Unirradiated Films Research Articles

Electron beam induced modifications of bismuth sulphide (Bi 2S 3) thin films: Structural and optical properties

Thin films of Bi 2S 3 prepared by electrodeposition method are subjected to electron beam irradiation for different doses from 0 to 100 kGy in steps of 20 kGy in air at room temperature. The changes in structural, surface morphological and optical properties that occurred before and after irradiation in Bi 2S 3 thin films are studied using X-ray diffraction, scanning electron microscopy and UV–vis spectroscopy. It is shown that electron irradiation can be used as a tool to decrease the crystallite size of the irradiated films from 418 to 285 Å as the dose varies from 20 to 100 kGy. The decrease in crystallinity of the films leading to the band gap energy of the films get blue shifted from unirradiated films. These results are explained in the light of thermal spike model.

Dielectric properties of electron irradiated PbZrO3 thin films

The present paper deals with the study of the effects of electron (8 MeV) irradiation on the dielectric and ferroelectric properties of PbZrO3 thin films grown by sol-gel technique. The films were (0.62 μm thick) subjected to electron irradiation using Microtron accelerator (delivered dose 80, 100, 120 kGy). The films were well crystallized prior to and after electron irradiation. However, local amorphization was observed after irradiation. There is an appreciable change in the dielectric constant after irradiation with different delivered doses. The dielectric loss showed significant frequency dispersion for both unirradiated and electron irradiated films. T c was found to shift towards higher temperature with increasing delivered dose. The effect of radiation induced increase of ɛ′(T) is related to an internal bias field, which is caused by radiation induced charges trapped at grain boundaries. The double butterfly loop is retained even after electron irradiation to the different delivered doses. The broader hysteresis loop seems to be related to radiation induced charges causing an enhanced space charge polarization. Radiation-induced oxygen vacancies do not change the general shape of the AFE hysteresis loop but they increase P s of the hysteresis at the electric field forced AFE to FE phase transition. We attribute the changes in the dielectric properties to the structural defects such as oxygen vacancies and radiation induced charges. The shift in T C, increase in dielectric constant, broader hysteresis loop, and increase in P r can be related to radiation induced charges causing space charge polarization. Double butterfly and hysteresis loops were retained indicative of AFE nature of the films.

XRD and SEM Investigation of Swift Heavy Ion-Irradiated Polyvinylidene Fluoride Thin Films

Polyvinylidene fluoride (PVDF) films of different thicknesses are irradiated with 100 meV Ag-ion and 75 meV Oxygen-ion beams at different fluences to study the effects of swift heavy ion (SHI) irradiation in PVDF. The change in physical, chemical, and surface morphological properties of irradiated films are investigated using x-ray diffraction, Field emission scanning electron microscopy (FESEM), and energy dispersive analysis by x-ray (EDAX) techniques by taking unirradiated (pristine) films as reference. The diffraction pattern shows that PVDF polymer is in semi-crystalline form and possesses crystalline α-, β-, and γ-phases. A decrease in the crystallinity and crystallite size has been observed when PVDF is irradiated with 100 meV Ag-, and also Oxygen ions at a higher fluence of 5.675 × 1012 ions/cm2. However, an increase in crystallinity and decrease in crystallite size are observed when PVDF is irradiated with oxygen-ion beam at lower fluence 5.625 × 1011 ions/cm2. The structural parameters such as degree of crystallinity, crystallite size, microstrain, and dislocation density have also been estimated. EDAX result shows that the chemical composition of PVDF is invariant under SHI irradiation, which is in agreement with our earlier results of FTIR. FESEM analysis shows granular microstructure with small porosity on SHI irradiation.

Technical Note: Homogeneity of Gafchromic®EBT2 film

The self-developing Gafchromic EBT film is a radiochromic film, widely used for relative photon dosimetry. Recently, the manufacturer has replaced the well-investigated EBT film by the new Gafchromic EBT2 film. It has the same sensitive component and, in addition, it contains a yellow marker dye in order to protect the film against ambient light exposure and to serve as a base for corrections of small differences in film response. Furthermore, the configuration of the film layers as well as the binder material have been changed in comparison to the EBT film. When investigating the properties of EBT2 film, all characteristics were found to be similar to those of EBT film, except for the film response homogeneity. Thus, in this article special focus was put on examining the homogeneity of EBT2 film.A scan protocol established for EBT film and published previously was used. The uniformity of the film coloration was investigated for unirradiated and irradiated EBT2 film sheets. The dose response of EBT2 film was measured and the influence of film inhomogeneities on dose determination was evaluated.Inhomogeneities in pixel values of up to +/- 3.7% within one film were detected. The relative inhomogeneities were found to be approximately independent of the dose. Nonuniformities of the film response lead to uncertainties in dose determination of +/- 8.7% at 1 Gy. When using net optical densities for dose calibration, uncertainties in dose determination amount to more than +/- 6%.EBT2 films from the lot investigated in this study show response inhomogeneities, which lead to uncertainties in dose determination exceeding the commonly accepted tolerance levels. It is important to test further EBT2 lots regarding homogeneity before using the film in clinical routine.

Enhanced ionic conductivity in oxygen ion irradiated poly(vinylidene fluoride-hexafluoropropylene) based nanocomposite gel polymer electrolytes

In the present work, effect of Swift Heavy Ion (SHI) irradiation by 90 MeV O 7+ ion with four different fluences on P(VdF − HFP)–(PC + DEC)–LiClO 4-dedoped (insulating) polyaniline (PAni) nanofibers polymer electrolytes have been investigated. The irradiated films have been investigated by ac impedance, XRD, FTIR, DSC and SEM analyses. It has been observed that irradiation with swift heavy ion shows increase in ionic conductivity of the composite gel polymer electrolyte films at lower fluences (≤10 11 ions/cm 2) and decrease at higher fluences (≥10 11 ions/cm 2) as compared to the unirradiated film. Maximum ionic conductivity of 1.2 × 10 − 2 S/cm at room temperature has been found after irradiation with fluence 10 11 ions/cm 2. The increase in ionic conductivity at lower fluences could be attributed to the scissioning of polymer bonds, which leads to larger segmental motion of polymer backbone resulting in faster ionic transport through the polymer matrix. However at higher fluences (≥10 11 ions/cm 2) the polyaniline nanofibers get phase separated out from P(VdF − HFP)–(PC + DEC)–LiClO 4 leading to decrease in ionic conductivity. The phase separation phenomenon has been confirmed by DSC, FTIR and dielectric loss spectra. The surface morphology of the irradiated films has been examined by SEM.

Reversible wettability of nanostructured ZnO thin films by sol–gel method

Nanostructured ZnO thin films were deposited on Si(1 1 1) and quartz substrate by sol–gel method. The thin films were annealed at 673 K, 873 K, and 1073 K for 60 min. Microstructure, surface topography, and water contact angle of the thin films have been measured by X-ray diffractometer, atomic force microscopy, and water contact angle apparatus. XRD results showed that the ZnO thin films are polycrystalline with hexagonal wurtzite structure. AFM studies revealed that rms roughness changes from 2.3 nm to 7.4 nm and the grain size grow up continuously with increasing annealing temperature. Wettability results indicated that hydrophobicity of the un-irradiated ZnO thin films enhances with annealing temperature increase. The hydrophobic ZnO surfaces could be reversibly switched to hydrophilic by alternation of UV illumination and dark storage (thermal treatment). By studying the magnitude and the contact angle reduction rate of the light-induced process, the contribution of surface roughness is discussed.

Impedance studies on high energy Li 3+ irradiated PZT thin films

The ferroelectric Pb(Zr 0.48Ti 0.52)O 3 (PZT) thin films prepared by the pulsed laser deposition technique were studied for their response to high energy lithium ion irradiation through impedance spectroscopy. The Debye peaks, observed in the impedance and modulus plots of irradiated films, shifts towards higher frequencies compared to those of unirradiated films. This is equivalent to the trend observed with increase in temperature in the unirradiated films due to the dielectric relaxation. The irradiated films showed a decrease in the grain resistance compared to the unirradiated films. The activation energy of dielectric relaxation increases from 1.25 eV of unirradiated film to 1.62 eV of irradiated film. The observed modifications in the irradiated film were ascribed to the modifications in the grain structure due to the high value of electronic energy loss.

Femtosecond Laser-induced Crystallization of Amorphous Indium Tin Oxide Film on Glass Substrate for Patterning Applications

A method is proposed for patterning crystalline indium tin oxide (c-ITO) structures on amorphous ITO (a-ITO) thin films using a femtosecond laser. In the proposed approach, the a-ITO film is transformed into a c-ITO film over a predetermined area of the glass substrate via the heat energy supplied by the laser beam and the unirradiated a-ITO film is then removed using an acidic etchant solution. The c-ITO patterns are observed using scanning electron microscopy (SEM). The results confirm that the pattern width can be precisely controlled via an appropriate selection of the repetition rate, laser power and scanning speed. In addition, the experimental results show that a high repetition rate (80 MHz) reduces the thermal cycling effect and yields a corresponding improvement in the surface properties of the c-ITO patterns.

Upper critical field and Raman spectra of MgB2 thin films irradiated with low energy oxygen ion

The structure, upper critical field, and Raman spectrum of epitaxial MgB2 thin films irradiated by 300 keV O2+ ions have been investigated. Lattice parameter c expands after irradiation. There is a significant increase in upper critical field in the moderately irradiated films, while the critical temperature is reduced slightly. The values of critical field at zero temperature exhibit a maximum for samples with a moderate irradiation level for the applied magnetic field both perpendicular and parallel to the film surface. The temperature dependence of the anisotropy parameter, which is defined as the ratio of the upper critical field with the field parallel to the film surface and perpendicular to the film surface, reveals that oxygen ion irradiation mainly affects the σ band at a low irradiation level. With increasing irradiation level, π band scattering is strongly enhanced, and finally both bands are in the dirty limit. A broad peak centered around 570 cm−1 is observed in the Raman spectrum of the unirradiated films, and the peak position has a visible redshift in the irradiated samples. In particular, high-frequency spectral structures appear and become dominant, while the E2g broad band diminishes gradually with increasing irradiation fluence. The results are discussed by considering the disorder-induced change in carrier scattering within and between the σ and π bands and a violation of the Raman selection rules due to oxygen ion irradiation.

Effect of irradiation on the properties of nanocrystalline silicon carbide films

The effect of irradiation with electrons on the optical and electrical properties of the nanocrystalline rhombohedral 21R-SiC and 27R-SiC films is studied. The cycles of irradiation of nanocrystalline SiC films on sapphire substrates with electrons with the energy 10 MeV are conducted in the range of fluences from 5 × 1014 to 9 × 1019 cm−2. It is established that, at the irradiation doses above 1019 cm−2, the optical absorption of the films at the photon energies E > E g becomes less efficient than the optical absorption of unirradiated films. It is established that the Urbach energy as a function of the irradiation dose exhibits a minimum at the dose ∼1017 cm−2 for the 21R-SiC films and ∼5 × 1017 cm−2 for the 27R-SiC films, suggesting that radiation induces some ordering in the films. As the dose is increased from 5 × 1017 up to 9 × 1019 cm−2, an increase in the Urbach energy and a decrease in the optical band gap are observed. The effect is attributed to an increase in the concentration of radiation defects in the films.

Effect of 1.25 MeV gamma irradiation in α-phased PVDF

The radiation induced changes taking place in α-phased poly(vinylidene fluoride) (PVDF) films exposed to gamma rays were investigated in correlation with the applied doses. Samples were irradiated in vacuum at room temperature by a 1.25 MeV Co 60 source with the doses in the range of 0–300 kGy. Optical and chemical properties of the irradiated as well as un-irradiated PVDF films were studied using UV–visible and FTIR techniques. Gamma irradiation was found to induce changes vary depending on the radiation dose.

Solubility of Co clusters in Co-implanted ZnO thin films by 200 MeV Ag15+ ions irradiation

We have investigated the structural, electrical resistivity, pink noise (1/f noise) and magnetic properties of 200 MeV Ag15+ ions (fluence ∼1 × 1012 ions cm−2) irradiated Co-implanted ZnO thin films. The ZnO films were grown on Al2O3 substrate by the PA-MBE technique and 80 keV Co ion implantation with 1 × 1016 ions cm−2 dose value. The structural studies of an unirradiated film show the presence of Co clusters, which dissolve in the ZnO matrix on swift heavy ion (SHI) irradiation. The temperature-dependent electrical resistivity plots of pristine (unirradiated) and irradiated films demonstrated semiconducting nature. The resistivity data were fitted in the Mott's variable range hopping (VRH) model and the activation energies were estimated. The magnitude of normalized noise SV/V2 increases with decrease in temperature and estimated Hooge's parameters have higher values as compared to other semiconductors. We observe a clear magnetic hysteresis loop with coercivity ∼65 Oe for both the films at room temperature, establishing the ferromagnetic nature. The correlation between the electrical transport and magnetic properties in the present system formulates it to be a potential aspirant for the spintronics-oriented devices.

Thermal and optical studies on unirradiated and γ-irradiated polyester track detector

Thermal and optical properties of unirradiated and γ-irradiated polyester track detector films in the dose range of 0–14.5 Mrad have been studied by thermogravimetry (TG) and UV-Visible spectroscopic technique. The samples were irradiated with 60Co γ-rays for doses of 4.7, 8.1 and 14.5 Mrad. The TG studies indicate that unirradiated and the γ-irradiated samples degrade in two steps. The kinetics of the two steps of degradation were also evaluated from the TG curves. Irradiation enhances the degradation rate and the effect increases further with increasing radiation dose. The optical band gaps of the unirradiated as well as the irradiated samples were also determined from the UV-Visible spectra. These studies can be used for the estimation of γ-dose using changes in absorbance and the activation energy due to γ-irradiation.

Electronic and atomic structure modifications of copper nitride films by ion impact and phase separation

We have studied electronic and atomic structure modifications of Cu 3N films under 100 keV Ne and 100 MeV Xe ion impact. Cu 3N films were prepared on R(11–2 surface)-cut-Al 2O 3 substrates at 250 °C by using a RF-magnetron sputter deposition method. X-ray diffraction (XRD) shows that unirradiated films are polycrystalline with (1 0 0) orientation of cubic structure. We find that the electrical resistivity (∼10 Ω cm before ion impact) decreases by more than two orders of magnitude after the Ne impact at a fluence of ∼10 13 cm −2, where no Cu phase separation is observed. For further ion impact (larger than ∼10 15 cm −2), XRD shows Cu diffraction peak (Cu phase separation), and the resistivity decreases further (three orders of magnitude). Decomposition and phase separation are discussed based on these results, as well as temperature dependence of the resistivity and optical absorption. The results of 100 MeV Xe ion impact are compared with those of Ne ion impact.

Study of the optical properties of gamma irradiated high-density polyethylene

The effect of gamma irradiation on the optical properties of high-density polyethylene (HDPE) films has been studied. The samples were irradiated with gamma rays to dose levels up to 700 kGy. UV–Vis spectrophotometry measurements were carried out for the unirradiated and gamma irradiated HDPE films. The optical parameters, namely maximum molar absorption coefficient (εmax), dipole strength (M), transition dipole moment (μ), dipole length (L), oscillator strength (F), energy gap (Eg) and activation energy (Ea), were determined as a function of the gamma dose. The obtained results show an increase in the values of εmax, M, μ, L and F with increasing irradiation dose. On the other hand, Eg and Ea were found to decrease as the dose increases. The oscillator strength and the energy gap show linear relations, with correlation coefficients more than 99%, as a function of the irradiated dose up to 600 kGy. Therefore, it is possible to use HDPE films as gamma dosimeters in the dose range from 0 to 600 kGy by means of the UV–Vis spectrophotometry technique.

Ion bombardment induced changes in the optical and electrical properties of polycarbonate

The changes in the optical and electrical properties of polycarbonate (PC) films, bombarded with He and Ar ion beams, have been studied. The PC films were divided into two groups where the first group was bombarded with 130 keV He ions of fluences ranged from 1 × 10 14 cm −2 to 2 × 10 16 cm −2, while the second one was bombarded with 320 keV Ar of fluences (1 × 10 13 cm −2 and 1 × 10 15 cm −2). The surface morphology of the unirradiated and irradiated PC films was studied using scanning electron microscopy (SEM) technique. The optical properties of the two groups have been carried out using UV–Vis spectrophotometer and the direct current (DC) electrical conductivity was also performed. The obtained results showed a decrease in the optical energy gap, the optical activation energy and the electrical activation energy with increasing the fluence of both He and Ar ions. Meanwhile, an increase in the DC conductivity was obtained with increasing the fluence of the ions. The bombardment of the PC films with He and Ar ion beams induced formation of carbon clusters near the polymer surface and, also, resulted in scission in the polymer chains.

SU‐GG‐T‐276: Comparison of the Epson Perfection V700 Photo Flatbed and the Vidar VXR‐16 Dosimetry PRO AdvantageTM Film Scanners for Use with Radiochromic Film

Purpose: The purpose of this study was to compare the performance and utility of a commercially available flatbed scanner with that of a widely‐used medical film scanner for use with radiochromic film. Method and Materials: This project compares the Vidar VXR Dosimetry Pro and the Epson Perfection V700 Photo flatbed scanner. Using radiochromic EBT film irradiated to a known range of doses 0–512 cGy using eight 3×3 cm fields on a single film, both scanners were characterized for scan repeatability, orientation effects, uniformity, and scanner noise. RIT V5.0 was used to determine pixel value (PV) of Vidar scans, while ImageJ software was used for the Epson scans. Results: For the range of doses measured, average pixel values of a central 1.5×1.5 cm region of interest (ROI) were reproducible within 0.1% standard deviation with Vidar and approximately 0.2% with Epson. Epson mean PV differed by up to 18% for all dosed regions from landscape to portrait orientation, while only up to 5% for Vidar. From 0 to 512 cGy, identical films showed a 10% wider PV range for Vidar than Epson. Scanner noise was minimal; Epson showed a maximum SD of 1.00% from the mean of the central ROI, Vidar showed 1.14%. In both systems, cross profiles for an unirradiated film showed deviations in PV no more than 2% of the mean. Conclusion: No clear significant accuracy advantage was noted in either system, provided the leading and trailing 1 cm film edges were neglected with the Vidar system. Although the Epson scanner is a relatively inexpensive method for analyzing radiochromic film, the lack of commercially available software for it could be a major disadvantage. Hence, an institution already having a Vidar system may find its use with radiochromic film attractive.

Effect of γ‐irradiation on the physical properties and dyeability of poly(vinyl butyral) blends with polystyrene and poly(ethylene glycol)

AbstractCast films of polymer blends essentially based on poly(vinyl butyral) (PVB) and equal ratios of polystyrene (PS) and poly(ethylene glycol) (PEG) were prepared from benzene and butyl alcohol solutions of the individual polymers. The effect of γ‐irradiation on the thermal decomposition and tensile mechanical properties was investigated. Moreover, the effect of γ‐irradiation on the dye affinity of PVB/PS and PVB/PEG for basic and acid dyestuffs was studied. The thermogravimetric analysis (TGA) study showed that the unirradiated PVB polymer films prepared in benzene displayed higher thermal stability than the same polymer films prepared in butanol. However, in all cases the thermal stability was found to increase with increasing γ‐irradiation dose. On the other hand, PVB/PS blend possesses higher thermal stability than PVB/PEG, as shown from the determination of the weight loss (%) at different heating temperatures, the temperatures of the maximum rate of reaction and the activation energy. While, pure PS films showed the stress‐strain behavior of brittle polymers, PVB/PS films showed the behavior of tough polymers with yielding properties. The results of dyeing clearly showed that the solvent type, blend composition, and irradiation dose are determining factors for the dye affinity for basic or acid dyes. For example, unirradiated PVB films prepared from butanol displayed a higher affinity for the basic and acid dyes than the same polymer prepared from the same benzene. However, PVB prepared from butanol showed higher affinity to the dyes than PS prepared from the same solvent. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers

Effects of accumulated laser pulses on (Pb,Sr)TiO 3 films post-excimer laser annealed at low temperatures

In this article, we report the effect of excimer laser annealing (ELA) on the characteristics of (Pb,Sr)TiO 3 (PSrT) films. The unirradiated and irradiated films are characterized by atomic force microscope (AFM), X-ray photoelectron spectroscopy, X-ray diffractometer (XRD), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). It is found that the crystallinity is improved and the oxygen content is increased by ELA. Besides, the surface morphology becomes rough after ELA. Moreover, PSrT films irradiated by ELA are found to increase the grain size near the surface. The material properties of unirradiated and irradiated films, as well as the characteristics of PSrT films irradiated with various laser pulses, will be explored in this study.

Radiation Effects on Optical Properties of Ethylene Vinyl Acetate Copolymer Films

The optical properties of ethylene vinyl acetate (EVA) film have been studied. The effects of gamma irradiations on the optical spectrum of EVA films have been investigated using spectrophotometric measurements of reflectance and transmittance in the wavelength range 200–1100 nm. The absorption spectra were recorded in the UV–vis region for the unirradiated and irradiated films (from 0 to 50 kGy). Optical constants such as refractive index (n), extinction coefficient (K), and complex dielectric constant have been determined, as well as the optical dispersion parameters and high frequency dielectric constants. A large dependence of the fundamental optical constants on the irradiation dose was noticed. On irradiation, a higher refractive index was obtained as compared with that for unirradiated film. The dispersion parameters, such as E 0 (single‐oscillator energy), E d (dispersive energy), and M −1 and M −3 (moments), are discussed in terms of the single‐oscillator Wemple–DiDomenico model.