Argon Gas Cluster Ion Beam Research Articles

Gas-cluster ion sputtering: Effect on organic layer morphology.

Analysis of the surface of thin Irganox 1010 films before and after sputtering with an argon gas-cluster ion beam was performed with AFM and XPS to determine the effect that Zalar rotation has on the chemistry and morphology of the surface. The analysis is based on the change in roughness of the surface by comparing the same location on the surface before and after sputtering. The ion beam used was an of size n = 1000 and energy 4 keV. The XPS analysis agreed with previous results in which the ion beam did not cause measurable accumulation of damaged material. Based on the AFM results, the Irganox 1010 surface became rougher as a result of ion sputtering, and the degree of roughening was quantified, as was the sputter rate. Furthermore, Zalar rotation during ion sputtering did not have a significant effect on surface roughening, surprisingly.

Chemical depth profile of layered a-CSiO:H nanocomposites

Layered nanocomposites with a controlled distribution of mechanical properties across the nanostructure were constructed from oxygen-free (a-CSi:H) and oxygen-bound (a-CSiO:H) individual layers. These were deposited at different power or pulse periods from pure tetravinylsilane and tetravinylsilane in a mixture with oxygen gas using plasma-enhanced chemical vapor deposition operating in pulse mode. XPS depth profiling using argon gas cluster ion beams was used to determine the atomic concentration of carbon, silicon, and oxygen in the individual layers forming the nanocomposite. These layers had a total thickness of about 100 nm. The XPS analysis revealed that the oxygen-free layers were oxidized due to post-deposition oxidation in the ambient air. Oxygen was even diffused in an oxygen-bound layer, which was confirmed by repeated XPS depth profiling within three months after nanocomposite deposition. The upper oxygen-bound layer at the nanocomposite surface behaved as a barrier and reduced oxygen diffusion. The high energy-resolution XPS spectra (C 1s, Si 2p, and O 1s) were analyzed to gain more insight into bonding species formed in layered nanocomposite. This detailed analysis showed that oxygen atoms originating from the ambient air were bound in the oxidized a-CSi:H layers and formed the same bonding states as those in the as-deposited oxygen-bound layers.

ToF-SIMS analysis of ion implanted standard to quantify insecticide in mosquito netting with cesium and argon gas cluster sputtering beams

Ion implantation has been investigated for quantification of species in organic materials. Quantitative analysis of two insecticides in mosquito netting was recently achieved by ion implantation and time-of-flight secondary ion mass spectroscopy analysis with a Cs+ sputtering beam [Zhou et al., J. Vac. Sci. Technol., B 34, 03H107 (2016) and Zhou et al., J. Vac. Sci. Technol., B 35, 031802 (2017)]. Gas cluster ion beams (GCIBs) are of increasing utility in depth profiling of organic materials, and it was of interest to try the ion implantation approach with argon GCIB. The study was conducted on permethrin treated mosquito netting and on the substrate material [high density polyethylene (HDPE)] which was ion implanted with chlorine. The negative ion mass spectrum of permethrin is dominated by Cl−. Analysis of the ion implanted HDPE with Cs+ provided the expected Gaussian distribution, but analysis with argon GCIB shows a very sharp change in matrix species intensity at the penetration depth of the ion implant. This is presumably due to the degradation of the polymer structure by the implant. Even with reduced chlorine implant dose, the ability to use the analysis of the standard to quantify chlorine in insecticide treated fiber with GCIB was limited because of secondary ion yield variations. Analysis of netting which was no longer effective against mosquitoes showed significantly less chlorine at the surface than fresh netting, similar to the results obtained with the Cs+ sputtering beam. The results are useful to understand the effectiveness of insecticide treated nets and have implications for the analysis of other organic materials with the use of ion implantation for quantification.

Damage and repair of organic and inorganic surfaces by Ar+ ion and gas cluster ion beam sputtering

X-ray photoelectron spectroscopy has been used to study the interactions of argon ion and argon gas cluster ion beams with the surfaces of organic and inorganic materials. These methods of sputtering surfaces are commonly used to remove surface material to construct depth profiles by surface-sensitive techniques like XPS and SIMS. Standard argon ion sputtering has been known to damage polymer surfaces. This is demonstrated here on poly(ethylene terephthalate) and polytetrafluoroethylene. Subsequently, the damaged surfaces could be returned to their pristine state by sputtering with GCIB, which does not damage polymer surfaces. While GCIB can remove surface polymer material without damaging the underlying material, it is shown here to cause damage to the chalcogenide material, copper indium gallium selenide. Sputtering with a gas cluster ion beam was shown to selectively remove selenium from the copper indium gallium selenide structure. Additionally, chemical reduction of copper, indium, and gallium was observed. Subsequent to inducing damage to the CIGS surfaces with gas cluster ion beam, the surface could be returned to its pristine state by sputtering with argon ions to remove the damaged layer. This work demonstrates the applicability of various sputtering methods for organic and inorganic materials, suggests the route of damage formation, and shows the ability to remove the surface damage by a compatible sputtering method.

Detection of ZrO₂ Nanoparticles in Lung Tissue Sections by Time-of-Flight Secondary Ion Mass Spectrometry and Ion Beam Microscopy.

The increasing use of nanoparticles (NP) in commercial products requires elaborated techniques to detect NP in the tissue of exposed organisms. However, due to the low amount of material, the detection and exact localization of NP within tissue sections is demanding. In this respect, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and Ion Beam Microscopy (IBM) are promising techniques, because they both offer sub-micron lateral resolutions along with high sensitivities. Here, we compare the performance of the non-material-consumptive IBM and material-consumptive ToF-SIMS for the detection of ZrO2 NP (primary size 9–10 nm) in rat lung tissue. Unfixed or methanol-fixed air-dried cryo-sections were subjected to IBM using proton beam scanning or to three-dimensional ToF-SIMS (3D ToF-SIMS) using either oxygen or argon gas cluster ion beams for complete sample sputtering. Some sample sites were analyzed first by IBM and subsequently by 3D ToF-SIMS, to compare results from exactly the same site. Both techniques revealed that ZrO2 NP particles occurred mostly agglomerated in phagocytic cells with only small quantities being associated to the lung epithelium, with Zr, S, and P colocalized within the same biological structures. However, while IBM provided quantitative information on element distribution, 3D ToF-SIMS delivered a higher lateral resolution and a lower limit of detection under these conditions. We, therefore, conclude that 3D ToF-SIMS, although not yet a quantitative technique, is a highly valuable tool for the detection of NP in biological tissue.

Amorphous carbon nanocomposite films doped by titanium: Surface and sub-surface composition and bonding

Hydrogen free Ti-doped amorphous carbon layers were prepared by dual beam pulsed laser deposition using two excimer lasers. The air-exposed surfaces were analyzed by high-energy resolved and angular-resolved core-level photoelectron spectroscopy, and were then step-by-step sputtered with an argon gas cluster ion beam (ArGCIB), which is known to be a very gentle technique with respect to changes in surface chemistry. The results show that the top surface of the sample and its sub-surface region differ in composition and in bonding. The top surface is enriched by oxygen-bearing species. Carbon-bearing species located on the surface are mostly in sp3 hybridization. Titanium carbide clusters, TiC, are not directly exposed at the surface. They are embedded in a carbon network with dominating C sp2 hybridization. Their interface is formed by a distinct carbon-rich titanium carbide with stoichiometry close to TiC3. The surface damage induced by ArGCIB was found to be minimal, verifiably affecting carbon atoms in the carbon network.

Chemical stability of polymers under argon gas cluster ion beam and x-ray irradiation

In this work, the authors examine chemical stability of polymers under x-ray photoemission spectroscopy (XPS) depth profiling coupled with argon gas cluster ion sputtering. The depth profiles measured for polystyrene, poly(3-dodecylthiophene), and poly(methyl methacrylate) thin films do not reveal changes in the XPS spectra due to cluster bombardment. Nevertheless, x-ray irradiation influences the shape of the sputter craters. The observed features are attributed to cross-linking or chain scission occurring in the polymers.

Additive chemistry and distributions in photoresist thin films

The lithographic performance of thin photoresist films is a function of the distribution of formulation components, such as photoacid generator (PAG) molecules, and how these components undergo chemical modification and migrate within the film during the lithography processing steps. Argon gas cluster ion beam – secondary ion mass spectrometry depth profiles were used to monitor the PAG and quencher base distributions before and after exposure and postexposure bake processing steps for different photoresist formulations. PAG and quencher base distributions were correlated to depth of focus lithographic performance results.

Improved mass resolution and mass accuracy in TOF-SIMS spectra and images using argon gas cluster ion beams.

The popularity of argon gas cluster ion beams (Ar-GCIB) as primary ion beams in time-of-flight secondary ion mass spectrometry (TOF-SIMS) has increased because the molecular ions of large organic- and biomolecules can be detected with less damage to the sample surfaces. However, Ar-GCIB is limited by poor mass resolution as well as poor mass accuracy. The inferior quality of the mass resolution in a TOF-SIMS spectrum obtained by using Ar-GCIB compared to the one obtained by a bismuth liquid metal cluster ion beam and others makes it difficult to identify unknown peaks because of the mass interference from the neighboring peaks. However, in this study, the authors demonstrate improved mass resolution in TOF-SIMS using Ar-GCIB through the delayed extraction of secondary ions, a method typically used in TOF mass spectrometry to increase mass resolution. As for poor mass accuracy, although mass calibration using internal peaks with low mass such as hydrogen and carbon is a common approach in TOF-SIMS, it is unsuited to the present study because of the disappearance of the low-mass peaks in the delayed extraction mode. To resolve this issue, external mass calibration, another regularly used method in TOF-MS, was adapted to enhance mass accuracy in the spectrum and image generated by TOF-SIMS using Ar-GCIB in the delayed extraction mode. By producing spectra analyses of a peptide mixture and bovine serum albumin protein digested with trypsin, along with image analyses of rat brain samples, the authors demonstrate for the first time the enhancement of mass resolution and mass accuracy for the purpose of analyzing large biomolecules in TOF-SIMS using Ar-GCIB through the use of delayed extraction and external mass calibration.

Optimal conditions for gas cluster ion beams in studying inorganic interface species: improved chemical information at a ZnO interface

We have observed for the first time a subtle chemical change in the oxidation state of Zn at the interface between a ZnO thin film and a glass substrate using gas cluster ion beam (GCIB) depth‐profiling. A combination of monoatomic and gas clusters was used for etching, allowing the removal of the surface rapidly using the monoatomic ion beam yet still yield a less damaged surface by removing the damaged layer using the argon GCIB as a final step. With this combined method, the depth‐profile shows the transition of Zn from oxide to metal at the interface, which the monoatomic ion source if used alone would damage. This data indicates that the initial layers of the film did not undergo as much oxidation during the deposition compared with the rest of the film; therefore, metallic zinc resulted at the interface. We also examined the ZnO thin film under a range of conditions of argon ion profiling from monoatomic to cluster ions to study the most efficient method for depth‐profiling of multiple layers of inorganic materials. The monoatomic ion beam does not show the transition phenomena at the interface, which was observed in cluster depth‐profiling, probably because of atomic mixing effects. This suggests that care be taken in selection of etch parameters when studying interfaces. We recommend the combination of monoatomic sputtering followed by GCIB etching as the most efficient method for looking at interfaces of inorganic thin layers from the point of view of time taken and minimising damage at interface. Copyright © 2016 John Wiley & Sons, Ltd.

Structural analysis of the outermost hair surface using TOF-SIMS with gas cluster ion beam sputtering

A hair cuticle, which consists of flat overlapping scales that surround the hair fiber, protects inner tissues against external stimuli. The outermost surface of the cuticle is covered with a thin membrane containing proteins and lipids called the epicuticle. In a previous study, the authors conducted a depth profile analysis of a hair cuticle's amino acid composition to characterize its multilayer structure. Time-of-flight secondary ion mass spectrometry with a bismuth primary ion source was used in combination with the C60 sputtering technique for the analysis. It was confirmed that the lipids and cysteine-rich layer exist on the outermost cuticle surface, which is considered to be the epicuticle, though the detailed structure of the epicuticle has not been clarified. In this study, depth profile analysis of the cuticle surface was conducted using the argon gas cluster ion beam (Ar-GCIB) sputtering technique, in order to characterize the structure of the epicuticle. The shallow depth profile of the cuticle surface was investigated using an Ar-GCIB impact energy of 5 keV. Compared to the other amino acid peaks rich in the epicuticle, the decay of 18-methyleicosanic acid (18-MEA) thiolate peak was the fastest. This result suggests that the outermost surface of the hair is rich in 18-MEA. In conclusion, our results indicate that the outermost surfaces of cuticles have a multilayer (lipid and protein layers), which is consistent with the previously proposed structure.

アルゴンガスクラスターイオンビームと実用表面分析

Argon Gas Cluster Ion Beam (Ar-GCIB) is now widely spread in the field of practical surface analysis, such as X-ray photoelectron spectroscopy (XPS) and Time-of-Flight secondary ion mass spectrometry (TOF-SIMS), because of its unique sputtering effect of low chemical degradation for organic materials. GCIB provides the lateral sputtering effect and the high sputtering yield of which are never achieved by monotonic Ar ion beam on organic materials, so that the low chemical degradation of organic materials with high depth resolution and high sputtering rate could be achieved. Of course, a study of the GCIB sputtering phenomena with chemically reactive gasses, instead of Ar gas, for the advanced materials is one of the interesting things from an academic point of view. But the Ar-GCIB technique is expected to use for more practical applications, especially in the industrial field. In this paper, some practical applications of Ar-GCIB with recent XPS and TOF-SIMS instruments will be briefly introduced.

X線光電子分光分析法と飛行時間型二次イオン質量分析法におけるアルゴンガスクラスターイオンビームの応用

X線光電子分光分析法と飛行時間型二次イオン質量分析法におけるアルゴンガスクラスターイオンビームの応用

Removal of Organic Contamination from Graphene with a Controllable Mass-Selected Argon Gas Cluster Ion Beam

Since the discovery of graphene, organic surface contamination has posed difficulties both for accurate characterization of the material’s intrinsic properties and for development of graphene devices. In this study, we investigate the use of a mass-selected argon gas cluster ion beam for removing organic contaminants, such as residual poly(methyl methacrylate) (PMMA), from single-layer graphene. The influence of cluster ion size, energy, and ion dose has been investigated to identify the important factors for minimizing damage to the graphene layer during the cleaning process. Raman spectroscopy was used to analyze the variation in the D-peak and G-peak intensity ratio, an indicator of damage to the graphene lattice, as a function of ion beam dose and kinetic energy per atom (E/n) in the cluster ions. Using a mass-selected 5 keV Ar5000 beam with a dose of 5.0 ions/nm2, we were able to demonstrate removal of polymer residue and other carbonaceous material from single-layer chemical vapor deposition (CVD)-g...

Molecular Depth Profiling with Argon Gas Cluster Ion Beams

Argon gas cluster ion beams (Ar-GCIBs) are remarkable new projectiles for secondary ion mass spectrometry (SIMS) depth profiling of organic materials. However, the optimal cluster size and kinetic energy to provide the best quality of depth profiles, in terms of high ionization efficiency of the target molecules, little chemical damage, and short experiment time, for organic materials is not fully understood. Hence, the effect of cluster size and kinetic energy on the quality of molecular depth profiling is investigated on a simple platform composed of trehalose thin films to acquire more fundamental information about the ion/solid interaction. The results suggest that the sputter yield (Y/n) of argon clusters is linearly dependent upon kinetic energy per atom (E/n). When E/n > 5 eV/atom, normal depth profiles are obtained with relatively high sputter yields. When E/n ≤ 5 eV/atom, however, distorted depth profiles in the steady state region are observed, which exhibit a low sputter yield and variable ioni...

Angle dependence of argon gas cluster sputtering yields for organic materials.

The first angle-dependent measurements of the sputtering yield of an organic material using argon gas cluster ions under a wide range of conditions are reported in order to develop an analytical description of the behavior important for the development of the application of secondary ion mass spectrometry to organic and biological systems. Data are presented for Irganox 1010 using argon gas cluster ion beams of 5 and 10 keV energy, E, with cluster sizes, n, from 1000 to 5000. The measurements are conducted in an X-ray photoelectron spectrometer for a range of angles from 0 to 80° from the surface normal. The results support the Universal Equation for argon gas cluster sputtering yields with the angle dependence incorporated into the equation via a simple angle dependence of the parameter A. This explains how and why the angular dependence of the sputtering yield changes significantly with increasing E/n. These results are also accurately confirmed using the published measurements for polystyrene by Rading et al.

Study on the molecular distribution of organic composite films by combining photoemission spectroscopy with argon gas cluster ion beam sputtering

In situ molecular distribution analysis based on photoemission spectroscopy combined with Ar gas cluster ion beam sputtering process.

Observed damage during Argon gas cluster depth profiles of compound semiconductors

Argon Gas Cluster Ion Beam (GCIB) sources have become very popular in XPS and SIMS in recent years, due to the minimal chemical damage they introduce in the depth-profiling of polymer and other organic materials. These GCIB sources are therefore particularly useful for depth-profiling polymer and organic materials, but also (though more slowly) the surfaces of inorganic materials such as semiconductors, due to the lower roughness expected in cluster ion sputtering compared to that introduced by monatomic ions. We have examined experimentally a set of five compound semiconductors, cadmium telluride (CdTe), gallium arsenide (GaAs), gallium phosphide (GaP), indium arsenide (InAs), and zinc selenide (ZnSe) and a high-κ dielectric material, hafnium oxide (HfO), in their response to argon cluster profiling. An experimentally determined HfO etch rate of 0.025 nm/min (3.95 × 10−2 amu/atom in ion) for 6 keV Ar gas clusters is used in the depth scale conversion for the profiles of the semiconductor materials. The assumption has been that, since the damage introduced into polymer materials is low, even though sputter yields are high, then there is little likelihood of damaging inorganic materials at all with cluster ions. This seems true in most cases; however, in this work, we report for the first time that this damage can in fact be very significant in the case of InAs, causing the formation of metallic indium that is readily visible even to the naked eye.

TOF‐SIMS analysis of lithium air battery discharge products utilizing gas cluster ion beam sputtering for surface stabilization

TOF‐SIMS investigation on various lithium reference materials has been carried out for the characterization of reaction products on electrodes of lithium air batteries (LAB). In conjunction with argon gas cluster ion beam (GCIB) sputtering which can stabilize the surface of lithium compounds effectively, characteristic secondary ion species have been found for identification and differentiation among them. On the surface of real discharged carbon cathodes of LAB, lithium peroxide and related products were recognized under coexistence of electrolyte components and confirmed by the experiment using 18O2 as reaction gas in the discharging process. Copyright © 2014 John Wiley & Sons, Ltd.

Quantitative analysis of lipids with argon gas cluster ion beam secondary ion mass spectrometry

Ar gas cluster ion beam (Ar‐GCIB) SIMS has been developed as one of the powerful tools used for analyzing organic materials because of the high secondary ion yield of large organic molecules due to ‘soft’ sputtering mechanism of this technique. However, for practical analysis of complex biological samples, high quantitative accuracy is strongly required besides high sensitivity. In this study, some pure and compound lipid samples were measured with our originally equipped Ar‐GCIB SIMS apparatus with the aim of determining the quantitative accuracy of this technique. It was found that the detection limit of the Ar‐GCIB SIMS apparatus was lower than 0.1%. In addition, there was almost no matrix effect between the organic substances of similar chemical structures. Copyright © 2014 John Wiley & Sons, Ltd.