Cluster Ion Beam Research Articles

Formation of irregular morphology on nanostructured surface by gas cluster ion beam

Ar1000 cluster ion beam was used to fabricate irregular structures of a micrometer scale on the surface of pressed Si powder of 60 nm nanoparticles (NPs). The average density of the target material played an important role in the surface features formation. The samples with lower average density, i.e. with larger distance between adjacent NPs demonstrated more developed surface morphology, which implied an importance of the degree of freedom of NP and its beam induced mobility in formation of the surface features. At higher average density a process of particle erosion was accompanied by the debris formation, which filled the gaps between the NPs, blocked the particle mobility, and, eventually, resulted in conventional smoothing effect.

Secondary ion mass spectrometry using energetic cluster ion beams: Toward highly sensitive imaging mass spectrometry

Imaging mass spectrometry (IMS), based on linking mass-analysis data for ions and their original positions in a sample, allows the visualization of the spatial distribution of atomic and/or molecular species in the sample, and is therefore an essential analytical method for the characterization of chemical and biological materials. For sensitive elemental and chemical imaging using IMS, a sufficient amount of ions to be analyzed should be supplied from the analyzing area on the sample surface. Secondary ion mass spectrometry (SIMS) using energetic cluster ions (ECIs) with energies of sub-MeV and above as primary ions (ECI-SIMS) can provide the secondary ions necessary for the characterization of organic materials with high emission yields. Hence, ECI-SIMS is a good method for highly sensitive IMS. We report recent progress in ECI beam manipulation techniques for applications of ECI-SIMS to highly sensitive IMS together with the characteristics of ECI impacts on organic materials.

Simple and effective cleaning method for RuO2 nanosheet films for flexible transparent conducting electrodes

A critical and practical issue in employing low dimensional nanomaterials as transparent conducting electrodes (TCEs) is the simple and effectual cleaning of the nanomaterials; the presence of contaminants increases the contact resistance at the interface region in practical applications. In this study, various cleaning methods are examined to remove surface contaminants on RuO2 nanosheets (NSs), which are the promising materials for TCEs. The Ar gas cluster ion beam (GCIB) sputtering technique can effectively remove organic surface contaminants, although it has critical drawbacks in the mass production. The simple deionized water treatment can provide satisfactory cleaning performance, which is comparable with that of the Ar GCIB sputtering method. Other methods such as solution-based treatments that use ethanol and chloroform and the heating method do not provide a comparable cleaning performance. The conductive atomic force microscopy demonstrates highly increased conductivity of water-cleaned RuO2 NS films at the nanoscale. This study proposes a practical method for the cleaning of RuO2-based nanomaterials for their application as TCEs and emphasizes their significance of the cleaning process to achieve a higher performance for TCEs based on low dimensional nanomaterials.

TOF-SIMS imaging reveals tumor heterogeneity and inflammatory response markers in the microenvironment of basal cell carcinoma

Basal cell carcinoma (BCC) is the most common skin malignancy. In fact, it is as common as the sum of all other skin malignancies combined and the incidence is rising. In this focused and histology-guided study, tissue from a patient diagnosed with aggressive BCC was analyzed by imaging mass spectrometry in order to probe the chemistry of the complex tumor environment. Time-of-flight secondary ion mass spectrometry using a (CO2)6 k + gas cluster ion beam allowed a wide range of lipid species to be detected. Their distributions were then imaged in the tissue that contained small tumor islands that were histologically classified as more/less aggressive. Maximum autocorrelation factor (MAF) analysis highlighted chemical differences between the tumors and the surrounding stroma. A closer inspection of the distribution of individual ions, selected based on the MAF loadings, showed heterogeneity in signal between different microtumors, suggesting the potential of chemically grading the aggressiveness of each individual tumor island. Sphingomyelin lipids were found to be located in stroma containing inflammatory cells.

A massive-ion beam driver for high-energy-density physics and future inertial fusion

Several heavy ion drivers for heavy ion inertial fusion have been proposed in the US and Europe, based on linear induction accelerator technology [1] and existing RF technology [2], respectively, although they have not been realized on a large scale. Developing accelerator technology may provide an alternative efficient, robust, and relatively cheap massive-ion beam driver for future particle beam inertial fusion. Here, we propose an accelerator complex for accelerating giant cluster ions, instead of lead or bismuth ions, toward 120 GeV by using induction acceleration over the entire energy region. The proposed two-way multiplex induction synchrotron that is the main accelerator for the giant cluster ion beam would be equivalent to 10 synchrotrons of the same size for a single beam.

Structural colors and physical properties of elytra in the jewel beetle, Chrysochroa fulgidissima, using surface analytical techniques

Structural coloration frequently originates from the interaction of light with multilayers of thin films in living organisms. One example where structural colors are created by multilayers is the jewel beetle, Chrysochroa fulgidissima, which has highly iridescent green elytra with longitudinal red stripes. We examine the structure, chemical information, and physical properties of the epicuticle of the jewel beetle by using atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nanoindentation, and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). AFM and SEM were used to analyze the surface structures of the green elytra and red stripes of the jewel beetle's wing. SEM and TEM images obtained from the cross‐sectioned cuticle samples of green and red areas indicated that the color arises from interference reflectors and reflectors consist of successive repeating layers of different electronic densities. Nanoindentation results showed that the green area of the elytron possesses a higher hardness and reduced modulus compared with the red area. To analyze the surface of the elytra and to compare multilayers of the green area with those of the red area, mass spectra and depth profiles were acquired by ToF‐SIMS with C60 and Ar cluster ion beams. The epicuticle consists of several layers with alternating high and low abundances of inorganic and organic fragment ions, with approximately 16 layers in the green and 12 layers in the red area. Therefore, ToF‐SIMS combined with other analytical techniques indicate that multilayer reflection is a major mechanism of the jewel beetle's iridescence causing structural coloration.

Surface topography and composition of NiPd alloys under oblique and normal gas cluster ion beam irradiation

Polycrystalline NiPd and Ni5Pd alloys were irradiated with argon gas cluster ion beam and atomic ion beam. In situ XPS measurements showed surface enrichment with Ni. For cluster ions, the degree of the enrichment was significantly higher, and the ion current density influenced on it. Under oblique cluster ion beam, ripples developed on the surface, and the elements of the alloy redistributed along the surface according to the ripple pattern. For normal cluster ion beam direction, sputtering rate was determined by a crystalline orientation, which limited the smoothing effect.

Dependence of Megaelectron Volt Time-of-Flight Secondary Ion Mass Spectrometry Secondary Molecular Ion Yield from Phthalocyanine Blue on Primary Ion Stopping Power.

Time-of-flight secondary ion mass spectrometry (TOF SIMS) is a well-established mass spectrometry technique used for the chemical analysis of both organic and inorganic materials. In the last ten years, many advances have been made to improve the yield of secondary molecular ions, especially those desorbed from the surfaces of organic samples. For this reason, cluster ion beams with kiloelectron volt energies for the excitation were mostly used. Alternatively, single-ion beams with megaelectron volt energies can be applied, as was done in the present work. It is well-known that a secondary molecule/ion yield depends strongly on the primary ion stopping power, but the nature of this dependence is not completely clear. Therefore, in the present work, the secondary ion yield from the phthalocyanine blue (C32H16CuN8, organic pigment) was measured for the various combinations of ion masses, energies, and charge states. Measured values were compared with the existing models for ion sputtering. An increase in the secondary yield with the primary ion energy, electronic stopping, velocity, and charge state was found for different types of primary ions. Although this general behavior is valid for all primary ions, there is no single parameter that can describe the measured results for all primary ions at once.

Molecular dynamics simulation of argon cluster ion collisions with argon atoms

The process of collisions of accelerated argon cluster ions with residual gas atoms was analyzed by molecular dynamic simulation. The cluster ions under consideration had an icosahedral structure. Their initial temperature was assumed to be equal to 35 K. The influence of the value of accelerating potential and initial size of cluster ions on the results of their impact breaking is investigated. The number of atoms in cluster ions varied from 309 to 1415. The accelerating potential value varied in the range from 10 to 100 keV. An evolution of cluster ions after the collision was observed for 1.51 μs. The simulation showed that after collisions, fragments of cluster ions can be survived, whose size, temperature and phase state (partial or complete melting) are determined by the ratio of the two above-mentioned parameters. Subsequent intensive evaporative cooling of these fragments leads to the full recovery of an ordered structure in them: icosahedral or crystalline. By the end of the considered time interval, temperature and size decrease of the fragments due to evaporation significantly slows down. It was also found that with weak or moderate damage of cluster ions, the processes occurring at the initial stage of the fragment formation (several dozen picoseconds) have a vibration nature. The frequency of these vibrations in the considered variants was in the range of 220–285 GHz. In addition, the parameters for atom scattering both knocked out from cluster ions at collisions and those leaving the fragments during evaporation were determined. The simulation results were used to investigate the formation process of so-called accelerated neutral atom beams, which arise by interaction of gas cluster ion beams with residual gas. Assumptions were made about the composition of the formed beams.

Surface potential measurements of a polymer film following primary ion gun irradiation for ToF-SIMS analysis of insulator using a Kelvin probe and the observation of effects from the vacuum gauge

When an insulator sample is analyzed via time-of-flight secondary ion mass spectrometry (ToF-SIMS), charges accumulate on the sample surface due to the primary ion beam. These local surface charges and surface potentials cause many problems during analysis. A Kelvin probe was used to measure the surface potentials of the insulator sample. The surface potential induced on the surface of the sample and its temporal change was measured following the irradiation of the gas cluster ion beam. It was confirmed that the estimated surface potential value is affected by the high vacuum gauge, and there is an inflow of charges that possess polarities opposite to that of the surface potential. The amount of current flowing from the high vacuum gauge was calculated using the surface potential data that was measured. The amount of charge flowing onto the surface of the insulator was varied from several tens of fA to several fA, which was depended on its vacuum degree and position of high vacuum ion gauge. Additionally, neutralization of surface charges by the neutral gas effect was also weakly observed. This leaked current from the high vacuum gauges is likely to have a small but lasting impact on the ToF-SIMS insulator analysis.

Bismuth adducted intact molecular ions [M + Bi]+ under low-energy bismuth cluster ion beams

The authors propose the use of a low-energy (sub-keV/atom) bismuth cluster ion beam for time-of-flight secondary ion mass spectrometry (TOF-SIMS). 2 keV Bi3+ at an incident angle of 65° generated bismuth-adducted secondary molecular ions [M + Bi]+, which are not observed under normal TOF-SIMS conditions. This low-energy Bi primary ion beam was used for the depth profiling of Irganox1010/Irganox1098 multilayered organic thin films. [M + Bi]+ gave a better dynamic range for both Irganox1010 and Irganox1098 layers. The results suggest that a 2 keV Bi3+ ion beam is more suitable for the depth profiling of organic thin films than a 54 keV Bi3++ ion beam of typical TOF-SIMS conditions.

Evaluation of the Surface Film Formed on Cu in Li[N(CF3SO2)2]-Tetraglyme Solvate Ionic Liquids

Rechargeable lithium-sulfur batteries have been investigated as a next generation battery due to low cost and abundant resources. Li-S batteries using conventional organic electrolytes have been realized by addition of some additives forming some protecting films on the Li anode in order to avoid self-discharge due to dissolution of lithium polysulfides in the electrolytes. On the other hand, it has been known that the solubility of lithium polysulfides is very low in the ionic liquids composed of [N(CF3SO2)2]– (bis(trifluoromethylsulfonyl)amide, TFSA–) because of its weak coordinating ability. The equimolar mixture of LiTFSA and tetraglyme (G4) has been known to give a liquid composed of [Li(G4)]+ and TFSA– at room-temperature. This liquid is called a solvate ionic liquid (SIL). LiTFSA-G4 SILs have such favorable properties as high lithium ion concentration and low solubility of lithium polysulfides. Therefore, the LiTFSA-G4 SILs have been studied as the promising electrolytes for rechargeable Li-S batteries. In order to realize Li-S batteries using the LiTFSA-G4 SILs, it is necessary to evaluate the performance of the Li anode in the SILs. We have already reported that the coulombic efficiency of deposition and dissolution of lithium on a Cu substrate was improved by the formation of the surface film (solid-electrolyte interphase) on the Cu substrate at the potential of Li(I)/Li[1]. In the present study, the surface film formed in LiTFSA-G4 SILs with and without a diluent, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (HFE), has been characterized using electrochemical impedance spectroscopy (EIS), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS) without exposing the samples to air. LiTFSA-G4 SILs were prepared by mixing LiTFSA and G4 at the specified molar ratios (50.0 : 50.0 and 54.5 : 45.5). EIS was conducted using an air-tight three electrode cell. A Cu disk electrode (3 mm in diameter) was used as the working electrode. Li foil was used as the counter and reference electrode. The surface film was prepared on the Cu electrode by keeping the potential at 0 V vs. Li/Li(I). The EIS spectra were taken at 0 V vs. Li/Li(I) with an amplitude of 5 mV in the frequency range from 1 Hz to 20 kHz. TEM grids made of Cu and Cu foils in contact with Li foil were immersed in the SILs with different compositions for three days. The samples were washed with monoglyme (G1) and dried under dry Ar atmosphere. The samples were installed into TEM equipped with EDX using a transfer holder. XPS spectra were obtained by focused Al Kα radiation with Ar+ and Ar gas cluster ion beam (GCiB) etching guns. The impedance spectra assignable to the surface films formed on the Cu electrodes at 0 V vs. Li/Li(I) were observed in the SILs with and without addition of HFE. The resistance of the surface film in 54.5-45.5 mol% LiTFSA-G4 SIL was larger than that in 50.0-50.0 mol% one, suggesting the ionic conductivity of the surface film reflect the concentration of Li(I) in the electrolyte. The resistance of the surface film increased with addition of HFE probably due to a decrease in the concentration of Li(I). The formation of the surface films with the thickness of 20-100 nm was confirmed by TEM. The shrinkage of the films was observed during TEM observation, indicating the decomposition of organic substances and/or elevation of temperature occurred by electron irradiation. Although no spot was observed in the electron diffraction diagram at the beginning of the observation, the spots assignable to LiF and Li2S appeared after the shrinkage of the film by electron irradiation, indicating LiF was not formed electrochemically at 0 V vs. Li/Li(I) in the SILs. In addition, no peak assignable to LiF was not observed in the XPS spectra of the surface films with Ar GCiB etching gun. Therefore, the surface films formed in the SIL were considered to composed of the organic substances derived from reductive decomposition of G4 and the ions existing in the SIL.Reference[1] Y. Katayama, N. Tachikawa, and N. Serizawa, 235th ECS meeting, A02-0265, Dallas, (2019).

Validated Analysis of Component Distribution Inside Perovskite Solar Cells and Its Utility in Unveiling Factors of Device Performance and Degradation.

Time-of-flight secondary-ion mass spectrometry (ToF-SIMS) has been used for gaining insights into perovskite solar cells (PSCs). However, the importance of selecting ion beam parameters to eliminate artifacts in the resulting depth profile is often overlooked. In this work, significant artifacts were identified with commonly applied sputter sources, i.e., an O2+ beam and an Ar-gas cluster ion beam (Ar-GCIB), which could lead to misinterpretation of the PSC structure. On the other hand, polyatomic C60+ and Ar+ ion beams were found to be able to produce depth profiles that properly reflect the distribution of the components. On the basis of this validated method, differences in component distribution, depending on the fabrication processes, were identified and discussed. The solvent-engineering process yielded a homogeneous film with higher device performance, but sequential deposition led to a perovskite layer sandwiched by methylammonium-deficient layers that impeded the performance. For device degradation, it was found that most components remained intact at their original position except for iodide. This result unambiguously indicated that iodide diffusion was one of the key factors governing the device lifetime. With the validated parameters provided, ToF-SIMS was demonstrated as a powerful tool to unveil the structure variation amid device performance and during degradation, which are crucial for the future development of PSCs.

Method of formation of super-smooth optical surfaces using GCIB and ANAB processing

Optical glass–ceramic is a promising material for the elements of precision optical systems operating in a wide temperature range. However, conventional methods such as the chemical–mechanical or ion polishing do not allow to form a substrate surface with less than 0.2 nm root mean square roughness. The method of gas cluster ion beam (GCIB) and accelerated neutral atom beam (ANAB) processing of glass–ceramic substrates is proposed to obtain super-smooth optical surfaces.The experimental samples were characterized by atomic force microscopy and X-ray diffractometry. It is shown that the surface is modified with the disappearance of linear defects (scratches) and the roughness parameters are improved. Only residual chaotic relief with the average roughness value (Ra) of 0.2 – 0.3 nm is observed after GCIB treatment. Subsequent ANAB processing allows to decrease the Ra parameter down to 0.15 nm. The improvement of surface characteristics is confirmed by the analysis of PSD-function in the investigated range of spatial frequencies. As a result of this work the method for super-smooth optical substrates fabrication was developed and the characteristics of obtained surfaces were investigated.

Intuitive Model of Surface Modification Induced by Cluster Ion Beams.

Topography development is one of the main factors limiting the quality of depth profiles during depth profiling experiments. One possible source of topography development is the formation of self-organized patterns due to cluster ion beam irradiation. In this work, we propose a simple model that can intuitively explain this phenomenon in terms of impact-induced mass transfer. By coupling our model with molecular dynamics simulations, we can predict the critical incidence angle, which separates the smoothening and roughening regimes. The results are in quantitative agreement with experiments. It is observed that the problems arising from topography development during depth profiling with cluster projectiles can be mitigated by reducing the beam incidence angle with respect to the surface normal or increasing its kinetic energy.

Surface ripples induced by gas cluster ion beam on copper surface at elevated temperatures

The temperature dependence of the ripples formation on a copper surface under off-normal gas cluster ion beam irradiation was investigated. At room temperature, well developed asymmetric ripples perpendicular to the beam were obtained with “droplets” of copper at the crests. At elevated temperatures, surface smoothing was found instead of rippling. On some grains the ripples perpendicular to the ion beam still remained. To explain this fact, electron backscattered diffraction analysis of the samples surfaces was performed. It showed that the ripple formation at elevated temperatures is governed both by the ion beam direction and by the crystalline orientation of a grain with respect to the beam.

Argon gas cluster ion beam used to identify intact proteins through enzymatic digestion

Using the beam with time-of-flight secondary ion mass spectrometry, researchers improved the signal-to-noise ratio and showed on-surface detection was identical to in-solution detection.

Electrochemical, 3D topography, XPS, and ToF-SIMS analyses of 4-methyl-2-phenylimidazole as a corrosion inhibitor for brass

This work presents the first corrosion analysis of 4-methyl-2-phenylimidazole (MePhI) corrosion inhibitor for brass immersed in 3 wt.% NaCl solution, wherein MePhI was shown to be highly effective. The structure of the surface layer, the formation of an organo-metallic complex, the spatial distribution of MePhI, and the thermal stability of the MePhI surface layer were described in detail using time-of-flight secondary ion mass spectrometry analysis and X-ray photoelectron spectroscopy. A gas cluster ion beam source using different sizes and accelerating energies of the clusters was also employed to slowly sputter the organic surface layer associated with the surface layer analysis.

Cell Adhesion on PEEK Surface with Gas Cluster Ion Beam Irradiation

Cell Adhesion on PEEK Surface with Gas Cluster Ion Beam Irradiation

The electronic band structure analysis of OLED device by means of in situ LEIPS and UPS combined with GCIB

Low‐energy inverse photoelectron spectroscopy (LEIPS) and ultraviolet photoelectron spectroscopy (UPS) incorporated into the multitechnique XPS system were used to probe the ionization potential and the electron affinity of organic materials, respectively. By utilizing gas cluster ion beam (GCIB), in situ analyses and depth profiling of LEIPS and UPS were also demonstrated. The band structures of the 10‐nm‐thick buckminsterfullerene (C60) thin film on Au (100 nm)/indium tin oxide (100 nm)/glass substrate were successfully evaluated in depth direction.