Formation Of Copper Clusters Research Articles

Analysis of radiation-induced small Cu particle cluster formation in aqueous CuCl2

Synchrotron x-ray radiation is being used extensively as a structure probe to investigate the coordination environment and thus gain insight into the ion–water and ion–ion interactions in aqueous solutions. However, under favorable conditions, there may be instances where the incident x-ray beam can induce oxidation and/or reduction in the solution, thus altering its chemistry. Successive x-ray absorption fine structure spectra, measured in the fluorescence mode from a 55 ppm Cu in CuCl2 aqueous solution, show the formation of copper clusters and their growth as a function of time of irradiation. Initially, the clusters have a nearest neighbor distance of 2.48±0.02 Å which, with increase in time of irradiation, increases to 2.55±0.01 Å, indicating that the clusters approach the lattice dimensions of bulk copper. Similarly, the Debye–Waller factor of the copper clusters is found to increase by ∼50%–55% over the range of time of irradiation. Analysis of spectra measured in the intermediate time period shows signal contributions from a mixture of clusters that can be represented by a mixture of a small cluster (5–10 Å across) and bulk copper. The nearest neighbor coordination number is found to increase in a manner consistent with the decrease in the surface to volume ratio as the average cluster size approaches its bulk dimensions. The initiation of cluster growth occurs through agglomeration of copper atoms that possibly react to form dimers upon reaction. The copper ions in the solution are reduced to the metallic state by reacting with hydrated electrons produced as a result of radiolysis of water by the incident x-ray beam.

Diffusion of metals deposited on a polyimide film (Kapton) under and out of irradiation

Copper and titanium layers deposited on a polyimide film (Kapton) have been studied under two adverse conditions: annealing and irradiation. Metals were deposited by sputtering at room or elevated temperatures (from 251 to 410°C). Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy studies have shown copper layer unwetting for annealing temperatures below the Kapton glass transition temperature ( T g ≈ 360°C). We have observed copper cluster formation on the polyimide surface by surface diffusion that impedes the diffusion in depth. When the annealing temperature is above T g, copper clusters formation occurs together with immersion under polyimide surface until 80 nm depth. The microscopy study of a copper layer deposited at room temperature shows the evolution of copper/Kapton interface after an irradiation by 300 keV krypton ions at a fluence of 3 × 10 16ions/cm 2. We observe a large modification of the polymer surface up to 500 nm in depth, as compared with the nonirradiated surface, with a succession of more contrasting blocks at the surface. RBS, EDS and ERD analyses indicate the modified polymer layer is impoverished in oxygen, nitrogen and hydrogen, which seems to confirm the formation of new carbonaceous materials. Electron microscopy shows clearly the presence of spherical copper clusters inside the modified film with an average size (10 nm radius) that agrees with the known existence of voids in Kapton. The copper distribution observed by microanalysis is in agreement with the quantitative results that we obtain by RBS. Our studies of oxidized titanium layers have shown that, contrarily to copper layers, the oxidized titanium/Kapton systems do not experience changes after irradiation and annealing neither above T g nor below T g.

Investigations of Cl− adsorption at the Au(111) electrode in the presence of underpotentially deposited copper atoms

Adsorption of Cl − at the Au(111) electrode in the presence of underpotentially deposited copper adatoms is described. It is shown that the underpotential deposition of copper promotes adsorption of Cl − , and at high or intermediate underpotentials a mixed overlayer which consists of copper adatoms and coadsorbed Cl − ions is formed. At intermediate underpotentials, the surface concentration of Cl − in the mixed overlayer amounts to 8 × 10 14 ions cm −2 which is only 10% less than the concentration of Cl − in the close-packed monolayer of Cl − . This surface concentration of Cl − is independent of the concentration of Cl − and Cu 2+ in the bulk. In solutions of low Cl − or Cu 2+ concentrations and at low underpotentials the surface concentration of Cl − decreases when the copper coverage approaches a monolayer. In solutions of high copper and chloride concentrations and low underpotentials the surface concentration of Cl − increases above the value of 8 × 10 14 ions cm −2 . The increase in the surface concentration of Cl − is observed when the copper coverage exceeds one monolayer. Therefore it may suggest formation of copper clusters or a trilayer.

Investigations of SO 42− adsorption at the Au(111) electrode in the presence of underpotentially deposited copper adatoms

Abstract Adsorption of Cl − at the Au(111) electrode in the presence of underpotentially deposited copper adatoms is described. It is shown that the underpotential deposition of copper promotes adsorption of Cl − , and at high or intermediate underpotentials a mixed overlayer which consists of copper adatoms and coadsorbed Cl − ions is formed. At intermediate underpotentials, the surface concentration of Cl − in the mixed overlayer amounts to 8 × 10 14 ions cm −2 which is only 10% less than the concentration of Cl − in the close-packed monolayer of Cl − . This surface concentration of Cl − is independent of the concentration of Cl − and Cu 2+ in the bulk. In solutions of low Cl − or Cu 2+ concentrations and at low underpotentials the surface concentration of Cl − decreases when the copper coverage approaches a monolayer. In solutions of high copper and chloride concentrations and low underpotentials the surface concentration of Cl − increases above the value of 8 × 10 14 ions cm −2 . The increase in the surface concentration of Cl − is observed when the copper coverage exceeds one monolayer. Therefore it may suggest formation of copper clusters or a trilayer.

Calculation of the heat of copper cluster formation in MgO lattice by the interacting bonds method

The heat of formation of some copper clusters in a MgO lattice has been calculated by the interacting bonds method.

Calculation of the heat of surface cluster formation and oxygen adsorption on copper-magnesium oxide catalysts by the interacting bonds method

The heat of copper cluster formation on MgO surface has been calculated by the interacting bonds method. Oxygen adsorption on these catalysts is discussed.