Characterization of Carbon Nanotubes and Nanowires and Their Applications

This thesis establishes comprehensive methodology for characterization of metallic nanowires (NWs) and carbon nanotubes (CNTs), and evaluation of their performance for interconnect applications at microwave/ mm-wave/THz frequencies. The research focus is on the development of modeling and measurement methods to determine constitutive material parameters, i.e. conductivity, and contact resistance of platinum (Pt) NWs, as well as on the development of modeling approaches to evaluate characteristic parameters for antennas, nano-coaxial lines, and single wire transmission lines composed of CNTs. Applicability of traditional two-port measurements is investigated for accurate determination of material parameters for Pt NWs over a broad frequency range. Two test-setups are developed. First, several configurations with directly contacted Pt NWs to a host coplanar waveguide (CPW) structure are designed and realized to determine the conductivity and contact resistance. Full-wave finite element and circuit models are used to determine the two parameters by fitting simulations to measurements. It is found that the single measurement setup with direct contacts cannot determine the two parameters simultaneously. To solve this problem, two approaches based on transmission line and lumped element models for Pt NWs are developed. Both approaches employ a set of two NWs with different lengths. The feasibility of both approaches is thoroughly studied and relevant conclusions are made. An approach based on lumped element models is validated experimentally, and it is shown that the contact resistance and conductivity of 300 nm diameter Pt NWs are about 50 W and 0.013sbulk, respectively. In the second setup, the capacitive coupling contact between the Pt NWs and the CPW structure is exploited to determine the NW’s conductivity. Two variations of this setup, specifically in-slot and on-dielectric configurations, are developed. Full-wave finite-element models are utilized to demonstrate suitability of the two configurations and to determine the conductivity of Pt NWs by fitting to measurements. Structural and elemental analyses of fabricated devices are conducted to assess fabrication and measurement issues. Full-wave modeling for individual CNTs and CNT bundles is performed by the use of method of moments and finite element method codes in order to CNTs as antennas, nano-coaxial lines, and single wire transmission lines. Characteristic parameters, such as impedance, gain, efficiency, and line loss for each interconnect are evaluated and compared to those of their copper-based counterparts. Results show better performance of CNTs over conventional metals at microwave frequencies. The extension of modeling and metrology for semiconducting NWs and CNTs, and the study of graphene at microwave frequencies are proposed as directions for future work

Analysis of the issues that emerged in the revision of the national social studies curriculum in South Korea: Text mining and semantic network analysis of the comments at the public hearing on YouTube

In South Korea, curriculum is revised, made public and implemented under a system known as a nation led curriculum. The South Korean national curriculum was completely revised 10 times between 1946 and 2015. At present, a complete revision is underway to replace the current 2015 national curriculum which is called the 2022 revised national curriculum. This study aims to analyze stakeholders’ responses to the YouTube public hearing   on social studies curriculum according to the 2022 revised national curriculum in South Korea in order to understand the context and causes of the issues that emerged. Text mining, semantic network analysis and word cloud techniques were employed to identify issues. As a result, three issues were identified in the social studies curriculum: the balanced development of general elective subjects in high school; the separation of social sciences and geography and division of textbooks in middle school social studies and the separate listing of four subjects, specifically geography, social sciences, history and morals. The issues revealed in this study provide beneficial implications for future social studies curriculum development, revision as well as the development of future research

Two-dimensional charge distributions of the Δ\Delta baryon: Interpolation between the nonrelativistic and ultrarelativistic limit

We investigate how the charge distributions of both the unpolarized and transversely polarized $\Delta$ baryon change as the longitudinal momentum~($P_{z}$) of the $\Delta$ baryon increases from $P_{z}=0$ to $P_{z}=\infty$ in a Wigner phase-space perspective. When the $\Delta$ baryon is longitudinally polarized, its two-dimensional charge distribution is kept to be spherically symmetric with $P_{z}$ varied, whereas when the $\Delta$ baryon is transversely polarized along the $x$-axis, the quadrupole contribution emerges at the rest frame ($P_{z}=0$). When $P_{z}$ grows, the electric dipole and octupole moments are induced. The induced dipole moment dominates over other higher multipole contributions and governs the deformation of the charge distribution of the $\Delta$ baryon.Comment: 22 pages, 12 figure

Instanton effects on electromagnetic transitions of charmonia

We investigate the mass spectrum and electromagnetic transitions of charmonia, emphasizing the instanton effects on them. The heavy-quark potential consists of the Coulomb-like potential from one-gluon exchange and the linear confining potential. We introduce the nonperturbative heavy-quark potential derived from the instanton vacuum. We also consider the screened confining potential, which better describes the electromagnetic decays of higher excited states. Using this improved heavy-quark potential, we compute the mass spectrum and electromagnetic decays of the charmonia. Focusing on the instanton effects, we discuss the results compared with the experimental data and those from other works. The instanton effects are marginal on the electromagnetic decays of charmonia.Comment: 10 pages and 4 figures. The final version to be published in Progress of Theoretical and Experimental Physic

511 keV γ\gamma-ray emission from the galactic bulge by MeV millicharged dark matter

We propose a possible explanation for the recently observed anomalous 511 keV line with a new "millicharged" fermion. This new fermion is light [${\cal O}({\rm MeV})$]. Nevertheless, it has never been observed by any collider experiments by virtue of its tiny electromagnetic charge $\epsilon e$. In particular, we constrain parameters of this millicharged particle if the 511 keV cosmic $\gamma$-ray emission from the galactic bulge is due to positron production from this new particle.Comment: 3 pages, 1 figure, A talk given by J.C.Park at the 16th International Conference on Supersymmetry and the Unification of Fundamental Interactions (SUSY08), Seoul, Korea, June 16-21, 200

Soft X-ray resonant Kerr rotation measurement and simulation of element-resolved and interface-sensitive magnetization reversals in a NiFe/FeMn/Co trilayer structure

We report experimental observations of element- and buried interface-resolved magnetization reversals in an oppositely exchange-biased NiFeFeMnCo trilayer structure by soft x-ray resonant Kerr rotation measurements. Not only Co-, Ni-, Fe-specific exchange-biased loops but also interfacial uncompensated (UC) Fe reversal loops coupled to the individual Co and NiFe layers are separately observed. From the experimental results interpreted with the help of the model simulations of soft x-ray resonant Kerr rotation, the effective thicknesses of interfacial UC regions at the buried interfaces of both FeMnCo and NiFeFeMn are found to be tUC =13??2 A and 6??4 A, respectively. The depth sensitivity as well as element specificity of the x-ray resonant Kerr effect offer an elegant way into the investigations of element- and depth-resolved magnetization reversals of ferromagnetic ultrathin regions at buried interfaces in multicomponent multilayer films.open91