Surface modifications by swift heavy-ion irradiation of indium phosphide

InP (001) samples were irradiated with 200 MeV Au ions at different fluences. The surface nanotopographical changes due to increasing fluence of swift heavy ions were observed by Atomic Force Microscopy (AFM), where the onset of a large increase in surface roughness for fluences sufficient to cause complete surface amorphization was observed. Transmission Electron Microscopy (TEM) was used to observe bulk-ion tracks that formed in InP, and high resolution TEM (HRTEM) revealed that single-ion tracks might not be amorphous in nature. Surface-ion tracks were observed by AFM in the form of ill-defined pits (hollows) of ~12 nm in diameter (width). In addition, Rutherford backscattering was utilized to follow the formation of disorder to amorphization in the irradiated material. The interpretation of the large increase in surface roughness with the onset of amorphization can be attributed to the plastic phenomena induced by the change of states from crystalline to amorphous by ion irradiation. The text was submitted by the authors in English.     

Structural phase transformation in ZnS nanocrystalline thin films by swift heavy ion irradiation

Zinc sulfide (ZnS) thin films in zinc-blende (ZB) and wurtzite (W) phases have been fabricated by pulsed laser deposition. 150 MeV Ni ion beam irradiation has been carried out at different fluences ranging from 10¹¹ to 10¹³ ions/cm² at room temperature for ion induced modifications. Structural phase transformation in ZnS from W to ZB phase is observed after high energy ion irradiation which leads to the decrease in bandgap. Generation of high pressure and temperature by thermal spike during MeV ion irradiation along the ion trajectory in the films is responsible for the structural phase transformation.     

Evolution of surface morphology of NiO thin films under swift heavy ion irradiation

NiO nanoparticle thin films grown on Si substrates were irradiated by 107 MeV Ag⁸⁺ ions. The films were characterized by glancing angle X-ray diffraction and atomic force microscopy. Ag ion irradiation was found to influence the shape and size of the nanoparticles. The pristine NiO film consisted of uniform size (∼100 nm along major axis and ∼55 nm along minor axis) elliptical particles, which changed to also of uniform size (∼63 nm) circular shape particles on irradiation at a fluence of 3 × 10¹³ ions cm⁻². Comparison of XRD line width analysis and AFM data revealed that the particles in the pristine films are single crystalline, which turn to polycrystalline on irradiation with 107 MeV Ag ions.     

Lattice damage in InGaN induced by swift heavy ion irradiation

The microstructural responses of In_0.32Ga_0.68N and In_0.9Ga_0.1N films to 2.25 GeV Xe ion irradiation have been investigated using x-ray diffraction, Raman scattering, ion channeling and transmission electron microscopy. It was found that the In-rich In_0.9Ga_0.1N is more susceptible to irradiation than the Ga-rich In_0.32Ga_0.68N. Xe ion irradiation with a fluence of 7× 10¹¹ ions·cm^-2 leads to little damage in In_0.32Ga_0.68N but an obvious lattice expansion in In_0.9Ga_0.1N. The level of lattice disorder in In_0.9Ga_0.1N increases after irradiation, due to the huge electronic energy deposition of the incident Xe ions. However, no Xe ion tracks were observed to be formed, which is attributed to the very high velocity of 2.25 GeV Xe ions. Point defects and/or small defect clusters are probably the dominant defect type in Xe-irradiated In_0.9Ga_0.1N.     

Structural phase diagram for ZnS nanocrystalline thin films under swift heavy ion irradiation

The synthesis of nanocrystalline ZnS thin films by pulsed laser deposition and their modification by swift heavy ions are presented. The irradiations with 150 MeV Ni ions at fluences of 1×10¹¹, 1×10¹² and 1×10¹³ ions/cm² have been used for these studies. Irradiation results in structural phase transformation and bandgap modification of these films are investigated by using X-ray diffraction and UV-visible absorption measurements, respectively. Since stoichiometry changes induced by irradiation can contribute to the modification of these properties, elastic recoil detection analysis has been performed on pristine and 150 MeV Ni ions irradiated ZnS thin films using a 120 MeV Ag ion beam. The stoichiometry of the films has been found to be similar for pristine and ion irradiated samples. A structural phase diagram based on thermal and pressure spikes has been constructed to explain the structural phase transformation.     

Opto-chemical response of Makrofol-KG to swift heavy ion irradiation

In the present study, the effects of swift heavy ion beam irradiation on the structural, chemical and optical properties of Makrofol solid-state nuclear track detector (SSNTD) were investigated. Makrofol-KG films of 40 μm thickness were irradiated with oxygen beam (O^8 +) with fluences ranging between 10¹⁰ ion/cm² and 10¹² ion/cm². Structural, chemical and optical properties were investigated using X-ray diffraction, FTIR spectroscopy and UV–visible spectroscopy methods. It is observed that the direct and indirect band gaps of Makrofol-KG decrease after the irradiation. The XRD study shows that the crystalline size in the films decreases at higher fluences. The intensity plots of FTIR measurements indicate the degradation of Makrofol at higher fluences. Roughness of the surface increases at higher fluence.     

Effect of swift heavy ion irradiation on photoluminescence properties of ZnO/PMMA nanocomposite films

We report a study on the SHI induced modifications on structural and optical properties of ZnO/PMMA nanocomposite films. The ZnO nanoparticles were synthesized by the chemical route using 2-mercaptoethanol as a capping agent. The structure of ZnO nanoparticles was confirmed by XRD, SEM and TEM. These ZnO nanoparticles were dispersed in the PMMA matrix to form ZnO/PMMA nanocomposite films by the solution cast method. These ZnO/PMMA nanocomposite films were then irradiated by swift heavy ion irradiation (Ni⁸⁺ ion beam, 100 MeV) at a fluence of 1×10¹¹ ions/cm². The nanocomposite films were then characterized by XRD, UV-vis absorption spectroscopy and photoluminescence spectroscopy. As revealed from the absorption spectra, absorption edge is not changed by the irradiation but the optical absorption is increased. Enhanced green luminescence at about 527 nm and a less intense blue emission peak around 460 nm were observed after irradiation with respect to the pristine ZnO/PMMA nanocomposite film.     

Physical mechanism of swift heavy ion irradiation effect in graphene

ABSTRACT

The damage production induced by swift heavy ion irradiation in single-layer graphene (SLG) is investigated by molecular dynamics method. By given energy to a cylindrical region, the latent track consisting of nanopore and non-six-member rings can be produced, which depends on the electronic energy loss (dE/dx). For SLG, the minimum value needed to generate defects lies in 6.5–10?keV/nm. The latent track formation begins with the decomposition of the structure in energy deposition region until the atomic fragments escape from the surface and gradually decompose into atomic clusters. At the same time, the structure of system also changes. The source power of this phenomena is the accumulation and outward propagation of atomic stress in energy deposition region.     

Study of intermixing and Zr-silicide formation using swift heavy ion irradiation

Swift heavy ion (SHI) beam induced irradiation is an established technique for investigating structural modifications in thin films depending on the S _e sensitivity of material. Intermixing due to 120 MeV Au ion irradiation at different fluences from 10¹² to 10¹⁴ ions/cm² has been reported as a function of ion fluence in a-Si/Zr/a-Si thin films on Si substrate. The samples are characterized before (pristine) and after irradiation using Grazing Incident X-ray Diffraction (GIXRD) and Rutherford Backscattering Spectroscopy (RBS), which confirm the formation of ZrSi at thin film interface. It is suggested that mixing is mainly due to electronic energy loss since the energy transferred from high energy ions seems to create a transient molten zone along the ion track. It is found that the interface mixing increases linearly with the increase in ion fluence. The mixing effect explained in the framework of Thermal spike model. The irradiation effect on the surface roughness of the system is measured using Atomic Force Microscopy (AFM) technique. The current conduction mechanism and Schottky barrier height are also calculated by taking I–V curves across the Metal/Si junction.     

Optical spectroscopy study of damage induced in 4H-SiC by swift heavy ion irradiation

Single crystals of 4H-SiC were irradiated with swift heavy ions (332 MeV Ti, 106 MeV Pb and 2.7 GeV U) in the electronic energy loss regime. The resulting damage was investigated with UV-visible optical absorption spectroscopy and micro-Raman spectroscopy. The evolution of the Raman data with fluence shows an accumulation of isolated point defects without amorphization of the material and a partial recrystallization of the structure, but only at the lowest fluence. Furthermore, the longitudinal optical phonon-plasmon coupling mode disappears upon irradiation, suggesting a strong perturbation of the electronic structure. This evolution is consistent with the optical bandgap decrease and the Urbach edge broadening that was also previously observed for the irradiation with 4 MeV Au ions.     

Two waveguide layers in lithium niobate crystal formed by swift heavy Kr ion irradiation

We report the formation of two waveguide layers in a lithium niobate crystal by irradiation with swift heavy Kr ions with high(Ge V) energies and ultralow fluences. The micro-Raman spectra are measured at different depths in the irradiated layer and show that the high electronic energy loss can cause lattice damage along the ion trajectory, while the nuclear energy loss causes damage at the end of the ion track. Two waveguide layers are formed by confinement with two barriers associated with decreases in the refractive index that are caused by electronic and nuclear energy losses, respectively.     

Effect of swift heavy ion irradiation in Fe/W multilayer structures

Present study reports effect of swift heavy ion irradiation on structural and magnetic properties of sputtered Fe/W multilayer structures (MLS) having bilayer compositions of [Fe(20 Å)/W(10 Å)]_5BL and [Fe(20 Å)/W(30 Å)]_5BL. These MLS are irradiated by 120 MeV Au⁹⁺ ions up to fluence of 4 × 10¹³ ions/cm². X-ray reflectivity (XRR), wide-angle X-ray diffraction (WAXD), cross-sectional transmission electron microscopy (X-TEM) and magneto optical Kerr effect (MOKE) techniques are used for structural and magnetic characterization of pristine and irradiated MLS. Analysis of XRR data using Parratt's formalism shows a significant increase in W/Fe interface roughness. WAXD and X-TEM studies reveals that intra-layer microstructure of Fe-layers in MLS becomes nano-crystalline on irradiation. MOKE study shows increase in coercivity at higher fluence, which may be due to increase in surface and interface roughness after recrystallization of Fe-layers.     

Effect of secondary electrons from latent tracks created in YBCO by swift heavy ion irradiation

Swift heavy ions (SHI) with electronic energy loss exceeding a value of 14.4 keVnm⁻¹ create amorphized latent tracks in YBCO type superconductors. In the low fluence regime of an ion beam where tracks do not overlap, a decrease of the superconducting transition temperature as probed through resistivity studies, is not expected due to availability of percolating current paths. The present study however shows T_c decrease by about 1–3 K in thin films of YBCO when irradiated by 250 MeVAg ions at 79 K at a fluence of 5×10¹⁰–1×10¹² ionscm⁻². The highest fluence used in the present study is three times less than the fluence where track overlapping becomes significant. The T_c tends to increase towards the preirradiation value on annealing the films at room temperature. To explain this unusual result, we consider the effect of ion irradiation in inducing materials modification not only through creation of amorphized latent tracks along the ion path, but also through creation of atomic disorder in the oxygen sublattice in the Cu–O chains of YBCO by the secondary electrons. These electrons are emitted radially from the tracks during the passage of the SHI. Considering the correlation between the charge state of copper and its oxygen coordination, we show in particular that the latter process is a consequence of the inelastic interaction of the SHI induced low-energy secondary electrons with the YBCO lattice, which result in chain oxygen disorder and T_c decrease.     

Observation of grain growth in swift heavy ion irradiated NiO thin films

NiO thin films grown on Si(100) substrates by electron beam evaporation, were sintered at 500 °C and 700 °C. The films were irradiated with 120 MeV Au⁹⁺ ions. Irradiation had different effects depending upon the initial microstructure of the films. Irradiation of the films at a fluence of 3 × 10¹¹ ions cm⁻² leads to grain growth for the films sintered at 500 °C and grain fragmentation for the films sintered at 700 °C. At still higher fluences of irradiation, grain size in 500 °C sintered film decreased, but the same improved in 700 °C sintered film. Associated with the grain size, texturing of the films was also shown to undergo significant modifications under irradiation.     

Conducting swift heavy ion track networks

In this paper, the electronic behavior of conducting swift heavy ion track networks is studied. On the one hand, the transient conductivity of ion tracks in metal oxides on silicon in status nascendi is exploited for this purpose, and on the other hand, conducting tracks are produced by ion irradiation of insulating membranes (either self-supported or deposited onto silicon substrates), subsequent etching and finally inserting conducting materials of whatever provenience (in this work preferentially electrolytes). Depending on their manufacture, the conducting tracks either act as electronically active or passive elements. When applying a voltage across individual tracks in the first case, one observes current spikes with negative differential resistances. These tracks interact among themselves, leading to phase-locked synchronous coupled oscillations with complex patterns that are quite similar to those emerging from neural networks. The other case corresponds to networks of electronically passive conducting tracks which become overall electronically active only through their collective interactions. Though the aforementioned effects had been experimentally described earlier, they are re-visited here to make clear that the corresponding systems have to be considered as being artificial neural networks. On this occasion, some new findings are added.     

Structural modifications of diamond like carbon films induced by MeV nitrogen ion irradiation

Diamond-like carbon (DLC) films were deposited on Si(1 0 0) substrates using plasma deposition technique. The deposited films were irradiated using 2 MeV N⁺ ions at fluences of 1×10¹⁴, 1×10¹⁵ and 5×10¹⁵ ions/cm². Samples have been characterized by using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). Analysis of Raman spectra shows a gradual shift of both D and G band peaks towards higher frequencies along with an increase of the intensity ratio, I(D)/I(G), with increasing ion fluence in irradiation. These results are consistent with an increase of sp² bonding. XPS results also show a monotonic increase of sp²/sp³ hybridization ratio with increasing ion fluence. Plan view TEM images show the formation of clusters in the irradiated DLC films. HRTEM micrographs from the samples irradiated at a fluence of 5×10¹⁵ ions/cm² show the lattice image with an average interplanar spacing of 0.34 nm, revealing that the clusters are graphite clusters. The crystallographic planes in these clusters are somewhat distorted compared to the perfect graphite structure.     

快重离子束实现点火的可行性

采用蒙特卡罗方法计算了低温下C,Si,Ar,Au和U等多种重粒子在等物质的量氘氚等离子体密度1000 g/cm3、热斑直径50 m中的电子能量损失,不同点火形式下入射能量和作用时间,以及燃料约束时间为20 ps条件下的束流强度。通过对数据的分析研究了这些重粒子辐照实现氘、氚燃料快点火的可能性。结果表明,重粒子束流加热等离子体实现快点火理论上可行,而且有一定的优势;较重的离子加热聚变等离子体的效果更好。重粒子束流加热等离子体到聚变温度需要的束流强度在MA左右;单个粒子的能量在GeV以上;相互作用时间为ps以下。     

Study of size dependent features of swift heavy ion irradiation in nanosized zinc ferrite

In the present work zinc ferrite nanoparticles of different crystallite size were irradiated with 200 MeV Ag¹⁵⁺ ion beam. The structural and magnetic characterization performed for these samples indicate the presence of size dependent irradiation induced changes in the nanoparticles. The superparamgnetic nanoparticles do not alter their behavior after irradiation; however paramagnetic samples exhibit weak ferrimagnetism in the irradiated specimen. Results obtained from these measurements are in agreement with results obtained from the electron paramagnetic resonance spectroscopy.     

快重离子束实现点火的可行性

采用蒙特卡罗方法计算了低温下C,Si,Ar,Au和U等多种重粒子在等物质的量氘氚等离子体密度1000 g/cm3、热斑直径50 m中的电子能量损失,不同点火形式下入射能量和作用时间,以及燃料约束时间为20 ps条件下的束流强度。通过对数据的分析研究了这些重粒子辐照实现氘、氚燃料快点火的可能性。结果表明,重粒子束流加热等离子体实现快点火理论上可行,而且有一定的优势;较重的离子加热聚变等离子体的效果更好。重粒子束流加热等离子体到聚变温度需要的束流强度在MA左右;单个粒子的能量在GeV以上;相互作用时间为ps以下。     

Material modifications induced by swift heavy ions in NbTi superconducting wires

The Facility for Antiproton and Ion Research (FAIR) to be built at GSI in Darmstadt will be equipped with superconducting magnets. Due to the high ion beam intensities and related beam losses, radiation damage of the Cu/NbTi superconducting wires used in the magnet coils has to be considered. Here we report first experimental results on NbTi multifilament wires exposed to 2.6 GeV U ions at room temperature. Radiation-induced effects were examined using X-ray diffraction and transmission electron microscopy. With increasing ion fluence the amount of the α-Ti phase decreases. This is crucial because α-Ti precipitates are the main flux-pinning centres in the Nb–Ti superconducting alloy. The equilibrium hcp α-Ti transforms into the hexagonal ω-Ti phase.