Compositionally graded film

In this section, a film with a linear variation in mismatch strain, from em = 0 at the interface y = 0 to Cm = etop at the free surface y = /if, is considered. In this case, 

Any variation of the elastic properties of the system in the y—direction is neglected in this development. 

The energy of formation of the dislocation, which is independent of the distribution of mismatch, is given by (6.8). On the other hand, the work done by the background mismatch stress field is completely determined by the mismatch strain distribution according to (6.30). With the distribution of mismatch as specified in (6.40), this work is 

As before, the critical thickness her of the film is defined as the smallest value of hf for which a stable equilibrium position rj for the dislocation can be found such that Wd( ) + Ikm(r/) = 0. 

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The combined gradual change in the methane-to-argon ratio and increase in discharge power resulted in the formation of a composition-graded film. During this cycle, the deposition rate of the methane plasma polymer decreased whereas that of copper or silver increased. 

Elecrocopper was plated onto the composition graded film layered by the double-graded process with oxygen and hydrogen treatment. 

Table 21.7 Surface Chemical Analysis of Composition-Graded Film Layered by the Double-Graded Process [eopper eleetrode used] after Extended Time (48 h) Exposure to Atmosphere...

The stability of composition-graded films seems to be good because the adhesion value and chemical analysis data obtained by XPS do not show any significant changes after aging 2 months in a desiccator. 

The shear strength of coatings metallized by employing composition-graded films is dependent on the extent and strength of chemical bonding between the substrate surface and the plasma polymer film. 

The composition-graded film as a preplate for metallization is stable in the environment without moisture. 

In this section, the effect on substrate curvature of the variation of mismatch strain and material properties through the thickness of layered films is analyzed. The derivation of the Stoney formula (2.7) in Section 2.1 refers only to the resultant membrane force in the film any through-the-thickness variation of mismatch strain in the film is considered only peripherally. Film thickness was taken into account explicitly in Section 2.2, but it was assumed there that mismatch strain and elastic properties of the material were uniform throughout the film. However, there are situations of practical significance for which this is not the case. Two of the most common cases are compositionally graded films in which the mismatch strain and the elastic properties vary continuously through the thickness of the film, and multi-layered films for which the mismatch strain and the elastic properties are discontinuous, but piecewise constant, from layer to layer throughout the thickness of the film. In both cases, the mismatch strain and the material properties are assumed to be uniform in the plane of the interface. With reference to the cylindrical r, 6,. z—coordinate system introduced in Section 2.1, the mismatch strain and film properties are now assumed to vary with z for fixed r and 6, but both are invariant with respect to r and 9, for fixed z. 

COMPOSITION-GRADED TRANSITIONAL BUFFERING FILM/ELECTROCOPPER... 

The composition depth profiles obtained from XPS data of the composition-ungraded and graded films in the case of a copper electrode used are given in Figure 21.5. 

Figure 21.8 XPS spectra of the surface of composition graded transitional buffering film layered by double-graded process curve a, surface curve b, 1 min sputter curve c, 5 min sputter curve d, oxidized copper surface.

Figure 21.9 The proposed seetional model of a eomposition-graded transitional buffering film layered by double-graded proeess A, pure methane plasma polymer layer B, composition-graded layer of methane plasma polymer and metal C, sputtered metal layer with earbon contamination.

Composition-graded composite films of plasma polymer and metal can be controlled to give surfaces capable of being electroplated. 

A typical data set from the ball-on-flat tribometer is shown in fig. 13.13. The data show time vs. friction force for a Fantesk starch-oil composite dry-film lubricant comprising soybean oil in purified food-grade starch (PFGS). The data display a number of features typically observed from such measurements. The friction force displays an initial sharp increase to a maximum, which immediately falls to a steady-state value for the remainder of the measurement period. The maximum friction force corresponds to the static friction, i.e., the resistance of the ball to the relative motion from an initial state of rest. The steady-state friction force corresponds to the kinetic friction. The COF for the test was obtained by dividing the average steady-state friction force by the normal load, which is 1500 gf... 

FIGU RE 13.14 Effect of meadowfoam oil concentration in purified food-grade starch (pfgs) on the coefficient of friction of Fantesk starch-oil composite dry-film lubricant. 

Freund, L. B. (1996), Some elementary connections between curvature and mismatch strain in compositionally graded thin films. Journal of the Mechanics and Physics of Solids 44, 723-736. 

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