Hae-Jin Kim

Self-Healing Phenomenon and Dynamic Hardness of C60-Based Nanocomposite Coatings

The phenomenon of surface self-healing in C60-based polymer coatings deposited by ion-beam assisted physical vapor deposition was investigated. Nanoindentation of the coatings led to the formation of a protrusion rather than an indent. This protrusion was accompanied by an abnormal shape of the force-distance curve, where the unloading curve lies above the loading curve due to an additional force applied in pulling the indenter out of the media. The coatings exhibited a nanocomposite structure that was strongly affected by the ratio of C60 ion and C60 molecular beam intensities during deposition. The coatings also demonstrated the dynamic hardness effect, where the effective value of the hardness depends significantly on the indentation speed.

Fundamental Investigation of the Wear Progression of Silicon Atomic Force Microscope Probes

Atomic force microscopy (AFM) is a key instrument in nanotechnology; however, AFM probe wear is a critical concern with AFM-based technologies. In this work, the wear progression of silicon AFM probes with different radii was thoroughly explored under various normal forces and sliding speeds. The results showed that the initial wear coefficient increased as the normal force increased. However, after a certain sliding distance, the wear coefficient was stable due to the flattening of the probe even with increasing normal force. It was also observed that the wear coefficient decreased with increasing probe radius and the wear of the probe increased as the sliding speed increased. From the overall results, it was concluded that the contact pressure plays a significant role in wear progression and may be responsible for a lower wear coefficient even with increasing adhesion forces due to wear. The wear rate was found to have an exponential dependence on contact stress, as proposed in recent literatures.

Durability of the Flexible Shape Memory Device

The demand for flexible devices including solar cells, memories and batteries has increased rapidly over the past decades. In most flexible devices, polymer-based materials are used to enable the mechanical deformations such as bending or folding. Shape Memory Polymers (SMPs) is a high molecular compound polymer with flexibility and shape recovery characteristics. In this work, flexible shape memory device was fabricated by simply coating the conducting material, carbon nano-tube (CNT), on a shape memory polymer. Furthermore, durability of the device under various type of mechanical deformations was assessed. It is believed that the result of this work will aid in realization of a stretchable and wearable electronic device for practical applications.