• Carbon letters
• /
• v.21
• /
• pp.16-22
• /
• 2017

Cobalt was electrodeposited onto chemical vapor deposition (CVD) graphene/Si/$SiO_2$ substrates, during different time intervals, using an electrolyte solution containing a low concentration of cobalt sulfate. The intention was to investigate the details of the deposition process (and the dissolution process) and the resulting magnetic properties of the Co deposits on graphene. During and after electrodeposition, in-situ magnetic measurements were performed using an (AGFM). These were followed by ex situ morphological analysis of the samples with ${\Delta}t_{DEP}$ 30 and 100 s by atomic force microscopy in the non-contact mode on pristine CVD graphene/$SiO_2$/Si. We demonstrate that it is possible to electrodeposit Co onto graphene, and that in-situ magnetic measurements can also help in understanding details of the deposition process itself. The results show that the Co deposits are ferromagnetic with decreasing coercivity ($H_C$) and demonstrate increasing magnetization on saturation ($M_{SAT}$) and electric signal proportional to remanence ($M_r$), as a function of the amount of the electrodeposited Co. It was also found that, after the end of the dissolution process, a certain amount of cobalt remains on the graphene in oxide form (this was confirmed by X-ray photoelectron spectroscopy), as suggested by the magnetic measurements. This oxide tends to exhibit a limited asymptotic amount when cycling through the deposition/dissolution process for increasing deposition times, possibly indicating that the oxidation process is similar to the graphene surface chemistry.

• Korean Journal of Materials Research
• /
• v.28 no.1
• /
• pp.6-11
• /
• 2018

There are various manufacturing processes for pure $SiO_2$ that is used as abrasives, chemicals, filters, and glasses, and in metallurgy and optical industries. In the optical fiber industry, to produce $SiO_2$ preform, $SiCl_4$ is utilized as a raw material. However, the combustion reaction of $SiCl_4$ has caused critical environmental issues, such as ozone deficiency by chlorine compounds, the greenhouse effect by carbon dioxide and corrosive gas such as hydrochloric acid. Thus, finding an alternative source that does not have those environmental issues is important for the future. Octamethylcyclotetrasiloxane (OMCTS or D4) as a chlorine free source is recently promising candidate for the $SiO_2$ preform formation. In this study, we first conducted a vaporizer design to vaporize the OMCTS. The vaporizer for the OMCTS vaporization was produced on the basis of the results of the vaporizer design. The size of the primary particle of the $SiO_2$ formed by OMCTS was less than 100 nm. X-ray diffraction patterns of the $SiO_2$ indicated an amorphous phase. Fourier-transform infrared spectroscopy analysis revealed the Si-O-Si bond without the -OH group.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.25 no.5B
• /
• pp.985-991
• /
• 2000

In this paper, the optimum structure of 2GHz magnetic thin film planar inductor were designed and fabricated to reduce the inductor area and to maximize the inductance L and quality factor Q of the inductor. The optimum design was performed utilizing Co90Fe10 layer multilayered with SiO2 layers to avoid the eddy-current skin effect and considering new lumped element model. New magnetic thin film inductors operating at 2GHz were fabricated on a Si substrate utilizing photo-lithography and lift-off techniques. The frequency characteristics of L, Q, and impedance in more than fifty identical inductors were measured using an RF Impedance Analyzer(HP4291B with HP16193A test fixture). The self-resonant frequencies(SRF) of the inductors were measured by a Vector Network Analyzer(HP8510). The developed inductors have SRF of 1.8 to 2.3GHz, L of 47 to 68nH, and Q of 70 to 80 near 1GHz. Finally, high frequency, high performance, planar micro-inductor(area=30.8 x 30.8il$^2$) with maximized L and Q were fabricated succefully.

• Journal of the Korean Ceramic Society
• /
• v.50 no.6
• /
• pp.485-488
• /
• 2013

A SiC-$CeO_2$ composite membrane was successfully fabricated using an ally-hydridopolycarbosilane (AHPCS) binder and treated by dip-coating at 60 times with a $CeO_2$ sol solution. The dip-coated SiC membrane was calcined at 773 K and then sintered at 1173 K under an air atmosphere. The coated membrane was characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and a BET surface analysis. The difference in permeation performance between $H_2$ and CO gases was measured by varying the temperature. The permeation flux of $H_2$ on the SiC membrane with layered $CeO_2$ was obtained as $8.45{\times}10^{-6}\;mol/m^2sPa$ at room temperature. The CO permeation flux was $2.64{\times}10^{-6}\;mol/m^2sPa$ at room temperature. The reaction enthalpy (${\Delta}H^{\circ}$) for the hydrogen permeation process was calculated as -7.82 J/mol by Arrhenius plots.

• Journal of Adhesion and Interface
• /
• v.7 no.4
• /
• pp.32-38
• /
• 2006

A series of organic-inorganic hybrids, PCL/EP/$SiO_2$, involving epoxy resin and triethoxysilane-terminated polycaprolactone elastomer (PCL-TESi) were prepared via polymerization of diglycidyl ether of bisphenol A (DGEBA) with amine curing agent KB-2 and sol-gel process of PCL-TESi. The curing reactions were started from the initially homogeneous mixture of DGEBA, KB-2 and the PCL-TESi. The organicinorganic hybrids containing up to 4.95% (wt) of $SiO_2$ were obtained and characterized by FT-IR, transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). It was experimentally shown that the swelling property in toluene, morphologies and thermal properties of the resulting hybrids were quite dependent on the contents of $SiO_2$. The crosslink network density decreases with increasing of the PCL-TESi. And in TEM, the phase separated morphology of these hybrids was found, which resulted from the coagulation of Si-O-Si networks resulting from $-Si(OC_2H_5)_3$ of PCL-TESi self-curing by hydrolytic silanol condensation, with the advancement of the curing reaction in the modified epoxy resin systems. Meanwhile, the change of the $SiO_2$ content made the morphologies changed from aggregated particles of Si-O-Si in the hybrid to nanocluster of interconnected Si-O-Si particles, then to aggregated Si-O-Si dispersing in the continuous cured epoxy phase again, and last to co-continuous interpenetrating network. The glass transition behavior of the hybrid material was cooperative motion of large chain segments, which were hindered by the inorganic Si-O-Si network. And in TG analysis, the characteristic temperature at 5% of weight loss was evidently increased from $120.5^{\circ}C$ of pure cured epoxy to $277.6^{\circ}C$ of 3.84% (wt) of $SiO_2$ modified epoxy due to the existence of Si-O-Si when PCL-TESi was added in the hybrid.

• Journal of Magnetics
• /
• v.19 no.3
• /
• pp.227-231
• /
• 2014

We fabricated textured polycrystalline $CoFe_2O_4$ thin films on $Pt(111)/TiO_2/SiO_2/Si$ substrate through a sol-gel method. We varied the thickness of the films, by using precursor solutions with different concentrations of 0.1, 0.2, and 0.3 M, and by depositing 5, 8, or 10 layers on the substrate by spin-coating. X-ray diffraction spectra indicated that when the precursor concentration of the solution was higher than 0.1 M, the spin-coated films were preferentially oriented in the <111> direction. Inspection of the surface morphology by scanning electron microscopy revealed that $CoFe_2O_4$ thin films prepared with 0.2 M solution and 5-time spin-coatings had smoother surface, as compared to the other conditions. Each coating had an average thickness of about 50 nm. The magnetic properties measured by vibrating sample magnetometer showed magnetic anisotropy, as evidenced from the difference in the in-plane and out-of-plane hysteresis loops, which we attributed to the textured orientation of the $CoFe_2O_4$ thin films.

• Journal of Magnetics
• /
• v.8 no.3
• /
• pp.118-120
• /
• 2003

As an alternative promising way of producing high coercivity Sr-ferrite for a permanent magnet application, intensive mechanical milling process was applied to the raw materials of the Sr-ferrite with different composition. Synthesising reactivity for the Sr-ferrite of the mechanically milled raw material containing $SrCO_3$, $La_2O_3$, $Fe_2O_3$, $Co_3O_4$, and $SiO_2$ was inferior to that of the raw material containing $SrCO_3$ and $Fe_2O_3$, The Sr-ferrite prepared from mechanically milled raw materials had profoundly improved magnetic properties compared to the Sr-ferrite prepared by conventional method. Beneficial effect of the substituting ($La_2O_3$, $Co_3O_4$) and additive ($SiO_2$) oxides for improving the magnetic properties was not exploited in the Sr-ferrite prepared from the mechanically milled raw material. The Sr-ferrite powder prepared from the mechanically milled raw materials was magnetically isotropic in nature.

• Korean Journal of Materials Research
• /
• v.24 no.2
• /
• pp.81-86
• /
• 2014

The nitrogen solubility and nitride capacity of $CaO-SiO_2-Al_2O_3-MgO-CaF_2$ slag systems were measured by using gas-liquid equilibration at 1773K. The nitrogen solubility of this slag system decreased with increasing CO partial pressure, with the linear relationship between nitrogen contents and oxygen partial pressure being -3/4. This system was expected to show two types of nitride solution behavior. First, the nitrogen solubility decreased to a minimum value and then increased with the increase of CaO contents. These mechanisms were explained by considering that nitrogen can dissolve into slags as "free nitride" at high basicities and as "incorporated nitride" within the network at low basicities. Also, the basicity of slag and nitride capacity were explained by using optical basicity. The nitrogen contents exhibited temperature dependence, showing an increase in nitrogen contents with increasing temperature.

• Korean Journal of Materials Research
• /
• v.13 no.11
• /
• pp.737-741
• /
• 2003

Polycrystalline $Ti_{l-x}$ $Co_{x}$ $O_2$thin films on $SiO_2$ (200 nm)/Si (100) substrates were prepared using liquid-delivery metalorganic chemical vapor deposition. Microstructures and ferromagnetic properties were investigated as a function of doped Co concentration. Ferromagnetic behaviors of polycrystalline films were observed at room temperature, and the magnetic and structural properties strongly depended on the Co distribution, which varied widely with doped Co concentration. The annealed $Ti_{l-x}$ $Co_{x}$ $O_2$thin films with $x\leq$0.05 showed a homogeneous structure without any clusters, and pure ferromagnetic properties of thin films are only attributed to the X$l-x_{l-x}$ $Co_{x}$X$O_2$phases. On the other hand, in case of thin films above x = 0.05, Co-rich clusters formed in a homogeneous $Ti_{l-x}$ $Co_{x}$ $O_2$phase, and the overall ferromagnetic (FM) properties depended on both FMTCO and FMCo. Co-rich clusters with about 10-150 nm size decreased the value of Mr (the remanent magnetization) and increased the saturation magnetic field.

• Journal of Surface Science and Engineering
• /
• v.37 no.6
• /
• pp.319-325
• /
• 2004

Fe thin films containing Si particles were prepared on metallic substrates by electrodeposition method in sulfate solutions and the content of codeposited Si particles in the films was investigated as a function of applied current density, the content of Si particels in the solution, solution pH, solution temperature and concentration of $FeSO_4$$7H_2$O in the solution. The amount of Si codeposited in the film was not dependent on the applied current density, solution pH and solution temperature, while it was dependent on the content of Si particles in the solution and the concentration of $FeSO_4$$7H_2$O in the solution. The amount of Si codeposited in the film increased with increasing content of Si particles in the solution but reached a maximum value of about 6 wt% when the content of Si particles in the solution exceeds 100 g/l. On the other hand, the content of Si codeposited in the film increased up to about 17 wt% with decreasing concentration of $FeSO_4$$7H_2$O in the solution. These results would be applied to the fabrication of very thin Fe-6.5 wt% Si sheets for electrical applications.