• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.06a
• /
• pp.429-429
• /
• 2008

The structural stability and the elastic modulus of hexagonal ZnO nanowires and nanotubes are investigated using atomistic simulations based on the shell model. The ZnO nanowire with (10-10) facets is energetically more stable than that with (11-20). Our calculations indicate that the structural change of ZnO nanowires with (10-10) facets is sensitive to the diameter. With decreasing the diameter of ZnO nanowires, the unit-cell length is increased while the bond-length is reduced due to the change of surface atoms. Unlike the conventional layered nanotubes, the energetic stability of single crystalline ZnO nanotubes is related to the wall thickness. The potential energy of ZnO nanotubes with fixed outer and inner diameters decreases with increasing wall thickness while the nanotubes with same wall thickness are independent of the outer and inner diameters. The transformation of single crystalline ZnO nanotubes with double layer from wurtzite phase to graphitic suggests the possibility of wall-typed ZnO nanotubes. The size-dependent Young's modulus for ZnO nanowires and nanotubes is also calculated. The diameter and the wall thickness play a significant role in the Young's modulus of single crystalline ZnO nanowires and nanotubes, respectively.

• Proceeding of EDISON Challenge
• /
• 2016.03a
• /
• pp.288-291
• /
• 2016

Recently, there has been a lot of researches related to two-dimensional (2D) materials due to their new properties and applications emerging upon 2D confinement. A new type of graphene like two-dimensional layer material, nitrogenated holey two-dimensional structure C2N-h2D, that is possession of evenly distributed holes and nitrogen atoms with proper bandgap has been synthesized. Previous calculation studies already have shown that the variance of the orbital interaction, band structure of few-layer C2N-h2D suggests that interlayer coupling does play an important role in its electronic properties. In this point, using first-principles density functional theory calculation, we here explore the effect of porous embedded iron atom and iron substrate on encapsulated few layer C2N-h2D. We show the atomic structures and the corresponding electronic structures of Fe@C2N to elucidate the effect of iron. Finally, this study demonstrates that embedded iron C2N has AA-stacking as most favorable stacked structure in contrast to pure C2N. In addition, iron substrate modifies its encapsulated C2N from semi-metallic states to metallic state.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2004.07a
• /
• pp.146-149
• /
• 2004

Porous silicon(PS) as an excellent light diffuser can be used as an antireflection layer without other antireflection coating(ARC) materials. PS layers were obtained by electrochemical etching(ECE) anodization of silicon wafers in hydrofluoric acid/ethanol/de-ionized(DI) water solution($HF/EtOH/H_2O$). This technique is based on the selective removal of Si atoms from the sample surface forming a layer of PS with adjustable optical, electrical, and mechanical properties. A PS layer with optimal ARC characteristics was obtained in charge density (Q) of 5.2 $C/cm^2$. The weighted reflectance is reduced from 33 % to 4 % in the wavelength between 400 and 1000 nm. The weighted reflectance with optimized PS layers is much less than that obtained with a commercial SiNx ARC on a potassium hydroxide(KOH) pre-textured multi-crystalline silicon(mc-Si) surface.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.364-364
• /
• 2010

Defects existing on the clean Si(5 5 12)-$2{\times}1$, composed of one-dimensional(1-D) structures such as honeycomb (H) chain, $\pi$-bonded ($\pi$) chains, dimer-adatom (D-A) row, and tetramer (T) row, have been investigated by scanning tunneling microscopy (STM). It is found that the defects can be classified to two categories: One is originated from phase boundaries in D-A and T rows having $2{\times}$ periodicities, by which buckling directions are reversed, and the other is caused by missing atoms on $\pi$ chains, D-A rows, and T rows. All these defects are symmetric with respect to the [6 6 $\bar{5}$] direction, which is due to one-dimensional symmetry along the [1 $\bar{1}$ 0] direction. Especially it is worth noticing that on H chains none of such defects exist, which implies that the H chain is energetically the most stable among 1-D structures existing on Si(5 5 12)-$2{\times}1$.

• Journal of the Korean institute of surface engineering
• /
• v.31 no.3
• /
• pp.142-150
• /
• 1998

Stainless steel is being used widely for various purposes due to its good corrosion resistance. There has been much research to produce colored stainless steel by several methods such as anodizing and ion plating. In this experiment, we coated TiN(C,O,H)films SUS304 substraate with the DC magnetron spttering system made by Leybold Heraeus and studied the interlater structure and abhesive strength of the films as a function of additional gases, acetylene, hydrogen and oxygen. When the acetylene gas was added into the chamber, the specimen with the interlayer phase had good adhesion due to the toughness of the $\gamma'-Fe_4N$ plase induced from a solid solution of carbon atoms, while low adhesion appeared on the specimen of the non interlayer phase. The formation of the interlayer phase($\gamma'-Fe_4N$) was due to hydrogen embrittlement and internal stress induced by $\gamma'-Fe_4N$ formation in the interlayer. We could fine the interlayer phase ($\gamma'-Fe_4N$) at the interface between the film and the substrate of the TEM image when $\gamma'-Fe_4N$ was detected by the X-ray duffraction metheod.

• Bulletin of the Korean Chemical Society
• /
• v.21 no.10
• /
• pp.953-954
• /
• 2000

The equilibrium geometrical structures of silver atom clusters at their electronic ground states have been theo-retically determined by using the nonrelativistic semiempirical INDO/1 method. The clusters investigated are Agn, Agn+, and Agn- (n = 7 , 8, 9). In order to find the most stable structure, i.e., the global minimum in energy hypersurface, geometry optimization and energy calculation processes have been repeatedly performed for all the possible graphical models by changing the bond parameters (resonance integral values). The heptamers are pentagonal bipyramidal-Ag7(D5h), Ag7+ (D5h), Ag7- (D5h); the octamers are pentagonal bipyramidal with one atom capped-Ag8(D2d), Ag8+ (Cs), Ag8- (D2d); the nonamers are pentagonal bipyramidal with two atoms capped -Ag9(C2v), Ag9+ (C2v), Ag9- (C2v). Our structures are in good agreement with those by ab initio calculations ex-cept for the anionic Ag9- cluster. And it is noted that the INDO/1 method can accurately predict the Ag cluster geometries when a proper set of bond parameters is used.

• Nuclear Engineering and Technology
• /
• v.55 no.8
• /
• pp.2879-2888
• /
• 2023

In fusion environments, large scales of helium (He) atoms are produced by a radical transformation along with structural damage in structural materials, resulting in material swelling and degradation of physical properties. To understand its irradiation effects, this paper investigates the stability, electronic structure, energetics, charge density distribution, PDOS and TDOS, and diffusion processes of He impurities in 6HSiC materials. The formation energy indicates that a stable, favorable position for interstitial He is the HR site with the lowest energy of 2.40 eV. In terms of vacancy, the He atom initially prefers to substitute at pre-existing Si vacancy than C vacancy due to lower substitution energy. The minimum energy paths (MEPs) with migration energy barriers are also calculated for He impurity by interstitial and vacancy-mediated diffusion. Based on its calculated energy barriers, the most possible diffusion path includes the exchange of interstitial and vacancy sites with effective migration energies ranging from 0.101 eV to 1.0 eV. Our calculation provides a better understanding of the stabilization and diffusion behaviors of He impurities in 6H-SiC materials.

• Journal of Korean Vacuum Science & Technology
• /
• v.6 no.3
• /
• pp.133-138
• /
• 2002

The growth of Au films grown on a Si(100)-2x1 surface and Si films on a Ge(100)-2x1 substrate is studied using Positron-annihilation induced Auger Electron Spectroscopy(PAES), Electron induced Auger Electron Spectroscopy(EAES), and Low Energy Electron Diffraction(LEED). Previous work has shown that PAES is almost exclusively sensitive to the top-most atomic layer due to the trapping of positrons in an image potential well just outside the surface before annihilation. This surface specificity is exploited to profile the surface atomic concentrations during the growth of Au on Si(100) and Si on Ge(100) and EAES provides concentrations averaged over the top 3-10 atomic layers simultaneously. The difference in the probe-depth makes us possible to use PAES and EAES in a complementary fashion to estimate the surface and near surface concentration profiles. The results show that (i) the intermixing of Au and Si atoms occurs during the room temperature deposition, (ii) the segregated Ge layer is observed onto the Si layers deposited at 300k. In addition, the prior adsorption of hydrogen prevents the segregation of Ge on top of the deposited Si and that the hydrogen adsorption is useful in growing a thermally stable structure.

• Transactions of the Korean hydrogen and new energy society
• /
• v.10 no.1
• /
• pp.9-17
• /
• 1999

The hydriding and dehydriding kinetics were studied for a Mg-25wt.%Ni mixture which has the most excellent hydrogen-storage characteristics among many mechanically-alloyed mixtures. The hydriding and dehydriding rates were measured and the rate-controlling steps were determined by comparing the hydriding and dehydriding rates with the theoretical rate equations. The rate-controlling step in the hydriding reaction is the Knudsen flow and the ordinary gaseous diffusion of hydrogen molecules through interparticle channels, cracks, etc. in the various ranges of weight percentage of absorbed hydrogen $H_a$ below $H_a$=4.0. In the $H_a$ range 4.0 < $H_a{\leq}4.25$, the diffusion of hydrogen atoms through the growing hydride layer is considered the rate-controlling step. The rate-controlling step in the dehydriding reaction is the Knudsen flow and the ordinary gaseous diffusion of hydrogen molecules for all the ranges of weight percentage of desorbed hydrogen $H_d$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.11a
• /
• pp.124-127
• /
• 2002

LC aligning capabilities and the variation of pretilt angles with ion beam irradiation on the a-C:H thin films, and electro-optical (EO) performances of the ion beam aligned twisted nematic (TN)-liquid crystal display (LCD) with oblique ion beam exposure on the a-C:H thin film were studied. A high pretilt angle of $3.5{^{\circ}}$ via ion beam irradiation on the a-C:H thin film was measured. Also, the LC pretilt angle decreased due to the increase in surface roughness at over 2 min of IB exposure time. It is considered that this roughness increase due to increasing IB exposure time that generated destroy of oriented rings of atoms related to LC alignment. An excellent voltage-transmittance (V-T) curve of the ion beam aligned TN-LCD was observed with oblique ion beam exposure on the a-C:H thin film for 1 min. Also, a faster response time for the ion beam aligned TN-LCD with oblique ion beam exposure on the a-C:H thin film for 1 min can be achieved. Finally, the residual DC property of the ion beam aligned TN-LCD with ion beam exposure of 1 min on the a-C:H thin film is almost same as that of the rubbing aligned TN-LCD on a PI surface.