Doo-Man Chun

Precise measurement of the transverse piezoelectric coefficient for thin films on anisotropic substrate

In this study, we propose a reliable measurement method for the effective transverse piezoelectric coefficient for thin films especially on anisotropic substrate. This coefficient for piezoelectric Pb(Zr, Ti)O3 (PZT) thin films was calculated by measuring the electric field-induced tip displacement of unimorph cantilevers composed of PZT thin films and Si substrates. We evaluated the reliability of the proposed measurement method by comparing it with numerical analysis and confirmed that the relative error of the piezoelectric coefficient (e31, f) was less than 1%. We prepared 16 different unimorph cantilevers composed of identical PZT films on different Si beam geometries that had various substrate thicknesses and cantilever widths. Although the effective transverse piezoelectric coefficient e31, f of PZT thin films ranged from −6.5 to −14 C/m2 as a function of the applied voltage, the difference among the 16 samples with an applied voltage of 25 V was within 10%. These results demonstrate that the propo...

Nickel Line Patterning Using Silicon Supersonic Micronozzle Integrated with a Nanoparticle Deposition System

In this study, 3-µm- and 20-nm nickel powders were deposited on Si substrates to pattern a metal line using a nanoparticle deposition system (NPDS) at room temperature. The stand-off distance (SoD), the distance between the substrate and the end of nozzle, was varied from 300 to 1000 µm to determine its effect on deposition properties. A Ni line was successfully formed on the Si substrate. When 3-µm Ni powders were used, the thickness of the deposited layer on the Si substrate was measured to be 5.4 µm, and its width was 176.4 µm at a SoD of 300 µm. In contrast, the deposited average thickness at a SoD of 500 µm was 1.1 µm, with a width of 190.6 µm. Moreover, the deposited thickness was measured to be 6.4 µm using 20-nm Ni powders at a SoD of 300 µm. Thus, it was found that the deposited thickness decreased as SoD increased, indicating an inversely proportional relationship. For deposition behavior, depending on the size of powders, it was found that 20-nm Ni powders resulted in a thicker deposition than did 3-µm Ni powders, as momentum transfer between carrier gas and powders is inversely proportional to the powder size. Thus, as the powder size decreased, its spray velocity increased; hence, it is more effective to use nano powders for Ni line patterning. Surface resistivity of the deposited Ni line was 1.83 ×10-7 Ωm using 20-nm powders and 1.61 ×10-7 Ωm using 3-µm powders. These values are close to the standard resistivity value for bulk Ni, which is 6.9 ×10-8 Ωm, making NPDS a promising technique for metal line-fabrication equipment.

DEPOSITION OF Al2O3 POWDERS USING NANO-PARTICLE DEPOSITION SYSTEM

In this paper, alumina film was deposited using supersonic micronozzle in nano-particle deposition System (NPDS). Powder deposition at room temperature is important in the field of film deposition since high processing temperature can be a serious limitation for the deposition on flexible substrate. Previously, many studies have been reported on particle deposition, such as aerosol deposition method (ADM) or cold spray method. However, these deposition methods cannot be applied to various types of powders. Recently, NPDS using aluminum nozzle was designed to resolve these problems but it cannot deposit precise patterns less than 1 mm. In this study, alumina particles were deposited using Silicon-based micronozzle in NPDS. Three-dimensional silicon micronozzle was fabricated using semiconductor processing method, specifically deep reactive ion etching (DRIE) method. The silicon micronozzle fabricated by Bosch process is advantageous over the conventionally used nozzle, since the hardness of silicon is higher than that of aluminum and the lifetime can be increased. In this study, alumina nano-particles were accelerated to supersonic level at the neck of micronozzle and deposited on the substrate in a low vacuum condition. The film characteristics were evaluated using field-emission scanning electronic microscope (FE-SEM) and alpha step to measure its thickness of the deposited layer. The deposition result showed that alumina powders were successfully deposited using the fabricated micronozzle by means of NPDS.

Laser Printing of Superhydrophobic Patterns from Mixtures of Hydrophobic Silica Nanoparticles and Toner Powder

In this work, a new and facile dry printing method was developed for the direct fabrication of superhydrophobic patterns based on silica nanoparticles. Mixtures of hydrophobic fumed silica nanoparticles and toner powder were printed on paper and polymer sheets using a commercial laser printer to produce the superhydrophobic patterns. The mixing ratio of the toner powder (for the laser printer) to hydrophobic silica was also investigated to optimize both the printing quality and the superhydrophobicity of the printed areas. The proper mixing ratio was then used to print various superhydrophobic patterns, including triangular, square, circular, and complex arrangements, to demonstrate that superhydrophobic surfaces with different patterns can be fabricated in a few seconds without any post-processing. The superhydrophobicity of each sample was evaluated by contact angle measurements, and all printed areas showed contact angles greater than 150°. The research described here opens the possibility of rapid production of superhydrophobic surfaces with various patterns. Ultimately, the obtained findings may have a significant impact on applications related to self-cleaning, control of water geometry and position, fluid mixing and fluid transport.

SURFACE MODIFICATION OF POLYETHYLENE (PE) BY THE DEPOSITION OF TITANIUM DIOXIDE (TiO2) NANOPARTICLES TO ENHANCE THE PHOTOCATALYTIC ACTIVITIES

In recent years, there has been growing interest in the preparation of TiO2-deposited materials for the application in different fields of photocatalytic activities, such as photocatalysis, dye-sensitized solar cells, antireflective coatings, and electro-chromic devices. TiO2 particles were deposited on the PE surface by spraying method at room temperature. The deposition analysis was conducted by atomic force microscopy (AFM), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM) for monitoring the variation in morphology and different properties. It was found that the surface was deposited uniformly with higher concentration of particles and did not affect the inherent properties of polymers. The deposited TiO2 particles favor the photodegradation of synthetic nonbiodegradable polymeric materials, which will ultimately decompose in the environment.

Nano/micro particle beam for ceramic deposition and mechanical etching

Nano/micro particle beam (NPB) is a newly developed ceramic deposition and mechanical etching process. Additive (deposition) and subtractive (mechanical etching) processes can be realized in one manufacturing process using ceramic nano/micro particles. Nano- or micro-sized powders are sprayed through the supersonic nozzle at room temperature and low vacuum conditions. According to the process conditions, the ceramic powder can be deposited on metal substrates without thermal damage, and mechanical etching can be conducted in the same process with a simple change of process conditions and powders. In the present work, ceramic aluminum oxide (Al2O3) thin films were deposited on metal substrates. In addition, the glass substrate was etched using a mask to make small channels. Deposited and mechanically etched surface morphology, coating thickness and channel depth were investigated. The test results showed that the NPB provides a feasible additive and subtractive process using ceramic powders.

Nano particle deposition system (NPDS) for ceramic and metal coating at room temperature and low vacuum condition

Nano particle deposition system (NPDS) is the newly developed ceramic and metal coating process. Nano and micro sized powders are sprayed through the supersonic nozzle at room temperature and low vacuum condition and deposited on various substrates. In this research, ceramic titanium dioxide (TiO2) coatings were deposited on metal substrates (SUS, Cu, Al) and polymer substrates (PET, PMMA), and metal tin (Sn) coating was deposited on SUS substrate. Coatings were fabricated with rectangular and line shapes at high deposition rate and without causing thermal damage on the substrates. Deposition images and material properties such as chemical composition and morphology were measured. The test results showed that the NPDS provides a new coating method of ceramic and metal materials with large surface area.

Effect of Multiwalled Carbon Nanotubes on the Mechanical Properties of Carbon Fiber-Reinforced Polyamide-6/Polypropylene Composites for Lightweight Automotive Parts

The development of lightweight automotive parts is an important issue for improving the efficiency of vehicles. Polymer composites have been widely applied to reduce weight and improve mechanical properties by mixing polymers with carbon fibers, glass fibers, and carbon nanotubes. Polypropylene (PP) has been added to carbon fiber-reinforced nylon-6 (CF/PA6) composite to achieve further weight reduction and water resistance. However, the mechanical properties were reduced by the addition of PP. In this research, multiwalled carbon nanotubes (CNTs) were added to compensate for the reduced mechanical properties experienced when adding PP. Tensile testing and bending tests were carried out to evaluate the mechanical properties. A small amount of CNTs improved the mechanical properties of carbon fiber-reinforced PA6/PP composites. For example, the density of CF/PA6 was reduced from 1.214 to 1.131 g/cm3 (6.8%) by adding 30 wt % PP, and the tensile strength of 30 wt % PP composite was improved from 168 to 173 MPa (3.0%) by adding 0.5 wt % CNTs with small increase of density (1.135 g/cm3). The developed composite will be widely used for lightweight automotive parts with improved mechanical properties.

Design of Repeat-Antenna Package for Mobile Communication Made of Ferrite-Loaded Glass-Fabric/Epoxy Composites

This paper presents the material design and structural analysis of the repeat antenna used in mobile communication and shows the possibility of replacing the aluminum package of the repeat-antenna system by ferrite-loaded glass-fabric/epoxy composites. The three-phase composite material provided high strength and electromagnetic shielding at 1.8–2.0 GHz, one of frequency ranges used for mobile communication. The Ni–Zn ferrite as an absorbing material was fabricated, and Ni–Zn ferrite/epoxy composite was measured with a network analyzer to obtain complex permittivity and permeability. The characteristics of Ni–Zn ferrite specimens with conductive carbon black were studied, and the matching frequency was adjusted to 2 GHz frequency by controlling the amount of conductive carbon black. The ferrite-loaded glass-fabric/epoxy composite specimens were fabricated, and tensile and bending tests were carried out to evaluate mechanical properties. The structural analysis of antenna package of ferrite-loaded glass-fabric/epoxy composite was conducted for under wind pressure and compared with that of aluminum antenna package.

SmartPulley: Web-based Design Support System for Automotive Steel Pulley

In this research, a web-based design support system is constructed for the design process of automotive steel pulley to gather engineering knowledge from pulley design data. In the design search module, a clustering tool for design data is proposed using K-means clustering algorithm. To obtain correlational patterns between design and FEA (Finite Element Analysis) data, a Multi-layer Back Propagation Network (MBPN) is applied. With the analyzed patterns from a number of simulation data, an estimation of minimum von mises can be provided for given design parameters of pulleys. The case study revealed fast estimation of minimum stress in the pulley within 12% error.