Gas Aggregation Cluster Source Research Articles

A New Approach to Single‐Step Fabrication of TiOx‐CeOx Nanoparticles

Mixed metal oxide (MMO) nanoparticles (NPs) are hybrids consisting of two or more nanoscale metal oxides. Advantages of MMO NPs over single metal oxides include improved catalytic activity, enhanced electrical and magnetic properties, and increased thermal stability due to the synergy of the different oxide components. This study presents a novel fabrication route for TiO2‐CeO2 NPs enriched with oxygen vacancies using a Haberland‐type gas aggregation cluster source. The NPs, deposited from different segmented Ti/Ce targets under varying O2 addition, were examined with respect to final composition, morphology, and Ti, Ce surface oxidation states. Particle formation mechanisms are proposed for the observed morphologies. Additionally, available O2 during deposition and its impact on the formation of defective sites were investigated. Defective sites in TiO2‐CeO2 NPs were analyzed using transfer to X‐ray photoelectron spectroscopy and transmission electron microscopy without contact to ambient oxygen. The incorporation of Ce to the target exhibits synergistic effects on the synthesis process. Segmented Ti/Ce targets enable the deposition of a broad range of mixed oxide NPs with diverse compositions and morphologies at considerably enhanced deposition rates, which is vital for practical applications. The presented fabrication approach is expected to be applicable for a broad variety of MMO NPs.

Enhancement of W Nanoparticles Synthesis by Injecting H2 in a Magnetron Sputtering Gas Aggregation Cluster Source Operated in Ar

AbstractSynthesis of W nanoparticles by magnetron sputtering combined with gas aggregation operated in Ar suffers from a continuous decrease of the synthesis rate, ceasing in a finite time interval, in the range of minutes to tens of minutes. Experimentally, we noticed that adding small amounts of H2 to Ar (5–20%) increases the synthesis rate, which remains constant over time, at a value dependent on the amount of injected hydrogen. Mass spectrometry investigations revealed, in the hydrogen presence, a dominance of the ArH+ ions over the Ar+ ones, associated also with an increased number of W+ and WH+ species in plasma, sustaining a substantial increase in the nucleation rate.

Resistive Switching Effect in Ag‐poly(ethylene Glycol) Nanofluids: Novel Avenue Toward Neuromorphic Materials

AbstractConventional computation techniques face challenges of deviations in Moore's law and the high‐power consumption of data‐centric computation tasks. Neuromorphic engineering attempts to overcome these issues by taking inspiration from neuron assemblies, ranging from distributed synaptic plasticity through orchestration of oscillator‐like action potential toward avalanche dynamics. Although solid networks of nanoparticles (NPs) are proven to replicate fingerprints of criticality and brain‐like dynamics, the aspect of dynamic spatial reconfigurations in the connectivity of networks remains unexplored. In this work, Ag/poly(ethylene glycol) (PEG) nanofluids are demonstrated as potential systems to mimic the spatio‐temporal reconfiguration of network connections. The nanofluids are prepared by directly loading Ag NPs from the gas aggregation cluster source into liquid PEG. The NPs exhibit a negative zeta potential in PEG; if the potential difference is applied between two electrodes submerged in this nanofluid, the NPs migrate toward the anode, accumulate in its vicinity, and form a conductive path. Spikes of electric current passing through the path are detected, accompanied by resistive switching phenomena, similar to the random switching dynamics in solid NPs networks. The unique behavior of Ag/PEG nanofluids makes them promising for the realization of spatio‐temporal reconfigurations in network topologies with the potential to transition to 3D.

Role of discharge voltage in the fabrication of TiO2 nanoparticles by gas aggregation cluster source (GAS)

Well-distributed TiO2 NPs were fabricated by using a Haberland-type gas aggregation cluster source (GAS). The main attention was devoted to revealing the connection between the process parameters and the final structure, which is critical to use these particles for various applications including photocatalysis, self-cleaning, water-splitting, and sensing. Although oxygen flow, discharge voltage, and annealing temperature have a strong effect on TiO2 NPs formation, the present investigations indicate that the discharge voltage is the key parameter for controlling the final crystal structure.

High-defined and size-selective deposition of nanoparticles by their manipulation in an electrostatic field

This study combines numerical simulation with an experimental investigation of high-level designed nanostructured surfaces built from metal nanoparticles (NPs). The ultimate goal of this research is to prepare highly designed isotropic surfaces with high purity, defined size, homogeneous surface coverage, and high deposition rate, i.e., the properties appreciated e.g., in precise nanoengineering of microsensors and/or nanoelectronics, etc. The approach is based on manipulation of electrically charged nanoparticles, produced by a gas aggregation cluster source (GAS), in the electrostatic field propagated by two parallel electrodes mounted at the GAS output orifice. The model derived by numerical simulation enables prediction of the distribution and properties of the NPs across the (x, y) substrate plane as a function of the electrical potential superimposed by the charged NPs in the volume and the external electrical field. A good qualitative agreement was found between the model and the properties of GAS-deposited NPs onto the Si substrate (the deposited surface was analyzed by the atomic force microscopy (AFM) imaging), which reveals the electrostatic manipulation of the charged NPs beam as a promising tool for deposition of highly tailored nanostructures.

Tuning the morphology of sputter-deposited platinum catalyst: From compact layers to dispersed nanoparticles

A comprehensive study on adjusting the morphology of sputter-deposited platinum was performed. Platinum was deposited under various Ar pressure ranging from 0.3 to 3.2 Pa using a conventional magnetron system as well as at 57 Pa using a gas aggregation cluster source integrated into the magnetron sputtering system. The morphology and structure of deposited layers were characterized with a broad portfolio of characterization techniques such as scanning electron microscopy, transmission electron microscopy, grazing incidence small angle X-ray scattering and X-ray diffraction. The results revealed a continuous evolution of the Pt layer morphology from a thin-film-like layer of tightly packed Pt nanoparticles to a deposit composed of dispersed particles of 5-7 nm in size as the Ar pressure increased. The electrochemically active surface area of deposited Pt, as calculated from cyclic voltammograms, increased with deposition pressure from 11.7 m2·gPt−1 to 22.3 m2·gPt−1 and 24 m2·gPt−1 for Pt deposited at 0.3, 3.2 and 57 Pa, respectively. This increase in active sites was reflected in a significant improvement in the mass activity of platinum exemplary confirmed using a methanol electrooxidation reaction.

Fabrication of Plasmonic Indium Tin Oxide Nanoparticles by Means of a Gas Aggregation Cluster Source.

In this work, we demonstrate, for the first time, the possibility to fabricate indium tin oxide nanoparticles (ITO NPs) using a gas aggregation cluster source. A stable and reproducible deposition rate of ITO NPs has been achieved using magnetron sputtering of an In2O3/SnO2 target (90/10 wt %) at an elevated pressure of argon. Remarkably, most of the generated NPs possess a crystalline structure identical to the original target material, which, in combination with their average size of 17 nm, resulted in a localized surface plasmon resonance peak at 1580 nm in the near-infrared region.

Gas phase fabrication of morphology-controlled ITO nanoparticles and their assembled conductive films.

ITO nanoparticles were generated in the gas phase with a magnetron plasma gas aggregation cluster source. Their morphologies were modified by modulating the discharging power of magnetron sputtering. The shape of the nanoparticles changed from rough spheroid formed with a higher discharging power to multi-branch formed with a lower discharging power. With a discharging power of 25 W, the ITO nanoparticles were enriched with tripod and tetrapod-shaped nanoparticles. The formation mechanism of multi-branch nanoparticles was attributed to the oriented attachment of the initially nucleated smaller nanocrystallites. Transparent conductive ITO nanoparticle films were fabricated by depositing the preformed nanoparticles with controlled thickness. The electron conduction in the film was dominated by electron tunnelling and/or hopping in the percolative channels comprised of closely spaced ITO nanoparticle assemblies and could be tuned from highly resistive nonmetal-like to highly conductive metal-like by changing the deposition thickness. The film also displayed a SPR band in the near-IR region. The conductivity of the multi-branch ITO nanoparticle film was significantly superior to that of the spheroidal nanoparticle film. For a 46 nm thick multi-branch ITO nanoparticle film, a surprisingly low specific resistance of 3.09 × 10-4 Ω cm, which is comparable to the top-class conductivity of bulk ITO films, was obtained after annealing at a mild temperature of 250 °C, with a transmittance larger than 85%.

Computational fluid dynamics predicts the nanoparticle transport in gas aggregation cluster sources

In a typical sputter-based gas aggregation cluster source (GAS), nanoparticles (NPs) are created from supersaturated vapours of the target material. The NPs then escape from the source with the expanding gas through an exit orifice. The carrier gas flow profile is one of the most critical parameters, which strongly affects the NP losses on the walls and determines the efficiency of the NP transport to the substrate. In this work, computational fluid dynamics (CFD) simulations are performed to understand the flow of the carrier gas inside the aggregation chamber. We focus on the impact of the inlet and outlet geometry on the carrier gas flow and, therefore, on the NP transportation. Two types of GAS with either a conventional planar magnetron or a cylindrical magnetron are considered. In the planar configuration, the working gas inlet is from behind the magnetron, and the gas flows around the target towards the orifice along the system axis, which may cause some vertices. The situation is even more critical for the cylindrical magnetron, where the gas inlet position and geometry have a drastic influence on the gas flow. Brownian diffusion is found to prevail for NPs smaller than 5 nm, regardless of the gas flow. This leads to their losses on the walls. Larger NPs experience a stronger drag force from the carrier gas flow, which should exceed 10 m s−1 to prevent loss of NPs on the walls and keep NP transport efficient. Therefore, the CFD simulations help to visualise the motion of the NPs and optimise the geometry of the GAS for future applications.

Sparse CNT networks with implanted AgAu nanoparticles: A novel memristor with short-term memory bordering between diffusive and bipolar switching.

With this work we introduce a novel memristor in a lateral geometry whose resistive switching behaviour unifies the capabilities of bipolar switching with decelerated diffusive switching showing a biologically plausible short-term memory. A new fabrication route is presented for achieving lateral nano-scaled distances by depositing a sparse network of carbon nanotubes (CNTs) via spin-coating of a custom-made CNT dispersion. Electrochemical metallization-type (ECM) resistive switching is obtained by implanting AgAu nanoparticles with a Haberland-type gas aggregation cluster source into the nanogaps between the CNTs and shows a hybrid behaviour of both diffusive and bipolar switching. The resistance state resets to a high resistive state (HRS) either if the voltage is removed with a retention time in the second- to sub-minute scale (diffusive) or by applying a reverse voltage (bipolar). Furthermore, the retention time is positively correlated to the duration of the Set voltage pulse. The potential for low-voltage operation makes this approach a promising candidate for short-term memory applications in neuromorphic circuits. In addition, the lateral fabrication approach opens the pathway towards integrating sensor-functionality and offers a general starting point for the scalable fabrication of nanoscaled devices.

Novel gas aggregation cluster source based on post magnetron

AbstractIn this communication, a new gas aggregation cluster source is introduced equipped with post cylindrical magnetron. The rotation of magnetic circuit improves the usage of cylindrical copper target in terms of its homogenous consumption. Copper nanoparticles were successfully synthesized. Their deposition rate fluctuates at slow rotations of magnetic circuit. Cyclic trapping and release of nanoparticles from electrostatic capture zones are likely responsible for this effect. The instabilities are not observed at higher rotation speeds. The argon flow is found to be very complex within the cluster source; however, it seems crucial for its operation. The efficiency of transport of nanoparticles and their size increase with gas flow. The highest values of deposition rate of around 19 mg/h are obtained.

Residual- and linker-free metal/polymer nanofluids prepared by direct deposition of magnetron-sputtered Cu nanoparticles into liquid PEG

Colloidal solutions of metal nanoparticles (NPs) are typically produced by multi-step methods using a variety of chemicals. Resultant nanofluids require extra purification steps to remove the reactions by-products and modification steps to introduce anticoagulants for the solution stabilization. Here, we suggest a single-step method to produce nanofluid in which only two components are present: 22 nm-sized Cu NPs as a filler and polyethylene glycol (PEG, 400 g/mol) as a liquid base. The method employs magnetron sputtering to synthesize Cu NPs in a gas aggregation cluster source and their subsequent loading into vacuum-compatible PEG. The resultant nanofluid demonstrates strong plasmonic and photoluminescent activity, and shows enhanced stability over time, in contrast to conventional colloidal solutions. The approach offers an alternative for the production of nanofluids in which the processes of the NP formation are decoupled from the processes of their mixing with the liquid base.

Interaction of size-selected Ag-clusters on Au-thin films: a composition study with in-situ XPS analysis at an elevated temperature

In this paper, we describe a novel method of synthesis of bimetallic Ag–Au alloy nanoparticles with an estimated Ag to Au concentration ratio of ∼3:1 by using a gas-aggregation cluster source. The real time chemical changes occurred on the surface of the alloy film during different stages of annealing at an elevated temperature are observed by in-situ x-ray photoelectron spectroscopy analysis. It is found that the concentration of both Ag and Au of the alloy film simultaneously decreases with the increase of the annealing time. The chemical states of the elements present on the surface are analyzed from the HR-XPS data, which are recorded for the dominant elements present on the surface. From the analyses, it is found that a small part of metallic Ag gets oxidized for higher annealing time whereas no trace of oxidation of Au is observed. The surface morphology of the as-deposited and post-annealed alloy films are characterised by FESEM and AFM measurements. Due to thermal diffusion of Ag and Au, resultant narrow size distributions of the bimetallic Ag–Au nanoparticles are observed on the surface. The film morphologies suggest that the evolutions of bimetallic Ag–Au nanoparticles are nearly spherical in shape with an average aspect ratio value of ∼1.5.

A cluster source for photoelectron spectroscopy in VUV and X-ray ranges

A detailed description of a custom-made gas aggregation cluster source is given as well as of its coupling to permanent molecular beam end-stations of the beamlines DESIRS and PLEIADES at the French national facility synchrotron SOLEIL. Using (hydrated) hypoxanthine clusters as a case study, the production of clusters with different source parameters is discussed based on Vacuum Ultra-Violet (VUV) mass spectrometry. The ability of the cluster source to perform photoelectron spectroscopy is illustrated by photoelectron spectra obtained for valence and core shells.

Operation of a magnetron sputtering gas aggregation cluster source in a plasma jet regime for synthesis of core–shell nanoparticles

Operation of a magnetron sputtering gas aggregation cluster source in a plasma jet regime is presented. In specific experimental conditions, the plasma extends from the inside of the cluster source in the deposition chamber as a plasma jet, transporting also the nanoparticles (NPs) produced in the cluster source. The chemistry of the NP surface is modified in-flight by injecting a chemical precursor in the plasma jet, resulting in core–shell NPs. Also, the plasma jet presents a low gas temperature, safely interacting with materials sensitive to thermal degradation (like polymers). These findings prove the potential of the presented plasma jet for applications in nanotechnology.

Biological activity and antimicrobial property of Cu/a-C:H nanocomposites and nanolayered coatings on titanium substrates

Infection associated with titanium based implants remains the most serious problem in implant surgery hence it is important to find optimal strategies to prevent infections. In the present study, we investigated the surface properties, antibacterial activity and biocompatibility of nanocomposite coatings based on an amorphous hydrocarbon (a-C:H) film containing copper nanoparticles (CuNPs) deposited on Ti discs via a gas aggregation cluster source. Three different Cu/a-C:H coatings with approximately the same amount of embedded CuNPs with and without barrier a-C:H layer were fabricated. The obtained results revealed that different structures of the produced coatings have significantly different release rates of Cu ions from the coatings into the aqueous media. This subsequently influences the antibacterial efficiency and osteoblast cell viability of the treated coatings. Coatings with the highest number of CuNPs resulted in excellent antibacterial activity exhibiting approximately 4 log reduction of E.coli and S.aureus after 24 h incubation. The cytotoxicity study revealed that after 7 day cell seeding, even the coating with the highest Cu at.% (4 at.%) showed a cell viability of ̴90%. Consequently, the coating, formed with a properly tailored number of CuNPs and a-C:H barrier thickness offer a strong antibacterial effect without any harm to osteoblast cells.

Influence of discharge power on the size of the Pd cluster generated with a magnetron plasma gas aggregation cluster source

Pd clusters were generated with a DC magnetron plasma gas aggregation cluster source.The dependence of the size distribution and ionization degree of the Pd clusters on the discharge power was studied. By tuning the discharge power from 15W to 50W, the mean size of the Pd clusters decreased from 13.8 nm to 4.2 nm, and the ratio of neutral and charged Pd clusters to the total rose from about 16.7% to about 76.7%. The effect was explained with a model by considering the enhanced production of Pd ions at higher magnetron discharge power. A simulation based on Direct Simulation Monte Carlo (DSMC) method verified the proposed mechanism of cluster growth.

Synthesis and microstructure investigation of heterogeneous metal‐plasma polymer Ag/HMDSO nanoparticles

Metal‐polymer nanocomposites have gained increasing attention due to the wide potential applications field. Synthesis of nanoparticles from the gas phase is an intensively studied alternative to the chemical preparation methods. We present a one‐step procedure that combines magnetron‐based gas aggregation cluster source of silver nanoparticles and simultaneous plasma‐enhanced chemical vapour deposition of hexamethyldisiloxane (HMDSO). The key parameter of the process, significantly influencing the morphology and microstructure of studied nanoparticles, was found to be the amount of HMDSO added to the deposition chamber as witnessed by small angle X‐ray scattering and X‐ray diffraction methods combined with transmission electron microscopy and UV–Vis spectrophotometry. The presence of HMDSO in the chamber leads to changes in the size distribution and also in the architecture of prepared nanoparticles. The increasing amount of HMDSO induces the formation of individual core‐shell nanoparticles, chains of core‐shell nanoparticles, and for the highest concentration of HMDSO, the synthesis of multi‐core‐shell nanoparticles. The size of crystallites in the silver cores of nanoparticles decreases with addition of HMDSO, which prevents further aggregation.

Theoretical and experimental analysis of defined 2D-graded two-metal nanoparticle-build surfaces

The paper presents a theoretical as well as an experimental study of 2D-graded, two-metal nanocomposite structures built from nanoparticles (NPs). We derived a theoretical description of a planar surface (x,y) with defined NPs distribution; the linear, exponential and logarithm graded distributions are presented. The analytical model employees gradient functions of (i)nanoparticle volume surface density and (ii) volume chemical composition ratio; both mutually orthogonal across the (x,y) plane. Such graded surfaces, with variable d/d(x,y) properties, supported by an analytical model are appreciated in many applications, e.g. for tunable plasmonic absorption as studied in our case. The relevance of our approach was experimentally approved by preparation of 2D-linearly graded Ag-Cu nanocomposite; here the amount of nanoparticles, as well as chemical composition ratio, varies linearly along with the principal and minor diagonal, respectively. The nanocomposites were prepared by a two-step deposition of Ag and Cu NPs produced by a gas aggregation cluster source equipped by a movable mask.

Effect of magnetic field on the formation of Cu nanoparticles during magnetron sputtering in the gas aggregation cluster source

AbstractReliable production of nanoparticles (NPs) by magnetron sputtering in a gas aggregation source (GAS) is of great interest because of many potential applications. The size, shape, or structure of NPs can be tuned by the operational parameters of the GAS. In this study, fabrication of copper (Cu) NPs is investigated dependent on the magnetron magnetic field (MF)–a not much studied parameter. Decrease of the MF from 83 to 35 mT results in changes in the shape and size distribution of the NPs. MF also strongly affects the NPs deposition rate (DR). Electromagnetic trapping of the NPs in the vicinity of the magnetron target is proposed to be responsible for the changes in DR and polydispersity. The highest DR was reached at 45 mT.