Search

Metal matrix composites have a diverse range of applications. We have probed local structural modifications taking fullerene C70 as a model matrix material. In this study, thin films of fullerene C70 were grown on polished silicon and quartz substrates by resistive heating of fullerene C70. In order to understand local structural changes, these semi-crystalline films were irradiated with 120 keV N+ ions at different fluences ranging from 1 × 1013 to 3 × 1016 ions.cm−2. Microscopic analysis shows an increase in topological roughness up to a fluence of 1 × 1015 ions.cm−2 and then a decrease. The size of the particles decreases with increase in the fluence. Various spectroscopic analyses conducted on differently irradiated fullerene C70 films show that the bandgap decreases with the increase in the fluence which will increase the conductivity of the irradiated thin films. These results are proved by I-V measurements showing the decrease in the resistivity at higher fluences. Therefore, this characteristic trait makes fullerene C70 to be used as a prominent matrix component in the composites. Raman spectroscopic investigations reveal that C70 is completely transformed into amorphous carbon at a fluence of 3 × 1016 ions.cm−2. Different vibrational modes in FT-IR are also reported in the present work.

A bi-functional nanocomposite thin film containing Ag nanoparticles embedded in fullerene C 70 is synthesized by thermal co-evaporation technique. Tuning of plasmonic resonance of Ag-C 70 nanocomposite is obtained by annealing the nanocomposite thin film at different temperatures from 80 to 300 °C for 30 min. The optical and structural properties of nanocomposite thin film with respect to high temperature are studied by UV–visible absorption spectroscopy and X-ray diffraction. Transmission electron microscopy is performed to investigate the temperature dependent size evolution of Ag nanoparticles in fullerene C 70 matrix. Growth of Ag nanoparticles is observed with increasing temperature above 200 °C due to enhanced diffusion of Ag in fullerene C 70 and Ostwald ripening. The optical and structural properties of metal-fullerene nanocomposite is not significantly affected upto a temperature of 150 °C, after that a progressive blue shift of ~ 27 nm in SPR wavelength is observed with increasing temperature. The tuning of SPR is ascribed to the thermal induced structural transformation of fullerene C 70 matrix into amorphous carbon and also to mutual polarization of the particles.

Au-C70 nanocomposite thin films are deposited using thermal co-evaporation technique. Low atomic concentration of Au (∼3%) are used to avoid any deterioration of the properties of fullerene C70 when used with Au. These thin films are annealed in inert atmosphere at different temperatures for 30 min in order to promote the formation of nanocomposite material. Both the Au nanoparticles and fullerene C70 matrix are evolved by thermal treatment. Spherical shaped Au nanoparticles with a diameter of 3.8 ± 0.1 nm are clearly observed in the TEM images at 350 °C. The characteristic D and G bands of amorphous carbon are evidenced by Raman scattering spectroscopy in the film annealed at 350 °C. The surface plasmon resonance (SPR) absorption band of Au nanoparticles in carbon is obtained at 565 nm after treatment at 300 °C and it is blue shifted to 549 nm for the sample annealed at 350 °C.

We study the optical and microstructural properties of silver/amorphous carbon (Ag/a-C) nanocomposite thin film and its modification induced by swift heavy ion irradiation. Ag nanoparticles (NPs) embedded in a-C matrix were synthesized by co-sputtering of Ag and graphite by 1.5 keV neutral Ar atom beam. These Ag NPs were irradiated by 120 MeV Ag ions at different fluences ranging from 1 × 10 12 to 3 × 10 13 ions/cm 2 . Optical absorption studies revealed that surface plasmon resonance of Ag NPs in pristine film occurs at a wavelength of ~ 430 nm and it shows a blue shift (~ 26 nm) with increasing ion fluence up to 3 × 10 13 ions/cm 2 . Transmission electron microscopy and Rutherford backscattering spectroscopy were used to quantify particle size and metal atomic fraction, respectively, in the nanocomposite films. The growth of Ag NPs with bi-model distribution at a fluence of 3 × 10 13 ions/cm 2 was observed with ion irradiation. Raman spectroscopy was used to investigate the effect of heavy ion irradiation on carbon matrix. The blue shift in plasmonic wavelength is explained in terms of increase in sp 2 content in carbon matrix by heavy ion irradiation due to thermal energy deposition which leads to a decrease in dielectric properties of the matrix.

The present work reports the formation of Ni nanoparticles inside the SiO2 matrix and deals with the influence of Ni concentration on structural and magnetic properties of Ni–SiO2 nanocomposite thin films. The films with varying Ni concentration (20–55 at% measured by Rutherford back scattering spectroscopy) were deposited using DC/RF magnetron co-sputtering. TEM and XRD analysis reveal the formation of FCC Ni nanoparticles in all the samples. The particle size varies from 3 to 10 nm as a function of Ni concentration. The surface roughness of the films is also found to increase with increase in nickel concentration. Magnetic measurements show that the Ni nanoparticles behave as superparamagnets when their size is ≤6 nm, in spite of their large volume fractions. The results show that the magnetic properties of the nanoparticles can be controlled by their size and Ni concentration in the samples.

The magnetic properties of Zn 1− x Co x S ( x =0.025 and 0.05) thin films grown on α-quartz substrates at different temperatures ( T S ) of 200, 400 and 600 °C by means of pulsed laser deposition are presented. The films are crystallized with wurtzite structure. Optical absorption and transmission electron microscopy measurements indicate that Co ions are substituted to Zn on tetrahedral sites. Their magnetic response is composed of ferromagnetic and paramagnetic components of which respective strengths depend on T S and Co concentration. This behavior is interpreted as due to fluctuations in the magnetic ordering, depending on grain size and site location in grain boundaries or in crystal cores.

Structural and spectroscopic modifications of nanocrystalline (nc) ZnO films induced by Swift heavy ion (SHI) irradiation is reported. Films were irradiated at incremented ion fluences. Structural study reveals that the nanocrystals become more oriented at low fluences, while a release of strain and decrease in grain size is observed at high fluence. The surface morphology study also shows a decrease in crystallite size and agglomeration of grains at high fluence. On the other hand micro-Raman and Fourier transform infrared (FTIR) results show that the longitudinal optical (LO) mode is strengthened and red shifted, while the transverse optical (TO) mode get dampened at high fluence. But the amorphization of crystallites was not observed under the used irradiation conditions. The observed structural and spectroscopic modifications are explained in terms of high density of lattice defects and disorder created by dense electronic excitations induced by SHI irradiation. (C) 2011 Elsevier Ltd. All rights reserved.

Swift heavy ion induced stress in a pulsed laser deposited textured ZnO thin film is reported. In situ X-ray diffraction (XRD) measurements are carried out during ion irradiation at incremented fluences under 120 MeV Ag(+9) ions. The average grain size, lattice constant 'c', and stress in the film are calculated from the diffraction pattern. The nature of the stress is intrinsic and the origin can be attributed to the strong density of defects like dislocations at the grain boundaries as evidenced by micro-Raman, Fourier transform infrared (FTIR) spectroscopy and Atomic Force microscopic (AFM) studies. (C) 2010 Elsevier Ltd. All rights reserved.

We have investigated interfacial chemistry in a 100 nm Ni on PTFE (polytetrafluoroethylene) bilayer system induced by 120 MeV Au ions with fluences varying from 1 x 10(12) to 5 x 10(13) ions/cm(2). In-situ quadrupole mass analysis (QMA) shows emission of Fluorine (F) and different fluorocarbons (C(x)F(y)) such as CF, CF(3), C(2)F(3) etc. during irradiation. Electron spectroscopy for chemical analysis (ESCA) studies show that Ni reacts with chemically reactive species such as F(-)/F(center dot). and C(x)F(y) ions or radicals emitted during irradiation forming NiF(2) and metal-polymer complexes (-CFNi-). Rutherford backscattering spectrometry (RBS) was used to analyze the atomic transport at the interface and strong interface mixing is observed at the ion fluence 5 x 10(13) ions/cm(2). Atomic force microscopy (AFM) studies before and after irradiation show that surface roughness is increased from 6.9 to 12.4 nm with increasing fluence. Observed results have been explained on the basis of the chemical reactions taking place within molten ion tracks in the polymer and hot zones around the ion paths created in the Ni film. The studies show that swift heavy ion irradiation introduces strong chemical alteration in the system and induces chemical reactions within the ion track, which enhance ion beam mixing in Ni-PTFE bilayer systems. (C) 2010 Elsevier Ltd. All rights reserved.

The effects of ion irradiation on electrical and magnetic properties of C60 films are investigated and correlated to changes of structure. Conducting nanowires are formed along the linear path of swift heavy ions. Their continuity and radial dimension are correlated with the energy density deposited by such ions in electronic excitations. Whatever the slowing down process of ions, irradiation at high ion fluences induces the formation of an amorphous C phase exhibiting a ferromagnetic response up to room temperature. An additional paramagnetic signal is recorded from films irradiated with swift ions, which is ascribed to the formation of oriented defects decorated with oxygen.

International audience; In the present study, we have investigated the swift heavy ion induced structural modification of ZnO thin film deposited by atom beam sputtering. The films were irradiated by 100 MeV Ag ions at different fluences from 5 x 10(10) ions/cm(2) to 3 x 10(13) ions/cm(2). The influence of the irradiation fluence on structural and optical properties of these thin films was investigated. The structural properties have been studied using X-ray diffraction. The Zn-O bonding was confirmed by Fourier transform infrared spectroscopy and surface morphology was investigated by atomic force microscopy. XRD confirmed that the grain size and texture of the ZnO thin film are increased after the irradiation. The absorption peak intensity corresponding to Zn-O bonding is also increased as a result of energy deposition by swift heavy ion as revealed by FTIR. The AFM study of the films implied that roughness remains almost constant. Power spectral density was also estimated from the AFM micrograph to extract the value of roughness exponent. (C) 2009 Elsevier B.V. All rights reserved.

We report synthesis of a transparent magnetic semiconductor by incorporating Ni in zinc oxide (ZnO) matrix. ZnO and nickel-doped zinc oxide (ZnO: Ni) thin films (similar to 60 nm) are prepared by fast atom beam (FAB) sputtering. Both undoped and doped films show the presence of ZnO phase only. The Ni concentration ( in at%) as determined by energy dispersive X-ray (EDX) technique is similar to 12 +/- 2%. Magnetisation measurement using a SQUID magnetometer shows that the Ni-doped films are ferromagnetic, having coercivity (H(c)) values 192, 310 and 100 Oe and saturation magnetization (M(s)) values of 6.22, 5.32 and 4.73 emu/g at 5, 15 and 300 K, respectively. The Ni-doped film is transparent (> 80%) across visible wavelength range. Resistivity of the ZnO: Ni film is similar to 2.5 x 10(-3) Omega cm, which is almost two orders of magnitude lower than the resistivity (similar to 4.5 x 10(-1) Omega cm) of its undoped counterpart. Impurity d-band splitting is considered to be the cause of increase in conductivity. Interaction between free charges generated by doping and localized d spins of Ni is discussed as the reason for ferromagnetism in the ZnO: Ni film. (C) 2008 Elsevier B.V. All rights reserved.

Zn(1-x)M(x)O (M=Co, Ni, Mn) films with different concentrations of transition metal (10-30%)were synthesized by pulsed laser deposition. The substrates were heated at 400 degrees C and the depositions were performed either under secondary vacuum or under an oxygen pressure of 30 Pa. The occurrence of ion channeling in the films during Rutherford Backscattering Analysis, together with X-ray diffraction, optical absorption and transmission electron microscopy, clearly show that the M atoms are in solid solution on Zn sites. Magnetic properties were investigated by means of magnetometry at 5 and 300 K and Electron Spin Resonance. The Zn(1-x)Co(x)O and Zn(1-x)Ni(x)O films deposited under low 02 pressure exhibit both a ferromagnetic and a paramagnetic response up to 300 K, while films deposited under high 02 pressure and Zn(1-x)Mn(x)O films are paramagnetic. Broad spin resonance peaks are recorded at room temperature, from ferromagnetic films only. The nearly isotropic magnetic response of these films, which is observed in ESR when varying the field orientation with respect to the surface, seems to indicate that the crystalline anisotropy oppose the shape anisotropy, because of the strong [001] texture of the films. (C) 2008 Elsevier B.V. All rights reserved.

Damage caused by swift heavy ions with three different electronic stopping powers (120 MeV Au9+ (22 keV/nm), 90 MeV I7+ (17 keV/nm) and 70 MeV Ni5+ (11 keV/nm)) in three pyrochlores (Gd2Zr2O7, Nd2Zr2O7 and Gd2Ti2O7) with progressively increasing radius ratios (r(A)/r(B) of A(2)B(2)O(7)) of cations is reported. Since I+7 is one of the ions used, these measurements also simulate fission fragment damage in pyrochlores and identify a potential host lattice for inert matrix fuel. X-ray diffraction on the irradiated materials indicate amorphization in Gd2Ti2O7 at the lowest S-e used, and a transition to anion-deficient fluorite (Fm (3) over barm) structure with about 1% decrease in volume in Nd2Zr2O7 and Gd2Zr2O7 at higher S-e. In Nd2Zr2O7 this is followed by amorphization and Gd2Zr2O7 does not amorphize even at the highest S-e employed. Raman analysis of Gd2Zr2O7 and Nd2Zr2O7, indicate an increase of Zr coordination number after irradiation and the bands become broader due to disordering. Analysis of the results shows that the radiation susceptibility of these pyrochlores in the electronic stopping regime strongly depends on the radius ratio of A to B cations and hence on the energy required for formation of cation antisites and anion Frenkel pairs, similar to their susceptibility in the nuclear stopping regime. Published by Elsevier B.V.

Silver nanoparticles (Ag NPs) embedded in silica were prepared by a novel process of atom beam sputtering (ABS). Optical and structural properties of Ag NPs were studied by using ultraviolet–visible absorption, transmission electron microscopy and X-ray diffraction. The processes involving nucleation and growth of Ag NPs are discussed. The superiority of the ABS over ion implantation and ion beam mixing is discussed. These Ag NPs are found to be glucose sensitive, indicating their possible application in medical diagnostics.

Three phase transitions (face centered to simple cubic, surface rearrangement from (2×2) to (1×1) and glass transition) in fullerene thin films and the effect of 150 MeV Ti ion irradiation on these transitions have been studied, using temperature dependence of electrical resistivity measurements. The structural properties of the C60 thin films are studied by X-ray diffraction, atomic force microscopy and UV–vis spectroscopy. It is observed that defect creation by ion irradiation in the films lead to quenching and broadening of structural phase transitions but the transition temperatures did not show significant shifting under ion irradiation.

Effects of swift heavy ions irradiation on silica films containing Fe under the form of solute ions or metal particles have been investigated, using electron spin resonance and magnetometry. The results indicate that electronic excitations induce the reduction of solute ions and the precipitation of metal particles when the Fe concentration is not too low. The hammering effect of ions on the silica matrix causes a tilt of easy magnetization axis when the volume fraction of particles is of a few percents, but this axis remains in the film plane for fraction over 10%.

The modification of fullerenes vibrational properties by energetic ion irradiation is investigated, using Fourier transform infrared (FTIR) spectroscopy . The C60 thin films have been irradiated with 200 MeV Au ions at fluence from 1 × 1012 to 1 × 1013 ions/cm2. It is observed that 577 cm−1 mode is the most sensitive but 527 cm−1 IR active mode is more resistive for swift heavy ion irradiation. To understand change in the molecular structure of fullerene molecule under swift heavy ion (SHI) irradiation, we determined damage cross-section for all four T1u (527, 577, 1183, 1428 cm−1) IR active modes. It is observed that damage cross-section (σ) is different for different vibrational modes. The effective radii (r) of the damage cylindrical zone are also evaluated.

Sol–gel materials are converted into glassy ceramics when subjected to ion irradiation or heat treatments. In addition, a demixing occurs in the obtained glasses when their structure is metastable. In the present work, we have irradiated silicon-based gels with 120 MeV and 2 GeV Au ions at different fluences from 8 × 109 to 2 × 1013 ions/cm2. Ion irradiation leads to formation of carbon nanoclusters, which have semiconducting properties. Photoluminescence and optical absorption spectroscopies are used to identify the semiconducting properties of carbon clusters. High resolution transmission electron microscopy (HRTEM) and energy filtered imaging of C atoms show that C particles with a size of not, vert, similar4 nm are produced and they are aligned along ion tracks. Elastic recoil detection analysis has been performed to determine the kinetics of the H evolution and to evaluate the track radius, which matches with the radius obtained from HRTEM. The obtained aligned carbon clusters (wires) would find useful applications as field emitters or nanocontacts.

Thin films of high-quality polycrystalline silicon (poly Si) on different substrates are of interest for manufacturing thin film transistors, solar cells, and image sensors. In this study, we present the results of an investigation of poly Si films on glass, formed by nickel-induced crystallization. The process is based on isothermal annealing in air at 550 and 560 °C of co-sputtered Ni+Si films deposited on glass at different substrate temperatures, with and without the application of an electric field to the films. The poly Si films were investigated by Raman spectroscopy and Rutherford back-scattering. It was established that the substrate temperature and the Ni-concentration in the precursor amorphous Si+Ni films are important parameters for nickel-induced crystallization.

The formation of high-quality polycrystalline silicon (poly-Si) on low cost substrates has important applications in the development of thin film solar cells, transistors, image sensors, etc. In this study, we present the results of an investigation of poly-Si and poly-SiGe films on glass, formed by aluminum induced crystallization (AIC). The process is based on the isothermal annealing at temperatures between 500 and 540 °C of co-sputtered Si+Al, Si+Ge or sputtered a-Si films on glass, with and without thermally evaporated or sputtered Al film. The crystallized films were investigated by Raman spectroscopy, optical microscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Raman spectra demonstrate the crystalline structure of the poly-Si and poly-SiGe films prepared by AIC. The grain sizes of the poly-Si films estimated from the SEM and optical microscopy images are up to 25 μm for the different annealing conditions.

The processes of nucleation and growth of silver clusters under ion irradiation are investigated respectively in ion-exchanged glasses containing no clusters and in sputtered films, in which all the metal is precipitated before the irradiation. The studied samples were irradiated with He or Au ions of energy in the range of 1–100 MeV and the yields of precipitation or growth were assessed by combining measurements of luminescence and of optical absorption. The two processes result from electronic excitations and the nuclear collisions have insignificant effect. The nucleation rate is proportional to the product of the reduction cross section of Ag + ions by the ion fluence and the process involves the transient formation of Ag 3 2+ ions. Ag atoms must be released from clusters in order to permit the growth of some others in a matrix free of solute atoms (sputtered films) and this desorption is the stage limiting the growth rate. The desorbed atoms remain in solid solution when the density of electronic excitations exceeds a threshold value.

Ion irradiation of silicon-based gels with the stoichiometry SiO1.5H1, prepared from triethoxysilane, and containing Fe3+, Ni2+ or Cu2+ ions in solid solution permits to obtain the precipitation of metallic nanoparticles. Comparison of the particles volume fractions in films irradiated with 1.5 MeV He or 3 MeV Au ions on basis of their optical absorption or magnetic resonance indicates that electronic excitations are responsible for the reduction and precipitation processes, while atomic displacements induce a partial redissolution by mixing. Moreover, the precipitation yield increases almost in proportion to the ion fluence. Measurements of magnetization as a function of the temperature show that the Fe and Ni particles in irradiated films are superparamagnetic and their range of sizes is narrower than in films heat treated in vacuum at 600–1000 °C.

a-Si 1− x C x :H thin films doped with different concentrations of Tb have been deposited by magnetron co-sputtering. The carbon content in the films is varied in order to change the optical gap. RBS analysis shows that Tb is homogeneously distributed in the bulk. Optical absorption spectra in the visible are studied and changes in the optical gap and the defect absorption with increasing Tb concentration are observed. The laser excited photoluminescence (PL) of the films is studied after annealing at 300°C in Ar atmosphere. It consists of a broad band covering the whole visible spectrum. The position of the PL band does not change when the carbon content in the films is increased from 10 to 25 at%. It is tentatively assigned to the Tb 3+ impurity.

Ag nanoclusters in a SiO2 matrix prepared by RF magnetron co-sputtering and subsequent irradiation with heavy 4.5 MeV Au+ ions were formed. The refractive index and optical absorption spectra of the films were studied. The method of the disappearing diffraction pattern was used for the refractive index determination. The refractive index enhances with increasing Ag concentration, as expected from the light scattering theory. SiO2:Ag thin films exhibit a plasmon resonance in the visible region. In the as-deposited films the Ag nanoclusters are less than 1 nm and are formed during the deposition. The intensity of the plasmon peak is low. After irradiation with 4.5 MeV Au+ ions the intensity of the peak increases and the peak becomes narrower. The TEM study shows that this is related to the change in the size of the Ag nanoclusters.

SiOx thin films with various oxygen contents (1.1⩽x⩽1.7) have been prepared by thermal evaporation of silicon monoxide in vacuum. The film composition is controlled by changing both deposition rate (between 0.2 and 6 nm/s) and depositing the films at two different residual pressures, (2×10−4 or 1×10−3 Pa). Long-term stability of all films is ensured by a post-deposition anneal at 520 K for 30 min and this is explained with reference to the annealing-induced decrease of the volume fraction occupied by pores in the film. The oxygen content, x, of each film is determined using both infrared absorption and Rutherford backscattering measurements and the x-values obtained in each case are quite different. The observed difference is related to the low density of the films, particularly those deposited at high residual pressure and high deposition rates, which, in addition to the oxygen deficiency, decreases the frequency of the TO stretching mode. An increase of the oxygen content of the films is observed upon annealing at 970 K accompanied by formation of amorphous silicon particles. Phase separation is completed after annealing at 1300 K and Si nanocrystals embedded in SiO2 matrix are produced, but the infrared absorption results show that the level of chemical disorder in the matrix is appreciably higher than that in ‘pure’ SiO2 thin films.

The release of H from Si-based polymers under irradiation by He, C, Si, Cu, Ag and Au ions of different energies has been studied. The ions and energies have been chosen in such a way that they cover a wide range of electronic and nuclear energy loss values. Results are analysed in the frame of three different models. A model of track percolation leading to an exponential decay of the H concentration as a function of ion fluence fits the kinetics of H evolution only on a limited range of fluence. An explanation is proposed in the second model, assuming that the radiolytic efficiency in the core of tracks changes when the tracks overlap. A better agreement is found however with a model implying the diffusion of molecular hydrogen in the material after combination of two radicals formed within a critical recombination volume.

Spectra of optical extinction in the visible range for SiO 2 :Ag colloid films prepared by ion implantation and ion beam mixing are compared to calculations for isolated clusters and for interacting clusters in an effective medium. Whereas for low metal concentrations the shape of the spectra is determined by the cluster size, at higher concentrations it largely depends on their mutual interaction. This interaction induces a broadening of the resonance in implantated films and on the contrary a narrowing in ion beam mixed films. The difference is ascribed to a particular arrangement of the clusters, with a bimodal size distribution, in the latter films.

The mixing of noble metals (M) with various oxides under 4.5 MeV ion irradiation and the concurrent process of metal segregation were studied by means of Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). Simulations of the widening of RBS M peaks due to the spheroidization of the M layer, using particles sizes measured in TEM, indicate that the effect is noticeable but does not determine the mean square spread of the M depth distribution. RBS analyses show that recoil implantation is the predominant mechanism of injection of M atoms into the oxide matrix. The spreading is controlled either by the recoil implantation or the radiation-enhanced diffusion of M atoms according to their mobility. In particular this mobility depends on the M mass and on the oxide ionicity.

Layers of noble metals M embedded in various oxide matrices (SiO 2 , Al 2 O 3 , TiO 2 , ZrO 2 , and also Si for a purpose of comparison) were irradiated with incremented fluences of MeV heavy ions. A major contribution of recoil implantation to displacements accounts for the linear rates of atoms relocation as a function of the ion fluence, measured by means of RBS. According to the temperature and to the initial thickness of the M layer, the in depth-straggling of M atoms varies in proportion to the ion fluence or to its square. This change of straggling rate is explained by its control either by the radiation-enhanced diffusion or by the recoil implantation process, when the solution of diffusion equations relative to an infinitely thin source cannot be applied. The mobility of M atoms in the oxide depends on the latter ionicity and on the M mass.

Thin layers of noble metals (M=Cu, Ag, Pd, Pt, Au) embedded in silica were submitted to irradiation with increasing fluences Φ of 4.5 MeV Au ions. Concurrently to the mixing of metal and silica atoms, the irradiation promotes the clustering of the metallic phase. Metallic particles were observed in transmission electron microscopy in order to determine if their size contributes for a large part to the spreading of the M distribution measured by Rutherford Backscattering Spectrometry (RBS). The part of this spreading due to the recoil implantation of M atoms into the silica matrix and to their radiation-enhanced diffusion is yet larger. The variance of the distribution increases in proportion to Φ or to its square, depending on whether it is controlled by the diffusion (thin films) or the recoil implantation process (thicker films).

The electronic structure and chemical bonding of unirradiated and irradiated Poly-1,4-phenylene-ether-sulphone (PES) films have been studied with fluorescent X-ray emission spectroscopy. PES films have been irradiated with 150 keV Ar + ions at concentrations of 5 × 10 13 , 1 × 10 14 , 1 × 10 15 and 7.5 × 10 15 cm −2 . The electronic structure of PES has also been calculated with MO LCAO calculations using a deMon density functional theory (DFT) program and shows good agreement with the experimentally obtained X-ray fluorescence spectra (S L 2,3 , C Kα and O Kα). It is found that the C Kα X-ray emission spectra (XES) of irradiated PES films display marked changes at very high concentrations (1 × 10 15 − 7.5 × 10 15 cm −2 ), similar to the spectroscopic characteristics of amorphous carbon. According to our measurements, the low-energy shift of the S Kα 1,2 XES is observed for concentrations greater than 5 × 10 13 cm −2 which is related to the reduction of –SO 2 – to –S– following the transfer of an oxygen atom from the –SO 2 – functional group to the radical site.

Fluorescent soft X-ray carbon Kα and silicon L 2,3 emission spectra (XES) have been used to characterize the bonding of carbon atoms in polyimide (PI) and polycarbosilane (PCS) films. The PI films have been irradiated with either 40 keV nitrogen or argon ions, at concentrations ranging from 1×10 14 to 1×10 16 cm −2 . The PCS films have been irradiated with 5×10 15 carbon ions cm −2 of 500 keV and/or annealed at 1000°C. We find that the fine structure of the carbon XES of the PI films changes with implanted ion concentrations above 1×10 14 cm −2 which we believe is due to the degradation of the PI film into amorphous C:N:O. The bonding configuration of free carbon precipitates embedded in amorphous SiC which are formed in PCS films after irradiation with C ions or combined treatments (irradiation and subsequent annealing) is similar to that found in diamond-like films or in graphite-like films, respectively.

Sol–gel derived Fe 2 O 3 films containing about 10 wt% of Er 2 O 3 were deposited on porous silicon by dipping or by a spin-on technique followed by thermal processing at 1073 K for 15 min. The samples were characterized by means of PL, SEM and X-ray diffraction analyses. They exhibit strong room-temperature luminescence at 1.5 μm related to erbium in the sol–gel derived host. The luminescence intensity increases by a factor of 1000 when the samples are cooled from 300 to 4.2 K. After complete removal of the erbium-doped film by etching and partial etching the porous silicon, the erbium-related luminescence disappears. Following this, luminescence at 1.5 μm originating from optically active dislocations (“D-lines”) in porous silicon was detected. The influence of the conditions of synthesis on luminescence at 1.5 μm is discussed.

Fluorescent soft X-ray carbon Ka emission spectra (XES) have been used to characterize the bonding of carbon atoms in polyimide (PI) and polycarbosilane (PCS) films. The PI films have been irradiated with 40 keV nitrogen or argon ions, at fluences ranging from 1 · 10 14 to 1 · 10 16 cm ˇ2 . The PCS films have been irradiated with 5 · 10 15 carbon ions cm ˇ2 of 500 keV and/or annealed at 1000∞C. We find that the fine structure of the carbon XES of the PI films changes with implanted ion fluence above 1 · 10 14 cm ˇ2 which we believe is due to the degradation of the PI into amorphous C:N:O. The width of the forbidden band as determined from the high-energy cut-oA of the C Ka X-ray excitation decreases with the ion fluence. The bonding configuration of free carbon precipitates embedded in amorphous SiC which are formed in PCS after irradiation with C ions or combined treatments (irradiation and subsequent annealing) is close to either to that in diamond-like films or in silicidated graphite, respectively. ” 1998 Elsevier Science B.V. All rights reserved.

Thin films of polysiloxanes and polycarbosilanes with various substituents were converted into SiOC and SiC ceramics by irradiation with ions of increasing masses. The transformation kinetics as a function of the ion dose was assessed by means of ion beam analyses (RBS, NRA, ERDA), compaction measurements, spectroscopies of infrared absorption and Raman scattering. The kinetics depends strongly on the linear density of electronic excitations. The formed radicals tend to react with the atmosphere after irradiations when this density is too low for permitting their combination into crosslinks. Part of the C atoms segregate into clusters with a noticeable degree of tetragonal hybridization, varying with the nature of side groups in the polymeric precursor. This precipitation affords to the films interesting properties: (1) a strong yellow photoluminescence, within a given range of ion doses where the quantum dots of C are not too coarse or too numerous; (2) at higher doses, a hardness reaching that of amorphous SiC and three times that of films converted by heat treatment at 1000–1200°C (as evidenced by nanoindentation tests); (3) a greatly improved thermochemical stability.

We have studied the photoluminescence (PL) of inorganic polymers submitted to irradiations with increasing fluences of energetic He, C or Au ions and correlated the changes in luminescence spectra to structural transformations, evidenced by means of ion beam analyses, Raman, FTIR and spectroscopic ellipsometry. The films exhibit a strong yellow emission when the energy transferred by the ions to electron shells of target atoms is within a given range of 20 to 60 eV/atom. For this optimal amount of ionizations, the precipitation of quantum dots made of free carbon becomes noticeable. The vanishing of the luminescence for larger energy transfers is attributed to the percolation or growth of these dots, combined with a subcritical depletion in the H content of the surrounding SiO 1.5 C x : H y matrix.

The application of ion-beam mixing to the doping of silica films with metals either in solution or in the form of nanoclusters requires a preliminary investigation of the mixing mechanisms. This was undertaken by means of RBS and XRD for Au, Pt, W, Ag and Cu films mixed with silica by 4.5 MeV Au or 200 keV Ar ions, at 100 or 300 K. In all cases metal atoms migrated preferentially inwards. At room temperature, the radiation enhanced diffusion of Au, Pt, Ag and Cu in the silica matrix competed with their coalescing into coarser particles, under the effect of interfacial stresses. The mixing rate was proportional to the ion dose or to its square, depending on the system and temperature. This unusual quadratic law is attributed to the formation of solute metal-vacancy complexes.

This paper reports the first measurements of the composition, hardness and optical properties of polyphosphazene-silica hybrid materials submitted to heavy ion irradiations. Their hardness, established by means of nanoindentation tests, increases progressively as an amorphous three-dimensional network is built and it saturates at a value slightly lower than for pure polymers. Their spectra of optical absorption in the visible range have been determined by means of spectroscopic ellipsometry. Being typical of insulators in the as-grown state, they become progressively amorphous semiconductors under the effect of ion irradiation, but never metallic-like as would be the case if the polymeric part was transformed into amorphous carbon. The silica component segregates at high irradiation fluences.

The modifications of optical absorption spectra and of hardness induced by irradiations with various ion species in three polymers have been determined quantitatively by means of spectroscopic ellipsometry and of nanoindentation tests. Their analysis in terms of amounts of energy deposited respectively in nuclear collisions and in electronic excitations indicates that the latter have a predominant effect on both properties. The efficiency of ionizations depends on the ablity of radicals formed under each ion impact to interact.

Nanoindentation tests have been performed with a sharp diamond pyramid (of apical angle 35°) into kapton implanted with various ion species in order to obtain quantitative profiles of hardness. The hardening as a function of the ion nature, energy and fluence was correlated to the structure and compositional modifications analyzed by means of Rutherford Backscattering Spectrometry (RBS), Elastic Recoil Detection Analysis (ERDA) and IR spectroscopies. The amorphous hydrocarbon formed at high fluences of Ne, N, O, or Si ions with energies of 180, 300 and 360 keV was 12 to 15 times harder than the pristine material. But radial cracks along the interface were systematically detected when the indentor penetrated into the substrate, because of its too large plastic deformation with respect to that of the superficial layer. They were characterized by reproducible discontinuities in the depth variation at a critical value of the imposed load, and the film flaking was confirmed by SEM observations.

‘Amorphous diamond’ films (80% sp3 hybridization, no other elements) have been grown by ion implantation at low energies or quenching of a Cn+ laser-plasma on Si, ZnS and Ti alloys, then irradiated with ions of higher energies. Irradiations into the bulk of films transform them into vitreous carbon, while they are beneficial for the dielectric and mechanical properties when damages are created selectively in the vicinity of the interface. Most of the effect is due to an increasing amount of carbide precipitates in underlayers.

The differences in the oxidation kinetics of pure Ni surfaces prepared by various methods of polishing have been correlated to the modifications of structural, mechanical and physicochemical states of the polished surfaces and of the NiO films. These states were characterized by roughness measurements, by determination of stresses and strains by diffraction experiments using X-rays and electrons, and by surface analysis by SIMS and GDOS. Reference is made to similar experiments on surfaces doped by ion implantation to interpret the selective role of each surface contaminent.

Resume L'emission secondaire d'alliages FeNi, NiCr et FeCr sous bombardement d'argon et en presence d'oxygene s'interprete simplement si l'on admet que les probabilites d'ionisation PNMN et PNMM des elements N et M ejectes des alliages NM sont des fonctions lineaires des concentrations atomiques CM et CN de ces elements. Une hypothese est avancee selon laquelle les echanges electroniques avec les plus proches voisins au cours de la sortie de l'atome ejecte determinent ces probabilites.

Corrosion tests have been carried out at 1200°C in various H2/H2O/CH4 mixtures, for a range of pre-oxidized materials, including an austenitic Fe45Ni25Cr alloy and a series of ferritic, austenitic and two phase alumina-forming grades. The corrosion process has been studied principally by metallographic examination of the scales and of the underlying alloys, together with local chemical and physical analysis. The results are interpreted with the aid of thermodynamic phase-stability diagrams.

The growth kinetics of NiO films depends on their structure, internal state of stress and purity level. The specific role of S, Si and Y impurities was studied on pure Ni matrices implanted with low doses of these elements (2 × 1015 −5 × 1015/cm2). The modifications of the transport properties in the growing films were studied by means of thermogravimetry and of SIMS profiles of the depth distribution of a marked isotope 18O. The stress level in the oxide crystal was deduced from the modifications of interreticular distances measured by X-ray diffraction at large angles. Nickel oxidizes slower when implanted with S, Si or Y. Sulfur dissolves in the oxide film, while Si and Y form microscopic precipitates. The three dopants act preponderantly as hardening particles modifying the stress system and its catalytic effect upon the inward diffusion of Ni vacancies.

The plasticity of nickel surfaces implanted with increasing doses of phosphorus or boron ions has been assessed by means of indentation tests at the sub-micron level, with continuous recording of depth as a function of load or time. For low concentrations of metalloid in supersaturated solution, the lattice disorder has a marked hardening effect. Significant further hardening at high doses is seen in the case of boron, but not phosphorus; it correlates with the increase in the proportion of amorphous phase. The changes are found to be comparable with those seen in chemically-grown deposits. We discuss also the effect of an anneal leading to relaxation or crystallisation, and the changes produced in elastic recovery parameter.

S.I.M.S. and optical spectrometry were used to determine the composition of oxide scales developed on several FeNi2025Cr5AlY alloys, oxidized at high temperature (1273–1573K) under a pure oxygen atmosphere. The oxide scales were made up of an alumina layer containing a certain amount of spinel, independently of the iron and nickel content; yttrium enters in solid solution in the alumina layer. The growth of the alumina layer depends mainly on anionic diffusion, but does not obey a parabolic rate. The amount of yttrium in the alloys must be limited to 300 ppm (approximately the solubility of this element in the alloys), in order to have an optimum effect on oxidation kinetics and oxide adherence. This improvement in adherence is due to yttrium solute atoms in the alumina, rather than to mechanical keying by yttria particles.