• Applied Chemistry for Engineering
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• v.16 no.4
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• pp.461-473
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• 2005

Nanotechnology has attracted great attention as one of essential fields in modern science. In particular, the fabrication of nanostructures with nanometer dimension in size is the starting point and essential part of nanotechnology research. Anodic aluminum oxide (AAO) nanotemplate technique has many merits including ease of fabrication, low cost process, and nanotemplate fabrication in large area. Moreover, AAO nanotemplate technique can realize self-ordered hexagonal pore structure with extremely high aspect ratio which is difficult to achieve with conventional lithographic techniques. Simple control of pore dimensions such as diameter, length, and density by varying anodizing condition would be advantageous, too. AAO nanotemplate has been the topic of intensive investigations for the past decade due to above strong points, and the application to various fields of nanotechnology is expected. In this review paper, the fabrication and application of AAO nanotemplate are introduced.

• Journal of the Speleological Society of Korea
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• no.76
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• pp.37-42
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• 2006

The Dielectric Barrier Discharge (DBD) is a nonequilibrium gas discharge that is generated in the space between two electrodes, which are separated by an insulating dielectric layer. The dielectric layer can be put on either of the two electrodes or be inserted in the space between two electrodes. If an AC or pulse high voltage is applied to the electrodes that is operated at applied frequency from 50Hz to several MHz and applied voltages from a few to a few tens of kilovolts rms, the breakdown can occur in working gas, resulting in large numbers of micro-discharges across the gap, the gas discharge is the so called DBD. Compared with most other means for nonequilibrium discharges, the main advantage of the DBD is that active species for chemical reaction can be produced at low temperature and atmospheric pressure without the vacuum set up, it also presents many unique physical and chemical process including light, heat, sound and electricity. This has led to a number of important applications such as ozone synthesizing, UV lamp house, CO2 lasers, et al. In recent years, due to its potential applications in plasma chemistry, semiconductor etching, pollution control, nanometer material and large area flat plasma display panels, DBD has received intensive attention from many researchers and is becoming a hot topic in the field of non-thermal plasma.

• Elastomers and Composites
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• v.45 no.2
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• pp.80-86
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• 2010

Carbon nanotubes (CNTs) exhibit excellent mechanical, electrical, and magnetic properties as well as nanometer scale diameter and high aspect ratio, which make them an ideal reinforcing agent for high strength polymer composites. The functionalized CNTs are believed to be very promising in the fields such as preparation of functional and composite materials. CNT-Polymer composites are expected to have good processability characteristics of the polymer and excellent functional properties of the CNTs. However, since CNTs usually form stabilized bundles due to Van der Waals interactions, are extremely difficult to disperse and align in a polymer matrix. The biggest issues in the preparation of CNT-reinforced composites reside in efficient dispersion of CNTs into a polymer matrix, and the alignment and control of the CNTs in the matrix. There are several methods for the dispersion of nanotubes in the polymer matrix such as solution mixing, bulk mixing, melt mixing, in-situ polymerization and chemical functionalization of the carbon nanotubes, etc. These methods and preparation of high performance CNT-polymer composites are described in this review.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.24.2-24.2
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• 2009

Nanostuctures such as nanodot and nanowire have been extensively studied as building blocks for nanoscale devices. However, the direct growth of the nanostuctures at the desired position is one of the most important requirements for realization of the practical devices with high integrity. Self-assembled nanotemplate is one of viable methods to produce highly-ordered nanostructures because it exhibits the highly ordered nanometer-sized pattern without resorting to lithography techniques. And selective epitaxial growth (SEG) can be a proper method for nanostructure fabrication because selective growth on the patterned openings obtained from nanotemplate can be a proper direction to achieve high level of control and reproducibility of nanostructucture fabrication. Especially, SiGe has led to the development of semiconductor devices in which the band structure is varied by the composition and strain distribution, and nanostructures of SiGe has represented new class of devices such nanowire metal-oxide-semiconductor field-effect transistors and photovoltaics. So, in this study, various shaped SiGe nanostructures were selectively grown on Si substrate through ultrahigh vacuum chemical vapor deposition (UHV-CVD) of SiGe on the hexagonally arranged Si openings obtained using nanotemplates. We adopted two types of nanotemplates in this study; anodic aluminum oxide (AAO) and diblock copolymer of PS-b-PMMA. Well ordered and various shaped nanostructure of SiGe, nanodots and nanowire, were fabricated on Si openings by combining SEG of SiGe to self-assembled nanotemplates. Nanostructure fabrication method adopted in this study will open up the easy way to produce the integrated nanoelectronic device arrays using the well ordered nano-building blocks obtained from the combination of SEG and self-assembled nanotemplates.

• Advances in nano research
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• v.13 no.2
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• pp.187-197
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• 2022

The synthesis of organic and hybrid organic-inorganic perovskites directly from solution improves the cost- and energy-efficiency of processing. To date, numerous research efforts have been devoted to investigating the influence of the various solvent parameters for the synthesis of lead halide perovskites, focused on the effects of different single solvents on the efficiency of the resulting perovskites. In this work, we investigated the effect of solvent blends for the first time on the structure and phase of perovskites produced via the Lewis base vapor diffusion method to develop a new synthetic approach for water-stable CsPbBr₃ particles with nanometer-sized dimensions. Solvent blends prepared with DMF and water-miscible solvents with different Gutmann's donor numbers (D_N) affect the Pb ions differently, resulting in a variety of lead bromide species with various colors. The use of a DMF/isopropanol solvent mixture was found to induce the formation of the Ruddlesden-Popper perovskite based on lead bromide. This perovskite undergoes a blue color shift in the solvated state owing to the separation of nanoplatelets. In contrast, the replacement of isopropanol with DMSO, which has a high DN, induces the formation of spherical CsPbBr₃ perovskite nanoparticles that exhibit green emission. Finally, the integration of acetone in the solvent system leads to the formation of lead bromide complexes with a yellow-orange color and the perovskite CsPbBr₃.

• Current Optics and Photonics
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• v.7 no.1
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• pp.38-46
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• 2023

Optical Fourier-domain reflectometry (OFDR) sensors have been widely used to measure distances with high resolution and speed in a noncontact state. In the electroplating process of a printed circuit board, it is critically important to monitor the copper-plating thickness, as small deviations can lead to defects, such as an open or short circuit. In this paper we employ a phase-based OFDR sensor for in situ relative distance sensing of a sample with nanometer-scale resolution, during electroplating. We also develop an optical-path difference (OPD)-regulated sensing probe that can maintain a preset distance from the sample. This function can markedly facilitate practical measurements in two aspects: Optimal distance setting for high signal-to-noise ratio OFDR sensing, and protection of a fragile probe tip via vertical evasion movement. In a sample with a centimeter-scale structure, a conventional OFDR sensor will probably either bump into the sample or practically out of the detection range of the sensing probe. To address this limitation, a novel OPD-regulated OFDR system is designed by combining the OFDR sensing probe and linear piezo motors with feedback-loop control. By using multiple OFDR sensors, it is possible to effectively monitor copper-plating thickness in situ and uniformize it at various positions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.3
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• pp.479-485
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• 2006

The double gate(DG) MOSFET is a promising candidate to further extend the CMOS scaling and provide better control of short channel effect(SCE). DGMOSFETs, having ultra thin undoped Si channel for SCEs control, ale being validated for sub-20nm scaling. A novel analytical transport model for the subthreshold mode of DGMOSFETs is proposed in this paper. The model enables analysis of short channel effect such as the subthreshold swing(SS), the threshold voltage roil-off$({\Delta}V_{th})$ and the drain induced barrier lowering(DIBL). The proposed model includes the effects of thermionic emission and quantum tunneling of carriers through the source-drain barrier. An approximative solution of the 2D Poisson equation is used for the distribution of electric potential, and Wentzel-Kramers-Brillouin approximation is used for the tunneling probability. The new model is used to investigate the subthreshold characteristics of a double gate MOSFET having the gate length in the nanometer range $(5-20{\sim}nm)$ with ultra thin gate oxide and channel thickness. The model is verified by comparing the subthreshold swing and the threshold voltage roll-off with 2D numerical simulations. The proposed model is used to design contours for gate length, channel thickness, and gate oxide thickness.

• 한국신재생에너지학회:학술대회논문집
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• 2005.11a
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• pp.561-566
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• 2005

Polycrystalline silicon films were deposited using hot wire CVD (HWCVD). The deposition of silicon thin films was approached by the theory of charged clusters (TCC). The TCC states that thin films grow by self-assembly of charged clusters or nanoparticles that have nucleated in the gas phase during the normal thin film process. Negatively charged clusters of a few nanometer in size were captured on a transmission electron microscopy (TEM) grid and observed by TEM. The negatively charged clusters are believed to have been generated by ion-induced nucleation on negative ions, which are produced by negative surface ionization on a tungsten hot wire. The electric current on the substrate carried by the negatively charged clusters during deposition was measured to be approximately $-2{\mu}A/cm^2$. Silicon thin films were deposited at different $SiH_4$ and $H_2$ gas mixtures and filament temperatures. The crystalline volume fraction, grain size and the growth rate of the films were measured by Raman spectroscopy, X-ray diffraction and scanning electron microscopy. The deposit ion behavior of the si1icon thin films was related to properties of the charged clusters, which were in turn controlled by the process conditions. In order to verify the effect of the charged clusters on the growth behavior, three different electric biases of -200 V, 0 V and +25 V were applied to the substrate during the process, The deposition rate at an applied bias of +25 V was greater than that at 0 V and -200 V, which means that the si1icon film deposition was the result of the deposit ion of charged clusters generated in the gas phase. The working pressures had a large effect on the growth rate dependency on the bias appled to the substrate, which indicates that pressure affects the charging ratio of neutral to negatively charged clusters. These results suggest that polycrystalline silicon thin films with high crystalline volume fraction and large grain size can be produced by control1ing the behavior of the charged clusters generated in the gas phase of a normal HWCVD reactor.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.588-588
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• 2013

Nanoscale noble-metals have attracted enormous attention from researchers in various fields of study because of their unusual optical properties as well as novel chemical properties. They have possible uses in diverse applications such as devices, transistors, optoelectronics, information storages, and energy converters. It is well-known that nanoparticles of noble-metals such as silver and gold show strong absorption bands in the visible region due to their surface-plasmon oscillation modes of conductive electrons. Silver nanocubes stand out from various types of Silver nanostructures (e.g., spheres, rods, bars, belts, and wires) due to their superior performance in a range of applications involvinglocalized surface plasmon resonance, surface-enhanced Raman scattering, and biosensing. In addition, extensive efforts have been devoted to the investigation of Gold-based nanocomposites to achieve high catalytic performances and utilization efficiencies. Furthermore, as the catalytic reactivity of Silver nanostructures depends highly on their morphology, hollow Gold nanoparticles having void interiors may offer additional catalytic advantages due to their increased surface areas. Especially, hollow nanospheres possess structurally tunable features such as shell thickness, interior cavity size, and chemical composition, leading to relatively high surface areas, low densities, and reduced costs compared with their solid counterparts. Thus, hollow-structured noblemetal nanoparticles can be applied to nanometer-sized chemical reactors, efficient catalysts, energy-storage media, and small containers to encapsulate multi-functional active materials. Silver nanocubes dispersed in water have been transformed into Ag@Au nanoboxes, which show highly enhanced catalytic properties, by adding $HAuCl_4$. By using this concept, $SiO_2$-coated Ag@Au nanoboxes have been synthesized via galvanic replacement of $SiO_2$-coated Ag nanocubes. They have lower catalytic ability but more stability than Ag@Au nanoboxes do. Thus, they could be recycled. $SiO_2$-coated Ag@Au nanoboxes have been found to catalyze the degradation of 4-nitrophenol efficiently in the presence of $NaBH_4$. By changing the amount of the added noble metal salt to control the molar ratio Au to Ag, we could tune the catalytic properties of the nanostructures in the reduction of the dyes. The catalytic ability of $SiO_2$-coated Ag@Au nanoboxes has been found to be much more efficient than $SiO_2$-coated Ag nanocubes. Catalytic performances were affected noteworthily by the metals, sizes, and shapes of noble-metal nanostructures.

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.4
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• pp.285-291
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• 2012

Purpose: This study was conducted to identify the surface characteristics of titanium discs coated with MS275/PLGA by electrospray and which is effective to mesenchymal stem cell proliferation. Materials and methods: We used anodized surface coated with PLGA as a control group and anodized surface coated with MS275 $0.5{\mu}M$, $1{\mu}M$, $1.5{\mu}M$ as test groups. To examine that the coating particles are nanometer sized, FE-SEM was used and AFM was utilized to determine the difference of coating surface roughness. We checked the mesenchymal stem cell proliferation by using MTT assay on $1^{st}$, $4^{th}$, $7^{th}$ days. Results: There was no significant difference between control groups and test groups in AFM results (P>.05). In MTT assay results, mesenchymal stem cell proliferation was increased with time, at $7^{th}$ day, cell viability on discs coated with $1.5{\mu}M$ MS275 was significantly higher than control group (P<.05). As SEM showed, the number of cells on all discs was increased and the morphology of cell attachment was also wider and closer with time. Conclusion: Titanium surface coated with MS275/PLGA showed significantly higher cell proliferation and the more density of MS275 was dispersed on titanium discs, the faster cells grew.