Papers by Author: J.Y. Kim

Abstract: Generally, structures used in outer space are subjected to severe situations, including sublimation, a strong evaporation of lubricants, thermal stresses, high temperature gradients, irradiation, impact from microscopic meteorites, and other factors. Recently, various kinds of coatings have been applied to structural parts under heavy contact stresses to ensure a longer wear-free life and/or reduce the friction coefficients. Accordingly, the current study applied FEM to analyze space parts with a coating layer thermo-mechanically subjected to a contact load. First, a steady state temperature distribution of the space part was obtained, then a quasi-static external load was applied. Thereafter, the total solution was computed and the thermal strain subtracted to obtain the mechanical strains for determining the stresses of the individual part. When using FEM, the model needs to discretize into many sub-domain finite elements. Since the difference, however, in the dimension between the coating layer and the substrate is so large, the analysis needs to be considered carefully. Consequently, the problem was analyzed in two steps. First, the whole model was analyzed using rather coarse meshes, then a small region was cut near the loading point and analyzed using very fine meshes. This method is based on Saint-Venant's principle. Finally, the effect of a thermal load on the stress of a space part with a coating layer was checked with and without cracks in the substrate. Accordingly, the results demonstrate the stresses on a space part under a thermo-mechanical load, along with the effects of various coating materials and a crack in the substrate on the stress distribution.

Abstract: Novel fabrication routes of oxide/semiconducting hybrid nanotubes or coaxial nanocables with 30~200 nanometers of radius and ~10 micrometers of length using atomic layer deposition (ALD) and soluble nano-templates was reported. In order to fabricate the hybrid nanotubes using nanotemplates, which were treated with surface modification using SAMs in order to achieve selective deposition only onto inner wall of the template. Deposition of metal oxide layers (TiO2, ZrO2) conformally and uniformly onto the wall of templates using ALD. To fabricate metal oxide/CdS nanocables or coaxial nanotubes, CdS was deposited onto metal oxide nanotubes by chemical bath deposition. Coaxial nanocables was also 30-200 nm in diameter and 1-10
in lengths.

Abstract: Microcontact printing of hydrophobic OTS (Octadecyl-Trichloro-Silane) material was made on various substrates, and finely patterned CdS thin film has been fabricated by CBD (Chemical Bath Deposition) method. In the preliminary experiment, it is confirmed that the size of colloid particle and roughness of surface of CdS thin film are increased with increase of pH, fabrication time and temperature. The optimum condition for the selective deposition of CdS film pattern using the SAM with microcontact printing was determined to be pH 10, temperature of 75°C, deposition time of 15 minute. Various patterns of different shape of CdS thin film were fabricated uniformly and satisfactorily in large area by the conditions determined in the present work. The stoichiometric composition of CdS was confirmed to be 1:1 by EDS and XPS.