Polycrystalline Copper Surfaces Research Articles

Seebeck Coefficient Modulation of Graphene Grown on Faceted Cu Surfaces

The thermoelectric properties of polycrystalline copper (Cu) surfaces partially covered with graphene grown by Joule‐heating chemical vapor deposition using scanning thermoelectric microscopy are investigated. Atomic‐resolution atomic force microscopy topographic images of graphene grown on Cu(100) surfaces showed a 1D stripe pattern of Moiré superlattices, while thermoelectric voltage images clearly distinguish wrinkle defects caused by thermal mismatch between graphene and Cu substrate. Regions of different signs were found in the thermoelectric voltage image of the graphene island, which are attributed to the faceted surface of the Cu substrate. In addition, faceted surfaces consisting of low‐ and high‐index Cu surfaces are formed on the Cu grain to minimize the surface energy. Due to these structural changes, charge transfer and chemical interactions at the interface between the graphene and Cu facets affect the electronic structure of the graphene, which is understood as the observed Seebeck coefficients with different signs in the thermoelectric microscopy measurements, which are sensitive to the local density of states.

Effect of surface orientation on blistering of copper under high fluence keV hydrogen ion irradiation

Copper and hydrogen are among the most common elements that are widely used in industrial and fundamental research applications. Copper surfaces are often exposed to hydrogen in the form of charged ions. The hydrogen ions can accelerate towards the surface, resulting in an accumulation of hydrogen below the surface. Harmless in low concentrations, prolonged hydrogen exposure can lead to dramatic changes on copper surfaces. This effect is visible to the naked eye in the form of blisters densely covering the exposed surface. Blisters are structural modifications that can affect the physical properties of the surface including, for example, vacuum dielectric strength.Using scanning electron microscopy we found that the blistering of the irradiated polycrystalline copper surface does not grow uniformly with ion fluence. Initially, only some grains exhibit blisters, while others remain intact. Our experiments indicate that grains with the {100} orientation are the most prone to blistering, while the grains oriented in the {110} are the most resistant to it. Moreover, we noticed that blisters assume different shapes correlating with specific grain orientation.Good agreement of experiments with the atomistic simulations explains the difference in the shapes of the blisters by specific behavior of dislocations within the FCC crystal structure. Moreover, our simulations reveal the correlation of the delay in blister formation on surfaces with certain orientations compared to the others with the dependence of the hydrogen penetration depth and the depth and amount of vacancies in copper on the orientation of the irradiated surface.

Wetting and spreading of Pb, Pb-Cu, and Ag-Cu melts on a polycrystalline copper surface with cobalt particles

The specific feature of Cu(Co) solid solutions with a sub-solidus composition involves the formation of submicron-sized cobalt particles on the free surface. In this work, Cu(Co) substrates with cobalt particles on the surface were produced through the annealing of a series of copper-based cobalt solid solutions containing 1–3 at% Co in a hydrogen atmosphere at 1050 °C, leading to the formation of a family of cobalt-based submicron-sized particles with a similar orientation within one grain on the surface. The wetting and spreading of lead and copper-based liquid alloys on the surfaces of these substrates were compared to the wetting of pure copper and pure cobalt. Experiments were conducted via the high-speed video recording of droplet transfer onto the Cu, Co, and Cu(Co) substrates at 400 °C (melt: pure lead), at 850 °C (Pb + 10.3 at% Cu), and at 1070 °C (Cu + 2.5 at% Ag) in a vacuum. The contact angle of the Pb melt on cobalt (46°) differed significantly from the contact angle on copper at 400 °C (32°), while at 850 °C, the wetting for both metals was almost complete (the wetting angles for Cu and Co were 5° and 7°, respectively). The wetting angle for the Cu(Co) solid solution surface with cobalt particles was almost equal to that for pure copper, and the spreading rates were comparable for the two cases. The wetting of the Cu, Co, and Cu(Co) surfaces by the Cu(Ag) melt did not demonstrate any significant differences between the equilibrium contact angles (tending to zero), while the spreading rate differed only slightly. The surface area covered by the particles reached 20%, despite the presence of the particles, which exerted no impact on the contact angle, due to two possible effects: (i) the formation of an adsorbed copper layer on the surface of the cobalt phase confirmed by room-temperature Auger electron spectroscopy, and (ii) the compensation of wetting deterioration by an increase in roughness.

Combined Effects of Concentration, pH, and Polycrystalline Copper Surfaces on Electrocatalytic Nitrate-to-Ammonia Activity and Selectivity

Wastewater nitrates (NO3–) represent an untapped source for nutrient recovery. This study explores the effects of NO3– concentration ranging from 0.1 to 1 M and pH conditions of 8, 10, and 14 on the electrochemical reduction to ammonia (NH3) with polycrystalline Cu electrodes. Cyclic voltammograms prove pH- and concentration-dependent reaction kinetics. Chronoamperometry tests probed the reaction selectivity to NH3 production for a fixed potential across different pH conditions. The maximum NH3 Faradaic efficiency achieved was 46% ± 11% for 1 M NaNO3 at pH 14 at −0.55 V vs the reversible hydrogen electrode (RHE), while the minimum was 25% ± 6% for 1 M NaNO3 at pH 8. Distinctly, at pH 8 and 10, 0.1 M NaNO3 results in higher NH3 Faradaic efficiencies compared to the 1 M solution. Product quantification reveals that as the pH decreases, more charge is utilized for the formation of NO2– as compared to NH3 as a product. Large trial-to-trial uncertainties motivated the application of in situ electrochemical impedance spectroscopy to provide insights into the causal factors. Fitted parameters from impedance measurements correlate with measured contributions of net charge utilized for NH3 and NO2– production. Trial-to-trial variations map with changes in both the charge-transfer resistance and the effective double-layer capacitance. Changes in surface roughness and consequently the electrochemically active surface area are more dominant for 0.1 M NaNO3 solutions, while other variations play a significant role for 1 M NaNO3 tests. Overall, these results indicate that catalytic performance of NO3– reduction on Cu is highly sensitive to pH, concentration, secondary ions, and surface composition.

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.

Thickness-dependent neutralization of low-energy alkali-metal ions scattering on graphene

A challenging effort is under way to understand the essence of the quantum size effect of two-dimensional materials in order to achieve the ultimate goal of arbitrarily tailoring their properties in the near future. Here we present experimental and theoretical study of resonant neutralization of low-energy alkali-metal ions on clean and graphene-covered polycrystalline copper surfaces. The ion neutralization strongly depends on the number of graphene layers, and it gradually saturates for three to five layers of graphene. This result is consistent with that for the graphite surface. The neutral fraction for the clean polycrystalline copper surface is found to be significantly higher than that for the graphene-covered surface, which is not consistent with known regularities. We quantitatively explain those observations through the small energy level width of resonant electron transfer that is determined by the special electronic structure of graphene layers. This finding indicates that resonant neutralization spectroscopy has promising applications in the detection of the quantum size effects of two-dimensional materials at an atomic layer level.

Flower-like open-structured polycrystalline copper with synergistic multi-crystal plane for efficient electrocatalytic reduction of nitrate to ammonia

Electrocatalytic reduction of nitrate to ammonia is a promising way to regulate the global nitrogen cycle, and is also an important complementary means of ammonia synthesis. However, the convenient preparation of open-structured catalysts with synergistic multi-crystal plane to achieve high efficiency and selectivity is a great challenge. Herein, a flower-like open-structured polycrystalline copper loaded on carbon fiber papers is successfully prepared by linearly varying the deposition potential. This facile approach constructs an open reaction environment with heterogeneous synergistic polycrystalline copper surfaces during the 8-electron reaction, fully enhancing the liquid-phase mass transfer process and the synergistic catalysis process. The optimal sample exhibits the glorious nitrate reduction performance with high ammonia yield of 101.4 μmol h−1 cm−2 and Faradaic efficiency of 93.91% in neutral solution. This work develops a unique self-supporting heterogeneous interface for synergistic catalytic of nitrate, and offers new ideas for simple and rapid implementation of high-performance catalysts for ammonia production from nitrate.

Mechanism of Spontaneous Surface Modifications on Polycrystalline Cu Due to Electric Fields.

We present a credible mechanism of spontaneous field emitter formation in high electric field applications, such as Compact Linear Collider in CERN (The European Organization for Nuclear Research). Discovery of such phenomena opens new pathway to tame the highly destructive and performance limiting vacuum breakdown phenomena. Vacuum breakdowns in particle accelerators and other devices operating at high electric fields is a common problem in the operation of these devices. It has been proposed that the onset of vacuum breakdowns is associated with appearance of surface protrusions while the device is in operation under high electric field. Moreover, the breakdown tolerance of an electrode material was correlated with the type of lattice structure of the material. Although biased diffusion under field has been shown to cause growth of significantly field-enhancing tips starting from initial nm-size protrusions, the mechanisms and the dynamics of the growth of the latter have not been studied yet. In the current paper we conduct molecular dynamics simulations of nanocrystalline copper surfaces and show the possibility of protrusion growth under the stress exerted on the surface by an applied electrostatic field. We show the importance of grain boundaries on the protrusion formation and establish a linear relationship between the necessary electrostatic stress for protrusion formation and the temperature of the system. Finally, we show that the time for protrusion formation decreases with the applied electrostatic stress, we give the Arrhenius extrapolation to the case of lower fields, and we present a general discussion of the protrusion formation mechanisms in the case of polycrystalline copper surfaces.

Temperature Dependence of The Growth Process of Grain Boundary Steps Formed on Ultra–Precision Finished Polycrystalline Copper Surface

Temperature Dependence of The Growth Process of Grain Boundary Steps Formed on Ultra–Precision Finished Polycrystalline Copper Surface

Sites of Initiation of Explosive-Emission Processes on the Surface of Single-Crystal and Coarse-Grained Polycrystalline Copper

Results of a study of sites of vacuum breakdown initiation on the electrolytically polished surface of single-crystalline and coarse-grained polycrystalline copper are presented. The coincidence of cathode erosion traces with sites of dislocation outcrops has been established.

Hydrogen Evolution Reaction on Transition Metals: Promoting Water Dissociation By Tuning the Surface Oxophilicity.

Hydrogen evolution reaction (HER) has been at the core of the development of fundamentals of electrochemistry and electrocatalysis. In acidic electrolytes, it has been generally accepted that the differences in reaction rates/activity are closely related to the differences in hydrogen adsorption free energy on different materials. In recent years, the fundamental investigation of the HER has been enjoying a renewed vigor, but this time in alkaline electrolytes, where there is much less consensus on the underlying activity descriptors. While some groups insist on the single descriptor of hydrogen binding energy, our group has continuously pointed out to the bifunctional nature of the HER in alkaline environments, i.e. a good catalyst needs both a beneficial OHad energetics and beneficial Had energetics. In most cases, the OHad-metal energetics is by far the more unfavorable of the two and OHad adsorption therefore represents the rate determining step. In some cases (e.g. polycrystalline iridium), the OHad-metal energetics no longer represents a significant obstacle in the HER process; hence the catalyst's rate determining step becomes Had adsorption and the catalyst starts behaving as it would in acid – as a pseudo mono-functional catalyst. For most materials, however, the HER rates in alkaline environments are significantly lower than in acid. One such example is copper (Cu), where reported values for HER activity in alkaline are indeed lower but are interestingly scattered over a wide range of values. In a manuscript recently published [1], we were interested in the underlying cause of these discrepancies. We explore how the different history the polycrystalline copper surfaces experienced changes their electrochemical properties (e.g. the HER activity). By using detailed spectroscopic surface analysis, we were able to find different extents of oxidation on various copper surfaces and link them to different hydrophilicity of the surfaces. With the established trends we propose that the formation of Cu(I)-OHad‐‐‐OH2 activated complex is essential in lowering the energy barrier for water dissociation, which leads to higher activity for the HER in alkali environments. [1] Farinazzo Bergamo Dias Martins, P. et al. Hydrogen evolution reaction on copper: Promoting water dissociation by tuning the surface oxophilicity. Electrochem. commun. 100, 30-33 (2019).

Calculation of Dynamic Hardness by Molecular Dynamics

Based on the molecular-dynamic simulation of the impact of a solid ball on the surface of polycrystalline copper, a method for calculating the dynamic hardness of nanocrystalline materials is proposed. It is proposed to carry out the calculation of hardness by dividing the impact work by the squeezed volume. It is shown that this expression of dynamic hardness is consistent with Meyer hardness in the case of quasistatic indentation. As a result of this simulation, it is shown that under conditions when the diameter of the impactor decreases and approaches the crystal lattice constant of the target, the dynamic hardness increases. Also, in the calculations, the impactor density varied approximately twice, which was equal to the density of steel and the density of tungsten carbide. For a striker diameter of 5 nm, dynamic hardness increases with the speed of the striker and does not depend on its density.

Места инициирования взрывоэмиссионных процессов на поверхности монокристаллической и крупнозернистой поликристаллической меди

Места инициирования взрывоэмиссионных процессов на поверхности монокристаллической и крупнозернистой поликристаллической меди

An in situ XPS study of L-cysteine co-adsorbed with water on polycrystalline copper and gold

The interactions of biomolecules with metal surfaces are important because an adsorbed layer of such molecules introduces complex reactive functionality to the substrate. However, studying these interactions is challenging: they usually take place in an aqueous environment, and the structure of the first few monolayers on the surface is of particular interest, as these layers determine most interfacial properties. Ideally, this requires surface sensitive analysis methods that are operated under ambient conditions, for example ambient pressure x-ray photoelectron spectroscopy (AP-XPS).This paper focuses on an AP-XPS study of the interaction of water vapour and l-Cysteine on polycrystalline copper and gold surfaces. Thin films of l-Cysteine were characterized with XPS in UHV and in a water vapour atmosphere (P ≤ 1 mbar): the structure of the adsorbed l-Cysteine layer depended on substrate material and deposition method, and exposure of the surface to water vapour led to the formation of hydrogen bonds between H2O molecules and the COO− and NH2 groups of adsorbed l-Cysteine zwitterions and neutral molecules, respectively. This study also proved that it is possible to investigate monolayers of biomolecules in a gas atmosphere with AP-XPS using a conventional laboratory Al-Kα x-ray source.

Solid-state wetting at the nanoscale: molecular dynamics and surface diffusion approach

The authors simulated spreading of solid copper (Cu) and gold (Au) nanoparticles (5–7 nm size) on the (100) face of the same metal by using molecular dynamics. Then, the results obtained for the copper (nanoparticle)/copper (substrate) system were qualitatively compared to some available experimental data on the spreading of copper microparticles (5–20 μm) on the surface of polycrystalline copper. Before simulating the nanoparticle spreading, the size dependence of the melting temperature was investigated for copper and gold nanoparticles. When temperatures were by 25–35 K lower than the copper particle melting temperature, the observed value 40° of the equilibrium contact angle qualitatively agreed with the range 20–25° that the authors evaluated using an experimental snapshot of a copper microparticle on the copper polycrystalline substrate at temperature by 33 K lower than the bulk copper melting point. However, the characteristic spreading times 0·5–10 ns found for nanoparticles in computer experiments differ from that for copper microparticles (3 h ≈ 105 s) by many orders of magnitude. The characteristic times of spreading for copper and gold nanoparticles were also estimated by using the capillary-induced surface diffusion concept, the similarity theory and an available experimental value of the spreading duration for solid copper microparticles. The theoretical estimations in question satisfactorily agree with the authors’ molecular dynamics results.

Electrochemically Prepared Polycrystalline Copper Surface for the Growth of Hexagonal Boron Nitride

The controlled and reproducible growth of hexagonal boron nitride (h-BN) by chemical vapor deposition on polycrystalline copper foil substrates remains a challenge as typical growth surfaces contain microscopic ridges (height ≈ 100 μm) arising from the foil manufacturing process. In this work, we report a method to prepare commercially cold-rolled polycrystalline copper substrates for greatly improved growth of h-BN by a combination of thermal annealing in a reducing environment and electrochemical polishing to create an excellent surface that enables control of BN nucleation sites. We report a root mean square roughness of ∼1.2 nm for the Cu substrate after electropolishing and a reduction of nucleation sites along with enlargement of h-BN crystals with this combined approach. We also assess the potential role of surface features that exist on the Cu surface as nucleation sites. The development of an electrochemical process to prepare two-dimensional (2D) material growth substrates and demonstration of g...

Roles of oxygen for methanol adsorption on polycrystalline copper surface revealed by sum frequency generation imaging microscopy

The adsorption of atmospheric pressure methanol on the polycrystalline copper surface has been studied by a combination of sum frequency generation imaging microscopy (SFGIM) and temperature programmed desorption (TPD). Methoxy species can be generated by exposing the polycrystalline copper surface to methanol vapor at room temperature. SFGIM results demonstrate that oxygen promotes the surface adsorption of methanol and the increase in the amount of methoxy produced on copper surface. SFGIM orientation analysis suggests the methoxy monolayer is oriented closer to the surface normal with introduction of oxygen. Employing the image statistical analysis approach, the heterogeneities and conformation distribution of methoxy monolayers on copper surface with and without oxygen adsorption are compared. These results illustrate SFGIM indeed could provide more insight for understanding the heterogeneous metal/metal oxide surface in the molecular level.

The Role of Atomic Structures on the Oxygen Corrosion of Polycrystalline Copper Surface

The mechanical property of materials for pressure vessel, like steel, Ti, Cu and their alloys always turns out to be poor in the severely corrosive environment. The knowledge of oxygen corrosion on metal surface at atomic level is still lack. Using reactive molecular dynamic simulation, the oxygen corrosion behavior on polycrystalline copper is studied at the early stage of oxidation. Results indicate a higher reactivity at the grain boundary. The preferential dissociation of oxygen molecules at grain boundary is ascribed to the diffusion-related trapping effect and dissociation barriers. In addition, the difference of oxygen corrosion between grain boundary and grain on copper surface is elucidated in terms of the atomic-structure-related radial distribution functions. This study directly shows us the origin of intergranular oxygen corrosion and provides us useful information for the corrosion prevention, especially in the situation that the atomic structure changes under the thermal or mechanical loadings.

The evolution of the polycrystalline copper surface, first to Cu(111) and then to Cu(100), at a fixed CO₂RR potential: a study by operando EC-STM.

A study based on operando electrochemical scanning tunneling microscopy (EC-STM) has shown that a polycrystalline Cu electrode held at a fixed negative potential, -0.9 V (vs SHE), in the vicinity of CO2 reduction reactions (CO2RR) in 0.1 M KOH, undergoes stepwise surface reconstruction, first to Cu(111) within 30 min, and then to Cu(100) after another 30 min; no further surface transformations occurred after establishment of the Cu(100) surface. The results may help explain the Cu(100)-like behavior of Cu(pc) in terms of CO2RR product selectivity. They likewise suggest that products exclusive to Cu(100) single-crystal electrodes may be generated through the use of readily available inexpensive polycrystalline Cu electrodes. The study highlights the dynamic nature of heterogeneous electrocatalyst surfaces and also underscores the importance of operando interrogations when structure-composition-reactivity correlations are intended.

Peculiarities of structure and properties of metal surfaces subjected to strain polishing

The influence of treatment by ball-type rolling on the structure and properties of polycrystalline copper and aluminum surfaces is analyzed. It is discovered that, depending on the speed of the linear motion of the ball along the surface, two different types of deformation effect are realized, which result in considerably different surface morphologies. It is shown that treatment by ball-type rolling shrinks the width of X-ray diffraction lines compared to their original state. Dynamic recrystallization is assumed to be a significant factor affecting the morphology and structure of the treated surface.