KOSEN 한인과학기술자네트워크

I.Electronic and Thermal and Thermoelectric Transport in Carbon Nanotubes and Nanowires The recent discovery of various 1-dimensional (1-d) nanomaterials such as carbon nanotubes and semiconductor/metal nanowires has ignited a great deal of theoretical and experimental work. The electronic properties of 1-dimensional (1D) nanoscaled materials including carbon nanotubes and semiconductor/metal nanowires have been intensively studied at the single nanotube/nanowire level, and have exhibited a variety of unique physical phenomena due to the enhanced quantum confinement of electrons in reduced dimensions. However, unlike the electronic properties, the experiments investigating the thermal properties of these materials have mostly focused on `bulk` measurements. In thermal transport measurements such as thermal conductivity and thermoelectricity, it is difficult to extract absolute values for these quantities from the `bulk` experiments due to the presence of numerous junctions between individual molecular wires, which often present extrinsic effects to the measurements. Most importantly, it is only at mesoscopic scales where one is able to study the quantum limit of energy (thermal) transport and thermoelectric effects. In this regard, mesoscopic thermal transport measurements are necessary to elucidate the intrinsic properties of these materials in the quantum limits. Such mesoscopic experiments in semiconducting devices have been recently demonstrated in Kim`s research group. Using novel hybridized synthesis techniques in combination with semiconductor device fabrication techniques, the Kim group is currently investigating the quantum limit of thermal transport and mesoscopic thermoelectric phenomena in 1D nanoscale materials.Specifically, the Kim group intends to address following open questions: The energy transport/dissipation in the quantum transport limit: How does energy transport/dissipate when the quantum phase coherence length of the energy carrier is comparable to the sample dimension? Thermoelectric phenomena in nanoscale materials: What determines the thermoelectricity in a confined nanoscale system? Nanoscale engineering for thermoelectric applications: Is efficient thermoelectric cooling/generation attainable with 1D nanoscale materials? For this purpose, we have established a collaboration work with sample providers outside Columbia University in order to obtain nanoscale materials for investigation of the aforementioned mesoscopic thermal/thermoelectric transport measurements. In addition, synthesizing and manipulating carbon nanotubes have been one of the greatest challenges to investigate physical properties and to use this material for device applications. The Kim group has made a few innovative progresses in this field by demonstrating (i) ultralong single walled and multiwalled carbon nanotube growth (ii) manipulation of multiwalled nanotubes for fabrication of hierarchical structures based on nanotubes; and (iii) investigation of electrical transport in different nanotube based nanostructures including resistance scaling in length of 1-dimensional channels. II. Transport Properties of Novel 2-dimensional Nanocrystals Applying an external electric field across a gate insulator attracts or repels charge carriers in a material and creates a thin charge accumulation or depletion layer at the surface/interface of the sample. The ability to control the charge carrier density through the electric field effect has provided new opportunities to investigate materials, whose properties strongly depend on carrier concentration. Those materials include organic conductors, high temperature superconductors, metal chalcogenide and semimetallic layered materials, such as graphite. The Kim group has developed experimental techniques to create and meosocopic graphite samples and graphene for transport measurement. We are now applying this experimental technique to create novel 2D nanocr