Nanoparticle formation by swift heavy ion irradiation of indium oxide thin film

In this study, a novel approach for the formation of indium oxide (IO) nanoparticles by irradiating IO thin film using 100?MeV Ag(8+) ions has been reported. High resolution transmission electron microscopy and energy dispersive x-ray analysis confirm the presence of single-crystalline IO nanoparticles after irradiation. The electronic excitations induced by 100?MeV Ag(8+) ions followed by thermal relaxation of the energy spike in IO thin film is responsible for the formation of latent tracks in the film. The electronic energy loss (S(e)) of 100?MeV Ag(8+) ions in IO is greater than the threshold electronic energy loss (S(eth)) required for the track formation in IO film, but is less than S(eth) required for crystalline silicon. Therefore, the tracks are formed in the IO film and not in the silicon substrate. This results in a stress induced at the IO film and silicon substrate interface which is responsible for dewetting of the tracks and the formation of nanoparticles. The theoretically calculated value of nanoparticle diameter using the thermal spike model is found to be in good agreement with the experimentally observed value of 30?nm.     

Synthesis of nanocrystalline tin oxide thin film by swift heavy ion irradiation

Nanocrystals of tin oxide were formed in e-beam evaporated films by swift heavy ion (SHI) irradiation. The nucleation of nanocrystals occurred due to electronic excitation by swift heavy ion. Nanophase thin films are characterized systematically by HRTEM, GAXRD, EDX, and UV/NIS absorption techniques. Nanocrystals having size of 8 nm radius are synthesized in different substrates during swift heavy ion irradiation and without subsequent annealing. SHI induced nanocrystallization could be achieved in both crystalline and non-crystalline substrates.     

Enhancement in CO gas sensing properties of hydroxyapatite thick films: Effect of swift heavy ion irradiation

This paper investigates the effect of swift heavy ion (SHI) irradiation on surface morphology of Hydroxyapatite (HAp) thick films and modification in gas sensing characteristics. The HAp nanopowder is synthesized by wet chemical process and the thick films are prepared by screen printing technique. These films are irradiated with Ag⁷⁺ ions with energy of 100 MeV at different fluences ranging from 3 × 10¹⁰ to 3 × 10¹³ ions/cm². X-ray diffraction and atomic force microscopy tools are employed to examine the phase and surface modification in HAp thick films due to swift heavy ion irradiation. The ion irradiation study shows that crystallinity decreases and grain size changes with increase in ion fluence. A precise study on gas sensing is carried out to confirm operating temperature of HAp thick film sensor to detect CO gas. Saturation region of the film with increasing gas concentration and other parameters such as response and recovery time are also investigated from the point of view of using HAp films as a sensor device. SHI irradiated HAp thick film shows enhancement in the gas response and saturation limit for CO gas. Furthermore, the irradiated HAp film shows fast response and recovery time for CO gas. The study concludes that nanoceramic HAp thick film is an excellent CO gas sensor at an operating temperature of 195 °C.     

Enhancement in CO gas sensing properties of hydroxyapatite thick films: Effect of swift heavy ion irradiation

This paper investigates the effect of swift heavy ion (SHI) irradiation on surface morphology of Hydroxyapatite (HAp) thick films and modification in gas sensing characteristics. The HAp nanopowder is synthesized by wet chemical process and the thick films are prepared by screen printing technique. These films are irradiated with Ag⁷⁺ ions with energy of 100 MeV at different fluences ranging from 3 × 10¹⁰ to 3 × 10¹³ ions/cm². X-ray diffraction and atomic force microscopy tools are employed to examine the phase and surface modification in HAp thick films due to swift heavy ion irradiation. The ion irradiation study shows that crystallinity decreases and grain size changes with increase in ion fluence. A precise study on gas sensing is carried out to confirm operating temperature of HAp thick film sensor to detect CO gas. Saturation region of the film with increasing gas concentration and other parameters such as response and recovery time are also investigated from the point of view of using HAp films as a sensor device. SHI irradiated HAp thick film shows enhancement in the gas response and saturation limit for CO gas. Furthermore, the irradiated HAp film shows fast response and recovery time for CO gas. The study concludes that nanoceramic HAp thick film is an excellent CO gas sensor at an operating temperature of 195 °C.     

Piezospectroscopic study of mechanical stress in Al2O3:Cr under swift heavy ion irradiation

The spatial distribution of mechanical stresses in Al₂O₃:Cr single crystal irradiated with (1 ÷ 3) MeV/amu Kr, Xe and Bi ions has been studied by using laser confocal scanning microscopy technique. The stress level as a function of the ion penetration depth has been evaluated from depth-resolved photostimulated R-line luminescence spectra exploiting the piezospectroscopic method. As it was found, the stress field generated by swift heavy ion irradiation is composed of stresses with maximal magnitude comparable with the ultimate stress limit of ruby crystals. Experimental data are discussed in the framework of a model considering the Cr³⁺ atoms as individual piezosensors.     

Redistribution of indium implanted in silicon due to thermal treatment and swift heavy ion irradiation

Silicon layers of 150 nm thickness supersaturated with indium up to ≈5 at% were prepared by multiple energy ion implantation. A redistribution of the implanted impurities caused by post-implantation annealing and following irradiation with swift Bi ions has been observed by means of Rutherford backscattering spectrometry in channelling configuration (RBS/C). It is demonstrated by TEM that the thermal decomposition of the supersaturated Si〈In〉 solution is accompanied by polycrystalline recrystallisation of amorphous silicon, precipitation of the second phase (In) both within the implanted layer and on the surface, as well as by impurity redistribution. The main features of the structure transformation under the influence of the Bi ion irradiation are discussed.     

Ion-induced elongation of gold nanoparticles in silica by irradiation with Ag and Cu swift heavy ions: track radius and energy loss threshold

Systematic investigations of the energy loss threshold above which the irradiation-induced elongation of spherical Au nanoparticles occurs are reported. Silica films containing Au nanoparticles with average diameters of 15-80 nm embedded within a single plane were irradiated with 12-54 MeV Ag and 10-45 MeV Cu ions at 300 K and at normal incidence. We demonstrate that the efficiency of the ion-induced nanoparticle elongation increases linearly with the electronic energy transferred per ion track length unit from the energetic ions to the silica film. Ion beam shaping occurs above a threshold value of the specific electronic energy transfer. Three relevant regions are identified with respect to the original size of the Au nanoparticles. For 15 and 30 nm diameter particles, elongation occurs for electronic stopping power larger than 3.5 keV nm(-1). For Au nanoparticles with 40-50 nm diameter an electronic stopping power above 5.5 keV nm(-1) is required for elongation to be observed. Elongation of Au nanoparticles with 80 nm diameter is observed for electronic stopping between ～ 7-8 keV nm(-1). For all combinations of ions and energies, the ion track temperature profiles are calculated within the framework of the thermal spike model. The correlation between experimental results and simulated data indicates a thermal origin of the increase in the elongation rate with increasing the track diameter.     

Phenomenological understanding of dewetting and embedding of noble metal nanoparticles in thin films induced by ion irradiation

The present experimental work provides the phenomenological approach to understand the dewetting in thin noble metal films with subsequent formation of nanoparticles (NPs) and embedding of NPs induced by ion irradiation. Au/polyethyleneterepthlate (PET) bilayers were irradiated with 150 keV Ar ions at varying fluences and were studied using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (X-TEM). Thin Au film begins to dewet from the substrate after irradiation and subsequent irradiation results in spherical nanoparticles on the surface that at a fluence of 5 × 10¹⁶ ions/cm² become embedded into the substrate. In addition to dewetting in thin films, synthesis and embedding of metal NPs by ion irradiation, the present article explores fundamental thermodynamic principles that govern these events systematically under the effect of irradiation. The results are explained on the basis of ion induced sputtering, thermal spike inducing local melting and of thermodynamic driving forces by minimization of the system free energy where contributions of surface and interfacial energies are considered with subsequent ion induced viscous flow in substrate.     

Synthesis of nearly monodisperse embedded nanoparticles by separating nucleation and growth in ion implantation

We investigate the formation of nanoparticles of Au in SiO(2) by multiple ion implantation steps and intermediate anneals to isolate nucleation and growth, thereby producing a narrow particle size distribution. We discuss the effects of varying the initial nucleation dose and the growth temperature and establish guidelines for synthesizing nanoparticles with improved size uniformity. By this method, we have obtained a standard deviation of 16% on an average diameter of 1.68 nm, compared to 28% when no attempt is made to isolate nucleation and growth.     

Ultrafast dynamics of copper nanoparticles embedded in soda-lime silicate glass fabricated by ion exchange

Copper nanoparticles embedded in soda-lime glass were fabricated by ion exchange followed by thermal treatment in hydrogen. The ultrafast dynamics of the embedded Cu nanoparticles formed under different fabrication conditions were investigated by applying femtosecond pump-probe technique. Non-Fermi electrons were suggested to be dominant in the transient behavior of the nanocomposites far from surface plasmon resonance of Cu. The long ion-exchange processing time was found to benefit and improve the ultrafast response of the fabricated nanocomposites.     

The melting behavior of faceted particles embedded in the solid state: A family of Wulff shapes

We consider the melting behavior of nanoscale particles embedded in a crystalline solid. Calculations of three-dimensional shapes following from a minimization of interfacial free energy show that melt configurations depend on the melt volume fraction, particle shape, and the relative energy densities of particle interfaces. Five members of the family of Wulff shapes with cubic symmetry containing only and facets are studied in detail. Although general trends are noted, the melting behavior is found to be complex and strongly dependent on particle shape. We assume that the melt volume is located in one contiguous region. In such a case, the driving force to replace high-energy facets decreases with the relative energy of those facets.     

The formation mechanism of periodic Zn nanocrystal arrays embedded in an amorphous layer by rapid electron beam irradiation

A periodic nano-island array of ～7?nm diameter Zn single crystals embedded in an amorphous Zn(2x)Si(1-x)O(2) layer was created by using rapid electron beam irradiation for 50?s. A sequential process of 900?°C thermal annealing followed by electron beam irradiation induces the formation of an amorphous Zn(2x)Si(1-x)O(2) layer containing periodic Zn nanocrystals. It is shown that the periodic Zn crystal array can be produced with good control of their size and spacing. Possible formation mechanisms for the Zn crystal nano-islands are described on the basis of the experimental results.     

Local lifetime control in silicon power diode by ion irradiation: introduction and stability of shallow donors

Enhanced formation of shallow donors (SDs) in hydrogen or helium-irradiated and subsequently annealed float-zone n-type silicon is investigated. Ion energies, irradiation fluences and annealing temperatures were chosen in ranges typically used for local lifetime control in silicon power devices. Introduced radiation defects and SDs were investigated by deep-level transient spectroscopy and C-V profiling. Results show that radiation damage produced by helium ions remarkably enhances formation of thermal donors (TDs) when the annealing temperature exceeds 375degC, i.e. when the majority of vacancy-related recombination centres anneal out. Proton irradiation introduces hydrogen donors (HDs) which form a Gaussian peak at the proton end-of-range. Their concentration linearly increases with proton fluence and changes dramatically during post-irradiation annealing between 100 and 200degC since HD constituents are reacting with radiation damage. Their annealing in this temperature range is influenced by the electric field. If annealing temperature exceeds 400degC, HDs disappear and the excessive shallow doping is caused, as in the case of helium irradiation, by TDs enhanced by radiation damage. Shallow doping introduced by both hydrogen and helium can have a detrimental influence on blocking voltage of power diodes if high irradiation fluences or wrong annealing conditions are chosen.     

Mid-infrared ridge waveguide in MgO:LiNbO3 crystal produced by combination of swift O5+ ion irradiation and precise diamond blade dicing

We report on the fabrication of ridge waveguide operating at mid-infrared wavelength in MgO:LiNbO₃ crystal by using O⁵⁺ ion irradiation and precise diamond blade dicing. The waveguide shows good guiding properties at the wavelength of 4 μm along the TM polarization. Thermal annealing has been implemented to improve the waveguiding performances. The propagation loss of the ridge waveguide has been reduced to be 1.0 dB/cm at 4 μm after annealing at 310 °C. The micro-Raman spectra indicate that the microstructure of the MgO:LiNbO₃ crystal has no significant change along the ion track after swift O⁵⁺ ion irradiation.     

Thermal performance of nanofluids in metal foam tube: Thermal dispersion model incorporating heterogeneous distribution of nanoparticles

This study presents the application of a modified single-phase method by thermal dispersion model incorporating heterogeneous distribution of nanoparticle concentration for evaluating thermal performance of a nanofluid in a circular porous metal foam tube. Numerical approach was conducted for Re = 200–1000, mean concentration of 0.5–2%, and metal foam porosity of 0.7–0.9. It is observed that the predicted data by application of the thermal dispersion approach are in satisfactory agreement with those obtained experimentally, whereas applying the general homogeneous model results in an underestimation. The results reveal that the heterogeneity of the concentration distribution is directly proportional to nanoparticle mean concentration, Reynolds number, and the metal foam porosity. The velocity and temperature profiles at a cross section have been found to be flatter in dispersion model compared to those obtained from the homogeneous model. Furthermore, it is achieved that the Nusselt number varies directly relative to mean concentration and Reynolds number, whereas it inversely alters relative to the porosity. This reduction is found to be more profound at lower porosities.     

Ceramic coatings by ion irradiation of polycarbosilanes and polysiloxanes: Part II Hardness and thermochemical stability

The hardnesses of polycarbosilane and polysiloxane coatings subjected to irradiation with increasing doses of He, C and Au ions were measured by means of nanoindentation tests. Diamond-like carbon clusters which are formed during irradiation enhance the hardnesses of the ceramic films which reach in some cases three times that of conventionally annealed specimens. When submitting irradiated films to an additional anneal, the clusters resulting from the segregation of atoms from methyl groups remain more diamond like than those formed directly by radiolysis of phenyl rings, especially when the radiolytic transformation is incomplete (the film having received a low irradiation dose). Moreover, owing to the selective release of hydrogen and the recombination of free radicals at room temperature, no evolution of CHx and COx nor oxidation of unpaired Si atoms occurs during this post-irradiation anneal, contrary to the observations during direct thermal conversion. This revised version was published online in November 2006 with corrections to the Cover Date.     

Magnetic properties of nanocomposites formed by magnetic nanoparticles embedded in a non-magnetic matrix: a simulation approach

In this work, simulations of magnetic properties of nanocomposites formed by magnetic nanoparticles embedded in a non magnetic matrix are presented. These simulations were carried by means of the Monte Carlo Method and Heisenberg model. Properties as magnetization and Hysteresis loops were obtained varying different parameters as the nanoparticle size, distance between nanoparticles and temperature. The model employed includes interaction between ions belonging to each nanoparticle and also the interaction between nanoparticles. Results show that the magnetization and the coercive force decrease as a function of the nanoparticles distance.     

Controlling the growth of ZnO quantum dots embedded in silica by Zn/F sequential ion implantation and subsequent annealing

We report the formation of embedded ZnO quantum dots (QDs) by Zn and F ion sequential implantation and subsequent annealing. Optical absorption and photoluminescence spectrum measurements, transmission electron microscopy bright field images and selected area electron diffraction patterns indicate that ZnO QDs were formed after annealing in air or vacuum at temperatures higher than 500?°C. Atomic force microscopy images show a comparatively flat surface of the annealed samples, which indicates that only very few Zn atoms are evaporated to the surfaces. The formation of ZnO QDs during the thermal annealing can be attributed to the direct oxidization of Zn nanoparticles by the oxygen molecules in the substrate produced during the implantation of F ions. The quality of ZnO QDs increases with the increase of annealing temperature.     

Thermal evolution and optical properties of Cu nanoparticles in SiO2 by ion implantation

SiO₂ samples were implanted by 45 keV Cu ions at a dose of 1 × 10¹⁷ /cm², and subjected to furnace annealing at temperatures ranging from 200 to 600 °C in nitrogen atmosphere. The results indicate that the Cu nanoparticles have been synthesized by Cu ion implantation, and subsequent annealing induces the diffusion and nucleation of nanoparticles partially. The results from XPS measurements show that the Cu⁰ is the dominate charge state in the implanted and subsequent annealed samples. With increasing annealing temperature, the size and distribution of Cu nanoparticles have been modified gradually. The surface plasmon resonance (SPR) of Cu nanoparticles at 570 nm has been observed by optical transmission spectroscopy. The strongest SPR signal at 400-600 °C indicates that lots of Cu nanoparticles have grown and show good optical properties. Moreover, the luminescence has been investigated in Cu implanted and subsequent annealed samples. Possible luminescence mechanisms, such as radiation induced defects, Cu (ions or atoms) related luminescence centers, etc., have been discussed.