The performance of hard disk drives is enhanced considerably by the addition of small amounts of a additives to lubricants. An example of such an additive is a cyclic phosphazine (X-1p) lubricant (The Dow Chemical Co., Midland, MI.) It is widely used by many disk drive manufacturers as an additive to the traditional perfluoropolyalkyl ether (PFPE) lubricants such as Fomblin Z-DOL (Ausimount USA, Thorofare, NJ). It has been shown to improve significantly the performance of hard disk drives under adverse conditions, particularly hot and humid environments. The amount of the X-1p additive used is low and typically covers <10% of hard disk surface as a molecular monolayer. The surface coverage of the X-1p has to be controlled precisely in order to achieve the optimal performance.
Traditionally, the amount (or thickness) of the X-1P is measured by X-ray photoelectron spectroscopy (XPS) or wet chemical extraction followed by GC/MS analysis. The sensitivity of X-1P used in manufacturing. The time consuming GC/MS approach only measures the total amount of X-1P on the entire surface of a hard disk, thus the calculation of its average distribution lacks spatial information. In addition, both XPS and GC/MS are destructive techniques. These limitations prevent them from potential on-line or at-line monitoring of the hard disk manufacturing.
PM-IRRAS is ideally suited for analyzing the lubricant and its additives on such hard disks. It has been used successfully for both qualitative and quantitative analysis of thin films on hard disks by a number of disk and lubricant manufactures in their analytical laboratories. Shown in Figure 6.12 are unnormalized PM-IRRAS spectra of a lubed disk and bare disk substrate. The PEM modulation efficiency was tuned to maximize spectral intensity around 1300cm-1. The absorption peaks for the lubricant (Z-DOL) and the additive (X-1P) are very small and they occur above the J2(ψ0) curve in the region where strong water vapor absorption occurs but this was removed nearly completely by the dual-channel data collect.
The normalized PM-IRRAS spectra for a set of hard disks that have different amounts (or thickness) of Z-DOL are shown in Figure 6.13, where a clear correlation between the intensity of the Z-DOL band at 1281cm-1 and the amount of the Z-DOL lubricant is observed. The plot in Figure 6.14 shows a linear relationship between the baseline-corrected PM-IRRAS peak height of the Z-DOL band at 1281cm-1 and the thickness of the lubricant determined by GC/MS method. A similar relationship can be also found for the amount of X-1P additive added in the lubricant.
It can be seen from this application that PM-IRRAS is a superior technique for qualitative identification and thickness determination of the hard disk lubricants and additives. All measurements were made without any sample preparation or alternation. The high sensitivity of PM-IRRAS allows the measurement to be made in a few minutes compared to the time consuming chemical extraction process in the GC/MS approach.
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