Seungchan Cho

Dual-nanoparticulate-reinforced aluminum matrix composite materials

Aluminum (Al) matrix composite materials reinforced with carbon nanotubes (CNT) and silicon carbide nanoparticles (nano-SiC) were fabricated by mechanical ball milling, followed by hot-pressing. Nano-SiC was used as an active mixing agent for dispersing the CNTs in the Al powder. The hardness of the produced composites was dramatically increased, up to eight times higher than bulk pure Al, by increasing the amount of nano-SiC particles. A small quantity of aluminum carbide (Al(4)C(3)) was observed by TEM analysis and quantified using x-ray diffraction. The composite with the highest hardness values contained some nanosized Al(4)C(3). Along with the CNT and the nano-SiC, Al(4)C(3) also seemed to play a role in the enhanced hardness of the composites. The high energy milling process seems to lead to a homogeneous dispersion of the high aspect ratio CNTs, and of the nearly spherical nano-SiC particles in the Al matrix. This powder metallurgical approach could also be applied to other nanoreinforced composites, such as ceramics or complex matrix materials.

Effective load transfer by a chromium carbide nanostructure in a multi-walled carbon nanotube/copper matrix composite.

Multi-walled carbon nanotube (MWCNT) reinforced copper (Cu) matrix composites, which exhibit chromium (Cr) carbide nanostructures at the MWCNT/Cu interface, were prepared through a carbide formation using CuCr alloy powder. The fully densified and oriented MWCNTs dispersed throughout the composites were prepared using spark plasma sintering (SPS) followed by hot extrusion. The tensile strengths of the MWCNT/CuCr composites increased with increasing MWCNTs content, while the tensile strength of MWCNT/Cu composite decreased from that of monolithic Cu. The enhanced tensile strength of the MWCNT/CuCr composites is a result of possible load-transfer mechanisms of the interfacial Cr carbide nanostructures. The multi-wall failure of MWCNTs observed in the fracture surface of the MWCNT/CuCr composites indicates an improvement in the load-bearing capacity of the MWCNTs. This result shows that the Cr carbide nanostructures effectively transferred the tensile load to the MWCNTs during fracture through carbide nanostructure formation in the MWCNT/Cu composite.

Barrier Characteristics of ZrN Films Deposited by Remote Plasma-Enhanced Atomic Layer Deposition Using Tetrakis(diethylamino)zirconium Precursor

The barrier characteristics of ZrN films deposited by remote plasma-enhanced atomic layer deposition (PEALD) using Zr[NEt2]4 [tetrakis(diethylamino)zirconium, TDEAZ] and N2 remote plasma have been investigated using various deposition parameters, such as temperature, plasma power, and processing pressure. The optimized processing temperature, plasma power, and pressure were 300 °C, 200 W, and 1 Torr, respectively. ZrN films deposited by remote PEALD using TDEAZ and N2 remote plasma showed a carbon content of about 6 at. %. The resistivity of ZrN films was about 400 µΩcm. The barrier characteristics of Cu/ZrN/Si samples have been investigated by X-ray diffraction (XRD) analysis, Auger electron spectroscopy (AES), and etch-pit test after annealing in vacuum for 1 h in the temperature range of 500–700 °C with an interval of 50 °C. The structure of ZrN films remained amorphous up to 550 °C and crystallized after annealing above 600 °C. The barrier characteristics of ZrN films remained up to 550 °C. ZrN films deposited by remote PEALD are believed to be applicable as barriers for Cu metallization in a semiconductor process.

Electro-magnetic properties of composites with aligned Fe-Co hollow fibers

A novel Fe-Co binary hollow fiber was synthesized by electroless plating using hydrolyzed polyester fiber and its anisotropy characteristic was investigated for electromagnetic wave absorbing materials. The hollow fibers in parallel with magnetic field show higher saturated magnetization of 202 emu/g at the applied magnetic field of 10 kOe and lower coercivity (27.658 Oe), compared with the random and vertical oriented hollow fibers. From complex permittivity measurement, the Fe-Co hollow fiber composites clearly display a single dielectric resonance, located at ∼14 GHz. The Fe-Co hollow fibers not only provide excellent EM properties in GHz frequency ranges, resulting mainly from the strong resonance, but also adjust the soft magnetic properties through fiber alignments. The cavitary structure of the Fe-Co hollow fibers, not only giving rise to a dielectric loss resonance and also adjusting its peak frequency, may be a pathway to useful EM wave absorptive devices in GHz frequency ranges.

Fabrication of CNT dispersed Cu matrix composites by wet mixing and spark plasma sintering process

Multi-walled carbon nanotube (MWCNT)-copper (Cu) composites are successfully fabricated by a combination of a binder-free wet mixing and spark plasma sintering (SPS) process. The SPS is performed under various conditions to investigate optimized processing conditions for minimizing the structural de...

Electromagnetic wave absorbing properties of magnetic particles and carbon nanomaterials reinforced composites

A RAM (Radar Absorbing Materials) composite was prepared based on hybrid fillers containing magnetic loss material with excellent oxidation resistance and high magnetization and dielectric loss material CNF with controllable permittivity and high dispersibility. As the loading of CNF as a dielectric loss filler is increased, the permittivity is increased and the permeability of Co-CNF composites is almost same value for the fixed loading of Co as a magnetic loss filler. Highly dispersed Co and CNF as the hybridized loss materials by the dispersion processes of the homogenizer and three-roll mill enhance the efficiency of the electromagnetic wave absorbing properties. Highly dispersed magnetic particles and CNF as the hybridized loss materials enhance the efficiency of the electromagnetic wave absorbing properties at a thin thickness of 2 mm or less.

Chromium carbide/Carbon Nanotube Hybrid Structure Assisted Copper Composites with Low Temperature Coefficient of Resistance

In order to explore the possibility of using carbon nanotube (CNT) to introduce and control the temperature coefficient of resistance (TCR) of metal matrix composite, relatively thick and short multi-walled CNTs (MWCNTs) were introduced in the metal matrix with in-situ formation of chromium carbide (Cr7C3) at the CNT/copper (Cu) interface. We demonstrate that incompatible properties such as electrical conductivity and TCR can be achieved simultaneously by introducing MWCNTs in the Cu matrix, with control of the interfacial resistivity using the MWCNT/Cr7C3–Cu system. High electrical conductivity of 94.66 IACS and low TCR of 1,451 10–6 °C−1 are achieved in the 5 vol.% MWCNT–CuCr composite. In-situ formation of Cr7C3 nanostructures at the MWCNT/Cu interface by reaction of diffused Cr atoms and amorphous carbon of MWCNTs would assist in improving the electrical properties of the MWCNT–CuCr composites.

Characteristics of Hafnium Oxide Gate Dielectrics Deposited by Remote Plasma-enhanced Atomic Layer Deposition using Oxygen Plasma

Hafnium oxide films were deposited on Si(100) substrates by remote plasma-enhanced atomic layer deposition (PEALD) method at using TEMAH [tetrakis(ethylmethylamino)hafnium] and plasma. films showed a relatively low carbon contamination of about 3 at %. As-deposited and annealed films showed amorphous and randomly oriented polycrystalline structure. respectively. The interfacial layer of films deposited using remote PEALD was Hf silicate and its thickness increased with increasing annealing temperature. The hysteresis of films became lower and the flat band voltages shifted towards the positive direction after annealing. Post-annealing process significantly changed the physical, chemical, and electrical properties of films. films deposited by remote PEALD using TEMAH and plasma showed generally improved film qualities compare to those of the films deposited by conventional ALD.

Characterization of Nickel Composite Plating with TiO 2 Particles for Photolysis of Organic Compound

Many fundamental studies have been carried out regarding waste water and hazardous gas treatment technology using the photolysis effect of . However, photolysis of both organic and organic-inorganic binders immobilizing makes permanent use impossible. In this study we manufactured a catalytic electrode by nickel- composite plating in order to immobilize . The surface properties according to the current density changes of cathode and concentration changes of powder in nickel plating bath has been analysed with EDX, XRF, SEM, Raman spectrometer etc. The characterization of the catalytic electrode in decomposition of organic compound has been obtained by using UV-Visible spectrophotometer through analysing concentration changes of methyl orange solution containing the catalytic electrode vs. time with projecting UV-light in the solution. The study shows that a catalytic electrode of nickel- composite plating with high-efficiency in decompostion of organic compound has been formed under high concentration of powder and low current density of cathode.