Single Crystal Foils Research Articles

Prestrain Guided Yield of Large Single-Crystal Nickel Foils with High-Index Facets.

Single-crystal metal foils with high-index facets are currently being investigated owing to their potential application in the epitaxial growth of high-quality van der Waals film materials, electrochemical catalysis, gas sensing, and other fields. However, the controllable synthesis of large single-crystal metal foils with high-index facets remains a great challenge because high-index facets with high surface energy are not preferentially formed thermodynamically and kinetically. Herein, single-crystal nickel foils with a series of high-index facets are efficiently prepared by applying prestrain energy engineering technique, with the largest single-crystal foil exceeding 5×8 cm2 in size. In terms of thermodynamics, the internal mechanism of prestrain regulation on the formation of high-index facets is proposed. Molecular dynamics simulation is utilized to replicate and explain the phenomenon of multiple crystallographic orientations resulting from prestrain regulation. Additionally, large-sized and high-quality graphite films are successfully fabricated on single-crystal Ni(012) foils. Compared to the polycrystalline nickel, the graphite/single-crystal Ni(012) foil composites show more than five-fold increase in thermal conductivity, thereby showing great potential applications in thermal management. This study hence presents a novel approach for the preparation of single-crystal nickel foils with high-index facets, which is beneficial for the epitaxial growth of certain two-dimensionalmaterials.

Texture in cold rolled and high-temperature annealed Cu foils

Thick single crystal Cu foil substrates with specific crystallographic orientations such as {111} and {110} planes parallel to the rolling plane are desired for epitaxial growth of two-dimensional materials such as graphene. In this study, annealing experiments of a 46 μm thick cold-rolled foil were carried out at temperatures in the range of 300-1040 °C. The texture evolution during annealing was followed by electron backscatter diffraction (EBSD) orientation mapping. It was found that the texture evolution may be divided into three stages: at relatively low annealing temperatures, a strong cube texture develops with a small population of grains having relatively larger deviations from the cube orientation; at medium temperatures, these grains with large deviations grow abnormally; and at the highest temperature, annealing twins form in the abnormally growing grains giving rise to new orientations including some with the {111} planes parallel to the rolling plane.

Enhanced plastic deformability of copper single crystals under low-frequency vibrational loading

Tensile tests on copper single crystal ([110]) foils using low-frequency vibrational loading of frequencies ranging from 0 to 50 Hz were performed at room temperature to explore the mechanisms of vibration-facilitated plastic deformation in metallic materials. It was found that the total elongation of copper single crystal foils under vibrational loading increased gradually with increasing vibration frequency, indicating enhanced plastic deformability. This behavior could be rationalized with the formation of equiaxial dislocation cells (EDC) in copper single crystal ([110]) foils under vibrational loading, which reflects the activation of multiple codirectional slip systems induced by the approximate biaxial tensile stress state during the unloading stage of vibrational loading. Additionally, the formation of Lüders bands under vibrational loading at high frequencies validates their dislocation-proliferation-mediated nucleation mechanism. This work would help to understand the vibration-lowered forming resistance in metallic materials of FCC lattice structures.

Bottom‐Up‐Etching‐Mediated Synthesis of Large‐Scale Pure Monolayer Graphene on Cyclic‐Polishing‐Annealed Cu(111) (Adv. Mater. 8/2022)

Single-Crystal Foils In article number 2108608, Bin Wu, Jichen Dong, Yunqi Liu, and co-workers report the development of a cyclic electrochemical polishing and thermal annealing approach to obtain single-crystal Cu(111) foils. Pure monolayer graphene is produced on Cu(111) based on a general “bottom-up etching” method. In particular, the obtained graphene shows high and uniform electronic quality using terahertz time-domain spectroscopy (THz-TDS) measurement.

The Effect of Ethanol on Abnormal Grain Growth in Copper Foils.

Single-crystal Cu not only has high electrical and thermal conductivity, but can also be used as a promising platform for the epitaxial growth of two-dimensional materials. Preparing large-area single-crystal Cu foils from polycrystalline foils has emerged as the most promising technique in terms of its simplicity and effectiveness. However, the studies on transforming polycrystalline foil into large-area single-crystal foil mainly focus on the influence of annealing temperature and strain energy on the recrystallization process of copper foil, while studies on the effect of annealing atmosphere on abnormal grain growth behavior are relatively rare. It is necessary to carry out more studies on the effect of annealing atmosphere on grain growth behavior to understand the recrystallization mechanism of metal. Here, we found that introduction of ethanol in pure argon annealing atmosphere will cause the abnormal grain growth of copper foil. Moreover, the number of abnormally grown grains can be controlled by the concentration of ethanol in the annealing atmosphere. Using this technology, the number of abnormally grown grains on the copper foil can be controlled to single one. This abnormally grown grain will grow rapidly to decimeter-size by consuming the surrounding small grains. This work provides a new perspective for the understanding of the recrystallization of metals, and a new method for the preparation of large-area single-crystal copper foils.

Magnetocatalysis: The Interplay between the Magnetic Field and Electrocatalysis

Magnetocatalysis: The Interplay between the Magnetic Field and Electrocatalysis

Single crystal Cu (110) inducing lateral growth of electrodeposition Li for dendrite-free Li metal-based batteries

Inducing uniform nucleation and unidirectional growth of lithium (Li) electrodeposition is of vital significance to achieve dendrite-free lithium metal batteries. Herein, a lateral growth model of Li electrodeposition on the single crystal Cu with (110) crystallographic plane is realized. The influence of grain boundaries and crystal grains on the electrodeposition of Li metal and related mechanisms are further explained from the perspective of thermodynamics. The combined simulation and experiment results reveal that the electrodeposited Li grows along (110) crystallographic plane of single crystal Cu foil due to the homogeneous physical and chemical properties surfaces, indicating a typical lateral growth model. With the achieved smooth and flat Li metal electrodeposition layer on the single crystal Cu substrate, the Li|Cu half cell exhibits a high initial Coulombic efficiency of ~98% under different current densities of 0.5 and 1.0 mA cm−2, and Li|NCM523 full cell displays remarkable cycle stability with a high cycle retention of 76.71% even after 300 cycles at the current density of 1 C. This work not only proposes the electrocrystalline growth model of Li metal, but also provides guidance for the commercialization of safe and stable LMBs.

Cu(OH)2 Nanorods/Ni(OH)2 Nanosheets as Highly Efficient Catalyst for Hydrogen Evolution Reaction

AbstractReasonably designing the catalyst in‐situ grown on conductive substrate is a promising avenue to ameliorate the hydrogen evolution reaction (HER). In this work, we fabricated Cu(OH)2 nanorods (NRs) and Ni(OH)2 nanosheets (NSs) on single crystal Cu foil for the first time. The structure and morphology of all samples were systematically investigated by XRD and SEM, respectively. XPS was carried out to measure the element composition and valence state. The synergistic effect of metal double hydroxides significantly improved the catalytic performance of hydrogen evolution in neutral electrolytes. And it also showed a high catalytic stability. The overpotential at 10 mA/cm2 and Tafel slope of Cu(OH)2 NRs @ Ni(OH)2 NSs were 200 mV and 120 mV/dec, respectively, which was markedly better than other materials reported previously.

Deciphering Catalytic Selectivity on Uneven Terraces

Understanding the relationship between catalytic selectivity and surface structures of heterogeneous catalysts is essential for high-performance catalysis. In this issue of <i>Chem</i>, Zhu et al. report a puzzle-solving strategy relying on single-crystal foils and Pearson correlation analysis to determine the dependence of catalytic activity on the principal surface parameters.

Synthesis of large-area graphene films on rolled-up Cu foils by a “breathing” method

Chemical vapor deposition (CVD) is considered to be the most promising method for the synthesis of large-area high-quality graphene films. However, with an increase in reactor size, manufacturing difficulty and significant increases in CVD reactor costs will occur. These effects result in considerable limitations on the size and throughput of graphene films. We report a “breathing” CVD method to effectively utilize the reactor space for producing large-area graphene films with a small reactor. A rectangular Cu foil substrate is rolled into a spiral to increase the substrate loading density. Graphite mat strips are placed between the Cu layers at the two ends of the spiral to avoid Cu layer adhesion at high temperature while leaving enough space inside the Cu spiral for gas exchange. Reactant gases are introduced in a way similar to breathing by repeatedly increasing and decreasing the pressure inside the reactor as well as the Cu spiral, which assists gas exchange. In addition, in order to avoid the collapse of the middle Cu layers due to high temperature softening and gravity, the Cu spiral is placed vertically. With this method, both the size and throughput of graphene films can be an order of magnitude larger than conventional methods, as demonstrated by the synthesis of the large-area high-quality graphene films of 1.1 m × 0.25 m with a 2-in. diameter quartz tube CVD reactor. The transverse length (1.1 m) of the graphene film is 25 times the inner diameter (0.044 m) of the reactor tube. This method can also be used for the synthesis of other large-area 2D films and the production of large-area metal single crystal foils.

Surface Reconstruction of Ag and Au–Ag Model Nano-catalysts During Exposure to Oxidising Gas Atmospheres

At the industrial level, Ag catalysts in the form of silver crystals held by a silver gauze are largely used for formaldehyde production and ethylene epoxidation. These self-supported structures undergo surface reconstructions and morphological changes upon exposure to moderately high temperatures (473–900 K) and oxidising atmospheres. These phenomena have been studied and well understood on single crystal surfaces and polycrystalline foils: different oxygen surface and sub-surface species have been identified and reconstruction processes explained. To verify the scalability of the surface science results and ultimately understand these phenomena on catalysts at the industrial scale, further studies on more complex samples are needed. Attempts to close this “materials gap” have been carried out in this present study where experiments have been performed on model single catalytic nanoparticles, i.e. the apexes of field emitter tips, using both field emission (FE) and field ion (FI) microscopies. Pure Ag samples are exposed to a pressure of 3 × 10–5 mbar of O2 at temperatures up to 700 K. These conditions reflect those used on the industrial scale. Important surface/morphological reconstructions are observed both in FE and FI modes. For comparison, experiments have been repeated on Au-8.8%at. Ag field emitter tips, representative samples for Au–Ag catalytic nanofoams, using to 3 × 10–5 mbar of NO2 at temperatures up to 450 K. Similar behaviour are observed and the influence of the oxidising gas is discussed.

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.

Growth of Single-Layer and Multilayer Graphene on Cu/Ni Alloy Substrates

ConspectusGraphene, a one-atom-thick layer of carbon with a honeycomb lattice, has drawn great attention due to its outstanding properties and its various applications in electronic and photonic devices. Mechanical exfoliation has been used for preparing graphene flakes (from monolayer to multilayer with thick pieces also typically present), but with sizes limited typically to less than millimeters, its usefulness is limited. Chemical vapor deposition (CVD) has been shown to be the most effective technique for the scalable preparation of graphene films with high quality and uniformity. To date, CVD growth of graphene on the most commonly used substrates (Cu and Ni foils) has been demonstrated and intensively studied. However, a survey of the existing literature and earlier work using Cu or Ni substrates for CVD growth indicates that the bilayer and multilayer graphene over a large area, particularly single crystals, have not been obtained.In this Account, we review current progress and development in the CVD growth of graphene and highlight the important challenges that need to be addressed, for example, how to achieve large single crystal graphene films with a controlled number of layers. A single-layer graphene film grown on polycrystalline Cu foil was first reported by our group, and since then various techniques have been devoted to achieving the fast growth of large-area graphene films with high quality. Commercially available Cu/Ni foils, sputtered Cu/Ni thin films, and polycrystalline Cu/Ni foils have been used for the CVD synthesis of bilayer, trilayer, and multilayer graphene. Cu/Ni alloy substrates are particularly interesting due to their greater carbon solubility than pure Cu substrates and this solubility can be finely controlled by changing the alloy composition. These substrates with controlled compositions have shown the potential for the growth of layer-tunable graphene films in addition to providing a much higher growth rate due to their stronger catalytic activity. However, the well-controlled preparation of single crystal graphene with a defined number of layers on Cu/Ni substrates is still challenging.Due to its small lattice mismatch with graphene, a single crystal Cu(111) foil has been shown to be an ideal substrate for the epitaxial growth of graphene. Our group has reported the synthesis of large-size single crystal Cu(111) foils by the contact-free annealing of commercial Cu foils, and single crystal Cu/Ni(111) alloy foils have also been obtained after the heat-treatment of Ni-coated Cu(111) foils. The use of these single crystal foils (especially the Cu/Ni alloy foils) as growth substrates has enabled the fast growth of single crystal single-layer graphene films. By increase of the Ni content, single crystal bilayer, trilayer, and even multilayer graphene films have been synthesized. In addition, we also discuss the wafer-scale growth of single-layer graphene on the single crystalline Cu/Ni(111) thin films.Recent research results on the large-scale preparation of single crystal graphene films with different numbers of layers on various types of Cu/Ni alloy substrates with different compositions are reviewed and discussed in detail. Despite the remarkable progress in this field, further challenges, such as the wafer-scale synthesis of single crystal graphene with a controlled number of layers and a deeper understanding of the growth mechanism of bilayer and multilayer graphene growth on Cu/Ni substrates, still need to be addressed.

Properties of CuGa2 Formed Between Liquid Ga and Cu Substrates at Room Temperature

Ga and Ga-based alloys have received significant attention due to their potential application in the liquid state for low-temperature bonding in microelectronics. This study investigated the interfacial reactions between liquid Ga and pure Cu substrates at room temperature. The directional thermal expansion behaviour of the resulting CuGa2 was analysed by synchrotron x-ray powder diffraction with supporting observations of single crystal foils in high-voltage transmission electron microscopy. The mechanical properties of CuGa2 were evaluated by nano-indentation. CuGa2 was found to have advantages over other intermetallics that are present in assemblies made with current generation lead-free solders, including Ag3Sn, Cu6Sn5 and Cu3Sn. In addition to enabling lower process temperatures, solder alloys that form CuGa2 at the interface with Cu offer the possibility of providing more reliable connections in the very small joints that play an increasingly important role as the trend to miniaturisation of electronics continues.

Preparation and uses of large area single crystal metal foils

Various preparations and uses of single crystal metals are discussed. We briefly review (i) preparation methods of single crystal metals such as growth from melts, epitaxial deposition in vapors and solutions, and abnormal grain growth in solids and (ii) uses of single crystal metals according to their produced shapes (“bulk” vs “film and foil”). We pay special attention to recent advances in the preparation of large area single crystal metal foils and their potential uses.

Turning many into one

Metallurgy Single-crystal metal foils are valuable for their surface properties that allow for synthesis of materials like graphene. Jin et al. present a strategy for creating colossal single-crystal metal foils called “contact-free annealing” (see the Perspective by Rollett). The method relies on hanging and heating commercially available, inexpensive, cold-rolled metal foils. Almost as if by magic, the polycrystalline grains rotate and anneal into a large single-crystal sheet with a specific crystal orientation. The strategy allows for the creation of much larger and much cheaper single-crystal metal foils. Science , this issue p. [1021][1]; see also p. [996][2] [1]: /lookup/doi/10.1126/science.aao3373 [2]: /lookup/doi/10.1126/science.aav6733

Identifying Key Factors towards Highly Reflective Silver Coatings

This paper attempts to identify key factor(s) for highly reflective silver (Ag) coatings. Investigation was made over the crystal orientation and surface roughness, using several types of surfaces, including electroplated Ag polycrystal films, physical vapour deposited polycrystal Ag films, and single crystal Ag foils with different crystal orientations. In each type of the surfaces, surface roughness was varied so that, for different combinations of crystal orientation, roughness would elucidate the key factors towards highly reflective Ag coatings. It is found that surface roughness plays a critical role in determining the reflectance, while the crystal orientation has negligible effect. The mean reflectance and one-way ANOVA analysis indicate that the single crystal Ag foils with three orientations performed statistically the same in the same roughness group at significance levelα= 0.05. Moreover, correlation between the surface reflectance and surface roughness has been proposed for the benefit of coating design. Refection data obtained from the polycrystalline silver samples are used to verify the accuracy of the proposed correlations. It was observed that the development surface area ratio,Sdr, is a better roughness indicator in predicting the reflectance of polycrystalline silver films than the arithmetic average roughness,Ra.

Sub-5 μm-thick spalled single crystal Si foils by decoupling crack initiation and propagation

Spalling of a brittle semiconductor substrate is an attractive method for fabricating sub-50 μm thick single crystal semiconductor wafers in large area. Here, a spalling process to fabricate single crystal Si foils with controlled thicknesses ranging from sub-5 to 38 μm is demonstrated using electroplated Ni stressor layers on Si substrates. In this study, the thickness profile of the Ni stressor layer was varied by changing the Ni electroplating current density, and the effect of thickness variation on the crack initiation and propagation in the underlying Si substrate was evaluated. The critical Ni thickness for crack initiation in our Ni/Si bilayer system was determined and we also show that the crack propagation depth, i.e., spalled Si thickness, is proportional to the thickness of the Ni layer at the central area of the Si wafer. Ni layer plated using 40 mA/cm2 resulted in sub-5 μm thick Si foil. In addition, the spalling mechanics of a Ni/Si bilayer system was analytically explored to give insight into the requirements of the Ni stressor layer for crack initiation.

Moderation and diffusion of positrons in tungsten meshes and foils

The efficiency of tungsten meshes and thin foils for moderation of fast positrons from 22Na has been investigated in transmission geometry and a fair agreement has been found with previous experimental results where directly comparable. For foils, the dependence on material thickness is found to be similar to the prediction of the Vehanen-Mäkinen diffusion model; however, the magnitude is 5–10 times lower. A broad consensus is observed between experiment and the results of a three-dimensional model developed in this work. For a given thickness, meshes are found to be generally better than foils by around a factor of 10 with a maximum efficiency (∼10−3) comparable to that achieved with thin single crystal foils, in accord with previous measurements and the results of the present model.

Rapid Hydrogen Transportation Along Grain Boundary in Nickel

The permeability and diffusivity of hydrogen in directionally solidified polycrystalline and single crystal nickel foils were measured by gas permeation method. The results showed that both hydrogen diffusivity and permeability were higher in directionally solidified nickel specimen than those in single crystal one at the temperature ranging from 300 to 480 °C, and confirmed the existence of short-circuit diffusion along the grain boundaries (GBs) in the directionally solidified nickel. The results suggested that the rapid diffusion along GBs was more obviously characterized in terms of higher permeability rather than higher diffusivity. The contribution of grain boundary to hydrogen transportation was represented by the differences of diffusivity (and permeability) in single crystal nickel and directionally solidified nickel. By modifying the Fick’s first diffusion law and counting the grain boundary density, the hydrogen diffusivity and permeability of rapid diffusion along GBs were calculated. The results suggested both the diffusivity and permeability fit the Arrhenius relationship well at different temperature.