Soon Gil Yoon

Green synthesis, characterization and antimicrobial activity of silver nanoparticles using methanolic root extracts of Diospyros sylvatica

The current research study focuses to formulate the biosynthesized silver nanoparticles for the first time from silver acetate using methanolic root extracts of Diospyros sylvatica, a member of family Ebenaceae. TEM analysis revealed the average diameter of Ag NPs around 8nm which is in good agreement with the average crystallite size (10nm) calculated from X-ray Diffraction (XRD) analysis. Further the study has been extended to the antimicrobial activity against test pathogenic Gram (+) ve, Gram (-) ve bacterial and fungal strains. The bioinspired Ag-NP showed promising activity against all the tested bacterial strains and the activity was enhanced with increased dosage levels.

Low Voltage Switching Characteristics of 60 nm Thick SrBi2Ta2 O 9 Thin Films Deposited by Plasma-Enhanced ALD

60 nm thick SrBi 2 Ta 2 O 9 (SBT) thin films were fabricated using plasma-enhanced atomic layer deposition (ALD) with an alternating supply of single cocktail source and oxygen plasma. The linear relationship between the number of cycles and film thickness and a constant deposition rate with source pulse time suggests that a self-limiting process that has distinct characteristics of ALD was achieved. The 60 nm thick SrBi 2 Ta 2 O 9 films that were annealed at 750°C completely crystallized to the layer-structured perovskite phase. The SBT capacitors showed excellent ferroelectric switching properties. Low voltage switching below 1.5 V was achieved successfully in the 60 nm SBT capacitor.

(Bi, La)4Ti3O12 (BLT) thin films grown from nanocrystalline perovskite nuclei for ferroelectric memory devices

Using nanocrystalline perovskite nuclei, (117) oriented-(Bi,La)4Ti3O12(BLT) thin films were grown using a noble bake process for nonvolatile ferroelectric memory devices. The c-axis oriented BLT thin films have a remanent polarization (2Pr) of 8.0μC∕cm2 at a 3V driving voltage, and the (117) oriented films have a 2Pr value of about 25μC∕cm2. The BLT capacitors, grown on a platinum electrode via nanocrystalline perovskite nuclei, had fatigue and imprint free characteristics after applying 1×1011 switching cycles and for ten years at a 125°C stress. The average sensing margin of the (117) oriented BLT thin films was approximately 700mV for a 0.65μm2 cell size and a sufficient signal margin for ten years was indicated, based on the extrapolation of the measured data for high density ferreoelectric random access memory applications.

Self-catalytic growth of indium oxide flower-like nanostructures by nano-cluster deposition (NCD) at low temperature

Flower-shaped indium oxide nanostructures were grown at a low temperature (250 °C) on Si (100) substrates by NCD technique without using metal catalyst. Bud shaped leaf like structures are obtained with lengths and diameters in the range of 150–250 nm and 75–125 nm, respectively, which are compacted into a flower-shaped structure. Transmission electron microscopy and selected area electron diffraction patterns taken on the leaf-like structure show crystalline cubic phase, with preferential orientation along (222) and (400) directions. The composition of indium and oxygen was confirmed from XPS analysis. The room temperature photoluminescence (PL) spectrum of flower-like In2O3 nanostructure shows a blue emission centered around 428 nm under the 383 nm UV excitation, which is mainly attributed to the oxygen vacancy in the In2O3 nano/microstructures. A growth model for the formation mechanism of the self-catalytic growth of flower shaped structure is proposed.

Nonvolatile programmable metallization cell memory switching element based on Ag-doped SbTe solid electrolyte

We report that industrially qualified SbTe chalcogenide film can be applied to programmable metallization cell memory switching device. To fabricate the switching device, Sb35Te65, Ag, and W (top electrode) were consequently sputtered on TiW (bottom electrode)/SiO2∕Si substrate, and Ag diffusion process was not added. During Ag sputtering, it is apparent that Ag is diffused into Sb35Te65 film to form Ag-doped Sb35Te65 solid electrolyte, and that some of the diffused Ag reacts with Te to form Ag–Te bond in the solid electrolyte.

Ferroelectric properties of SrBi2Ta2O9 thin films with Bi2O3 buffer layer by liquid-delivery metalorganic chemical vapor deposition

Ferroelectric SrBi 2 Ta 2 O 9 thin films were deposited on the Bi 2 O 3 buffered Pt/Ti/SiO 2 /Si substrates using liquid-delivery metalorganic chemical vapor deposition. The SBT films with a 5-nm-thick Bi 2 O 3 buffer layer were well crystallized at a deposition temperature of 540 °C, and with increasing annealing temperature, the SBT thin films showed stronger (115) orientation than those without Bi 2 O 3 buffer layer. The value of the remanent polarization of SBT films with Bi 2 O 3 buffer layer were improved significantly in comparison with those for films without a Bi 2 O 3 buffer layer. The remanent polarization (2P r ) and coercive field (E c ) of SBT films without and with a Bi 2 O 3 buffer layer annealed at 750 °C were 11.9 and 20.8 μC/cm 2 , and 57 and 37.8 kV/ cm at an applied voltage of 5 V, respectively.

Carbon nanotube synthesis using magnetic fluids on various substrates

A new carbon nanotube synthesis method using a magnetic fluid is developed. The catalyst particles can be formed by simple spin coating of the magnetic fluid of Fe3O4 nano particles mixed with polyvinyl alcohol on substrates and subsequent heat treatment. A quantitative analysis of the catalyst particles distribution on Si substrate is carried out. The mixing of the magnetic fluid in polyvinyl alcohol gives viscosity to the solution, secures uniform particle distribution without agglomeration, and controls the catalyst particle density on the substrate. The distribution of the catalyst particles is mainly controlled by the NH4OH concentration in the magnetic fluid solutions. Carbon nanotubes grown on various substrates of Si, alumina, and various metal plates revealed different morphologies due to the difference in the wetting of the catalyst particles on the substrate in the various particle-substrate systems.

(YGd)BO3:Eu Phosphor Particles Prepared from the Solution of Polymeric Precursors by Spray Pyrolysis

(YGd)BO3:Eu phosphor particles with spherical-like shape and fine size were prepared by posttreatment of as-prepared particles by spray pyrolysis. In order to improve the morphological characteristics of (YGd)BO3:Eu phosphor particles, the key concept used in this work is the introduction of the esterification reaction between citric acid and ethylene glycol inside liquid droplets. (YGd)BO3:Eu phosphor particles prepared by spray pyrolysis from an aqueous solution exhibited an irregular shape and broad size distribution after posttreatment. On the other hand, the as-prepared particles by spray pyrolysis from the solution with polymeric precursors became (YGd)BO3:Eu phosphor particles with spherical-like shape, micron size and narrow size distribution after posttreatment. In the case of polymeric precursor solution, the particles with regular shape and fine size were obtained by the reformation and recrystallization process during posttreatment of as-prepared particles. The mean size of (YGd)BO3:Eu phosphor particles prepared from polymeric precursors solution was 1.1 µm after posttreatment at 1075°C for 3 h. The photoluminescence intensities of the particles prepared from the solution with and without polymeric precursors were similar to that of the commercial product.

Control of Crystallographic Orientation in Ferroelectric Bi3.15La0.85Ti3 O 12 Thin Films by Rapid Thermal Annealing

Ferroelectric Bi 3 . 1 5 La 0 . 8 5 Ti 3 O 1 2 (BLT) thin films were fabricated on SiO 2 /Si 3 N 4 /SiO 2 substrates by a sol-gel spin coating method. The orientations of the BLT thin films were controlled by an intermediate rapid thermal annealing (RTA) process. The BLT thin films prepared using the RTA process at 500°C and a subsequent furnace annealing at 700°C. It was found that 400 A thin BLT films with one layer coating were partially crystallized at even for a rapid thermal process temperature lower than 500°C. Transmission electron microscopy analysis indicated that c axis oriented nuclei were formed at 500°C RTA and these nuclei function as seeds in the growth of BLT films with an almost perfect c axis orientation during the final furnace annealing stage. The surface morphology of c axis oriented BLT thin films showed smooth and plate-like grains while rod-like shapes were observed in the (117) oriented films.

Whisker Growing Assisted 화학침착 공정으로 제조된 SiC f /SiC 복합체의 파괴거동과 기계강도 평가

SiCf/SiC composites with whiskers and pyrolytic carbon (PyC) coated whiskers in the matrix were fabricated for enhancement of the fracture behaviors by the whisker growing assisted chemical vapor infiltration (WA-CVI) process, respectively. SiC f /SiC composites were also prepared by the conventional CVI process as reference material. The mechanical properties and fracture behaviors were analyzed by comparison of the two types of composites prepared by WA-CVI and conventional CVI. The densities of SiC f /SiC composites were in the range of 2.6~2.65 g/㎤. The flexural strengths of composite with whiskers and with those coated by PyC were 650 ㎫ and 600 ㎫, respectively. The tensile strength of composites with whiskers was ~285 ㎫.