주제: Development of Carbon-based Materials to Shield Electromagnetic Wave Radiation in 5G Frequency Area

Owing to their unique geometries, carbon coils could be predicted to have the particular properties such as high elasticity, low electrical resistance, chirality, and high specific surface area. Indeed, carbon coils devices or sensors were supposed to show the femto-scaled sensitivity and ultra-high resolution. It is expected that nanomaterials with helical morphology can be divided into different categories based upon the helical nature of the material: single helix, double helix, triple helix, and so on. Although the carbon coils was regarded as a promising material candidates to use in various application area, the formation of carbon coils is quite accidental with poor reproducibility. For the practical application of these materials, therefore, the controlled-characteristics for the coil morphology and geometry (diameter, pitch, length, and turning direction) with the large scale synthesis should be preferentially achieved.

In this work, SF₆ was used as an additive in source gases to take the advantage for fluorine species characteristics regarding the enhancement of the nucleation sites of carbon coils. We could obtain the controlled-geometry carbon coils merely by manipulating SF₆ incorporation times. By this technology, mass production of controlled-geometry carbon coils could be possible. Therefore, carbon nanomaterials with helical morphology can be envisaged to be used as components in nanoelectronics and nanotechnology devices. This is due to the ability of coiled materials to exhibit interesting electromagnet properties since a current flowing through a wire wound into a coil produces both electric and magnetic fields. This property of electromagnetism has created a revolution in many fields from the development of plasma televisions to memory storage devices. In addition, the synthesis of carbon-nanocoil—carbon-microcoil (CNC–CMC) hybrid materials, namely carbon nanocoils (CNCs) formed together with the growth of the carbon microcoils (CMCs), were achieved using C₂H₂ as the source gas and SF₆ as an additive gas in a thermal chemical vapor deposition system. During the reaction, SF₆ was injected into the reactor in modulated on/off cycles. The CNC–CMC hybrid materials were not observed without the on/off cycles of SF₆ flow. When we varied the number of the on/off cycles, the density of CNCs formed in the CNC–CMC hybrid materials increased with increasing the cycle number. The cause for the difference in CNC–CMC formation with the cycle number was investigated. Based on the results, a growth mode of the CNC–CMC hybrid materials was proposed. Furthermore, the formation of the carbon nanocoils-carbon microcoils (CNC-CMC) hybrid materials, namely the formation of the numerous carbon nanocoils (CNCs) on the surface of the carbon microcoils (CMCs), could be achieved using C₂H₂ as the source gas and CS₂ as the additive gas in a thermal chemical vapor deposition system. During the reaction, CS₂ was injected into the reactor in modulated on/off cycles. The density of CNCs formed on the surface of CMCs increased with increasing the on/off cycle number. At as-grown state, the CNC-CMC hybrid materials showed the higher electrical conductivity values than those of the materials composed of CMCs-only. Composites of CNC-CMC hybrid materials in polyurethane (CNC-CMC@PU) and CMCs in polyurethane (CMC@PU) were fabricated. The CNC-CMC@PU composites showed the higher shielding effectiveness than those of CMC@PU composites, irrespective of the mixture ratios of carbon nanomaterials in PU. Based on the resulting shielding effectiveness and the electrical conductivity values we conclude that the formation of the CNC-CMC hybrid materials can enhance the shielding effectiveness through the reflection-based mechanism as well as the absorption-based mechanism. In this talk, I will show some of valuable results including our works. In addition, I would like to discuss regarding the prospective research subjects with all the participants.