M. Nikolaeva

Iron silicide formed in a-Si:Fe thin films by magnetron co-sputtering and ion implantation

Thin films containing iron silicides are prepared by two methods. The first one consists in depositing a-Si:H:Fe thin films by magnetron co-sputtering followed by rapid thermal annealing (RTA). The second one is ion implantation of Fe in a-Si:H thin films and RTA treatment. The samples are characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Rutherford back-scattering (RBS). FTIR spectra show absorption bands typical for β-FeSi 2 at 263, 293, 308, 345 and 425 cm -1 . It is shown that the optimal concentration of Fe in the co-sputtered films to obtain β-FeSi 2 is 35-40% and the optimal RTA temperature is 900°C. XPS spectra show that β-FeSi 2 is formed in as-deposited and annealed co-sputtered a-Si:H:Fe and implanted a-Si:H thin films.

Ion beam assisted formation of Ag nanoparticles in SiO2 and their optical properties

Abstract Ag nanoclusters in SiO 2 matrix were formed by magnetron co-sputtering followed by ion irradiation. The refractive index and optical extinction spectra of the films were studied. The SiO 2 :Ag thin films exhibit a plasmon resonance in the visible region. In the as-deposited films the Ag nanoclusters are less then 0.5 nm in size. The intensity of the plasmon peak is low. After irradiation with 4.5 MeV Au ions the intensity of the peak increases and it becomes narrower. The FWHM of the plasmon peak corresponds to a mean radius increasing with the ion fluence. The method of the disappearing diffraction pattern was used for the refractive index determination. It is a critical angle method and is applicable for measurements of layers with thickness comparable with the used wavelength. Moreover it is insensitive to surface gradients of the real part of the refractive index and roughness, which disturb elipsometric data. The refractive index enhances with the increasing Ag concentration and irradiation ion fluence, as is expected from the light scattering theory.

Room-temperature photoluminescence from Tb3+ ions in SiO2 and a-SiC:H thin films deposited by magnetron co-sputtering

The laser excited photoluminescence (PL) of SiO 2 and a-SiC:H thin films doped with Tb deposited by co-sputtering has been studied. In the case of SiO 2 :Tb the PL is due to 4f-4f transitions of Tb 3 + ions starting from the 5 D 4 level which is resonantly excited by the 488 nm Ar + laser line. The PL in this case has no temperature quenching from 18 K up to room temperature. The inhomogeneous broadening of the PL bands predominates over the homogeneous one. In the case of a-SiC:H:Tb a broad band covering the whole visible spectrum is observed. It is tentatively assigned to a recombination centre created by the Tb impurity.

Mixing of metals in Si with 4.5 MeV Au ions

Abstract The mechanism of ion beam mixing of Fe, Er, Pd, Ag, Au layers embedded in a-Si, a-SiC, a-Si:H or a-SiC:H under 4.5 MeV Au irradiation is studied by means of RBS and TEM. Contrary to what is generally observed for irradiation at lower energies recoil implantation contributes significantly to the process by forcing atoms to enter in solid solution into the matrix. Insoluble species migrate over some distance before precipitating in nanometric clusters. Fe, Pd and Er form silicides, growing either by unidirectional diffusion of Si in the metal layer or two-dimensional diffusion of recoil implanted atoms parallel to this layer. But hydrogenation of the matrix promotes a diffusion of Er in a-Si:H and enhances the diffusion rate of noble metals in a-SiC:H.

Ion-induced changes in the average radius of Ag clusters and the refractive index of SiO2 : Ag thin films

Ag nanocrystals in a SiO2 matrix were formed by magnetron co-sputtering followed by ion irradiation. The SiO2 : Ag thin films exhibited an absorption resonance in the visible region, due to plasmon polarization of the small Ag crystals. In the as-deposited films, the size of the silver nanoclusters was less than 0.5 nm. After irradiation with 4.5-MeV Au+ ions, the intensity of the absorption peak increased and the peak became narrower, indicating that the crystals had grown. To estimate the average radius, 〈R〉, of the clusters, a computer program based on the Mie theory was used. It was found that 〈R〉 increases linearly as a function of the Au+ ion fluence The method of the disappearing diffraction pattern was used for determining the real part of the refractive index. This index was enhanced with increasing irradiation fluence, probably because the films became more compact.

Optical applications of ion beam irradiation

Abstract Layers of various metals (M) buried in Si, SiO 2 or Al 2 O 3 were irradiated with various fluences of heavy MeV ions in order to obtain either silicides or nanometric particles that are expected to exhibit interesting optical properties. The mixing of noble metals, Fe and Er with these matrices proceeds either via isotropic diffusion in the metal layer or the growth of compound particles by planar diffusion or a dual mechanism involving recoil implantation and radiation-enhanced diffusion of M atoms in the matrix. Noble metals form clusters in the oxides directly by lateral segregation and by reprecipitation after diffusing over some distance. Both types of clusters contribute to the absorption resonance of the metal plasmon in the visible part of the spectrum, so that the absorption intensity is not a simple function of the mixing yield. Irradiation of co-sputtered SiO 2 :M layers with a low ion fluence induces more homogeneous precipitation and provides these layers with as interesting optical properties as those obtained by mixing.