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.     

Study of Au-Pd core-shell nanoparticles by using slow positron beam

Binary Au-Pd nanoparticles were synthesized by ultrasonic irradiation of solutions containing Au³⁺ and Pd²⁺ ions (the ion ratio from 0.3:0.7 to 0.9:0.1 mM) and cationic surfactant (SDS: sodium dodecyl sulfate). In each case the core-shell structure (Au core, Pd shell) was confirmed by scanning transmission electron microscopy (STEM). The mean diameters of them were all about 9 nm, and the thickness of the Pd shell depends on the ratio of Pd²⁺ and Au³⁺ ions in solution. In order to study the electronic states of core-shell nanoparticles and their dependence on shell thickness, Doppler broadening measurements were performed for Au-Pd core-shell nanoparticles by using slow positron beam technique. The ratio curves of Au-Pd particles did not match with those of pure Pd and pure Au, but a small difference in the low electron momentum region was observed among nanoparticles depending on Pd shell thickness.     

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.     

Luminescence studies on swift heavy ion irradiated nanocrystalline aluminum oxide

Pellets of nanocrystalline aluminum oxide synthesized by a combustion technique are irradiated with 120 MeV Au⁹⁺ ions for fluence in the range 5×10¹¹-1×10¹³ ions cm⁻². Two photoluminescence (PL) emissions, a prominent one with peak at ∼525 nm and a shoulder at ∼465 nm are observed in heat treated and Au⁹⁺ ion irradiated aluminum oxide. The 525 nm emission is attributed to F₂²⁺-centers. The PL intensity at 525 nm is found to increase with increase in ion fluence up to 1×10¹² ions cm⁻² and decreases beyond this fluence. Thermoluminescence (TL) of heat-treated and swift heavy ion (SHI) irradiated aluminum oxide gives a strong and broad TL glow with peak at ∼610 K along with a weak shoulder at 500 K. The TL intensity is found to increase with Au⁹⁺ ion fluence up to 1×10¹³ ions cm⁻² and decreases beyond this fluence.     

Substrate effect on electronic sputtering yield in polycrystalline fluoride (LiF, CaF2 and BaF2) thin films

Influence of substrate on electronic sputtering of fluoride (LiF, CaF₂ and BaF₂) thin films, 10 and 100 nm thin, under dense electronic excitation of 120 MeV Ag²⁵⁺ ions irradiation is investigated. The sputtering yield of the films deposited on insulating (glass) and semiconducting (Si) substrates are determined by elastic recoil detection analysis technique. Results revealed that sputtering yield is higher, up to 7.4 × 10⁶ atoms/ion for LiF film on glass substrate, than that is reported for bulk materials/crystals (∼10⁴ atoms/ion), while a lower value of the yield (2.3 × 10⁶ atoms/ion) is observed for film deposited on Si substrate. The increase in the yield for thin films as compared to bulk material is a combined effect of the insulator substrate used for deposition and reduced film dimension. The results are explained in the framework of thermal spike model along with substrate and size effects in thin films. It is also observed that the material with higher band gap showed higher sputtering yield.     

MeV Au ion induced modifications at Co/Si interface

We report on room temperature MeV Au ion induced modifications at the Co/Si interfaces. Nanometers size thin film of Co and Si were grown by ultra high vacuum (UHV) electron beam evaporation technique on Si(1 1 1) surface and were irradiated by 1.5 MeV Au²⁺ ions at a fluence of 5 × 10¹⁴ ions cm⁻². High-resolution transmission electron microscopy (HRTEM) along with energy filter imaging technique has been employed to study the formation of Co-Si alloy at the interface. Formation of such surface alloy has been discussed in the light of ion-matter interaction in nanometer scale regime.     

Swift heavy ion induced surface modifications in nano-crystalline Li-Mg ferrite thin films

The swift heavy ion (190 MeV Au¹⁴⁺) induced modifications in surface morphologies of the nanocrystals of ferrite thin films have been extensively studied through the images of atomic force microscopy (AFM). In most of the irradiated films significant features like, the ditch and dike structures, have been observed through out the surface. We try to explain the observed changes on the basis of thermal spike model followed by momentum transfer induced lateral mass transport. In addition to these changes some new and interesting features have been noticed after irradiation in 8F and 9F ferrite thin films. These new features are attributed to sputtering phenomenon due to the presence of defects like latent tracks.     

Structural and magnetic study of swift heavy ion irradiated W/Fe multilayer structure

The present study reports the effect of swift heavy ion irradiation on structural and magnetic properties of sputtered W/Fe multilayer structure (MLS) having bilayer compositions of [W(10 Å)/Fe(20 Å)]_10BL. The MLS is irradiated by 120 MeV Au⁹⁺ ions of fluences 1×10¹³ and 4×10¹³ ions/cm². Techniques like X-ray reflectivity (XRR), cross-sectional transmission electron microscopy (X-TEM) and DC magnetization with a vibrating sample magnetometer (VSM) 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 layer roughness. X-TEM studies reveal that intra-layer microstructure of Fe layers in MLS becomes nano-crystalline on irradiation. DC magnetization study shows that with spacer layer thickness interlayer coupling changes between ferromagnetic to antiferromagnetic.     

Ion beam modification of porous silicon using high energy Au ions and its impact on photoluminescence spectra

This paper presents investigation of impact of high-energy ion-irradiation on properties of light emitting porous silicon (PS) through photoluminescence (PL) spectroscopy. Irradiation was performed with 100 MeV Au⁺⁷ ions from a pelletron accelerator at ion doses in 10¹⁰-10¹⁴ cm⁻² range. The effect was associated with a blueshift (∼40 nm) and an enhancement of the PL intensity, in general. The efficiency and stability of PL with respect to ambients was seen to be relatively improved. The PL properties of PS were found to be stable against low to medium dose irradiation (<10¹³ cm⁻²), whereas, higher dose led to further degradation of the optical properties. The effects have been explained in terms of a decrease in the non-radiative recombination probability of electron-hole pairs due to chemical restructuring of the surface and a reduced crystallite size as a result of irradiation.     

Phase formation by ion beam mixing in the Ti/Si multilayer system

The irradiation effect of 350 MeV Au⁺ ions on Ti/Si multilayers has been studied using Rutherford backscattering spectroscopy, X-ray reflectivity (XRR) and grazing incidence X-ray diffraction (GIXRD). Intermixing effects have been studied as a function of fluences of 0.46 × 10¹⁴, 1.82 × 10¹⁴ and 4.62 × 10¹⁴ cm⁻². Rutherford backscattering spectra (RBS) confirm mixing at the interface. X-ray reflectivity patterns show damage at the interfaces with the absence of a continuous fringe pattern at high fluence doses in comparison to the pristine interface. Mixing leads to titanium di-silicide (TiSi₂) phase formation as a shown by grazing incidence X-ray diffraction patterns. The observed intermixing is attributed to energy deposited by the incident ions in the electronic system of the target. Swift heavy ion irradiation induced intermixing increases with fluence.     

X-ray and AFM studies of polydisperse TiO2 (anatase) particles

Titanium dioxide (TiO₂) materials of a high chemical purity, as-prepared by the thermal hydrolysis, as well as subsequently modified by adsorption of different metal cations (Fe³⁺, Co²⁺, Cu²⁺), have been investigated by the X-ray diffraction, X-ray fluorescence and AFM microscopy methods. All TiO₂ powders have a fine-dispersated anatase structure and consist of grown together nanocrystallites of ∼8-17 nm. TiO₂ particles, usually ranging from 100 to 600 nm, show the ability to form large agglomerates, up to 2 μm in size. Contrary to the pure anatase, metal-modified TiO₂ particles possess a positive charge on their surface and can be lifted away by the AFM tip from the substrate surface during the scanning. This effect is mostly pronounced for the Fe-modified TiO₂ sample, where particles up to 250 nm are removed. The possible interaction mechanisms between different TiO₂ particles and the silicon tip are discussed. The electrostatic force has been found to play an essential role in the sample-tip interaction processes, and its value depends on the type of metal cation used.     

Swift ion irradiations of Fe/Fe/Si trilayers

We report here on changes in magnetism and microstructure when implanting, at 92 or 300 K, up to 5 × 10¹⁵ Au²⁶⁺-ions cm⁻² of 350 MeV into ^natFe(45 nm)/⁵⁷Fe(20 nm)/Si trilayers. This choice of ions and energy allowed to test the irradiation effects in the regime of pure electronic stopping. The samples were analysed before and after irradiation by Rutherford back-scattering spectroscopy, X-ray diffraction, conversion electron Mössbauer spectroscopy, and magneto-optical Kerr effect. Up to 1 × 10¹⁵ ions cm⁻², there was interface broadening at a mixing rate of Δσ²/Φ = 55(5) nm⁴, followed by full Fe-Si inter-diffusion. The Mössbauer spectra revealed fractions of α-Fe and amorphous ferromagnetic and paramagnetic iron silicides, but no crystalline Fe-Si phase. The magnetic remanence in the as-deposited Fe-layer showed small components of uniaxial and four-fold magnetization. For increasing ion fluence, the component with four-fold symmetry grew at the expense of the uniaxial component. For the highest fluences, an isotropic magnetization was found.     

Effect of 100 MeV Ni ion irradiation on MOCVD grown n-GaN

Metal-organic chemical vapor deposition (MOCVD) grown n-type Gallium nitride (GaN) has been irradiated with 100 MeV Ni⁹⁺ ions at room temperature. Atomic force microscopy (AFM) images show the nano-clusters' formation upon irradiation and the irradiated GaN surface roughness increases with the increasing ion fluences. High-resolution X-ray diffraction (HR-XRD) analysis reveals the formation of Ga₂O₃ due to the interface mixing of GaN/Al₂O₃ upon irradiation. FWHM values of GaN (0 0 0 2) increases due to the lattice disorder. Photoluminescence studies show reduced band edge emission and yellow luminescence (YL) intensity with the increasing ion fluences. Change in the band gap energy between 3.38 and 3.04 eV was measured by UV-visible optical absorption spectrum on increasing the ion fluences.     

Polyethylene terephthalate (PET) bulk film analysis using C60, Au3, and Au primary ion beams

The damage characteristics of polyethylene terephthalate (PET) have been studied under bombardment by C₆₀⁺, Au₃⁺ and Au⁺ primary ions. The observed damage cross-sections for the three ion beams are not dramatically different. The secondary ion yields however were significantly enhanced by the polyatomic primary ions where the secondary ion yield of the [M + H]⁺ is on average 5× higher for C₆₀⁺ than Au₃⁺ and 8× higher for Au₃⁺ than Au⁺. Damage accumulates under Au⁺ and Au₃⁺ bombardment while C₆₀⁺ bombardment shows a lack of damage accumulation throughout the depth profile of the PET thick film up to an ion dose of ∼1 × 10¹⁵ ions cm⁻². These properties of C₆₀⁺ bombardment suggest that the primary ion will be a useful molecular depth profiling tool.     

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 160 MeV Ni ion irradiation on PbS quantum dots

PbS quantum dots of average size 10 nm are encapsulated in a matrix (polyvinyl alcohol (PVA)) following chemical route. They are irradiated with 160 MeV Ni¹²⁺ ion beam with fluences 10¹²-10¹³ ions/cm². Red shift in the absorption response in the optical absorption spectra reveal size enhancement of the quantum dots after irradiation and was confirmed by transmission electron microscopy (TEM). Photoluminescence (PL) study was carried out with excitation wavelength 325 nm on both unirradiated and irradiated samples at different fluences and fluence-dependent surface states and excitonic emission is observed in the PL study. The Huang-Rhys coupling constant decreases significantly after swift heavy ion (SHI) irradiation and shows a decreasing trend with increase in ion fluence.     

Targeted sonodynamic therapy using protein-modified TiO2 nanoparticles

Our previous study suggested new sonodynamic therapy for cancer cells based on the delivery of titanium dioxide (TiO₂) nanoparticles (NPs) modified with a protein specifically recognizing target cells and subsequent generation of hydroxyl radicals from TiO₂ NPs activated by external ultrasound irradiation (called TiO₂/US treatment). The present study first examined the uptake behavior of TiO₂ NPs modified with pre-S1/S2 (model protein-recognizing hepatocytes) by HepG2 cells for 24 h. It took 6 h for sufficient uptake of the TiO₂ NPs by the cells. Next, the effect of the TiO₂/US treatment on HepG2 cell growth was examined for 96 h after the 1 MHz ultrasound was irradiated (0.1 W/cm², 30 s) to the cells which incorporated the TiO₂ NPs. Apoptosis was observed at 6 h after the TiO₂/US treatment. Although no apparent cell-injury was observed until 24 h after the treatment, the viable cell concentration had deteriorated to 46% of the control at 96 h. Finally, the TiO₂/US treatment was applied to a mouse xenograft model. The pre-S1/S2-immobilized TiO₂ (0.1 mg) was directly injected into tumors, followed by 1 MHz ultrasound irradiation at 1.0 W/cm² for 60 s. As a result of the treatment repeated five times within 13 days, tumor growth could be hampered up to 28 days compared with the control conditions.     

Ionoluminescence and photoluminescence studies of Ag ion irradiated kyanite

Ionoluminescence (IL) of kyanite single crystals bombarded with 100 MeV swift Ag⁸⁺ ions with fluences in the range 1.87-7.5×10¹¹ ions/cm² has been studied. A pair of sharp IL peaks at ∼689 and 706 nm along with broad emission in the region 710-800 nm are recorded in both crystalline and pelletized samples. Similar results are recorded in Photoluminescence (PL) of pelletized kyanite bombarded with same ions and energy with fluences in the range 1×10¹¹-5×10¹³ ions/cm² with an excitation of 442 nm laser beam. The characteristic pair of sharp emission peaks at 689 and 706 nm in both IL and PL is attributed to luminescence centers activated by Fe²⁺ and Fe³⁺ ions. The reduction in IL and PL bands intensity with increase of ion fluence might be attributed to degradation of Si-O (2ν₃) bonds, present on the surface of the sample.     

Effect of H irradiation on the optical properties of vacuum evaporated AgInSe2 thin films

We prepared polycrystalline AgInSe₂ thin films by vacuum evaporation on glass substrate at a high temperature using the stoichiometric powder. The thin films were characterized by X-ray diffraction and UV-vis-NIR spectroscopy. The samples were subjected to the irradiation of 1.26 MeV protons (H⁺). The effect of irradiation on the optical properties has been investigated for different doses of H⁺. It is observed that the band gap of silver indium selenide thin films decreases gradually with ion irradiation dose.     

Excitation of thermoluminescence in Eu doped Ba0.12Sr0.88SO4 nanophosphor by low energy argon ions

In the present paper thermoluminescence properties of argon ions irradiated barium strontium mixed sulphate phosphor are reported. The Ba_0.12Sr_0.88SO₄ phosphor was prepared by chemical co-precipitation method. The X-ray diffraction study of prepared sample suggests orthorhombic structure with average grain size of 37 nm. The samples were irradiated with 1.2 MeV Argon ions at fluences varying between 10¹¹-10¹⁵ ions/cm². The argon ions penetrate to the depth of 1.89 μm and lose their energy mainly via electronic stopping. Due to ion irradiation, a large number of defects in the sample are formed. Thermoluminescence (TL) glow curves were recorded for each of the ion fluence. These curves exhibit one broad peak with maximum intensity at 498 K composed of three overlapping peaks. This indicates that different sets of traps are being activated within the particular temperature range each with its own value of activation energy (E) and frequency factor (s). The peaks were observed due to formation of trap levels by ion irradiation and subsequently activation of traps on thermal stimulation. The TL response of the nanophosphor is linear in the dose range 59 kGy-590 MGy. Kinetic parameters associated with the prominent peaks were calculated using glow curve deconvolution (GCD) and verified by different glow curve shape and sample heating rate methods.