Gas Aggregation Method Research Articles

Highly active ultralow loading Pt electrodes for hydrogen evolution reaction developed by magnetron sputtering

Developing cost-effective components for PEM electrolyzers is key to transforming renewable energy into H2. Platinum is a scarce and expensive material but also, is the most active known catalyst for hydrogen evolution reaction in PEM electrolysis; thus it is of utmost importance to focus on developing electrocatalysts that utilize the minimum amount of platinum without losses in cell performance to make PEM electrolysis affordable. In addition, and with the aim of scaling up electrode production, it is imperative to develop a robust automated industrial manufacturing process to avoid the waste of catalyst during electrode preparation. In this work, magnetron sputtering gas aggregation method is studied for developing three low loading Pt electrodes (0.105, 0.062, and 0.052 mg cm−2), achieving remarkable overpotentials as low as 8 mV at 10 mA cm−2 for HER, showing similar activity than commercial Pt electrodes with more than 4 times less Pt (compared to 0.3 mgcm−2 Pt commercial GDL).

Metal–organic framework‐derived high‐performance polypyrrole/Ni‐CAT/PI fiber paper‐based electromagnetic shielding composites for high‐frequency electromagnetic wave absorption

AbstractLight‐weight, portability and miniaturization are important characteristics for the next generation of high‐performance electromagnetic interference (EMI) shielding equipment. To meet the current demand for high‐performance EMI shielding materials, this paper proposes a simple and reliable method for preparing multilayer paper‐based composites. Paper‐based composites exhibit light weight, flexibility, easy processing and high temperature resistance. A conductive metal–organic skeleton (Ni‐CAT) layer and polypyrrole (PPy) layer were deposited on a polyimide (PI) fiber surface with an in situ synthesis and gas aggregation method to prepare paper‐based electromagnetic shielding composites with good properties. The results showed that the electromagnetic shielding effect (SE) of the paper‐based composites reached 41.0 dB. After the paper‐based composites underwent multiple ultrasonic washing and bending tests, their electrical conductivity retention rate was as high as 90%. Furthermore, the introduction of PPy/Ni‐CAT enhanced the bonding strength of the PI fibers, which caused the tensile strength of the paper‐based composites to reach 22.3 MPa. Due to the good thermal stability of the composites, they can withstand an open flame and protect the equipment during a fire. Thus, these paper‐based EMI shielding composites hold great promise for flexible electromagnetic shielding materials, protection of smart wearable devices and other fields.

Thermally-driven morphogenesis of niobium nanoparticles as witnessed by in-situ x-ray scattering

Highly porous structures consisting of niobium nanoparticles (Nb NPs) are prepared using magnetron sputtering and inert gas aggregation method. Alongside the thermally-driven evolution of nanoparticle morphology, the microstructural genesis is probed in-situ by x-ray diffraction for the temperature range up to 800 °C. The as-deposited Nb NPs are formed by the Nb core and NbOx shell. The elevated temperature triggers the gradual oxidation that proceeds until 200 °C. Above this point the structure is fully amorphous. Further increase of the temperature to 450 °C leads to a transition to the crystalline TT-Nb2O5 phase, which hexagonal structure was solved in the current study. The subsequent rise of the temperature to 600 °C results in the conversion to the orthorhombic T-Nb2O5 phase. Up to this state, the size of nanoparticles corresponds to the size of crystallites. The annealing above 600 °C causes coalescence of NPs with the formation of hundreds-of-nanometers large structures.

Controllable embedding of size‐selected copper nanoparticles into polymer films

AbstractThe ability to control the extent of metal nanoparticle (NP) embedding into polymer films has attracted attention for applications in quite a few research branches. In this study, the behavior of size‐selected copper NPs produced by the gas aggregation method and deposited on poly(methyl methacrylate) and polystyrene films is studied under thermal annealing above and below the glass transition temperature. Several important tendencies of the embedding dynamics in terms of dependence on NP size, annealing temperature, and time, as well as the type of polymer, are found and analyzed. Physical models explaining particle behavior and allowing the elaboration of practical recommendations on the controllable embedding of metal NPs into polymer films are suggested.

Plasma based formation and deposition of metal and metal oxide nanoparticles using a gas aggregation source

Metal clusters and nanoparticles (NPs) have been studied intensively due to their unique chemical, physical, electrical, and optical properties, resulting from their dimensions, which provided host of applications in nanoscience and nanotechnology. Formation of new materials by embedding NPs into various matrices (i.e. formation of nanocomposites) further expands the horizon of possible application of such nanomaterials. In the last few decades, the focus was put on the formation of metallic and metal oxide NPs via a so-called gas aggregation nanoparticle source employing magnetron sputtering (i.e. Haberland concept). In this paper, an overview is given of the recent progress in formation and deposition of NPs by the gas aggregation method. Examples range from noble metals (Ag, Au) through reactive metals (Al, Ti) to Si and the respective oxides. Emphasis is placed on the mechanism of nanoparticle growth and the resulting properties. Moreover, kinetic Monte Carlo simulations were developed to explain the growth mechanism and dynamics of nanoparticle formation depending on the experimental conditions. In addition, the role of trace amounts of reactive gases and of pulsed operation of the plasma on the nucleation process is addressed. Finally, the treatment of the NPs in the plasma environment resulting in nanoparticle charging, morphological and chemical modifications is discussed.

Molecular dynamics simulation of the growth of Cu nanoclusters from Cu ions in a plasma

A recently developed method of nanoclusters growth in a pulsed plasma is studied by means of molecular dynamics. A model that allows one to consider high-energy charged particles in classical molecular dynamics is suggested, and applied for studies of single impact events in nanoclusters growth. In particular, we provide a comparative analysis of the well-studied inert gas aggregation method and the growth from ions in a plasma. The importance to consider of the angular distribution of incoming ions in the simulations of the nanocluster growth is underlined. A detailed study of the energy transfer from the incoming ions to a nanocluster, as well as the diffusion of incoming ions on the cluster surface is carried out. Our results are important for understanding and control of the nanocluster growth process.

Radial Structure of Free Yb/YbO Nanoparticles Created by Oxidation Before or After Aggregation with Divalent Instead of Trivalent Oxide

Nanoparticles consisting of Yb and its divalent oxide YbO have been created by two different oxidation approaches based on the gas-aggregation method with magnetron sputtering. In one type of nanoparticles, the Yb oxide molecules, created by reactive sputtering before the aggregation, agglomerate predominantly in the interior of mixed-composition nanoparticles. In the other type, the oxide is formed by exposing the preformed metallic Yb nanoparticles to oxygen, which at certain conditions is believed to oxidize primarily the surface of such nanoparticles. Such segregated stoichiometry has been disclosed using Yb 4f core-level photoelectron spectroscopy at a series of oxidation conditions for each type of production. In contrast to a typical macroscopic case where Yb is trivalent, in both production cases, Yb is divalent in the oxide. By using the production methods suggested, it becomes possible to tailor the electronic and thus the physical and chemical properties of such nanoparticles, which are discussed in the literature as building blocks for photonic, electronic, and magnetic nanoscale devices.

Structural and Optical Characterization of Semiconducting TiN Nanoparticles Thin Film

We have succeeded in fabricating a thin film consisting of semiconducing TiN nanoparticles soft-landed on a substrate at room temperature using N2 reactive magnetron sputtering combined with a gas aggregation method. The total film thickness is about 1200 nm. Under the optimized experimental parameters for controlling the growth of TiN particles, the average diameter of TiN nanoparticles is 2.54 nm and their diameter distribution is from 1.1 to 3.8 nm. X-ray photoelectron spectroscopy (XPS) study reveals that the fabricated semiconducting TiN has N vacancies and/or defects as TixN1-x. The average lattice constant of the TiN particulates is estimated as 4.216 Å and contracted by 0.6% from that of bulk TiN, which is presumably caused by the vacancies and/or defects. Spectroscopic ellipsometry (SE) study revealed that the imaginary part of the dielectric constant of the present film shows typical semiconducting behavior and gives the optical band gap of the film as 3.65 eV in direct allowed optical transition mode.

Fabrication and structural characterization of TiO nanoparticle soft-landed on substrate by the magnetron sputtering-gas aggregation method

We have succeeded to fabricate the thin film mainly or entirely consisting of nano-crystallites TiO on a substrate at room temperature by using the magnetron sputtering combined with the gas aggregation method which has the capability to deposit grown small particles and/or clusters of the desired compound material on the substrate in soft-landed mode. The important experimental parameters to control the growth of TiO particles are identified as partial pressure of additional oxygen gas, growth-reaction distance Ltd, and LN2 cooling of growth chamber. The smallest averaged diameter of TiO nano-particles is 5.62 nm and size distribution being from 2 to 8 nm under 50 mm of Ltd. The compositional uniformity is confirmed by EDS and EELS. The chemical state of the film observed by Ti 2P XPS peak confirms the primarily growth of TiO and indicates the formation of minor content of amorphous Ti1-xOx and/or Ti1-xCx particularly at the surface of the film.

Unsupported lead clusters and electron diffraction

A beam of Pb clusters is produced with the inert gas aggregation method and probed by electron diffraction. Analysis of the diffraction patterns indicates that average cluster size can vary between 3 and 7 nm, according to nucleation conditions. The diffraction patterns from beams with larger average cluster size are very similar to patterns calculated from model decahedron clusters, while those for smaller cluster size do not appear to have simple geometrical face-centred cubic, decahedral, or icosahedral structure.

Influence of vacuum conditions on the light emission caused by passing a current through a silver cluster film

Performed experiments showed that silver clusters prepared by different technique, such as the thermal evaporation in vacuum and the gas aggregation method, had similar spectra of the light emission. The integral intensity of the light emission decreases as pressure of the residual gases increases. This change is reversible. The spectrum shape remains invariable; however, spectral lines of excitation of residual gases arise in the spectrum.

X-ray photoemission and absorption spectroscopy of supported nanoscale iron clusters

Fe particles with sizes in the range 1–5 nm, formed by a gas-aggregation method and deposited onto graphite and C60 supports, were studied by x-ray photoemission spectroscopy, x-ray absorption spectroscopy, and magnetic linear dichroism. Clusters deposited onto a C60 coated graphite substrate become embedded within the fullerene film, and have an increased resistance to oxidation compared to exposed clusters supported on a graphite surface. No evidence for hybridization between the electronic states of Fe and C60 is seen. The magnetic dichroism signal of the exposed clusters increases sharply with the film thickness because of the increased cluster interactions.

Mechanism of neutral cluster beam deposition

Pb cluster based films have been formed by the low energy neutral cluster beam deposition method and characterized by TEM. The deposits are rigid, uniform with the nanometer grain sizes, which are important for nanostructured material applications. The velocities of clusters in the beam obtained by gas aggregation method have been calculated based on the hydromechanic and thermodynamic principles. It is demonstrated that the deposition of the clusters on the substrate surface is a head-on collision and soft landing process, that is, low energy clusters land on the substrate surface without fragment and distortion. Based on these analyses, a physical model has been developed and computer simulations have been performed by assuming the random deposition as well as limited diffusion and coalescence process. The results indicate that the uniform and nearly random stacking properties of the cluster deposits can be described properly by the model.

Formation of alumina fine particles by a magnetron sputtering – gas aggregation method

The alumina particles have been generated by a magnetron sputtering — gas aggregation method. The analyses of transmission electron microscope (TEM) images and electron diffraction patterns revealed some of the particles are tiny crystals of θ-alumina. The dependence of the particle size on the geometry and the temperature of the source exit has been studied.

Binding energy and electronic properties in antimony clusters: Comparison with bismuth clusters

Antimony clusters are produced by the gas aggregation method. They are found to be built from Sb4 units. The Sb+4n clusters are demonstrated to relax their excess energy by evaporation of a tetramer and the binding energy of Sb4 in the cluster is measured to be about 1.3 eV, well below the binding energy of a Sb atom in the bulk (≊2.75 eV). The ionization potentials of Sb4n clusters are studied as a function of the size and the observed evolution confirms the nonmetallic character of their structure. These results are compared with those obtained for bismuth clusters which exhibit a very different behavior. Finally the possible metastable character of Sb4n structure is discussed and illustrated by experiments performed as a function of inert gas temperature in the clusters source.