Hyo-sug Lee

Effects of additional Ce3+ doping on the luminescence of Li2SrSiO4:Eu2+ yellow phosphor

Additional Ce3+ doping improves the luminescence of Li2SrSiO4:Eu2+, a yellow phosphor for ultraviolet or blue light-emitting diodes. By examining the photoluminescence of Li2SrSiO4:Eu2+, Li2SrSiO4:Ce3+, and Li2SrSiO4:Ce3+,Eu2+, it was confirmed that the energy transfer from Ce3+ to Eu2+ ions contributes little to the enhanced luminescence of Li2SrSiO4:Ce3+,Eu2+. Alternatively, we suggested that Ce3+ ions could stabilize the Li vacancies, inhibit the oxidization of Eu2+ to Eu3+, and consequently increase emission intensity, based on the characterizations with decay time and synchrotron light source x-ray absorption measurements. The proposed argument was validated with first principle calculations of the defect formation energies.

One-Dimensional Cyanide-Bridged MnIIIWV Bimetallic Complexes: Metamagnetism, Spontaneous Resolution, and Slow Magnetic Relaxation

The reaction of [W(CN)(6)(bpy)](-) with the corresponding Mn Schiff bases led to the formation of two antiferromagnetic (1) and ferromagnetic (2) chains. The formation of the conglomerate (2) is associated with chiral induction by the enantiomeric chelate-ring conformation of the Mn Schiff base. Modulation of the linking groups in the Mn Schiff bases affects the interchain contacts, causing alteration of the magnetic behaviors from metamagnetism (1) to slow magnetic relaxation (2).

Redox shuttle additives for chemical overcharge protection in lithium ion batteries

We disclosed that a few kinds of aromatic compounds having thianthrene derivatives with acetyl or other functional groups were stable up to about 4.2-4.3 V against lithium. These materials, called redox shuttle, have lately been employed as a chemical overcharge protection agent that consumes the excess current during battery overcharge. They oxidized above 4 V and worked as redox shuttle when introduced into the electrolyte of a Carbon/LiCoO2 prismatic battery within less than one hour rate (1C). We also studied thermal properties of batteries containing the above-mentioned materials with ARC (Accelerating Rate Calorimeter). We ascertained that the current supplied over the full charge was not stored, but instantly and quite completely consumed in an oxidation-reduction reaction.

Robust spin-on glass gap-fill process technology for sub-30nm interlayer dielectrics

A highly robust gap-fill process technology of spin-on glass (SOG) was developed for the interlayer dielectric (ILD) in sub-30nm devices. We revealed that the filling behavior of SOG within gaps during spin-coating is mainly dependent on the capillary effect. The highly wettable surface treatment prior to SOG coating was found to enhance the gap-fill performance remarkably. This technique plays a key role in maximizing capillary effect by raising surface wettability. The filling capability was also improved by optimization of baking temperature to minimize the viscosity of SOG. It was finally found that the defects of contact bridges due to poor filling of SOG were reduced to be almost free by those unique process refinements.

Prediction of Young's Moduli of Low Dielectric Constant Materials by Atomistic Molecular Dynamics Simulation

The interests of low- k dielectric materials to reduce capacitance in multilevel metal interconnects of integrated circuits are well known in the semiconductor industry. Mechanical properties of low- k film are currently the main issues. Improved hardness and modulus are desirable because, when building a multilayered stack and doing sequential processing, films go through chemical mechanical planarization. In this proceeding, we reports the Youngs moduli of the typical low k materials, and the effects of various factors for Youngs moduli of materials, such as, structures of precursors, density, and porosity. Using atomistic molecular dynamics simulation with experimental measurements, the Youngs moduli of films of amorphous silicon oxide in which 25% of Si-O-Si chains were replaced by Si-(CH 3 H 3 C)-Si, Si-CH 2 -Si, Si-(CH 2 ) 2 -Si, Si-(CH 2 ) 3 -Si, Si-(CH 2 ) 4 -Si, Si-(CH 2 ) 6 -Si, were measured and analyzed. The predicted trends of Youngs moduli of films formed by above precursors are in good consistent with those observed from experiments. The Youngs moduli of materials are largely dependent on the densities of materials. Youngs modulus of material increases as the density of the material increases. The chemical properties, chain length, and connectivity of material take effects on the Youngs modulus of material. Given the same densities of material the smaller number of cavities per unit volume the material has, the lower Youngs modulus it shows. Based on the results, the method of predict mechanical properties of materials by the conjunction of basic experimental measurements and atomistic simulation will be discussed.

Channel limitation of 1-D wire random network for transparent conducting electrodes application

1-D wire random network is a promising ITO substitute for flexible transparent conducting electrodes. However, the sheet resistance (Rs) of the 1-D network drastically increases when the network is patterned into narrow channels in electronic applications such as touch screen panel and light emitting diodes. In this work, the undesirable Rs increment of the 1-D wire random network is demonstrated based on Monte Carlo simulation, and critical factors that determine the channel width limitation are investigated. Moreover, aligned wire configuration in the random network is proposed in order to alleviate the constraint on the Rs of the narrow channel.