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Spin-off experiments were conducted at different temperatures for a nonfunctional PFPE Z25 film with an initial thickness of 2.4 nm, and comparison with the diffusion experiments was carried out. It is found that PFPE Z25 shows completely different rheological behaviors in spin-off and diffusion. Theoretical model based on the Fick law of diffusion was proposed, which is called the Layer Molecular Dynamic Diffusion (LMDD) model. The proposed model results in a much better agreement with the spin-off experimental results than the continuum theory being used at present. Contrary to the results in the diffusion experiment, the nanometer film of nonfunctional PFPE Z25 also shows a layered structure in the spin-off.

The accumulation of contaminants on the slider surface is of paramount importance in hard disk drives because only an ultra small amount of contaminants on the slider surface will cause catastrophic failures for hard disk drives with a spacing between the slider and the hard disk as small as 10 nm, which will be reduced further in the near future to about 5-6 nm in order to attain a recording density of 100 Gbit/in 2 . In this paper the pumping effect of the slider is proposed as one mechanism of the contaminant accumulation on the slider. Analysis of the pumping effect is conducted by considering the adsorption process and the shear flow process on the slider surface in terms of the continuum. It is found that the pumping effect can be divided into two different classifications depending on the value of the parameter k which is the ratio of the maximum shear flow of the adsorbed film to the maximum adsorption amount: the shear flow rate-controlling pumping effect for k < 0.1 and the adsorption rate-controlling pumping effect for k > 0.4. For the shear flow rate-controlling effect, the accumulation rate of the contaminant is directly proportional to the disk surface velocity, while inversely proportional to the flying height of the slider.

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