Electronic Energy Loss Threshold Research Articles

Coupled effects of electronic and nuclear energy deposition on damage accumulation in ion-irradiated SiC

Coupling between electronic and nuclear energy dissipation in ion-irradiated, single crystal 4H-SiC has been investigated using Si, Ti, and Ni ions over a range of energies at 300 K, and irradiation damage accumulation is characterized using Rutherford backscattering spectroscopy in channeling geometry. The damage production rate from nuclear energy loss (Sn) is observed to decrease with increasing electronic energy loss (Se) of the incident ions. A dynamic threshold (Se,th) in electronic energy loss is determined for each ion species, which defines two regions: i) Se > Se,th, where electronic energy dissipation fully suppresses damage production due to nuclear energy loss along incident ion paths, and ii) Se < Se,th, where simultaneous damage recovery due to Se competes with damage production processes. The electronic energy loss threshold (Se,th) increases sublinearly with incident ion atomic number. The assessment of Se,th and how it affects damage accumulation is important to advance the understanding of complex processes occurring under ion-solid interactions, as well as in the design of functional materials for opto-electronics and novel structural materials and devices tolerant to harsh thermal and radiation environments.

An attempt to apply the inelastic thermal spike model to surface modifications of CaF2 induced by highly charged ions: comparison to swift heavy ions effects and extension to some others material

Surface damage appears on materials irradiated by highly charged ions (HCI). Since a direct link has been found between surface damage created by HCI with the one created by swift heavy ions (SHI), the inelastic thermal spike model (i-TS model) developed to explain track creation resulting from the electron excitation induced by SHI can also be applied to describe the response of materials under HCI which transfers its potential energy to electrons of the target. An experimental description of the appearance of the hillock-like nanoscale protrusions induced by SHI at the surface of CaF2 is presented in comparison with track formation in bulk which shows that the only parameter on which we can be confident is the electronic energy loss threshold. Track size and electronic energy loss threshold resulting from SHI irradiation of CaF2 is described by the i-TS model in a 2D geometry. Based on this description the i-TS model is extended to three dimensions to describe the potential threshold of appearance of protrusions by HCI in CaF2 and to other crystalline materials (LiF, crystalline SiO2, mica, LiNbO3, SrTiO3, ZnO, TiO2, HOPG). The strength of the electron–phonon coupling and the depth in which the potential energy is deposited near the surface combined with the energy necessary to melt the material defines the classification of the material sensitivity. As done for SHI, the band gap of the material may play an important role in the determination of the depth in which the potential energy is deposited. Moreover larger is the initial potential energy and larger is the depth in which it is deposited.

Data consistencies of swift heavy ion induced damage creation in yttrium iron garnet analyzed by different techniques

Pronounced swelling is observed when single crystals of yttrium iron garnet Y3Fe5O12 (YIG) are irradiated in the electronic energy loss regime with various swift heavy ions. The out-of-plane swelling was measured by scanning across the border line between an irradiated and a virgin area of the sample surface with the tip of a profilometer. The step height varied between 20 and 600nm depending on fluence, electronic energy loss and total range of the ions. The step height divided by the ion range as a function of the ion fluence exhibits a linear increase in the initial phase and saturates at high fluences leading to a density decrease of around 1.7%. With complementary channeling-Rutherford-backscattering experiments (c-RBS), the damage fraction and the corresponding damage cross section were extracted and compared to the cross section deduced from swelling measurements. Irradiation effects were also characterized by scanning force microscopy (SFM). A threshold for damage creation as deduced from all the present physical characterizations is 5.5±1.0keV/nm. The value is in full agreement with previous measurements confirming that swelling and SFM characterizations can provide information concerning the electronic energy loss threshold for track formation. In contrast, track radii deduced from swelling measurements are smaller and radii from SFM are larger than deduced from c-RBS analysis. The results of Y3Fe5O12 of this work are compared with data obtained for other crystalline oxides and for ionic crystals.

Ion tracks in amorphous silica

Abstract

Damage creation threshold of Al2O3 under swift heavy ion irradiation

Among insulators, sapphire (Al2O3) is less sensitive than any amorphizable oxides regarding the irradiation with heavy ions in the electronic energy loss regime. Earlier experimental results indicated a critical energy loss for damage creation of around of 20keV/nm, while calculations based on the inelastic thermal spike model predict a value of ∼10keV/nm. In order to clarify this discrepancy, additional irradiation experiments were performed with different ions between Ni and U covering electronic energy losses between 10 and 43keV/nm and kinetic energies in the range from 1 to 11MeV/u. Irradiation effects were characterized by atomic force microscopy (hillock formation), profilometry (swelling), and channeling Rutherford backscattering (near-surface disorder). Combining the results from these measurements, an electronic energy loss threshold of 9.5±1.5keV/nm is extracted, indicating that the earlier threshold was overestimated and confirming the predictive power of the inelastic thermal spike model. Threshold predictions based on thermal spike model calculations are given for lower and higher beam energies.

Swift heavy ion irradiation of pyrochlore oxides: Electronic energy loss threshold for latent track formation

Pyrochlore pellets with the Gd 2(Ti 2− x Zr x )O 7 stoichiometry ( x = 0, 1 and 2) were irradiated with swift heavy ions in order to investigate the effects of electronic excitation and to determine the electronic stopping power threshold for track formation. XRD results showed that the electronic excitation induced by 870 MeV Xe and 780 MeV Kr ions leads to: (i) a crystalline–amorphous transition for Gd 2Ti 2O 7 and Gd 2TiZrO 7, (ii) a phase transition towards an anion-deficient fluorite structure (order–disorder transition) for Gd 2Zr 2O 7. Thus, zirconate pyrochlores present a better radiation resistance under swift heavy ion irradiation than titanate pyrochlores. Moreover results underline the existence of an electronic stopping power threshold around 13–14 keV/nm, below which phase transformations do not occur.

Behavior of crystalline silicon under huge electronic excitations: A transient thermal spike description

Recent experimental works devoted to the phenomena of mixing observed at metallic multilayers Ni/Si irradiated by swift heavy ions irradiations make it necessary to revisit the insensibility of crystalline Si under huge electronic excitations. Knowing that Ni is an insensitive material, such observed mixing would exist only if Si is a sensitive material. In order to extend the study of swift heavy ion effects to semiconductor materials, the experimental results obtained in bulk silicon have been analyzed within the framework of the inelastic thermal spike model. Provided the quenching of a boiling (or vapor) phase is taken as the criterion of amorphization, the calculations with an electron–phonon coupling constant g(300 K) = 1.8 × 10 12 W/cm 3/K and an electronic diffusivity D e(300 K) = 80 cm 2/s nicely reproduce the size of observed amorphous tracks as well as the electronic energy loss threshold value for their creation, assuming that they result from the quenching of the appearance of a boiling phase along the ion path. Using these parameters for Si in the case of a Ni/Si multilayer, the mixing observed experimentally can be well simulated by the inelastic thermal spike model extended to multilayers, assuming that this occurs in the molten phase created at the Ni interface by energy transfer from Si.

Heavy ion-induced deformation of radiation-amorphized U 3Si

Ten micrometre thick U 3Si layers were amorphized by ion bombardment with 250 MeV Xe ions at room temperature. Subsequently these layers were post-irradiated with either 250 MeV Xe ions or 120 MeV Kr ions below 100 K at a beam incidence angle of 45°. After irradiation, the surface morphology was examined at room temperature by optical microscopy. At small fluences the surface of amorphous U 3Si revealed a displacement in direction of the projection of the ion beam onto the surface. At larger fluences a ripple structure developed. The observations can be understood as consequences of a shear flow released by the formation of fluid ion tracks. From the experimental data an electronic energy loss threshold of 19 keV/nm is deduced for the formation of such tracks in amorphous U 3Si. Obviously, for estimating the in-pile damage the electronic energy loss of fast fission fragments cannot be ignored.

Chemical modifications of polymer films induced by high energy heavy ions

Polymer films including polyethylene terephthalate (PET), polystyrene (PS) and polycarbonate (PC) were irradiated at room temperature with ions of 35 MeV/u 40Ar, 25 MeV/u 84Kr, 15.1 MeV/u 136Xe and 11.4 MeV/u 238U to fluences ranging from 9×10 9 to 5.5×10 12 ions/cm 2. The radiation-induced chemical changes of the materials were investigated by Fourier-transform infrared (FTIR) and ultraviolet/visible spectroscopies. It is found that the absorbance in the ultraviolet and visible range induced by all irradiations follows a linear relationship with fluence. The radiation-induced absorbance normalized to one particle increases slowly with increasing of electronic energy loss below about 8 keV/nm followed by a sharp increase up to about 15 keV/nm above which saturation is reached. FTIR measurements reveal that the materials suffer serious degradation through bond breaking. The absorbance of the typical infrared bands decays exponentially with increase of ion fluence and the bond-disruption cross-section shows a sigmoid variation with electronic energy loss. In PET loss of crystallinity is attributed to the configuration transformation of the ethylene glycol residue from trans into the gauche. Alkyne end groups are induced in all the materials above certain electronic energy loss threshold, which is found to be about 0.8 keV/nm for PS and 0.4 keV/nm for PC. The production cross-section of alkyne end group increases with increasing of electronic energy loss and shows saturation at high electronic energy loss values. It is concluded that not only the physical processes but also the chemical processes of the energy deposition determine the modification of polymer.

Chemical modification of polycarbonate induced by 1.4 GeV Ar ions

Polycarbonate foil stacks were irradiated with 1.4 GeV Ar ions at room temperature. The induced modifications in chemical structure were studied by Fourier transform infrared (FTIR) and ultraviolet/visible absorption (UV/VIS) spectroscopies. FTIR measurements reveal that material degradation through bond breaking are the main effects. Significant reduction in absorbance of the typical infrared bands is observed at energy densities higher than 8×1022eV/cm3. Alkyne end groups are produced by the irradiations and the electronic energy loss threshold for production of the alkyne end group is found to be below 0.61 keV/nm. UV/VIS measurements indicate a shifting of the absorption edge from ultraviolet towards visible and a strong increase of absorbance in the ultraviolet and visible regions. The irradiation induced changes in absorbance at wavelengths of 380, 450 and 500 nm follow roughly linear relationship with fluence and scale rather good with the square of electronic energy loss. The results are briefly discussed.

Something new about the giant deformation of amorphous alloys irradiated with GeV ions

This paper reports new in situ electrical resistance results about the giant plastic deformation process occurring in amorphous Fe85B15 irradiated with swift heavy ions, which lead to revisit the description of this phenomenon. Above an electronic energy loss of ∼25 keV nm−1 the growth starts at the very beginning of the irradiation, whereas below this value no initial growth is observed due to the necessity of predamaging the original material to induce the deformation. Increasing the irradiation temperature leads to a strong reduction of the growth rate, but does not affect significantly the electronic energy loss threshold for the observation of an initial growth. These results are discussed in the framework of theoretical calculations based on a thermal spike model.

Damage in Refractory Oxides and ion Beam Mixing at Metal-Oxide Interfaces Induced by Gev Ions and 20 Mev Cluster Beam

AbstractDefect creation in refractory oxides known to be unsensitive to radiolysis, was shown to take place by high level electronic excitations induced by swift heavy ions or energetic cluster bombardments. Depending on the oxide a threshold in electronic energy loss for damage production was observed : MgO 22 keV/nm, AI2O3 20 keV/nm and LiNbO3 6 keV/nm. A very strong dependence on the energy deposited for the defect production was evidenced above the threshold. In MgO, both point and extended defects were created whereas in AI2O3 only extended defects were observed and in LiNbO3 amorphization in the ion track was evidenced.Atomic displacements due to the giant electronic excitations can be revealed at metal-oxide interfaces in the case of Na nanoprecipitates embedded in MgO single crystals.

Structural modifications of crystalline and amorphous Ni 3B irradiated with high-energy heavy ions

Crystalline and amorphous Ni 3B ribbons have been irradiated at low temperature with GeV heavy ions in order to study the structural modifications induced in metallic alloys by ion electronic energy loss. The atomic rearrangements produced by irradiation were characterized via in situ electrical resistance measurements and room-temperature X-ray and electron diffraction. Amorphous Ni 3B behaves as the other amorphous alloys already investigated: creation of disorder with a cross section increasing with the ion electronic stopping power, followed by an anisotropic growth of the sample dimensions. Crystalline Ni 3B shows a new and very interesting behavior: a huge electrical resistivity increase above an electronic energy loss threshold attributed to amorphization of the irradiated alloy.