R. A. Erck

Solid Lubrication of Ceramic Surfaces by IAD-Silver Coatings for Heat Engine Applications

In this study, we investigated the tribological characteristics of alumina ceramics that were coated with silver by means of ion-assisted deposition (IAD). Tests were performed at temperatures up to 400°C on an oscillating-slider wear test machine as a partial simulation of a ring/cylinder system. The results showed that higher test temperatures caused greater wear damage and increased friction of uncoated alumina. At 400°C, the wear rates of the alumina-alumina test pairs were eight to ten times higher than those of specimens tested at room temperature. The steady-state friction coefficients of the uncoated alumina were also rather high, typically ranging from 0.8 to 1.1. In contrast, the wear rate of I AD-silver -coated flats was negligible and the wear rate of counterface pins sliding against these coated flats was reduced by factors ranging from 4 to 73 depending on test temperature. Friction was also reduced to about one-half to one-third that of uncoated pairs. Surface and structure analytical inves...

Effect of film adhesion on tribological properties of silver-coated alumina

Abstract Soft metal films are seen as possible solid lubricants for sliding ceramics in high temperature environments. Ion bombardment of substrate and film can improve film adhesion and tribological properties of metal films deposited on ceramics. To provide a more detailed understanding of the relationship between measured adhesion strength, surface roughness, and wear performance of coatings, thin silver films were vapor deposited on smooth and roughened alumina substrates using 1 keV ion bombardment before and during deposition. A pull-type tester was used to measure the adhesion of films to the substrate. A ball-on-flat test machine was used to evaluate the wear of an uncoated alumina ball sliding on silver-coated substrates. Measurements of film adhesion and sliding wear, and a scanning electron microscopy examination of wear tracks, are reported. Ball wear on roughened surfaces was reduced by a factor of about 3 for poorly adhering coatings, but by a factor of about 130 for well-adhering coatings deposited after argon-oxygen sputter cleaning, compared with bare Al2O3. For films with the lowest wear, the silver coating wore off the tips of the asperities,but the film remained almost completely intact. For smooth flats, wear reductions by a factor of about 3 were obtained for well-adherent coatings.

MOCVD (BaxSr1−x)Ti1+yO3+z (BST) thin films for high frequency tunable devices

Abstract We have investigated the structural and electrical characteristics of (BaxSr1−x)Ti1+yO3+z (BST) thin films synthesized at 650°C on Pt/SiO2/Si substrates using a large area, vertical metalorganic chemical vapor deposition (MOCVD) reactor equipped with a liquid delivery system. Films with a Ba/Sr ratio of 70/30 were studied, as determined using X-ray fluorescence spectroscopy (XRF) and Rutherford backscattering spectrometry (RBS). A substantial reduction of the dielectric loss was achieved when annealing the entire capacitor structure in air at 700°C. Dielectric tunability as high as 2.3:1 was measured for BST capacitors with the currently optimized processing conditions.

Adhesion of Silver Films to Ion-Bombarded Alumina **

Silver films were deposited on alumina substrates using ion bombardment. Adhesion strength was measured as a function of deposition conditions, sputter-cleaning time, and bombarding ion species, using a pull-type adhesion tester. Argon- and argon/oxygen-ion sputtering produced large increases in adhesion strength, with the greatest increases occurring for oxygen-ion bombardment. Adhesion strength increased monotonically as a function of ion sputtering time. At a given deposition rate, further enhancement of adhesion is seen with concurrent ion bombardment. 16 refs., 3 figs., 1 tab.

Chemical solution deposition of PLZT films on base metal foils.

In an effort to develop cost effective, volumetrically efficient, high charge density and high energy density capacitors, Pb(Zr,Ti)O 3 and La-doped Pb(Zr,Ti)O 3 films were deposited by chemical solution deposition on nickel and alloy foils. PZT films deposited on bare foils exhibited lower permittivity and more electric field hysteresis compared to films deposited on platinized silicon substrates, due to the formation of low capacitance interfacial layers and/or diffusion of foil elements into the PZT. However, an ultimate dielectric breakdown strength of approximately 1.35 MV/cm was obtained for a film thickness of 1.8 μm, corresponding to a withstand voltage of 245 V. A reduced temperature dependence of capacitance was observed with decreasing film thickness. In order to improve the dielectric response, barrier layers of LaNiO 3 , Ru, or Ir were deposited on top of the metal foils used as substrates. The barrier improved relative permittivity and reduced hysteresis in relative permittivity as a function of dc bias.

Positive Temperature Coefficient of Resistance in MOCVD (Ba 0.75 Sr 0.25 )Ti 1+y O 3+z Films

The leakage and dielectric properties of a thickness series (90–480 nm) of {100} fiber-textured MOCVD (Ba 0.75 Sr 0.25 )Ti 1+y O 3+z (BST) thin films on Pt/SiO 2 /Si were investigated. The temperature and voltage dependence of the permittivity were consistent with previous observations, where thinner films demonstrated a suppressed temperature and electric field response that transitioned to a more bulk-like response with increasing film thickness. The current-voltage characteristics showed two distinct regimes. At low fields the current displayed weak field dependence and a monotonic increase with increasing temperature. In contrast, positive temperature coefficient of resistance (PTCR) was observed in the high-field leakage current behavior. The PTCR behavior was more pronounced for thicker BST films. Factors contributing to the observed PTCR effect are outlined and contrasted with the description for bulk BaTiO 3 ceramics.

Investigation of titanium nitride films prepared by ion-beam-assisted deposition at high Ar + /Ti ratio

Titanium nitride films were prepared by reactive ion beam assisted deposition (RIBAD) with Ar + /Ti ratios ranging from 1.0 to 2.3. The compositions, phases and textures of these films were studied by AES and XRD as a function of Ar + /Ti ratio and nitrogen partial pressure. The results indicate that the IBAD titanium nitride films deposited at high Ar + /Ti ratio and low nitrogen partial pressure may have reduced nitrogen concentration, (200) preferred orientation, and possibly contain the Ti 2 N phase.