Swift heavy ion induced phase transition in CdTe films deposited by spray pyrolysis in presence of electric field

CdTe polycrystalline thin films possessing hexagonal phase regions are obtained by spray deposition in presence of a high electric field. Thin film samples are irradiated with 100 MeV Ag ions using Pelletron accelerator to study the swift heavy ion induced effects. The ion irradiation results in the transformation of the metastable hexagonal regions in the films to stable cubic phase due to the dense electronic excitations induced by beam irradiation. The phase transformation is seen from the X-ray diffraction patterns. The band gap of the CdTe film changes marginally due to ion irradiation induced phase transformation. The value changes from 1.47 eV for the as deposited sample to 1.44 eV for the sample irradiated at the fluence 1×10¹³ ions/cm². The AFM images show a gradual change in the shape of the particles from rod shape to nearly spherical ones after irradiation.     

Effect of swift heavy ion irradiation on structure, optical, and gas sensing properties of SnO2 thin films

Swift heavy ion irradiation has been successfully used to modify the structural, optical, and gas sensing properties of SnO₂ thin films. The SnO₂ thin films prepared by sol-gel process were irradiated with 75 MeV Ni⁺ beam at fluences ranging from 1 × 10¹¹ ion/cm² to 3 × 10¹³ ion/cm². Structural characterization with glancing angle X-ray diffraction shows an enhancement of crystallinity and systematic change of stress in the SnO₂ lattice up to a threshold value of 1 × 10¹³ ions/cm², but decrease in crystallinity at highest fluence of 3 × 10¹³ ions/cm². Microstructure investigation of the irradiated films by transmission electron microscopy supports the XRD observations. Optical properties studied by absorption and PL spectroscopies reveal a red shift of the band gap from 3.75 eV to 3.1 eV, and a broad yellow luminescence, respectively, with increase in ion fluence. Gas response of the irradiated SnO₂ films shows increase of resistance on exposure to ammonia (NH₃), indicating p-type conductivity resulting from ion irradiation.     

Raman investigation of incident N-, Xe-ions induced effects in ZnO thin films

Highly c-axis orientation ZnO thin films with hundreds nanometers in thickness have been deposited on (1 0 0) Si substrate by RF magnetron sputtering. These films are implanted at room temperature by 80 keV N-ions with fluences from 5.0 × 10¹⁴ to 1.0 × 10¹⁷ ions/cm², implanted by 400 keV Xe-ions with 2.0 × 10¹⁴ to 2.0 × 10¹⁶ ions/cm², irradiated by 3.64 MeV Xe-ions with 1.0 × 10¹² to 1.0 × 10¹⁵ ions/cm², or irradiated by 308 MeV Xe-ions with 1.0 × 10¹² to 5.0 × 10¹⁴ ions/cm², respectively. Then the ZnO films are investigated using a Raman spectroscopy. The obtained Raman spectra show that a new Raman peak located at about 578 cm⁻¹ relating to simple defects or disorder phase appears in all ZnO films after ion implantation/irradiation, a new Raman peak at about 275 cm^-1 owing to N-activated zinc-like vibrations is observed in the N-implanted samples. Moreover, a new Raman peak at about 475 cm⁻¹ is only seen in the samples after 400 keV and 3.64 MeV Xe-ions bombardment. The area intensity of these peaks increases with increasing ion fluence. The effects of ion fluence, element chemical activity, atom displacements induced by nuclear collisions as well as energy deposition on the damage process of ZnO films under ion implantation/irradiation are discussed briefly.     

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 × 10¹⁴ cm⁻² to 2 × 10¹⁶ cm⁻², while the second one was bombarded with 320 keV Ar of fluences (1 × 10¹³ cm⁻² and 1 × 10¹⁵ 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.     

Effect of swift heavy ion irradiation on the surface morphology of highly c-axis oriented LSMO thin films grown by pulsed laser deposition

A detailed investigation of the surface morphology of the pristine and swift heavy ion (SHI) irradiated La_0.7Sr_0.3MnO₃ (LSMO) thin film using atomic force microscope (AFM) is presented. Highly c-axis oriented LSMO thin films were grown on LaAlO₃ (1 0 0) (LAO) substrates by the pulsed laser deposition (PLD) technique. The films were annealed at 800 °C for 12 h in air (pristine films) and subsequently, irradiated with SHI of oxygen and silver. The incident fluence was varied from 1 × 10¹² to 1 × 10¹⁴ ions/cm² and 1 × 10¹¹ to 1 × 10¹² ions/cm² for oxygen and silver ions, respectively. X-ray diffraction (XRD) studies reveal that the irradiated films are strained. From the AFM images, various details pertaining to the surface morphology such as rms roughness (σ), the surface rms roughness averaged over an infinite large image (σ_∞), fractal dimension (D_F) and the lateral coherence length (ξ) were estimated using the length dependent variance measurements. In case of irradiated films, the surface morphology shows drastic modifications, which is dependent on the nature of ions and the incident fluence. However, the surface is found to remain self-affine in each case. In case of oxygen ion irradiated films both, σ_∞ and D_F are observed to increase with fluence up to a dose value of 1 × 10¹³ ions/cm². With further increase in dose value both σ_∞ and D_F decreases. In case of silver ion irradiated films, σ_∞ and D_F decrease with increase in fluence value in the range studied.     

Swift heavy ion induced modifications of fullerene C70 thin films

Modifications of the C₇₀ molecule (fullerene) under swift heavy ion irradiation are investigated. C₇₀ thin films were irradiated with 120 MeV Au ions at fluences from 1 × 10¹² to 3 × 10¹³ ions/cm². The energetic ion impacts lead to the destruction of the C₇₀ molecule. To investigate the stability of C₇₀ fullerene, the damage cross-section and radius of the damaged cylindrical zones are evaluated by fitting the evanescence of C₇₀ vibration modes recorded by Raman spectroscopy. Conductivity measurements together with Raman and optical absorption studies revealed that an irradiation fluence of 3 × 10¹³ ions/cm² results in complete amorphization of the carbon structure of the fullerene molecules.     

Investigations on the effect of 100 MeV Ni ions irradiated chloride vapour phase epitaxy (Cl-VPE) grown GaN epilayers

Gallium nitride (GaN) epilayers have been grown by chloride vapour phase epitaxy (Cl-VPE) technique and the grown GaN layers were irradiated with 100 MeV Ni ions at the fluences of 5 × 10¹² and 2 × 10¹³ ions/cm². The pristine and 100 MeV Ni ions irradiated GaN samples were characterized using X-ray diffraction (XRD), UV-visible transmittance spectrum, photoluminescence (PL) and atomic force microscopy (AFM) analysis. XRD results indicate the presence of gallium oxide phases after Ni ion irradiation, increase in the FWHM and decrease in the intensity of the GaN (0 0 0 2) peak with increasing ion fluences. The UV-visible transmittance spectrum and PL measurements show decrease in the band gap value after irradiation. AFM images show the nanocluster formation upon irradiation and the roughness value of GaN increases with increasing ion fluences.     

Swift heavy ion irradiation induced modification of the microstructure of NiO thin films

NiO nanoparticle films (200 nm thick) grown on Si substrates by pulsed laser deposition method were irradiated by 200 MeV Ag¹⁵⁺ ions. The films were characterized by glancing angle X-ray diffraction, atomic force microscopy and optical absorption spectroscopy. Though electronic energy loss of 200 MeV Ag ions in NiO matrix was higher than the threshold electronic energy loss for creation of columnar defects, films remained crystalline with the initial fcc structure even up to a fluence of 5 × 10¹³ ions cm⁻², where ion tracks are expected to overlap. Irradiation however modified the microstructure of the NiO films considerably. The grain size decreased with increasing ion fluence, which led to reduced surface roughness and increased optical band gap due to quantum confinement. These results correlate well with variation of the power spectral density exponent with ion fluence, which indicate that at high ion fluences, the evolution of surface morphology is governed by surface diffusion.     

Structural and optical study of irradiation effect in GaN epilayers induced by 308 MeV Xe ions

Wurtzite GaN epilayers irradiated at room temperature with 308 MeV ¹²⁹Xe³⁵⁺ ions to fluences of 1 × 10¹³ and 3 × 10¹³ cm⁻² have been studied by contact mode atomic force microscopy (AFM), high-resolution X-ray diffraction (HRXRD), micro-Raman scattering and photoluminescence (PL) spectroscopy. The AFM images showed that the surface of GaN films was etched efficiently due to the Xe ion irradiation. The initial step-terrace structure on GaN surface was eliminated completely at a fluence of 3 × 10¹³ cm⁻². HRXRD and Raman results indicated that the Xe ion irradiation led to a homogenous lattice expansion throughout the entire ∼3 μm-thick GaN films. The lattice expansion as well as the biaxial compressive stress of the films was increasing with the increase of ion fluence. PL measurements showed that a dominant yellow luminescence band in the as-grown GaN films disappeared, but a blue and a green luminescence bands were produced after irradiation. Based on these results, the strong electronic excitation effect of 308 MeV Xe ions in GaN is discussed.     

Effect of SHI on dielectric and magnetic properties of metal oxide/PMMA nanocomposites

Magnetic nanoparticles embedded in polymer matrices have excellent potential for electromagnetic device applications like electromagnetic interference suppression, etc. The NiO nanoparticles were synthesized by simple method. These nanoparticles were dispersed in PMMA matrix and films were prepared by casting method with varying concentrations of nickel oxide nanoparticles. These films were irradiated with 50 MeV Li⁺³ ions at a fluence of 5 × 10¹² ions/cm². AC electrical properties of pristine and irradiated samples were studied in wide frequency range. Dependence of dielectric properties on frequency, ion beam fluence and filler concentration was studied. The results reveal the enhancement in dielectric properties after doping nanoparticles and also upon irradiation, which is also corroborated with field-cooled-zero-field-cooled (FC-ZFC) susceptibility measurement in which magnetization is increased upon irradiation. The Fourier transform infrared (FTIR) spectroscopy analysis revealed the change in the intensity of functional groups after irradiation. Average surface roughness observed to change with filler concentration and also with the irradiation fluence as obtained from AFM analysis.     

Morphological change in FePt nanogranular thin films induced by swift heavy ion irradiation

We have investigated morphology change of FePt nanogranular films (FePt)₄₇(Al₂O₃)₅₃ under irradiation with 210 MeV Xe ions. Here, electron tomography technique was extensively employed to clarify three-dimensional (3D) structure in irradiated specimens, in addition to conventional transmission electron microscopy (TEM) techniques such as bright-field observation and scanning TEM energy dispersive X-ray spectroscopy (STEM-EDX) analysis. The ion irradiation induces the coarsening of FePt nanoparticles with elongation along the beam direction. Electron tomography 3D reconstructed images clearly demonstrated that when the fluence achieves 5.0 × 10¹⁴ ions/cm², well-coarsened FePt balls have been formed on the irradiated surface, and the particles in the film interior have been deformed into rods along the ion trajectory. The alloy particles become inhomogeneous in composition after prolonged irradiation up to 1.0 × 10¹⁵ Xe ions/cm². The particle center is enriched with Pt, while Fe is slightly redistributed to the periphery.     

Modification of poly(ether ether ketone) by ion irradiation

Poly(ether ether ketone) was irradiated with 3.0 MeV Si²⁺, 3.25 MeV Cu²⁺ and 4.8 MeV Ag²⁺ ions to the fluences from 10¹² to 10¹⁴ cm⁻² and the effects of irradiation were studied using ERDA, RBS and FTIR methods. The irradiation leads to release of hydrogen from the PEEK surface layer modified by the ion beam. The release is mild for low ion fluences but it becomes more pronounced at the ion fluences above 10¹³ cm⁻². At highest ion fluences the hydrogen concentration falls to 20-35% of its initial value. In contrast to hydrogen no significant oxygen release was observed. The kinetic of the hydrogen release is similar for the three ion species. FTIR measurement shows deep structural changes of the polymer structure resulting from the ion irradiation.     

Optical and structural properties of ZnO thin films; effects of high energy electron irradiation and annealing

High energy electron irradiation (HEEI) effects on the as-grown and annealed ZnO thin films grown by electrochemical deposition were investigated. Both samples were exposed to the sequential electron irradiations of 6, 12 and 15 MeV energies at a fluence of 1 × 10¹² e⁻/cm². The results of X-ray diffraction suggest that a highly strong crystallographic structure can be produced by annealing process. Photoluminescence (PL) studies show that the EI produces violet emission which results from the zinc interstitial. Recombination lifetime (RL) values of the both films reveal that the high quality crystals are obtained. The decreasing trends of RL values with increasing electron energy have been explained by the formation of crystal defects due to the HEEI.     

Swift heavy ion irradiation induced texturing in NiO thin films

NiO thin films grown on Si(1 0 0) substrate by electron beam evaporation and sintered at 500 and 700 °C were irradiated with 120 MeV Au⁹⁺ ions. The FCC structure of the sintered films was retained up to the highest fluence (3 × 10¹³ ions cm⁻²) of irradiation. In the low fluence (?1 × 10¹³ ions cm⁻²) regime however, the evolution of the XRD pattern with fluence showed a wide variation, critically depending upon their initial microstructure. Though irradiation is known to induce disorder in the structure, we observe improvement in crystallization and texturing at intermediate fluences of irradiation.     

Evidence of nanostructure formation in Ge oxide by crystallization induced by swift heavy ion irradiation

Ge oxide films were irradiated with 150 MeV Ag ions at fluences varying between 10¹² and 10¹⁴ ions/cm². The irradiation-induced changes were monitored by FT-IR spectroscopy, atomic force microscopy, X-ray diffraction and photoluminescence spectroscopy. The FT-IR spectra indicate stoichiometric changes and an increase in Ge content on irradiation. X-ray diffraction shows a crystallization of the irradiated films and presence of both Ge and GeO₂ phases. The Ge nanocrystal size, as calculated from Scherrer’s formula, was around 30 nm. The morphological changes, observed in atomic force microscopy, also indicate formation of nanostructures upon ion irradiation and a uniform growth is observed for a fluence of 1 × 10¹⁴ ions/cm².     

Effect of 200 MeV Ag ion irradiation on structural and electrical transport properties of Fe3O4 thin films

Thin films of Fe₃O₄ have been deposited on single crystal MgO(1 0 0) and Si(1 0 0) substrates using pulsed laser deposition. Films grown on MgO substrate are epitaxial with c-axis orientation whereas, films on Si substrate are highly 〈1 1 1〉 oriented. Film thicknesses are 150 nm. These films have been irradiated with 200 MeV Ag ions. We study the effect of the irradiation on structural and electrical transport properties of these films. The fluence value of irradiation has been varied in the range of 5 × 10¹⁰ ions/cm² to 1 × 10¹² ions/cm². We compare the irradiation induced modifications on various physical properties between the c-axis oriented epitaxial film and non epitaxial but 〈1 1 1〉 oriented film. The pristine film on Si substrate shows Verwey transition (T_V) close to 125 K, which is higher than generally observed in single crystals (121 K). After the irradiation with the 5 × 10¹⁰ ions/cm² fluence value, T_V shifts to 122 K, closer to the single crystal value. However, with the higher fluence (1 × 10¹² ions/cm²) irradiation, T_V again shifts to 125 K.     

Formation of Au nanoparticles in silica by post-irradiation and thermal annealing

SiO₂ + Au thin films were prepared on SiO₂ substrates using ion beam assisted deposition (IBAD). The film was annealed at different temperatures. After each annealing, the optical absorption spectrum was taken to monitor the gold nanocluster formation in the thin film. By using Doyle’s formula, the size of the nanoclusters was determined and plotted as a function of the annealing temperature. Separately, other identical films were bombarded with ions of different energies and different fluence to monitor the nanoclusters forming during the bombardments. We have compared the effect of electronic energy deposition of the energetic ions with the effect of annealing at various temperatures.     

The peculiarities of formation of the metal nanoparticles in irradiated polymer metal complexes

The radiation-induced reduction of metal ions in the films of triple metal polymer complexes of polyacrylic acid-polyethyleneimine-copper(II) or nickel(II) (PAA-PEI-Cu²⁺ or PAA-PEI-Ni²⁺) was studied by EPR and transmission electron microscopy (TEM). It was shown that irradiation of the swollen polymer films in the water-alcohol environment resulted in effective reduction of the metal ions. The exchange between the swollen film and outer environment was found to be an important factor for ion reduction and stabilization of metal particles. EPR data have revealed pronounced effect of the ligand environment on the reduction efficiency. The electron microscopy studies have demonstrated that the dimensions of main fraction of metal particles obtained by the radiation-chemical reduction are in the range of 2-2.5 nm both for Cu and for Ni complexes.     

Effect of swift heavy ion irradiation on nanocrystalline CaS:Bi phosphors: Structural, optical and luminescence studies

Luminescence studies of CaS:Bi nanocrystalline phosphors synthesized by wet chemical co-precipitation method and irradiated with swift heavy ions (i.e. O⁷⁺-ion with 100 MeV and Ag¹⁵⁺-ion with 200 MeV) have been carried out. The samples have been irradiated at different ion fluences in the range 1 × 10¹²-1 × 10¹³ ions/cm². The average grain size of the samples before irradiation was estimated as 35 nm using line broadening of XRD (X-ray diffraction) peaks and TEM (transmission electron microscope) studies. Our results suggest a good structural stability of CaS:Bi against swift heavy ion irradiation. The blue emission band of CaS:Bi³⁺ nanophosphor at 401 nm is from the transition ³P₁ → ¹S₀ of the Bi³⁺. We have observed a decrease in lattice constant (a) and increase of optical energy band gap after ion irradiation. We presume this change due to grain fragmentation by dense electronic excitation induced by swift heavy ion. We have studied the optical and luminescent behavior of the samples by changing the ion energy and also by changing dopant concentration from 0.01 mol% to 0.10 mol%. It has been examined that ion irradiation enhanced the luminescence of the samples.     

Change in magnetic properties of MgB2 thin films after irradiation by 200 MeV Au ion beam

The SHI irradiation induced effects on magnetic properties of MgB₂ thin films are reported. The films having thickness 300-400 nm, prepared by hybrid physical chemical vapor deposition (HPCVD) were irradiated by 200 MeV Au ion beam (S_e ∼ 23 keV/nm) at the fluence 1 × 10¹² ion/cm². Interestingly, increase in the transition temperature T_c from 35.1 K to 36 K resulted after irradiation. Substantial enhancement of critical current density after irradiation was also observed because of the pinning provided by the defects created due to irradiation. The change in surface morphology due to irradiation is also studied.