Hyunju Lee

Formation of Copper Seed Layers and Copper Via Filling with Various Additives

Recently, the demand for the miniaturization of printed circuit boards has been increasing, as electronic devices have been sharply downsized. Conventional multi-layered PCBs are limited in terms their use with higher packaging densities. Therefore, a build-up process has been adopted as a new multi-layered PCB manufacturing process. In this process, via-holes are used to connect each conductive layer. After the connection of the interlayers created by electro copper plating, the via-holes are filled with a conductive paste. In this study, a desmear treatment, electroless plating and electroplating were carried out to investigate the optimum processing conditions for Cu via filling on a PCB. The desmear treatment involved swelling, etching, reduction, and an acid dip. A seed layer was formed on the via surface by electroless Cu plating. For Cu via filling, the electroplating of Cu from an acid sulfate bath containing typical additives such as PEG(polyethylene glycol), chloride ions, bis-(3-sodiumsulfopropyl disulfide) (SPS), and Janus Green B(JGB) was carried out. The desmear treatment clearly removes laser drilling residue and improves the surface roughness, which is necessary to ensure good adhesion of the Cu. A homogeneous and thick Cu seed layer was deposited on the samples after the desmear treatment. The 2,2`-Dipyridyl additive significantly improves the seed layer quality. SPS, PEG, and JGB additives are necessary to ensure defect-free bottom-up super filling.

Receptor-Meditated Endocytosis by Hyaluronic Acid@Superparamagnetic Nanovetor for Targeting of CD44-Overexpressing Tumor Cells

The present report proposes a more rational hyaluronic acid (HA) conjugation protocol that can be used to modify the surface of the superparamagnetic iron oxide nanoparticles (SPIONs) by covalently binding the targeting molecules (HA) with glutamic acid as a molecular linker on peripheral surface of SPIONs. The synthesis of HA-Glutamic Acid (GA)@SPIONs was included oxidization of nanoparticle’s surface with H2O2 followed by activation of hydroxyl group and reacting glutamic acid as an intermediate molecule demonstrating transfection of lung cancer cells. Fourier transform infrared (FTIR) and zeta-potential studies confirmed the chemical bonding between amino acid linker and polysaccharides. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assay showed that HA-SPIONs-treated cells remained 82.9% ± 2.7% alive at high particle dosage (200 µg/mL iron concentration), whereas GA-SPIONs and bare SPIONs (B-SPIONs) treated cells had only 59.3% ± 13.4% and 26.5% ± 3.1% survival rate at the same conditions, respectively. Confocal microscopy analysis showed increased cellular internalization of HA-SPIONs compared to non-interacting agarose coated SPIONs (AgA-SPIONs).

A coaxial structure of multiwall carbon nanotubes on vertically aligned Si nanorods and its intrinsic characteristics

We present a unique process for fabricating silicon nanorods wrapped with a graphitic material on a silicon substrate by the chemical vapor deposition method with no metal catalyst, as well as characterization of their intrinsic properties. First, well-ordered silicon nanorod axes were grown via an electroless metal deposition method, followed by chemical vapor deposition to wrap the axes with a carbon nanotube. Interestingly, the use of ethanol treatment before chemical vapor deposition prevents the formation of SiOx layers, which may be necessary as seed layers for carbon nanotube growth. Since this method for carbon nanotube growth does not involve a metal catalyst, the intrinsic properties of the Si NRs were well characterized. A few characterization methods (XPS, Raman spectroscopy, and EELS) were carried out to prove that the Si NRs were completely surrounded by CNTs. In addition, the conductance results (by terahertz time-domain spectroscopy) show that the charge carrier transport characteristics of the multiwall carbon nanotubes are found mainly in the outermost shell, and that the Si NR surface was well passivated by the multiwall carbon nanotube structure. This coaxial structure, which does not require a metal catalyst, represents a significant step forward for realizing applications for carbon nanotube devices.

Massage Therapy of Electrical Chair-Massager Effects on EEG Patterns

The aim of this study was to evaluate effects of EEG patterns induced by three types ((1) resting mode(control group), (2) light massage mode, (3) strong massage mode in the electrical chair-massager for 15 minutes) in a sample of 16 healthy adults. Changes in anxiety and stress were assessed, and electroencephalogram was recorded. Anxiety scores(STAI: State Anxiety Inventory, VAS: Visual Analog Scale) decreased in all groups. For anxiety scores, the strong massage group showed the greatest decrease in stress. All groups also showed an increase in delta and theta activity, but only strong massage group showed a signigicant difference. All groups showed a decrease in alpha activity. Also, EEG changes in two groups except a control group showed a decrease in beta activity.

Synthesis of Si Nanowire/Multiwalled Carbon Nanotube Core-Shell Nanocomposites

Si nanowire/multiwalled carbon nanotube nanocomposite arrays were synthesized. Vertically aligned Si nanowire arrays were fabricated by Ag nanodendrite-assisted wet chemical etching of n-type wafers using HF/AgNO3 solution. The composite structure was synthesized by formation of a sheath of carbon multilayers on a Si nanowire template surface through a thermal CVD process under various conditions. The results of Raman spectroscopy, scanning electron microscopy, and high resolution transmission electron microcopy demonstrate that the obtained nanocomposite has a Si nanowire core/carbon nanotube shell structure. The remarkable feature of the proposed method is that the vertically aligned Si nanowire was encapsulated with a multiwalled carbon nanotube without metal catalysts, which is important for nanodevice fabrication. It can be expected that the introduction of Si nanowires into multiwalled carbon nanotubes may significantly alter their electronic and mechanical properties, and may even result in some unexpected material properties. The proposed method possesses great potential for fabricating other semiconductor/CNT nanocomposites.

Characteristics of sulfur hexafluoride hydrate film growth at the vapor/liquid interface

gas has been widely used in many industrial fields as insulating, cleaning and covering gases due to its outstanding arc-extinguishing and insulating properties. However, global warming potential of gas is 23,900 times more than that of and it remains in the air during 3,200 years. For these reason, technological and economical effects could be expected for the separation of from gas mixtures by hydrate forming process. In this study, we carried out morphological studies for the hydrate crystal to understand its formation and growth mechanisms. hydrate film was initially formed at the interfacial boundary between gas and liquid regions, and then subsequent dendrite crystals growth was observed. The dendrite crystals grew to the direction of gas region probably due to the guest gas concentration gradient. The detailed growth characteristics of hydrate crystals such as nucleation, migration, growth and interference were discussed in this study.

Gender Differences of Physics Major College Students' Conceptual Understanding and Its Degree of Certainty in the Subject of Quantum Mechanics

This study aims to investigate the gender differences of college students concerning the levels of their understandings on the six major concepts in Quantum Mechanics (QM) and the degree of certainty of their knowledge. For this purpose, 182 physics major college students responded to the revised Quantum Mechanics Conceptual Survey (QMCS) and the Scale for Degree of Certainty on their Knowledge (SDCK). In the results, male students presented statistically-significant higher mean scores on both the QMCS and the SDCK. Specifically, female students held insufficient knowledge of ‘wave-particle duality’ and the ‘wave function’. In addition, a significant correlation between the scores on the QMCS and the SDCK was observed in both gender groups. The students presented decent levels of understanding on the concept of ‘quantization of states’ with a high level of certainty whereas they struggled to understand the concepts of ‘wave-particle duality’, ‘tunneling effect’ and ‘Schrodinger equation’ with a low degree of certainty.

Microstructural Characteristics of Electro-Plated Cu Films by DC and Pulse Systems

The aim of this work was to investigate the effects of electrodeposition conditions on the microstructural characteristics of copper thin films. The microstructure of electroplated Cu films was found to be highly dependent on electrodeposition conditions such as system current and current density, as well as the bath solution itself. The current density significantly changed the preferred orientation of electroplated Cu films in a DC system, while the solution itself had very significant effects on microstructural characteristics in a pulse-reverse pulse current system. In the DC system, polarization at high current above 30 mA, changed the preferred orientation of Cu films from (220) to (111). However, Cu films showed (220) preferred orientation for all ranges of current density in the pulse-reverse pulse current system. The grain size decreased with increasing current density in the DC system while it remained relatively constant in the pulse-reverse pulse current system. The sheet resistance increased with increasing current density in the DC system due to the decreased grain size.

Cyclic Voltammetry Study on Electrodeposition of CuInSe 2 Thin Films

Chalcopyrite (CIS) is considered to be an effective light-absorbing material for thin film photovoltaic solar cells. CIS thin films have been electrodeposited onto Mo coated and ITO glass substrates in potentiostatic mode at room temperature. The deposition mechanism of CIS thin films has been studied using the cyclic voltammetry (CV) technique. A cyclic voltammetric study was performed in unitary Cu, In, and Se systems, binary Cu-Se and In-Se systems, and a ternary Cu-In-Se system. The reduction peaks of the ITO substrate were examined in separate , , and solutions. Electrodeposition experiments were conducted with varying deposition potentials and electrolyte bath conditions. The morphological and compositional properties of the CIS thin films were examined by field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). The surface morphology of as-deposited CIS films exhibits spherical and large-sized clusters. The deposition potential has a significant effect on the film morphology and/or grain size, such that the structure tended to grow according to the increase of the deposition potential. A CIS layer deposited at -0.6 V nearly approached the stoichiometric ratio of . The growth potential plays an important role in controlling the stoichiometry of CIS films.

Characteristics of SiO 2 /Si Quantum Dots Super Lattice Structure Prepared by Magnetron Co-Sputtering Method

Solar cells have been more intensely studied as part of the effort to find alternatives to fossil fuels as power sources. The progression of the first two generations of solar cells has seen a sacrifice of higher efficiency for more economic use of materials. The use of a single junction makes both these types of cells lose power in two major ways: by the non-absorption of incident light of energy below the band gap; and by the dissipation by heat loss of light energy in excess of the band gap. Therefore, multi junction solar cells have been proposed as a solution to this problem. However, the and generation solar cells have efficiency limits because a photon makes just one electron-hole pair. Fabrication of all-silicon tandem cells using an Si quantum dot superlattice structure (QD SLS) is one possible suggestion. In this study, an matrix system was investigated and analyzed for potential use as an all-silicon multi-junction solar cell. Si quantum dots with a super lattice structure (Si QD SLS) were prepared by alternating deposition of Si rich oxide (SRO; (x