C. Tosello

Effect of nitrogen‐ion implantation on the unlubricated sliding wear of steel

The effect of 30‐keV nitrogen‐ion implantation on the unlubricated sliding wear of type‐38 NCD4 steel has been investigated. The effect of implants is seen to reduce the amount of wear for nitrogen doses above 1017 ions/cm2. The reduction in the wear persists also after removal of a material thickness greater than the penetration depth of the implanted nitrogen ions.

Detection and size determination of Ag nanoclusters in ion‐exchanged soda‐lime glasses by waveguided Raman spectroscopy

Waveguided Raman measurements have been performed in order to detect the presence of Ag nanoclusters in soda‐lime glass waveguides obtained by ion exchange. By subtracting a strong broadband luminescence and the Raman contribution of the glass matrix, a low frequency Raman peak is resolved. The peak is ascribed to surface acoustic vibrations of silver clusters. The involved modes are the quadrupolar spheroidal ones. The size distribution of the Ag clusters is deduced from the energy and the linewidth of the peak. Silver particles have small dimensions with an upper size limit of about 1.5 nm. This result is in good agreement with recent transmission electron microscopy measurements.Waveguided Raman measurements have been performed in order to detect the presence of Ag nanoclusters in soda‐lime glass waveguides obtained by ion exchange. By subtracting a strong broadband luminescence and the Raman contribution of the glass matrix, a low frequency Raman peak is resolved. The peak is ascribed to surface acoustic vibrations of silver clusters. The involved modes are the quadrupolar spheroidal ones. The size distribution of the Ag clusters is deduced from the energy and the linewidth of the peak. Silver particles have small dimensions with an upper size limit of about 1.5 nm. This result is in good agreement with recent transmission electron microscopy measurements.

Structural evolution of Fe-Al multilayer thin films for different annealing temperatures

The phase formation during thermal annealing of Fe/Al multilayer thin films prepared by electron-beam evaporation, with an overall atomic concentration ratio of Fe:Al = 1:1, has been studied by Rutherford backscattering spectrometry (RBS), x-ray diffraction spectroscopy (XRD), and conversion-electron Mossbauer spectroscopy (CEMS). At the annealing temperature of 473 K some degree of atomic mixing between Fe and Al layers is revealed only by CEMS. At 573 K a large degree of atomic mixing is indicated also by RBS, leading to the nucleation and growth of the B2 FeAl intermetallic phase, as detected by means of XRD and CEMS. At 673 K all Fe atoms have reacted and the multilayer film is transformed into a defective B2 phase. Annealing at higher temperature increases the structural order of the B2 phase. We suggest that the observed phase formation occurs in three stages: (1) formation of a thin intermixed layer between Fe and Al in the as-deposited sample; (2) Al migration into the initial intermixed layer; (3) B2 phase growth at the interface between the intermixed layer and the Fe layer.

Er-doped silica-based waveguides prepared by different techniques: RF-sputtering, sol-gel and ion-exchange

Erbium-activated silica-based planar waveguides were prepared by three different technological routes: RF-sputtering, sol–gel and ion exchange. Various parameters of preparation were varied in order to optimize the waveguides for operation in the NIR region. Particular attention was devoted to the minimization of the losses and the increase of the luminescence efficiency of the metastable 4I13/2 state of the Er3+ ion. Waveguide properties were determined by m-line spectroscopy and loss measurements. Waveguide Raman and luminescence spectroscopy were used to obtain information about the structure of␣the prepared films and about the dynamical processes related to the luminescence of the Er3+ ions.

Preparation of silver nanoparticles in silica films by combined thermal and electron-beam deposition

Thin films of silica containing Ag particles, grown by a co-deposition technique, have been studied by optical absorption, X-ray diffraction and low-frequency Raman scattering. Particle sizes were estimated from the vibrational frequencies of the quadrupolar spheroidal modes. Laser annealing increases the size of the particles and smoothes their surfaces.

Erbium-Activated Silica-Titania Planar Waveguides

Abstract(100 − x)SiO2-(x)TiO2-ErO3/2 planar waveguides, with 7 ≤ x ≤ 20 have been prepared by sol-gel route using the dip-coating technique. The thickness of the films was optimized to support a single propagating mode at 1550 nm, with a confinement coefficient higher than 0.75. The process of densification of the gel and the devitrification with the growth of TiO2 nanocrystals were studied by Raman scattering. Devitrification is important only for x ≥ 15, but it was not possible to obtain full densification of the samples, even at the lowest TiO2 content, without the appearance of nanocrystals.Emission in the C telecom band was observed; the spectral width of the 4I13/2 → 4I15/2 transition of Er3+ slightly increases with the titania content. For x ≤ 12 most of Er3+ ions (about 65%) decay exponentially with a lifetime of about 8 ms.

High quality factor Er3+-activated dielectric microcavity fabricated by rf sputtering

The authors report on one-dimensional dielectric photonic crystals activated by Er3+ ion and fabricated by rf-sputtering deposition. The cavity was constituted by an Er3+-doped SiO2 active layer inserted between two Bragg reflectors consisting of six pairs of SiO2∕TiO2 layers. Near infrared transmittance spectra evidence the presence of a stop band from 1350to1850nm and a cavity resonance centered at 1537nm. Intensity enhancement and narrowing of the I13∕24→I15∕24 emission band of Er3+ ion, due to the cavity effect, were observed. A cavity quality factor of 171 was achieved.

Mössbauer surface study of a nitrogen-implanted medium-carbon steel

The effect of nitrogen implantation on C40 medium-carbon steel is investigated by means of Mössbauer electron backscattering spectroscopy. Samples were implanted at various doses, after quenching from the austenitizing temperature and after quenching plus tempering, in order to detect the influence of the structure previous to the implantation. A different sequence of surface compound formation is observed in the two considered cases.

Erbium-activated silica–titania planar waveguides on silica-on-silicon substrates prepared by rf sputtering

Abstract Erbium-activated silica–titania planar waveguides were prepared by radio-frequency (rf) sputtering technique. Silica-on-silicon substrates obtained by plasma-enhanced chemical vapor deposition (PECVD) and rf sputtering (RFS) were employed. The refractive indices, the thickness and the propagation losses of the waveguides were measured. The refractive index and the roughness of the silica substrates produced by RFS appear to be dependent on the thickness. Thermal annealing, which is a necessary condition to obtain light propagation, induces a decrease of the refractive index in the silica substrates. The waveguide deposited on PECVD substrate exhibits several propagating modes with an attenuation coefficient 1.7 dB/cm compared with 12.2 dB/cm measured for the waveguide deposited on silica substrate produced by RFS technique. Emission of the 4 I 13/2 → 4 I 15/2 transition with a 53 nm bandwidth was observed.

On the optical absorption and nonlinearity of silica films containing metal nanoparticles

Abstract Metal nanocluster composite glasses (MNCGs) have been the subject of both experimental and theoretical investigation because of their peculiar optical properties. In particular, the enhanced third-order optical nonlinearity could be exploited in the all-optical switching device technology. Nevertheless, several factors such as thermal stability, wavelength tunability, response time regime, recycling frequency, laser-induced damage and optical absorption come into play in the definition of the material suitability. In this work, we present some results on MNCG films prepared by ion implantation. Nonlinear refractive index values are also presented for rf sputtered films, evidencing the presence of thermal nonlinearity in the optical response. Figures of merit that must be satisfied for ultrafast all-optical switching application of MNCGs are evaluated for this composite.