Damage Cross Section Research Articles

Amorphization of sapphire induced by swift heavy ions: A two step process

Single crystals of α-Al2O3 were irradiated with 0.7MeV/amu Xe ions at the GANIL accelerator with fluences extending from 5×1011 to 2×1014ions/cm2. The samples were characterized by Rutherford Backscattering Spectrometry in Channelling geometry (RBS-C) and surface profilometry for swelling measurements. RBS-C analysis evidence the presence of two incident ion effects on sapphire targets: the creation of partial disorder that saturates at ∼40% with a damage cross section of 7×10−14cm2, followed by a complete disorder starting from the surface and appearing at fluence larger than ∼1.2×1013ions/cm2. A correlation between relative disorder and swelling is observed. This study is in agreement with the appearance of amorphization of α-Al2O3 at high fluence as observed by Aruga et al. [T. Aruga, Y. Katano, T. Ohmichi, S. Okayasu, Y. Kazumata, Nucl. Instr. Meth. Phys. Res. B 166–167 (2000) 913–919].

Effects of dynamic recovery on amorphization kinetics in 6H-SiC

Irradiation-induced amorphization in 6H-SiC has been previously studied as a function of irradiation temperature for electrons and ions ranging from Ne to Au. Analysis of these data with a dynamic model for amorphization reveals that the amorphization dose increases and the critical amorphization temperature decreases as the ratio of in-cascade ionization to displacement rates increases. Model fits to the data yield the ratio of radiation-induced recovery cross section, σr, to damage cross section, σd, and an activation energy of 0.12±0.01eV for irradiation-induced recovery. The critical temperature exhibits a linear dependence on 1/ln(σr/σd), consistent with the model.

Fragmentation of molecular compounds on silicon wafers and low dielectric constant materials studied by time‐of‐flight secondary ion mass spectrometry using a polyatomic ion source

AbstractRecent time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) studies using primary cluster ion sources such as Aun+, SFn+, Bin+ or C60+ have shown polyatomic ions to be more appropriate for the detection of high mass molecular secondary ions than monoatomic ion sources like Ga+, thanks to secondary ion yield and ion formation efficiency enhancements.This work is part of a study aiming at improving molecular compound quantification at the surface of microelectronics industry substrates by taking advantage of a polyatomic ion source in ToF‐SIMS analysis. It focuses on the case of a phthalate‐related contamination. Fundamental parameters like secondary ion yield, damage cross section and secondary ion efficiency were studied as a function of the size and the energy of the primary ions. The substrate composition influence on the ToF‐SIMS results was also studied by comparing several substrates of interest in the microelectronics industry such as silicon wafers and low dielectric constant materials SiOxCyHz.Phthalate‐related secondary ions detected at the surface of the contaminated surfaces were compared and a fragmentation pathway of the di‐isononyl phthalate (DNP) molecule was determined. A drastic improvement of the secondary ion yield was provided when using a polyatomic ion source. Furthermore, a clear increase in damage cross section was observed as a function of the secondary ion size for a given Bin primary ion as well as an increase for a given fragment as a function of the number of Bi atoms in the Bin aggregate. This led to a lower static limit when taking into account higher phthalate fragments and primary ions of larger size. Copyright © 2008 John Wiley & Sons, Ltd.

Primary ion fluence dependence in time-of-flight SIMS of a self-assembled monolayer of octadecylphosphonic acid molecules on mica discussion of static limit

By using a self-assembled monolayer of octadecylphosphonic acid molecules, CH3(CH2)17PO(OH)2, on mica as a model of the “soft” materials, such as self-assembled monolayers (SAMs) and multilayers in many biological systems as well as artificially engineered molecular electronic systems, we have examined the effects of primary ion fluence on time-of-flight secondary ion mass spectrometry (TOF-SIMS) of the technologically important model. Our measurements clearly show that although the intensity per unit primary ion fluence of most atomic ions and many small fragment ions do not vary by more than 10% for the fluence range of 1010–1013 cm–2, the intensity of the parent molecular ion can drop by two orders of magnitude in this fluence range. While the changes are different for the primary ion beams of Bi3+ (25 keV, 45°), Bi+ (25 keV, 45°), and Ar+ (8 keV, 45°), they are all substantial, with the damage cross section induced by the Bi3+ beam being the largest (6 000 Å2). Since different secondary ions have quite different intensity changes, the analytical results derived from TOF-SIMS can vary significantly by the time and duration of the measurements in the TOF-SIMS experiment. Therefore, our results suggest that for TOF-SIMS of molecular layers such as SAMs, the primary ion fluence condition should be recorded and reported. In general, the validity of the static condition becomes questionable when the cumulative primary ion fluence exceeds 1 × 1011 cm–2.Key words: SIMS, static SIMS, TOF-SIMS, soft materials, self-assembled monolayer, bilayer, surface of biological materials.

Low-Energy Electron-Induced Processes in Fluorinated Copper Phthalocyanine Films Observed by F- Desorption: Why So Little Damage?

As an indication of damage induced by hot electrons in an organic electronic material, the desorption of F- ions from a thin perfluorinated copper phthalocyanide film on SiO2 under low-energy (0-25 eV) electron impact has been recorded mass spectrometrically. Yields and damage cross sections are very low. No strong features due to negative ion resonances are found in the electron energy dependence of the desorption yield; rather the yield function rises from a threshold at about 5-6 eV continuously (with some weak structure) throughout the measured range. We discuss these findings in terms of the electronic structure of the film, as well as parameters influencing the relevant bond breaking process. We emphasize the strong influence of energy redistribution, which quenches normally long-lived negative ion resonances and selects localized and strongly repulsive excitations, as often observed in electronically induced bond breaking at surfaces. The improved understanding should be helpful in the selection of low-damage materials for organic semiconductor devices and for selection of operation parameters.

Cluster ion sputtering: molecular ion yield relationships for different cluster primary ions in static SIMS of organic materials

AbstractAn analysis is made of the molecular secondary ion yield (MSIY) variation with primary ion source mass and number, n, of constituent particles. The theory is based on the linear cascade model, extended into the nonlinear regime for higher deposition energy densities using Sigmund and Claussen's thermal spike model. The analysis is generalised to remove sample specificity and is evaluated for light, organic materials. It provides the MSIY dependence for this material as a function of the primary ion particle parameters. This is applied to the data of Kersting et al. and of Kollmer for the (M − H)− de‐protonated secondary ion yields, Y(M − H)−, from Irganox 1010 for Ga+, Cs+, SF5+, Au+, Au2+, Au3+ and C60+ primary ions. The previously postulated dependence of Y(M − H)− on the sputtering yield squared is validated. This formulation permits the prediction of Y(M − H)− for new primary ions such as Bin+ and C70+. It is shown that further MSIY gains of possibly up to an order of magnitude are attainable. For analysis, raising the MSIY is extremely helpful but it is the efficiency (the ratio of the MSIY to the disappearance cross‐section) that is critical. The distinction between the damage and disappearance cross‐sections is clarified and a description involving both terms and correlating with data for all ions is given. It is shown that the efficiency increases with Y(M − H)−, initially linearly and finally with a square root dependence. The chemical nature of the primary ion species is shown to be relatively unimportant in these processes. © Crown copyright 2007. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.

Water on a close-packed Ru surface: A high-order commensurate adlayer with a high sensitivity towards electron beam damage

Water bilayers deposited on Ru(0001) have become a benchmark system for water interacting with solid surfaces. Here, we report diffraction data recorded using He-atom scattering demonstrating the presence of an only weakly disturbed bilayer of ${\mathrm{D}}_{2}\mathrm{O}$ on Ru. Results obtained by this method cannot be affected by e-beam damage which so far made the experimental determination of the structure of this important model difficult. We find a high-order commensurate, stable water bilayer exhibiting a structure which is not compatible with any of the previously published structural models for this system. The cross section for e-induced damage has also been determined.

Damage cross-section of carbon cluster ions [formula omitted] ( n = 1–5) collision with polycarbonate

Polycarbonate films were irradiated by MeV ions, including carbon clusters C n + ( n = 1–5) with the same atomic dose and energy, Cl +, Ti +, and Ni +. UV–VIS–NIR spectrophotometer was employed to detect the optical absorption of irradiated samples. From the absorption spectrum, it is found that the damage cross-section of samples irradiated by carbon clusters increases non-linearly with the increase in cluster size. It should be induced by the collective effect and the non-linear effect of cluster ions. Attenuated total reflectance was employed to analyze the change of chemical bonds on the surface of samples. Some new bonds such as –OH are formed.

Spallation Radiation Damage Calculations and Database: Cross-Section Discrepancies between the Codes

Abstract A radiation damage database at NCSU is described that contains, at present, cross sections for damage energy, displacements, helium, and hydrogen. For neutrons and protons at 20-3200 MeV energies, the targets include 23 target elements from Mg to U and eight practical alloys. The underlying calculations employ Bertini, ISABEL, and CEM2k intranuclear cascade models as provided within MCNPX, three level-density formulations (GCCI, HETC, and Jülich), and multistage pre-equilibrium model (MPM) on and off. The database also includes radiation damage cross sections for lower-energy neutrons and protons, as obtained from LA150, SPECTER, ENDF, and SRIM. Examples of the database contents are provided with regard to damage energy and displacement cross sections for neutrons on Al, Fe, and W. Also, neutron flux and displacement rate calculations are described for neutrons on Fe and the 316 stainless steel mercury container vessel at SNS. In addition, discrepancies between the codes are discussed.

Secondary ion emission from polymer layers by atomic and molecular ion bombardment: Data evaluation based on linear-cascade sputtering theory

This paper constitutes an attempt to rationalise impact-energy dependent yields of molecular secondary ions emitted from polymer samples under bombardment with atomic and molecular primary ions. The evaluation was based upon a comparison with sputtering yields calculated from linear-cascade sputtering theory, including threshold effects. To explore general trends, sputtering yields for carbon, silicon and silver were calculated under impact of normally incident C, F, S, Ga, Xe, Au, SF 5, C 11, C 60 and Au 5. The yields of carbon, for example, bombarded with C 60 are larger than for Ga by factors of ∼5 and ∼10 at 10 and 100 keV, respectively. However, owing to the fact that the effective threshold energy for sputtering increases with the number of constituents of the projectile, the yields for molecular ion impact start to exceed the yields for atomic ions only at energies between 0.5 and 5 keV. The analysed experimental results relate to molecular ion emission from one monolayer (1 ML) and 9 ML films of polymethacrylate on silver bombarded with Xe and SF 5 ions at energies E between 0.5 and 10 keV. Comparison of (initial) secondary ion yields S + ( m/ z 143) with calculated sputtering yields suggests that S + constitutes the sum of two contributions. The first, labelled S lo + , prevails at low energies and appears to reflect molecule ejection due to the mean effect of nuclear energy deposition (“ordinary” linear-cascade sputtering). The second contribution, S hi + , dominates at E > 1.5 keV, increases with a high power of E, but does not correlate with the calculated sputtering yield. It is suggested that S hi + is a measure of those impact events which occasionally generate a very high energy density at the surface, thus providing optimum conditions for very efficient ejection of molecules that are located at the rim of the agitated area. The SF 5/Xe secondary ion yield ratios are distinctly different for the two contributions, only about 0.3 for S lo + but ∼4 (1 ML) and ∼20 (9 ML) for S hi + . The pronounced secondary ion “yield enhancement” frequently reported in the literature for molecular versus atomic ion bombardment appears to be due to an enlargement of the S hi + contribution, more so the higher the impact energy and the more massive the projectile. The total (integrated) secondary ion yields, estimated by making use of the reported damage cross sections, were found to be the same for SF 5 bombardment of the 1-ML and the 9-ML samples. This finding calls for more attention towards obtaining high secondary ion yields at minimum sample consumption.

Polyethylene terephthalate (PET) bulk film analysis using C 60+, Au 3+, and Au + primary ion beams

The damage characteristics of polyethylene terephthalate (PET) have been studied under bombardment by C 60 +, Au 3 + and Au + primary ions. The observed damage cross-sections for the three ion beams are not dramatically different. The secondary ion yields however were significantly enhanced by the polyatomic primary ions where the secondary ion yield of the [M + H] + is on average 5× higher for C 60 + than Au 3 + and 8× higher for Au 3 + than Au +. Damage accumulates under Au + and Au 3 + bombardment while C 60 + bombardment shows a lack of damage accumulation throughout the depth profile of the PET thick film up to an ion dose of ∼1 × 10 15 ions cm −2. These properties of C 60 + bombardment suggest that the primary ion will be a useful molecular depth profiling tool.

ToF–SIMS analysis of a fluorocarbon-grafted PET with a gold cluster ion source

Cluster ions have been recognized as a superb primary species in time of flight secondary ion mass spectroscopy (ToF–SIMS) compared with monatomic primary ions, as they significantly enhance the secondary ion yields from bulk samples. Self-assembled monolayers provide an important system for studying the fundamental mechanism involved in the yield enhancement. We used a gold cluster ion source to analyze a new type of self-assembled monolayer: a fluorocarbon-grafted polyethylene terephthalate. In addition to the structure details, which helped to understand the grafting mechanism, ToF–SIMS analysis revealed that fluorocarbon secondary ion yield enhancements by cluster ions were due to the enhanced sputter efficiency. A larger information depth may also be expected from the enhancement. Both mathematical definitions of damage cross-section and disappearance cross-section were revisited under a new context. Another cross-section parameter, sputter cross-section, was introduced to differentiate the beam induced sputter process from damage process.

Molecular Depth Profiling with Cluster Ion Beams

Peptide-doped trehalose thin films have been characterized by bombardment with energetic cluster ion beams of C60+ and Aux+ (x = 1, 2, 3). The aim of these studies is to acquire information about the molecular sputtering process of the peptide and trehalose by measurement of secondary ion mass spectra during erosion. This system is important since uniform thin films of approximately 300 nm thickness can be reproducibly prepared on a Si substrate, allowing detailed characterization of the resulting depth profile with different projectiles. The basic form of the molecular ion intensity as a function of ion dose is described by a simple analytical model. The model includes parameters such as the molecular sputtering yield, the damage cross section of the trehalose or the peptide, and the thickness of a surface layer altered by the projectile. The results show that favorable conditions for successful molecular depth profiling are achieved when the total sputtering yield is high and the altered layer thickness is low. Successful molecular depth profiles are achieved with all of the cluster projectiles, although the degree of chemical damage accumulation was slightly lower with C60. With C60 bombardment, the altered layer thickness of about 20 nm and the damage cross section of about 5 nm2 are physically consistent with predictions of molecular dynamics calculations available for similar chemical systems. In general, the model presented should provide guidance in optimizing experimental parameters for maximizing the information content of molecular depth profiling experiments with complex molecular thin film substrates.

Infrared studies of swift heavy ion irradiated C60 thin films

The modification of fullerenes vibrational properties by energetic ion irradiation is investigated, using Fourier transform infrared (FTIR) spectroscopy . The C60 thin films have been irradiated with 200MeV Au ions at fluence from 1×1012 to 1×1013ions/cm2. It is observed that 577cm−1 mode is the most sensitive but 527cm−1 IR active mode is more resistive for swift heavy ion irradiation. To understand change in the molecular structure of fullerene molecule under swift heavy ion (SHI) irradiation, we determined damage cross-section for all four T1u (527, 577, 1183, 1428cm−1) IR active modes. It is observed that damage cross-section (σ) is different for different vibrational modes. The effective radii (r) of the damage cylindrical zone are also evaluated.

The Aun cluster probe in secondary ion mass spectrometry: influence of the projectile size and energy on the desorption/ionization rate from biomolecular solids

A Au-Si liquid metal ion source which produces Au(n) clusters over a large range of sizes was used to study the dependence of both the molecular ion desorption yield and the damage cross-section on the size (n = 1 to 400) and on the kinetic energy (E = 10 to 500 keV) of the clusters used to bombard bioorganic surfaces. Three pure peptides with molecular masses between 750 and 1200 Da were used without matrix. [M+H](+) and [M+cation](+) ion emission yields were enhanced by as much as three orders of magnitude when bombarding with Au(400) (4+) instead of monatomic Au(+), yet very little damage was induced in the samples. A 100-fold increase in the molecular ion yield was observed when the incident energy of Au(9) (+) was varied from 10 to 180 keV. Values of emission yields and damage cross-sections are presented as a function of cluster size and energy. The possibility to adjust both cluster size and energy, depending on the application, makes the analysis of biomolecules by secondary ion mass spectrometry an extremely powerful and flexible technique, particularly when combined with orthogonal time-of-flight mass spectrometry that then allows fast measurements using small primary ion beam currents.

The Magic of Cluster SIMS

Low topography, enhanced high-mass ion yields, and low damage cross sections have researchers thinking about new applications that may lead to the discovery of new biology.

Modification and Stability of Aromatic Self-Assembled Monolayers upon Irradiation with Energetic Particles

We have studied ion and electron irradiation of self-assembled monolayers (SAMs) of 2-(4'-methyl-biphenyl-4yl)-ethanethiol (BP2, CH3-C6H4C6H4CH2CH2-SH), phenyl mercaptan (PEM, C6H5CH2CH2-SH), and 4'-methyl-biphenyl-4-thiol (BP0, CH3-C6H4C6H4-SH) deposited on Au(111) substrates. Desorption of neutral particles from PEM/Au and BP2/Au was investigated using laser ionization in combination with mass spectrometry. The ion-induced damage of both BP2 and PEM SAMs is very efficient and interaction with a single ion leads to the modification of tens of molecules. This feature is the result of a desorption process caused by a chemical reaction initiated by an ion impact. Both for ions and electrons, experiments indicate that the possibility for scission of the Au-S bond strongly depends on the chemical nature of the SAM system. We attribute the possible origin of this effect to the orientation of the Au-S-C angle or adsorption sites of molecules. The analysis of electron-irradiated PEM/Au and BP2/Au, using ion-initiated laser probing, enabled measurements of the cross section for the electron-induced damage of the intact molecule or specific fragment. Analysis of electron-irradiated BP0/Au by using time-of-flight secondary ion mass spectrometry (TOF-SIMS) provides direct evidence for the quasi-polymerization process induced by electron irradiation.

Structural stability of C60 films under irradiation with swift heavy ions

In order to investigate the structural stability of fullerene (C60) under swift heavy ion irradiation, the irradiation experiments of thin C60 films were performed with 22MeV/amu Fe56 ions delivered by HIRFL at Lanzhou in China. The irradiated C60 films were analyzed by means of Raman scattering and Fourier transform infrared (FTIR) spectroscopes. The analysis results indicated that the damage cross-sections σ of the C60 molecule deduced from the data of the Raman spectra are between 1.1 and 4.5×10−14cm2 for the electronic energy loss from 3.5 to 8.7keV/nm and electronic energy transfer dominates the damage process of C60 films. The partial recovery of the damage in irradiated C60 films at certain electronic energy loss is attributed to an annealing effect of strong electronic excitation.

Degradation of the scintillation yield of anthracene under high-fluence carbon ion beams

We have measured the deterioration of the scintillation yield of anthracene samples under carbon beams at nine different energies between 25 and 100 MeV . The real-time measurement of the scintillation yield has been performed by means of an optical fibre connected to a compact photon counting head. Results are interpreted by the Birks model from which we deduce the fluence needed to reduce the scintillation yield by a factor of two and also an estimation of the damage cross-sections of scintillation centres.

Damage cross-sections for MeV energy He ion induced hydrogen ejection in polymers—material structure effects

Using the elastic recoil detection analysis (ERDA) method for hydrogen analysis, a 4He+ ion beam was used simultaneously for irradiating samples and as a tool to measure the hydrogen desorption yield as a function of irradiation dose. The influence of molecular structure on helium-induced desorption is studied for different polymers. The dose–response curves of hydrogen released from irradiated structures are presented and used to determine the damage cross-sections. The deduced desorption extent for a single impact is of the order of a few Angstroms, revealing localized regions of desorption. Hydrogen desorption is found to be sensitive to chemical composition of the target. The overall experimental data of the hydrogen desorption yield are described by the same function of the type Y (ϕ) = (C/ϕ n ) exp (−σ ϕ) where ϕ is the irradiation dose and C and n are a fitting parameter. The first part of the function describes ‘prompt ejection’, predominant at lower irradiation dose where the created latent tracks remain separated. The exponential term accounts for the ‘thermal ejection’ process activated by ion-track overlapping involved at higher irradiation doses. A threshold dose is found that separates the two regimes and above which the overlapping tracks form a highly heated condensed gas and activate chemical processes. Chemical modifications have been studied using infrared-absorption spectroscopy, which reveal the formation of stable molecules that could desorb intact.