Key Engineering Materials Vols. 326-328

Abstract: This paper shows a method of designing a nano-positioning planar scanner that can be used in a scanning probe microscope. The planar scanner is composed of flexure guides, piezoelectric actuators and feedback sensors. Furthermore, we used a motion amplifying mechanism in the piezoelectric actuator to achieve a large travel range. We theoretically determined the travel range of the total system and verified the range by using a program based on a finite element analysis. The maximum travel range of the planar scanner was greater than 120 μm. A planar scanner of an atomic force microscope can move samples with a few nm resolutions. To get stable AFM images of small feature samples, a closed loop control could not be used due to large random errors of the sensor. The orthogonality of a new planar scanner having a motion guide is measured and corrected by using a simple electronic circuit in the open loop scanning to reduce the scanner artifact.

Abstract: An atomic force microscope (AFM) with suitable tips has been used for nano fabrication/nanometric machining purposes. In this paper, acoustic emission (AE) was introduced to monitor the nanometric machining of a brittle material (silicon) using AFM. In the experiments, AE responses were sampled, as the tip load was linearly increased (ramped load), to investigate machining characteristics during continuous movement. By analyzing the experimental results, it can be concluded that measured AE energy is sensitive to changes in the mechanism of material removal including the ductile-brittle transition during nanometric machining. The critical depth of cut value for the transition is evaluated and discussed.

Abstract: We studied the surface characterization of milled–silicon nitride nano-powders by XPS and TEM. The change of the chemical state and morphology of the oxide layer on the surface of Si3N4 nano-particles before and after a conventional wet–ball–milling process are investigated by X–ray photoelectron spectroscopy for measuring the chemical state of the oxide layer and transmission electron microscopy for observing surface morphology. The native oxide layers of as-received Si3N4 powders confirmed by HREM observation and their chemical states were different each other. As increasing ball–milling time, the chemical composition and the volume of oxide layer in Si3N4 powders were changed. The chemical state of as–received Si3N4 powder was near to SiO2 phase. After ball–milling process for long time, that of the milled Si3N4 powder shifted to Si2N2O phase. As increasing ball-milling time, the oxide layer of Si3N4 powder was also increased.

Abstract: Many EHL (elastohydrodynamic lubrication) experiments have been performed with the regard to measuring the film thickness variations according to contact conditions, such as contact load, sliding-rolling ratio, contact accelerations for the verification purpose of lubricant characteristics. The measured images of film thickness by the interferometry system are easily converted into film thickness values even both in nanometer scale and resolution with the help of image processing technology. However, only the measurement of the EHL film thickness is not enough to verify the lubricant characteristics under the various contact conditions, because the lubricant is under very high contact pressures above 500MPa, where the lubricant is suddenly solidified and is no longer considered as a fluid itself. In this work, the EHL fluid film pressures are computed from the measured interferometric image of contact film thickness ranging from 10nm to several hundred nano meter, which should be taken with nano-scale resolution. The image processing technique makes it possible to convert the measured film thickness into contact fluid film pressures if the contact geometry and material properties are known. Without the nano-scale resolution for the measured film thickness, the converting computation from the measured film thickness to fluid film pressure is not possible due to the severe noises of interferometric image over the contact area. Measuring technology of the EHL film thickness with nano-scale is also explained with regards to nano scale resolution.

Abstract: It has been reported that the 5182 aluminum sheet shows Lüders band because of dissolved Mg atoms that cause fabrication process problem, especially surface roughness. The examination of serration phenomena has been made after the tensile deformation of the AA/PP/AA sandwich sheets as well as that of the 5182 aluminum. All sandwich sheets and the 5182 aluminum skin showed serration phenomena on their flow curves. However, the magnitude of serration was significantly diminished in the sandwich sheet with high volume fraction of the polypropylene core. According to the results of the analysis of the surface roughness after tensile test, Lüders band depth of the sandwich sheet evidently showed lower than that of the 5182 aluminum skin. The strain rate sensitivity, m-value, of the 5182 aluminum skin was -0.006. By attaching these skins to the polypropylene core, which has relatively large positive value of 0.050, m-value of the sandwich sheets changed to the positive value.

Abstract: A new method to fabricate the fine magnetic abrasives by using mechanical alloying is proposed. The mechanical alloying process is a solid powder process where the powder particles are subjected to high energetic impact by the balls in a vial. As the powder particles in the vial are continuously impacted by the balls, cold welding between particles and fracturing of the particles take place repeatedly during the ball milling process using a planetary mill. After the manufacturing process, fine magnetic abrasives which the guest abrasive particles clung to the base metal matrix without bonding material can be obtained. The shape of the newly fabricated fine magnetic abrasives was investigated using SEM and its polishing performance was verified by experiment. It is very helpful to finishing the micro structures such as injection mold and MEMS applications in final polishing stage. The areal rms surface roughness of the workpiece after several polishing processes has decreased to a few nanometer scales.

Abstract: In this paper, nano manufacturing using the FPN (Fountain Pen Nano-Lithography) with active membrane pumping is investigated. This FPN has integrated pumping chamber, micro channel, and high capacity reservoir for continuous ink feed. The most important aspect in this probe provided the control of fluid injection using active membrane pumping in chamber. The flow rates in channel by capillary force are theoretically analyzed with two different working fluids, DPD (diphenyldichlorosilane) and water, including the cantilever deflection and the control of mass flow rates by the deflection of membrane. The theoretical results are compared with numerical ones that calculated by commercial code, FLUENT.

Abstract: The mechanical alloying processes was employed to fabricate Al-4at.%Zr alloy with nano-sized grains and very fine Al3Zr compounds. The phase transformations and the stability of the phases formed during mechanical alloying and heat treatment processes were investigated. The grain sizes of the alloys immediately after milling and following the subsequent heat treatment at 550°C were 54.2nm and 106.4nm, respectively. Some of Zr atoms were dissolved into the Al matrix and most of them reacted with hydrogen produced by decomposition of PCA(process control agent) to form ZrH2 during mechanical alloying process. These ZrH2 hydrides decomposed gradually after the heat treatment. Stable Al3Zr with a DO23 structure was formed by heat treatment at temperature of more than 4500C. The hardness of the Al-4at.%Zr alloy was more than two times higher than those of other Al-based alloys.

Abstract: Ultrasound was superimposed during electrochemical etching of aluminum and the effect of ultrasonic power on the formation and growth of etch pits were analyzed with the measurement of fast potential transient and morphology study. Ultrasound contributed the increase of etch pit density by prohibiting anodic oxide film formation and induced uniform tunnel length distribution. Current step reduction experiments indicated the enhanced mass transfer both inside tunnel and bulk solution with the increase of ultrasonic power. The capacitance of etched foil was increased by 40% with 600W of 28 KHz ultrasonic power.

Abstract: Thin-film titania templates were fabricated under different processing conditions. The dependencies of pore morphology and pore formation rate on process parameters were evaluated. It was found that under optimized electrolyte condition and anodizing voltage, a self-organized nanostructure consisting of porous TiO2 was obtained. 1 M Na2SO4 solution with the addition of 0.35 wt.% NaF and voltage potential of 30V were used. SEM images of templates showed very thin layer of ~70 nm thickness with worm-like pores. Pore diameter and average pore spacing of center to center on the surface were ~10 nm and 20 nm, respectively. The nanoporous TiO2 thin film will be very useful gas sensing and photocatalytic materials due to their large surface areas and high reactivities.