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Secondary ion mass spectrometry (SIMS) is a method with high surface sensitivity that allows both elemental and molecular analysis. The MeV-SIMS technique uses heavy ion beams with energy in the MeV range, and samples can be measured under ambient conditions because of the high transmission capability of these ions at low vacuum pressures. Ambient MeV-SIMS is a suitable method for investigating the reactions at the electrode–electrolyte interface. In contrast, however, in this method, chemical noise originating from ionized residual gases can be found with high intensity. Under the conditions, signals from the surface have to be distinguished from the chemical noise. In this paper, MeV-SIMS measurements of a Li-containing electrolyte were performed and a method was established for separating out chemical noise and signals from the sample surface. The detection of a number of Li-containing electrolytic compounds from the sample surface by an ambient MeV-SIMS system was successful. [ABSTRACT FROM AUTHOR]

In this work, we characterized the surface damage layer and sputtering yield of polycrystalline L-leucine films before and after irradiation with Ar cluster or monomer ion beams with x ray photoelectron spectroscopy and ellipsometry. Irradiation with Ar monomer ion beams induced heavy damage on the surface of L-leucine films, such as bond breaking and carbonization. In contrast, no significant surface damage was observed in the films irradiated with Ar cluster ion beams. The sputtering yield of L-leucine decreased dramatically with increasing fluence of monomer Ar ions and approached the value of the sputtering yield of graphite; but under irradiation with Ar cluster ion beams, the sputtering yield remained constant with fluence. The differences in sputtering yield behavior were explained in relation with the surface damage layer on organic materials. Thus, cluster ion beams could potentially be used to mill down biological materials without significant damage on the surface and could contribute to various applications in the analysis and processing of life matter. [ABSTRACT FROM AUTHOR]

RATIONALE The analysis of organic and biological substances by secondary ion mass spectrometry (SIMS) has greatly benefited from the use of cluster ions as primary bombarding species. Thereby, depth profiling and three-dimensional (3D) imaging of such systems became feasible. Large Ar n+ cluster ions may constitute a further improvement in this direction. METHODS To explore this option, large Ar n+ cluster ions (with n ~1500 Ar atoms per cluster) were used to investigate the emission of positive secondary ions from two peptide specimens (angiotensin I and bradykinin) by orthogonal time-of-flight SIMS using bombarding energies 6, 10 and 14 keV. RESULTS For both peptides, the protonated molecular ion is observed in the mass spectra. In addition, distinct fragmentation patterns were observed; these indicate that fragment ions under Ar cluster irradiation form primarily via cleavage of bonds along the peptide backbone whereas the rapture of side chains occurs much less frequently. These features appear to be similar to low-energy collision-induced dissociation pathways. CONCLUSIONS Tentatively, these findings can then be ascribed to the concerted action of the large number of Ar atoms in the impact zone of cluster at the surface: these low-energy Ar species (with an average energy of few eV) may effect the cleavage of the peptide bonds and lead, eventually, to the emission of the fragment ions. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Molecular dynamics (MD) simulations of large argon clusters impacting on silicon targets were performed. The characteristics of crater formation, a typical collisional effect with large cluster impact were examined from the viewpoint of incident energy, cluster size and incident angle. The MD simulation results suggested that the condition where an incident cluster penetrates into the solid target and causes a crater is mainly dominated by the incident energy-per-atom rather than total incident energy of the cluster. Additionally, the MD simulations of sequential multiple cluster impacts and grazing-angle cluster irradiation on irregular surface structures were studied to characterize the surface modification effects with large cluster ion beam process. [Copyright &y& Elsevier]

Abstract: The gas cluster ion beam process has become a candidate technique for advanced nano-fabrication, where both throughput and precise functionality are required. It is demonstrated that both extreme high-speed and precise nano-processing with low damage can be realized using reactive cluster ion beams. To date, this technique has been successfully applied to photonic, magnetic, electronic, and biological materials processing. The energy and size of cluster have become well controllable and many kinds of gaseous materials become available as cluster source gas. The fundamentals and applications of gas cluster ion beam process are reviewed in this paper. [Copyright &y& Elsevier]

Abstract: We performed molecular dynamics (MD) simulations to study the characteristic sputtering process with large cluster ion impact. The statistical properties of incident Ar and sputtered Si atoms were examined using 100 different MD simulations with Ar1000 cluster impacting on a Si(001) target at a total acceleration energy of 50keV. The results show that the kinetic energy distribution of Ar atoms after impact obeys the high-temperature Boltzmann distribution due to thermalization through high-density multiple collisions on the target. On the other hand, the kinetic energy distribution of sputtered target atoms demonstrates a hybrid model of thermalization and collision-cascade desorption processes. [Copyright &y& Elsevier]

Abstract: Gas cluster ion beams can produce high rate sputtering with low damage compared with the more familiar monomer ion beam process. In order to realize high-speed surface processing, a high-energy gas cluster ion beam irradiation system was developed in which high-energy Ar cluster ion beams were generated. The mean size of the Ar cluster was about 1800 atoms, as measured using the time-of-flight (TOF) method. Si substrates were irradiated with the Ar cluster ions at acceleration energies between 20 and 80 keV. The sputtering yield increased with acceleration energy and reached about 230 atoms/ion at 80 keV, a value about 180 times higher than that of Ar monomer ions. Au films were also irradiated at acceleration energies between 20 and 80 keV and the surfaces were observed with Atomic Force Microscopy (AFM). The high-energy cluster ion irradiation caused a decrease in surface roughness. These results indicate that high-speed smooth etching can be realized with high-energy cluster ion beams. This processing method can be applied to fabricate nano-devices. [Copyright &y& Elsevier]

Abstract: The mechanism of the sputtering process by energetic large cluster ion impacts was studied using molecular dynamics (MD) simulations. MD simulations of Ar1000 clusters accelerated with 50 keV total energy impacting on a Si(100) target were performed with 50 trials at different impact points in order to improve the statistical reliance. From these MD simulations, a sputtering yield of about 20 Si atoms/impact was obtained. Si clusters such as Si2, Si3, etc. were also found in the sputtered particles, and the sputtering yields for each cluster size obey the power-decay rule with a decay index of 2.3–3. The investigation of trajectories of sputtered Si1 and Si2 showed that initial coordinates of sputtered particles residing within a region corresponds to a crater-shaped hole caused by cluster impact. As for the sputtering of dimers, it is found that, not only the emission of a preformed dimer (i.e. a pair of target atoms initially bound before the cluster impact), but the emission of dynamically formed dimers through multiple collisions is also probable event for cluster impact. [Copyright &y& Elsevier]

Abstract: Energy resolved time of flight (ERTOF) mass spectroscopy has been developed to measure the energy and size distributions in a gas cluster ion beam (GCIB). Gas cluster ions, being aggregates of a few to several thousands of atoms, were generated by the ionization of neutral clusters, which were created by the adiabatic expansion of a high pressure gas into a vacuum. As a result of the large cross section of cluster ions, the cluster size can be easily reduced by collision with fast neutrals and monomer ions. An ERTOF system consisted of a retarding grid in front of a drift tube with a pair of deflection electrodes that acted as a gate. This system was attached to an ionization chamber, where Ar gas clusters, generated by a nozzle in a source chamber, were ionized by electron impact. Current waveforms were measured with ERTOF as an increasing voltage was applied to the retarding grid. The size distribution of clusters having a particular kinetic energy was calculated from the difference in the current waveform obtained at a corresponding retarding voltage to that at a larger voltage. Using ERTOF, it was found that the GCIB consisted of two components; small sized clusters with low kinetic energy and large sized clusters with high kinetic energy. It was also noted that the depth to which a substrate, on which the cluster beam impinged, was etched increased with the proportion of large clusters to the GCIB, since the small clusters, resulting from disintegration of large sized clusters by collisions with monomer ions, fast neutrals and residual gas molecules, have too low a kinetic energy to remove atoms from the surface. Note that the etched depth was affected by both the energy and size distribution of cluster ions. Therefore, ERTOF measurement could be utilized to assure the reproducibility of processes for the manufacture of semiconductors and magnetic recording heads. [Copyright &y& Elsevier]

Abstract: Large gas cluster impacts cause unique surface modification effects because a large number of target atoms are moved simultaneously due to high-density particle collisions between cluster and surface atoms. Molecular dynamics (MD) simulations of large gas cluster impacts on solid targets were carried out in order to investigate the effect of high-density irradiation with a cluster ion beam from the viewpoint of crater formation and sputtering. An Ar cluster with the size of 2000 was accelerated with 20keV (10eV for each constituent atom) and irradiated on a Si(100) solid target consisting of 2000000 atoms. The radius of the Ar cluster was scaled by ranging from 2.3nm (corresponding to the solid state of Ar) to 9.2nm (64× lower density than solid state). When the Ar cluster was as dense as solid state, the incident cluster penetrated the target surface and generated crater-like damage. On the other hand, as the cluster radius increased and the irradiation particle density decreased, the depth of crater caused by cluster impact was reduced. MD results also revealed that crater depth was mainly dominated by the horizontal scaling rather than vertical scaling. A high sputtering yield of more than several tens of Si atoms per impact was observed with clusters of 4–20× lower volume density than solid state. [Copyright &y& Elsevier]

Abstract: We investigated the effects of size and energy of large incident Ar cluster ions on the secondary ion emission of Si. The secondary ions were measured using a double deflection method and a time-of-flight (TOF) technique. The size of the incident Ar cluster ions was between a few hundreds and several tens of thousands of atoms, and the energy up to 60keV. Under the incidence of keV energy atomic Ar ions, mainly atomic Si ions were detected, whereas Si cluster ions were rarely observed. On the other hand, under the incidence of large Ar cluster ions, the dominant secondary ions were (2⩽ n ⩽11). It has become clear that the yield ratio of secondary Si cluster ions was determined by the velocity of the incident cluster ions, and this strong dependence of the yield ratio on incident velocity should be related to the mechanisms of secondary ion emission under large Ar cluster ion bombardment. [Copyright &y& Elsevier]

Abstract: Secondary ions emitted from Si targets were measured with a quadrupole mass spectrometer under large Ar cluster and monomer ion bombardment. Incident ion beams with energies from 7.5 to 25keV were used and the mean size of the Ar cluster ion was about 1000atoms/cluster. Si n + ions with n values up to n =8 were detected under Ar cluster ion bombardment, whereas Si cluster ions were scarcely detected under Ar monomer ion bombardment. These cluster ion yields showed the power law dependence on the cluster size. [Copyright &y& Elsevier]

Abstract: We have proposed to use oxygen cluster ions, which are much larger than molecular ions, as primary ions for secondary ion mass spectrometry (SIMS). A high intensity gas cluster ion source with a current density of a few μAs/cm2 has been developed. Secondary ions emitted from Si have been investigated under O2 and Ar cluster ion bombardment. A large enhancement of the yield of secondary ions produced by large O2 and Ar cluster ions was found. The SIMS system utilizing large O2 cluster ions must give both excellent depth resolution and high secondary ion yield. [Copyright &y& Elsevier]

In secondary ion mass spectrometry (SIMS), the detection of large organic molecules is accomplished using cluster ion bombardment. Ion formation often proceeds via cationization, through the attachment of (alkali) metal ions to the molecule. To study this process and its efficiency, the emission of secondary ions sputtered from polyethylene glycol (PEG 3000) mixed with Na trifluoroacetic acid (NaTFA) was investigated for 10 keV A r 2000 + cluster irradiation by MS and MS/MS. Apart from cationized molecular ions [M n +Na] + (with repeat units n of up to ∼80), fragment species were found corresponding to the loss of a water moiety or of two H atoms, respectively. In addition, an abundant flux of doubly-charged molecular ions, [M n +2Na] 2+ was observed in the mass spectra. Quite surprisingly, even triply-charged ions [M n +3Na] 3+ were detected. The ratio of [M n +2Na] 2+ to [M n +Na] + increases with increasing size of the molecules and reaches unit for n ∼70. The yield of [M n +Na] + ions around m / z 3000 depends strongly on the molecular composition ratio of NaTFA/PEG in the samples and can be enhanced by a factor of 50 by increasing the Na content. In MS/MS operation, [M n +Na] + and [M n +2Na] 2+ ions were subjected to collisions with Ar atoms; for sufficiently high collision energies, dissociation leads to characteristic fragment species. Collisions of [M n +2Na] 2+ assert the existence of doubly-charged ions in the sputtered flux. Collision cross sections were found to amount to ∼(0.5–1)×10 −15  cm 2 for center-of-mass collision energies of ∼3 eV. [ABSTRACT FROM AUTHOR]

Highlights: [•] Argon cluster ion bombardment of biological solids leads to soft desorption processes. [•] Abundant emission of large phenylalanine cluster ions by Ar cluster impact. [•] Orthogonal TOF-SIMS provides efficient ion detection of large biological molecules. [Copyright &y& Elsevier]

Abstract: Molecular imaging of animal cells was successfully obtained by using the technique of MeV-energy probe secondary ion mass spectrometry (MeV-SIMS) and sample etching with Ar cluster ion beam. In order to indicate benefits of using Ar cluster beam for etching biomaterials, cholesterol and phospholipids were etched with Ar cluster ions and SIMS measurements for the before and after etching samples were performed. Moreover, secondary ion images of the animal cells etched with Ar cluster ions were acquired by using MeV-energy ion beam as a probe. [Copyright &y& Elsevier]

Abstract: Secondary ion emission with large gas cluster ion is reviewed from the point of view of secondary ion mass spectroscopy (SIMS). We have proposed to use large cluster ions to realize fragment-free ionization for SIMS analysis for various organic materials, such as amino acids and peptides. When large cluster ions with optimized size and energy were incident on biomolecular samples, the relative yields of the fragment ions decreased drastically with the velocity of incident cluster ions. Molecular depth profiling capability is also demonstrated by using large gas cluster ions as the primary ion for SIMS. [Copyright &y& Elsevier]

Abstract: Secondary ions produced from a Si target bombarded with Ar cluster ions much larger than the molecular ions have been investigated. Secondary ions have been measured for a Si target bombarded with large Ar cluster ions at an incident energy between 7.5 and 27.5keV using a time-of-flight technique. The mean size of the Ar cluster ion was about 1000atoms/cluster, and then the collision energy per atom is between a few tens of eV and a few hundreds of eV. Secondary silicon cluster ions were detected under large Ar cluster ion bombardment. In this study, we succeeded to accurately measure the dependence of secondary ion spectra obtained by large Ar cluster ions on the incident cluster-ion size using a time-of-flight technique combined a primary-ion beam deflector and a secondary-ion deflector. The dependence of the secondary ion spectra under large Ar cluster ion bombardment on the incident cluster size is discussed. [Copyright &y& Elsevier]

Abstract: We present new developments of a novel surface smoothing method so-called gas cluster ion beam–chemical mechanical polishing (GCIB–CMP). This method employs GCIB with irradiation angles above 60° from the surface normal, and therefore can be applied to the smoothing of sidewalls of a patterned structure. Surface morphology is compared between various optical materials Si, SiO2 and MgF2 irradiated by SF6 clusters. Si and SiO2 surfaces are substantially smoothed at 0.3nm and below in average roughness at incident angles around 80°. We estimate the expected performance improvement of Si and/or SiO2 based photonic devices having smooth sidewall surfaces formed by the GCIB–CMP method. [Copyright &y& Elsevier]

Abstract: Various imaging techniques using microbeam have been applied in biology. Secondary ion mass spectrometry (SIMS) is one of the prominent tools for biological imaging; SIMS can provide data on molecular distribution in biological samples smaller than 1μm. However, conventional SIMS has only low sensitivity for molecular ions; therefore there is a need for beams of more sensitive primary ions. Plasma desorption mass spectrometry (PDMS) is a method using high energy fission fragments from excitation of a 252Cf source, and it allows ionization of large molecules (typically up to 20kDa) due to the dense electronic excitation. Although PDMS is not in use today because of the development of soft ionization methods, ionization induced by high energy ion collision still remains the only method which combines high spatial resolution and sensitive detection of large molecules. In this work, the secondary ion yield of amino acid and phospholipid was measured for 6MeV Cu4+. The yields were compared to bismuth cluster ions, which achieve relatively high yield. It was confirmed that the swift heavy ion has a couple of hundred times higher yield for large molecules than bismuth cluster ions. [Copyright &y& Elsevier]

Abstract: Si was bombarded with size-selected 40keV Ar cluster ions and positive secondary ions were measured using the time-of-flight technique under high and ultra-high vacuum (HV and UHV respectively) conditions. Si+ ions were main species detected under the incidence of 40keV Ar cluster ions, and the yields of Si cluster ions such as Si4 + were also extremely high under both conditions. On the other hand, oxidized secondary ions such as SiO+ were detected with high intensity only under the HV condition. The yield ratios of oxidized ions decreased in UHV to less than 1% of their values in HV. The effect of residual gas pressure on Si cluster ion yields is relatively low compared to oxidized ions, and the UHV condition is required to obtain accurate secondary ion yields. [Copyright &y& Elsevier]