• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.6
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• pp.233-239
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• 2021

In this study, Ga₂O₃/diamond layers were grown on Si substrates to improve the thermal characteristics of Ga₂O₃ materials. Firstly, diamond thin film was grown on Si substrates by hot-filament chemical vapor deposition. Afterward, Ga₂O₃ layer was grown in the growth temperature range of from 450~600℃ by mist chemical vapor deposition. We found that layer separation happens at the Ga₂O₃/diamond interface at the growth temperature of 500℃. This is attributed to the different thermal expansion coefficient of the mixture of amorphous and crystalline structures during cooling process. Therefore, this study might contribute to the heat-sink-layer bonded power semiconductor applications by stabilizing the thermal properties at Ga₂O₃/diamond interface.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2001.11a
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• pp.68-68
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• 2001

Thin films of polycrystalline silicon (poly-Si) is a promising material for use in large-area electronic devices. Especially, the poly-Si can be used in high resolution and integrated active-matrix liquid-crystal displays (AMLCDs) and active matrix organic light-emitting diodes (AMOLEDs) because of its high mobility compared to hydrogenated _amorphous silicon (a-Si:H). A number of techniques have been proposed during the past several years to achieve poly-Si on large-area glass substrate. However, the conventional method for fabrication of poly-Si could not apply for glass instead of wafer or quartz substrate. Because the conventional method, low pressure chemical vapor deposition (LPCVD) has a high deposition temperature ($600^{\circ}C-1000^{\circ}C$) and solid phase crystallization (SPC) has a high annealing temperature ($600^{\circ}C-700^{\circ}C$). And also these are required time-consuming processes, which are too long to prevent the thermal damage of corning glass such as bending and fracture. The deposition of silicon thin films on low-cost foreign substrates has recently become a major objective in the search for processes having energy consumption and reaching a better cost evaluation. Hence, combining inexpensive deposition techniques with the growth of crystalline silicon seems to be a straightforward way of ensuring reduced production costs of large-area electronic devices. We have deposited crystalline poly-Si thin films on soda -lime glass and SiOz glass substrate as deposited by PVD at low substrate temperature using high power, magnetron sputtering method. The epitaxial orientation, microstructual characteristics and surface properties of the films were analyzed by TEM, XRD, and AFM. For the electrical characterization of these films, its properties were obtained from the Hall effect measurement by the Van der Pauw measurement.

• Journal of Sensor Science and Technology
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• v.32 no.1
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• pp.10-15
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• 2023

It is well known that polycrystalline ceramics fabricated via the templated grain growth method along a desired crystallographic direction, generally along [001], exhibits enhanced piezoelectric response. Generally, the piezoelectric properties of textured ceramics depend on the degree of texture, as piezoelectric properties peak in single crystals. Therefore, understanding the relationship between the degree of texture and piezoelectric properties is fundamental. Here, we present state-of-the-art textured piezoceramics by focusing on critical issues such as the quality of templates used for texturing and proper evaluation of the degree of texture analysis. The relationship between the degree of texture and its impact on the properties of textured materials is exclusively defined by the Lotgering factor (L.F.) calculated from the X-ray diffraction profiles. Additionally, we show that L.F. is not a suitable indicator of the degree of texture, contrary to previous interpretations. This statement was further supported by the fact that the true degree of texture can be better quantified by the multiples of random distribution. This argument was justified by comparing the quantitative values of the degree of texture obtained from both methods to those of the piezoelectric charge coefficient of textured and random ceramics.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.533-537
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• 2003

Compared to sintered polycrystalline diamond (PCD), the deposited thin film diamond has a great advantage on the fabrication of cutting tools with complex geometries such as drills. Because of high performance in high speed machining non-ferrous difficult-to-cut materials in the field of automobiles industry, aeronautics and astronautics industry, diamond-coated drills find large potentialities in commercial applications. However, the poor adhesion of the diamond film on the substrate and high surface roughness of the drill flute adversely affect the tool lift and machining quality and they become the main technical barriers for the successful development and commercialization of diamond-coated drills. In this paper, diamond thin films were deposited on the commercial WC-Co based drills by the electron aided hot filament chemical vapor deposition (EACVD). A new multiple coating technology based on changing gas pressure in different process stages was developed. The large triangular faceted diamond grains may have great contribution to the adhesive strength between the film and the substrate, and the overlapping ball like blocks consisted of nanometer sized diamond crystals may contribute much to the very low roughness of diamond film. Adhesive strength and quality of diamond film were evaluated by scanning electron microscope (SEM), atomic force microscope (AFM), Raman spectrum and drilling experiments. The ring-block tribological experiments were also conducted and the results revealed that the friction coefficient increased with the surface roughness of the diamond film. From a practical viewpoint, the cutting performances of diamond-coated drills were studied by drilling the SiC particles reinforced aluminum-matrix composite. The good adhesive strength and low surface roughness of flute were proved to be beneficial to the good chip evacuation and the decrease of thrust and consequently led to a prolonged tool lift and an improved machining quality. The wear mechanism of diamond-coated drills is the abrasive mechanical attrition.

• Journal of the Korean Magnetics Society
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• v.2 no.1
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• pp.61-68
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• 1992

Structural, magnetic and magneto-optical(1.0~3.2eV) properties of rare earth (Ce, Pr, Eu), transition metal(Ni, Co), and Al substituted polycrystalline Ba ferrite films grown by rf sputtering have been investigated. TEM studies revealed that crystal grains in the films were reduced in size from several hundred nm to the order of 1 nm with the decrease of rf power density during sputtering. By substituting Al, square hysteresis loops have successfully been obtained. It has been found that Niions strongly enhances Faraday rotation of the films in the visible range. It has been confirmed that Co ions also strongly enhances Faraday rotation of the films in the near infrared. En- hancement in Faraday rotation by Ce, Pr, and Eu ions has not been observed. The origin of the enhancement in magnetic and magneto-optical properties of the films is discussed.

• Journal of the Korean Magnetics Society
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• v.4 no.3
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• pp.214-218
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• 1994

$Y_{3}Fe_{5}O_{12}$ based garnet films(thin or thick) offer a great promise for the application of microwave communication components. We investigated the magnetic and crystallographic preperties of $Y_{3}Fe_{5}O_{12}$ thick films prepared by KrF eximer laser ablation of a stoichiometric garnet target. It was possible to obtain almost epitaxially oriented films on $Al_{2}O_{3}$(1102) plane. Although the crystalline quality depends on substrate temperature and $O_{2}$ partial pressure used($Po_{2}$), 4.1m thick films of $4{\pi}M_{s}=1300$ Gauss and $H_{c}=37.5$ Oe were obtained at the substrate temperature of $700^{\circ}C$ with the $Po_{2}$ of 100 mTorr after annealing the as-deposited films at $700^{\circ}C$ for 2 hours. These films are expected to be used for magnetostatic spin wave filters at narrow bandwidth frequency.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.5A
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• pp.425-431
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• 2010

The phase distribution in a multi-phase material strongly affects its material properties. Therefore, a proper method to describe the phase distribution of a material is needed. In this research, probability distribution functions, two-point correlation and lineal-path functions, are used to represent the probabilistic phase distributions of a material. The probability distribution function is calculated using a numerical method and is described as an analytical form via exponential curve fitting with three parameters. Application of analytical form of probability distribution function is investigated using two-phase polycrystalline solids and soil samples. It is confirmed that the probability distribution functions can be represented as an exponential form using curve fitting which helps identifying the applicability of a representative volume element(RVE).

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.4
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• pp.363-369
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• 1994

Bimuth telluride base thermoelectrics are prepared by AC current applied hot pressing method. It is possible to minimize the defects arising from the vaporization of Te, thanks to the very short processing time compared to the single crystal growing method. The optimum conditions for the AC applied hot pressing of 95 mol% $Bi_2Te_3-5 mol% Bi_2Se_3$ thermoelectrics are sintering at $400^{\circ}C$, for 2 minutes, under 1500 kgf/$\textrm{cm}^2$, with the particle size of $125 to 250 {\mu}m$, range of powder. The resultant Z value (figure of merit) was $2.2{\times}10^{-3}/K$.

• Progress in Superconductivity and Cryogenics
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• v.25 no.2
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• pp.5-9
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• 2023

The effect of La_0.7Sr_0.3MnO₃ (LSMO) addition on the superconducting property of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+δ ((Bi, Pb)-2223) polycrystalline samples was studied. LSMO (0.3 wt.% to 2.0 wt.%) added (Bi, Pb)-2223 samples were prepared by using a solid-state reaction method. The XRD analyses show that as the LSMO addition increases, the volume fraction of the Bi-2223 phase is gradually decreased. The critical temperature (T_c) exhibits a gradual decrease with a single transition as the LSMO amount increases up to 1.0 wt.%, but a further addition of LSMO induces an abrupt decrease of T_c with a dual transition. The analyses on the local structure of the CuO₂ plane from the X-ray absorption fine structure (EXAFS) measurements showed that for the samples with low concentration of LSMO up to 1.0 wt.%, the Cu-O bond length and the CuO₂ plane ordering do not degrade from the values of pure (Bi, Pb)-2223, while they get worsen with a further increase of LSMO addition. These results open up the possibility of LSMO as artificial pinning centers of the (Bi, Pb)-2223 system for power application.

• Advances in nano research
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• v.13 no.4
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• pp.325-339
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• 2022

Endophytes ascertain a symbiotic relationship with plants as promoters of growth, defense mechanism etc. This study is a first report to screen the endophytic population in Waltheria indica, a tropical medicinal plant. 5 bacterial and 3 fungal strains in leaves, 3 bacterial and 1 yeast species in stems were differentiated morphologically and identified by biochemical and molecular methods. The phylogenetic tree of the isolated endophytes was constructed using MEGA X. Silver nanoparticles were biosynthesized from a rare endophytic bacterium Cupriavidus metallidurans isolated from the leaf of W. indica. The formation of silver nanoparticles was confirmed by UV-Visible spectrophotometer that evidenced a strong absorption band at 408.5 nm of UV-Visible range with crystalline nature and average particle size of 16.4 nm by Particle size analyzer. The Fourier Transform Infra-Red spectrum displayed the presence of various functional groups that stabilized the nanoparticles. X-ray diffraction peaks were conferred to face centered cubic structure. Transmission Electron Microscope and Scanning Electron Microscope revealed the spherical-shaped, polycrystalline nature with the presence of elemental silver analyzed by Energy Dispersive of X-Ray spectrum. Selected area electron diffraction also confirmed the orientation of AgNPs at 111, 200, 220, 311 planes similar to X-ray diffraction analysis. The synthesized nanoparticles are evaluated for antimicrobial activity against 7 bacterial and 3 fungal pathogens. A good zone of inhibition was observed against pathogenic bacteria than fungal pathogens. Thus the study could hold a key aspect in drug discovery research and other pharmacological conducts of human clinical conditions.