Jongsik Kim

Effect of aging treatment on heavily deformed microstructure of a 6061 aluminum alloy after equal channel angular pressing

Abstract Pre-ECAP solid-solution treatment combined with post-ECAP aging treatment has been found to be more effective than pre-ECAP peak-aging treatment in enhancing the strength of a 6061 Al alloy. An increase of ∼40% in UTS and yield stress was obtained in the post-ECAP aged material compared to the T6 treated commercial 6061 Al alloy.

Control of band gaps of conjugated polymers by copolymerization

Abstract Dihexylfluorenes have been coupled with a chemical unit such as vinylene, phenylene, vinylenephenylene or vinylenealkoxyphenylene to preserve conjugation in the alternating copolymers by employing the reactions of Heck, Suzuki and Wittig. All the copolymers display good photoluminescence (PL) and the PL spectra are broad to show vibronic structures as well as emission of the interchain excitons or excimers, except PDHFPP which shows a sharp PL spectrum. The broad spectra become sharp on dilution in chloroform to 10−5 mol l−1 due to a diminishing effect of the interchain excitons or excimers. The electronic state of polydihexylfluorene with the PL emission peak at 420 nm is changed to a lower-energy state when a vinylene or vinylene-para-phenylene unit is coupled to the alkylfluorene unit. The decrease in the energy state is pronounced when the two alkoxy units are attached to the phenylene unit to show the PL emission peak at 510 nm. However, no change in the electronic energy state is observed when a phenylene, vinylene-meta-phenylene or glycol-capped vinylenephenylene unit is coupled with the dialkylfluorene unit.

Field-emission enhancement from change of printed carbon nanotube morphology by an elastomer

The surface morphology of screen-printed carbon nanotube films was modified by using the poly-dimethylsiloxane (PDMS) elastomer. The entangled carbon nanotube (CNT) bundles were broken up into individual free standing nanotubes to remarkably improve the field-emission characteristics over the as-deposited CNT film. In addition, the cathode film morphology of top-gated triode structures can be treated by using the proposed surface treatment technique, which is a low-cost process.

Improved efficiency of polymer LEDs using electron transporting layer

We report the use of fluorene based copolymers containing quinoline (POF66, P1F66) and pyridine(PFPV) units as electron transporting polymers for multi-layered LEDs. Double-layer device structure combining P1F66 as electron-transporting layer with the emissive MEH-PPV showed a maximum quantum efficiency of 0.03%, which is 30 fold increased compared with ITO/MEHPPV/Al single-layer device. The ETL with the electron deficient moiety improved the LED performance by the characteristics of electron transporting as well as hole blocking between emissive layer and metal cathode.

Rational Selection of Fe2V4O13 over FeVO4 as a Preferred Active Site on Sb-Promoted TiO2 for Catalytic NOX Reduction with NH3

FeVO4 (Fe1) is a particular class of metal vanadate that has recently been highly profiled as an active site to selectively reduce NOX with NH3 (NH3-SCR). This primarily results from NOX/NH3-accessible VO43− anions and an electronic inductive effect between the Fe and V species, leading to the formation of abundant catalytic defects available for NOX turnover. Motivated by a structural inspection of the vanadates reported to date, this study detailed the use of Fe2V4O13 (Fe2) as a novel active site deposited on anatase (TiO2) for NH3-SCR. While providing the aforementioned structural benefits, Fe2/TiO2 also enhanced the redox character as well as the number of sites accessible to NOX/NH3 over Fe1/TiO2 because of the greater electronic inductive effect of Fe2. Therefore, Fe2/TiO2 converted NOX better than Fe1/TiO2 in the presence of H2O. To further improve the NH3-SCR performance of Fe2/TiO2, its catalytic surface was modified via two steps. The first step was to incorporate 1.9 wt% Sb into Fe2/TiO2. Sb could promote the redox feature of Fe2/TiO2 and help its surface to preferentially interact with NH3/NOX, thereby making the resulting Fe2–Sb1.9/TiO2 outperform Fe2/TiO2 during NH3-SCR in the presence of H2O. The second step was to functionalize the Fe2–Sb1.9/TiO2 surface with SO32−/SO42− species. The resulting Fe2–Sb1.9/TiO2 (S) was validated to further increase redox cycling of Fe2–Sb1.9/TiO2, favor NO2 production from NO oxidation for fast NH3-SCR, and hamper surface interplay with SO2. Fe2–Sb1.9/TiO2 (S), therefore, showed higher NOX conversions than a control simulating a commercial catalyst during NH3-SCR feeding H2O and SO2. Fe2–Sb1.9/TiO2 (S) also showed greater durability than the control because of its enhanced resistance to SO2, ammonium (bi)sulfates, and alkali metals.

Micro-architecture embedding ultra-thin interlayer to bond diamond and silicon via direct fusion

The continuous demand on miniaturized electronic circuits bearing high power density illuminates the need to modify the silicon-on-insulator-based chip architecture. This is because of the low thermal conductivity of the few hundred nanometer-thick insulator present between the silicon substrate and active layers. The thick insulator is notorious for releasing the heat generated from the active layers during the operation of devices, leading to degradation in their performance and thus reducing their lifetime. To avoid the heat accumulation, we propose a method to fabricate the silicon-on-diamond (SOD) microstructure featured by an exceptionally thin silicon oxycarbide interlayer (∼3 nm). While exploiting the diamond as an insulator, we employ spark plasma sintering to render the silicon directly fused to the diamond. Notably, this process can manufacture the SOD microarchitecture via a simple/rapid way and incorporates the ultra-thin interlayer for minute thermal resistance. The method invented herein expects to minimize the thermal interfacial resistance of the devices and is thus deemed as a breakthrough appealing to the current chip industry.