Cluster Deposition Research Articles

Enhanced photocatalytic H2-production activity of bicomponent NiO/TiO2 composite nanofibers

Hydrogen has been regarded as an ideal candidate for the replacement of conventional fossil fuels due to its environmental friendliness and recycling possibility. In this work, mesoporous NiO/TiO2 bicomponent composite nanofibers were prepared by a electrospinning and calcination method. The H2-production activity of the prepared samples was examined by water splitting using methanol as scavenger under simulated solar Xenon lamp irradiation. The effect of NiO loading on the microstructure and photocatalytic H2-production activity of NiO/TiO2 composite samples was studied and discussed. The results demonstrated that the presence of a small amount of NiO obviously inhibited the growth of TiO2 crystallites. With increasing the NiO content, the average crystallite size further decreased. In contrast, the Brunauer–Emmett–Teller (BET) specific surface areas, pore volumes and average pore size steadily increased. Photocatalytic H2-production experiment confirmed that NiO was an efficient co-catalyst for the photocatalytic H2 production of TiO2. The optimal NiO loading was determined to be 0.25wt.%, giving a H2-production rate of 337μmolh−1g−1 with apparent quantum efficiency (QE) of 1.7%, which exceeded the rate on pure TiO2 by more than 7 times. The enhanced H2-production activity was due to the deposition of NiO clusters on the surface of TiO2, which suppressed the recombination of photogenerated electron–hole pairs, reduced the overpotential of hydrogen production and catalyzed production of hydrogen. This work showed that low-cost and earth-abundant NiO could be used as co-catalyst for photocatalytic hydrogen production.

Molecular dynamics simulation of energetic Cu55 clusters deposition on a Fe (0 0 1) surface

The energetic Cu55 clusters deposition on a Fe (001) surface was investigated by the molecular dynamics simulation. A many-body potential based on Finnis–Sinclair model is used to describe the interactions among atoms. The clusters with incident energies ranging from 0.5 to 30.0eV/atom, respectively, are deposited on the substrates with various temperatures (300, 700 and 1000K). The collective collisions play a dominant role in the interaction between the energetic cluster and the solid surface is demonstrated by analyzing the number of defects in the substrate and the “snapshots” during the deposition process. The energy of the cluster rapidly transfers to the substrate through the collective collisions. Then the atoms in the collision region are activated and get the migration energies to complete their migration and reconstruction. In addition, the effects of the incident energy and substrate temperature on the number of the cluster implantation atoms, the number of defects in the substrate, the spreading index and structure parameter of the cluster are investigated. The results show that the incident energy mainly influences the penetration and diffusion of the cluster, and the number of defects in the substrate and the epitaxial degree of the cluster are affected by both the incident energy and substrate temperature. By the contrast analysis, the moderate incident energy (about 5.0eV/atom) and the low substrate temperature (300K) are suited to grow high-quality epitaxial layers.

Titanium dioxide/zeolite integrated photocatalytic adsorbents for the degradation of amoxicillin

Integrated photocatalytic adsorbents (IPA) prepared from TiO2 and natural zeolite were applied to amoxicillin (AMX) degradation. The acid-alkali pre-treated zeolite annealed at 300°C under nitrogen resulted in the best degradation of AMX. The superior performance of this IPA material was explained using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray diffraction (XRD). SEM analysis showed an uneven surface as a result of TiO2 cluster deposition, which provides more active sites for adsorption and degradation. XRD results revealed that peaks from more photoactive anatase were more prominent in this IPA material. EDS analyses also confirmed the presence of high amounts of TiO2. Despite their large TiO2 loadings, comparison experiments with untreated zeolite suggested that the pores are still available for adsorption. The overall performance of the IPA material for the degradation of AMX was thus attributed to the adsorption capability of the zeolite carrier, the photocatalytic activity of TiO2 coating and acid-catalyzed hydrolysis (‘capture & destroy’). Degradation products resulting from TiO2/zeolite IPA-induced hydrolysis were identified by liquid chromatography-mass spectrometry (LC-MS) prior to photocatalytic treatment. AMX and its thermal degradants were almost completely removed after 240min of irradiation. The efficiency of the developed TiO2/zeolite material provides a potentially economical way of degrading pharmaceutical compounds and recovering photocatalysts simultaneously.

Magnetic Silicon Nanoparticles

Prospects for diamond-structured magnetic Si are investigated experimentally, by model calculations, and numerically. Our theoretical analysis, using bond-orbital, Vienna ab-initio simulation package, and SIESTA calculations, suggest that some diamond-Si imperfection may carry a magnetic moment. In particular, for tetrahedral Si5 clusters, we calculate a magnetic moment of 4 μB per cluster. These moments are more likely to be observed in nanoparticles, as compared with thin films, due to the larger surface-to-volume ratios of the former and to their more versatile atomic surface structure. Experimentally, we have prepared Si nanoparticles by cluster deposition and found a small magnetization of 2.9 emu/cm3 at 10 K.

Magnetization Measurements and XMCD Studies on Ion Irradiated Iron Oxide and Core-Shell Iron/Iron-Oxide Nanomaterials

Magnetite (Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) and core-shell iron/iron-oxide (Fe/FexOy) nanomaterials prepared by a cluster deposition system were irradiated with 5.5 MeV Si <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ions and the structures determined by X-ray diffraction as consisting of 100% magnetite and 36/64 wt% Fe/FeO, respectively. However, X-ray magnetic circular dichroism (XMCD) indicates similar surfaces in the two samples, slightly oxidized and so having more Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> than the expected magnetite structure, with XMCD intensity much lower for the irradiated core-shell samples indicating weaker magnetism. X-ray absorption spectroscopy (XAS) data lack a strong signature for FeO, but the irradiated core-shell system consists of Fe-cores with ~13 nm of separating oxide crystallite, so it is likely that most FeO (octahedral Fe <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ) exists deeper than the probe depth of the XAS (~5 nm). Exchange bias (Hex) for both samples becomes increasingly negative as temperature is lowered, but the irradiated Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> sample shows greater sensitivity of cooling field on Hex. Loop asymmetries and Hex sensitivities of the irradiated Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> sample are due to interfaces and interactions between grains, which were not present in samples before irradiation, as well as surface oxidation. Asymmetries in the hysteresis curves of the irradiated core/shell sample are related to the reversal mechanism of the antiferromagnetic FeO and possibly some near surface oxidation.

Nozzleless spray cooling using surface acoustic waves

Surface acoustic wave (SAW) atomization is an attractive approach for generating monodispersed microdroplets for a diversity of applications, from drug delivery to mass spectrometry, due to its reliability, miniaturizability, and portability. Here, we demonstrate a nozzleless spray cooling technique based on SAW atomization, with the key advantage of downward scalability: increasing the operating frequency facilitates the fabrication of a chip-sized atomizer to use in compact cooling of electronic devices. Using deionised water, cooling is improved by 15% when the atomization rate is increased by 40%; when the gap separating the SAW device and heat source is halved, the cooling is improved by 20%. By constructing the device such that the atomized droplets are easily deposited upstream of the flow circulation, the performance is improved further. The atomization of CuO nanoparticle suspensions (at 3%) increased the cooling performance by 30%. Merely increasing the nanoparticle mass concentration in the suspension from 1% to 3% leads to an improvement in the cooling by 10% due to the deposition and formation of nanoparticle clusters on the heated surface, thereby increasing the total surface area. Further increases in the nanoparticle concentration to 10% however results in a diminution in the cooling due to the increase in the suspension viscosity μ, that leads to a reduction in the atomization rate ṁ~μ−1/2 for a given input power. Finally, we demonstrate the concept of using tapered finger transducers to selectively enhance local cooling in a desired area by simply changing the excitation frequency, without requiring repositioning of the SAW device.

Nickel nanoparticles effect on the electrochemical energy storage properties of carbon nanocomposite films

The growth of nanostructured nickel : carbon (Ni : C) nanocomposite thin films by the supersonic cluster beam deposition of nickel and carbon clusters co-deposited from two separate beam sources has been demonstrated. Ni : C films retain the typical highly disordered structure with predominant sp2 hybridization, low density, high surface roughness and granular nanoscale morphology of cluster assembled nanostructured carbon, but display enhanced electric conductivity. The electric double layer (EDL) capacitance of Ni : C films featuring the same thickness (200 nm) and different nickel volumetric concentrations (0–35%) has been investigated by electrochemical impedance spectroscopy employing an aqueous solution of potassium hydroxide (KOH 1 M) as electrolyte solution. Evidence of increased electric conductivity, facilitated EDL formation and negligible porous structure modification was found as consequence of Ni embedding. This results in the ability to synthesize electrodes with tailored specific power and energy density by the accurate control of the amount of deposited Ni and C clusters. Moreover, nickel nanoparticles were shown to catalyze the formation of tubular onion-like carbon structures upon mild thermal treatment in inert atmosphere. Electrochemical characterization of the heated nanocomposite electrodes revealed that the presence of long range ordered sp2 structures further improves the power density and energy storage properties.

Cobalt advanced barrier metallization: A resistivity composition analysis

Cobalt is a high-potential material applicable as liner and seed replacement in BEoL metallization schemes. To enable seedless plating, the resistivity of thin cobalt liners (<5nm) has to be controlled. In the presented paper, the impacts of impurities, grain boundary scattering, surface scattering and roughness on the resistivity of thin cobalt layers is evaluated and modeled. For analysis, i-PVD TaNx barrier films are covered by MOCVD cobalt films with thicknesses in the range of 2–90nm. Film stacks are deposited in a 300mm AMAT Endura2™ cluster deposition tool without breaking the vacuum. An optional heat treatment at 400°C is applied to initiate morphology modification. The amounts of precursor induced impurities quantified by in situ ARXPS are found to be independent of the deposited film thickness. Ex situ characterizations of cobalt films are performed by four point probe measurement, XRR, AFM and TEM revealing resistivity, thickness, roughness and morphology of the cobalt films. A comparison of the measured data with established models for thin film resistivity from Fuchs–Sondheimer, Mayadas–Shatzkes and Namba shows the tremendous impact of the film roughness on resistivity. With implementing a modification on the Namba model to include thickness dependent roughnesses it is possible to reproduce the measured data of the annealed samples very well. Due to the good correlation between measured and calculated resistivity values and the reduced number of fitting parameters, the measurement method can be also used as a simple way to control thin film thicknesses.

Effect of the size-selective silver clusters on lithium peroxide morphology in lithium–oxygen batteries

Lithium-oxygen batteries have the potential needed for long-range electric vehicles, but the charge and discharge chemistries are complex and not well understood. The active sites on cathode surfaces and their role in electrochemical reactions in aprotic lithium-oxygen cells are difficult to ascertain because the exact nature of the sites is unknown. Here we report the deposition of subnanometre silver clusters of exact size and number of atoms on passivated carbon to study the discharge process in lithium-oxygen cells. The results reveal dramatically different morphologies of the electrochemically grown lithium peroxide dependent on the size of the clusters. This dependence is found to be due to the influence of the cluster size on the formation mechanism, which also affects the charge process. The results of this study suggest that precise control of subnanometre surface structure on cathodes can be used as a means to improve the performance of lithium-oxygen cells.

Novel mechanism of premature battery failure due to lithium cluster formation in implantable cardioverter-defibrillators.

Battery failure is an uncommon complication of implantable cardioverter-defibrillators (ICDs), but unanticipated battery depletion can have life-threatening consequences. The purpose of this study was to describe the prevalence of a novel mechanism of battery failure in St. Jude Medical Fortify and Unify ICDs. Cases of premature Fortify battery failure from a single center are reported. A search (January 1, 2010 through November 30, 2013) for Fortify and Unify premature batter failure was conducted of the Food and Drug Administration's Manufacturer and User Facility Device Experience Database (MAUDE). These findings were supplemented with information provided by St. Jude Medical. Premature battery failure for 2 Fortify ICDs in our practice were attributed to the presence of lithium clusters near the cathode, causing a short circuit and high current drain. The prevalence of this mechanism of premature battery failure was 0.6% in our practice. A MAUDE search identified 39 cases of Fortify (30) and Unify (9) premature battery depletion confirmed by the manufacturer, representing a 0.03% prevalence. Four additional Fortify and 2 Unify cases were identified in MAUDE as suspected premature battery depletion, but in these cases the pulse generator was not returned to the manufacturer for evaluation. St. Jude Medical identified 10 cases of premature battery failure due to lithium clusters in Fortify devices (9) and Unify devices (1), representing a 0.004% prevalence. The deposition of lithium clusters near the cathode is a novel mechanism of premature battery failure. The prevalence of this problem is unknown. Providers should be aware of this mechanism for patient management.

Low energy Cu clusters slow deposition on a Fe (001) surface investigated by molecular dynamics simulation

The slow deposition of low energy Cu clusters on a Fe (001) surface was investigated by molecular dynamics simulation. A many-body potential based on Finnis–Sinclair model was used to describe the interactions among atoms. Three clusters comprising of 13, 55 and 147 atoms, respectively, were deposited with incident energies ranging from 0.0 to 1.0 eV/atom at various substrate temperatures (0, 300 and 800 K). The rearrangement and the diffusion of cluster can occur, only when the cluster atoms are activated and obtained enough migration energy. The interaction between low energy cluster and substrate can be divided to the landing and the thermal diffusion phases. In the former, the migration energy originates from the latent heat of binding energy for the soft deposition regime and primarily comes from the incident energy of cluster for the energetic cluster deposition regime. In the latter, the thermal vibration would result in some cluster atoms activated again at medium and high substrate temperatures. Also, the effects of incident energy, cluster size and substrate temperature on the interaction potential energy between cluster and substrate, the final deposition morphology of cluster, the spreading index and the structure parameter of cluster are analyzed.

Sub-eV ion deposition utilizing soft-landing ion mobility for controlled ion, ion cluster, and charged nanoparticle deposition

Sub-eV ion deposition via soft-landing ion mobility has been utilized for a variety of applications. It has allowed for the deposition of a dielectric material onto graphene without introducing defects into the lattice structure. This deposition technique has also been used for surface enhanced Raman studies. Deposited silver has also been used as an alternative MALDI matrix for low mass compounds and shows promise for imaging applications.

Photoassisted Immersion Deposition of Cu Clusters onto Porous Silicon: A Langmuir–Hill Ligand–Locus Model Applied to the Growth Kinetics

Cu–porous silicon (Cu–PS) composite materials consisting of nanosized Cu clusters preferentially grown on the surface of PS were fabricated by photoassisted deposition of Cu nanoparticles onto PS. Structural and chemical characterization of the Cu particles grown in the PS matrix has been carried out by synchrotron X-ray absorption spectroscopy, from which different reaction stages have been identified within the photoassisted reaction. In particular, it was found that the reduction of Cu occurs in three main phases: (a) Cu nucleates homogeneously in a few seconds over the surface of PS by a coupled red-ox reaction; (b) clusters grow by new reduced ions, which tend to oxidize the previously deposited Cu atoms making increasingly heterogeneous Cu clusters; and (c) a competitive process between nucleation of new clusters and cluster coalescence gives rise to a bulklike Cu thin film. It was determined that the structures formed in the first two phases display surface plasmon resonance, with band intensity and broadening consistent with the increasing heterogeneity of the clusters. The growth kinetics has been fitted to a Langmuir–Hill model. Following these results, a reaction model has been proposed to explain the mechanisms involved in the first stages of Cu clustering.

Surface Dipoles and Electron Transfer at the Metal Oxide–Metal Interface: A 2PPE Study of Size-Selected Metal Oxide Clusters Supported on Cu(111)

Two-photon photoemission spectroscopy (2PPE) was employed to investigate the electronic interactions at the interface of size-selected metal oxide clusters (Mo3O9, W3O9, Ti3O6, Mo3O6, W3O6, and Ti5O10) and a Cu(111) surface. The cluster–Cu interactions were probed by work function shifts measured by 2PPE as a function of local cluster coverage. For all the clusters studied, the work functions shifted to higher energies after cluster deposition, indicating negative interfacial dipole moments pointing toward the surface. The magnitudes of the derived interfacial dipoles are found to be in the order Mo3O9 ≈ W3O9 > W3O6 ≈ Mo3O6 > Ti5O10 > Ti3O6. DFT calculations of the electrostatic potentials at the interface and Bader charge analyses were used to assess the relative contributions of electron transfer and the structure-dependent cluster dipole moment to the observed work function shifts (ΔΦ). For the fully oxidized Mo3O9 and W3O9 clusters (+6 cation oxidation states), DFT calculations indicate that electron ...

Kinetic Monte Carlo simulation of low-pressure chemical vapor deposition of silicon nitride: Impact of gas flow rate and temperature on silicon cluster size and density

In the present study, the deposition process of SiNx thin films obtained by a low-pressure chemical vapor deposition technique with a mixture of disilane (Si2H6) and ammonia (NH3) was simulated by using the kinetic Monte Carlo method. A new pattern describing the distribution of ammonia molecules in the simulation matrix was proposed. The influences of the NH3/Si2H6 gas flow ratio and the deposition temperature on the obtained films structure in terms of silicon cluster size and density were analyzed. The simulation results indicate that an increase in the gas flow ratio leads to the deposition of amorphous silicon clusters characterized by small sizes. Nevertheless, an increase in the temperature values of the process provokes an enhancement in the silicon cluster size along with a decrease in their density.

The Improvement of Pd Nanoclusters Electro-Catalytic Properties for FAO by the Addition of Co Element

Near-monodisperse Pd and PdCo nanoclusters were synthesized by physical vapor deposition using a plasma-gas-condensation cluster deposition system and tested for catalyzing formic acid oxidation. Under the condition of high vacuum and inert gas, NCs with clean surface and uniform size were obtained. The cyclic voltammetry tests revealed that the electrochemical surface area was increased from 49.7 m2g-1to 51.7 m2g-1and the peak current density of catalyzing FAO was raised from 0.115 mA cm-2to 0.125 mA cm-2when about 12wt. % Co element was added. Additionally, the tolerance to CO poisoning of Pd could also be improved by the addition of Co. The result indicated that this method offered a chemical-free way to prepare clean and efficient Pd-based nanoscale catalytics and encouraged deeper exploration for electrochemichal catalytic reactions.

Elucidation of the Chain-Folding Structure of a Semicrystalline Polymer in Single Crystals by Solid-State NMR.

Despite tremendous efforts over the last half-century to elucidate the chain-folding (CF) structure of semicrystalline polymers, the re-entrance sites of folded chains, the successive CF number n, and the adjacent re-entry fraction F have not been well characterized due to experimental limitations. In this report, 13C-13C double-quantum (DQ) NMR was used to determine for the first time the detailed CF structure of 13C CH3-labeled isotactic poly(1-butene) (iPB1) in solution-grown crystals blended with nonlabeled iPB1 across a wide range of crystallization temperatures (Tcs). Comparison of the results of DQ experiments and spin dynamics simulations demonstrated that the majority of individual chains possess completely adjacent re-entry structures at both Tc = 60 and ∼0 °C, as well as indicated that a low polymer concentration, not kinetics, leads to cluster formations of single molecules in dilute solution. The changes in crystal habits from hexagonal shapes at Tc = 60 °C to rounded shapes at ∼0 °C (kinetic roughness) are reasonably explained in terms of kinetically driven depositions of single molecule clusters on the growth front.

Effect of four different zinc salts and annealing treatment on growth, structural, mechanical and optical properties of nanocrystalline ZnS thin films by chemical bath deposition

ZnS thin films were deposited from four different zinc salts on glass substrates by chemical bath deposition method. Different anions of zinc salts affect the deposition mechanism and growth rate, which influence the properties of the films significantly. The ZnS thin film deposited from ZnSO4 is smoother, thicker, more homogeneous and compact, nearly stoichiometric, comparing with the films deposited from Zn(CH3COO)2 and Zn(NO3)2, and ZnCl2. The scratch test of bonding force between ZnS film and substrate shows that the ZnS film deposited from ZnSO4 has the most excellent adhesion with the substrate. The presence of SO42− promotes heterogeneous ZnS thin film growth via ions by ions deposition, and the films deposited from Zn(CH3COO)2 and Zn(NO3)2 are formed via clusters by clusters deposition. XRD and HRTEM results show that cubic ZnS films are obtained after single deposition, and the grain size of ZnS thin film deposited from ZnSO4 for 2.5h is 10nm. The average transmission of all films is greater than 85% in the wavelength ranging from 600 to 1100nm, and the transmission of films deposited from ZnSO4 or Zn(NO3)2 for 1.5, 2 and 2.5h is greater than 85% in the wavelength varying from 340 to 600nm, which can enhance the blue response. The band gaps of all ZnS thin films are in the range of 3.88–3.99eV. After annealing treatment, the mechanical and optical properties of the ZnS thin film deposited from ZnSO4 are improved significantly.

Solvent-controlled spin-coating method for large-scale area deposition of two-dimensional silica nanosphere assembled layers.

In this article, we show that introducing a N,N-dimethyl-formamide (DMF) solvent for silica nanosphere (SNS) monolayer spin-coating can offer a low-cost and simple spin-coating approach for SNS monolayer deposition even on large-area silicon surfaces. From our method, more than 95% monolayer coverage for a 2 in round Si surface was achieved, which is one of the highest reported coverage by a spin-coating method. We prove that DMF offers highly enhanced wettability and slow solvent evaporation rate compared to a conventional solvent, water, in addition to excellent SNS dispersibility in solution preventing SNS cluster deposition on the surface and consequently produces a close-packed SNS monolayer with good uniformity over the surface. In addition, the benefits of DMF are retained as the deposition area increases indicating its high tolerance to spin-coating area. Better than 90% SNS monolayer coverage on a 4 in Si substrate was achieved with the DMF spin-coating method. Moreover, DMF has the advantage that SNS spin-coating can be done under common ambient laboratory conditions with 100% pure DMF unlike previous approaches which require humidity and temperature controls or additional surfactant additions to the solution.

Nano-scale energetic films by superfluid helium droplet assembly

The helium droplet technique has been utilized to study a wide range of topics in chemical physics such as atomic scale manifestations of superfluidity, chemistry at ultra-low temperatures, and the assembly of exotic Van der Waals complexes. Our efforts have transitioned the helium droplet methodology from a cryogenic nano-scale matrix to a film deposition technique capable of creating nano-structured films of composite metal-based energetic materials (EM). Such materials are ideal candidates to study propagation of reactions at small scale, and could be alternatives to organic based EM due to their higher energy densities. The helium droplet methodology may also provide a solution overcoming issues of reaction-limiting effects such as the formation of oxide layers by exploiting 'magic-number' cluster sizes and core-shell cluster mechanisms. This proceeding describes our previously reported efforts to model and characterize the deposition of magnesium clusters by superfluid helium droplet assembly, our efforts to produce magnesium-Fomblin core-shell EM cluster-based films, and our early attempts at making intermetallic cluster-based films.