Kyu-Man Choi

Ferrate(VI): A green chemical for the oxidation of cyanide in aqueous/waste solutions

The higher oxidation state of iron, i.e. Fe(VI), was employed for the oxidation of the important toxic ion cyanide in aqueous/waste waters. Cyanide was oxidized to cyanate, which is 1,000 times less toxic than cyanide, and can often be accepted for its ultimate disposal. It was noted that Fe(VI) is a very powerful oxidizing agent, and can oxidize most of the cyanide within a few minutes, ca 5 minutes, of contact. The extent of the reduction of Fe(VI) was obtained using the UV-Visible measurements. Further, the UV-Visible data was used to explain the reaction kinetics involved in the redox reaction between ferrate(VI) and cyanide. The pseudo–first-order rate constant was calculated by maintaining the cyanide concentration in excess, with the overall second order rate constant values obtained for initial Fe(VI) concentrations of 1.0 and 0.1 mmol/L. The oxidation of cyanide was again confirmed using a cyanide probe. Fe(VI) was further employed for its possible application in the treatment of industrial wastewaters containing cyanide, along with some heavy metals, such as those obtained from electroplating industries.

Field activated lateral-type polysilicon emitter with extremely high emission current and very low turn-on voltage

A lateral-type poly-Si field emission device was fabricated by utilizing the local oxidation of silicon (LOCOS) process and a simple and efficient activation technique of the tip end was proposed to achieve a high emission current. The fabricated single field emitter exhibits excellent electrical characteristics such as a very low turn-on voltage of 2 V and an extremely high current of ∼500 μA at anode to cathode voltage of 30 V. These superior field emission characteristics are believed to be due to both an increased enhancement factor (β) by appropriate activation and originally sharpened tip by the LOCOS process.

Fabrication and characteristics of lateral type GaN field-emission arrays using metalorganic chemical vapor deposition

Lateral type GaN field-emission diodes were fabricated by metalorganic chemical vapor deposition. In forming the pattern, two kinds of procedures were proposed: a selective etching method with electron cyclotron resonance-reactive ion etching (ECR-RIE) or a simple selective growth utilizing Si3N4 film as the masking layer. The device fabricated using ECR-RIE exhibited electrical characteristics such as a turn-on voltage of 35 V for a 7 μm gap and an emission current of ∼580 nA/10 tips at an anode-to-cathode voltage of 100 V. The field emission characteristics of GaN tips were attributed to the tip structure, low electron affinity and short distance between the cathode and anode tips.

Lateral field emitter arrays with high emission currents and wide operation region by high field activation

A lateral-type polysilicon field emission triode, consisting of two symmetric gate tips aligned by a 70° angle with respect to sharp cathode tips, was fabricated by using the local oxidation of polysilicon process. The fabricated device exhibited a low turn-on voltage of 13 V and an emission anode current of 3.6 μA/tip at VAC=50 V and VGC=open. After high field activation treatment, the turn-on voltage was reduced to 2 V and the emission anode current was increased to 9 μA/tip at the same bias condition. With changing gate bias, the emission current showed three different I–V characteristics; a negative resistance region with large transconductance of 200 μS/50 triodes, a positive resistance region with relatively small transconductance, and a zero transconductance region.

Rapid and efficient removal of boron from deep sea water using synthesized polymer resin

AbstractThe present investigation aims to remove boron from deep sea water using the n-methyl d-glucamine-modified polymeric resin as synthesized in the laboratory. The resins are characterized by IR analysis and the morphology is discussed with the help of scanning electron microscopic images. Further, the resin is distributed in three different bead sizes i.e. 0.25, 0.5 and 1.0 mm, and assessed their removal efficiency for the boron removal under batch and column operations. Batch data show that a very fast uptake of boron took place and within 20 min of contact, almost a complete removal of boron occurred. Further, the kinetics of boron uptake is performed using linear equations of pseudo-first-order and pseudo-second-order rate equations. The applicability of pseudo-second-order rate law inferred that the boron is sorbed onto the solid surface by strong chemical forces, forming an “inner sphere complexes”. The batch and column data obtained for the boron removal is then critically compared with the co...

Characterization of lateral type field emitters with carbon‐based surface layer

Abstract Lateral type poly‐silicon field emitters were fabricated by utilizing the LOCOS (Local Oxidation of Silicon) process. For the implementation of an ideal field emission device with quasi‐zero tunneling barrier, a new and fundamental approach has used conducted by introducing an intelligent carbon‐based thin layer on the cathode tip surface via a field‐assisted self‐aligning of carbon (FASAC) process. Fundamental lowering of the turn‐on field for the electron emission was feasible through the control of both the tip shape and surface barrier height.

Synthesis of TiO2 using sol-gel method and comparison of photocatalytic characteristics

Abstract The aim of the present communication is to compare the physical and chemical properties of TiO2 powder and TiO2 coated thin film particularly the photochemical degradation of pollutants. TiO2 Powder was synthesized by the sol–gel method and was annealed with the temperatures ranging from 300 to 1100°C. TiO2 coating, about 8 μm thin film, was successfully fabricated by the sol–gel dip process on borosilicate glass used as a substrate having a surface area of 100 mm2 and was further annealed at the same temperatures 300–1100°C. TiO2 films and powder which were annealed at 300°C for 2 h have the structure of anatase and the particle phase composition was mainly dependent to the annealing temperature which was found to be changed from amorphous to crystalline anatase and rutile by increasing the temperature. These results were demonstrated based on the X-ray diffraction, SEM and UV–visible spectroscopic data. Further, the photocatalytic characteristics of the synthesized powder and film showed that t...

Lateral field emitter arrays with higher emission currents and wider operation region by high field activation

Lateral-type polysilicon field emission triode, consisting of two symmetric gate tips aligned by an angle of 70/spl deg/ with respect to the sharp cathode tips was fabricated by using local oxidation of polysilicon (LOCOS) process. The fabricated device has the electrical characteristics of a low turn-on voltage of 13 V and the emission anode current of 150 /spl mu/A/50tips at V/sub AC/ = 50 V and V/sub GC/ = open. After high field activation treatment, the turn-on voltage was down to 2 V and the emission current increased up to 525 /spl mu/A/50tips at V/sub AC/ = 50 V and V/sub GC/ = open. Furthermore, the emission current versus gate biases indicated a dramatic change of emission currents from gate tip-end resulting in an interesting operational behavior.