The static and dynamic properties of nanostructured thin oligomeric films.

摘要

Hard disk drives (HDDs) are experiencing a tremendous increase in the areal recording density. In the time frame of 2007-2008, the areal density of over 200 Gbits/in2 is expected to materialize. Although much of this growth has been fueled by the development of new read/write heads, some of this gain is achieved by reducing the flying height, which is defined as the spacing between the head and the disk surfaces. For instance, to increase the areal density of HDD to 1 Tbits/in2, the flying height has to be reduced to less than 3.5 nm, which in turn bring many issues into the head-disk interface (HDI).; The HDI in the HDD system consists of a read/write head flying over the disk surface on an air bearing, a molecularly-thin lubricant nanofilm ( i.e., perfluoropolyether, so-called PFPE), and a sputtered carbon overcoat to protect the slider and magnetic layer from mechanical and thermal damages. With the reduced flying height, the intermittent contact between the head and lubricant at the HDI becomes more frequent, where PFPE is considered sacrificial and is often depleted in the contact area. Therefore, the replenishment capability becomes important for the self-healing of PFPE films. Meanwhile, the lubricant must not spin-off from the disk surface due to the high disk rotation speed. To meet both requirements, PFPE molecule is end-functionalized, which ensures the presence of both bonded and mobile PFPEs. As a result, the PFPE film can exhibit a certain capability of replenishment while preventing itself from spinning-off the disk.; The work presented in this dissertation focuses on the static and dynamic properties of PFPE nanofilms via both experimental and theoretical means. The spontaneous spreading of PFPE nanofilms in one dimension was first measured via the optical surface analyzer. Using the "L-t" plot, the diffusion coefficient of PFPE films was first calculated to illustrate their dependences on the PFPE molecular architecture (i.e., molecular weight and endgroup functionality) as well as the film thickness. The contact angle measurements were further conducted to examine the surface free energy of functional PFPE films. Via the thermodynamic arguments, the film stability diagram was constructed as a function of molecular weight and film thickness, which can be further utilized to predict the uniformity of PFPE nanofilm surfaces. (Abstract shortened by UMI.)