Papers by Author: Seung Jae Moon

Abstract: Chromium depletion in AISI304 stainless steel can lead to intergranular corrosion due to temperature conditions and degree of deformation, and consequently to materials failure. The aim of this work is to study the effect of sensitization treatment on the corrosion resistance in AISI304 stainless steel after solution heat treatment at 1,000°C. Sensitization treatments were carried out at 670°C for 1 h, 2h, 5h and 10h in the electrical furnace. The intergranular corrosion resistance of the sensitized specimens was evaluated by double loop electrochemical potentiokinetic reactivation test. The microstructure of the specimens before and after the corrosion tests was observed through optical and scanning electron microscope. Solution treatment shows the dual structure, however, aging for 5 hours depicts the ditch structure. The ratio of current density increased as a function of aging time resulted in increase in the degree of sensitization.

Abstract: The thermal conductivity of amorphous silicon (a-Si) thin films is determined by using the non-intrusive, in-situ optical transmission measurement. The thermal conductivity of a-Si is a key parameter in understanding the mechanism of the recrystallization of polysilicon (p-Si) during the laser annealing process to fabricate the thin film transistors with uniform characteristics which are used as switches in the active matrix liquid crystal displays. Since it is well known that the physical properties are dependent on the process parameters of the thin film deposition process, the thermal conductivity should be measured. The temperature dependence of the film complex refractive index is determined by spectroscopic ellipsometry. A nanosecond KrF excimer laser at the wavelength of 248 nm is used to raise the temperature of the thin films without melting of the thin film. In-situ transmission signal is obtained during the heating process. The acquired transmission signal is fitted with predictions obtained by coupling conductive heat transfer with multi-layer thin film optics in the optical transmission measurement.

Abstract: The formation and growth mechanism of polysilicon grains in thin films via laser annealing of amorphous silicon thin films are studied. The complete understanding of the mechanism is crucial to improve the thin film transistors used as switches in the active matrix liquid crystal displays. To understand the recrystallization mechanism, the temperature history and liquidsolid interface motion during the excimer laser annealing of 50-nm thick amorphous and polysilicon films on fused quartz substrates are intensively investigated via in-situ time-resolved thermal emission measurements, optical reflectance and transmittance measurements at near infrared wavelengths. The front transmissivity and reflectivity are measured to obtain the emissivity at the 1.52 μm wavelength of the probe IRHeNe laser to improve the accuracy of the temperature measurement. The melting point of amorphous silicon is higher than that of crystalline silicon of 1685 K by 100-150 K. This is the first direct measurement of the melting temperature of amorphous silicon thin films. It is found that melting of polysilicon occurs close to the melting point of crystalline silicon. Also the optical properties such as reflectance and transmittance are used to determine the melt duration by the detecting the difference of the optical properties of liquid silicon and solid silicon.

Abstract: For the design of a vibrating micro-beam structure, modal and stability analyses of the structure actuated by electrostatic force is performed in the present study. Static deflection of the micro-beam caused by the electrostatic force is first obtained by solving the nonlinear equilibrium equation and the modal and stability characteristics are calculated at the static equilibrium position. It is found that the amplitude and the frequency of the applied electrostatic voltage influence the stability of the structure significantly. A design specification of a vibrating micro-beam structure can be effectively determined from the modal and the stability analysis results.