Damage Cross Section Research Articles

Structural and electrical damage induced by high-energy heavy ions in SiO2/Si structures

The structural and electrical properties of SiO2/Si structures irradiated by high-energy (≳0.5 GeV) Xe and Ni ions have been investigated. Structural analysis of the irradiated SiO2 films, performed with infrared spectroscopy, points to atomic displacements and broken and strained Si—O bonds induced by the irradiation. Using ir data, the damage cross section of the Xe and Ni ions has been deduced. The values are of about 8×10−13 and 6×10−14 cm2 for, respectively, 762 MeV Xe and 551 MeV Ni ions. Electrical measurements of irradiated SiO2/Si structures show an increase of the interface-state density Dit and of the oxide trapped-charge density N0t with the ion fluence. These results are compared with defects induced by heavy-ion irradiation in bulk silica and by light particle radiation in silicon dioxide. Electrically active point defects have been detected in irradiated silicon and are associated with vacancy complexes.

Amorphization in Gd2Ti2O7 and CaZrTi2O7 irradiated with 3 MeV argon ions

Irradiation of Gd2Ti2O7 and CaZrTi2O7 with 3 MeV Ar+ ions results in the simultaneous expansion of the unit-cell volume and radiation-induced amorphization. The damage cross sections for amorphization, which were determined hy X-ray diffraction, are 0.023 nm2 and 0.014 nm2, respectively. These damage cross sections are relatively low and suggest some inherent resistance of these structures to amorphization, in agreement with previous studies. Transmission electron microscopy and electron diffraction confirmed the amorphous character of both materials at high fluences. Raman spectroscopy indicated a decrease in scattered intensity with ion fluence for the Raman-active vibrational modes of Gd2Ti2O7 and CaZrTi2O7. In the case of Gd2Ti2O7, increases in both linewidth and wavenumher with ion fluence also were observed.

High energy heavy ion irradiation damage in yttrium iron garnet

We have studied the damage in ferrimagnetic yttrium iron garnet, Y3Fe5O12 or YIG, produced by energetic heavy ion bombardment, for which the electronic stopping power is much higher than the nuclear stopping power. Epitaxial thin films of YIG on (111)-Gd3Ga5O12 substrates were thus irradiated at room temperature with 50 MeV 32S, 50 MeV 63Cu, 235 MeV 84Kr, and with 59 MeV, 185 MeV and 792 MeV 132Xe ion beams. The film thicknesses were always smaller than the ion mean projected ranges, in order to avoid implantation effects in the layers. The resulting damage was then studied by high resolution X-ray diffraction, channeling Rutherford backscattering (RBS) spectroscopy and room temperature magnetization measurements.After these ion irradiations, the structural as well as the ferrimagnetic long-range orders are progressively destroyed. X-ray measurements on 84Kr irradiated samples show the presence of compressive lateral macrostresses in the films due to the coexistence of crystalline and disordered phases. These stresses are partly relaxed away at high fluences, when the amount of disordered phase is high enough (around 45%).Cross section data for this damage process are deduced from the RBS and 300 K saturation magnetization measurements for six different values of the electronic energy loss, between 7 and 27 MeVμm−1. The damage cross section increases nonlinearly as a function of the electronic stopping power, then seems to level off above 22 MeV μm −1. However the comparison with previous works indicates that the electronic stopping power might not be the only key-parameter in this process, where the ion beam energy parameters might play some role.

High-energy irradiation of magnetic insulators by lead ions: appearance of a plateau in the damage efficiency

Lead irradiation with an incident energy of 5.6 GeV has been used to study the induced damage in magnetic insulators (Y 3Fe 5O 12, BaFe 12O 19, NiFe 2O 4) for high values of the electronic stopping power (d E/d x). Using Mössbauer spectrometry, the damage efficiency ϵ = A/(d E/d x), where A is the damage cross section, is extracted and compared to previous results. Saturation of the damage efficiency is confirmed and in the range of d E/d x studied in our experiments the damage yield is proportional to the deposited energy. The damage efficiency in Y 3Fe 5O 12 and BaFe 12O 19 is fitted by a saturation law using the relation ϵ = ϵ max(1 − exp( − k(d E/d x) n )). A unique value of n = 4 is extracted while ϵ maxand k depend on the irradiated materials. ϵ max leads to a value indicating that the maximum damage efficiency arises when 5 eV is deposited on each atom. Using n = 4, this saturation law was applied with success to the spinel NiFe 2O 4 and to the amorphous metallic alloy a-Fe 85B 15.

Influence of the substrate temperature on the latent track damage cross section in magnetic insulators

As the latent track damage cross section and defect morphology are well known in magnetic insulators, irradiations of such inorganic materials (Y3Fe5O12, BaFe12O19 and SrFe12O19 in two different crystalline orientations) have been undertaken at different substrate temperatures. Xenon irradiations were performed at the following substrate temperatures 20, 100, 330 and 600 K and krypton irradiations only at 100 and 300 K. In the range of electronic stopping power dE/dx for which the damage morphology is known to be cylindrical and continuous, the latent track damage cross section is the same within the experimental errors whatever is the irradiation temperature between 20 and 300 K while according to the material annealing can occur at 600 K. In the range of dE/dx for which the damage morphology is discontinuous (spherical isolated defects or discontinuous cylindrical ones) the damage cross section is bigger at 300 K than at 100 K.

Correlation of mechanical property changes in neutron-irradiated pressure vessel steels on the basis of spectral effects

Comparisons are made of tensile data on specimens of A212B and A302B pressure vessel steels irradiated at low temperatures (40–90°C) and to low doses ( < 0.1 dpa) with 14 MeV D-T fusion neutrons in the Rotating Target Neutron Source (RTNS-II), with fission reactor neutrons in the Omega West Reactor (OWR) and the Oak Ridge Research Reactor (ORR), and with the highly thermal spectrum at the pressure vessel surveillance positions of the High Flux Isotope Reactor (HFIR). For each neutron spectrum, damage cross sections are determined for several defect production functions derived from atomistic computer simulations of collision cascades. Displacements per atom (dpa) and the numbers of freely migrating defects are tested as damage correlation parameters for the tensile data. The data from RTNS-II, OWR and ORR correlate fairly well when compared on the basis of dpa, but the data from HFIR show that only about one sixth as many dpa are needed to produce the same radiation-induced yield stress changes as in the other neutron spectra. In the HFIR surveillance position a significant fraction of the displacements is produced by recoils resulting from thermal neutron captures. Having energies of about 400 eV, these recoils are much more efficient per unit energy at producing freely migrating defects than the high energy recoils responsible for most of the displacements in the other neutron spectra considered. A significantly better correlation of data from HFIR with those from the other spectra is achieved when the property changes are compared on the basis of the production of freely migrating self-interstitial defects. This parameter may better represent the defects participating in the radiation strengthening process in this temperature and fluence regime.

Investigation of Beam Energy Threshold and Atom Diffusion Effects in Ionization Damage of Organic Molecular Crystals

The electron beam damage cross section σ(E) in thin aromatic molecular crystals has an appearance threshold near lkeV beam energy shown in fig. 1. By contrast no such threshold appears (fig. 2) for damage in sufficiently thin crystals of much more sensitive non-aromatic molecules. We conclude that the usually dominant valence excitation damage mechanism is suppressed by the aromatic π-electron screening, leaving the less probable carbon K-shell ionisation process as the key damage event. Alternative explanations based on critical momentum transfer to whole molecules in these weakly bonded crystals could also give a threshold effect but its position in energy would increase with the mass of the molecule which is contrary to observation.Quantitative investigation of this hypothesis is complicated by strong scattering and energy loss which can prevent the beam penetrating deeper layers in the crystal with sufficient energy to damage them. The results have therefore been simulated by Monte Carlo methods which explain well the dependence of the damage cross sections on both beam energy and crystal thickness.

Low-energy displacement damage and the effect on the AEM of Ceramics

The observation that the signal from light elements such as carbon, oxygen, and nitrogen decreases in strength with time is to be expected for displacement in ceramic materials at high voltage, not only because the momentum transfer from an electron is more favorable, but also because the lattices are often full of defects. Even though the sensitivities of these materials can be below that of close parked metals at high voltage, during analytical electron microscopy the beam currents are sufficiently intense that the effect can be substantial. The loss rates for the signal are however quite predictable in the early stages and need not interfere with quantitative assessments of composition.An example of the loss of carbon signal from titanium carbide is shown in Figure 1 and a determination of the overall cross-section for carbon loss at 100 keV indicates a value close to 0.3 barns. This is about the cross-section for carbon displacement at 20 eV which is a conservative estimate of the binding energy for carbon in the lattice. Early experiments on vanadium carbide (Venables, 1969) indicate a similar overall cross-section however the threshold energy for the electrons to induce the damage is about only 5 eV. These results are consistent with the transfer of about 5 eV from an incident electron inducing a very small displacement of the carbon atom, of the order of an interatomic distance, with a damage cross-section of about 200 barns. Since the process needs to be repeated several times before the carbon atom is lost from the specimen the measured cross-section is proportionality reduced.

Electron beam chemistry in solid films of poly(vinyl alcohol): exposures under vacuum and under nitrogen at atmospheric pressure; irradiation monitored using infrared spectroscopy

Thin films of poly(vinyl alcohol) (PVA) were exposed to a 25-kV electron beam under high vacuum conditions and to a 175-kV electron beam at atmospheric pressures of N{sub 2}. The decomposition of PVA by the electron beam sequentially formed materials that had polyketone- and polyethylene-like structures, respectively. Contrary to previous reports we show that the ketone groups formed as a result of the electron beam exposure are not due to an oxidation step by molecular oxygen. Damage cross sections for the electron beam decomposition (at 25 kV) were determined for PVA and the polyketone, and G values were determined for decomposition of {minus}OH groups and formation of ketone functional groups.

Damage of YBa 2Cu 3O x by ion irradiation

Specimens of high- T c superconductor YBa 2Cu 3O x have been irradiated with Si ions (7 MeV) up to 10 ions/nm 2. Monolayers of fine particles (less than 5 ω size) were prepared on metal plates and X-ray diffraction patterns were taken before and after the irradiations. Intensities of all diffraction peaks decrease continuously with increase in fluence with a damage cross section of 0.21 nm 2 without observation of a critical or threshold fluence. A 50% loss in crystallinity is observed at ∼ 3.6 eV/atom (0.12 dpa) although the rate of amorphization may increase beyond a fluence of ∼ 4 ions/nm 2. Bragg diffraction peaks have disappeared and amorphization is complete by ≈10 eV/atom (0.33 dpa). Peak positions shift toward lower 2θ values indicating lattice expansion contributed to by point defects. There is a gradual transformation from orthorhombic toward tetragonal structure with the b 0 parameter changing very little. c 0 increasing by ≈ 0.6%, and α 0 also increasing by ≈ 1% to approach b 0. The damage cross section of the tetragonal phase is larger than that of the orthorhombic phase.

Radiation damage of lithium ceramics by ion bombardment

Lithium compounds are being considered as fusion reactor breeder blanket ceramics. The present studies will examine the stability of the Li-compounds to radiation damage effects, and to the formation of non-crystalline phases. Ion bombardment studies have been carried out to determine damage cross-sections of the crystal structures of Li 2SiO 3, Li 2ZrO 3 to 7 MeV Si ions. Monolayers of fine powders, less than 5 μ particle size, are examined by X-ray diffraction and scanning electron microscopy before and after irradiation. The lithium compounds damage readily becoming largely non-crystalline by 4 ions/nm 2 with damage cross-sections of 0.8 ± 0.1 nm 2 for Li 2SiO 3 and 0.66 + 0.05 nm 2 for Li 2ZrO 3. By contrast, Li 2O has a fluorite structure and is expected to remain crystalline.

Ion dose dependence of the sputtering yield of Ru(0001) at very low fluences.

The neutral sputtered flux from a Ru single crystal oriented along the (0001) axis has been determined as a function of primary ion dose in real time using nonresonant photoionization techniques coupled with time-of-flight mass spectrometry. The data reveal, surprisingly, that the sputtering yield is twice as large from an undamaged surface as that from a slightly damaged surface. The sputtering yield decreases until steady state is reached at a primary ion fluence of only 2/times/10/sup 15/ ions cm/sup /minus/2/. Data analysis results in an estimated cross section for damage of (2.7/plus minus/1.0)/times/10/sup /minus/15/ cm/sup 2/.

Recent advances in secondary lon mass spectrometry (SIMS) for polymer surface analysis

AbstractSince the first tentative applications of SIMS to study polymer surfaces around 1980 the field has developed very rapidly. The important experimental parameters which allow true ‘static’ SIMS analysis of polymers are now well established following systematic studies of ion beam damage cross‐sections and the methodology of surface potential control is sufficiently understood to allow both positive and negative ion spectra to be routinely obtained from highly insulating materials.The principal advantage of SIMS over X‐ray photoelectron spectroscopy (XPS or ESCA) comes from the molecular specificity inherent in a mass spectrometric technique. Several classes of polymers have been studied to establish fragmentation processes; in the case of acrylic polymers these studies have been extensive and detailed. From the technological point‐of‐view it is the ability to identify ‘small’ organic molecules on polymer surfaces which is most exploited. The information depth in typical systems has been established by correlation with angle‐resolved XPS studies to be ∼ å, this degree of surface sensitivity allows bulk‐surface segregation effects in block copolymers to be followed as exemplified by studies of segmented poly (ether urethanes). Use can also be made of the isotope specificity of SIMS in derivatisation schemes or in polymerisation mechanism studies. Quantification of SIMS intensity data is now being explored. In the case of random methacrylate copolymers quantitative information on sequence statistics has been obtained.SIMS also has the potential for high spatial resolution analysis. The problems associated with unacceptable damage rates when working with sub‐micron focussed beams have been studied and this has led to the development of the time‐of‐flight (TOF) imaging SIMS instrument. TOF SIMS is capable of accessing a mass range of an order of magnitude greater than the conventional quadrupole instrument and the application of both imaging and non‐imaging TOF instrumentation to polymer surface analysis has recently commenced.

Metal/Silicon Reactions Studied by High Energy Jon Scattering

The initial stages of the metal/silicon reactions have been investigated for Au, Ag, Pd/Si(111) and Au, Ag/Si(001) systems with film thicknesses less than ∼15 ML (1 ML≈7×1014 atoms/cm2) using a MeV ion scattering/channeling technique. In addition to single metal depositions, sequential depositions of two different metals were performed. In the former case, obvious differences in the reactivities at the interfaces were observed for the Au/Si, Pd/Si (reactive) and Ag/Si systems (little reactive). Sequential depositions of Au and Ag brought forth interesting results. Predeposited Au of \\lesssim2 ML enhanced displacements of Si during subsequent Ag depositions, irrespective of the substrate orientations. The interfacial reactions of the noble metal(s)/Si and the Pd/Si systems are discussed in relation to the damage cross section of Si crystal atoms near the interfaces.

Evalutation of global radiation damage data for (homogeneous) amorphous structure materials

We want to evaluate the damage function D iα ( T) giving the “Global Damage” of type α produced in a cascade initiated by a recoil atom of type i of (recoil-) energy T. Global damage of type α may indicate for example the: • —number of vacancies of atoms of type j; • —ionization produced in the cascade; • —energy dissipated by electronic heating; • —energy dissipated by nuclear heating, etc. We establish an integral equation of the “importance—or adjoint”—type for D iα ( T) and solve it numerically. (To start directly from an equation for D iα ( T) is much easier for our purpose than to construct first the flux ϕ( E) of moving atoms by solving the Boltzmann equation and then to evaluate the damage by D = ∫ ϕ( E) Σ D( E)d E with Σ D as the damage cross-section.) The total damage of type α to a neutron spectrum ф(E) is then given by D α(ф)= ∑ i ∑dE∑dTф(E)∑ i(E, T)D iα(T) where Σ i ( E, T) is the neutron-reaction cross section for producing recoil atoms of type i with recoil energy T.

Analysis of mineral powder mixtures by heavy ion bombardment and X-ray diffraction

Abstract Powder mixtures are difficult to analyze since they give complex X-ray diffraction patterns where the patterns of the components are superimposed one over the other with very little indication of which diffraction lines belong to which compound. Heavy ion bombardment causes different damage effects to different inorganic crystal structures and this can be used to differentiate complex diffraction patterns. While some compounds retain their crystallinity under heavy ion bombardment, others become non-crystalline depending on their metamict damage cross-sections. The changes in the X-ray diffraction patterns after bombardment can distinguish the separate patterns unambiguously. In most cases, only the intensities of the diffraction peaks change with irradiation, peak widths and peak positions not altering perceptibly. In some cases, the diffraction peaks do change in width and position, though these can also be used in the analysis. Argon(3 MeV)ionsbombardamonolayerofpowderofsize ∼ 5 μm at a fluenc...

Adsorption of oxygen and carbon monoxide on vacuum-deposited smooth Pd(111) surfaces and the effect of sputter-roughening

Adsorption of oxygen and carbon monoxide on smooth and sputtered clean surfaces of epitaxial Pd(111)/mica films was studied. Electron beam irradiation effects on the adsorbates were important only for CO in the total dose range of 1×10 14 to 2×10 19 electrons/mm 2. The cross section for beam damage was approximately 2×10 -17 mm 2/electron for the CO ad/Pd(111) system. AES was used to measure the O(KVV)/Pd(M 4,5VV) intensity ratios for both O and CO adsorbates. Saturation values of 0.017±0.001 and 0.016±0.001 were obtained for O and CO respectively. The value for O is significantly lower than for sputter etched and annealed bulk crystals. No values have been reported for CO. On sputtered thin film surfaces, these ratios saturated at somewhat higher values when saturation ion doses were applied. The saturation ion dose was approximately 3×10 13 ions/mm 2. Beyond this value no additional oxygen or carbon monoxide could be adsorbed. Annealing returned the adsorption characteristics to what was obtained on the initially smooth surfaces.

Bombardment of α-quartz and related materials by argon (3 MeV) ions

Abstract The bombardment using argon ions of energy 3 MeV of several α-quartz isomorphous crystal structures has been carried out. Non-crystalline metamict forms have been obtained in all cases, using relatively low fluence. The metamict damage cross-sections D M obtained are: 3·l±0·3nm2 (GeO2), 2·7 ± 0·3nm2 (FePO4), 1·9 ± 0·4 nm2 (A1PO4), l·0±0·3nm2 (SiO2) and 0·7±0·3nm2 (GaPO4), and these values decrease with increasing melting points. Recrystallization is observed to occur at relatively low temperatures of less than 0·5 T m. These results are in contrast to earlier studies using fast-neutron irradiation, in which non-crystalline forms were obtained only for SiO2. This is probably due to annealing of the neutron damage for materials of lower melting point during the lengthy irradiation at the temperature of the atomic pile.

A comparison of an electron-beam-induced chemical reaction at T = 10 K and T = 300 K

An in-situ spectroscopic analysis of an electron-beam-induced chemical reaction, at T = 10 and 300 K, is reported. The results indicate that the damage cross-section at 10 K is 2.5 times smaller than at 300 K. Calculations are presented to support that electron beam heating of the sample is negligible and that the small decrease in damage is most likely due to a temperature-dependent radiation-physical process.

X-ray diffraction and leaching of CsAlSi5O12 and CsZr2(PO4)3 irradiated by argon (3 MeV) ions

Metamict damage cross-sections for the candidate nuclear fuel waste immobilization materials CsAlSi5O12 and CsZr2(PO4)3 irradiated with 3 MeV argon ions were found to be 0.6±0.2 nm2 and 0.7±0.3 nm2, respectively, from powder X-ray diffraction measurements. Based on caesium extraction into solution, heavy irradiation produced increases of up to a factor of 25 in the dissolution rates of the materials in deionized water and a brine at 100° C.