Seol-Ah Lee

Nanoparticle Synthesis and Electrocatalytic Activity of Pt Alloys for Direct Methanol Fuel Cells

A nanoparticle synthesis for naked PtRu, PtMo, PtW, and PtNi alloys of average 1.7 nm is reported. New nanoparticles in this method were examined in the anode electrocatalysis for direct methanol fuel cells (DMFCs). The high activity of Pt alloy electrocatalysts for methanol oxidation was rationalized by the proper alloy formation and surface chemical composition of nanoparticles to satisfy bifunctional and electronic effects, as evidenced by transmission electron microscopy (and energy-dispersive X-ray), X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical methods. The small-sized nanoparticles showed the possibility to help the enhancement of the DMFC unit cell performance.

The Effect of Two-Layer Cathode on the Performance of the Direct Methanol Fuel Cell

To reduce the effect of methanol permeated from the anode, the structure of the cathode was modified from a single layer with Pt black catalyst to two-layer with PtRh black and Pt black catalysts, respectively. The current density of the direct methanol fuel cell (DMFC) using the two-layer cathode was improved to 228 mA/cm-2 compared to that (180 mA/cm-2) of the DMFC using the single layer cathode at 0.3 V and 303 K. From the cyclic voltammograms (CVs), it is indicated that the amount of adsorbates on the metal catalyst in the two-layer cathode is less than that of adsorbates in the single layer cathode after methanol test. In addition, the adsorbates were removed very rapidly by electrochemical oxidation from the two-layer cathode. It is suggested fromex situ X-ray absorption near edge structure analysis that the d-electron vacancy of Pt atom in the two-layer cathode is not changed by the methanol test. Thus, Pt is not covered with the adsorbates, which agrees well with the results of CV.

Infinite Etch Selectivity during Etching of SiON with an Extreme Ultraviolet Resist Pattern in Dual-Frequency Capacitively Coupled Plasmas

We investigated the processing window for the etch selectivity of silicon oxynitride (SiON) layers to extreme ultraviolet (EUV) resists and the variation in line edge roughness of EUV resists during etching of SiON/EUV resist structures in a dual-frequency superimposed capacitively coupled plasma etcher. We varied the processing parameters of the CH 2 F 2 /(CH 2 F 2 + N 2 ) gas flow ratio and low frequency source power (P LF ) in CH 2 F 2 /N 2 /Ar plasma and the O 2 flow rate in CH 2 F 2 /N 2 /O 2 /Ar plasma. The CH 2 F 2 /N 2 flow ratio was found to play a critical role in determining the processing window for infinite etch selectivity of SiON/EUV resists due to disproportionate changes in the degrees of polymerization on SiON and EUV resist surfaces. The preferential chemical reaction between hydrogen and carbon in the hydrofluorocarbon (CH x F y ) polymer layer, and the nitrogen and oxygen in the SiON layer, presumably led to the formation of HCN, CO, and CO 2 etch by-products and resulted in smaller steady-state hydrofluorocarbon thicknesses on SiON. As a result, continuous SiON etching due to enhanced SiF 4 formation occurred while the CH x F y layer was deposited on the EUV resist surface. The critical dimension and line edge roughness increased with increasing CH 2 F 2 /(CH 2 F 2 + N 2 ) flow ratio due to an increased degree of polymerization.