N₂와 NH₃ 반응성가스를 사용하여 마그네트론 스퍼터링법으로 제작한 AlN박막의 특성

한창석,Han, Chang-Suk 한국재료학회 2015 한국재료학회지 Vol.25 No.3

Aluminum nitride, a compound semiconductor, has a Wurtzite structure; good material properties such as high thermal conductivity, great electric conductivity, high dielectric breakdown strength, a wide energy band gap (6.2eV), a fast elastic wave speed; and excellent in thermal and chemical stability. Furthermore, the thermal expansion coefficient of the aluminum nitride is similar to those of Si and GaAs. Due to these characteristics, aluminum nitride can be applied to electric packaging components, dielectric materials, SAW (surface acoustic wave) devices, and photoelectric devices. In this study, we surveyed the crystallization and preferred orientation of AlN thin films with an X-ray diffractometer. To fabricate the AlN thin film, we used the magnetron sputtering method with $N_2$, NH3 and Ar. According to an increase in the partial pressures of $N_2$ and $NH_3$, Al was nitrified and deposited onto a substrate in a molecular form. When AlN was fabricated with $N_2$, it showed a c-axis orientation and tended toward a high orientation with an increase in the temperature. On the other hand, when AlN was fabricated with $NH_3$, it showed a-axis orientation. This result is coincident with the proposed mechanism. We fabricated AlN thin films with an a-axis orientation by controlling the sputtering electric power, $NH_3$ pressure, deposition speed, and substrate temperature. According to the proposed mechanism, we also fabricated AlN thin films which demonstrated high a-axis and c-axis orientations.

Characteristic of Microstructure and Mechanical Properties in Ni-Al-Ti Alloy System

한창석,C. H. Bae,J. H. Lee 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.6

A transmission electron microscope (TEM) investigation was performed on the microstructural variations and hardness changes in a Ni-Al-Ti alloy system. The hardness after a solution treatment is high in NiAl- and NiTi-base alloys, suggesting a large contribution of solid solution strengthening in this alloy system. TEM observations revealed that spinodal and binodal types of decomposition occur depending on the chemical composition and aging temperature. However, the degree of age hardening is not large compared to the considerable microstructural variation. The temperature dependence of the compressive yield strength of various NiAl-containing morphologies of Ni2AlTi was also investigated. A transmission electron microscope (TEM) investigation was performed on the microstructural variations and hardness changes in a Ni-Al-Ti alloy system. The hardness after a solution treatment is high in NiAl- and NiTi-base alloys, suggesting a large contribution of solid solution strengthening in this alloy system. TEM observations revealed that spinodal and binodal types of decomposition occur depending on the chemical composition and aging temperature. However, the degree of age hardening is not large compared to the considerable microstructural variation. The temperature dependence of the compressive yield strength of various NiAl-containing morphologies of Ni2AlTi was also investigated.

B2형 금속간화합물 NiTi 중에 L2₁형 Ni₂AlTi상의 석출

한창석,Han, Chang-Suk 한국재료학회 2007 한국재료학회지 Vol.17 No.8

Precipitation behavior has been studied in NiTi-based ordered alloy using transmission electron microscopy. The hardness after solution treatment is high in NiTi alloy suggesting the large contribution of solid solution strengthening in this alloy system. However, the amount of age hardening is not large as compared to the large microstructural variations during aging. At the beginning of aging, the $L2_1-type$ $Ni_2AlTi$ precipitates keep a lattice coherency with the NiTi matrix. By longer periods of aging $Ni_2AlTi$ precipitates lose their coherency and change their morphology to the globular ones surrounded by misfit dislocations. Misfit dislocations, which are observed on {100} planes of H-precipitates have the Burgers vector of a <100> with a pure edge type. The lattice misfits of $NiTi-Ni_2AlTi$ system is estimated from the spacings of misfit dislocations to be 1.3% at 1273 K. The lattice misfits decrease with increasing aging temperature in this system.

TiAl에 석출한 질화물의 결정구조와 형태

한창석,구경완,Han, Chang-Suk,Koo, Kyung-Wan 한국재료학회 2008 한국재료학회지 Vol.18 No.1

The crystal structures and morphologies of precipitates in $L1_0$-ordered TiAl intermetallics containing nitrogen were investigated by transmission electron microscopy (TEM). Under aging at an approximate temperature of 1073 K after quenching from 1423 K, TiAl hardens appreciably due to the nitride precipitation. TEM observations revealed that needle-like precipitates, which lie only in one direction parallel to the [001] axis of the $L1_0$-TiAl matrix, appear in the matrix preferentially at the dislocations. Selected area electron diffraction (SAED) pattern analyses showed that the needle-shaped precipitate is perovskite-type $Ti_3AlN$ (P-phase). The orientation relationship between the P-phase and the $L1_0$-TiAl matrix was found to be $(001)_P//(001)_{TiAl}\;and\;[010]_P//[010]_{TiAl}$. By aging at higher temperatures or for longer periods at 1073 K, plate-like precipitates of $Ti_2AlN$ (H-phase) with a hexagonal structure formed on the {111} planes of the $L1_0$-TiAl matrix. The orientation relationship between the $Ti_2AlN$ and the $L1_0$-TiAl matrix is $(0001)_H//(111)_{TiAl}\;and\;_H//_{TiAl}$.

무전해 코발트계 석출막에 미치는 기판의 영향

한창석,천창환,한승오,Han, Chang-Suk,Chun, Chang-Hwan,Han, Seung-Oh 한국재료학회 2009 한국재료학회지 Vol.19 No.6

The deposition behavior and structural and magnetic properties of electroless Co-B and Co-Fe-B deposits, as well as the amorphous ribbon substrates, were investigated. These Co-based alloy deposits exhibited characteristic polycrystalline structures and surface morphology and magnetic properties that were dependent on the type of amorphous substrates. The catalytic activity sequence of the amorphous ribbon electrodes for anodic oxidation of DMAB was estimated from the current density-potential curve in the anodic partial electrolytic bath that did not contain the metal ions. Both the deposition rate and potential in the initial region were obtained in order of the catalytic activity, depending on the alloy compositions of the substrates. The deposition rate linearly varied against the deposition time. The initial deposition potential may have also determined the structural and magnetic properties of the deposit based on the thickness of ${\mu}m$ order. Furthermore, a basic study of the electroless deposition processes on an amorphous ribbon substrate has been carried out in connection with the structural and magnetic properties of the deposits.

Effect of Annealing on the Structural Properties of AlN Thin Films Containing Co Particles

한창석,Yong Ha Kim 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.1

This paper describes a new approach for preparing AlN thin films containing various Co contents by usinga two-facing targets type sputtering system. The as-deposited films exhibited a variable nature expectedfrom the AlN-rich phase, as well as an amorphous-like phase, depending on the Co content in the films. The films were annealed isothermally at different temperatures and their microstructure, magnetic proper-ties and resistivity were examined. The saturation magnetization of the as-deposited films was quite smalland almost constant, irrespective of the Co content in the films, because Co was not in the crystallinestate. At elevated annealing temperatures, the as-deposited AlN-Co amorphous films crystallized into twophases of AlN and Co. The saturation magnetization and resistivity of the films increased with increasingannealing time and temperature. The coercivity of the films was independent of the annealing time, but itincreased with increasing annealing temperature due to the increase in grain size. A saturation magnetiza-tion, coercivity and resistivity of 360 emu/cm3, ~25 Oe and 2200 µΩ-cm, respectively, were obtained. Fur-ther improvement in the soft magnetic properties might lead to this material being applied as a highdensity magnetic recording head material.

TiO₂ 광촉매를 이용한 공기 정화 시스템 설계에 관한 파라미터 연구

한창석,장혁상 대한환경공학회 2006 대한환경공학회 학술발표논문집 Vol.2006 No.12

Microstructure and Strength of B2-ordered (Ni,Co)Al

한창석 대한금속·재료학회 2008 METALS AND MATERIALS International Vol.14 No.3

A transmission electron microscopy (TEM) investigation of the morphologies and crystal structures of precipitates in supersaturated B2-ordered (Ni,Co)Al has revealed that rod-like precipitates of the (Ni,Co)₂Al phase with a hexagonal structure form parallel to the <111> direction of the B2 matrix. By aging at temperatures below 973 K, a long period superlattice structure of hexagonal (Ni,Co)₂Al was formed. The (Ni,Co)Al hardens appreciably by the precipitation of these phases. An energy dispersive spectroscopy (EDS) was used to analyze the compositions of each phase formed in the B2-(Ni,Co)Al. The effects of the dispersion of the (Ni,Co)₂Al phase on the temperature dependence of the strength of the B2-(Ni,Co)Al have been investigated over a temperature range from 298 K to 1173 K.

The Behavior of α-Cr Precipitation on the High Temperature Deformation of B2-Ordered NiAl

한창석,전창환,한성오 대한금속·재료학회 2009 METALS AND MATERIALS International Vol.15 No.2

Transmission electron microscope investigation has been performed concerning the effect of Cr-precipitation on the mechanical properties of B2-ordered NiAl containing 4 mol.% to 8 mol.% of Cr. By aging at temperatures around 973 K after solution annealing, fine spherical precipitates appeared homogeneously in the NiAl matrix and the alloys hardened appreciably. The selected area electron diffraction patterns have not revealed any additional extra-spots during aging, because the Cr-particles have a cube-cube orientation relationship and keep perfect coherency with the ordered matrix lattice. Dislocations bypass the particles during deformation. Although the dispersion of Cr-particles increases the yield strength of NiAl at intermediate temperature, the strength decreases appreciably at higher temperatures. Atom location by channeling enhanced microanalysis technique has been used to determine the site occupancy of Cr in NiAl. Transmission electron microscope investigation has been performed concerning the effect of Cr-precipitation on the mechanical properties of B2-ordered NiAl containing 4 mol.% to 8 mol.% of Cr. By aging at temperatures around 973 K after solution annealing, fine spherical precipitates appeared homogeneously in the NiAl matrix and the alloys hardened appreciably. The selected area electron diffraction patterns have not revealed any additional extra-spots during aging, because the Cr-particles have a cube-cube orientation relationship and keep perfect coherency with the ordered matrix lattice. Dislocations bypass the particles during deformation. Although the dispersion of Cr-particles increases the yield strength of NiAl at intermediate temperature, the strength decreases appreciably at higher temperatures. Atom location by channeling enhanced microanalysis technique has been used to determine the site occupancy of Cr in NiAl.

Fe 입자를 미세 분산 시킨 AlN 박막의 물리적 성질

한창석,김장우,Han, Chang-Suk,Kim, Jang-Woo 한국재료학회 2011 한국재료학회지 Vol.21 No.1

This paper describes the fabrication of AlN thin films containing iron and iron nitride particles, and the magnetic and electrical properties of such films. Fe-N-Al alloy films were deposited in Ar and $N_2$ mixtures at ambient temperature using Fe/Al composite targets in a two-facing-target DC sputtering system. X-ray diffraction results showed that the Fe-N-Al films were amorphous, and after annealing for 5 h both AlN and bcc-Fe/bct-$FeN_x$ phases appeared. Structure changes in the $FeN_x$ phases were explained in terms of occupied nitrogen atoms. Electron diffraction and transmission electron microscopy observations revealed that iron and iron nitride particles were randomly dispersed in annealed AlN films. The grain size of magnetic particles ranged from 5 to 20 nm in diameter depending on annealing conditions. The saturation magnetization as a function of the annealing time for the $Fe_{55}N_{20}Al_{25}$ films when annealed at 573, 773 and 873 K. At these temperatures, the amount of iron/iron nitride particles increased with increasing annealing time. An increase in the saturation magnetization is explained qualitatively in terms of the amount of such magnetic particles in the film. The resistivity increased monotonously with decreasing Fe content, being consistent with randomly dispersed iron/iron nitride particles in the AlN film. The coercive force was evaluated to be larger than $6.4{\times}10^3Am^{-1}$ (80 Oe). This large value is ascribed to a residual stress restrained in the ferromagnetic particles, which is considered to be related to the present preparation process.