Defect and Diffusion Forum Vol. 341

Abstract: The effect of various radiations to a polymer is more complex and intense, compared to that in other materials, in view of the more complex structure and low bonding energies (5 10 eV for covalent bonds of the main carbon chain). Since the energy delivered to the polymer in most irradiations (including even beta and gamma rays of 1 to 10 MeV) exceeds this energy by many orders of magnitude, there is a high risk of radiation damage to all kind of polymers. However, engineering polymers (PC, PMMA, PVC, etc. and newer ones) as well as electro-active and other functional polymers (conducting polymers, polymer electrolytes) are finding ever increasing applications, often as nanocomposites, e.g. chemical and biomedical applications, sensors, actuators, artificial muscles, EMI shielding, antistatic and anticorrosion coatings, solar cells, light emitters, batteries and supercapacitors. Critical applications in spacecrafts, particle accelerators, nuclear plants etc. often involve unavoidable radiation environments. Hence, we need to review radiation damage in polymers and encourage use of newer tools like positron annihilation spectroscopy, micro-Raman spectroscopy and differential scanning calorimetry (DSC). Present review focuses on irradiation effects due to low energy ions (LEIs) and swift heavy ions (SHIs) on electro-active and engineering polymers, since gamma-and electron-beam-irradiations have been more widely studied and reviewed. Radiation damage mechanisms are also of great theoretical interest. Contents

Abstract: We have These films were irradiated with 85 MeV C-ions at the fluences of 1 x 10¹¹ and 1 x 10¹² ions/cm². Changes in the optical, structural, dielectric, magnetic and thermal properties of (PMMA)/Ni nanocomposites of different concentrations of nickel nanoparticles (5%, 10%, 15%) due to swift heavy ion irradiation were studied by means of UVvisible spectroscopy, X-ray diffraction, impedance gain phase analyzer, SQUID and differential scanning calorimetry. Optical properties like band gap were estimated for pure polymer and nanocomposite films from their optical absorption spectra in the wavelength range 200-800 nm. It was found that the band gap value shifted to lower energy on doping with metal nanoparticles. Differential scanning calorimetry analysis revealed a decrease in the glass transition temperature upon irradiation, which may be attributed to the scissioning of polymer chain due to ion beam irradiation which is also corroborated with XRD analysis. Surface morphology of the pristine and irradiated films was studied by scanning electron microscopy (SEM). The breakage of chemical bonds resulted in an increase of free radicals, unsaturation etc. as revealed from FTIR analysis. The dielectric properties were observed to enhance with an increase in metal compound concentration as well as with irradiation dose. This may be due to metal/polymer bonding and conversion of polymeric structure into hydrogen-depleted carbon network. Zero-Field-Cooled (ZFC)/Field-Cooled (FC) magnetization and magnetic hysteresis measurements were performed using a superconducting quantum interference device (SQUID) magnetometer from temperatures ranging from 5 K to 300 K, to investigate the magnetic properties of nanocomposites. The changes in topography of surfaces were also observed upon irradiation.

Abstract: High energy ion beam induced modifications in polymeric materials is of great interest from the point of view of characterization and development of various structures and filters. Due to potential use of conducting polymers in light weight rechargeable batteries, magnetic storage media, optical computers, molecular electronics, biological and thermal sensors, the impact of swift heavy ions for the changes in electrical, structural and optical properties of polymers is desirable. The high energy ion beam irradiation of polymer is a sensitive technique to enhance its electrical conductivity, structural, mechanical and optical properties. Recent progress in the radiation effects of ion beams on conducting polymers are reviewed briefly. Our recent work on the radiation effects of ion beams on conductive polymers is described. The electrical, structural and optical properties of irradiated films were analyzed using V-I, X-Ray diffraction (XRD), scanning electron microscopy (SEM), UV-Visible spectroscopy and Fourier transform infrared spectroscopy methods.

Abstract: Borosilicate based glass formulations have been found suitable for vitrification of high level nuclear waste (HLW) generated during the reprocessing of spent nuclear fuel from nuclear reactors. These glasses possess desirable properties like high chemical, mechanical, thermal and radiation stability for HLW storage. Also, the amorphous nature of the glass helps accommodate the waste containing a variety of elements easily. Because of the presence of the radioactive components, such as, fission /activation products and minor actinides present in the waste, the glass containment experiences radiation damage that can significantly alter the glass structure which may influence their long term leaching behavior. Spectroscopic techniques provide direct and non-invasive method for investigating this radiation damage in the glasses. The present paper gives a glimpse of the current status and issues regarding the investigation of radiation damage in the glass matrices.

Abstract: t is well established that the properties of the materials can be tailored as per specific requirements as a result of swift heavy ion irradiation. This is because of the radiation damage induced changes in the properties of the materials as a result of the energy loss process of the incident ions along their trajectory. In order to correlate such induced changes with the energy loss of the impinging ions, the exact evaluation of energy loss for swift ions in different materials is extremely important. Keeping in mind the polymers as versatile materials, in the present work, we have focused on energy loss calculations for swift heavy ions with Z= 3-29 in different polymeric absorbers, e.g. Polypropylene PP (C₃H₆), Polycarbonate PC (C₁₆H₁₄O₃), Polyethylene terepthalate PET (C₁₀H₈O₄), Polyethylene naphthalate PEN (C₇H₅O₂), Diethylene glycol bis (allyl carbonate) CR-39 (C₁₂H₁₈O₇), Cellulose nitrate LR-115 (C₆H₉O₉N₂) and Polypyromellitimide KAPTON (C₂₂H₁₀O₅N₂) in the energy range 0.5-6.00 MeV/n. The present calculations have been made by employing the proper energy loss formulation applicable both at low as well as high energies, involving a new approach for effective charge parameterization without any empirical/semi-empirical means. A close agreement between these calculated and experimentally measured values has been observed. Such calculations will provide an input towards the modeling or simulation for swift heavy ion induced changes in the properties of materials.

Abstract: This paper is devoted to production of metallic micro-and nanowires (Cu, Co, Ni and Fe) using commercial track membranes. Specially prepared matrices were also fabricated and used for this purpose. The process of electrodeposition of these metals into the nanosized pores was investigated and found to be non-linear for small pores. The obtained ensembles of nanowires could be used as the effective templates for emission of molecules in mass-spectrometry. Mass-spectra of test peptide (gramicidin deposited on substrate - ensemble of copper nanowires) was obtained and investigated in different conditions.

Abstract: Swift heavy ion irradiation of material is a unique tool to modify the properties of the material and it provides an alternative to photons for introducing electronic excitations into the material. In the present investigation, the changes in structural, morphological and magnetic properties of SrFe₁₂O₁₉ ferrite (prepared using co-precipitation and SHS routes), induced by 200 MeV Ag⁺¹⁶ ion irradiation have been studied. In order to study the effect of the electronic stopping power (dE/dX) e on these properties the energy of the projectile was so chosen that it could easily pass through the samples. Structural properties of these ferrites have been studied and compared with the properties after Swift Heavy Ion (SHI) irradiation of 200 MeV Ag¹⁶⁺ at different fluences. Samples were characterized using different experimental techniques, like Fourier Transform Infra-red (FT-IR), X-ray Diffraction (XRD), Scanning Electrom Microscope (SEM), Vibrating Sample Magnetometer (VSM) and LCR meter. FTIR spectra for pristine as well as the irradiated samples were recorded for wave number ranges from 4000-400 cm^-1 using the KBr pellet method. FTIR measurement of the bonds' vibration modes in all samples were carried out to determine the change in MO bonding due to irradiation. The MO absorption band is observed in all samples. The intensity of absorption bands increased in irradiated samples, which confirms the formation of strong ferric oxide band. Crystallinity of pristine and irradiated samples was investigated by XRD technique. All XRD peaks were indexed using POWDER X software. XRD result confirms the formation of mono phase. It is observed from XRD analysis that after the irradiation, the intensity of all the peaks and FWHM were increased. There is no significant change in peak position but the intensity is decreased and FWHM is increased continuously with ion fluence. XRD patterns confirm that the ferrite structure is retained even after irradiation. Surface morphology of pristine and irradiated samples was studied using a scanning electron microscopy. It is observed from SEM images that the particle size decreases after irradiation and particles become more homogeneous. Dielectric and magnetic measurements were also carried out.

Abstract: The effect of ion beam bombardment on the optical and mechanical properties of ultra-high molecular weight polyethylene (UHMWPE) was investigated. UHMWPE polymer samples were bombarded with 150 keV N₂ ions under vacuum at room temperature to high fluences ranging from 1x10¹⁶ to 2x10¹⁷ ions cm^-2. The untreated as well as treated samples were investigated by ultraviolet-visible (UV-Vis) spectrophotometer and Vickers micro-hardness techniques. The direct and indirect optical band gap decreased from 2.9 and 1.65 eV for pristine sample to 1.7 and 1 eV for those bombarded with N₂ ion beam at the highest fluence, respectively. With increasing ion fluence, an increase in the number of carbon atoms per conjugation length, N and number of carbon atoms per cluster, M in a formed cluster were observed. A significant improvement in surface hardness was obtained by increasing the ion fluence.

Abstract: High-energy electron, proton, neutron, photon and ion irradiation of semiconductor diodes and solar cells has long been a topic of considerable interest in the field of semiconductor device fabrication. The inevitable damage production during the process of irradiation is used to study and engineer the defects in semiconductors. In a strong radiation environment in space, the electrical performance of solar cells is degraded due to direct exposure to energetically charged particles. A considerable amount of work has been reported on the study of radiation damage in various solar cell materials and devices in the recent past. In most cases, high-energy heavy ions damage the material by producing a large amount of extended defects, but high-energy light ions are suitable for producing and modifying the intrinsic point defects. The defects can play a variety of electronically active roles that affect the electrical, structural and optical properties of a semiconductor. This review article aims to present an overview of the advancement of research in the modification of glassy semiconducting thin films using different types of radiations (light, proton and swift heavy ions). The work which has been done in our laboratory related to irradiation induced effects in semiconducting thin films will also be compared with the existing literature.