Oxidation of copper in controlled clean air and standard laboratory air at 50°C to 150°C

Decoupled High-Mobility Graphene on Cu(111)/Sapphire via Chemical Vapor Deposition

The growth of high-quality graphene on flat and rigid templates, such as metal thin films on insulating wafers, is regarded as a key enabler for technologies based on 2D materials. In this work, the growth of decoupled graphene is introduced via non-reducing low-pressure chemical vapor deposition (LPCVD) on crystalline Cu(111) films deposited on sapphire. The resulting film is atomically flat, with no detectable cracks or ripples, and lies atop of a thin Cu2O layer, as confirmed by microscopy, diffraction, and spectroscopy analyses. Post-growth treatment of the partially decoupled graphene enables full and uniform oxidation of the interface, greatly simplifying subsequent transfer processes, particularly dry-pick up - a task that proves challenging when dealing with graphene directly synthesized on metallic Cu(111). Electrical transport measurements reveal high carrier mobility at room temperature, exceeding 104 cm2 V-1 s-1 on SiO2/Si and 105 cm2 V-1 s-1 upon encapsulation in hexagonal boron nitride (hBN). The demonstrated growth approach yields exceptional material quality, in line with micro-mechanically exfoliated graphene flakes, and thus paves the way toward large-scale production of pristine graphene suitable for high-performance next-generation applications.

Effects of Curing Agents on the Adhesion of Epoxy Resin to Copper: A Density Functional Theory Study

Epoxy resins are widely used adhesives in industrial fields. To use epoxy resin as an adhesive, it is necessary to mix the epoxy resin with a hardener. Hardeners have various functional groups and skeletons, and the properties of epoxy resins vary depending on the hardener. Although the adhesion of epoxy resins has been extensively studied using density functional theory (DFT) calculations, few studies have evaluated the effect of hardener molecules. Therefore, in this study, DFT calculations of adhesion energies and bonding structures on Cu (111) and Cu2O (111) surfaces are performed for model molecules of adducts of epoxy resin with hardeners having various functional groups and skeletons to evaluate the influence of the hardeners on the adhesion of epoxy resin to the metal surface. The adhesion energy to the Cu (111) surface is governed by the energy due to dispersion forces. Hardeners of the thiol type, which contain relatively heavy sulfur atoms, and hardeners with aromatic rings, displaying high planarity, enable the entire molecule to approach the metal surface, resulting in a relatively high adhesion strength. The calculations for the Cu2O (111) surface show the adhesion strength is more strongly influenced by interactions such as hydrogen bonds between the surface and adhesive molecules than by dispersion forces. Therefore, in adhesion to Cu2O (111), the benzylamine-epoxy adduct with hydrogen bonding and OH-π interactions with the surface, in addition to having a relatively flexible framework, shows a high adhesion strength.

Shear adhesive strength between epoxy resin and copper surfaces: a density functional theory study

Shear adhesive strengths of epoxy resin for copper and copper oxide surfaces are estimated based on quantum chemical calculations. Shear adhesion has periodicity, and its origin is revealed.

A Systematic Approach for the Reliability Evaluation of Electric Connector

Under the trend of high density and miniaturization, the current that the connector transmits per unit volume is getting higher and higher, which makes the reliability design of the connector more challenging. Under the pressure of high performance and low cost requirements, the design has to be more accurate and more efficient. Thus, in the design process, a systematic approach for reliability evaluation is required. However, there is no valid enough approach that is integrated, well-organized, and quantitative. In this article, a systematic approach for the reliability evaluation of connector was proposed, and by applying it on a typical object named a blade-spring connector, the validity of this approach was verified. After the framework of this approach has been established, the methods and models needed were provided, including the method to build up material selection criterion and the assessment models of stress relaxation, thermal diffusion, and sliding wear, respectively. Then, the feasibility of a newly developed copper alloy on the connector and the reliability behaviors of this connector were determined through this approach. The unsatisfactory aspects of reliability were pointed out and some possible redesign choices were provided. Results and discussion revealed that the proposed approach is a helpful tool for designing electric connectors, especially on the reliability design.

Microwave Monitoring of Atmospheric Corrosion of Interconnects

Traditional metrology has been unable to adequately address the reliability needs of emerging integrated circuits at the nano scale; thus, new metrology and techniques are needed. In this paper, we use microwave propagation characteristics (insertion loss and dispersion) to study the atmospheric interconnect corrosion under accelerated stress conditions. The results presented in this work indicate that the corrosion resilience of the test device is limited by the thermal aging of the passivation layer.

Retarding oxidation of copper nanoparticles without electrical isolation and the size dependence of work function

Copper nanoparticles (CuNPs) are attractive as a low-cost alternative to their gold and silver analogues for numerous applications, although their potential has hardly been explored due to their higher susceptibility to oxidation in air. Here we show the unexpected findings of an investigation into the correlation between the air-stability of CuNPs and the structure of the thiolate capping ligand; of the eight different ligands screened, those with the shortest alkyl chain, -(CH2)2-, and a hydrophilic carboxylic acid end group are found to be the most effective at retarding oxidation in air. We also show that CuNPs are not etched by thiol solutions as previously reported, and address the important fundamental question of how the work function of small supported metal particles scales with particle size. Together these findings set the stage for greater utility of CuNPs for emerging electronic applications.

Real-time plasmon spectroscopy study of the solid-state oxidation and Kirkendall void formation in copper nanoparticles

Oxidation and corrosion reactions have a major effect on the application of non-noble metals. Kinetic information and simple theoretical models are often insufficient for describing such processes in metals at the nanoscale, particularly in cases involving formation of internal voids (nano Kirkendall effect, NKE) during oxidation. Here we study the kinetics of solid-state oxidation of chemically-grown copper nanoparticles (NPs) by in situ localized surface plasmon resonance (LSPR) spectroscopy during isothermal annealing in the range 110-170 °C. We show that LSPR spectroscopy is highly effective in kinetic studies of such systems, enabling convenient in situ real-time measurements during oxidation. Change of the LSPR spectra throughout the oxidation follows a common pattern, observed for different temperatures, NP sizes and substrates. The well-defined initial Cu NP surface plasmon (SP) band red-shifts continuously with oxidation, while the extinction intensity initially increases to reach a maximum value at a characteristic oxidation time τ, after which the SP intensity continuously drops. The characteristic time τ is used as a scaling parameter for the kinetic analysis. Evolution of the SP wavelength and extinction intensity during oxidation at different temperatures follows the same kinetics when the oxidation time is normalized to τ, thus pointing to a general oxidation mechanism. The characteristic time τ is used to estimate the activation energy of the process, determined to be 144 ± 6 kJ mol^-1, similar to previously reported values for high-temperature Cu thermal oxidation. The central role of the NKE in the solid-state oxidation process is revealed by electron microscopy, while formation of Cu₂O as the major oxidation product is established by X-ray diffraction, XPS, and electrochemical measurements. The results indicate a transition of the oxidation mechanism from a Valensi-Carter (VC) to NKE mechanism with the degree of oxidation. To interpret the optical evolution during oxidation, Mie scattering solutions for metal core-oxide shell spherical particles are computed, considering formation of Kirkendall voids. The model calculations are in agreement with the experimental results, showing that the large red-shift of the LSPR band during oxidation is the result of Kirkendall voiding, thus establishing the major role of the NKE in determining the optical behavior of such systems.