Cluster Beam Research Articles

Cluster beams, nano-ripples, and bio applications

Gas cluster ions are aggregates of weakly bonded gas atoms or molecules. Upon the impact of an energetic gas cluster ion, multiple collisions occur between the target atoms and the atoms in the cluster ion. These impact processes are completely different from those of a collision-cascade process induced by a single atomic or molecular (monomer) ion. Although the impact process of gas cluster ions is different, ripples similar to those formed by monomer ions are formed by gas cluster ion impacts at oblique incidence. In this review, ripple formation by gas cluster ions is discussed with respect to their formation mechanism, characteristics, and applications as biosensors.

Infrared laser-induced isotope-selective dissociation of mixed (CF3Br)mArn van der Waals clusters

The paper presents the results of studies of IR laser-induced bromine-isotope-selective dissociation of small mixed (CF3Br)mArn van der Waals clusters (m = 1, 2 and 1 ≤ n ≤ 5 is the number of molecules and atoms in the clusters, respectively). The experiments used a pulsed CO2 laser to excite clusters and a quadrupole mass spectrometer to detect a molecular cluster beam. The research method is based on the selective vibrational excitation of clusters by IR laser radiation, leading to their predissociation. The possibilities of implementing bromine-isotope-selective dissociation of clusters are considered. The experimental setup and research method are briefly described. The results of determining the cluster dissociation efficiency and selectivity as functions of the energy and frequency of laser radiation are presented. It is shown that resonant vibrational excitation of clusters makes it possible to induce their isotope-selective dissociation. Thus, using a CF3Br/Ar mixture with a pressure ratio of 1/200, the enrichment factors of the 79Br isotope are found to be Kenr(79Br) = 1.15 ± 0.04 and 0.95 ± 0.03 under cluster irradiation conditions on the 9R(30) (ν = 1084.635 cm−1) and 9R(24) (ν = 1081.087 cm−1) lines, respectively The achieved dissociation selectivities for the clusters are, respectively, 1.16 ± 0.05 and 0.95 ± 0.04. The results obtained suggest that this method can be used to separate isotopes in molecules containing isotopes of heavy elements, which have a slight isotopic shift in the IR absorption spectra.

Enhanced Ion Yields Using High Energy Water Cluster Beams for Secondary Ion Mass Spectrometry Analysis and Imaging.

Previous studies have shown that the use of a 20 keV water cluster beam as a primary beam for the analysis of organic and bio-organic systems resulted in a 10-100 times increase in positive molecular ion yield for a range of typical analytes compared to C60 and argon cluster beams. This resulted in increased sensitivity to important lipid molecules in the bioimaging of rat brain. Building on these studies, the present work compares 40 and 70 keV water cluster beams with cluster beams composed of pure argon, argon and 10%CO2, and pure CO2. First, as previously, we show that for E/nucleon about 0.3 eV/nucleon water and nonwater containing cluster beams generate very similar ion yields, but below this value, the water beams yields of BOTH negative and positive "molecular" ions increase, in many cases reaching a maximum in the <0.2 region, with yield increases of ∼10-100. Ion fragment yields in general decrease quite dramatically in this region. Second, for water cluster beams at a constant E/nucleon, "molecular" ion yield increases with beam energy and hence cluster size due to increased sputter yield (ionization probability is constant). Third, as a consequence of the increased ion yield and the improved focusability using high-energy cluster beams, imaging in the 1 μm spatial resolution region is demonstrated on HeLa cells and rat brain tissue, monitoring molecules that were previously difficult to detect with other primary beams. Finally, the suggestion that the secondary ion emission zone has quasi-aqueous character seems to be sustained.

Experimental Study on the Biological Effect of Cluster Ion Beams in Bacillus subtilis Spores

Cluster ion beams have unique features in energy deposition, but their biological effects are yet to be examined. In this study, we employed bacterial spores as a model organism, established an irradiation method, and examined the lethal effect of 2 MeV C, 4 MeV C2, and 6 MeV C3 ion beams. The lethal effect per particle (per number of molecular ions) was not significantly different between cluster and monomer ion beams. The relative biological effectiveness and inactivation cross section as a function of linear energy transfer (LET) suggested that the single atoms of 2 MeV C deposited enough energy to kill the spores, and, therefore, there was no significant difference between the cluster and monomer ion beams in the cell killing effect under this experimental condition. We also considered the behavior of the atoms of cluster ions in the spores after the dissociation of cluster ions into monomer ions by losing bonding electrons through inelastic collisions with atoms on the surface. To the best of our knowledge, this is the first report to provide a basis for examining the biological effect of cluster ions.

Ag cluster beam deposition for TCO/Ag/TCO multilayer

Environment friendly, thin and flexible devices require the synthesis of Indium-free new transparent conducting materials (TCM) with improved structural, thermal, electrical and optical properties. To overcome the critical issues raised by thinning the TCM, we propose a multilayer structure in which nanogranular Ag film obtained by supersonic cluster beam deposition is sandwiched in between Alluminum doped Zinc Oxide (AZO) thin layers. The introduction of the nanogranular Ag film, when compared to the standard sputtered one, yields higher optical transmittance in the technologically relevant VIS-NIR region and superior mechanical reliability while preserving low electrical resistance. The present results open new perspectives to exploit the nanogranular nature of conductive films, synthesized via Supersonic Cluster Beam Deposition, to engineer transparent conducting materials.

Site-Specific Wetting of Iron Nanocubes by Gold Atoms in Gas-Phase Synthesis.

A key challenge in nanotechnology is the rational design of multicomponent materials that beat the properties of their elemental counterparts. At the same time, when considering the material composition of such hybrid nanostructures and the fabrication process to obtain them, one should favor the use of nontoxic, abundant elements in view of the limited availability of critical metals and sustainability. Cluster beam deposition offers a solvent‐ and, therefore, effluent‐free physical synthesis method to achieve nanomaterials with tailored characteristics. However, the simultaneous control of size, shape, and elemental distribution within a single nanoparticle in a small‐size regime (sub‐10 nm) is still a major challenge, equally limiting physical and chemical approaches. Here, a single‐step nanoparticle fabrication method based on magnetron‐sputtering inert‐gas condensation is reported, which relies on selective wetting of specific surface sites on precondensed iron nanocubes by gold atoms. Using a newly developed Fe–Au interatomic potential, the growth mechanism is decomposed into a multistage model implemented in a molecular dynamics simulation framework. The importance of growth kinetics is emphasized through differences between structures obtained either experimentally or computationally, and thermodynamically favorable configurations determined via global optimization techniques. These results provide a roadmap for engineering complex nanoalloys toward targeted applications.

Organic Light-Emitting Transistors Based on Pentacene and 4,5-Di(9H-carbazol-9-yl)phthalonitrile Doped onto 1,3-Bis(N-carbazolyl)benzene

In this study, multilayered, organic-based light-emitting transistors (OLETs) were produced and characterized. The neutral cluster beam deposition method was applied to successively deposit organic semiconducting layers of pentacene, 4,5-di(9H-carbazol-9-yl)phthalonitrile (2CzPN) doped onto 1,3-bis(N-carbazolyl)benzene (mCP), and 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi) as the hole-transport, emissive, and electron-transport layers, respectively. The effects of drain electrodes (Au or Li/Al) and TPBi on the device performance were examined under ambient conditions. The bilayered pentacene (bottom, 50 nm)/mCP:2CzPN (top, 50 nm) and trilayered pentacene (bottom, 50 nm)/mCP:2CzPN (middle, 50 nm)/TPBi (top, 10 nm) OLETs demonstrated both electrical switching functionality and control of electroluminescence (EL) in air. In particular, the EL intensity (IEL) was significantly enhanced in the asymmetric bilayered devices adopting a low work function Li/Al drain electrode owing to the lower electro...

Gas-phase deposited plasmonic nanoparticles supported on 3D-graphene/nickel foam for highly SERS detection

In this work, we proposed a novel three-dimensional (3D) plasmonic nanostructure based on porous graphene/nickel foam (GNF) and gas-phase deposited Ag nanoparticles (NPs). Ag NPs with high density were directly deposited on the surface of 3D GNF by performing a novel cluster beam deposition approach. In comparison with traditional Ag substrate (SiO2/Ag), such hot-spots enriched 3D nanostructure showed extremely high electromagnetic field enhancement under incident light irradiation which could be used as a sensitive chemical sensor based on surface enhanced Raman scattering (SERS). The experimental results demonstrated that the proposed nanostructure showed superior SERS performance in terms of Raman signal reproducibility and sensitivity for the probe molecules. 3D full-wave simulation showed that the enhanced SERS performance in this 3D hierarchical plasmonic nanostructure was mainly obtained from the hot-spots between Ag NPs and the near-field coupling between Ag NPs and GNF scaffolds. This work can provide a novel assembled SERS substrate as a SERS-based chemical sensor in practical applications.

Well dispersed SnO2 nanoclusters preparation and modulation of metal-insulator transition induced by ionic liquid

Tin dioxide (SnO2) has attracted broad interest due to its particular gas-sensor property. Nano- or atom-scale SnO2 material has always been the aim in order to ultimately improve the sensitivity. However, until now, it remains difficult to synthesize SnO2 nanoclusters by using traditional methods. In the present work, we have achieved the preparation of SnO2 nanoclusters by using the cluster beam deposition technique. The obtained nanoclusters were well characterized by high resolution transmission electron microscope HR-TEM. Results indicated the formation of the well-dispersed SnO2 nanoclusters with uniform size distribution (5–7 nm). Furthermore, an obvious metal insulator transition was observed by gating with ionic liquid. Combined with theory calculation, the corresponding mechanism was systematically analyzed from oxygen vacancy induced electron doping.

Composition dependent magnetic coupling in Fe-Cr alloy cluster arrays

Dense arrays of Fe-Cr alloy clusters with different Cr ratios were fabricated by gas-phase cluster beam deposition. The complex multiphase structure and various coupling effects in the cluster arrays were studied. A lattice mismatched tetragonal-like morphology of the Fe-Cr alloy cluster was observed at large Cr ratio. An exchange bias effect was observed and was shown to be dependent on the proportion of the Cr components in the alloy. With the increase of the Cr composition, the exchange bias field became smaller and stronger dipolar interactions between the clusters developed. Residual coercivity and magnetization, which were more remarkable in the tetragonal-like clusters, were observed above the ferromagnetic-superparamagnetic transition temperature. The experimental results of the coercive field and the bias field at different temperatures demonstrated that the tetragonal-like clusters had better thermal stability and greater anisotropy.

Nm-sized cryogenic hydrogen clusters for a laser-driven proton source.

A cryogenic hydrogen cluster-jet target is described which has been used for laser-plasma interaction studies. Major advantages of the cluster-jet are, on the one hand, the compatibility to pulsed high repetition lasers as the target is operated continuously and, on the other hand, the absence of target debris. The cluster-jet target was characterized using the Mie-scattering technique allowing to determine the cluster size and to compare the measurements with an empirical formula. In addition, an estimation of the cluster beam density was performed. The system was implemented at the high power laser system ARCTURUS, and the measurements show the acceleration of protons after irradiation of the cluster target by high intensity laser pulses with a repetition rate of 5 Hz.

Palladium-carbon composite nanoparticle films with enhanced electrocatalytic activity for hydrogen peroxide sensors

A nanocomposite electrocatalyst was prepared with the method of cluster beam deposition of palladium nanoparticle thin films on carbon nanoparticle supporting layers and used as sensitive nonenzyme hydrogen peroxide sensors. An enhancement on the electrocatalytic activity of the palladium nanoparticles toward H2O2 reduction was observed, which was related to the coverage of the carbon nanoparticles. With one monolayer of carbon nanoparticles, the H2O2 detection sensitivity reached the maximum, which was more than twice of that of the pure Pd nanoparticles.

Soft Piezoionic/Piezoelectric Nanocomposites Based on Ionogel/BaTiO3 Nanoparticles for Low Frequency and Directional Discriminative Pressure Sensing.

We report on the fabrication and electro-mechanical characterization of a nanocomposite system exhibiting anisotropic electrical response under the application of tactile compressive stresses (5 kPa) at low frequencies (0.1-1 Hz). The nanocomposite is based on a chemically cross-linked gel incorporating a highly conductive ionic liquid and surface functionalized barium titanate (BaTiO3) ferroelectric nanoparticles. The system was engineered to respond to mechanical stimulations by combining piezoionic and piezoelectric activity, generating electric charge due to a redistribution of the mobile ions across the polymer matrix and to the presence of the electrically polarized ceramic nanoparticles, respectively. The nanocomposite response was characterized in a quasi-static regime using a custom-designed apparatus. The results obtained showed that the combination of both piezo-effects led to output voltages up to 8 mV and anisotropy in the response. This allows to discriminate the sample orientation with respect to the load direction by monitoring the phase and amplitude modulation of the output signal. The integration of cluster-assembled gold electrodes produced by Supersonic Cluster Beam Deposition (SCBD) was also performed, enabling to enhance the charge transduction efficiency by a factor of 10, compared to the bare nanocomposite. This smart piezoionic/piezoelectric nanocomposite represents an interesting solution for the development of soft devices for discriminative touch sensing and objects localization in physically unstructured environments.

A quantitative determination of the polymerization of benzoxazine thin coatings by time‐of‐flight secondary ion mass spectrometry

Phenol‐paraphenylenediamine (P‐pPDA) benzoxazines exhibit excellent barrier properties, adequate to protect aluminum alloys from corrosion, and constitute interesting candidates to replace chromate‐containing coatings in the aeronautical industry. For the successful application of P‐pPDA coatings, it is necessary to decrease the curing temperature to avoid the delamination of the coating while preserving the mechanical properties of the alloy, as well as the barrier properties of the coating. However, decreasing the curing temperature leads to less polymerized films, the extent of which requires a quantitative assessment.While the conversion rate of the polymerization reaction is commonly evaluated for bulk samples using differential scanning calorimetry (DSC), a tool for its evaluation in thin films is missing. Therefore, a new approach was developed for that matter using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The relation between the SIMS data integrated from inside thin films and the DSC results obtained on bulk samples with the same curing cycle allowed to calibrate the SIMS data. With this preliminary calibration of the technique, the polymerization of P‐pPDA coatings can be locally determined, at the surface and along the depth of the coating, using dual‐beam depth profiling with large argon cluster beam sputtering.

Molecular dynamics simulation of formation of accelerated neutral atom and cluster beams

A molecular dynamics simulation of accelerated argon cluster ion collisions with residual gas atoms was carried out. Cluster ions having an icosahedral structure were considered. The dependence of the impact fragmentation results of cluster ions on their initial sizes and on the value of the accelerating potential was studied. The simulation demonstrated that in the case of impact breaking of cluster ions along with the forming of a “cloud” of individual atoms, the formation of heated fragments and their complete or partial melting are observed. Further intensive evaporative cooling of these fragments occurred, which caused the appearance and/or growth of an ordered (icosahedral or crystal) structure in them. The probability of charge loss of the fragments was estimated. It was demonstrated that certain of the fragments can to be a part of a mixed accelerated neutral atom and cluster beams.

Development of a Gas Cluster Ion Source and Its Application for Surface Treatment

A custom-built gas cluster ion source with an energy up to 20 keV is constructed. Ar, CO2, N2, and O2 are used as the working gases. The clusters are formed by metal conical nozzles with critical diameters of 65−135 um and a cone angle of 14°. To facilitate evacuation of the chambers we use the pulse mode of nozzle feeding. This allows an increase in the gas pressure in the stagnation zone (inlet pressure) up to 15 bar. The current of the clusters with an energy of 20 keV is 20 µA; the maximal current density is 3 µA/cm2. The mass spectra of the argon clusters formed at different pressures and electron ionization energy are studied by time-of-flight spectroscopy. The inlet pressure dependence of the mean cluster size is considered as a function of the condensation parameter Г*. An argon cluster beam is used to smooth the surface of the titanium coating and pressed silicon nanopowder. The roughness of the Ti coating surface decreases from 3.7 to 0.8 nm; the removal of microparticles from the surface is also observed. In the case of the surface of Si, besides the smoothing effect the formation of 100 nm craters is observed.

Spatial separation of pyrrole and pyrrole-water clusters

We demonstrate the spatial separation of pyrrole and pyrrole(H2O) clusters from the other atomic and molecular species in a supersonically-expanded beam of pyrrole and traces of water seeded in high-pressure helium gas. The experimental results are quantitatively supported by simulations. The obtained pyrrole(H2O) cluster beam has a purity of ∼100%. The extracted rotational temperature of pyrrole and pyrrole(H2O) from the original supersonic expansion is Trot=0.8±0.2 K, whereas the temperature of the deflected, pure-pyrrole(H2O) part of the molecular beam corresponds to Trot≈0.4 K.

Quantitative characterization of the interfacial morphology and bulk porosity of nanoporous cluster-assembled carbon thin films

The deposition of nanoporous carbon thin films with well-controlled morphology, high surface area and porosity is of great interest for different applications requiring autonomous and portable electrochemical devices for energy conversion and storage. The engineering of this class of devices and the evaluation of their performances require the measurement of the porosity and surface area of the active carbon layers. The quantitative characterization of these parameters by gas adsorption techniques is hampered by the small amount of material usually available on a thin film.Here we report a method based on the use of atomic force microscopy (AFM) and nitrogen adsorption technique for the quantitative characterization of the specific surface area and porosity of nanoporous carbon films. In particular, we apply it to nanostructured carbon films fabricated by supersonic cluster beam deposition (SCBD), studying the evolution of their structural properties with film thickness. We exploited the characteristics of SCBD in terms of high-throughput, stability, and reproducibility to fabricate films with controlled nano and microstructure over large substrates compatible with the requirements of gas adsorption measurements. Our approach demonstrates that the combination of AFM and nitrogen adsorption technique provides the possibility of undertaking systematic quantitative characterization of the nano- and mesostructure of cluster-assembled carbon films and of their evolution, which can be easily applied to porous thin films fabricated by many different techniques.

Bioplastic electromechanical actuators based on biodegradable poly(3-hydroxybutyrate) and cluster-assembled gold electrodes

We present the fabrication and characterization of electroactive actuators based on natural-derived bioplastic able to display reversible bending deformations in response to low intensity electric fields. We used biodegradable poly(3-hydroxybutyrate) (PHB) blended with a suitable ionic liquid to produce freestanding electroactive ionogel layers through a solvent casting process employing non-toxic solvents. The ionogels were provided with compliant cluster-assembled gold electrodes fabricated by means of supersonic cluster beam deposition (SCBD). These metal layers exhibit tailored electrical properties, large surface areas and mechanical resiliency against deformations. The manufactured actuators were characterized in terms of mechanical, morphological, electrochemical and electromechanical properties. We show that the mechanical properties of the ionogels are similar to those of low density polyethylene, while the actuators demonstrated large bending displacement and stable operational durability. Furthermore, due to the use of PHB in combination with a hydrophobic ionic liquid, the actuators did not exhibit hygroscopic behaviour.

Highly active oxygen evolution reaction model electrode based on supported gas-phase NiFe clusters

Under alkaline conditions mixed NiFe oxides/oxyhydroxides are among the most active catalysts for the oxygen evolution reaction (OER). Here we investigate Ni0.5Fe0.5 clusters as a well-defined model highly active electrocatalyst system for the OER. The electrodes were prepared using gas-phase deposition of mixed Ni0.5Fe0.5 metallic clusters produced by cluster beam deposition (CBD), a technique offering precise control of composition and loading. Highly dispersed Ni0.5Fe0.5 clusters were deposited at 1 equivalent monolayer and used as OER catalyst in 1 M KOH. The low loading allows assessment of the intrinsic catalytic activity and their extensive structural characterization by XAFS and XPS spectroscopies. Ni0.5Fe0.5 clusters demonstrate high stability as there is no apparent potential increase after a 12 h constant current density anodization test. After electrochemical aging, the lowest overpotential was achieved and amounts to 372 mV at 10 mA cm−2. The Tafel slope reaches 37 mV dec−1. The measured electrochemical activity is also compared with other systems. After OER reaction in KOH the cluster surface is enriched in NiOOH, while concomitant Fe depletion from the catalyst surface is observed. These findings help to shed light on the formed active phase at the nanoscale.