Oxidation Of Cu Particles Research Articles

Superior sinterability of copper oxalate-coated Cu particles in a double reductant system and rapid compression sinter-bonding characteristics between Cu finishes

High-speed die attachment by compression (2 MPa) sinter-bonding at 300 °C in air was accomplished using a paste containing bimodal-sized (average sizes: 2 μm and 340 nm) copper oxalate-coated Cu particles, yielding a Cu-to-Cu bonding owing to the formation of a Cu bond line that can provide mechanical durability at high temperatures and excellent thermal conductivity. The particles were fabricated by immersing Cu particles in an oxalic acid solution, and a double reductant recipe was adopted to minimize the oxidation of the Cu particles and Cu finishes. The copper oxalate coatings inhibited the oxidation of Cu particles until decomposition at 290 °C, and the in-situ decomposition induced the generation of active Cu atoms, which significantly elevated the sinterability. Therefore, a sufficient shear strength exceeding 20 MPa and a near-full-density bond-line structure were achieved after bonding for only 1 and 3 min, respectively. Furthermore, the bond line did not contain an organic residue, differently observed in a paste directly including carboxylic acid. Therefore, the suggested paste formulation demonstrates the feasibility of a rapid solid-state sinter-bonding technique using low-cost Cu particles.

Controlled oxidation of Cu particles by H2O2 to form Cu/CuO nanostructure with enhanced gas sensing performance

Gas sensors based on metal/metal oxide heterostructures have shown rapid advancements due to their excellent sensing performance. However, it is difficult to control the formation of Cu/CuO nanostructure due to the easy oxidation of copper and limits its sensing application. Herein, we reported the controlled oxidation of Cu superfine particles (SPs) to form Cu/CuO nanostructure via reducing CuO with monoethanolamine, oxidized with H2O2 and then in-situ annealed at 250 °C. The organic residue generated during the reducing step plays a key role in controlling the oxidation of Cu SPs to form Cu/CuO nanostructure. The nanomaterial was used to fabricate gas sensor, which presents excellent p-type sensing performance to ethanol with good selectivity and a good linear relationship in the range of 1 to 100 ppm ethanol. The response to 100 ppm ethanol can be up to 99.40 under 200 °C operating temperature, and the response under 250 °C is 30.66 with the shorter response and recovery time of 214 s and 74 s, respectively. The sensing mechanism can be explained by the adsorption–desorption model. This study provides a promising strategy for the synthesis of Cu/CuO nanostructure and open a new avenue for the development of highly sensitive ethanol sensor.

Transfer of Wire Arc-Sprayed Metal Coatings onto Plastic Parts

By means of In-Mold-Metal-Spraying (IMMS), metal coatings deposited by means of arc spraying process (ASP) can be transferred onto plastic parts during injection molding, thus realizing an efficient production of metallized plastic parts. Parts produced by means of IMMS can be used in electrical applications. In the current study, the electrical resistivity of coatings applied with different feedstock materials was determined. As a starting point, pressurized air is used as atomizing gas for ASP. In contrast to Zn coatings, Cu coatings applied with pressurized air exhibit a significantly higher electrical resistivity in comparison with massive material. One possible reason is the more pronounced oxidation of Cu particles during ASP. Therefore, N2 and a mixture of N2 and H2 were used as atomizing gas. As a result, the electrical resistivity of coatings applied by means of IMMS could be significantly reduced. Furthermore, standoff distance, current and pressure of the atomizing gas were varied to investigate the influence of these process parameters on the electrical resistivity of Zn coatings using a full factorial experiment design with center point. It can be observed that the electrical resistivity of the Zn coatings increases with decreasing current and increasing standoff distance and pressure.

Cyclodextrin inclusion compound crystals for growth of Cu–Au core–shell nanoparticles

The preparation and structural elucidation of the 2α-cyclodextrin/decylamine inclusion compound (IC) by proton nuclear magnetic resonance, rotating frame overhauser effect spectroscopy and powder X-ray diffraction have been achieved. The IC microcrystals were used as a support for the preparation of Au–Cu core–shell nanoparticles by the sputtering method. The coating of copper nanoparticles with gold was verified through anodic stripping voltammetry. The presence of metallic copper and the absence of copper oxides were determined by X-ray photoelectron spectroscopy. These results show that the formation of core–shell Cu–Au by sputtering is an effective approach to prevent the oxidation of Cu particles, leading to potential applications in nanoelectronics.

Highly productive synthesis process of well dispersed Cu2O and Cu/Cu2O nanoparticles and its thermal characterization

The article reports a simple, economical and highly productive synthesis process of cuprous oxide (Cu2O) and copper/cuprous oxide (Cu/Cu2O) nanoparticles with an average size of below 30 nm. A hydrolysis of copper (Cu) particles (200 nm or even microsize) employing low energy ball milling in aqueous circumstance results a controlled synthesis of Cu2O and cermets of Cu/Cu2O nanoparticles. Ground particles are found both in nanobar and spherical shape with cluster nano-clouds into aqueous solution. X-ray diffraction patterns of the sample powder confirm Cu2O nanoparticles and Cu/Cu2O cermets synthesized by complete and incomplete oxidation of Cu particles, respectively. The process is accomplished at room temperature in presence of de-ionized (DI) water and controlled by changing milling period and ball sizes. Enhanced thermal conductivity of Cu2O–water and Cu/Cu2O–water nanofluids are recorded and compared with non-ground Cu–water nanofluids.

Theoretical Study on Polyimide−Cu(100)/Ni(100) Adhesion

The interfacial properties of polyimide (PI)/M(100) (M = Cu and Ni) were investigated using density functional theory (DFT). A PMDA-ODA monomer unit was used to represent the full PI and the surface was represented by periodically repeated slabs. PI prefers the bridge and top sites on a Cu(100) surface but only forms weak CO−Cu interactions. PI favors the bridge site on a Ni(100) surface and can form strong C−Ni, N−Ni, and CO−Ni bonds. The adsorption energies of PI on Cu(100) and Ni(100) surfaces are −0.58 and −4.7 eV, respectively. Compared to the adsorption energies of O and O2 on a Cu(100) surface, the adsorption of PI on Cu(100) is not energetically favorable, which leads to the easy oxidation of Cu particles in a Cu/PI nanocomposite. The good adhesion at PI/Ni(100) suggests that Ni is a better candidate as a metal filler compared to Cu in the metal−polyimide composite.

18O-exchange with the substrate during 18O oxidation of Cu particles supported on 16O-oxidised Si(100)

An 16O 2-oxidised Si(100) surface, covered with 15 nm Cu particles, was oxidised in 18O 2 and subsequently reduced in H 2. After reduction, there still was a significant amount of 18O present in the sample. In this paper we concerned ourselves with revealing the origin of this remaining 18O. By performing some strategic experiments we found that there was no significant contribution to the residual 18O in the sample due the following processes: oxidation of the substrate to a further extent, the remain of an 18O-adlayer on the sample after reduction, and reactions of reduction products with the substrate. The remaining 18O was caused by self-diffusion of oxygen atoms: maximum entropy was achieved by mixing 16O atoms in the substrate with 18O located inside the copper particles. We drew this conclusion from the fact that 18O-exchange also occurred during vacuum annealing of an oxidised sample, which is impossible in the case of the other proposed mechanisms. Also, 18O could be extracted from a metallic Cu 2 SiO sample through 16O 2-oxidation, annealing of the sample in vacuo, and subsequent reduction of the sample.

The oxidation of Cu particles supported on oxidised Si(100) as studied by nuclear reaction analysis and ellipsometry

The oxidation of Cu particles supported on oxidised Si(100) by molecular oxygen was investigated by means of ellipsometry and Nuclear Reaction Analysis. Stepwise oxidation of a sample containing 15 nm Cu particles at 473 K and 0.1 Pa showed that the sample was eventually oxidised to CuO 0.74 ± 0.08, which is very close to CuO 0.67, known from the literature. The ellipsometric parameter δΔ followed a highly non-linear curve upon oxygen exposure, exhibiting a maximum during oxidation, but stabilising when the CuO 0.74 ± 0.08 oxide composition was reached. The oxide stoichiometry was less than Cu 2O at the maximum of the δΔ-curve, indicating that the CuO 0.67-phase nucleated in the sample before the formation of Cu 2O had been completed. During surface oxidation, the sensitivity of δΔ to the amount of oxygen was similar to that of copper single crystals. The sensitivity of δΔ to oxygen increased significantly while samples were oxidised to Cu 2O and further: it was almost three times larger than the sensitivity of δΔ to oxygen for surface oxidation.

Ellipsometric studies of the oxidation kinetics of Cu particles supported on oxidised Si(100)

The oxidation of Cu particles supported on oxidised Si(100) by molecular oxygen was investigated by means of ellipsometry and Auger electron spectroscopy. The oxidation between 373 and 673 K of three different particle sizes was investigated: 4, 5 and 15 nm particles respectively. The δΔ curves of oxidation were divided into a part corresponding to surface oxidation, oxidation of the particles from Cu to Cu 2O and oxidation from Cu 2O to CuO 0.67. All measured δΔ curves scaled in the exposure, indicating a first order dependence on the oxygen pressure. The following activation energies for the oxidation from Cu to Cu 2O were obtained: E act = 28 ± 5 kJ/mol for 4 nm, E act = 30 ± 5 kJ/mol for 5 nm and E act = 25 ± 5 kJ/mol for 15 nm particles. For the oxidation of Cu 2O to CuO 0.67: E act = 38 ± 4 kJ/mol for 4 nm, E act = 36 ± 4 kJ/mol for 5 nm and E act = 37 ± 4 kJ/mol for 15 nm particles.

XPS/NRA investigations of particle size effects during the oxidation of Cu particles supported on oxidised Si (100)

In this study we investigate the effects of the particle size on the oxidation of supported Cu particles under equivalent experimental conditions with respect to temperature and pressure. We compare the results of oxidation of 4 and 15 nm Cu particles supported on oxidised Si(100) at room temperature and 573 K. At room temperature and p = 10 Pa, the oxidation of Cu 0 to Cu 2+ at the surface of 4 nm particles proceeds significantly slower than in the case of 15 nm particles. At 573 K and p = 0.1 Pa, a reverse trend is observed: oxidation of 4 nm particles from Cu 0 to a Cu 2+-oxide proceeds significantly faster than in the case of 15 nm particles. At both temperatures Cu 0 was oxidised to Cu 2+-oxide through an intermediate Cu +-oxide.