Energy Of Cluster Ions Research Articles

Sputtering and ripples formation by gas cluster ions on LiNbO-=SUB=-3-=/SUB=- crystal

The work addresses the creation of surface structures on lithium niobate single crystals. Surface topography of lithium niobate surface sputtered with gas cluster ion beams was investigated. Surface ripples induced on the surface were analyzed using power spectral density functions approach, their evolution with ion fluence and their dependence on the cluster ion energy discussed. Sputter yield value was shown to decrease with surface roughness increase, the reasons of the effect are indicated. Local piezoresponse of the rippled surface was studied. Keywords: ferroelectrics, LiNbO3 crystal, gas cluster ions, self-organization, AFM, PSD function.

Capability of CI-Orbitrap for Gas-Phase Analysis in Atmospheric Chemistry: A Comparison with the CI-APi-TOF Technique.

Chemical ionization Orbitrap mass spectrometry (CI-Orbitrap) represents a promising new technique for gas-phase analysis in analytical and atmospheric chemistry mainly due to its very high mass resolving power. In this work, we performed the first side-by-side comparison between a CI-Orbitrap and the widely used atmospheric pressure interface time-of-flight mass spectrometry (CI-APi-TOF) using two different chemical ionization methods, i.e., acetate-ion-based (CH3COO-) and aminium-ion-based (n-C3H7NH3+) schemes. The capability of the CI-Orbitrap at accurately measuring low concentrations of gaseous species formed from the oxidation of α-pinene was explored. Although this study reveals a lack of linearity of the CI-Orbitrap when measuring product ions at very low concentrations (<1 × 106 molecules cm-3), very good agreement between both techniques can be achieved by applying a newly developed linearity correction. It is experimentally shown that the correction function is independent of the reagent ion used. Thus, accurate quantification of organic compounds at concentrations as low as 1 × 105 molecules cm-3 by the CI-Orbitrap can be achieved. Finally, by means of tandem mass spectrometry, the unique capability of the Orbitrap allows the direct determination of the binding energy of cluster ions between analyte and reagent ions, that is needed for the assessment of a chosen ionization scheme.

Association and Proton Transfer Reactions With a Series of Organic Molecules.

In this study, we present reactions of with a series of analytes (A): acetone (C3H6O), methyl vinyl ketone (C4H6O), methyl ethyl ketone (C4H8O), and eight monoterpene isomers (C10H16) using a Selective Reagent Ionization Time-of-Flight Mass Spectrometer (SRI-ToF-MS). We studied the ion-molecule reactions at collision energies of 55 and 80 meV. The ketones, having a substantially lower proton affinity than NH3, produce only cluster ions (A) in detectable amounts at 55 meV. At 80 meV, no cluster ions were detected meaning that these adduct ions are formed by strongly temperature dependent association reactions. Bond energies of cluster ions and proton affinities for most monoterpenes are not known and were estimated by high level quantum chemical calculations. The calculations reveal monoterpene proton affinities, which range from slightly smaller to substantially higher than the proton affinity of NH3. Proton affinities and cluster bond energies allow to group the monoterpenes as a function of the enthalpy for the dissociation reaction . We find that this enthalpy can be used to predict the (A) cluster ion yield. The present study explains product ion formation involving ion chemistry. This is of importance for chemical ionization mass spectrometry (CIMS) utilizing as well as (H2O) as reagent ions to quantitatively detect atmospherically important organic compounds in real-time.

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...

Depth profiling organic/inorganic interfaces by argon gas cluster ion beams: sputter yield data for biomaterials, in‐vitro diagnostic and implant applications

Argon gas cluster ion beam sources are likely to become much more widely available on XPS and SIMS instruments in the next few years. Much attention has been devoted to their ability to depth profile organic materials with minimum damage. What has not been the focus of attention (possibly because it has been very difficult to measure) is the large ratio of sputter yield for organic materials compared with inorganic materials using these sources and the special opportunities this presents for studies of organic/inorganic interfaces. Traditional depth profiling by monatomic argon ions introduces significant damage into the organic overlayer, and because sputter rates in both organic and inorganic are similar for monatomic ions the interface is often ‘blurred’ due to knock‐on and other damage mechanisms. We have used a quartz crystal technique to measure the total sputter yield for argon cluster ions in a number of materials important in medical implants, biomaterials and diagnostic devices, including polymethyl methacrylate, collagen, hydroxyapatite, borosilicate glass, soda lime glass, silicon dioxide and the native oxides on titanium and stainless steel. These data fit a simple semi‐empirical equation very well, so that the total sputter yield can now be estimated for any of them for the entire range of cluster ion energy typical in XPS or SIMS. On the basis of our total sputter yield measurements, we discuss three useful ‘figures‐of‐merit’ for choosing the optimum cluster ion energy to use in depth profiling organic/inorganic samples. For highest selectivity in removing the organic but not the inorganic material the energy‐per‐atom in the cluster should be below 6 eV. A practical balance between selectivity and reasonably rapid depth profiling is achieved by choosing a cluster ion energy having between around 3 and 9 eV energy‐per‐atom. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Controllable fabrication of amorphous Si layer by energetic cluster ion bombardment

We report on the fabrication of an amorphous Si (a-Si) thin layer by means of bombardment of a Si(100) surface using monoenergetic C60 cluster ions with energies from 50 keV to 400 keV. The C60 cluster implantation produces nanogranules on the surface of a-Si layer detected by atomic force microscopy. The structural disorder and thickness of the modified layer were identified using Raman spectrometry, ion channelling, spectroscopic ellipsometry (SE) and transmission electron microscopy (TEM). According to SE and TEM data the thickness of a-Si layer gradually increases with cluster ion energy reaching to about 30 nm in the 200 keV C60-bombarded Si sample. There is also thin layer of nanocrystalline Si found between the a-Si layer and pristine Si crystal. The obtained results represent an attractive method for creation of the a-Si layer as a functional material for opto- and nano-electronics. The study describes nanostructure created by cluster ion implantation as well as demonstrates the structural consequences of fast cluster energy dissipation in solids such as local heating and shock waves.

2pcore-level binding energies of size-selected free silicon clusters: Chemical shifts and cluster structure

The 2$p$ core-level electron binding energies of size-selected silicon cluster ions have been determined from soft x-ray photoionization efficiency curves. Local chemical shifts and global charging energy contributions to the 2$p$ binding energy can be separated, because core-level and valence-band electron binding energies exhibit the same inverse radius dependence. The experimental 2$p$ binding energy distributions show characteristic size-specific patterns that are well reproduced by the corresponding electronic density of states obtained from density functional theory modeling. These results demonstrate that 2$p$ binding energies in silicon clusters are dominated by initial state effects, i.e., by the interaction with the local valence electron density, and can thus be used to corroborate structural assignments.

Theoretical characterization of laser- and sympathetically-cooled ions in surface-electrode ion traps

Using molecular dynamics simulations we characterize theoretically Coulomb clusters of laser- and sympathetically-cooled ions in a five-wire surface-electrode ion trap. We show that the asymmetry of the trapping potential leads to significantly different cluster structures and ion energy distributions in comparison to conventionally used linear Paul traps and to an asymmetric segregation of the ions in bi-component Coulomb clusters. We explore the impact of our results on the implementation of sympathetic cooling of molecular ions in surface-electrode traps and discuss possible challenges for the realization of such experiments.

X-ray photoelectron spectroscopy study of polyimide thin films with Ar cluster ion depth profiling

X-ray photoelectron spectroscopy depth profiling of polyimide thin films on silicon substrates using an Ar cluster ion beam results in an extremely low degradation of the polyimide chemistry. In the range from 2.5 to 20 kV, a lower cluster ion energy produces a lower sputter induced damage to the polymer and results in an improved polyimide to silicon interface width. The sputtering rates of the polyimide are found to increase exponentially with an increase in the Ar cluster ion energy.

The emission process of secondary ions from solids bombarded with large gas cluster ions

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 60 keV. 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 Si n + (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.

Classical interatomic potential model for Si/H/Br systems and its application to atomistic Si etching simulation by HBr+

An interatomic potential model for Si/H/Br systems has been developed for performing classical molecular dynamics simulations of Si etching processes by HBr plasmas. The potential form used here is the improved Stillinger–Weber potential function involving a correction term in order to predict the reaction dynamics more accurately. Parameters were determined based on ab initio data obtained from previous works on Si/Br systems by [Ohta et al. J. Appl. Phys. 104, 073302 (2008)]. By using this model, we performed Si etching simulations by monoenergetic HBr+ and Br+ beams. H atom has about 1% of the translational energy of cluster ions due to the small H/Br mass ratio (=1.0/79.9); therefore, H atoms in HBr+ behave like H radicals. This results in higher etch yields by HBr+ than those by Br+ in the low-energy region (less than 100 eV). This can be attributed to the chemical enhancement induced by the formation of Si–H bonds. On the other hand, yields by HBr+ and Br+ were almost the same in the high-energy region (more than 100 eV), where physical sputtering was relatively dominant and the contribution of H was small.

High depth resolution SIMS analysis using metal cluster complex ion bombardment

SIMS depth profiles were measured using metal cluster complex ions of Ir4(CO)7+ as a primary ion beam in order to obtain high depth resolution. Depth resolution was evaluated as a function of primary ion species, energy and incident angle using a multiple boron delta-doped silicon sample. The depth resolution obtained using cluster ion bombardment was considerably better than that obtained by oxygen ion bombardment under the same bombardment condition due to reduction of atomic mixing in the depth. The best depth resolution was 0.9 nm under the bombardment condition of 5 keV, 45° with oxygen flooding, which approaches the value measured with state of the art SIMS analyses. However, depth resolution was not improved by decreasing the cluster ion energy (less than 5 keV), even though the roughness of the sputtered surface was suppressed. The limit of depth resolution improvement may be caused by a carbon cover-layer that prevents the formation of surface oxide that buffers atomic mixing. To overcome this issue, it will be necessary to eliminate carbon from the cluster ion.

Cluster size dependence on energy and velocity distributions of gas cluster ions after collisions with residual gas

Cluster size dependence on energy distribution and velocity of gas cluster ion beam (GCIB) after collision with residual gas was studied using size-controlled GCIB system to make it clear the irradiation energy and cluster size under poor vacuum conditions. From the energy distribution measurements, an Ar cluster ion which was accelerated at high voltage (30kV) was easier to lose its kinetic energy than that accelerated at low voltage (10kV). Also, at the same acceleration voltage, the smaller Ar cluster ion lost its energy rapidly than larger one. These results indicated that the energy loss during beam transport is determined by the velocity of cluster ions. If cluster was originated from the gas which has strong binding force such as CO2, large cluster ions kept their kinetic energy at constant even after frequent collisions with residual gas.

SIMS depth profile study using metal cluster complex ion bombardment

SIMS depth profiles using a metal cluster complex ion of Ir4(CO)7+ were studied. An unusual increase of the sputtering yield under the condition of small incident angle may be attributed to the suppression of taking oxygen from flooding O2 by the formation of a carbon cover-layer derived from Ir4(CO)7+ ion. Even though the roughness of the sputtered surface is small, the depth resolution was not improved by decreasing the cluster ion energy to less than 5keV, because the carbon cover-layer prevents the formation of surface oxide that buffers atomic mixing. To overcome this issue, it will be necessary to eliminate carbon from the cluster ion.

The effect of incident cluster ion energy and size on secondary ion yields emitted from Si

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.

Li ion scattering from Au nanoclusters on TiO2(110)

The neutralization of low energy 7Li+ scattered from Au nanoclusters deposited on TiO2(110) was measured with time-of-flight spectroscopy as a function of cluster size, emission angle, and ion energy. The neutralization shows maxima for cluster diameters approximately 3 nm, and again for thick Au films. The data are compared to previous experiments with Na projectiles. Possible explanations of the observed effects are discussed.

Infrared spectroscopy of the Li+(H2O)Ar complex: the role of internal energy and its dependence on ion preparation

The internal energy or effective temperature of cluster ions has become an important issue in characterizing the structures observed in these species. This report considers the role played by the method of ion preparation (laser vaporization-supersonic expansion versus ion impact-evaporative cooling) in governing the internal energy of a specific species, Li(+)(H(2)O)Ar. Vibrational predissociation spectroscopy of the O-H stretch modes revealed rotational features, which were used to characterize the structure and effective rotational temperature of the cluster ion. In addition, the impact of the lithium ion on the H(2)O molecule was analyzed in terms of the vibrational frequency shifts, relative IR intensities, and H(2)O geometry.

ITO surface smoothing with argon cluster ion beam

Argon gas cluster ion beam (GCIB) was employed to improve the surface smoothness of indium tin oxide (ITO) substrates. The dependence of the smoothness as well as of the sputtered depth on cluster ion energy and dose has been studied. Results show that relatively low-energy (10keV) clusters with mean size of 2000 Ar atoms are sufficient to reduce the mean roughness of the ITO surface to about one fourth of its initial value.Organic electroluminescent (EL) devices (α-NPD/Alq3/Mg–Ag) were formed on the smoothed surfaces and a considerable improve of the devices’ EL efficiency was observed.

Analysis of charge, mass and energy of large gas cluster ions and applications for surface processing

In a previous study averages of +3.2 charges, 64keV energy and 10,400 atoms were measured for a high intensity Ar gas cluster ion beam [D.R. Swenson, Nucl. Instr. and Meth. B 222 (2004) 61]. At this energy multiple collisions with Ar gas atoms are observed to progressively abrade the clusters. The mass loss is consistent with a simple theory that assumes thermalization of the collision energy followed by evaporation. The measurements are important for cluster–surface interactions because they allow cluster energy and dose to be measured for multi-charged clusters. It is shown that higher energy clusters that cause larger craters are more affected by the cluster–gas collisions, and this effect can be beneficial when using a cluster beam to smooth a surface.

Size and energy distribution of gas cluster ion beam measured by energy resolved time of flight mass spectroscopy

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.