Cluster Deposition Research Articles

Tuning the charge states of CrW2O9 clusters deposited on perfect and defective MgO(001) surfaces with different color centers: A comprehensive DFT study

The structures and electronic properties of bimetallic oxide CrW2O9 clusters supported on the perfect and defective MgO(001) surfaces with three different color centers, FS (0), FS (+), and FS (2+) centers, respectively, have been investigated by density functional theory calculations. Our results show that the configurations, adsorption energies, charge transfers, and bonding modes of dispersed CrW2O9 clusters are sensitive to the charge states of the FS centers. Compared with the gas-phase configuration, the CrW2O9 clusters supported on the defective surfaces are distorted dramatically, which exhibit different chain structures. On the perfect MgO surface, the depositions of clusters do not involve obvious charge transfer, while the situation is quite different on the defective MgO(001) surfaces in which significant electron transfer occurs from the surface to the cluster. Interestingly, this effect becomes more remarkable for electron-rich oxygen vacancies (FS (0) center) than that for electron-poor oxygen vacancies (FS (+) and FS (2+) centers). Furthermore, our work reveals a progressive Brønsted acid sites where spin density preferentially localized around the Cr atoms not the W atoms for all kinds of FS-centers, indicating the better catalytic activities can be expected for CrW2O9 cluster on defective MgO(001) surfaces with respect to the W3O9 cluster.

CFD simulation of nozzle characteristics in a gas aggregation cluster source

Computational fluid dynamics (CFD) simulation for the sharp-edged nozzle was made using the OpenFOAM source code. Jet dynamics characteristics for the gas stream from a sharped-edged nozzle are then simulated under two-dimensional and axisymmetric steady state condition. Gas and particle velocities in a jet are obtained under different input and boundary conditions to provide an insight into the jet characteristics. For the range of downstream distances considered, the results indicate that a jet is characterized by an initial rapid decay of the axial velocity at the jet center while the cross-sectional flow evolves toward a top-hat profile downstream. Numerical simulation of the free-jet expansion from six types of nozzles indicated that the flow fields had significant differences in the early stages of the expansion. The effects of nozzle geometry on the nanoparticles were investigated. Simulation results indicated that the geometry of nozzle affected the cluster penetration efficiency and beam diameter. The extent to which to the Brownian diffusion can affect the particle extraction from nozzle is investigated. Simulations have shown that the Brownian motion perturbs the clusters from the trajectories dictated by the carrier gas and increases the rate of cluster deposition on the nozzle.

The effect of metal cluster deposition route on structure and photocatalytic activity of mono- and bimetallic nanoparticles supported on TiO2 by radiolytic method

TiO2 (P25) was modified with small and relatively monodisperse mono- and bimetallic clusters (Ag, Pd, Pt, Ag/Pd, Ag/Pt and Pd/Pt) induced by radiolysis to improve its photocatalytic activity. The as-prepared samples were characterized by X-ray fluorescence spectrometry (XRF), photoluminescence spectrometry (PL), diffuse reflectance spectroscopy (DRS), X-ray powder diffractometry (XRD), scanning transition electron microscopy (STEM) and BET surface area analysis. The effect of metal type (mono- and bimetallic modification) as well as deposition method (simultaneous or subsequent deposition of two metals) on the photocatalytic activity in toluene removal in gas phase under UV–vis irradiation (light-emitting diodes- LEDs) and phenol degradation in liquid phase under visible light irradiation (λ>420nm) were investigated. The highest photoactivity under Vis light was observed for TiO2 co-loaded with platinum (0.1%) and palladium (0.1%) clusters. Simultaneous addition of metal precursors results in formation of larger metal nanoparticles (15–30nm) on TiO2 surface and enhances the Vis-induced activity of Ag/Pd-TiO2 up to four times, while the subsequent metal ions addition results in formation of metal particle size ranging from 4 to 20nm. Subsequent addition of metal precursors results in formation of BNPs (bimetallic nanoparticle) composites showing higher stability in four cycles of toluene degradation under UV–vis. Obtained results indicated that direct electron transfer from the BNPs to the conduction band of the semiconductor is responsible for visible light photoactivity, whereas superoxide radicals (such as O2− and OOH) are responsible for pollutants degradation over metal-TiO2 composites.

Rotational Isomerism, Electronic Structures, and Basicity Properties of "Fully-Reduced" V14-type Heteropolyoxovanadates.

We investigated computationally the α-, γ-, and β-isomeric structures, relative stabilities, and the electronic and basicity properties of magnetic [V(IV)14E8O50](12-) (hereafter referred to as {V14E8}) heteropolyoxovanadates (heteroPOVs) and their heavier chalcogenide-substituted [V(IV)14E8O42X8](12-) ({V14E8X8}) derivatives for E = Si(IV), Ge(IV), and Sn(IV) and X = S, Se, and Te. We used density functional theory (DFT) with scalar relativistic corrections in combination with the conductor-like screening model of solvation. The main purpose of this investigation is to introduce the structure-property relations in heteroPOVs as well as to assist the synthesis and molecular deposition of these molecular vanadium-oxide spin clusters on surfaces. "Fully-reduced" polyoxoanions {V14E8} and {V14E8X8} are virtually comprised of [V(IV)14O38](20-) {V14} skeletons of different symmetries, that is, D2d for α-, D2 for γ-, and D4h for β-isomers, which are stabilized by the four {E2O3}(2+) and four {E2OX2}(2+) moieties, respectively. Our DFT calculations reveal stability trends α > γ > β for polyoxoanions {V14E8} and {V14E8X8}, based on relative energies and HOMO-LUMO energy gaps. The α-isomeric polyoxoanions {V14E8} and {V14E8X8} with the high negative net charges may easily pick up protons at the terminal E-Ot and E-Xt sites, respectively, which is evidenced by strongly negative enthalpies of monoprotonation. Energetically favorable sites on polyoxoanions α-{V14E8} and α-{V14E8X8} for electrostatic pairing with countercations were also determined. Among β and γ isomers, the hitherto unknown γ-[V14Sn8O50](12-) and γ-[V14Sn8O42S8](12-) seem to be the most viable targets for isolation. Furthermore, these Sn-substituted polyoxoanions are of high interest for electrochemical studies because of their capability to act as two-electron redox catalysts.

Ceria nanoclusters on graphene/Ru(0001): A new model catalyst system

The growth of ceria nanoclusters on single-layer graphene on Ru(0001) has been examined, with a view towards fabricating a stable system for model catalysis studies. The surface morphology and cluster distribution as a function of oxide coverage and substrate temperature has been monitored by scanning tunneling microscopy (STM), whereas the chemical composition of the cluster deposits has been determined by Auger electron spectroscopy (AES). The ceria nanoparticles are of the CeO2(111)-type and are anchored at the intrinsic defects of the graphene surface, resulting in a variation of the cluster densities across the macroscopic sample surface. The ceria clusters on graphene display a remarkable stability against reduction in ultrahigh vacuum up to 900K, but some sintering of clusters is observed for temperatures >450K. The evolution of the cluster size distribution suggests that the sintering proceeds via a Smoluchowski ripening mechanism, i.e. diffusion and aggregation of entire clusters.

Numerical simulation of nanocluster motion through a DC magnetron nanocluster source

The commercial computational fluid dynamics (CFD) software OpenFOAM was used to simulate the gas flow field in a direct current (DC) magnetron nanocluster source. The density of free metal atoms in the aggregation region influenced the cluster formation and the cluster intensity. In order to improve the density of nanoclusters, two factors should be considered: redeposition of the sputtered atoms within the cathode region and the loss of the nanoclusters on the chamber wall. The angles of the jet and the vortex in the aggregation region have a significant influence on the number of nanoclusters. The extent to which to the Brownian diffusion can affect the particle extraction from source is investigated. Simulations have shown that the Brownian motion perturbs the clusters from the trajectories dictated by the carrier gas and increases the rate of cluster deposition on the source internal wall.

Uniform deposition of size-selected clusters using Lissajous scanning

Size-selected clusters can be deposited on the surface using size-selected cluster ion beams. However, because of the cross-sectional intensity distribution of the ion beam, it is difficult to define the coverage of the deposited clusters. The aggregation probability of the cluster depends on coverage, whereas cluster size on the surface depends on the position, despite the size-selected clusters are deposited. It is crucial, therefore, to deposit clusters uniformly on the surface. In this study, size-selected clusters were deposited uniformly on surfaces by scanning the cluster ions in the form of Lissajous pattern. Two sets of deflector electrodes set in orthogonal directions were placed in front of the sample surface. Triangular waves were applied to the electrodes with an irrational frequency ratio to ensure that the ion trajectory filled the sample surface. The advantages of this method are simplicity and low cost of setup compared with raster scanning method. The authors further investigated CO adsorption on size-selected Ptn (n = 7, 15, 20) clusters uniformly deposited on the Al2O3/NiAl(110) surface and demonstrated the importance of uniform deposition.

Poly(methyl methacrylate) composites with size-selected silver nanoparticles fabricated using cluster beam technique

An embedment of metal nanoparticles of well-defined sizes in thin polymer films is of significant interest for a number of practical applications, in particular, for preparing materials with tunable plasmonic properties. In this article, we present a fabrication route for metal–polymer composites based on cluster beam technique allowing the formation of monocrystalline size-selected silver nanoparticles with a ±5–7% precision of diameter and controllable embedment into poly (methyl methacrylate). It is shown that the soft-landed silver clusters preserve almost spherical shape with a slight tendency to flattening upon impact. By controlling the polymer hardness (from viscous to soft state) prior the cluster deposition and annealing conditions after the deposition the degree of immersion of the nanoparticles into polymer can be tuned, thus, making it possible to create composites with either particles partly or fully embedded into the film. Good size selection and rather homogeneous dispersion of nanoparticles in the thin polymer film lead to excellent plasmonic properties characterized by the narrow band and high quality factor of localized surface plasmon resonance. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1152–1159

Palladium clusters deposited on the heterogeneous substrates

To improve the performance of the Pd composite membrane prepared by the cold spraying technology, it is extremely essential to give insights into the deposition process of the cluster and the heterogeneous deposition of the big Pd cluster at the different incident velocities on the atomic level. The deposition behavior, morphologies, energetic and interfacial configuration were examined by the molecular dynamic simulation and characterized by the cluster flattening ratio, the substrate maximum local temperature, the atom-embedded layer number and the surface-alloy formation. According to the morphology evolution, three deposition stages and the corresponding structural and energy evolution were clearly identified. The cluster deformation and penetrating depth increased with the enhancement of the incident velocity, but the increase degree also depended on the substrate hardness. The interfacial interaction between the cluster and the substrate can be improved by the higher substrate local temperature. Furthermore, it is found that the surface alloys were formed by exchanging sites between the cluster and substrate atoms, and the cluster atoms rearranged following as the substrate lattice arrangement from bottom to up in the deposition course. The ability and scope of the structural reconstruction are largely determined by both the size and incident energy of the impacted cluster.

Atomistic Study of the Copper Cluster Deposition on Si(001) and Si(111) Surface

The deposition of a single Cu cluster on the Si (001) and Si (111) surfaces was studied by molecular dynamics simulations. EAM, SW and Morse potentials were used to describe the interaction of Cu-Cu, Si-Si, and the Cu-Si atoms, respectively. The results show that the crystallographic surface of the substrate had a large effect on film growth. On the Si (111) surface, the cluster structure demonstrate good uniformity and epitaxial relation to the substrate. There is no appreciable intermixing or silicide formation at the film-substrate interface, nor silicon segregation on the surface with incident energy between 0.1 and 1.0eV/atom. However, as the incident energy increases to 3.0eV/atom, intermixing began to appear for Cu13 and Cu19 clusters. For the Cu147 cluster intermixing starts to appear at a lower energy of 1.6eV/atom. In contrast, intermixing appears on the Si (001) surface for a range of incident energy from 0.1 to 3.0eV/atom for all the three clusters studied. Furthermore, the epitaxial relation with the Si substrate result in (001)- or (111)-oriented Cu clusters on Si (001) or Si (111), respectively. This behavior is consistent with experimental observations. We found that the effect of cluster deposition on film property depends not only on the substrate-film material combination and cluster size but also on the substrate crystallographic orientation and incident energy.

Effect of hybrid oxidation on the titanium oxide layer's properties investigated by spectroscopic methods

In this work the study of hybrid Ti Grade 2 during oxidation using FADT – fluidized bed atmospheric diffusive treatment and PVD – magnetron sputtering have been investigated. Additionally, the influence of the oxidation method on the change in the mechanism of oxygen transport to the substrate have been discussed (phenomenon responsible for the improvement of bioactivity). Presented method consists in forming the titanium surface layer saturated with oxygen due to the diffusion and deposition of a thin homogeneous oxide coating on the Ti surface. Discussed processes diminish the surface roughness and increase bio-compatibility of the surface, which results in easier hydroxyapatite cluster deposition. The diffusion process was conducted on Al2O3 fluidized bed, with air as the fluidizing factor at 913 K for 8 h. The deposition of the oxide coatings were carried out with magnetron sputtering, with the use of a TiO2 target at a pressure of 3 × 10−2 mbars and power of 350 W. To evaluate the effects of hybrid oxidation and to determine the mechanism of oxygen transport, the following research methods have been applied: spectroscopy (GDOS, SIMS, RS), microscopic methods (SEM-EDS, SEM-EBSD, TEM-EFTEM), X-ray tests (μ-XRD, GID). Obtained test results were used to identify the type of oxide coatings, to assess the thickness of the layers and to study the influence of crystallographic orientation on oxygen transport and concentration in the surface layer and in the oxide coating. It has been found that the formation of oxide coatings created by using the hybrid method (FADT + PVD leads to a change in oxygen concentration in the substrate due to introduced defects. This phenomenon is in opposition to the conventional methods such as: electrochemical or laser oxidation. In contrast, forming a tight homogeneous oxide coating on Ti surface improves the biocompatibility, which is particularly important in the context of biomedical applications.

Electric field modulation of magnetic anisotropy and microwave absorption properties in Fe50Ni50/Teflon composite films

Fe50Ni50 nanoparticle films with the size about 6 nm were deposited by a high energetic cluster deposition source. An electric field of about 0 - 40 kV was applied on the sample platform when the films were prepared. The field assisted deposition technique can dramatically induce in-plane magnetic anisotropy. To probe the microwave absorption properties, the Fe50Ni50 nanoparticles were deliberately deposited on the dielectric Teflon sheet. Then the laminated Fe50Ni50/Teflon composites were used to do reflection loss scan. The results prove that the application of electric field is an effective avenue to improve the GHz microwave absorption performance of our magnetic nanoparticles films expressed by the movement of reflection loss peak to high GHz region for the composites.

Interfacial properties of a carbyne-rich nanostructured carbon thin film in ionic liquid

Nanostructured carbon sp2 (ns-C) thin films with up to 30% of sp-coordinated atoms (carbynes) were produced in a high vacuum by the low kinetic energy deposition of carbon clusters produced in the gas phase and accelerated by a supersonic expansion. Immediately after deposition the ns-C films were immersed in situ in an ionic liquid electrolyte. The interfacial properties of ns-C films in the ionic liquid electrolyte were characterized by electrochemical impedance spectroscopy and cyclic voltammetry (CV). The so-prepared carbyne-rich electrodes showed superior electric double layer (EDL) capacitance and electric conductivity compared to ns-C electrodes containing only sp2 carbon, showing the substantial influence of carbynes on the electrochemical properties of nanostructured carbon electrodes.

Nanoparticle formation and dusty plasma effects in DC sputtering discharge with graphite cathode

We developed a model for the nucleation, growth and transport of carbon dust particles in a DC discharge. The carbon source comes from the sputtering of a graphite cathode resulting in the production of primary clusters and then of nanoparticles. We consider the ionic cluster growth as well as the particle growth and charging and the influence of both on the discharge equilibrium. We found that the discharge becomes electronegative for long duration when particle density reaches 109 cm−3 and particle size 45 nm. The corresponding transition modifies the electric field profile in the vicinity of the field reversal region in the negative glow. We then analyze the space and time evolution of the different discharge characteristics and the mechanisms involved in the discharge. We showed that particle density is governed by nucleation, coagulation and transport, while particle size is mainly governed by the deposition of the small neural clusters emitted at the cathode on the particle surface.

Ni(2+)-zeolite/ferrosphere and Ni(2+)-silica/ferrosphere beads for magnetic affinity separation of histidine-tagged proteins.

Magnetic Ni(2+)-zeolite/ferrosphere and Ni(2+)-silica/ferrosphere beads (Ni-ferrosphere beads - NFB) of a core-shell structure were synthesized starting from coal fly ash ferrospheres having diameters in the range of 0.063-0.050 mm. The strategy of NFB fabrication is an oriented chemical modification of the outer surface preserving the magnetic core of parent beads with the formation of micro-mesoporous coverings. Two routes of ferrosphere modification were realized, such as (i) hydrothermal treatment in an alkaline medium resulting in a NaP zeolite layer and (ii) synthesis of micro-mesoporous silica on the glass surface using conventional methods. Immobilization of Ni(2+) ions in the siliceous porous shell of the magnetic beads was carried out via (i) the ion exchange of Na(+) for Ni(2+) in the zeolite layer or (ii) deposition of NiO clusters in the zeolite and silica pores. The final NFB were tested for affinity in magnetic separation of the histidine-tagged green fluorescent protein (GFP) directly from a cell lysate. Results pointed to the high affinity of the magnetic beads towards the protein in the presence of 10 mM EDTA. The sorption capacity of the ferrosphere-based Ni-beads with respect to GFP was in the range 1.5-5.7 mg cm(-3).

Технология кластерного осаждения меди с ассистированием струей инертного газа

Технология кластерного осаждения меди с ассистированием струей инертного газа

Catalysis Applications of Size-Selected Cluster Deposition

In this Perspective, we review recent studies of size-selected cluster deposition for catalysis applications performed at the U.S. DOE National Laboratories, with emphasis on work at Argonne National Laboratory (ANL) and Brookhaven National Laboratory (BNL). The focus is on the preparation of model supported catalysts in which the number of atoms in the deposited clusters is precisely controlled using a combination of gas-phase cluster ion sources, mass spectrometry, and soft-landing techniques. This approach is particularly effective for investigations of small nanoclusters, 0.5–2 nm (<200 atoms), where the rapid evolution of the atomic and electronic structure makes it essential to have precise control over cluster size. Cluster deposition allows for independent control of cluster size, coverage, and stoichiometry (e.g., the metal-to-oxygen ratio in an oxide cluster) and can be used to deposit on any substrate without constraints of nucleation and growth. Examples are presented for metal, metal oxide, a...

Toward Control of Gold Cluster Aggregation on TiO2 via Surface Treatments

Well-defined Au–TiO2 materials were synthesized by deposition of triphenylphosphine-protected Au9 clusters on TiO2 (Aeroxide P-25), pre-treated in eight different ways and subsequently exposed to two post-treatments. X-ray photoelectron spectroscopy and UV–vis diffuse reflectance spectroscopy studies showed that in most cases the PPh3 ligand shell was removed upon deposition even before post-treatment, coinciding with some cluster aggregation. However, clusters deposited on TiO2 treated using H2SO4 and H2O2 showed remarkable resistance to aggregation, even after high-temperature calcination, while clusters on H2-treated TiO2 showed the greatest resistance to aggregation under ozonolysis.

Light absorption with branched gold cauliflower-like nanostructure arrays

In the present study, we have investigated the growth of branched gold (Au) cauliflower-shaped nanoparticles on Cicada's wing nanonipple arrays. The gas aggregation dc magnetron sputtering nanocluster source without size filtration was employed for fabrication of the samples. It was observed that the operating conditions of dc magnetron sputtering, such as gas pressure in the aggregation chamber and discharge power, control the deposition of charged clusters. By changing the operational conditions, a nanocauliflower-like (NCF) structure grew on the nanonipples. This Au nanostructure with a cauliflower-shaped surface feature was monitored using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The optical properties of these branched gold nanostructure arrays were also studied. Reduction of light reflection and the consequent light trapping suggest use of this branched structure for achieving broadband light absorption in Plasmonic solar cells as a result of plasmonic effects.

Morphology and growth behavior of O2-free chemical bath deposited ZnS thin films

We investigate the role of reagent concentrations and ambient O2 on the morphology and growth behavior of ZnS thin films grown with the chemical bath deposition method. We investigate the role of substrate on film morphology, and find significant differences between films deposited on SiO2 versus Si. The films are also sensitive to dissolved O2 in the bath, as it causes a layer of SiO2 to form at the ZnS/Si interface during deposition. Degassing of solutions and an N2 atmosphere are effective to minimize this oxidation, allowing deposition of ZnS films directly onto Si. Under these conditions, we examine film properties as they relate to reagent bath concentrations. As the reagent concentrations are decreased, both the film roughness and growth rate decrease linearly. We also observe deformation and shifting of X-ray diffraction peaks that increases with decreasing reagent concentrations. The shifts are characteristic of lattice compression (caused by the substitution of oxygen for sulfur), and the deformation is characteristic of distortion of the lattice near crystal grain interfaces (caused by tensile stress from interatomic forces between neighboring crystal grains). At the weakest concentrations, the low roughness suggests a mixed growth mode in which both clusters and individual ZnS nanocrystallites contribute to film growth. With increasing reagent concentrations, the growth mode shifts and becomes dominated by deposition of clusters.