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The authors investigate the formation of Ge nanocrystals by thermal annealing of substoichiometric GeOx films fabricated by electron-beam evaporation. At the same time, they also monitor the evolution of the GeOx matrix. The phase separation into semiconductor and oxide phases and the evolution of Ge nanocrystals were monitored by a combination of x-ray diffraction (XRD), Raman, and transmission electron microscopy (TEM) measurements. TEM shows spherical particles of sizes in the range of 2–9nm. They infer that an annealing temperature of 500°C is sufficient to generate a reasonable density of Ge nanocrystals in an amorphous GeOx matrix. Both XRD and Raman measurements suggest a simultaneous crystallization of the matrix at an annealing temperature of 600°C.

Thin films of carbon-containing Au nanoparticles (NPs), prepared by the co-sputtering using a neutral Ar atom beam, were irradiated by 120 MeV Ag ions and also annealed, separately, at increasing temperatures in inert atmosphere. The surface plasmon resonance (SPR) band of the nanocomposite film was observed to be blue shifted (similar to 50 nm) in both cases, with increasing fluence and temperature. The structural changes of Au NPs embedded in amorphous carbon matrix were investigated using X-ray diffraction and transmission electron microscopy. A growth of Au NPs was observed with increasing fluence and also with increasing temperature. A percolation of Au NPs was observed at 500 degrees C. A growth of Au NPs with ion irradiation is explained in the framework of a thermal spike model. Raman spectroscopy revealed the ordering of a-C thin films with increasing fluence and temperature, which is ascribed to a change of refractive index and the blue shift of the SPR band.

The effect of volume fraction of silver (Ag) on the growth of silver nanoparticles (AgNPs) embedded in ion-irradiated silica films is reported. Films with low volume fraction (LVF) and high volume fraction (HVF) of Ag in silica matrix were prepared by magnetron co-sputtering. The growth of AgNPs under 120 MeV Ag ion irradiation is monitored in situ using grazing incidence X-ray diffraction (GIXRD). It is observed that the film with LVF shows the growth of AgNPs in a nearly single ion impact region, while the film with HVF shows a monotonous growth even in the region of multiple ion impacts. Rutherford backscattering spectrometry (RBS) experiments are also performed to determine the exact volume fraction of Ag in the silica matrix and to understand the role of sputtering and diffusion processes on the growth of AgNPs. Surface plasmon resonance (SPR) is carried out to obtain further evidence of the mechanisms of growth. Our study reveals that the growth of embedded nanoparticles strongly depends on the volume fraction of metal in the matrices and affects the dipolar interactions among such noble metal NPs. (C) 2013 Elsevier B.V. All rights reserved.

Present study demonstrates the role of metal-insulator interface and ion irradiation induced defects on the ferromagnetic properties of the non-magnetic materials. Magnetic properties of the Pd nanoparticles(NPs) embedded in the a-silica matrix synthesized using atom beam sputtering technique, were determined using SQUID magnetometry measurements which showed that ferromagnetic response of Pd increased by 3.5 times on swift heavy ion(SHI) irradiation. The ferromagnetic behavior of the as-deposited Pd NPs is due to strain induced by the surrounding matrix and modification in the electronic structure at the Pd-silica interface as revealed by insitu XRD and XPS investigations, respectively. The defects created by the SHI bombardment are responsible for enhancement of the magnetization in the Pd NPs.

The important central question related to origin of ferromagnetic properties in the non-magnetic materials at nano-dimensions has been investigated by a novel approach of studying the evolution of magnetic properties by intentionally creating defects. The ferromagnetic response of Pd is found to increase by 20 times for nanoparticle (NP) dispersed in carbon matrix and increase by about 3.5 times in case of Pd nanoparticles dispersed in SiO2 matrix on exposure to swift heavy ion irradiation. Ferromagnetic response is found to increase by about 9.3 times on subjecting the Pd nanoparticles to hydrogen loading-deloading cycle. Ferromagnetic properties of Pd nanoparticles dispersed in carbon and SiO2 matrices, despite having same size and concentration, are observed to be vastly different due to matrix effect. These changes in ferromagnetic properties are correlated to the change in the electronic structure due to matrix, nanoparticle size, and creation of defects in the nanoparticle core and at NP-matrix interface during post deposition treatments. Giant enhancement in the magnetic properties and change in electronic properties point toward a core and surface magnetic structure in metal nanoparticle. (C) 2012 American Institute of Physics.

Ag:ZrO2 nanocomposite films have been synthesized by a sol-gel dip coating process at room temperature, followed by irradiation using swift heavy ions. The effect of electronic energy loss and fluences on the evolution and consequently on the tailoring of plasmonic properties of films has been studied. The optical study exhibits that color of films converts from transparent in pristine form into shiny yellow when films are irradiated by 100 MeV Ag ions at a fluence of 3 x 10(12) ions/cm(2). However, irradiation by 120 MeV O ions up to the fluence of 1 x 10(14) ions/cm(2) does not induce any coloration in films. The coloration is attributed to the evolution of plasmonic feature resulting in a surface plasmon resonance (SPR) induced absorption peak in the visible region. Increase in fluence from 3 x 10(12) to 6 x 10(13) ions/cm(2) of 100 MeV Ag ions induces a redshift in SPR induced peak position from 434 to 487 nm. Microstructural studies confirms the conversion of Ag2O3 (in pristine films) into cubic phase of metallic Ag and the increase of average size of particles with the increasing fluence up to 6 x 10(13) ions/cm(2). Further increase in fluence leads to the dissolution of Ag atoms in the ZrO2 matrix. (c) 2011 American Institute of Physics

Zinc sulfide (ZnS) thin films in zinc-blende (ZB) and wurtzite (W) phases have been fabricated by pulsed laser deposition. 150 MeV Ni ion beam irradiation has been carried out at different fluences ranging from 10(11) to 10(13) ions/cm(2) at room temperature for ion induced modifications. Structural phase transformation in ZnS from W to ZB phase is observed after high energy ion irradiation which leads to the decrease in bandgap. Generation of high pressure and temperature by thermal spike during MeV Ion irradiation along the ion trajectory in the films is responsible for the structural phase transformation. (C) 2010 Elsevier Ltd. All rights reserved

Structural modifications in the zircon and scheelite phases of ThGeO(4) induced by swift heavy ions (93 MeV Ni(7+)) at different fluences as well as pressure quenching effects are reported. X-ray diffraction and Raman measurements at room temperature on the irradiated zircon phase of ThGeO(4) indicate the occurrence of stresses that lead to a reduction of the cell volume up to 2% followed by its transformation to a mixture of nano-crystalline and amorphous scheelite phases. Irradiation of the zircon phase at liquid nitrogen temperature induces amorphization at a lower fluence (7.5 x 10(16) ions/m(2)), as compared to that at room temperature (6 x 10(17) ions/m(2)). Scheelite type ThGeO(4) irradiated at room temperature under goes complete amorphization at a lower fluence of 7.5 x 10(16) ions/m(2) without any volume reduction. The track radii deduced from X-ray diffraction measurements on room temperature irradiated zircon, scheelite and low temperature irradiated zircon phases of ThGeO(4) are, 3.9, 3.5 and 4.5 nm, respectively. X-ray structural investigations on the zircon phase of ThGeO(4) recovered after pressurization to about 3.5 and 9 GPa at ambient temperature show the coexistence of zircon and disordered scheelite phases with a larger fraction of scheelite phase occurring at 9 GPa. on the other hand, the scheelite phase quenched from 9 GPa shows crystalline scheelite phase pattern. (c) 2009 Elsevier B.V. All rights reserved.

The effects of swift heavy ion (SHI) irradiation in epitaxial thin film of magneto-electric GaFeO3 (GFO) deposited on (0 0 1) oriented yttria-stabilized zirconia substrate are reported. The structural modifications during the irradiation are studied using in-situ x-ray diffraction and it is observed that SHI induces stress. Thus the induced stress leads to the formation of elongated array of GFO nano-grains and the crystallographic tilting between film and substrate as observed from reciprocal space mapping (RSM). The epitaxy is found to persist even with a dose of ions cm−2 from the RSM. The irradiation is found to affect the magnetic properties of GFO viz., the transition temperature and the redistribution of iron at soft and hard magnetic sites. These observations indicate the possibility of tuning structural and magnetic properties of GFO with SHI.

Intermixing induced in W/Si multilayers by irradiation with 150 MeV Ag+ ions has been studied. In situ x-ray reflectivity measurements during heavy ion irradiation allows one to monitor the evolution of interface mixing as well as internal stresses as a function of time during irradiation. The technique of x-ray reflectivity is sensitive enough to measure diffusion length down to 0.1 nm. A finite intermixing occurs in the system, in spite of it having a positive heat of mixing. High accuracy of the technique allows one to discern subtle effects of factors like stress or film thickness, on swift heavy ion irradiation induced intermixing. The measurements provide clear evidence of an enhanced intermixing in the presence of tensile stress in the film. Mixing efficiency decreases with increasing film thickness. The film thickness dependence of mixing efficiency can be understood in terms of the thermal spike model by taking into consideration the changes in electron mobility due to scattering from surface and interfaces.

Uniformly distributed and defect-free vertically aligned ZnO nanorods (NRs) with high aspect ratio are deposited on Si by sputtering technique. X-ray diffraction along with transmission electron microscopy studies confirmed the single crystalline wurtzite structure of ZnO. Absence of wide band emission in photoluminescence spectra showed defect-free growth of ZnO NRs which was further conformed by diamagnetic behavior of the NRs. H2 sensing mechanism based on the change in physical dimension of channel is proposed to explain the fast response (∼21.6 s) and recovery times (∼27 s) of ZnO NRs/Si/ZnO NRs sensors. Proposed H2 sensor operates at low temperature (∼70 °C) unlike the existing high temperature (>150 °C) sensors.

Zinc nanoparticles (NPs) embedded in silica were irradiated with swift heavy ions (SHIs) of seven different combinations of species and energies. The shape elongation induced by the irradiations was evaluated by optical linear dichroism (OLD) spectroscopy, which is a sensitive tool for determining the change in the mean aspect ratio (AR) of NPs. Although the mean AR change indicated a linear fluence dependence in the low- and medium-fluence regions, it indicated a nonlinear dependence in the high-fluence region. The data reveal that the elongation efficiency of Zn is correlated with the electronic stopping power 'Se in silica' and is not correlated with either the 'Se in Zn' or the nuclear stopping power. The elongation efficiency plotted as a function of the 'Se in silica' revealed a linear relationship, with a threshold value of ∼2 keV nm(-1), which is the same dependence exhibited by the ion-track formation in silica. The log-log plot showed that the elongation efficiency increased linearly with Se above a critical value of ∼3 keV nm(-1) and steeply decreased with Se to the power of 5 below the critical Se. The steep decrease can be ascribed to the discontinuous nature of the ion tracks, which is expected at Se ∼ 2-4 keV nm(-1) in silica. The fluence Φ dependences of AR - 1 under various irradiations are well-normalized with the electronic energy deposition of SHIs, i.e., the product of Se and Φ, with a Se greater than the same critical value of ∼3 keV nm(-1). The normalized data above the critical value fell on a linear relation, AR(Φ) - 1 ∝ SeΦ, for SeΦ2 keV nm(-3) and a sublinear relation, AR(Φ) - 1 ∝ (SeΦ)(1/2) for SeΦ2 keV nm(-3). On the basis of these experimental results, we discuss some insights into the elongation mechanism.

Self-aligned ZnO nanorods (NRs) were grown on n-Si(100) substrate by RF sputtering techniques. The NRs are uniformly grown on 2-inch wafer along [0001] direction. Single-crystalline wurtzite structure of ZnO NRs was confirmed by X-ray diffraction. The average diameter, height, and density of NRs are found 48 nm, 750 nm, and 1.26 × 1010 cm−2, respectively. The current-voltages (I-V) characteristics of ZnO NRs/Si heterojunction (HJ) were studied in the temperature range of 120–300 K and it shows a rectifying behavior. Barrier height (ϕB) and ideality factor (η) were estimated from thermionic emission model and found to be highly temperature dependent in nature. Richardson constant (A*) was evaluated using Richardson plot of ln(Io/T2) versus q/kT plot by linear fitting in two temperature range 120–180 K and 210–300 K. Large deviation in Richardson constant from its theoretical value of n-Si indicates the presence of barrier inhomogeneities at HJ. Double Gaussian distribution of barrier height with thermionic...

Softening and stiffening of phonons in rutile titanium dioxide films are investigated by in situ micro-Raman studies during energetic ion irradiation. The in situ study minimized other possible mechanisms of phonon dynamics. Initial softening and broadening of Raman shift are attributed to the phonon confinement by structural defects and loss of stoichiometry. The stiffening of A1g mode is ascribed to large distortion of TiO6 octahedra under the influence of lattice strain in the (110) plane, which gives rise to lengthening of equatorial Ti-O bond and shortening of apical Ti-O bond. The shortening of apical Ti-O bond induces stiffening of A1g mode in the framework of the bond-order-length-strength correlation mechanism.

In this study, in-situ X-ray diffraction has been carried out to investigate the effect of temperature and pressure on hydrogen induced lattice parameter variation in size selected Pd-Ag and Pd-Cu alloy nanoparticles. The nanoparticles of three different mobility equivalent diameters (20, 40, and 60 nm) having a narrow size distribution were prepared by gas phase synthesis method. In the present range of temperature (350 K to 250 K) and pressure (10−4 to 100 millibars), no α (H/Pd ≤ 0.03) ↔ β (H/Pd ≥ 0.54) phase transition is observed. At temperature higher than 300 °C or pressure lower than 25 millibars, there is a large difference in the rate at which lattice constant varies as a function of pressure and temperature. Further, the lattice variation with temperature and pressure is also observed to depend upon the nanoparticle size. At lower temperature or higher pressure, size of the nanoparticle seems to be relatively less important. These results are explained on the basis of the relative dominance of physical absorption and diffusion of H in Pd alloy nanoparticles at different temperature and pressure. In the present study, absence of α ↔ β phase transition points towards the advantage of using Pd-alloy nanoparticles in applications requiring long term and repeated hydrogen cycling.

The electrochemical studies were carried out on specimens of amorphous Ti 60 Ni 40 both before and after irradiation with Ni 11+ 150 MeV ions at fluence of 1 × 10 13 ions/cm 2 using potentiodynamic polarization method in 1 M HNO 3 aqueous medium. The corrosion behavior of the virgin and irradiated specimens of Ti 60 Ni 40 was also compared with that of the nanocrystalline specimen of the same alloy. It was observed that the irradiated amorphous specimen exhibits superior corrosion resistance than that of the amorphous specimen. However, the value of corrosion current density ( I corr ) for irradiated specimen was found to be comparable with that for the nanocrystalline specimen. The better corrosion resistance of the irradiated amorphous specimen can be understood in terms of the evolution of Ti 2 Ni nanocrystalline phase after irradiation with heavy ions.

Important correlation between valence band spectra and hydrogenation properties in Pd alloy nanoparticles is established by studying the properties of size selected and monocrystalline Pd, Ag, Cu, Pd-Ag, and Pd-Cu nanoparticles. The X-ray photoelectron spectroscopy and elastic recoil detection analysis show that size induced Pd4d centroid shift is related to enhanced hydrogenation with H/Pd ratio of 0.57 and 0.49 in Pd-Ag and Pd-Cu nanoparticles in comparison to reported bulk values of 0.2 and 0.1, respectively. Pd-alloy nanoparticles show lower hydrogen induced lattice distortion. The reduced distortion and higher hydrogen reactivity of Pd-alloy nanoparticles is important for numerous hydrogen related applications.

This paper reports the effect of 100 MeV Ag swift heavy ion (SHI) irradiation with fluences ranging from 1 × 1011 to 1 × 1013 ions cm−2 on the optical properties of Ag0.10(Ge0.20Se0.80)0.90 thin films. It has been observed that the SHI irradiation changes the refractive index (n) and the oscillator strength (E d). The data on the dispersion of the refractive index, n(λ), have been determined using the single-effective-oscillator model. We observed an increase in E d and refractive index (n) at lower ion fluence (1 × 1011 ions cm−2), followed by the reversal in the trend at higher fluences. The optical gap has been determined by Tauc's plot. The values of decrease with ion fluence. Results have been explained in terms of the structural changes in thin films.

In this study, the effect of swift heavy ion irradiation on the magnetic properties of the Pd nanoparticles has been investigated. Structural investigations along with superconducting quantum interface device measurements show that ferromagnetic properties of the Pd nanoparticles are due to the deviation of their electronic structure from that of bulk. The electronic structure is further modified due to the creation of defects on ion irradiation, which results in 20 times increase in the saturation magnetization. The present study establishes that the defect induced modification of Pd 4d electronic structure is responsible for the ferromagnetic properties of the Pd nanoparticles.

A detailed structural study involving in situ glancing angle x-ray diffraction (GAXRD) analysis carried out on Pd nanoparticle and thin film samples at hydrogen concentrations of 2%, 5%, and 10% over temperature ranging from −100 to 55 °C and hydrogen pressures ranging from 250 to 1000 mbars is reported. Variation in the lattice constant has been interpreted in terms of hydrogen content in α and β PdHx phases, and decrease in XRD peak intensity has been interpreted in terms of hydrogen induced degradation in crystalline quality and temperature induced lattice disorder. It is observed that Pd–H interaction is strongly influenced by the temperature and pressure dependences of physisorption, chemisorption, and diffusion. These results show that the increased surface area, interparticle gaps, and electronic enhancement result in enhanced Pd–H interaction in case of nanoparticles. In addition, the presence of single β phase and lower crystallinity degradation is observed in the case of Pd nanoparticles in comp...

This study is carried out to verify the role of thin film microstructure in determining the energy relaxation processes of swift heavy ions in CdS polycrystalline thin films. Two sets of CdS thin film samples, differing in their microstructures, prepared using thermal evaporation and spray pyrolysis, are irradiated with 100 MeV Ag ions using Pelletron accelerator. It is observed that the effects produced differ significantly in the two films. For the evaporated films, defect annealing dominates for lower irradiation fluences but at higher fluences the effects due to defect creation and their migration are dominant. A transformation from the metastable cubic to hexagonal phase together with the creation of a significant amount of compressive strain is seen in these films for irradiation at the highest fluence. The optical absorption of the samples shows an increase in band gap from 2.34 eV for the as grown film to 2.43 eV for the sample irradiated at the highest fluence that is further confirmed by photoluminescence (PL) studies. In contrast, the spray deposited samples undergo a significant improvement of crystalline quality for all fluences as shown by an increase in x-ray diffraction peak intensity, sharper optical absorption edge, reduction in defect PL intensity, and removal of asymmetry in the line shape of the longitudinal optical phonon on its lower wavenumber side in Raman spectra.

Polypyrrole thin films doped with para-toluene sulphonic acid were prepared by the electrochemical process. High-energy ion beam irradiation of the polymers is an effective technique to enhance the electrical conductivity, structural property and mechanical properties. So polypyrrole and allyl diglycol carbonate (CR-39 (DOP)) films were irradiated by oxygen ions (energy 100MeV, charge state O +7 ) with fluence varying from 1 × 10 10 to 1 × 10 13 ionscm −2 . The effects of swift heavy ions (SHI) on the structural, optical and surface properties of polypyrrole (Ppy) and CR-39 (DOP) polymers were studied in this work using x-ray diffraction (XRD), UV‐visible spectroscopy and scanning electron microscopy (SEM). XRD patterns of the pristine and irradiated polymer show that the crystallinity improved after the irradiation with SHI. At the low fluence, crystallinity was found to increase but at high fluence, it decreases which could be attributed to cross-linking and degradation mechanism. The UV‐visible spectra show a shift in the absorbance edge towards higher wavelength, which can be correlated with the transition involved in the polymer and variation in the band gap using Tauc’s expression. The band gap of polypyrrole was found to decrease from 3.4 to 3.0eV after irradiation. CR-39 (DOP), however, showed a very large change in the band gap from 4.8 to 3.4eV. The SEM study shows a systematic change in the surface morphology of the polymers with increasing ion fluence. (Some figures in this article are in colour only in the electronic version)

A systematic analysis of the data on swift heavy ion irradiation in semiconductors shows that the effects produced are determined not only by the electronic energy deposition but also by a number of other material characteristics. The study is carried out to highlight the role of film microstructure in determining the energy relaxation processes of heavy ions in semiconductors. To verify the idea, two sets of CdTe polycrystalline thin film samples, prepared using thermal evaporation and spray pyrolysis, which differ in their microstructure are irradiated with 100?MeV Ag7+ ions using a 15 UD Pelletron accelerator. Differences are noticed in the response of the two sets of films to the beam and are correlated with the differences in their microstructure. For the evaporated films defect annealing dominates at lower fluences, but at higher fluences the effects due to defect generation are dominant. An increase in the lattice constant with fluence due to an increase in the tensile strain is also observed in this case. For the spray deposited samples, however, defect generation always dominates and no change in the lattice parameter is observed. The optical band gap undergoes a red shift for both sets of films due to the introduction of band-tail states.

An in situ x-ray diffraction (XRD) setup is designed and installed in the materials science beam line of the Pelletron accelerator at the Inter-University Accelerator Centre for in situ studies of phase change in swift heavy ion irradiated materials. A high vacuum chamber with suitable windows for incident and diffracted X-rays is integrated with the goniometer and the beamline. Indigenously made liquid nitrogen (LN2) temperature sample cooling unit is installed. The snapshots of growth of particles with fluence of 90 MeV Ni ions were recorded using in situ XRD experiment, illustrating the potential of this in situ facility. A thin film of C60 was used to test the sample cooling unit. It shows that the phase of the C60 film transforms from a cubic lattice (at room temperature) to a fcc lattice at around T=255 K.

Single crystals of L-threonine were subjected to 50 MeV Li3+ ion irradiation at various ion fluences. Radiation induced changes in the structural, electrical, thermal and optical properties of the crystals have been studied in detail. The ion fluence dependence on these properties has also been discussed. Surface modifications in the crystals have been explored through atomic force microscopy. It has also been observed that the powder second-harmonic generation efficiency of irradiated L-threonine varies with the ion fluence studied.

Thin silica films containing Au nanoparticles were prepared by cosputtering. The kinetics of the growth of nanoparticles under 90 MeV Ni ion irradiation was studied by in situ x-ray diffraction. The growth of nanoparticles from 4 (for pristine) to 9 nm at a fluence of 1×1014 ions/cm2 was observed, in accordance with the observations made by transmission electron microscopy analyses. The present study shows that the ion irradiation is an effective tool for tailoring the size of nanoparticles. The results are discussed in the framework of thermal spike model.