• Journal of the Korean Magnetics Society
• /
• v.19 no.4
• /
• pp.121-125
• /
• 2009

Amorphous $Ge_1$_$_xMn_x$ semiconductor thin films grown by low temperature vapor deposition were annealed at various temperatures from 400 to $700^{\circ}C$ for 3 minutes in high vaccum chamber. The electrical and magnetotransport properties of as-grown and annealed samples have been studied. X-ray diffraction patterns analysis revealed that the samples still maintain amorphous state after annealling at $500^{\circ}C$ for 3 minutes and they were crystallized when annealing temperature increase to $600^{\circ}C$. Temperature dependence of resistivity measurement implied that as-grown and annealed $Ge_1$_$_xMn_x$ films have semiconductor characteristics, the increase of resistivity with annealling temperature was obseved. The $700^{\circ}C$-annealed sample exhibited negative magnetoresistance (MR) at low temperatures and the MR ratio was ${\sim}$8.5% at 10 K. The asymmetry was present in all MR curves. The anomalous Hall Effect was also observed at 250 K.

• Korean Journal of Food Science and Technology
• /
• v.28 no.3
• /
• pp.580-586
• /
• 1996

Gelatinization behavior and morphology of epichlorohydrin-crosslinked potato starches (XPs) were investigated. Native potato starch showed a very steep single stage swlling pattern, but crosslinked starches showed various patterns with the degree of crosslinking. Swelling power, solubility and light transmittance were reduced drastically as the degree of crosslinking increased. Brabender initial pasting temperature and peak temperature of crosslinked starches increased because the crosslinking reinforces the intermolecular net work of the starches. Although the swelling of the potato starch granule was inhibited by crosslinking as compared to that of the native one, Brabender peak viscosities (6.5% w/v, db) were on the order of 2,500 units for the native potato starch, 3,700 for the XP with 2.300 anhydroglucose units per crosslinking (AGU/CL) and 3,400 for the XP with 2,100 AGU/CL, due to the decreased breakdown of the swollen granule resulting from the resistance to heat and shear. The XP with 1,900 AGU/CL, however, did not show the peak viscosity and the viscosity was on the order of 500 units because of the excessive unhibition of the swelling. Unlike the native potato starch, 6.5%(m/v, db) pastes of the crosslinked potato starches could form gels, which could be predicted from the Brabender setback and consistency index. When the degree of crosslinking is low, random contraction and radial swelling of the granule was possible. As the degree of crosslinking increased, morphological change became similar to the single dimensional tangential swelling observed from the lenticular wheat starch. These morphological change during heating in excess water explained the gelatinization behaviors of crosslinked starches tested.

• Bulletin of the Korean Chemical Society
• /
• v.32 no.1
• /
• pp.263-272
• /
• 2011

Highly luminescent and monodisperse InP quantum dots (QDs) were prepared by a non-organometallic approach in a non-coordinating solvent. Fatty acids with well-defined chain lengths as the ligand, a non coordinating solvent, and a thorough degassing process are all important factors for the formation of high quality InP QDs. By varying the molar concentration of indium to ligand, QDs of different size were prepared and their absorption and emission behaviors studied. By spin-coating a colloidal solution of InP QD onto a silicon wafer, InP QD thin films were obtained. The thickness of the thin films cured at 60 and $200^{\circ}C$ were nearly identical (approximately 860 nm), whereas at $300^{\circ}C$, the thickness of the thin film was found to be 760 nm. Different contrast regions (A, B, C) were observed in the TEM images, which were found to be unreacted precursors, InP QDs, and indium-rich phases, respectively, through EDX analysis. The optical properties of the thin films were measured at three different curing temperatures (60, 200, $300^{\circ}C$), which showed a blue shift with an increase in temperature. It was proposed that this blue shift may be due to a decrease in the core diameter of the InP QD by oxidation, as confirmed by the XPS studies. Oxidation also passivates the QD surface by reducing the amount of P dangling bonds, thereby increasing luminescence intensity. The dielectric properties of the thin films were also investigated by capacitance-voltage (C-V) measurements in a metal-insulator-semiconductor (MIS) device. At 60 and $300^{\circ}C$, negative flat band shifts (${\Delta}V_{fb}$) were observed, which were explained by the presence of P dangling bonds on the InP QD surface. At $300^{\circ}C$, clockwise hysteresis was observed due to trapping and detrapping of positive charges on the thin film, which was explained by proposing the existence of deep energy levels due to the indium-rich phases.

• Journal of the Korean Electrochemical Society
• /
• v.10 no.4
• /
• pp.306-310
• /
• 2007

Characteristics of GDL (Gas Diffusion Layer) mainly determine the gas diffusion and water removal in a cell, thereby changing the performance and affecting durability of PEFC. To optimize the water management and understand the two phase flow in a GDL, it is important to study the behaviors of GDL micro structure under the real operating condition. In the clamped condition of cell, the GDL beneath the rib is more compressed than beneath the channel. Many researches on physical, electrochemical, mechanical behaviors of gas diffusion layer has been conducted. However, changes in surface properties under clamped condition have rarely studied. In present study, the morphology of broken connections of carbon fibers and detachment of PTFE coatings on the fibers were shown from the microscopic observations. In addition, changes in wetting properties of GDL by compression were investigated by using XPS and liquid uptake methods. The hydrophobic characteristics of GDL surface beneath the rib of the flow field plate are changed due to the deformation of micro structure.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.06a
• /
• pp.62-62
• /
• 2008

As micro-system move toward higher speed and miniaturization, requirements for embedding the passive components into printed circuit boards (PCBs) grow consistently. They should be fabricated in smaller size with maintaining and even improving the overall performance. Miniaturization potential steps from the replacement of surface-mount components and the subsequent reduction of the required wiring-board real estate. Among the embedded passive components, capacitors are most widely studied because they are the major components in terms of size and number. Embedding of passive components such as capacitors into polymer-based PCB is becoming an important strategy for electronics miniaturization, device reliability, and manufacturing cost reduction Now days, the dielectric films deposited directly on the polymer substrate are also studied widely. The processing temperature below $200^{\circ}C$ is required for polymer substrates. For a low temperature deposition, bismuth-based pyrochlore materials are known as promising candidate for capacitor $B_2Mg_{2/3}Nb_{4/3}O_7$ ($B_2MN$) multi layers were deposited on Pt/$TiO_2/SiO_2$/Si substrates by radio frequency magnetron sputtering system at room temperature. The physical and structural properties of them are investigated by SEM, AFM, TEM, XPS. The dielectric properties of MIM structured capacitors were evaluated by impedance analyzer (Agilent HP4194A). The leakage current characteristics of MIM structured capacitor were measured by semiconductor parameter analysis (Agilent HP4145B). 200 nm-thick $B_2MN$ muti layer were deposited at room temperature had capacitance density about $1{\mu}F/cm^2$ at 100kHz, dissipation factor of < 1% and dielectric constant of > 100 at 100kHz.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.06a
• /
• pp.477-477
• /
• 2008

For more than three decades, the gate dielectrics in CMOS devices are $SiO_2$ because of its blocking properties of current in insulated gate FET channels. As the dimensions of feature size have been scaled down (width and the thickness is reduced down to 50 urn and 2 urn or less), gate leakage current is increased and reliability of $SiO_2$ is reduced. Many metal oxides such as $TiO_2$, $Ta_2O_4$, $SrTiO_3$, $Al_2O_3$, $HfO_2$ and $ZrO_2$ have been challenged for memory devices. These materials posses relatively high dielectric constant, but $HfO_2$ and $Al_2O_3$ did not provide sufficient advantages over $SiO_2$ or $Si_3N_4$ because of reaction with Si substrate. Recently, $HfO_2$ have been attracted attention because Hf forms the most stable oxide with the highest heat of formation. In addition, Hf can reduce the native oxide layer by creating $HfO_2$. However, new gate oxide candidates must satisfy a standard CMOS process. In order to fabricate high density memories with small feature size, the plasma etch process should be developed by well understanding and optimizing plasma behaviors. Therefore, it is necessary that the etch behavior of $HfO_2$ and plasma parameters are systematically investigated as functions of process parameters including gas mixing ratio, rf power, pressure and temperature to determine the mechanism of plasma induced damage. However, there is few studies on the the etch mechanism and the surface reactions in $BCl_3$ based plasma to etch $HfO_2$ thin films. In this work, the samples of $HfO_2$ were prepared on Si wafer with using atomic layer deposition. In our previous work, the maximum etch rate of $BCl_3$/Ar were obtained 20% $BCl_3$/ 80% Ar. Over 20% $BCl_3$ addition, the etch rate of $HfO_2$ decreased. The etching rate of $HfO_2$ and selectivity of $HfO_2$ to Si were investigated with using in inductively coupled plasma etching system (ICP) and $BCl_3/Cl_2$/Ar plasma. The change of volume densities of radical and atoms were monitored with using optical emission spectroscopy analysis (OES). The variations of components of etched surfaces for $HfO_2$ was investigated with using x-ray photo electron spectroscopy (XPS). In order to investigate the accumulation of etch by products during etch process, the exposed surface of $HfO_2$ in $BCl_3/Cl_2$/Ar plasma was compared with surface of as-doped $HfO_2$ and all the surfaces of samples were examined with field emission scanning electron microscopy and atomic force microscope (AFM).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.06a
• /
• pp.169-169
• /
• 2008

To keep pace with scaling trends of CMOS technologies, high-k metal oxides are to be introduced. Due to their high permittivity, high-k materials can achieve the required capacitance with stacks of higher physical thickness to reduce the leakage current through the scaled gate oxide, which make it become much more promising materials to instead of $SiO_2$. As further studying on high-k, an understanding of the relation between the etch characteristics of high-k dielectric materials and plasma properties is required for the low damaged removal process to match standard processing procedure. There are some reports on the dry etching of different high-k materials in ICP and ECR plasma with various plasma parameters, such as different gas combinations ($Cl_2$, $Cl_2/BCl_3$, $Cl_2$/Ar, $SF_6$/Ar, and $CH_4/H_2$/Ar etc). Understanding of the complex behavior of particles at surfaces requires detailed knowledge of both macroscopic and microscopic processes that take place; also certain processes depend critically on temperature and gas pressure. The choice of $BCl_3$ as the chemically active gas results from the fact that it is widely used for the etching o the materials covered by the native oxides due to the effective extraction of oxygen in the form of $BCl_xO_y$ compounds. In this study, the surface reactions and the etch rate of $Al_2O_3$ films in $BCl_3/Cl_2$/Ar plasma were investigated in an inductively coupled plasma(ICP) reactor in terms of the gas mixing ratio, RF power, DC bias and chamber pressure. The variations of relative volume densities for the particles were measured with optical emission spectroscopy (OES). The surface imagination was measured by AFM and SEM. The chemical states of film was investigated using X-ray photoelectron spectroscopy (XPS), which confirmed the existence of nonvolatile etch byproducts.

• Korean Chemical Engineering Research
• /
• v.46 no.1
• /
• pp.118-123
• /
• 2008

In the present study, the effect of oxyfluorination treatment on multi-walled nanotubes (MWNTs) supports was investigated by analyzing surface functional groups. The surface characteristics were determined by Fourier transformed-infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). After the deposition of platinum nanoparticles on the above treated carbon supports, a crystalline size and a loading level had been investigated. Electrochemical properties of the treated MWNTs-supported Pt (Pt/MWNTs) catalysts were analyzed by current-voltage curve measurements. From the results of surface analysis, an oxygen and fluorine-containing functional group had been introduced to the surface of carbon supports. The oxygen and fluorine contents were the highest value at the treatment of 100 temperature. The Pt/100-MWNTs showed the smallest particle crystalline size of 3.5 nm and the highest loading level of 9.4% at the treatment of 100 temperature. However, the sample treated at the higher temperature showed the larger crystalline size and the lower loading level. This indicated that the crystalline size and the loading level could be controlled by changing the temperature of oxyfluorination treatment. Accordingly, an electrochemical activity was enhanced by increasing the temperature of treatment upto 100, and then decreased in the case of 200 and 300. The highest specific current density of 120 mA/mg had been obtained in the case of Pt/100-MWNTs.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.11
• /
• pp.1721-1725
• /
• 2010

This paper reports the fabrication of geometry-controlled carbon microneedles by a backside exposure method and pyrolysis. The SU-8 microneedles are a polymer precursor in a carbonization process, which geometries such as base diameter, spacing, and aspect ratio can be controlled in a photolithography step. Using this fabrication method, highly reproducible carbon microneedles, which have high aspect ratios of more than 10 and very sharp nanotips, can be realized. The quartz surface with carbon microneedles becomes very hydrophilic and its wettability is adjusted by carrying out the silane treatment. In the carbon microneedle array ($3\;{\mu}m{\times}3\;{\mu}m$), the contact angle is extremly enhanced (${\sim}180^{\circ}$); this will be advantageous in developing low-drag microfluidics and labs-on-a-chip as well as in other bio-applications.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.26 no.5
• /
• pp.188-192
• /
• 2016

In this work, the SiC powders were synthesized through the carbonized matter from the mixture of silica powder and rice husks. The SiC powders, obtained from the carbothermal reduction reaction of silica and carbonized rice husks, were investigated by XRD patterns, XPS, FE-SEM and FE-TEM. In the XRD patterns, the specimens showed clearly very high strong peak of (111) plane near $35^{\circ}$ as well as weak (220) and (311) peak respectively at approximately $60^{\circ}$ and $72^{\circ}$. Under Ar atmosphere, the power synthesized from the mixture (in case of mixing ratio, 6 : 4) of carbonized rice husks and silica showed mainly cubic SiC crystalline phase showing relatively lower ratio of hexagonal phase without residual carbon in XRD pattern. In the TEM analysis, the specimen, synthesized from carbonized rice husks and silica with mixing ratio of 6 : 4 under Ar atmosphere, showed relatively fine particles under $5{\mu}m$ and a crystalline SiC phase of (100) diffraction pattern.