Dong-Sun Yoo

Characterization of CdS Nanoparticles Embedded in Polyvinyl Alcohol

CdS nanoparticles embedded in a PVA (polyvinyl alcohol) matrix were prepared and characterized by using cadmium chloride (CdCl2) and sodium sulfide (Na2S). When CdCl2 of various molar concentrations was a mixed with a PVA aqueous solution, the -OH groups in PVA acted as coordinating sites for cadmium ion (Cd 2+ ) aggregations to form PVA-Cd 2+ composites. The CdS nanoparticles embedded in PVA were successfully grown at these sites by dipping PVA-Cd 2+ composites into a solution that contained 0.5 mM of S 2 ions from Na2S. The optical band gaps of the nanoparticles were increased from 2.51 eV to 2.74 eV by decreasing the molar concentration of CdCl2 from 5 mM to 0.5 mM, indicating that the size of the nanoparticles increased with increasing CdCl2 molar concentration. X-ray diraction results showed that the CdS nanoparticles were in a cubic phase while their sizes, estimated to be 4.7 nm, 4.8 nm and 5.9 nm for CdCl2 concentrations of 0.7 mM, 1.0 mM and 3.0 mM, respectively, were almost identical to the values calculated by using BrusOs formula. The PL emission spectra of the CdS nanoparticles formed by 0.7 mM of Cd 2+ showed two peaks, one at 471 nm and the other at 606 nm, which were attributed to the band edge and to surface defects, respectively.

Blocking of metallic impurities in polymer EL Device by PI interlayer

It has been reported that one of the major reasons of the degradation mechanism of EL devices rely greatly on metallic impurity diffusion from ITO. The impurities in MEH-PPV works as a quenching center and degradation initiator. To block impurity diffusion into PPV layer, polyimide thin film which deposited by Ionized Cluster Beam Deposition was inserted between ITO and MEH-PPV. Metallic impurity diffusion from ITO electrode were analyzed by XPS.