High Fluence Ion Irradiation of Thin Fullertte Films

Abstract

Thin fullerite films - partly covered with a thin Au layer -have been irradiated with 100 keV Arⁿ⁺ (n = 1, 6, and 12), 250 keV N⁺, and 30 keV Au⁺ ions up to high fluences, and subsequently analyzed by profilometry, Rutherford Backscattering Spectrometry (RBS), and Atomic Force Microscopy (AFM). Depending on the system, either an increase or a decrease of the film thickness after the irradiations was found, and the probing RBS α particles suffered sometimes an enhanced, and sometimes a reduced energy loss upon passage through the films. The comparison of profilometry and RBS results on uncovered and covered samples allows us to separate the different effects which influence the behavior of high-fluence irradiated fullerite samples clearly from each other. Such effects might be the incorporation of the projectile ions, density changes, phase changes, sputtering, and transport of neighbored unirradiated matter into the irradiated zone.

It is remarkable that ion irradiation of fullerite can lead as well to a densified material, with densities of about 2.1 g-cm^?3, as to a foam-like carbonaceous material with a density around 0.35 g-cm^?3 - depending on the type of projectile and its range. The latter case appears to be characteristic for high-fluence heavy noble gas implantation into fullerite. Fullerite sputtering was reconfirmed to decrease inversely with the fluence.     

Proton induced modification in makrofol-DE

Irradiation effects of a 3 MeV proton beam on polycarbonate (makrofol-DE (MFD)) have been studied with respect to its electrical, thermal and structural behaviour by using an LCR meter, DSC/TGA and FTIR spectroscopy. The dielectric loss/constant was observed to change with the fluence. Thermal analysis revealed that chain scission is the dominant phenomena in irradiated samples based on the reduction of its thermal stability by about 19% at a fluence of 10¹⁵ ions/cm², which is also corroborated by FTIR spectra. No significant change in intensity of the absorbance bands of the irradiated sample was observed up to a fluence of 10¹⁴ ions/cm² while on increasing fluence (10¹⁵ ions/cm²) the polymer structure was modified. It appears from DSC thermograms thatT _g is observed to change with fluence.     

Ion beam studies of multi-quantum wells of III-nitrides

III-Nitrides have attracted much attention due to their versatile and wide range of applications, such as blue/UV light emitting diodes. Strained layer super lattices offer extra degree of freedom to alter the band gap of lattice-mismatched heterostructures. Swift heavy ion irradiation is a post-growth technique to alter the band gap of semiconductors, spatially. In the present study, strained AlGaN/GaN multi-quantum wells (MQWs) were grown on sapphire with insertion of AlN and GaN as buffer layers between substrate and epilayers. Such grown AlGaN/GaN MQWs, AlGaN/GaN heterostructures and GaN layers were irradiated with 200 MeV Au and 150 MeV Ag ions at a fluence of 5 × 10¹¹ ions/cm² and 5 × 10¹² ions/cm² respectively. As-grown and irradiated samples have been characterized by high resolution XRD, photoluminescence and RBS/channelling. Measured strain values show that strain increases upon irradiation and the luminescence properties are enhanced. RBS/channelling confirms the increase in strain values upon irradiation. In this paper we describe the effects of swift heavy ion irradiation on structural and optical properties.     

Studies on Ag and Li ions irradiated LAHCl single crystals

Semi-organic single crystals of LAHCl were grown by unidirectional solution growth method. The grown single crystals were subjected to Ag⁸⁺ and Li⁴⁺ ions irradiation of energy 100 MeV and 50 MeV, respectively. Breaking of bonds in the irradiated LAHCl molecules and the lattice deformations are analyzed by Fourier transform infrared spectroscopy and X-ray diffraction studies, respectively. The modifications induced by ion irradiation in dielectric, mechanical stability and nonlinear optical property are studied at different ion fluence.     

Radiation hardness of cryogenic silicon detectors

We shall review test results which show that silicon detectors can withstand at 130 K temperature a fluence of 2×10¹⁵ cm^–2 of 1 MeV neutrons, which is about 10 times higher than the fluence tolerated by the best detectors operated close to room temperature. The tests were carried out on simple pad devices and on microstrip detectors of different types. The devices were irradiated at room temperature using reactor neutrons, and in situ at low temperatures using high-energy protons and lead ions. No substantial difference was observed between samples irradiated at low temperature and those irradiated at room temperature, after beneficial annealing. The design of low-mass modules for low-temperature trackers is discussed briefly, together with the cooling circuits for small and large systems.     

Photoluminescence and Raman studies in swift heavy ion irradiated polycrystalline aluminum oxide

Polycrystalline aluminum oxide is synthesized by combustion technique and XRD studies of the sample revealed the α-phase. The synthesized sample is irradiated with 120 MeV swift Au⁹⁺ ions for the fluence in the range from 1 × 10¹¹ to 1 × 10¹³ ions cm⁻². A broad photoluminescence (PL) emission with peak at ∼ 447 nm and two sharp emissions with peak at ∼ 679 and ∼ 695 nm are observed in pristine when sample was excited with 326 nm. However, in the irradiated samples the PL intensity at ∼ 447, 679 and 695 nm decreases with increase in ion fluence. The α-Al₂O₃ gives rise to seven Raman modes with Raman intensity with peaks at ∼ 253, 396, 417, 546, 630, 842, 867 cm⁻¹ observed in pristine. The intensity of these modes decreases with increase in ion fluence. However, the Raman modes observed at lower fluences are found to disappear at higher fluence.     

Ion bombardment of Poly-Allyl-Diglycol-Carbonate (CR-39)

Ion bombardment is thought to have great potential for improving the optical properties of polymeric materials. In this paper, Poly-Allyl-Diglycol-Carbonate (CR-39) polymer samples were bombarded with 320 keV Ar and 130 keV He ions, at different ion fluences. Effects of ion bombardment on the optical properties of CR-39 have been investigated using UV-vis spectrophotometer and photoluminescence (PL) spectroscopy. UV-vis spectra of irradiated samples reveal that the optical band gap decreases with increasing the ion fluence for both Ar and He ions. The width of the tail of localized states in the band gap (E_u) was evaluated using the Urbach edge method. The decrease in the PL intensity with the increase in the ion fluence was observed. This decrease is attributed to ion bombardment induced defects and clusters in the CR-39 which serves as non-radiative centers.     

Microstructural changes in oxygen-irradiated zirconium-based alloy characterised by X-ray diffraction techniques

We have carried out irradiation with 116 MeV O⁵⁺ ions on Zr–1Sn–1Nb–0.1Fe (ZIRLO) alloy at different doses and the microstructural parameters of the irradiated samples have been characterised by X-ray Diffraction Line Profile Analysis (XRDLPA). The average volume-weighted and surface-weighted domain size, microstrain and dislocation density have been estimated as a function of dose. There was a drastic decrease in domain size from unirradiated sample to the sample at a dose of 1 × 10¹⁷ O⁵⁺/m², but these values saturated with increasing dose of irradiation. The values of microstrain were found to increase with dose. The dislocation density increased almost by an order of magnitude for the samples irradiated with 1 × 10¹⁸ O⁵⁺/m² and 5 × 10¹⁸ O⁵⁺/m² as compared to the unirradiated samples.     

Study of microhardness and electrical properties of proton irradiated polyethersulfone (PES)

Polyethersulfone (PES) films were irradiated with 3 MeV proton beams in the fluence range 10¹³–10¹⁵ ions/cm². The radiation induced changes in microhardness was investigated by a Vickers’ microhardness tester in the load range 100–1000 mN and electrical properties in the frequency range 100 Hz-1 MHz by an LCR meter. It is observed that microhardness of the film increases significantly as fluence increases up to 10¹⁴ ions/cm². The bulk hardness of the films is obtained at a load of 400 mN. The increase in hardness may be attributed to the cross linking effect. There is an exponential increase in conductivity with log frequency and the effect of irradiation is significant at higher fluences. The dielectric constant/loss is observed to change significantly due to irradiation. It has been found that dielectric response in both pristine and irradiated samples obey the Universal law and is given by ɛ ∝ f ⁿ⁻¹. These results were corroborated with structural changes observed in FTIR spectra of irradiated samples.     

Photoinduced polarization investigations in 75 MeV oxygen ion irradiated kapton-H polyimide

The photoinduced polarization in 75 MeV oxygen ion irradiated (fluence: 1.8 × 10¹¹, 1.8 × 10¹² and 1.8 × 10¹³ ions/cm²) kapton-H polyimide has been investigated by analyzing charge decay characteristics for different polarizing parameters viz. electric fields (40 to 600 kV/cm), temperature (40 to 250 °C) and illumination intensity (1200 to 2800 1x). The fields induced as well as thermal ionization of excitons under illumination are the main causes which provide photopolarization. The charge decay spectra reveal the presence of both shallow and deep trapping sites in pristine and irradiated kapton-H polyimide. The variation in the photopolarization with fluence shows the occurrence of secondary radiation induced crystallinity (SRIC). The SRIC is also responsible for the increase in initial current (I_0P) with intensity of illumination in low fluence irradiated samples. A decrease in I_0P with intensity of illumination in high fluence irradiated samples has been associated to the conversion of trapping sites into recombination centers.     

Influence of SHI irradiation on the structure and surface topography of CdTe thin films on flexible substrate

Impact of ion irradiation on thin films is an emerging area for materials modification. CdTe thin films grown by thermal evaporation on flexible molybdenum (Mo) substrate were irradiated with Swift (100 MeV) Ag⁺⁷ ions for various ion fluence in the range 10¹²–10¹³ ions/cm². The modifications in the composition, structure and surface morphology have been studied as a function of ion fluence. The Energy Dispersive X-ray Analysis (EDS) shows slightly Te-rich composition for both as-grown and irradiated films with no significant change after irradiation. X-ray diffraction (XRD) analysis indicates a consistent shift in the (111) peak position towards higher diffraction angle and an increase in the full width at half maximum (FWHM) with increase in ion fluence. The change in the residual stress during irradiation has been evaluated and is related to the corresponding microstructural changes in the films. The initial tensile stress is found to be relaxed after irradiation. Atomic Force Microscopy (AFM) studies revealed significant grain splitting after irradiation and formation of hillocks at higher ion fluence. The surface roughness was significantly increased at higher ion fluence.     

Effect of Ni7+ Ion Irradiation on Structure and Ammonia Sensing Properties of Thermally Oxidized Zinc and Indium Films

ZnO and In2O3 films were prepared by thermal oxidation of vacuum deposited zinc and indium films, respectively onto the glass substrate at 30 C. The fabricated films have been irradiated with 100-MeV Ni7+ ions at different fluences ranging from 5×1011 to 5×1013 ions/cm2. The structural and gas sensing properties of pristine and irradiated films have been discussed. X-ray diffraction (XRD) pattern of pristine and irradiated films reveal that the films are polycrystalline in nature and crystallinity increases after irradiation. In this study, highly porous In2O3 nanorods evolved when being irradiated at a fluence of 5×1013 ions/cm2 while ZnO film shows decrease in number of nanowires. The ammonia sensing performance of the Ni7+ irradiated In2O3 films shows an improvement as compared to its pristine counterpart.     

Computer Simulation of C60 Fullerene Fragmentation by Electron Beam

Abstract

Computer simulation of electron‐induced ionization and fragmentation of free C₆₀ fullerenes, as well as of fullerenes in fullerite films, was carried out. It was found that stable complexes of heavy fullerene's fragments are formed under electron irradiation in fullerite films. These complexes are characterized by different spatial configurations and electron structures and can cause long‐term mechanical stresses.     

Phenomenological understanding of dewetting and embedding of noble metal nanoparticles in thin films induced by ion irradiation

The present experimental work provides the phenomenological approach to understand the dewetting in thin noble metal films with subsequent formation of nanoparticles (NPs) and embedding of NPs induced by ion irradiation. Au/polyethyleneterepthlate (PET) bilayers were irradiated with 150 keV Ar ions at varying fluences and were studied using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (X-TEM). Thin Au film begins to dewet from the substrate after irradiation and subsequent irradiation results in spherical nanoparticles on the surface that at a fluence of 5 × 10¹⁶ ions/cm² become embedded into the substrate. In addition to dewetting in thin films, synthesis and embedding of metal NPs by ion irradiation, the present article explores fundamental thermodynamic principles that govern these events systematically under the effect of irradiation. The results are explained on the basis of ion induced sputtering, thermal spike inducing local melting and of thermodynamic driving forces by minimization of the system free energy where contributions of surface and interfacial energies are considered with subsequent ion induced viscous flow in substrate.     

Irradiation effects in semiconductor

Samples of crystalline silicon, porous silicon, gallium arsenide and silicon diodes were exposed to 50–80 MeV silicon and oxygen ions in the fluence range of the order of 10¹³ to 10¹⁴ ions/cm². The irradiated samples were characterized to obtain information on the relative concentration and depth distribution of the induced defects. For comparison a few silicon diodes and crystalline silicon samples were also exposed to 6 MeV electrons. The main techniques used for the analysis of silicon samples were low angle X-ray diffraction, photo-luminescence spectroscopy and lifetime of minority carriers, whereas diodes were characterized on the basis of switching parameters. It is observed that a large number of defects are produced in the surface region of each of the irradiated semiconductor sample though the energy deposited in the surface region through electronic loss is three orders of magnitude greater than that of nuclear collisions.     

ENERGY LOSS AND ENERGY STRAGGLING OF LIGHT IONS IN FULLERITE

To determinate the stopping cross section in fullerite a feasible approach, taking into account the high radiation sensitivity and mechanical fragility of fullerite films, should be employed. In this work, the stopping cross sections of ¹H, ³H, ⁴He and ⁷Li ions for several selected energies were measured by Rutherford backscattering, neutron depth profiling and alpha spectroscopy using sandwich structures of samples composed of fullerite deposited on a firm substrate (Si, steel) with an intermediate marker (Au, N, Li, B, Pu). In addition, ion transmission through a thin C film supporting a fullerite layer was also utilized. The measured stopping cross sections follow the theoretical predictions calculated for carbon, but are systematically (10-35%) higher than the theoretical ones (with the exception of 5 — 5.5 MeV ⁴He). The observed deviation of the experimental data can partly be explained by the chemical state effects in fullerite, which accounts for about 20-50% of the difference. The measured energy straggling exceeds Bohr's value by a factor of about 2 for alpha spectroscopy and ion transmission, and 2.5 or 9.5 for Rutherford backscattering and neutron depth profiling, respectively. The discrepancy can be explained by a thickness variation, such as surface roughness of the fullerite films.     

Microstructure and electrochemical properties of Zircaloy-4 under Fe ion irradiation

To investigate the microstructure and electrochemical properties of Zircaloy-4 induced by Fe ion irradiation with the energy of 150 keV at liquid nitrogen temperature, transmission electron microscope analysis (TEM) was employed to analyze the surface layer of the samples irradiated at a dose ranging from 1×10¹³ to 1×10¹⁶ ions/cm², and potentiodynamic polarization measurements were used to evaluate the corrosion resistance of Zircaloy-4 in a 1 N H₂SO₄ solution at room temperature. TEM analyses show that Fe ion irradiation lead to a structural change and amorphous phase formation on the surface of the samples. Moreover, it is indicated from the corrosion tests that with an increase of the irradiation dose, the passive current density increases at first and then decreases rapidly, while the natural corrosion potential goes down at first and then up rapidly. The critical point, where the corrosion properties are transformed from a damaging stage to protecting stage, is at the damage level of 3.19 dpa. Finally, the mechanism for the change of corrosion resistance of the Zircaloy-4 samples is discussed.     

Analysis of organometallics dispersed polymer composite irradiated with oxygen ions

Thin films of polymethyl methacrylate (PMMA) were synthesized. Ferric oxalate was dispersed in PMMA films. These films were irradiated with 80 MeV O⁶⁺ ions at a fluence of 1×10¹¹ ions/cm². The radiation induced changes in electrical conductivity, Mössbauer parameter, microhardness and surface roughness were investigated. It is observed that hardness and electrical conductivity of the film increases with the concentration of dispersed ferric oxalate and also with the fluence. It indicates that ion beam irradiation promotes (i) the metal to polymer bonding and (ii) convert the polymeric structure into hydrogen depleted carbon network. Thus irradiation makes the polymer harder and more conductive. Before irradiation, no Mössbauer absorption was observed. The irradiated sample showed Mössbauer absorption, which seems to indicate that there is significant interaction between the metalion and polymer matrix. Atomic force microscopy shows that the average roughness (R _a) of the irradiated film is lower than the unirradiated one.     

Energetic ion irradiation induced crystallization of Ni–Mn–Sn ferromagnetic shape memory alloy thin film

The ion irradiation induced crystallization of Ni–Mn–Sn ferromagnetic shape memory alloy (FSMA) thin film is investigated. Thin films of Ni–Mn–Sn FSMA synthesized by DC magnetron sputtering on Si substrate at 200 °C are irradiated by a beam of 120 MeV Ag ions at different fluence varying from 1 × 10¹² to 6 × 10¹² ions/cm². X-ray diffraction pattern reveals that the pristine film grows in L2₁ cubic austenite phase with poor crystallinity and crystallinity of the film improves with increasing ion fluence, which is attributed to the strain relaxation by the energy deposited by incoming ions and promotes the grain growth. Grain growth is further confirmed by Atomic force microscopy. The temperature dependent magnetization measurements show improvement in the magnetic and shape memory properties of the films with increasing fluence, which is ascribed to the ordering of austenite phase. Nanoindentation measurements show that with increasing fluence of 120 MeV Ag ions, films exhibit a greater stiffness and smaller tendency towards plastic deformation.     

Electrical and morphological properties of poly(3-hexyl thiophene) irradiated with 100 MeV silver ions

Poly(3-hexyl thiophene) has been prepared by a chemical oxidation process. The pristine polymer was irradiated with various fluences of (silver (Ag⁸⁺)) swift heavy ions viz. 10¹⁰, 10¹¹, and 10¹² ions/cm². All the samples, irradiated and without irradiation, have been characterized by various techniques such as surface electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), FT-IR and UV spectroscopy. The dc conductivity of all the samples has been investigated in 77-300 K. The room temperature conductivity of pristine samples is 2.39 × 10⁻⁸ which increases to 1.65 × 10⁻⁶ Ohm⁻¹ cm⁻¹ at the fluence of 10¹¹ ions/cm². The observed conduction mechanism for all the samples could be explained in terms of Mott's variable range hopping model.