• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.6
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• pp.44-51
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• 1999

The electrical conduction mechanism of high dielectric $(Ba,Sr)TiO_3$ (BST) thin film capacitor, which is the promising cell capacitor for high density DRAM, was investigated in low field region (<0.2MV/cm). It is known that the current in the low field region consists of dielectric relaxation current and leakage current. The current-time (I-t) measurement technique under the constant voltage was used for extracting successfully each current component. The conduction mechanism of the BST capacitor was deduced from the dependency of the current on the measurement temperature, strength of electric field, the polarity of applied electric field and post annealing process. From these results, it was suggested that the dielectric relaxation current and the leakage current are originated from the redistribution of internally trapped electron by hopping process and Pool-Frenkel conduction mechanism, respectively. It was also concluded that traps causing these two current components are due to oxygen vacancies within the BST film.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.174-174
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• 2010

Gallium Nitride(GaN) attracts great attention due to their wide band gap energy (3.4eV), high thermal stability to the solid state lighting devices like LED, Laser diode, UV photo detector, spintronic devices, solar cells, sensors etc. Recently, researchers are interested in synthesis of polycrystalline and amorphous GaN which has also attracted towards optoelectronic device applications significantly. One of the alternatives to deposit GaN at low temperature is to use Single Source Molecular Percursor (SSP) which provides preformed Ga-N bonding. Moreover, our group succeeds in hybridization of SSP synthesized GaN with Single wall carbon nanotube which could be applicable in field emitting devices, hybrid LEDs and sensors. In this work, the GaN thin films were deposited on c-axis oriented sapphire substrate by MBE (Molecular Beam Epitaxy) using novel single source precursor of dimethyl gallium azido-tert-butylamine($Me_2Ga(N_3)NH_2C(CH_3)_3$) with additional source of ammonia. The surface morphology, structural and optical properties of GaN thin films were analyzed for the deposition in the temperature range of $600^{\circ}C$ to $750^{\circ}C$. Electrical properties of deposited thin films were carried out by four point probe technique and home made Hall effect measurement. The effect of ammonia on the crystallinity, microstructure and optical properties of as-deposited thin films are discussed briefly. The crystalline quality of GaN thin film was improved with substrate temperature as indicated by XRD rocking curve measurement. Photoluminescence measurement shows broad emission around 350nm-650nm which could be related to impurities or defects.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.328-340
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• 1991

The combustion process in the combustion chamber has been investigated by taking pressure, temperature, chemical equilibrium and the shape of flame. To predict temperature of a flame in a combustion chamber is one of very important problems in the field of combustion and the temperature is a important factor of ignition and counteraction to inflammation. In this paper, the flame temperature was determined by the method of the Rayleigh scattering of Ar-Ion Laser (514.5nm). The Rayleigh scattering has been got considerably attention because of its strong cattering intensity. As a result, it is shown that I can measure the shape of flame by schlieren photography and that I can get the flame temperature variation in constant volume combustion chamber by Laser Rayleigh Scattering.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.1053-1060
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• 2003

The temperature variation of the concrete pavement in the early age significantly affects the initiation and propagation of its early age cracks. This implies that the measurement and analysis of early age temperature trend are necessary to examine the causes of early age cracks in the concrete pavement. In this study, it is investigated how the early age temperature trend in the concrete pavement affects the random crack initiation and behaviors of saw-cut joints using the actual construction site which is located at the KHC test road. During 72 hours after placing the concrete pavement, the ambient air temperature and temperatures at the top, middle, and bottom in the concrete pavement were measured and the random crack initiation in concrete slabs and early age behaviors in the joints were surveyed. The investigation results indicate that the first random crack was initiated at one of the slabs placed in the early morning which have higher temperature changes during early 72 hours. In addition, the joints that were saw-cut in the morning were cracked more rapidly than those saw-cut in the afternoon.

• Current Photovoltaic Research
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• v.3 no.3
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• pp.97-100
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• 2015

The kesterite $Cu_2ZnSnSe_4$ (CZTSe) thin film solar cells were synthesized by selenization of sputtered Cu/Sn/Zn metallic precursors on Mo coated soda lime glass substrate in Ar atmosphere. Cu/Sn/Zn metallic precursors were deposited by DC magnetron sputtering process with 30 W power at room temperature. As-deposited metallic precursors were placed in a graphite box with Se pellets and selenized using rapid thermal processing furnace at various temperature ($480^{\circ}C{\sim}560^{\circ}C$) without using a toxic $H_2Se$ gas. Effects of Selenization temperature on the morphological, crystallinity, electrical properties and cell efficiency were investigated by field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD), J-V measurement system and solar simulator. Further details about effects of selenization temperature on CZTSe thin films will be discussed.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.4
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• pp.192-199
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• 2004

Elastic-factor of elastic epoxy were investigated by TMA (Thermomechanical Analysis), DMTA (Dynamic Mechanical Thermal Analysis), TGA (Thermogravimetric Analysis) and FESEM (Field Emission Scanning Electron Microscope) for structure-images analysis as toughness-investigation to improve brittleness of existing epoxy resin. A range of measurement temperature of the TMA and DMTA was changed from -20($^{\circ}C$) to $200^{\circ}(C)$, and TGA was changed from $0^{\circ}(C)$ to $600^{\circ}(C)$. Glass transition temperature (Tg) of elastic epoxy was measured through thermal analysis devices with the content of 0(phr), 20(phr) and 35(phr). Also, thermal expansion coefficient (a), high temperature, modulus and loss factor were investigated through TMA, TGA, and DMTA. In addition, the structure of specimens was analyzed through FESEM, and then elastic-factor of elastic epoxy was visually showed by FESEM. As thermal analysis results, 20(phr) was more excellent than 30(phr) thermally and mechanically. Specially, thermal expansion coefficient, high temperature, modulus, and damping properties were excellent. By structure-images analysis through FESEM, we found elastic-factor of elastic epoxy that is not existing epoxy, and proved high impact.

• Smart Structures and Systems
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• v.33 no.3
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• pp.189-199
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• 2024

To properly extract the strain components under varying operational conditions is very important in bridge health monitoring. The abnormal sensor readings can be correctly identified and the expected operational performance of the bridge can be better understood if each strain components can be accurately quantified. In this study, strain components under varying load conditions, i.e., temperature variation and live-load variation are evaluated based on field strain measurements collected from a real concrete box-girder bridge. Temperature-induced strain is mainly regarded as the trend variation along with the ambient temperature, thus a smoothing technique based on the wavelet packet decomposition method is proposed to estimate the temperature-induced strain. However, how to effectively extract the vehicle-induced strain is always troublesome because conventional threshold setting-based methods cease to function: if the threshold is set too large, the minor response will be ignored, and if too small, noise will be introduced. Therefore, an autoencoder framework is proposed to evaluate the vehicle-induced strain. After the elimination of temperature and vehicle-induced strain, the left of which, defined as the model error, is used to assess the operational performance of the bridge. As empirical techniques fail to detect the degraded state of the structure, a clustering technique based on Gaussian Mixture Model is employed to identify the damage occurrence and the validity is verified in a simulation study.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.52 no.4
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• pp.153-158
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• 2003

This thesis deal with ferroelectric and ferromagnetic materials. PZT/Ferrite ceramics were made by the making process using PZT powder and garnet ferrite powder. PZT and ferrite are mixed as much 90%-10%, 50%-50%, and so on. After making samples, we are polishing samples until thickness is 0.1~0.2mm. We measured all kinds of samples in room temperature and applied magnetic field from -4500 to 4500 Oersted and conducted test of magnetical and electrical measurement using VSM and lpC resolution electrometer calibrated with RT66A pulsed tester. From this measurement, we can calculate tunability of these samples using C value obtained from P-E loop. As a result, it was able to measure magnetic characteristic when two matter had each other component ratio, and it was compound. However, it confirmed the possibility that was able to have ferroelectric characteristic with you in PZT 90% and ferrite 10%. Therefore, If this thing comes for PZT 50% and ferrite 50% have ferroelectric characteristic as him in a compound sample ore, can use this in an oscillator, supersonic waves detector in addition to a piezoelectric element. It may contribute to multipurpose of an element and demands such as a miniaturization of equipment, efficiency, reduce of a price which can use a characteristic of two components.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.1172-1172
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• 2001

Compact Near Infrared Diode Array Spectrometers offer new possibilities for on line quality assurance in the agricultural sector. Due to their speed and complete robustness towards temperature fluctuations and mechanical shock Diode Array Spectrometers are suitable for the use on Agricultural Harvest Machines. The growing consumer consciousness of food quality in combination with falling manufacturing prices demands procedures for an effective quality control system. The various conventional types of NIR instruments which have so far been used in laboratories are unsuitable for mobile applications under the rough conditions of field cropping not only because of their slow speed of measurement but also because of their shock sensitive filter wheels and monochromators necessary for fractionating polychromatic light. Another advantage of the on line use is the reduction of the sampling error because of the continuously measurement of the whole product. Considering the large economic importance of the dry matter content on agricultural products it is of particular advantage that water belongs to those constituents which are most easily assessed in the near infrared. While other constituents of economic importance such as starch, oil and protein in grains and seeds have a much lesser effect on NIR signals, their contents can nonetheless be assessed with high analytical precision on freshly harvested grains and seeds. In the last years several applications for on line quality assessment on harvesting machines were developed and tested. The talk will give an overview and outlook on existing and future possibilities of this new field of NIR applications.

• Journal of Korean Society for Atmospheric Environment
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• v.12 no.2
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• pp.189-198
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• 1996

Mercury (Hg) is ubiquitous throughout the earth's atmosphere. The uniqueness of its atmospheric geochemistry is well-known with the high environmental mobility and relatively long atmospheric residence time (c.a., 1 year) associated with its high chemical stability. Despite a growing recognition of the environmental significance of its global cycling, the prexisting Korean database for atmospheric Hg is extremely rare and confined to a number of concentration measurements conducted under relatively polluted urban atmospheric environments. To help activate the research on this suvject, an in-depth analysis on the current development in the measurements of atmospheric mercury and the associated fluxes has been made using the most using the most updated data ests reported worldwide. As a first step toward this purpose, the most reliable techniques commonly employed in the measurements of its concentration in the background atmosphere are introduced in combination with the flux measurement techniques over soil surface such as: dynamic enclosure (or field flux chamber) method and field micrometeorological method. Then the results derived using these measurement techniques are discussed and interpreted with an emphasis on its mobilization across the terrestrial biosphere and atmosphere interface. A unmber of factors including air/soil temperature, soil chemical composition, soil water content, and barometric pressure are found out to be influential to the rate and amount of such exchange processes. Although absolute magnitude of such exchange processes is insignificant relative to that of the major component like the oceanic environment, this exchange process is thought to be the the predominant natural pathway for both the mobilization and redistribution of atmospheric Hg on a local or regional scale.