High Electronic Energy Deposition Research Articles

Grain subdivision and structural modifications by high-energy heavy ions in UO2 with different initial grain size

Irradiation with 84 MeV Xe ions at peak fluence above 7 × 1017 ions/cm2 has been carried out on two UO2 samples with different initial grain sizes at 300 °C and 500 °C. Characterization of both grain structure and bubble morphology has been performed using transmission electron microscopy, image analysis and precession electron diffraction. The bubble size in the large-grained sample was smaller than that in the standard-grain sample, confirming fission gas precipitation resistance in the former. The ion irradiation in the high electronic energy deposition range has caused formation of a large density of dislocations which resulted in grain polygonization for the sample with standard grain size, which was observed in multiple lamellas extracted next to each other at peak dose. The sample with large grains showed inconsistent behavior. In one case, dislocation pile-up occurred, but no sub-grain formation was observed. An adjacent location showed sub-grain formation, even if to less extent compared to the standard grain-size sample. These findings suggest a limited polygonization resistance in large-grained UO2 compared to standard-grain UO2. Recrystallization of both sample surfaces was present, leaving unclear if this is a surface effect or a consequence of the highest energy deposition rate in this area.

Effect of ion beam parameters on engineering of nanoscale voids and their stability under post-growth annealing

Swift heavy ion (SHI) irradiation of damaged germanium (d-Ge) layer results in porous structure with voids aligned along ion trajectory due to local melting and resolidification during high electronic energy deposition. The present study focuses on the irradiation temperature- and incident angle-dependent growth dynamics and shape evolution of these voids due to 100 MeV Ag ions irradiation. The d-Ge layers were prepared by multiple low-energy Ar ion implantations in single crystalline Ge with damage formation of ~7 displacements per atom. Further, these d-Ge layers were irradiated using 100 MeV Ag ions at two different temperatures (77 and 300 K) and three different angles (7°, 30° and 45°). After SHI irradiation, substantial volume expansion of d-Ge layer is detected which is due to formation of nanoscale voids. The volume expansion is observed to be more in the samples irradiated at 77 K as compared to 300 K at a given irradiation fluence. It is observed that the voids are of spherical shape at low ion irradiation fluence. The voids grow in size and change their shape from spherical to prolate spheroid with increasing ion fluence. The major axis of spheroid is observed to be aligned approximately along the ion beam direction which has been confirmed by irradiation at three different angles. The change in shape is a consequence of combination of compressive strain and plastic flow developed due to thermal spike generated along ion track. Post-SHI irradiation annealing shows increase in size of voids and reversal of shape from prolate spheroid towards spherical through strain relaxation. The stability of voids was studied with the effect of post-growth annealing.

Swift heavy ion irradiation of crystalline CdTe

The influence of high electronic energy deposition in cadmium telluride (CdTe) was investigated using Rutherford backscattering spectrometry in channelling configuration as well as high-resolution transmission electron microscopy. Swift heavy ion irradiation was performed at room temperature with 185 MeV Au ions at perpendicular and non-perpendicular ion incidence. Independent of the ion incidence angle, neither ion beam induced point defects nor amorphous ion tracks were observed along the ion path. In contrast, the irradiated layer possesses a high crystalline quality even after irradiation with high ion fluences, i.e. multiple ion overlap. Nevertheless, irradiation with swift heavy ions leads to the formation of extended defects in a thin layer close to the sample surface. With increasing ion fluence the concentration of these extended defects increases continuously. This suggests that high electronic energy deposition causes the formation of defects, however, the combination of the high defect mobility within the thermal spike and the high ionicity of CdTe may benefit an effective recovery of the ionic bonds and consequently an easy recovery of the lattice, i.e. a nearly perfect recrystallization. The experimentally observed high defect resistivity enables a high doping of foreign atoms in CdTe over a wide depth range without the formation of lattice defects which is important for the use of CdTe as an effective absorber for solar cells.

Enhanced photoelectrochemical properties of 100 MeV Si8+ ion irradiated barium titanate thin films

Effects of high electronic energy deposition on the structure, surface topography, optical property and photoelectrochemical behavior of barium titanate (BaTiO3) thin films were investigated by irradiating films with 100MeV Si8+ ions at different ion fluences in the range of 1×1011–2×1013ionscm−2. BaTiO3 thin films were deposited on indium tin oxide coated glass substrate by sol gel spin coating method. Irradiation induced modifications in the films were analyzed using the results from XRD, SEM, cross sectional SEM, AFM and UV–Vis spectrometry. Maximum photocurrent density of 0.7mAcm−2 at 0.4V/SCE and applied bias hydrogen conversion efficiency (ABPE) of 0.73% was observed for BaTiO3 film irradiated at 5×1011 ionscm−2, which can be attributed to maximum negative value of the flatband potential and donor density and lowest resistivity.

Modified structural, morphological and photoelectrochemical properties of 120 MeV Ag9+ ion irradiated BaTiO3 thin films

The effects of high electronic energy deposition on the structure, surface topography, optical property and photoelectrochemical behavior of barium titanate thin (BaTiO3) films have been investigated by irradiating films with 120 MeV Ag9+ ions at different ion fluences in the range of 1 × 1011–3 × 1012 ions cm−2. Barium titanate thin films were deposited on indium tin oxide-coated glass substrate by sol–gel spin coating method. The structure of the film was crystalline with tetragonal phase. Surface topography was studied by atomic force microscopy detailing the values of roughness of the films. Maximum photocurrent density of 1.78 mA cm−2 at 0.4 V/SCE and applied bias photon-to-current efficiency (ABPE) of 0.91% was observed for BaTiO3 film irradiated at 1 × 1011 ions cm−2.

Irradiation induced crossover from 1D to 3D transport behaviors of PEDOT‐titanium dioxide hybrid nanocomposites

AbstractConductive poly(3,4‐ethylenedioxythiophene)/TiO2 nanocomposites were synthesized via a facile oxidative polymerization approach using dodecylbenzene sulfonic acid as a dopant and ammonium peroxydisulfate as an oxidant and irradiated with 90 MeV O7+ ions at the fluences of 5 × 1010, 1 × 1011, 5 × 1011, and 1 × 1012 ions cm−2 using 15UD Pelletron accelerator under high vacuum. X‐ray diffraction studies show that microstrain and domain crystallite size of the nanocomposites increases with the increase of ion fluence resulting in highly ordered PEDOT‐TiO2 nanocomposites. Thermogravimmetric analysis shows that the thermal stability of the nanocomposites increases with the increase of irradiation fluences which can be attributed to the crosslinking of polymer chains due to high electronic energy deposition. Scanning electron micrographs show that there is grain growth after swift heavy ion (SHI) irradiation resulting highly dense and less porous microstructure of nanocomposite films. DC conductivity of unirradiated nanocomposites exhibits Mott's 1D variable range hopping (VRH) mechanism. However, there is cross over to 3D VRH mechanism at higher irradiation fluence of 5 × 1011 and 1 × 1012 ions cm−2. There is an enhancement in the electrical conductivity of the nanocomposites upon SHI irradiation correlating crosslinking with DC conductivity of the nanocomposites.

Void formation in amorphous germanium due to high electronic energy deposition

The effect of high electronic energy deposition in amorphous germanium has been studied experimentally by Au irradiation with ion energies of up to 185 MeV and different angles of incidence and by molecular dynamics computer simulations. In both cases, the energy deposition leads to void formation accompanied by strong swelling of the amorphous germanium. The simulation results prove that the formation of the voids is mainly based on a shock wave mechanism and the swelling is determined by the competing processes of the formation and growth of voids on the one hand and the shrinking and annihilation of voids on the other hand. In full agreement between experiment and simulation, the amount of the swelling is a linear function of the total energy deposited into electronic processes and there exists a threshold value of the electronic energy loss per ion and depth for swelling. A comparison of the threshold values obtained by the experiment and the simulation suggests that approximately 20% of the energy deposited into electronic processes is converted into atomic motion.

Influence of electronic energy deposition on the structural modification of swift heavy-ion-irradiated amorphous germanium layers

Swift heavy-ion (SHI) irradiation of amorphous germanium (a-Ge) layers leads to a strong volume expansion accompanied by a nonsaturating irreversible plastic deformation (ion hammering), which are consequences of the high local electronic energy deposition within the region of the a-Ge layer. We present a detailed study of the influence of SHI irradiation parameters on the effect of plastic deformation and structural modification. Specially prepared a-Ge layers were irradiated using two SHI energies and different angles of incidence, thus resulting in a variation of the electronic energy deposition per depth ${\ensuremath{\epsilon}}_{e}$ between 14.0 and 38.6 keV nm${}^{\ensuremath{-}1}$. For all irradiation parameters used a strong swelling of the irradiated material was observed, which is caused by the formation and growth of randomly distributed voids, leading to a gradual transformation of the amorphous layer into a sponge-like porous structure as established by cross-section scanning electron microscopy investigations. The swelling depends linearly on the ion fluence and on the value of ${\ensuremath{\epsilon}}_{e}$, thus clearly demonstrating that the structural changes are determined solely by the electronic energy deposited within the amorphous layer. Plastic deformation shows a superlinear dependence on the ion fluence due to the simultaneous volume expansion. This influence of structural modification on plastic deformation is described by a simple approach, thus allowing estimation of the deformation yield. With these results the threshold values of the electronic energy deposition for the onset of both structural modification and plastic deformation due to SHI irradiation are determined. Furthermore, based on these results, the longstanding question concerning the reason for the structural modification observed in SHI-irradiated crystalline Ge is answered.

Radiation damages in CeO 2 thin films irradiated with ions having the same nuclear stopping and different electronic stopping powers

In order to characterize a possible modification due to high-density electronic excitation, thin films of CeO 2 have been irradiated with 10-MeV Ni and 120-MeV Xe ions, both having the same nuclear stopping powers, while having different electronic stopping powers. The comparison of the fluence dependence of X-ray diffraction (XRD) peaks suggests that the defect production cross section for 120-MeV Xe is nearly one order of magnitude higher than that for 10-MeV Ni. The comparative study demonstrates the prominent damage observed for 120-MeV Xe irradiation is due to high electronic energy deposition.

Structural modifications of Gd2Zr2-xTixO7 pyrochlore induced by swift heavy ions: Disordering and amorphization

The isometric, pyrochlore structure type, A2B2O7, exhibits a wide variety of properties that find application in a large number of different technologies, from electrolytes in solid oxide fuel cells to actinide-bearing compositions that can be used as nuclear waste forms or inert matrix nuclear fuels. Swift xenon ions (1.43 GeV) have been used to systematically modify different compositions in the Gd2Zr2-xTixO7 binary at the nanoscale by radiation-induced phase transitions that include the crystalline-to-amorphous and order-disorder structural transformations. Synchrotron x-ray diffraction, Raman spectroscopy, and transmission electron microscopy provide a complete and consistent description of structural changes induced by the swift heavy ions and demonstrate that the response of pyrochlore depends strongly on chemical composition. The high and dense electronic energy deposition primarily results in amorphization of Ti-rich pyrochlore; whereas the formation of the fully disordered, defect-fluorite structure is the dominant process for Zr-rich pyrochlore.

Enhancement in sensitivity of copper sulfide thin film ammonia gas sensor: Effect of swift heavy ion irradiation

The studies are carried out on the effect of swift heavy ion (SHI) irradiation on surface morphology and electrical properties of copper sulfide (CuxS) thin films with three different chemical compositions (x values). The irradiation experiments have been carried out on CuxS films with x=1.4, 1.8, and 2 by 100 MeV gold heavy ions at room temperature. These as-deposited and irradiated thin films have been used to detect ammonia gas at room temperature (300 K). The SHI irradiation treatment on x=1.4 and 1.8 copper sulfide films enhances the sensitivity of the gas sensor. The results are discussed considering high electronic energy deposition by 100 MeV gold heavy ions in a matrix of copper sulfide.

High-energy heavy-ion induced physical and surface-chemical modifications in polycrystalline cadmium sulfide thin films

The effect of high electronic energy deposition on the structure, surface topography, optical properties, and electronic structure of cadmium sulfide (CdS) thin films have been investigated by irradiating the films with 100 MeV Ag+7 ions at different ion fluences in the range of 1012–1013 ions/cm2. The CdS films were deposited on glass substrate by thermal evaporation, and the films studied in the present work are polycrystalline with crystallites preferentially oriented along (002)-H direction. It is shown that swift heavy ion (SHI) irradiation leads to grain agglomeration and hence an increase in the grain size at low ion fluences. The observed lattice compaction was related to irradiation induced polygonization. The optical band gap energy decreased after irradiation, possibly due to the combined effect of change in the grain size and in the creation of intermediate energy levels. Enhanced nonradiative recombination via additional deep levels, introduced by SHI irradiation was noticed from photoluminescence (PL) analysis. A shift in the core levels associated with the change in Fermi level position was realized from XPS analysis. The chemistry of CdS film surface was studied which showed profound chemisorption of oxygen on the surface of CdS.

Synthesis of Nanoscale Copper Nitride Thin Film and Modification of the Surface Under High Electronic Excitation

Nanoscale (approximately 90 nm) Copper nitride (Cu3N) films are deposited on borosilicate glass and Si substrates by RF sputtering technique in the reactive environment of nitrogen gas. These films are irradiated with 200 MeV Au15+ ions from Pelletron accelerator in order to modify the surface by high electronic energy deposition of heavy ions. Due to irradiation (i) at incident ion fluence of 1 x 10(12) ions/cm2 enhancement of grains, (ii) at 5 x 10912) ions/cm2 mass transport on the films surface, (iii) at 2 x 10(13) ions/cm2 line-like features on Cu3N/glass and nanometallic structures on Cu3N/Si surface are observed. The surface morphology is examined by atomic force microscope (AFM). All results are explained on the basis of a thermal spike model of ion-solid interaction.

Studies on the high electronic energy deposition in polyaniline thin films

We report here the physico-chemical changes brought about by high electronic energy deposition of gold ions in HCl doped polyaniline (PANI) thin films. PANI thin films were synthesized by in situ polymerization technique. The as-synthesized PANI thin films of thickness 160nm were irradiated using Au7+ ion of 100MeV energy at different fluences, namely, 5×1011ions/cm2 and 5×1012ions/cm2, respectively. A significant change was seen after irradiation in electrical and photo conductivity, which may be related to increased carrier concentration, and structural modifications in the polymer film. In addition, the high electronic energy deposition showed other effects like cross-linking of polymer chains, bond breaking and creation of defect sites. AFM observations revealed mountainous type features in all (before and after irradiation) PANI samples. The average size (diameter) and density of such mountainous clusters were found to be related with the ion fluence. The AFM profiles also showed change in the surface roughness of the films with respect to irradiation, which is one of the peculiarity of the high electronic energy deposition technique.

Studies on high electronic energy deposition in transparent conducting indium tin oxide thin films

We have examined the effect of swift heavy ions using 100 MeV Au8+ ions on the electrical properties of transparent, conducting indium tin oxide polycrystalline films with resistivity of 0.58 × 10−4 Ω cm and optical transmission greater than 78% (pristine). We report on the modifications occurring after high electronic energy deposition. With the increase in fluency, x-ray line intensity of the peaks corresponding to the planes (1 1 0), (4 0 0), (4 4 1) increased, while (3 3 1) remained constant. Surface morphological studies showed a pomegranate structure of pristine samples, which was highly disturbed with a high dose of irradiation. For the high dose, there was a formation of small spherical domes uniformly distributed over the entire surface. The transmittance was seen to be decreasing with the increase in ion fluency. At higher doses, the resistivity and photoluminescence intensity was seen to be decreased. In addition, the carrier concentration was seen to be increased, which was in accordance with the decrease in resistivity. The observed modifications after high electronic energy deposition in these films may lead to fruitful device applications.

Behavior of metallic nanoparticles in Al matrix under high electronic energy deposition

Metallic nanoparticles (Pb and Bi) embedded in a crystalline Al matrix were irradiated with 30MeV C60 cluster ions at 300K. Experimental evidence of partial amorphization of bismuth nanoparticles is observed. On the other hand, Pb inclusions remain crystalline. The condition under which embedded nanoparticles can be amorphized is discussed.

Effect of high electronic excitation in swift heavy ion irradiated semiconductors

The damage evolution due to high electronic energy deposition during 375MeV Xe and 593MeV Au ion irradiation was studied in the semiconductors InP, GaP, GaAs, AlAs and Ge using RBS and TEM. In InP the high electronic energy deposition leads to the formation of amorphous tracks. In the other materials no effect of the electronic energy deposition on damage formation was found. The TEM investigations show that in InP each impinging ion produces a track. With the use of the extended thermal spike model lattice temperatures and maximum radii of the molten zones were calculated for InP and Ge. Whereas in InP the lattice temperature exceeds the melting temperature confirming the observed formation of amorphous tracks, this is not the case for Ge. The calculated radii of the molten zones in InP are in good agreement with the track radii determined from the TEM images.

Effect of high electronic energy deposition in semiconductors

Track formation due to high electronic energy deposition during swift heavy ion irradiation is well known in insulating materials as well as in some intermetallic compounds and metals. In semiconductors the physical situation was much less clear, and only during the last few years several experimental results on the effect of high electronic energy deposition were published, which are summarised and discussed in the present paper. Like in insulators, swift heavy ion irradiation may cause amorphous tracks in some semiconductors, such as InP, InSb, InAs, GaSb and Ge, if a certain value of the electronic energy deposition ε e per ion and unit length characteristic for the material and the ion is exceeded. The critical values of ε e are much higher than in the other materials, and the corresponding ion energies are close to the maximum ion energies available with the existing high energy accelerators. On the other hand, with cluster ions, as e.g. C 60, tracks are easily formed in Si, Ge and GaAs with ion energies of several tens of MeV. Beside damage and track formation, annealing of damage was observed in the semiconductors, and it can be concluded that the effect of high electronic energy deposition represents itself as a competition between damage formation and annealing. Which of the two processes dominates is mainly determined by the electronic energy deposition. Qualitatively the observed behaviour can be explained in the framework of the thermal spike model. However, a quantitative description of all data available is not successful in the framework of this concept. This is obviously due to the fact that the effects are influenced not only by the electronic energy deposition, but also by a variety of other parameters, such as the ion velocity, the ion mass, the charge state of the impinging ions and the radial distribution of the electronic energy around the ions' path. All these parameters have to be taken into account within a theoretical description. However, the present situation is characterised by a lack of sufficient experimental data, and further systematic work is required to make progress in this interesting field.

Influence of the Swift Heavy Ion Irradiation on the Short Range Order in Amorphous FeNiSiB Alloys

The influence of the high-energy heavy ion irradiation on the short range order and magnetic texture in amorphous FeNiSiB alloys are studied by Mossbauer spectroscopy. The rf-Mossbauer measurements reveal clear changes of the local structure induced due to high electronic energy deposition and related to the anisotropic growth effect. In the substantial volume fraction of irradiated samples the spins change their orientation from the in-plane to the perpendicular one.

Phase transformation induced by swift heavy ion irradiation of pure metals

It is now unambiguously established that high electronic energy deposition (HEED), obtained by swift heavy ion irradiation, plays an important role in the damage processes of pure metallic targets: (i) annealing of the defects created by elastic collisions in Fe, Nb, Ni and Pt, and (ii) creation of additional defects in Co, Fe, Ti and Zr. For Ti, we have recently evidenced by transmission electron microscopy observations that the damage creation by HEED is very important and leads to a phase transformation. Titanium evolves from the equilibrium hcp alpha-phase to the high pressure omega-phase. We studied the influence of three parameters on this phase transformation: ion fluence, electronic stopping power and irradiation temperature. The study of Ti and the results concerning other metals (Fe, Zr, etc.) and the semi-metal Bi allow us to propose criteria to predict in which metals HEED could induce damage: those which undergo a phase transformation under high pressure. As a matter of fact, beryllium is strongly damaged when submitted to HEED and seems to behave very similarly to titanium. The fact that such phase changes from a crystalline form to another form were only observed in those metals in which high pressure phases exist in the pressure-temperature diagram, strongly supports the Coulomb explosion model in which the generation of (i) a shock wave and (ii) collective atomic movements are invoked to account for the observed damage creation.