C. L. Bauer

Spreading of perfluoropolyalkylether films on amorphous carbon surfaces

Spreading of perfluoropolyalkylether thin films on amorphous carbon surfaces has been studied by scanning microellipsometry. Two types of perfluoropolyalkylethers with the same main-chain structure and various molecular weights (between 1000 and 6000 g/mol) were used: Zdol, with OH functional end groups, and Z, with nonfunctional CF3 groups. For Zdol, the thickness of the molecular layers in the spreading profile increase as Mn0.6, where Mn is the mean molecular weight, with the second layer being nearly twice as thick as the first layer. This layered structure was not observed for Z in the molecular weight range under study. As expected, the thickness-dependent diffusion coefficient D(h) was found to decrease with increased molecular weight. Possible molecular conformations near the solid surface are discussed. The spreading of binary blends of Zdol–Zdol, Z–Z, and Zdol–Z were also studied. The results show that the spreading of the binary blend of the same kind of polymer with different molecular weight behaved like that of a lubricant with an intermediate molecular weight. The diffusion coefficient of a blend was found to obey the additivity of viscosity. For Zdol–Z blends, however, the faster moving Z molecules migrate through the network of the slower moving Zdol molecules, and form a monolayer ahead of Zdol.Spreading of perfluoropolyalkylether thin films on amorphous carbon surfaces has been studied by scanning microellipsometry. Two types of perfluoropolyalkylethers with the same main-chain structure and various molecular weights (between 1000 and 6000 g/mol) were used: Zdol, with OH functional end groups, and Z, with nonfunctional CF3 groups. For Zdol, the thickness of the molecular layers in the spreading profile increase as Mn0.6, where Mn is the mean molecular weight, with the second layer being nearly twice as thick as the first layer. This layered structure was not observed for Z in the molecular weight range under study. As expected, the thickness-dependent diffusion coefficient D(h) was found to decrease with increased molecular weight. Possible molecular conformations near the solid surface are discussed. The spreading of binary blends of Zdol–Zdol, Z–Z, and Zdol–Z were also studied. The results show that the spreading of the binary blend of the same kind of polymer with different molecular weight ...

Spreading of PFPE lubricants on carbon surfaces: effect of hydrogen and nitrogen content

The spreading of OH-terminated perfluoropolyalkylether (PFPE), Zdol, on amorphous carbon surfaces was studied as a function of hydrogen or nitrogen content in the carbon film, using scanning micro-ellipsometry. A layered structure of the thickness profiles was observed, which remained qualitatively the same for all carbon types. The sharpness of the second layer was gradually eroded as either hydrogen or nitrogen content in the films was increased. The thickness-dependent diffusion coefficient was calculated using the Matano interface method. It was observed that the surface mobility of Zdol increased as hydrogen content increased, but decreased as nitrogen content increased. Implications of these results on the boundary lubrication properties of Zdol on carbon films are discussed.

Surface diffusion and flow activation energies of perfluoropolyalkylether

Surface diffusion of perfluoropolyalkylether (PFPE) Fomblin Z15 and Fomblin Zdol (hydroxyl terminated PFPE) on silicon wafers was investigated over the temperature range of 25 to 50°C using scanning microellipsometry. Zdol exhibits a much lower mobility and a distinctly different thickness profile as compared to Z15. The activation energy for surface diffusion of Zdol is higher than that of Z15, reflecting the stronger affinity of its hydroxyl end groups for the substrate. The viscosity flow activation energy Eη*is compared with that of surface diffusion Ed*yielding Ed*≈ Eη*for Z15, and Ed*≈ 1.5Eη*for Z

Mechanisms of interdiffusion in copper/nickel thin‐film couples

Mechanisms of interdiffusion in copper/nickel thin‐film couples have been investigated in the temperature interval 573–777 K by in situ measurement of contact resistance, Auger depth profiling (ADP), and transmission electron microscopy. Correlation between evolution of contact resistance and measured Auger concentration profiles has been established and mechanisms incorporating rapid grain boundary diffusion, followed by defect‐assisted diffusion into grain interiors (Type B kinetics), are proposed to explain the accelerated reactions observed. A modified Whipple model and two independent methods, based on ADP and contact resistance measurements, are used to calculate grain boundary and intragranular diffusion coefficients, respectively. The calculated grain boundary diffusion coefficient is (0.82 cm2/s) exp(−1.48eV/kT) for nickel in copper, and approximately 4×10−13 cm2/s for copper in nickel at 673 K. An average intragranular diffusion coefficient for nickel in copper is determined to be (2.6×10−6 cm2/...

Degradation and subsequent healing by electromigration in Al‐1 wt % Si thin films

Electrical resistance of Al‐1 wt % Si thin‐film conductors has been measured as a function of time t, temperature, and current polarity in order to investigate both generation and recovery of (microstructural) damage caused by electromigration. The fractional change of electrical resistance ΔR/R is characterized by three distinct stages: (i) undetectable ΔR/R during an incubation period τ; (ii) linear increase of ΔR/R with t−τ; and (iii) abrupt decrease of ΔR/R when polarity is reversed, followed by gradual resumption of the previous linear increase. Examination of the conductor surface during these three stages by scanning electron microscopy reveals: (i) undetectable microstructural damage; (ii) generation of (first) holes and (then) hillocks; and (iii) recovery followed by further generation of microstructural damage. Results are interpreted by (i) generation of stress σ in grain boundaries; (ii) formation of holes when σ exceeds a critical tensile stress σ+c and hillocks when σ exceeds a critical comp...

Lubricant replenishment on carbon coated discs

The replenishment of a lubricant on a carbon coated disc was characterized through theoretical modeling employing experimentally acquired diffusion coefficient data. To quantify the reflow behaviour of a lubricant film, a parameter, the critical reflow time, was defined as the time to replenish a depleted hole of 1 /spl mu/m diameter in a 2 nm thick lubricant film. The results based on solving 2D diffusion equations showed that the critical reflow time is a strong function of the endgroup polarity and molecular weight of a lubricant, as well as the H and N content in the carbon film. Based on these results, design criteria have been provided for enhanced wear durability of magnetic media.

Extensions of thermal grooving for arbitrary grain‐boundary flux

Groove profiles are computed under isotropic conditions for the intersection of a periodic array of grain boundaries with an external surface, assuming that grain boundary flux I is directed to (I≳0) or away from (I<0) the surface. When I=0, the surface assumes an equilibrium (time‐independent) profile. For I≠0, in a range bounded by upper and lower limits that depend on geometry and material parameters, a global steady‐state develops in which the entire surface advances (I≳0) or recedes (I<0) from its original position at constant velocity. Beyond these limits, the surface near the groove roots becomes diffusively detached from the remaining surface. A rapidly growing ridge (I≳0) or slit (I<0) then develops along each grain boundary, whose tip ultimately translates at constant velocity in a local steady state, leaving the remaining surface behind. These velocity regimes govern the ultimate stability of polycrystalline materials subjected to large electric (electromigration) or stress (creep) fields, espe...

Characterization of the early stages of electromigration at grain boundary triple junctions

The formation and growth of holes and hillocks at grain boundary triple junctions in thin‐film conductors of gold on gallium arsenide and thin‐film conductors of aluminum‐1 wt. % silicon on (oxidized) silicon during the early stages of electromigration have been investigated through measurement of fractional change of electrical resistance ΔR/R and microstructural characterization by scanning and transmission electron microscopy. Each grain boundary triple junction is characterized by a unique structure factor ΔY, which defines the degree of cumulative flux divergence and, consequently, the degree of susceptibility to formation and growth of holes or hillocks. Resultant holes are characterized by a shape factor  f, which defines the degree of noncircularity and, consequently, relates fractional change of hole area to ΔR/R. Estimates of the upper limit for ΔY and the average value of  f  are in good agreement with measured values of ΔR/R and consistent with observed microstructure.

Faceting of migrating 〈110〉 coincidence boundaries in aluminium bicrystals

Abstract Faceting of 40·0° (∊ = 9), 109·5° (∊ = 3), and 129·5° (∊ = 1) 〈110〉 coincidence boundaries, where ∊ denotes reciprocal volumetric density of coincidence sites, has been observed during grain boundary migration in 99·998 a/o aluminium bicrystals. Facet inclinations generally correspond to low-to-moderate density coincidence planes, implying that structure of the migrating boundaries can be described in terms of an ensemble of non-coherent twin interfaces, many of which have not heretofore been observed. Possible causes of faceting and its effect on grain boundary migration are suggested.

Thermally Activated Dislocation Depinning in Dilute Copper Alloys

Internal friction and Youngs modulus measurements have been performed on a series of dilute copper—silicon, copper—germanium, and copper—tin alloys at temperatures ranging from 4° to 300°K in order to determine the extent of thermally activated dislocation depinning from solute atoms. Specimens are in the form of singel‐crystal bars, and are excited piezoelectrically in their fundamental longitudinal mode of vibration at 80 kHz.For temperatures in excess of 180°K, the amplitude‐dependent internal friction is characterized by an Arrhenius temperature dependence with an activation energy that varies linearly with the stress amplitude. A low‐temperature modification of the Granato—Lucke theory accounts for the temperature dependence of the internal friction below about 120°K; however, the stress dependence is contradictory to that predicted theoretically. In general, thermal depinning is enhanced at high temperatures and stress levels, and in crystals containing long dislocation segment lengths and solute a...