• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.21 no.5
• /
• pp.218-224
• /
• 2011

LAS ($Li_2O-Al_2O_3-SiO_2$) ceramics were sintered by a solid-state reaction. $CaCO_3$ and $ZrO_2$ were added to the ${\beta}$-spodumene ($Li_2O-Al_2O_3-4SiO_2$) composition of the LAS system for enhancement of sintering behavior and mechanical strength, respectively. We have investigated the sintering characteristics, microstructures, mechanical properties and thermal expansion characteristics according to the change of the amount of additive and sintering temperature of the ${\beta}$-spodumene. At 0.1 mol% $CaCO_3$, the densification of ${\beta}$-spodumene was significantly improved. At 0.04 mol% $ZrO_2$, the strength of ${\beta}$-spodumene was also improved. For all the selected all compositions, the thermal expansion coefficient was measured by a dilatometer, which revealed 1.2 to $1.7{\times}10^6/^{\circ}C$.

• Korean Journal of Optics and Photonics
• /
• v.20 no.4
• /
• pp.211-216
• /
• 2009

Much research into two-dimensional (2-D) photonic crystal (PC) structures has been conducted for realization of ultrasmall optical integrated circuits. A 2-D silicon (Si) PC slab structure with air cladding (n=1) is one of the representative structures in 2-D PCs. While air-clad Si PC slab structures have good optical characteristics, their suspension in air can lead to mechanical weakness, making integration with some optical devices difficult. In this paper, we propose improving the mechanical robustness of PC structure by developing a 2-D Si PC structure with symmetric silica cladding (n=1.44) and comparing its optical properties to that of the air-clad structure. First, we investigate the optical properties of a 2-D Si PC slab structure with air cladding by using a 3-D finite difference time domain method. We determined that a photonic bandgap of 330 nm and a non-leaky propagating bandwidth of 100 nm in the optical communication range are possible. Next, we investigate the optical properties of 2-D Si PC slab structures with silica cladding. Even though the refractive index of the silica cladding is higher than that of air, we developed a silica-clad structure with good optical properties: a photonic band gap of approximately 230 nm and a non-leaky propagating bandwidth of 90 nm, comparable to that of the air-clad PC structures.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.7 no.6
• /
• pp.1056-1063
• /
• 2006

Thermal evaporated 10 nm-Ni/l nm-Ir/(or polycrystalline)p-Si(100) and 10 nm-$Ni_{50}Co_{50}$/(or polycrystalline)p-Si(100) films were thermally annealed using rapid thermal annealing fur 40 sec at $300{\sim}1200^{\circ}C$. The annealed bilayer structure developed into Ni(Ir or Co)Si and resulting changes in sheet resistance, microstructure, phase and composition were investigated using a four-point probe, a scanning electron microscopy, a field ion beam, an X-ray diffractometer and an Auger electron spectroscope. The final thickness of Ir- and Co-inserted nickel silicides on single crystal silicon was approximately 20$\sim$40 nm and maintained its sheet resistance below 20 $\Omega$/sq. after the silicidation annealing at $1000^{\circ}C$. The ones on polysilicon had thickness of 20$\sim$55 nm and remained low resistance up to $850^{\circ}C$. A possible reason fur the improved thermal stability of the silicides formed on single crystal silicon substrate is the role of Ir and Co in preventing $NiSi_2$ transformation. Ir and Co also improved thermal stability of silicides formed on polysilicon substrate, but this enhancement was lessened due to the formation of high resistant phases and also a result of silicon mixing during high temperature diffusion. Ir-inserted nickel silicides showed surface roughness below 3 nm, which is appropriate for nano process. In conclusion, the proposed Ir- and Co- inserted nickel silicides may be superior over the conventional nickel monosilicides due to improved thermal stability.

• Journal of Powder Materials
• /
• v.28 no.5
• /
• pp.423-428
• /
• 2021

Here, we report the development of a new and low-cost core-shell structure for lithium-ion battery anodes using silicon waste sludge and the Ti-ion complex. X-ray diffraction (XRD) confirmed the raw waste silicon sludge powder to be pure silicon without other metal impurities and the particle size distribution is measured to be from 200 nm to 3 ㎛ by dynamic light scattering (DLS). As a result of pulverization by a planetary mill, the size of the single crystal according to the Scherrer formula is calculated to be 12.1 nm, but the average particle size of the agglomerate is measured to be 123.6 nm. A Si/TiO₂ core-shell structure is formed using simple Ti complex ions, and the ratio of TiO₂ peaks increased with an increase in the amount of Ti ions. Transmission electron microscopy (TEM) observations revealed that TiO₂ coating on Si nanoparticles results in a Si-TiO₂ core-shell structure. This result is expected to improve the stability and cycle of lithium-ion batteries as anodes.

• Composites Research
• /
• v.29 no.4
• /
• pp.194-202
• /
• 2016

A graphene film, two-dimensional carbon sheet, is a promising material for future electronic devices and so on. In graphene applications, the effect of substrate on the atomic/electronic structures of graphene is significant, so we studied an interaction between graphene film and substrate. To study the effect, we investigated the graphene films grown on Ni substrate with two crystal face of (111) and (100) by Raman spectroscopy, comparing with graphene films transferred on $SiO_2/Si$ substrate. In our study, the doping effect caused by charge transfer from Ni or $SiO_2/Si$ substrate to graphene was not observed. The bonding force between graphene and Ni substrate is stronger than that between graphene and $SiO_2/Si$. The graphene films grown on Ni substrate showed compressive strain and the growth of graphene films is incommensurate with Ni (100) lattice. The position of 2D band of graphene synthesized on Ni (111) and (100) substrate was different, and this result will be studied in the near future.

• Journal of Powder Materials
• /
• v.19 no.6
• /
• pp.442-445
• /
• 2012

The quantum dots (QD) have unique electrical and optical properties due to quantum dot confinement effect. The optical properties of QDs are decided by various synthesis conditions. In a prior QDs study, a study on the QDs size with synthesis condition such as synthesis time and temperature is being extensively researched. However, the research on QDs size with composition ratio has hitherto received scant attention. In order to evaluate the ratio dependence of CdSe crystal, synthesis ratio of Se precursor is changed from 16.7 mol%Se to 44 mol%Se. As the increasing Se ratio, the band gap was increased. This is caused by red shift of emission. We confirmed optical property of CdSe QDs with composition ratio.

• Journal of the Korean Ceramic Society
• /
• v.49 no.6
• /
• pp.642-647
• /
• 2012

$TiO_2$ thin films for a pulse power capacitor were deposited by RF magnetron sputtering. The effects of the deposition gas ratio and thickness on the crystallization and electrical properties of the $TiO_2$ films were investigated. The crystal structure of $TiO_2$ films deposited on Si substrates at room temperature changed to the anatase from the rutile phase with an increase in the oxygen partial pressure. Also, the crystallinity of the $TiO_2$ films was enhanced with an increase in the thickness of the films. However, $TiO_2$ films deposited on a PET substrate showed an amorphous structure, unlike those deposited on a Si substrate. An X-ray photoelectron spectroscopy(XPS) analysis revealed the formation of chemically stable $TiO_2$ films. The dielectric constant of the $TiO_2$ films as a function of the frequency was significantly changed with the thickness of the films. The films showed a dielectric constant of 100~110 at 1 kHz. However, the dissipation factors of the films were relatively high. Films with a thickness of about 1000nm showed a breakdown strength that exceeded 1000 kV/cm.

• Korean Journal of Materials Research
• /
• v.15 no.3
• /
• pp.166-171
• /
• 2005

Fe-6Al-9Si(N) alloy powders were synthesized by hybrid process of chemical nitrification and mechanical milling. The nitriding treatment on Fe-6Al-9Si alloy powders formed $\gamma'-Fe_4N$ phase on the powders surface. The nitriding-treated powders were pulverized by horizontal high-energy ball milling machine. The longer ball milling time tended to reduce the size of alloy powders. In ball milling for 36h, extremely fine powders with about $7\~9wt\%$ nitrogen were obtained. Through X-ray diffraction analysis on the powders, it was found out that the longer milling time caused a disappearance of the crystallinity of $\alpha-Fe$ in the powders. TEM study confirmed that the powders is comprised of a few tens nano-meter sized crystals, including $\alpha-Fe$ phase with partially $\gamma'-Fe_4N$ phase. Hysteresis curves of the synthesized powders measured by VSM revealed lower saturation magnetization and higher coercivity, which seemed to be attributed to nitrogen-impregnation and severe residual stress developed during the high energy milling. Microstructure observation on the powder annealed at 873 K for 1 h showed 10 to 20 nm sized $\alpha-Fe$ crystal. Such a enhanced crystallinity significantly increased the magnetization and decreased the coercivity, which was attributed to not only the crystallinity but also residual stress relaxation.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.08a
• /
• pp.297-297
• /
• 2010

Precise control of the position and density of doping elements at the nanoscale is becoming a central issue for realizing state-of-the-art silicon-based optoelectronic devices. As dimensions are scaled down to take benefits from the quantum confinement effect, however, the presence of interfaces and the nature of materials adjacent to silicon turn out to be important and govern the physical properties. Utilization of visible light is a promising method to overcome the efficiency limit of the crystalline Si solar cells. Si quantum dots (QDs) have been proposed as an emission source of visible light, which is based on the quantum confinement effect. Light emission in the visible wavelength has been reported by controlling the size and density of Si QDs embedded within various types of insulating matrix. For the realization of all-Si QD solar cells with homojunctions, it is prerequisite not only to optimize the impurity doping for both p- and n-type Si QDs, but also to construct p-n homojunctions between them. In this study, XPS and SIMS were used for the development of p-type and n-type Si quantum dot solar cells. The stoichiometry of SiOx layers were controlled by in-situ XPS analysis and the concentration of B and P by SIMS for the activated doping in Si nano structures. Especially, it has been experimentally evidenced that boron atoms in silicon nanostructures confined in SiO2 matrix can segregate into the Si/$SiO_2$ interfaces and the Si bulk forming a distinct bimodal spatial distribution. By performing quantitative analysis and theoretical modelling, it has been found that boron incorporated into the four-fold Si crystal lattice can have electrical activity. Based on these findings, p-type Si quantum dot solar cell with the energy-conversion efficiency of 10.2% was realized from a [B-doped $SiO_{1.2}$(2 nm)/$SiO_2(2\;nm)]^{25}$ superlattice film with a B doping level of $4.0{\times}10^{20}\;atoms/cm^2$.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.24 no.1
• /
• pp.33-40
• /
• 2014

Poly vinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) membrane were prepared by the electrospinning technique. We had applied a DLC coating process and then the surface of the membrane and the contact angle change was investigated. Electrospun fibrous PVdF-HFP membrane surface became to wrinkled shape by Ar plasma treatment and treatment conditions. The wrinkled surface of PVdF-HFP membrane became super-hydrophilic. However, after DLC coating process, it became super-hydrophobic. The resulting surfaces were characterized by water contact angle measurement, X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FE-SEM). Resultantly it was recognized that the wettability characteristics of the membrane surfaces depended on the chemical composition and surface morphology.