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The effect of a discrete elastic element on the transverse vibration of a Bernoulli–Euler beam has been well-studied; however, the same cannot be said for a beam with a viscous damper. While the former can be analyzed via separation of variables and the solution of the eigenvalue problem, this article presents a method for computing the resonances of the latter case. The nature of a discrete viscous damper's effect on the fundamental frequency of a beam is revealed as the method is applied to the case of a cantilevered beam. In this process, it is shown that damping has the capacity to increase the fundamental frequency of the beam, and that there exists both a particular location and critical value of damping that maximize this frequency.

Amorphous alloys are a promising alternative to Pd alloy membranes for hydrogen separation because of their lower cost and comparable hydrogen permeability. A series of amorphous alloy membranes consisting of Ni 60 Nb 20 Zr 20 (at%), (Ni 0.6 Nb 0.4 ) 100− x Zr x and (Ni 0.6 Nb 0.3 Ta 0.1 ) 100− x Zr x (where x = 0, 10, 20 or 30) were prepared by melt spinning and then coating the foil surfaces with a thin (500 nm) layer of Pd using physical vapor deposition (PVD). A (Ni 0.6 Nb 0.4 ) 70 Zr 30 membrane exhibited the highest hydrogen permeability (1.4 × 10 −8 mol m −1 s −1 Pa −0.5 ) of any of the materials, measured in pure hydrogen at 450 °C. Membrane permeability increased with Zr content, but membranes higher in Zr were more susceptible to brittle failure and were more thermally unstable. Decreases in hydrogen permeability were almost always observed during long-term permeability tests at 400 and 450 °C. The addition of Ta slightly increased the thermal stability, but moderately lowered the hydrogen permeability. An AES depth profile of the membrane surface showed that metallic interdiffusion had taken place between the Pd coating and the bulk membrane, which probably accounts for the reduction in hydrogen permeability over time at 400–450 °C.

An organometallic chemical vapor deposition (OMCVD) process was developed for the preparation of protective erbium oxide coatings resistant to corrosion by liquid plutonium. The coatings were deposited from the precursor compound Er(tmhd) 3 using a standard hot-wall reactor. The substrates used for process development were 304 stainless-steel flats; coatings were subsequently deposited on the internal surfaces of high-aspect-ratio tubular parts, as well as a variety of curved samples. The coatings have the correct oxygen/erbium ratio, and small concentrations of carbon and hydrogen impurities. The impurities are present in the form of unreacted or partially-reacted precursor molecules, presumably concentrated at the grain boundaries of the material. The films are polycrystalline with a grain size of 40–50 nm, and exhibit excellent adhesion and mechanical toughness. The small grain size and the resultant favorable mechanical properties may be attributable in part to the presence of the organic fragments at the grain boundaries. Coatings deposited on stainless-steel flats are resistant to corrosion by liquid plutonium, although an erbia-thickness threshold is observed. The failure mechanism for samples with thicknesses below the threshold value is most likely related to flaws in the film morphology, for example large pinholes, rather than grain-boundary attack.

The knowledge of tribological properties of silicon is important due to its potential application for micromechanical devices. The present work focuses on the friction and wear studies of single crystal silicon (100) implanted with carbon and nitrogen at 60 keV. These tests were performed using a pin-on-disc (POD) apparatus with a 52100 pin, under contact stress of 225 MPa and at 35% relative humidity. Changes in surface roughness before and after the wear tests were studied using atomic force microscopy (AFM). Transmission electron microscopy (TEM) investigations and ion-channeling measurements revealed amorphous phases for all the implanted species at all doses. Although the surface hardness measurements performed by nano-indentation indicated no improvement in surface hardness for samples implanted with carbon, the tribological studies indicated an improvement in wear and frictional properties. We relate this improved wear behavior to the formation of amorphous SiC.

A hybrid process, aerosol-assisted chemical vapor deposotion (AACVD), is described for reproducible preparation of superconducting thin films of YBa 2 Cu 3 O 7−χ . The process consists of atomizing a toluene solution of the Y, Ba, and Cu tetramethylheptanedionato complexes using an aerosol generator. The aerosol is transported into a CVD reactor where solvent and precursor evaporation and deposition occur at atmospheric pressure on heated substrates. The process provides stable evaporation rates for all three precursors, yielding constant film stoichiometry throughout the deposition period and from film to film. Superconducting films may be deposited in-situ at substrate heater temperatures above 825°C, or may be formed at lower temperatures by deposition followed by post-deposition annealing at higher temperatures. The microstructure and quality of films are highly dependent on the conditions employed in deposition and in the case of films deposited below 825°C, the post-deposition annealing conditions. Superconducting films prepared by the AACVD/post-annealing process have a metallic normal state resistivity signature with a zero resistance temperature typically above 88K, and are highly c -axis oriented. Transport critical current densities measured at 75 K on polycrystalline films prepared by the AACVD process are 220 000 A/cm 2 and 84 000 A/cm 2 at self-field and 0.1 T, respectively.

Bozoian et al. have developed an analytical theory which predicts the incident ion energy at which elastic-scattering cross sections begin to deviate from their Rutherford values as the result of nuclear perturbations. The predictions are in good agreement with experimental data for proton and helium-ion beams, and should be applicable to heavier projectiles. The theory has also been extended to account for isotopic variation of the incident beam. As a further test of the theory, we have performed a series of backscattering measurements using both 6Li and 7Li ion beams. Lithium-ion backscattering is of importance to thin-film analysis because it offers improved depth sensitivity and kinematic mass resolution as compared to helium. Elastic-backscattering cross sections for O, F, Al, and Ti were measured relative to those ofhigh-Z reference elements over an energy range of 2.5–9.25 MeV, and the energies at which they began to deviate from their Rutherford values were determined. The experimental results are compared to predictions from the analytical theory, and from optical-model calculations.

Recent experiments have demonstrated the utility of high-energy backscattering for thin-film analysis, often exploiting elastic-scattering resonances to increase sensitivity to low-Z elements. However, higher-Z elements may also exhibit deviations from Rutherford scattering, and it is desirable to examine the problem theoretically so that such deviations can be predicted and corrected for. We have used the optical-model computer code SCAT86 to calculate the projectile energy Enr at which the scattering cross section begins to deviate from its Rutherford value. The results agree well with data for both alpha particle and proton projectiles, but the interaction potentials are complicated, and the program does not provide an analytical predictive formula. We have therefore developed a simple classical model which treats the interaction as a sum of Coulomb and Yukawa-like potentials. For small deviations from Coulomb scattering, the problem can be solved analytically, providing a simple expression for Enr which agrees well with both experimental data and SCAT86. The classical approach is valid for all but small-angle forward scattering and can easily be extended to heavier projectiles such as Li.

Angular distributions of sputtered atoms have been obtained for 3, 25, and 50 keV Ar+ bombardment of a liquid Ga-In eutectic alloy target. Sputtered material was collected on graphite foils which were subsequently analyzed by Rutherford backscattering spectroscopy, and the resulting distributions were fit by a functional form, N (θ) α. cos^nθ. For each energy, the angular distribution of sputtered In atoms was overcosine, with n_(In) ≈ 1.8 ±0.1. The distributions of the sputtered Ga atoms were sharper, varying from n_(Ga) ≈ 3.2 ± 0.2 at 25 and 50 keV, to n_(Ga) = 4.9 ± 0.3 at 3 keV. A comparison of the sputtered flux composition with the alloy surface composition profile gives F_1, the fraction of sputtered atoms originating from the first atomic layer. The fraction was found to be f_1 = 0.87 ± 0.01 for 25 and 50 keV bombardment, and increased to 0.94 ± 0.01 at 3 keV. The variations of n_(ga), and F_1 with projectile energy may be the result of a decrease in the average recoil-atom energy for the 3 keV bombardment. The large values found for F_1 support a prediction that the sputtered-atom escape depth is determined by the elastic-collision mean free path of recoil atoms.

Angular distributions of Ga and In atoms sputtered from a liquid Ga-In eutectic alloy target have been measured for 3, 25, and 50 keV Ar^+ bombardment. Although the bulk composition of the alloy is 16.5 at.% In, thermodynamic surface segregation results in a surface monolayer of > 94 at.% In. A comparison of the measured sputtered-flux composition with the alloy surface composition profile indicates that the fraction of sputtered atoms originating in the first atomic layer, F_1, is ≈ 0.87 at 25 and 50 keV, and increases to 0.94 at 3 keV. Measurements of the secondary-ion flux for 25–250 keV Ar^+ bombardment indicate that F_1 is independent of projectile energy up to 250 keV, in agreement with the predictions of the collision-cascade model. The increase observed at 3 keV may be the result of a decrease in the average energy of recoil atoms participating in the collision cascades.

Secondary-ion emission has been observed for the liquid phase Ga-In eutectic alloy, and from pure Ga and In targets, under Ne + , Ar + , Kr + , and Xe + bombardment in the energy range of 25–250 keV. The fraction of low-energy sputtered ions originating from beneath the first atomic layer is independent of projectile energy, as expected from the collision-cascade theory of sputtering, but decreases slightly with increasing projectile mass. The relative dimer ion yield from each target is nearly independent of projectile energy and mass. A published statistical recombination theory of neutral dimer formation predicts a proportionality to the sputtering yield, but the discrepancy may be explained if dimers are primarily formed when a single recoil atom causes the correlated ejection of several atoms from a localized region of the surface.