Formation Of Copper Clusters Research Articles

Development of the ReaxFF Reactive Force Field for Cu/Si Systems with Application to Copper Cluster Formation during Cu Diffusion Inside Silicon

Development of the ReaxFF Reactive Force Field for Cu/Si Systems with Application to Copper Cluster Formation during Cu Diffusion Inside Silicon

Evaluation of the energetics of copper-vacancy clusters in Fe

A theoretical study is conducted to evaluate the nucleation free energy of copper-vacancy clusters in Fe as a function of the numbers of copper atoms and of vacancies in a cluster. Using this free energy value, cluster nucleation processes during irradiation are investigated. The results clearly show that there are two different types of cluster nucleation paths on the free energy surface; one is the formation of empty voids by jumping over the ridge of the free energy surface, and the other corresponds to a path for the formation of copper clusters by going around the ridge. The dependence of easy nucleation paths on the damage rate is discussed.

Formation of copper clusters on the surface of a xenon buffer layer

We applied the molecular dynamics technique to the study of the formation of three-dimensional nanoclusters on a xenon surface. The main physical mechanisms were established of the processes of formation of their structure. Equilibrium configurations of copper clusters on the solid xenon layer were determined and the energies of their formation were calculated.

Influence of autocatalytic coating bath parameters on the formation of copper over surface treated boron carbide particles

The functional and structural applications of boron carbide (B4C) for neutron shielding and engineering sectors are limited due to brittleness and low temperature oxidation; however its use is enhanced by the synthesis of its composites. During composite synthesis, the interfacial compatibility of boron carbide with the matrices can be improved by the formation of metallic coatings. The present study aims at formation of autocatalytic copper coating over surface treated B4C particles with varying bath parameters and evaluating its influence on coating morphology and uniformity. An effective coating of copper over alkali treated boron carbide was obtained at pH12 and a bath temperature of 30°C. Above pH 12 as well as higher bath temperatures of 50 and 75°C leads to predominant co-deposition of metallic copper clusters within the reaction bath. SEM observations of coated boron carbide particles show the formation of copper clusters in the size range of 200–400nm. The morphology of Cu coating changes from cauliflower-like structure to angular shape with increase in bath temperature and pH. The Debye–Scherrer crystal size calculation shows that copper crystallite size vary from 17 to 25nm.

Detection of Harmful Gases by Copper-Containing Metal–Organic Framework Films

The stabilization of copper clusters in nanosized metal–organic framework crystals, Cu-Y(BTC), was achieved by a solvent-exchange approach, followed by hydrogen reduction. The formation of copper clusters in the Y(BTC) nanocrystals generated during the hydrogen reduction process was followed by UV–vis spectroscopy. The Cu-Y(BTC) nanocrystals were further assembled in thin films with a thickness of 250 nm. The distribution and size of the copper clusters in the films were studied by CO chemisorption, followed by FT-IR spectroscopy combined with transmission electron microscopy. It was shown that the copper clusters with a mean diameter of 6 nm were homogeneously distributed and stabilized in the Cu-Y(BTC) films. Further, the Cu-Y(BTC) films were utilized for detection of single harmful gases, such as CO, chloroform, and 2-ethylthiophene, or mixtures of two compounds. The high sensitivity, selectivity, and reversibility of the Cu-Y(BTC) films toward single CO, chloroform, and 2-ethylthiophene were demonstra...

Design and capabilities of an experimental setup based on magnetron sputtering for formation and deposition of size-selected metal clusters on ultra-clean surfaces

The design and performance of an experimental setup utilizing a magnetron sputtering source for production of beams of ionized size-selected clusters for deposition in ultra-high vacuum is described. For the case of copper cluster formation the influence of different source parameters is studied and analyzed. Size-selected clusters are deposited on substrates and the efficiency of an electrostatic quadrupole mass selector is tested. Height analysis using atomic force microscopy (AFM) demonstrates relative standard size deviations of 7%-10% for the particles of various sizes between 6 nm and 19 nm. Combined analysis by AFM and transmission electron microscopy reveals that the clusters preserve almost spherical shape after the deposition on amorphous carbon substrates. Supported nanoparticles of a few nanometres in diameter have crystalline structure with a face-centered cubic (fcc) lattice.

Evolution of Copper Nanospecies in the Synthesis Stages of MCM-41-Type Mesoporous Molecular Sieves

The redox behavior of copper nanospecies in the synthesis stages of MCM-41-type materials has been followed by ESR technique. These copper-modified mesoporous molecular sieves (Cu-MMS) were synthesized by direct incorporation method, and different treatments of the initial synthesis gel were evaluated. From ESR and UV–vis-DRS data, a synergistic approach about the distribution of copper species in the different catalysts has been made: the hydrothermal treatment favors the incorporation of isolated cooper species into the framework, whereas both the aging treatment and the lack of subsequent treatment promote the formation of copper clusters into the mesoporous channels. The Hamiltonian parameters g// ≈ 2.3 and g⊥ ≈ 2.06 have confirmed the presence of isolated Cu2+ ions in octahedral coordination with tetragonal distortion within siliceous framework, whereas the g ≈ 2.2 value was assigned to the presence of Cu2+ clusters. Only the catalyst aged at room temperature has presented additional signals characte...

Plume dynamics and cluster formation in laser-ablated copper plasma in a magnetic field

Laser-ablated copper plasma plume expanding in a nonuniform magnetic field and ambient gas is investigated to understand plume dynamics using optical emission spectroscopy and fast imaging of the plume. A peculiar oscillatory behavior of the plume observed in magnetic field is discussed. The appearance and enhancement of Cu2 (A–X) band in ambient gas and in the presence of magnetic field is reported. The presence of magnetic field favors the formation of copper clusters in the expanding plumes.

Hydrogen reduction of the Cu(acac)2 complex sorbed by cucurbit[8]uril

The hydrogen reduction of bis(2,4-pentanedionato)copper(II) sorbed by the cavitand cucurbit[8]uril has been studied. After sorption of the complex at 180°C, the crystal structure of the resulting phase differs from the structure of the individual compounds. EPR shows that the reduction of the complex with hydrogen at 250°C for 15 min leads to the loss of one of the ligands and formation of the coordination bond between the Cu2+ ion and a nitrogen atom of cucurbit[8]uril and the oxygen atom of the water molecule or OH− group located in the cavitand cavity. The molecular structure of the resulting supramolecular compound has been optimized by density functional theory quantum-chemical calculations with the exchange-correlation functional with the use of the PRIRODA program package. EPR, EXAFS, and XANES show that an increase in the reduction time or temperature (to 280°C) leads to the formation of copper clusters.

EXAFS and EPR studies of inclusion compounds of the trans-[Cu(en)2(H2O)2]2+ in cucurbit[8]uril

This work describes EXAFS and EPR studies of inclusion compounds of the trans-[Cu(en)2(H2O)2]2+ complex in the macrocyclic cavitand CB[8] at different stages of heat treatment in the hydrogen atmosphere in a temperature range of 200–330°C. The structure and composition of the nearest environment of copper atoms are characterized, and the interatomic distances and coordination numbers are determined. It is shown that the structure of the copper complex inside the cavitand CB[8] remains unchanged at the first stage of complex preparation and upon heating up to 280°C in hydrogen atmosphere. The copper environment corresponds to four nitrogen atoms and two oxygen atoms. Further temperature treatment at 330°C causes decomposition of the complex inside the cavitand without the formation of copper clusters.

Cluster formation, evolution and size distribution in Fe–Cu alloy: Analysis by XAFS, XRD and TEM

Fe–Cu alloys containing 1.3 at.% copper were studied as model systems for cluster formation in reactor pressure vessel steels. The samples were annealed at 775 K for different times and subsequently analyzed using X-ray absorption fine structure spectroscopy at the Cu–K-edge, X-ray diffraction and transmission electron microscopy. The results show that copper cluster formation might occur even with short annealing times. These clusters of about 1 nm size can switch easily from bcc iron-like structures to fcc copper, if the local copper concentration is high enough. While a short annealing time of 2.5 h at 775 K maintains a good dilution of copper in the bcc iron matrix, annealing for 312 h leads to large fcc copper precipitates. A linear combination analysis suggests that in the sample annealed 8 h, copper clusters are mostly formed with the same structure as the matrix. A co-existence of bcc and fcc clusters is obtained for 115 h of annealing. Transmission electron microscopy indicates the presence of precipitates as large as 60 nm size for an annealing time of 312 h, and X-ray diffraction provided complementary data about the clusters size distributions in all of the four samples.

Ab Initio Molecular Dynamics Simulation on the Aggregation of a Cu Monolayer on a WN(001) Surface

We present a first-principles simulation study of copper aggregation on a WN(001) surface. Copper cluster formation energies and activation barriers were systematically evaluated, and the results indicate that these energies do not significantly vary with cluster size if the cluster grows two dimensionally. Moderately higher activation barriers but more favorable thermochemical energies are required for growing three dimensional clusters on the substrate. Ab initio molecular dynamics simulations were performed to examine the dynamic behavior of a copper monolayer originally commensurate with the WN substrate at several atomic layer deposition (ALD) operating temperatures as well as at room temperature. The results reveal that the copper film undergoes substantial agglomeration on the WN(001) surface at ALD operating temperatures, which is consistent with experimental observations, whereas the copper monolayer remains largely stable at room temperature.

Density Function Theory Study of Copper Agglomeration on the WN(001) Surface

We report a first-principles study of copper agglomeration on the WN(001) surface using density functional theory. Small copper cluster formation was explicitly examined by calculating the minimum energy pathways, yielding detailed information on the adsorption structures and energies. The results show that copper agglomeration is a competitive process against surface wetting and agglomeration may occur under typical atomic layer deposition (ALD) conditions.

Dynamics of copper atoms on Si(1 1 1)-7 × 7 surfaces

This study investigated the dynamics of copper atoms adsorbed on Si(1 1 1)-7 × 7 surfaces between 300 K and 623 K using a variable-temperature scanning tunneling microscope (STM). The diffusion behavior of copper clusters containing up to ∼6 atoms into a particular half unit cell of the 7 × 7 reconstructed Si(1 1 1) surface was considered. The movements and the formation of copper clusters were tracked in detail. The activation energies and pre-exponential factors for various diffusion paths were estimated. Finally, the Cu-etching-Si process and the quasi-5 × 5 incommensurated phase of Cu/Si islands were discussed.

Diverse copper clusters confined in microporous nanocrystals

A selective formation of copper clusters in zeolite nanoparticles with GIS type structure is demonstrated. The size and the shape of the metal clusters are depending on the amount of copper incorporated in the small pores of the GIS crystalline structure and on their aperture. Different kinetics of reduction of the metal cations to clusters is observed under controlled radiolytic treatment of suspensions with constrained nanosized GIS particles. The solvated electrons produced in the bulk water under gamma radiolysis migrate into the GIS nanocrystals and subsequently reduce Cu II to Cu I starting from the external surface layers and progressing towards the center of the particles; this results in the coexistence of both Cu II cations and Cu 0 atoms. In the samples with low copper content, the formation of Cu I species is not observed, which is associated with the confinement of copper into the small zeolite pores preventing the reaction between Cu 2+ and Cu n 0. The copper loading of the nanocrystals, the conditions of radiolytic treatment and the features of the framework type crystalline structure determine the development of the reduction process resulting in selective formation of Cu I or Cu 0 species in the GIS nanocrystals.

Density functional theory characterization of the formation of copper clusters on Fs and [formula omitted] centers on a MgO surface

Electronic structure and chemical reactivity of Cu n clusters ( n = 1–4) supported on a regular site (O 5c) and on an oxygen vacancy ( F s and F s + ) of the MgO (1 0 0) surface were investigated using density functional theory. It was found that neutral oxygen vacancies, F s centers, are good trapping sites for Cu atoms and nucleation centers while F s + centers are not. Both, first ionization potential and the chemical reactivity present odd–even oscillations in the free and supported clusters, these oscillations are related to the electronic nature of the layer open/closed for clusters with odd and even n, respectively, this behavior is similar for supported clusters on an F s center compared with free clusters. It is also found that the ionization potential and the chemical reactivity are modified when the clusters are supported on the MgO vacancies.

Copper nucleation on [formula omitted] in the presence of sulphur

The cleanliness and atomic structure of a zinc oxide single crystal is of major importance to the formation of copper clusters. We have used synchrotron radiation induced photoelectron spectroscopy to study the structure of copper deposited at room temperature in ultrahigh vacuum onto a ZnO ( 1 1 2 ¯ 0 ) single crystal, and the effect of subsequent annealing to 400 °C. Further, sulphur interacts with copper particles on the zinc oxide surface upon exposing the sample to hydrogen sulphide until saturation. The experiments show that copper deposited at room temperature follows “monolayer followed by simultaneous multilayer” or “2-Dimensional islands” growth mode, and annealing at 400 °C causes cluster formation and migration of copper into the ZnO substrate. In contrast, annealing after sulphur exposure induces an opposite migration: Copper migrates from ZnO bulk to the surface, reacting with the adsorbed sulphur.

Formation of copper clusters on a thiophene mediated Si(111)-(7×7) surface via molecular anchors

Thiophene selectively binds to the pair of adjacent Si adatom and Si rest atom on the Si(111)-(7×7) surface, leading to the covalent attachment of C–S–C linkages onto the surface. Cu atoms are found to preferentially adsorb onto the S atoms of the functional C–S–C groups in the formation of copper nanoclusters on the thiophene-mediated Si(111)-(7×7) surface.

The Formation of Neutral Copper Clusters from Experimental Binding Energies and Reactivity Descriptors

In this paper we study and rationalize the formation of neutral copper clusters from dimer to nonamer using the available experimental data of binding energies and electronic properties. A complete and consistent picture of the formation of copper clusters in terms of the changes in chemical potential and hardness emerges indicating that the one-atom growth reactions are mainly driven by changes in hardness. An analytic expression for the binding energy as a function of the cluster size is proposed and used to predict the growth pattern of copper clusters.

One-dimensional organization of copper nanoparticles by chemical reduction of lipid-copper hybrid nanofibers

One-dimensional organization of copper nanoparticles has been achieved by chemical reduction using lipid-copper hybrid nanofibers as a template; the reduction of copper ions and the resulting formation of copper clusters occurred at intervals of 2–5 nm along the nanofibers.