L. M. Gratton

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.

Analysis of the hydrogen permeation properties of TiN-TiC bilayers deposited on martensitic stainless steel

Abstract The efficiency of TiN-TiC bilayer coatings, deposited by ion-beam-assisted deposition on martensitic steel, as a hydrogen permeation barrier was investigated by a gas phase method; the hydrogen permeability in the TiN-TiC bilayers is very low, at least 104 times lower than in the steel substrate in the temperature interval 470–570 K. Possible physical mechanisms, responsible for the reduced permeability of the ceramic bilayers, are discussed. In particular, from our experimental results, it can be concluded that chemisorption and/or hydrogen jumping from surface sites to the first subsurface atomic layer represents the hydrogen permeation limiting process.

Aluminum and iron surface modification by deuterium ion implantation and thermal desorption process

Abstract Fe and Al thin films were implanted at room temperature with 20 keV D 2 ions at 3×10 16 ions/cm 2 fluence. The correlation between the effusion of the implanted deuterium and the evolution of the surface morphology was studied by thermal desorption spectroscopy (TDS) and scanning electron microscopy (SEM). Deuterium effusion from Fe thin films occurs at ∼430 K and is controlled by the D 2 surface recombination process. The deuterium effusion profile from Al thin films appears more structured. SEM analysis reveals blisters in the as-implanted samples and the increase of their number density and size up to a temperature of ∼500 K. TDS analysis indicates effusion of parts of the implanted deuterium in the 500–600 K temperature range: deuterium is released from the blisters as indicated by the decrease of their number density and size observed by SEM in this temperature interval. The major part of deuterium effuses at ∼630 K and the effusion process is controlled by the migration of deuterium through the surface oxide layer: the effusion process has an activation energy of 1.8±0.1 eV which is very close to the activation energy for deuterium diffusion in γ-Al 2 O 3 . The deuterium effusion kinetics from Fe–Al multilayers is nearly the same as in Fe thin film samples.

A simple measurement of the sliding friction coefficient

We present a simple computer-aided experiment for investigating Coulombs law of sliding friction in a classroom. It provides a way of testing the possible dependence of the friction coefficient on various parameters, such as types of materials, normal force, apparent area of contact and sliding velocity.

Deuterium permeation through SiO2 thin film deposited on stainless steel substrate

The diffusivity of deuterium in low temperature deposited silicon oxide thin films has been studied in the temperature interval from 485 to 655 K using a D2 gas phase permeation technique. The measured deuterium diffusion coefficient varies from (5.8 ± 2.0) × 10−14 cm2/s at 485 K to (5.1 ± 1.8) × 10−13 cm2/s at 655 K and has an activation energy of 0.34 ± 0.02 eV in the entire temperature range with a pre-exponential factor of the order of 10−10 cm2/s. Grain boundary diffusion through the polycrystalline silicon oxide thin film is suggested to be the rate limiting factor in the deuterium transport process.

Ion beam effects FeNi bilayers

Abstract Ion beam mixing induced by 100 keV Ar+ irradiation in FeNi bilayers has been studied. Conversion electron Mossbauer spectroscopy has been used for structural analysis of the irradiated specimens. An FeNi Invar alloy formed in the mixed region, among other phases, exhibits deviation of the average iron hyperfine field from the Slater-Pauling curve. Two other distinct phases have been identified as solid solutions of nickel in b.c.c. iron and iron in f.c.c. nickel.

Making Light Rays Visible in 3-D.

Students become deeply involved in physics classes when spectacular demonstrations take over from abstract and formal presentations. In this paper we propose a simple experimental setup in which the wave behavior of light can be made spectacularly evident along the whole path of the light beam in a practically unlimited number of configurations.1 The idea is simply that of adopting a fog-making machine to show, by means of light scattering along its path, that diffraction and interference are effective processes, i.e., they do not “switch on” just at the detection screen, as one could somehow be tempted to imagine in a more conventional setup. In our experiment, an ultrasonic mist maker is used to produce a small, homogeneous volume of water vapor fog (see Fig. 1). The fog is produced through water fragmentation caused by the mechanical action of a ceramic electrode that oscillates at ultrasonic frequency.2

Effect of ion-beam irradiation on magnetic anisotropy in Fe-Tb multilayers

Abstract A 57 Fe(6 nm)/Tb(0.7 nm) × 10 multilayer sample, deposited on a Kapton substrate in UHV, was irradiated with low-dose 100 keV Ar ions. By conversion electron Mossbauer spectroscopy it was observed that the angle between the normal to the surface of the film and the average direction of atomic spins increases upon irradiation, implying a decrease in perpendicular magnetic anisotropy (PMA). A detailed analysis of Mossbauer spectra suggests that irradiation produces an appreciable change in the thickness of the interface layer without the formation of any interfacial alloy phase. The observed change in PMA may be attributed to relaxation of interfacial stresses.

Irradiation effects at the Ni-Fe interface

Abstract Layered thin film samples of 100 nm 56 Fe/3 nm 57 Fe/43 nm Ni (coating) or 100 nm 56 Fe/3 nm 57 Fe/63 nm Ni (coating) have been irradiated with 100 keV Ar + or 200 keV Kr 2+ ions, respectively, at doses up to 6 × 10 16 ions/cm 2 . In order to study the effects of irradiation at the Ni/Fe interface, the samples have been analyzed before and after ion bombardment by means of Rutherford backscattering spectrometry, conversion electron Mossbauer spectroscopy and nuclear reaction analysis. For the first time the resonant 58 Ni(p, γ) 59 Cu reaction at E p = 1424 keV has been used to obtain Ni concentration depth profiles at a Ni/Fe interfac Three distinct Fe-Ni phases have been identified by their hyperfine field in the ion beam mixed region after irradiation: a solid solution of Ni in bcc α-Fe, an fcc Fe-Ni alloy (possibly either Ni 3 Fe or Fe 0.64 Ni 0.36 invar alloy), and a nonmagnetic Fe-rich fcc Fe (γ-Fe) phase. The mixing efficiency for fcc Fe-Ni phase formation and for Ni migration into the Fe-rich region as a function of dose has been determined quantitatively indicating that Kr 2+ is more effective than Ar + , as expected and that saturation occurs at higher Ar + doses.

Effective temperature in the impact surface region during 100 keV Xe+ implantation of copper bars

The temperature evolution of a copper bar during 100 keV Xe ions implantation has been experimentally recorded. The thermal behaviour of the implanted bar is quantitatively described by a simple model calculation. It is shown that the experimental results may be reproduced by considering a radiative energy dissipation from hightemperature surface regions intersected by ion impact. The quantities characterizing these “thermal-spike” regions like average temperature and lifetime are consistent with earlier thermodynamical estimations reported in the current literature.