Hiroaki Amakawa

Mechanical design and force calibration of dual-axis micromechanical probe for friction force microscopy

A dual-axis micromechanical probe that combines a double cantilever and torsion beams is presented. This probe can reduce the mechanical cross-talk between the lateral and vertical force detections. In addition, dual-axis forces can be detected by measuring the dual-axis displacement of the probe end using the optical lever-based method used in conventional friction force microscopes (FFMs). In this paper, the mechanical design of the probe, the details of the fabrication method, FFM performance, and calibration of the friction force are discussed. The mechanical design and the microfabrication method for probes that can provide a force resolution of the order of 1nN without mechanical cross-talk are presented. Calibration of the lateral force signal is possible by using the relationship between the lateral force and the piezodisplacement at the onset of the probe scanning. The micromechanical probe enables simultaneous and independent detection of atomic and friction forces. This leads to accurate invest...

Spreading properties of monolayer lubricant films: Effect of bonded molecules

Monolayer lubricant films applied to head-disk interface of hard disk drives consist of bonded and mobile molecules. We measured the diffusion coefficient of mobile molecules that spread through the spaces not covered with bonded molecules and revealed its dependence on the coverage fraction. The diffusion coefficient gradually decreased with increasing coverage from 0.2 to 0.8, and its trend was well represented by reptation theory. However, the diffusion coefficient significantly decreased at a coverage higher than 0.8, in contrast to the prediction of reptation theory. The reason for this decrease is thought to be the disappearance of minimum spaces required for mobile molecules to spread through.

Dual-axis micromechanical probe for independent detection of lateral and vertical forces

A dual-axis micromechanical probe that combines a double cantilever and torsion beams is presented. This probe can reduce the mechanical cross-talk between the lateral and vertical forces and detect dual-axis forces by measuring the dual-axis displacement of the probe end using the optical lever-based method used in conventional friction force microscopes. By reducing the cross-talk, this new probe design yields improved frictional force measurements for the identification of materials.

Study of surfactant-added TMAH for applications in DRIE and wet etching-based micromachining

In this paper, etching anisotropy is evaluated for a number of different crystallographic orientations of silicon in a 0.1 vol% Triton-X-100 added 25 wt% tetramethylammonium hydroxide (TMAH) solution using a silicon hemisphere. The research is primarily aimed at developing advanced applications of wet etching in microelectromechanical systems (MEMS). The etching process is carried out at different temperatures in the range of 61?81 ?C. The etching results of silicon hemisphere and different shapes of three-dimensional structures in {1?0?0}- and {1?1?0}-Si surfaces are analyzed. Significantly important anisotropy, different from a traditional etchant (e.g. pure KOH and TMAH), is investigated to extend the applications of the wet etching process in silicon bulk micromachining. The similar etching behavior of exact and vicinal {1?1?0} and {1?1?1} planes in TMAH + Triton is utilized selectively to remove the scalloping from deep reactive-ion etching (DRIE) etched profiles. The direct application of the present research is demonstrated by fabricating a cylindrical lens with highly smooth etched surface finish. The smoothness of a micro-lens at different locations is measured qualitatively by a scanning electron microscope and quantitatively by an atomic force microscope. The present paper provides a simple and effective fabrication method of the silicon micro-lens for optical MEMS applications.

Nonuniform Distribution of Molecularly Thin Lubricant Caused by Inhomogeneous Buried Layers of Discrete Track Media

A method of estimating the thickness distribution on a surface with inhomogeneous buried layers is presented. It revealed that the lubricant distributes nonuniformly on discrete track media (DTM). First, the estimation method was theoretically developed. To balance the disjoining pressures of the lubricants in the track and off-track regions, the lubricant takes different film thicknesses in the two regions because the regions consist of different materials and have different intermolecular interactions. Formulating the balance of the disjoining pressures by using the theory for intermolecular force, we obtained the thicknesses in the two regions. Next, the validity of the theoretical estimation was experimentally verified. When a nonpolar lubricant was applied to a nanometer-thick oxide layer on a silicon surface, which was locally fabricated by probe oxidation, AFM images showed that the lubricant height in the oxide region decreased and the thickness distribution agreed well with that predicted by theory. Using the developed theory, we estimated the lubricant thicknesses on DTM. Even if lubricant is uniformly applied onto the disk, it moves from the off-track to track regions due to the pressure balance. Thus, the theory predicts that the lubricant is thicker in the track regions than the off-track region at equilibrium.

Finite element analysis on crosstalk effect of dual-axis micro-mechanical probe for friction force microscope

A new structure of micro-probe for friction force microscope (FFM) was presented, which has a double cantilever beam for the detection of the friction force and a torsion beam for that of the normal force. It is expected to overcome mechanical crosstalk by friction and normal forces, which causes a significant error in quantification of local friction forces for conventional FFM probes. However, the crosstalk of the dual-axis probe has not been investigated enough. In this study, the mechanical crosstalk of dual-axis and conventional I- and V-type probes, which is relations between displacements and the applied forces, was investigated using finite element method (FEM). This simulation calculated the displacement for the applied force when another force was applied in the perpendicular to the applied one. The mechanical crosstalk of the dual-axis probe was only varied 0.001 %, though that of V- and I-type probes was varied drastically. This means that the mechanical crosstalk of the dual-axis probe is significantly smaller than that of the conventional probes. It is clarified that the dual-axis probe enables us to quantify frictional phenomena accurately.

Quantification of Friction Force for Dual-Axis Probe Friction Force Microscope

Conventional friction force microscopes (FFMs) had the disadvantage of low force sensitivity due to mechanical interference between torsion caused by friction force and deflection by normal force. In order to overcome disadvantage, we developed a dual-axis micro-mechanical probe, which measures the lateral force by the double cantilever and the vertical force by the torsion beam. However, the calibration method of the lateral force has not been established. In this study, we present a new calibration method using a step-structure.Copyright