-substrate interface. Statistical data on the average length of the NWs versus annealing time indicates unexpected early saturation in between 10 and 40 min at 320–340 ℃. A semi-empirical model proofs quantitatively that the emerging delays of the NWs relative to the start of copper oxidation determine the plateau of the average length versus time. The excess concentration of copper found in the cuprous oxide layer is cautioned to accompany the early saturation effect having critical restrictions regarding the oxidation time and temperature. This study sustains the development of control and monitoring methods, applied to the growth of CuO NWs.

Effect of copper pretreatment on optical and electrical properties of camphor-based graphene by chemical vapour deposition

Polycrystalline copper (Cu) foil is widely used as catalytic substrate for graphene growth in chemical vapor deposition (CVD) technique. The surface properties of the Cu foil strongly affect the growth behavior and final quality of CVD-grown graphene. The effect of pretreatment of Cu foil using four different solutions (acetone, acetic acid, HCl and HNO3) on the graphene growth held in atmospheric pressure CVD and its subsequent impact on electrical and optical properties are investigated. Natural camphor is used as the solid carbon precursor. The surface characteristics before and after the growth are studied using scanning electron microscopy and atomic force microscopy. The pretreatment conditions of Cu and the growth of graphene from camphor were correlated using Raman spectroscopy, optical and electrical characteristics. Our findings suggest that HCl-pretreated Cu foil exhibited large domain, uniform coverage of the transferred graphene with excellent optical (> 93% at 550 nm) and electrical properties (sheet resistance of 861 ± 40 Ω/sq), with promisingly low RMS value of roughness (38 nm). The pretreatment process improved the quality of graphene by removing the surface impurity particles and surface native oxides. A Schottky junction diode of graphene/n-silicon is fabricated by transferring the graphene to SiO2/Si substrate under dark and illuminated conditions is also demonstrated to establish its potential in micro- and opto-electronics.

Fast growth of centimeter-scale single-crystal copper foils with high-index planes by the edge-incision effect

Single-crystal copper substrates have gained importance for the preparation of high-quality graphene and hexagonal boron nitride monolayer films by chemical vapor deposition (CVD). Especially, large-scale single-crystal copper foils with high-index planes are synthesized recently and attract great interests. However, the current synthesis methods of single-crystal copper foils and films are energy and time-consuming. Here, we show a rapid and efficient approach for the preparation of centimeter-scale single-crystal copper foils by making small incisions at the edges of polycrystalline copper foils before high-temperature annealing. 1.5 cm × 4 cm pieces of grain-boundary-free copper foils can be prepared by annealing at 1080 °C for 60 min. The annealed copper foil manifests a single high-index plane and is grain-boundary-free over the whole area. We also show that CVD of graphene on the high-index single-crystal copper affords a higher growth rate than on low-index copper substrates.

Permanent Boron Doped Graphene with high Homogeneity using Phenylboronic Acid

In this paper, we report on boron doped graphene synthesis using phenylboronic acid as a single source of carbon and boron. The growth conditions were established and optimized to improve the opto-electronic properties of a graphene film. The effects of the phenylboronic acid amount and growth time on the synthesis of graphene were investigated under similar growth conditions on polycrystalline copper foil in a three-zone CVD system. Based on Raman and XPS analysis, boron doped graphene was successfully synthesized under the given growth conditions in this study. It was also found that increasing the amount and growth times led to thicker graphene films. However, a single layer region was only found for a film grown using 0.5 gr phenylboronic acid along with 30-minute growth time, which is in contrast with the current literature. Additionally, carbon atoms were found to be substituted by the boron atoms in the honeycomb structure as revealed by the XPS measurements. Substitutional doping enables the doping to be stable for a long time, which is crucial for the doping to be employed in semiconducting technology particularly in optoelectronics.

Strain relaxation in different shapes of single crystal graphene grown by chemical vapor deposition on copper

The chemical vapor deposition (CVD) growth of single-crystal graphene on polycrystalline copper foils is a complex process affected by thermodynamics, kinetics, and growth conditions. These factors lead to the diversity of island shapes of single crystal graphene. Here, we present an experimental atomic force microscopy (AFM) study of the different shapes of single-crystal graphene grown on the inner surface of copper enclosures using the low pressure CVD technique. Most remarkably, this study indicates that graphene single crystal appears to form below the adjacent copper foil surface. This feature is revealed in cross sectional AFM scans of the height, which indicate that the graphene surface lies below the neighboring foil surface by ∼15–30 nm. Our results also show that an impurity assisted growth mechanism governs the growth of single crystal graphene via isotropic diffusion, producing two-fold, four-fold, and six-fold symmetries in the resulting flakes. In addition, single crystal graphene produced via anisotropic diffusion is also present here, but they do not exhibit signs of an impurity assisted growth mechanism. Finally, we find that strain relaxation in two-fold and four-fold symmetric graphene structures via isotropic diffusion is more complicated than the six-fold structures via isotropic diffusion, which results in multiple steps orientations in low symmetry structures.

A novel electrochemical sensor based on double-walled carbon nanotubes and graphene hybrid thin film for arsenic(V) detection

In this work, we demonstrate the preparation of hybrid thin films based on double-walled carbon nanotubes and graphene for electrochemical sensing applications. The hybrid films were synthesized on polycrystalline copper foil by thermal chemical vapor deposition under low pressure. This carbonaceous hybrid film has exhibited high transparency with a transmittance of 94.3 %. The occurrence of this hybrid material on the electrode surface of screen-printed electrodes was found to increase electroactive surface area by 1.4 times, whereas electrochemical current was enhanced by 2.4 times. Such a highly transparent and conductive hybrid film was utilized as a transducing platform of enzymatic electrochemical arsenic(V) sensor. The as-prepared sensor shows the linear detection of arsenic(V) in the range from 1 to 10 ppb, with a limit of detection as low as 0.287 ppb. These findings provide a promising approach to develop new multifunctional electrochemical sensing systems for environmental monitoring and biomedical diagnostics.

Seeded growth of large single-crystal copper foils with high-index facets.

The production of large single-crystal metal foils with various facet indices has long been a pursuit in materials science owing to their potential applications in crystal epitaxy, catalysis, electronics and thermal engineering1-5. For a given metal, there are only three sets of low-index facets ({100}, {110} and {111}). In comparison, high-index facets are in principle infinite and could afford richer surface structures and properties. However, the controlled preparation of single-crystal foils with high-index facets is challenging, because they are neither thermodynamically6,7 nor kinetically3 favourable compared to low-index facets6-18. Here we report a seeded growth technique for building a library of single-crystal copper foils with sizes of about 30×20 square centimetres and more than 30 kinds of facet. A mild pre-oxidation of polycrystalline copper foils, followed by annealing in a reducing atmosphere, leads to the growth of high-index copper facets that cover almost the entire foil and have the potential of growing to lengths of several metres. The creation of oxide surface layers on our foils means that surface energy minimization is not a key determinant of facet selection for growth, as is usually the case. Instead, facet selection is dictated randomly by the facet of the largest grain (irrespective of its surface energy), which consumes smaller grains and eliminates grain boundaries. Our high-index foils can be used as seeds for the growth of other Cu foils along either the in-plane or the out-of-plane direction. We show that this technique is also applicable to the growth of high-index single-crystal nickel foils, and we explore the possibility of using our high-index copper foils as substrates for the epitaxial growth of two-dimensional materials. Other applications are expected in selective catalysis, low-impedance electrical conduction and heat dissipation.

Electrochemically scrambled nanocrystals are catalytically active for CO2-to-multicarbons

Promotion of C-C bonds is one of the key fundamental questions in the field of CO2 electroreduction. Much progress has occurred in developing bulk-derived Cu-based electrodes for CO2-to-multicarbons (CO2-to-C2+), especially in the widely studied class of high-surface-area "oxide-derived" copper. However, fundamental understanding into the structural characteristics responsible for efficient C-C formation is restricted by the intrinsic activity of these catalysts often being comparable to polycrystalline copper foil. By closely probing a Cu nanoparticle (NP) ensemble catalyst active for CO2-to-C2+, we show that bias-induced rapid fusion or "electrochemical scrambling" of Cu NPs creates disordered structures intrinsically active for low overpotential C2+ formation, exhibiting around sevenfold enhancement in C2+ turnover over crystalline Cu. Integrating ex situ, passivated ex situ, and in situ analyses reveals that the scrambled state exhibits several structural signatures: a distinct transition to single-crystal Cu2O cubes upon air exposure, low crystallinity upon passivation, and high mobility under bias. These findings suggest that disordered copper structures facilitate C-C bond formation from CO2 and that electrochemical nanocrystal scrambling is an avenue toward creating such catalysts.

Non-destructive depth profile reconstruction of single-layer graphene using angle-resolved X-ray photoelectron spectroscopy

We analyze air-exposed and cleaned graphene samples grown by the chemical vapor deposition method on polycrystalline copper. Raman spectra verify their single-layer nature. C 1s and C KVV Auger spectra confirm the dominant C sp2 coordination in the films. We use angular-resolved C 1s, O 1s, and Cu 3p photoelectron spectra to acquire non-destructive concentration depth profiles and for in-depth distribution of resolved bonding states by the Maximum Entropy Method. The elemental distributions show that the air-exposed surfaces of the samples are enriched by carbon- and oxygen- bearing species, resulting in an overlayer 0.6 nm in thickness. The in-depth distributions of the resolved bonding states reveal that the oxygen bonded to carbon is located at the top surface and the oxygen bonded to copper is located at the graphene/copper interface. Almost no oxygen is present at the surface of the samples cleaned by annealing. The percentage of carbon falls by ~40%. The thickness of the carbon overlayer falls to about 0.3 nm, and the graphene layer completely covers the substrate. We emphasize that the results for the in-depth distribution of element concentrations and for resolved chemical bonding states are obtained nondestructively, i.e. without any modifications to surface composition and bonding. • Single-layer graphene grown on polycrystalline copper foil was identified by Raman spectroscopy • Dominant C sp 2 bonding in graphene was verified by C 1s and X-ray induced C KVV Auger spectra • The depth profile reconstructions of C, O and Cu concentrations and their bonding states were calculated by the Maximum Entropy Method • The copper substrate was fully covered by the graphene • The thickness of air-exposed graphene overlayer was reduced by cleaning from ~0.6 to ~0.3 nm.

Bottom-Up Synthesis of Graphene Monolayers with Tunable Crystallinity and Porosity.

We present a method for a bottom-up synthesis of atomically thin graphene sheets with tunable crystallinity and porosity using aromatic self-assembled monolayers (SAMs) as molecular precursors. To this end, we employ SAMs with pyridine and pyrrole constituents on polycrystalline copper foils and convert them initially into molecular nanosheets-carbon nanomembranes (CNMs)- via low-energy electron irradiation induced cross-linking and then into graphene monolayers via pyrolysis. As the nitrogen atoms are leaving the nanosheets during pyrolysis, nanopores are generated in the formed single-layer graphene. We elucidate the structural changes upon the cross-linking and pyrolysis down to the atomic scale by complementary spectroscopy and microscopy techniques including X-ray photoelectron and Raman spectroscopy, low energy electron diffraction, atomic force, helium ion, and high-resolution transmission electron microscopy, and electrical transport measurements. We demonstrate that the crystallinity and porosity of the formed graphene can be adjusted via the choice of molecular precursors and pyrolysis temperature, and we present a kinetic growth model quantitatively describing the conversion of molecular CNMs into graphene. The synthesized nanoporous graphene monolayers resemble a percolated network of graphene nanoribbons with a high charge carrier mobility (∼600 cm2/(V s)), making them attractive for implementations in electronic field-effect devices.

Improved CO2 reduction activity towards C2+ alcohols on a tandem gold on copper electrocatalyst

The discovery of materials for the electrochemical transformation of carbon dioxide into liquid fuels has the potential to impact large-scale storage of renewable energies and reduce carbon emissions. Here, we report the discovery of an electrocatalyst composed of gold nanoparticles on a polycrystalline copper foil (Au/Cu) that is highly active for CO2 reduction to alcohols. At low overpotentials, the Au/Cu electrocatalyst is over 100 times more selective for the formation of products containing C–C bonds versus methane or methanol, largely favouring the generation of alcohols over hydrocarbons. A combination of electrochemical testing and transport modelling supports the hypothesis that CO2 reduction on gold generates a high CO concentration on nearby copper, where CO is further reduced to alcohols such as ethanol and n-propanol under locally alkaline conditions. The bimetallic Au/Cu electrocatalyst exhibits synergistic activity and selectivity superior to gold, copper or AuCu alloys, and opens new possibilities for the development of CO2 reduction electrodes exploiting tandem catalysis mechanisms. The electrochemical transformation of CO2 into liquid fuels is a major challenge. Now, Jaramillo, Hahn and co-workers present a Au/Cu catalyst highly active to C2+ alcohols at low overpotentials as a result of a tandem mechanism where CO2 is reduced to CO on Au and further reduced to C2+ alcohols on nearby Cu.