Ar Cluster Ion Research Articles

Diamond-like carbon and nanocrystalline diamond film surfaces sputtered by argon cluster ion beams

Conventional (monoatomic) ion beam sputtering of solid surfaces is currently used for surface cleaning and concentration depth profiling. Due to ion-surface interactions, however, a modified near-surface layer arises, characterized with the changed composition and chemical bonding. As a consequence, this complicates data interpretation. A lot of efforts have been devoted to eliminate the problem. Now, the most promising method seems to be application of multi atomic or molecular ion beams.In the present contribution we examine the influence of argon cluster ion beam on composition and chemical bonding of diamond-like carbon (DLC) and nanocrystalline diamond (NCD) film surfaces by using high-energy resolution core-level photoelectron spectroscopy (XPS). Particularly, peak widths and hybridization of carbon atoms is evaluated from C 1s lines. The extent of bonding transformation from C sp3 to C sp2 depended on average energy per Ar atom in the clusters. For the energy as low as a few eV per Ar atom the modification is mild. Prime novelty statementThe novelty of the presented research is the examination of the interaction between Argon cluster ion beam with DLC and NCD surfaces via high-energy resolved C 1s photoelectron spectra. Our results show that bonding transformation from C sp3 to C sp2 due to Ar cluster ion beam sputtering was found mild, if the average argon atom energy in clusters is comparable to the bond strength of the surface target atoms.

A Nondestructive Method for Probing Mechanical Properties of a Thin Film Using Impacts with Nanoclusters

The impact of an argon (Ar)-cluster ion on a thin film is evaluated in order to investigate a new method for probing the mechanical properties of the thin metallic film. Using a molecular dynamic (MD) method, we show that an Ar nanocluster ion with an incident velocity of 4[Formula: see text]km/s dissociates in approximately 1[Formula: see text]ps without sputtering the atoms of a target sample. After the impact, the Ar ion is scattered from the target surface with several neutral Ar atoms. The number of neutral atoms combining with the Ar ion and the velocity of the Ar ion depend on the mass density and Young’s modulus of the target. Analyzing these dependencies, we find that the mass density and Young’s modulus of thin films can be simultaneously determined by measuring the mass and velocity of the Ar-cluster ion scattered from the sample surface.

Graphene, Graphene Oxide and Silicon Irradiation by Cluster Ions of Argon and Highly Charged Ions

ABSTRACTDefect formation in the samples of graphene, graphene oxide and silicon irradiated with Ar cluster and highly-charged ion irradiations were studied. Ar cluster ions, with acceleration energy E = 30 kV (Exogenesis nAccel00, Boston, USA) and total Ar cluster ion fluences ranged from 1x109cm-2to 1x1013cm-2were directed toward various surfaces. Highly-charged ions (HCI) bombardment on surfaces with highly charged Xeq+(q= 22) was employed at Eurasian National University, Kazakhstan, using a DC-60 cyclotron accelerator. Multi-layer graphene oxide, single-layer graphene- (SLG), few-layer of graphene (FLG) and polished Si are used for irradiation experiments. The study of irradiated samples was conducted by Raman spectroscopy, atomic force microscopy (AFM). Uniformly distributed defects and craters were observed on the surfaces of graphene, graphene oxide and silicon irradiated with cluster and HCI beams in our experiments. Ab-initio density-functional theory (DFT) was used to study point defects and molecular-dynamics (MD) simulations were used for studying formation of craters due to gas cluster ion impacts in graphene. The results of simulations were compared with experimental craters and surface shape.

Sampling Depths, Depth Shifts, and Depth Resolutions for Bi(n)(+) Ion Analysis in Argon Gas Cluster Depth Profiles.

Gas cluster sputter depth profiling is increasingly used for the spatially resolved chemical analysis and imaging of organic materials. Here, a study is reported of the sampling depth in secondary ion mass spectrometry depth profiling. It is shown that effects of the sampling depth leads to apparent shifts in depth profiles of Irganox 3114 delta layers in Irganox 1010 sputtered, in the dual beam mode, using 5 keV Ar₂₀₀₀⁺ ions and analyzed with Bi(q+), Bi₃(q+) and Bi₅(q+) ions (q = 1 or 2) with energies between 13 and 50 keV. The profiles show sharp delta layers, broadened from their intrinsic 1 nm thickness to full widths at half-maxima (fwhm's) of 8-12 nm. For different secondary ions, the centroids of the measured delta layers are shifted deeper or shallower by up to 3 nm from the position measured for the large, 564.36 Da (C₃₃H₄₆N₃O₅⁻) characteristic ion for Irganox 3114 used to define a reference position. The shifts are linear with the Bi(n)(q+) beam energy and are greatest for Bi₃(q+), slightly less for Bi₅(q+) with its wider or less deep craters, and significantly less for Bi(q+) where the sputtering yield is very low and the primary ion penetrates more deeply. The shifts increase the fwhm’s of the delta layers in a manner consistent with a linearly falling generation and escape depth distribution function (GEDDF) for the emitted secondary ions, relevant for a paraboloid shaped crater. The total depth of this GEDDF is 3.7 times the delta layer shifts. The greatest effect is for the peaks with the greatest shifts, i.e. Bi₃(q+) at the highest energy, and for the smaller fragments. It is recommended that low energies be used for the analysis beam and that carefully selected, large, secondary ion fragments are used for measuring depth distributions, or that the analysis be made in the single beam mode using the sputtering Ar cluster ions also for analysis.

ToF-SIMS and laser-SNMS analysis of Madin-Darby canine kidney II cells with silver nanoparticles using an argon cluster ion beam.

The use of nanoparticles is one of the fastest expanding fields in industrial as well as in medical applications, owing to their remarkable characteristics. Silver nanoparticles (AgNPs) are among the most-commercialized nanoparticles because of their antibacterial effects. Laser postionization secondary neutral mass spectrometry (laser-SNMS) and time-of-flight secondary ion mass spectrometry in combination with argon cluster ion sputtering was used for the first time to investigate the effects of AgNPs on Madin-Darby canine kidney (MDCK) II cells. Depth profiles and high-resolution three dimensional (3D) images of nanoparticles and organic compounds from cells were obtained using an Ar cluster ion beam for sputtering and Bi3 (+) primary ions for the analysis. The 3D distribution of AgNPs and other organic compounds in MDCK II cells could be readily detected with very high efficiency, sensitivity, and submicron lateral resolution. The argon cluster ion beam is well suited for the sputtering of biological samples. It enables a high sample removal rate along with low molecular degradation. The outer membrane, the cytoplasm, and the nuclei of the cells could be clearly visualized using the signals PO(+) and C3H8N(+) or CN(+) and C3H8N(+). The laser-SNMS images showed unambiguously that AgNPs are incorporated by MDCK II cells and often form silver aggregates with a diameter of a few micrometers, mainly close to the outside of the cell nuclei.

高分子混合試料のArクラスタースパッタリング正・負二次イオン スペクトルにおけるマトリックス効果の評価

高分子混合試料のArクラスタースパッタリング正・負二次イオン スペクトルにおけるマトリックス効果の評価

3D ToF-SIMS Analysis of Peptide Incorporation into MALDI Matrix Crystals with Sub-micrometer Resolution.

The analytical sensitivity in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is largely affected by the specific analyte-matrix interaction, in particular by the possible incorporation of the analytes into crystalline MALDI matrices. Here we used time-of-flight secondary ion mass spectrometry (ToF-SIMS) to visualize the incorporation of three peptides with different hydrophobicities, bradykinin, Substance P, and vasopressin, into two classic MALDI matrices, 2,5-dihydroxybenzoic acid (DHB) and α-cyano-4-hydroxycinnamic acid (HCCA). For depth profiling, an Ar cluster ion beam was used to gradually sputter through the matrix crystals without causing significant degradation of matrix or biomolecules. A pulsed Bi3 ion cluster beam was used to image the lateral analyte distribution in the center of the sputter crater. Using this dual beam technique, the 3D distribution of the analytes and spatial segregation effects within the matrix crystals were imaged with sub-μm resolution. The technique could in the future enable matrix-enhanced (ME)-ToF-SIMS imaging of peptides in tissue slices at ultra-high resolution. Graphical Abstract ᅟ.

Peptide fragmentation caused by Ar cluster ions depending on primary ion energy.

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) with an Ar cluster ion beam as a primary ion source provides useful information in terms of peptide analysis. It is, however, difficult to interpret the spectra. The ToF-SIMS peptide spectra obtained with Ar clusters having different energies have been investigated in order to classify the secondary ions into the peptide fragment ions and those related to contaminants or the substrate. Three peptides having different molecular weights from 600 to 1300 u were measured with Ar cluster beams having different energies per atom from 4 to 40 eV/atom. In the spectra normalized to a geometric average of all the spectra, the amino acid fragment ions are distinguished from other secondary ions. In the mass range above 600 u, the peptide fragment ions increase with mass while those not related to the peptide decrease with mass. Energy-dependence fragmentation helps in understanding the peptide spectra. Specific peptide fragment ions of the larger peptides are likely to be detected under lower energy than energy higher than 10 eV/atom. Although it is difficult to interpret the TOF-SIMS spectra of a peptide obtained with an Ar cluster ion beam, the secondary ions can be classified by comparing those obtained with different energy Ar cluster ion beams.

ToF-SIMS observation for evaluating the interaction between amyloid β and lipid membranes.

The adsorption behaviour of amyloid beta (Aβ), thought to be a key peptide for understanding Alzheimer's disease, was investigated by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). Aβ aggregates depending on the lipid membrane condition though it has not been fully understood yet. In this study, Aβ samples on different lipid membranes, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), were observed with ToF-SIMS and the complex ToF-SIMS data of the Aβ samples was interpreted using data analysis techniques such as principal component analysis (PCA), gentle-SIMS (G-SIMS) and g-ogram. DOPC and DMPC are liquid crystal at room temperature, while DPPC is gel at room temperature. As primary ion beams, Bi3(+) and Ar cluster ion beams were used and the effect of an Ar cluster ion for evaluating biomolecules was also studied. The secondary ion images of the peptide fragment ions indicated by G-SIMS and g-ogram were consistent with the PCA results. It is suggested that Aβ is adsorbed homogeneously on the liquid-crystalline-phase lipid membranes, while it aggregates along the lipid on the gel-phase lipid membrane. Moreover, in the results using the Ar cluster, the influence of contamination was reduced.

Extraction of hidden information of ToF-SIMS data using different multivariate analyses

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a powerful tool for determining surface information of complex systems such as polymers and biological materials. However, the interpretation of ToF-SIMS raw data is often difficult. Multivariate analysis has become effective methods for the interpretation of ToF-SIMS data. Some of multivariate analysis methods such as principal component analysis and multivariate curve resolution are useful for simplifying ToF-SIMS data consisting of many components to that explained by a smaller number of components. In this study, the ToF-SIMS data of four layers of three polymers was analyzed using these analysis methods. The information acquired by using each method was compared in terms of the spatial distribution of the polymers and identification. Moreover, in order to investigate the influence of surface contamination, the ToF-SIMS data before and after Ar cluster ion beam sputtering was compared. As a result, materials in the sample of multiple components, including unknown contaminants, were distinguished. Copyright © 2014 John Wiley & Sons, Ltd.

Angular distributions of particles sputtered from multicomponent targets with gas cluster ions

The experimental angular distributions of atoms sputtered from polycrystalline W, Cd and Ni based alloys with 10keV Ar cluster ions are presented. RBS was used to analyze a material deposited on a collector. It has been found that the mechanism of sputtering, connected with elastic properties of materials, has a significant influence on the angular distributions of sputtered components. The effect of non-stoichiometric sputtering at different emission angles has been found for the alloys under cluster ion bombardment. Substantial smoothing of the surface relief was observed for all targets irradiated with cluster ions.

Ar cluster ion beam sputtering of InSb investigated by ToF‐SIMS

Ar gas cluster ion beam (GCIB) sputtering of InSb was investigated, and the sputtering rate and depth resolution of time‐of‐flight secondary ion mass spectrometry sputter depth profiling were examined. The practical sputtering rate for InSb using 20 keV Ar2500+ irradiation was confirmed at the incident angles of 0°, 40°, and 60°, and the sputtering rate was too low to perform sputtering at 80°. The preferential sputtering and surface roughness observed under GCIB irradiation was lower than that observed under 3 keV Ar+ irradiation. Characteristic ripple formation was confirmed under 20 keV Ar2500+ irradiation and had a strong influence on the depth resolution. The highest depth resolution was obtained at the incident angle of 0° because no ripple formation occurred and the level of surface roughness was low among the irradiation of GCIB at incident angles of 0°, 40°, and 60°. The present results revealed that GCIB sputtering is an effective method for sputter depth profiling of InSb. Copyright © 2014 John Wiley & Sons, Ltd.

Molecular imaging of biological tissue using gas cluster ions.

An Ar n+ (n = 1-6000) gas cluster ion source has been utilized to map the chemical distribution of lipids in a mouse brain tissue section. We also show that the signal from high mass species can be further enhanced by doping a small amount of CH4 into the Ar cluster to enhance the ionization of several biologically important molecules. Coupled with secondary ion mass spectrometry instrumentation which utilizes a continuous Ar cluster ion projectile, maximum spatial resolution and maximum mass resolution can be achieved at the same time. With this arrangement, it is possible to achieve chemically resolved molecular ion images at the 4-µm resolution level. The focused Ar n+/[Ar x (CH4) y ]+ beams (4-10 µm) have been applied to the study of untreated mouse brain tissue. A high signal level of molecular ions and salt adducts, mainly from various phosphocholine lipids, has been seen and directly used to map the chemical distribution. The signal intensity obtained using the pure Ar cluster source, the CH4-doped cluster source and C60 is also presented.

Reduced Preferential Sputtering of TiO<sub>2</sub> using Massive Argon Clusters

In this study, we demonstrate low damage etching of titania for depth profile analysis using large Ar cluster ions. Sample damage caused by impinging ion beams is discussed and a comparison is made between monatomic Ar+ ions and Arn+ cluster ions with respect to surface damage. Monatomic ions of beam energy 5 kV cause considerable changes to the structure of amorphous titania resulting in the preferential removal of oxygen and damage to the lattice structure. Titanium is reduced from the +4 oxidation state to +3 and +2 oxidation state during this preferential removal. In contrast, the use of clusters greatly diminishes this damage and also reduces the incorporation of the impinging ion into the sample surface. Here we discuss the use of Arn+ clusters as a new methodology for reducing the damaging effects caused by ion bombardment.

Peptide structural analysis using continuous Ar cluster and C60 ion beams

A novel application of time-of-flight secondary ion mass spectrometry (ToF-SIMS) with continuous Ar cluster beams to peptide analysis was investigated. In order to evaluate peptide structures, it is necessary to detect fragment ions related to multiple neighbouring amino acid residues. It is, however, difficult to detect these using conventional ToF-SIMS primary ion beams such as Bi cluster beams. Recently, C60 and Ar cluster ion beams have been introduced to ToF-SIMS as primary ion beams and are expected to generate larger secondary ions than conventional ones. In this study, two sets of model peptides have been studied: (des-Tyr)-Leu-enkephalin and (des-Tyr)-Met-enkephalin (molecular weights are approximately 400Da), and [Asn(1) Val(5)]-angiotensin II and [Val(5)]-angiotensin I (molecular weights are approximately 1,000Da) in order to evaluate the usefulness of the large cluster ion beams for peptide structural analysis. As a result, by using the Ar cluster beams, peptide molecular ions and large fragment ions, which are not easily detected using conventional ToF-SIMS primary ion beams such as Bi3 (+), are clearly detected. Since the large fragment ions indicating amino acid sequences of the peptides are detected by the large cluster beams, it is suggested that the Ar cluster and C60 ion beams are useful for peptide structural analysis.

Interfacial Micropore Defect Formation in PEDOT:PSS-Si Hybrid Solar Cells Probed by TOF-SIMS 3D Chemical Imaging

Conducting p-type polymer layers on n-type Si have been widely studied for the fabrication of cost-effective hybrid solar cells. In this work, time-of-flight secondary ion mass spectrometry (TOF-SIMS) is used to provide three-dimensional chemical imaging of the interface between poly(3,4-ethylene-dioxythiophene):polystyrenesulfonate (PEDOT:PSS) and SiOx/Si in a hybrid solar cell. To minimize structural damage to the polymer layer, an Ar cluster sputtering source is used for depth profiling. The present result shows the formation of micropore defects in the interface region of the PEDOT:PSS layer on the SiOx/Si substrate. This interfacial micropore defect formation becomes more prominent with increasing thickness of the native oxide layer, which is a key device parameter that greatly affects the hybrid solar cell performance. Three-dimensional chemical imaging coupled with Ar cluster ion sputtering has therefore been demonstrated as an emerging technique for probing the interface of this and other polymer-inorganic systems.

Smoothing metallic glasses without introducing crystallization by gas cluster ion beam

We show that 30 keV Ar cluster ion bombardment of Ni52.5Nb10Zr15Ti15Pt7.5 metallic glass (MG) can remove surface mountain-like features and reduce the root mean square surface roughness from 12 nm to 0.7 nm. X-ray diffraction analysis reveals no crystallization after cluster ion irradiation. Molecular dynamics simulations show that, although damage cascades lead to local melting, the subsequent quenching rate is a few orders of magnitude higher than the critical cooling rate for MG formation, thus the melted zone retains its amorphous nature down to room temperature. These findings can be applied to obtain ultra-smooth MGs without introducing crystallization.

ToF-SIMS depth profiling of organic solar cell layers using an Ar cluster ion source

Time-of-flight secondary ion mass spectroscopy (ToF-SIMS) is a very powerful technique for analyzing the outermost layers of organic and biological materials. The ion fluence in static SIMS is usually kept low enough to prevent decomposition of the organic/molecular species and as a result ToF-SIMS is able to detect and image high mass molecular species, such as polymer additives. Depth profiling, in contrast, uses a high ion fluence in order to remove material between each analysis cycle. Unfortunately, the high ion fluence results in not only erosion but also decomposition of the organic species. Recently, high mass Ar cluster ion sources have become available and are enabling depth profiling through organic layers. In this paper, the authors demonstrate that they can obtain and maintain molecular information throughout an organic solar cell test layer when erosion is performed using an Ar1500+ cluster ion source for material removal. Contrary they show that they cannot maintain molecular information when low energy monoatomic ion beams are used for material removal.

Evaluation of charge state of gas cluster ions by means of individual crater observations

In this study, charge states of gas cluster ions were evaluated from observations of individual impact craters. Since the diameter of craters formed by gas cluster ion impact increases in proportion to the cubic root of the acceleration energy, and is not dependent on cluster size when energy is greater than 10eV/atom, the charge state of a cluster ion can be evaluated from the diameter of its individual crater. From AFM images of SiO2 irradiated with Ar cluster ions produced using low electron ionization voltages (Ve), craters with diameters of about 4nm were observed. However, larger diameter craters started to appear with increasing Ve. From the distribution of charge states at Ve of 200V, it was shown that there were some Ar cluster ions with six charges. There was no apparent dependence of charge state of Ar-GCIB on electron ionization current (Ie). This result indicates that ionization electron bias is the key parameter to control charge states of gas cluster ions.

Revealing surface oxidation on the organic semi-conducting single crystal rubrene with time of flight secondary ion mass spectroscopy

To address the question of surface oxidation in organic electronics the chemical composition at the surface of single crystalline rubrene is spatially profiled and analyzed using Time of Flight - Secondary Ion Mass Spectroscopy (ToF-SIMS). It is seen that a uniform oxide (C42H28O) covers the surface while there is an increased concentration of peroxide (C42H28O2) located at crystallographic defects. By analyzing the effects of different primary ions, temperature and sputtering agents the technique of ToF-SIMS is developed as a valuable tool for the study of chemical composition variance both at and below the surface of organic single crystals. The primary ion beams C60(3+) and Bi3(+) are found to be most appropriate for mass spectroscopy and spatial profiling respectively. Depth profiling of the material is successfully undertaken maintaining the molecular integrity to a depth of ~5 μm using an Ar cluster ion source as the sputtering agent.