Yosuke Kajihara

Real-Time Visualization of a Shearing Nanometer-Thick Lubricant Film by Two-Stage Imaging Ellipsometric Microscopy

A two-stage imaging ellipsometric microscopy with high lateral resolution and a wide field of view has been developed that will enable real-time visualization of the dynamic behavior of the nanometer-thick lubricant film used in head-disk interfaces incorporating contact or intermittent contact recording technology when it is sheared by the head. The first stage forms an object image at a low magnification ratio, which reduces the angle between the object image and the image sensor. This enables the first object image to be positioned perpendicular to the optical axis of the second stage. The second stage forms a final image on the image sensor at a high magnification ratio. As a result, both submicrometer lateral resolution and a wide field of view (115 μm × 85 μm) were achieved. A lubricant film sheared by an optical fiber probe with a micro ball at its end was visualized, and a bump due to meniscus formation during the intermittent contact was observed. This ellipsometric microscopy can thus visualize nanometer-thick sheared lubricant film in real time, which will be useful in the development of hard disk drives with higher recording density.

Novel Methods for Real-Time Observation of Molecularly Thin Lubricant Films by Ellipsometric Microscopy: Application to Dewetting Observation

Methods based on ellipsometric microscopy were discussed for real-time observation of molecularly thin lubricant on magnetic disks and vertical-objective ellipsometric microscopy was applied to the observation of dewetting of the lubricant. The observation revealed that the dewetting patterns in the early stage are strongly correlated with the signs of disjoining pressure and its derivative with respect to the film thickness. Conversely, our findings suggest that the tendency of the disjoining pressure can be estimated by analyzing the dewetting patterns in the early stage.

Simultaneous Measurement of Film Deformation and Friction Force During Shearing of Molecularly Thin Lubricants

The shearing deformation of the lubricant film was measured by using two-stage imaging ellipsometric microscope (TIEM) combined with an optical-fiber-based friction force measurement method. The TIEM enables high-lateral-resolution and real-time measurements of the thickness distribution of the nanometer-thick lubricant films during shearing. By adding a relay lenses illumination system and a high-power LED light source to the TIEM, a thickness resolution of 0.14 nm was achieved. The results of an experiment using this apparatus demonstrated that the asynchronous component of the probe oscillation, which is induced by friction force between the probe and lubricant or disk and corresponds to acoustic emission avalanches in the head-disk interface of hard disk drives, can occur when the probe is in contact with the lubricant film. The time constant of replenishment of the sheared lubricant film was of the order of hundreds of microseconds, which is much shorter than the timescale of diffusion phenomena.

Theoretical and experimental study on two-stage-imaging microscopy using ellipsometric contrast for real-time visualization of molecularly thin films

A two-stage-imaging ellipsometric-contrast microscope (TIEM) has been developed to measure the distribution of film thickness over a wide area of molecularly thin liquid films with a high lateral resolution, wide field of view, high thickness resolution, and high-speed. Moreover, this ellipsometric microscope enables us to achieve simultaneous measurements with other measurement apparatuses. We present the principle used to parallelize an object image to an imaging sensor and to reduce the incident angle entering the imaging sensor. In addition, we discuss the characteristic shape deformation of the object image due to oblique observation. The performance of the actual setup for TIEM was experimentally studied. A lateral resolution of about 1 μm was obtained by measuring the modulation transfer function of the TIEM. We also found that the shape deformation approximately agreed with that from theory. Furthermore, for molecularly thin films, we confirmed linearity between the film thickness and the light intensity measured with TIEM, which enables us to quantify the thickness of the films. TIEM can open up a new field of real-time imaging of thin films such as visualization of a liquid lubricant film under shear.

Vertical-objective-based ellipsometric microscope for backside illuminated real-time visualization of nm-thick lubricant films

The vertical-objective-based ellipsometric microscope (VEM) is presented which can be used for real-time visualization of nm-thick lubricant films with high lateral resolution. The performance of hard disk drives (HDDs) depends on the dynamics of the nm-thick liquid lubricant films due to decrease of head-disk gap to 2 to 3 nm. The contact or near-contact head disk interface is needed to increase the recording intensity. However, meniscus formation or lubricant pick-up will occur. Therefore, real-time visualization of shearing nm-thick liquid lubricant films plays an important role in the analysis of these phenomena. However, the current VEM can not provide this contact or near-contact situation due to the short working distance (WD) of the high magnification objective lens. In this report, we propose a backside illuminated VEM, whose illumination system and objective lenses are set on the opposite of the sliding probe to solve this problem, and the feasibility of the method is discussed.