Papers by Author: Kwang Real Lee

Abstract: A-C: H (Hydrogenated amorphous carbon) diamond like carbon(DLC) film is the low stabilities of chemical and mechanical properties at high temperatures. Some researchers reported that Raman spectra shown significant conversion of DLC films to nano-crystalline graphite on heating in ambient air at temperatures above 300°C and conversion to nano-crystalline graphite was completed by 450~600°C In this study, DLC films(thickness : 1.5-m) were deposited on p-type (100) silicon films by using C6H6 and C6H14 plasma produced with a 13.6MHz RF source. To investigate the mechanical stability of DLC films below 250°C, we thermally aged the films for different aging temperatures (150°C, 200°C, 250°C) and times (0: virgin, 120, 240, 360 hours). By using indentation test and Raman spectra analyses, it has been found that the H3/E2 decreases with increasing I(D)/I(G) ratio. Also we confirmed that sample-2(precursor gas: C6H14) had better mechanical characteristic and thermal stability than the sample-1(precursor gas: C6H6).

Abstract: First principle calculations were performed on the electronic and magnetic structures of the transition metals doped GaN. Seven elements in 3d transition metals from V to Cu were used as a dopant. Magnetic phase was stable compared to non-magnetic phase for all transition metals doped GaN. Total magnetic moments followed Hund’s rule to maximize the magnetic moment. Transition element projected magnetic moments showed that most of magnetic moments were concentrated on transition metals in the cases of V, Cr, and Mn doped GaN, which could not be used for DMS. Since Fe and Ni doped GaNs are intrinsic insulators, Fe and Ni doped GaNs could not be used for DMS materials unless additional dopants are introduced. The most probable candidates for DMS applications were predicted to be Co or Cu doped GaNs, respectively.

Abstract: Developments of tetrahedral amorphous carbon (ta-C) films having low residual compressive stress are essential to extend the applicability of the films. The annealing of the ta-C films was known to be an effective way for the reduction the stress of the films. However, the effects of annealing on the atomic structure of ta-C films have not been fully understood. The atomic structure changes by the annealing were studied using molecular dynamics simulation. The simulation showed that the annealing caused an increase of the atomic volume of ta-C film, which explained the stress reduction partially. However, the tendency of the stress reduction was different to high and low stress films. The annealing substantially reduced the stresses of high stress films compared to those of low stress films. Atomic structure analysis showed that the reason for the asymmetric stress reduction resulted from the relaxation of highly distorted bonds that existed in as-deposited films.

Abstract: The local acceleration effects, which are peculiar phenomena during atomic scale deposition process, were investigated byMolecular Dynamics (MD) simulation. The values of local acceleration were distributed widely for various surface orientations. Deposited atoms were accelerated along the potential energy surface, and accelerated values were evidently dependent on the local configuration of the surface. In contrast, the local acceleration became negligibly small for clusters consisting of many atoms.

Abstract: The evaluation of elastic property for thin diamond-like carbon (DLC) films has been presented with buckle analysis of compressive stressed film on patterned substrate. When substrate has been patterned with adhesion release layer, the morphologies of buckle configuration on patterned layer has been controlled from straight sided (Euler) buckle to nonlinear telephone cord type buckle with respect to the pattern width. By using the simple equation for Euler buckle, the elastic modulus has been easily calculated, shown well consistent with the results by nano-indentation test.