Chi-Sup Jung

Low Dimensional Electro-optic Properties of Ferroelectric Polymer Films

Department of Laser and Optical Information Technology, Cheongju University, Cheongju 360-764, Korea(Received February 14, 2014; Revised February 23, 2014; Accepted February 25, 2014)Abstract: The electro-optic properties in Langmuir Blodgett films of poly (vinylidene fluoride trifluoroethylene) are investigated in the crossover region between two and three dimensions. The absence of finite size effect is observed in the films thinner than 20 nm, which confirms that these films are two dimensional ferroelectrics. The copolymer LB film of P(VDF-TrFE) exhibits the largest electro-optic response(26 pm/V) at 10 layer thickness. The cross-over behavior of electro-optic effect around the 10 layer thickness was discussed with the formation of nanomesa after thermal annealing. Keywords: Langmuir-Blodgett, P(VDF-TrFE), Ferroelectric, Electro-optic, Finite size effect

Phase Transition Properties of Ferroelectric Polymer Films

Department of Laser and Optical Information Technology, Cheongju University, Cheongju 360-764, Korea(Received December 18, 2013; Revised January 16, 2014; Accepted January 24, 2014)Abstract: Phase transition properties of the copolymer films of polyvinylidene fluoride (PVDF) and trifluoroethylene(TrFE), P(VDF-TrFE), were studied with X-ray diffraction (XRD) and polarization modulated ellipsometry (PME). XRD studies on both Langmuir-Blodgett (LB) films and spin coated films exhibit conversions from ferroelectric phase to paraelectric phase at 108±2℃ on heating and paraelectric phase to ferroelectric phase at 78±2℃ on cooling. The presence of the ferroelectric-paraelectric phase transition is also confirmed by the PME technique for the first time in this study. PME was proved to be a very sensitive tool in the measurement of the structural changes at the nano-thickness films.Keywords: Langmuir-Blodgett, P(VDF-TrFE), Ferroelectric, Phase transition, XRD, Ellipsometry

Fabrication and properties of mechanically grooved silicon solar cells with buried contact Cu electrode

Mechanically grooved silicon solar cells with buried contact copper electrode were attempted. In order to groove a simple mechanical grooving system was home-made, in which synchronous motors in hard disc driver (HDD), audio amplifier, signal generator were used. For the anti-reflection films sputtering condition for SiNx films was optimized. With increasing input power, pressure, index of refraction of the films increased so that a very low etching rate of 0.8 nm/min could be achieved with a condition of Ar and N2 flow rate of 5 SCCM, input power of 300 W and sputtering pressure of 1 × 10-2 torr. Annealing condition for the formation of nickel silicie from electroless plated Ni-P layer was optimized as well as plating condition of copper electrode. However, the conversion efficiency of the BCSC in this study is 3.6% which is unexpectedly small. It seems that the reason for the low efficiency is due to short circuit forming in the lancet of the pyramid.

Properties of Si/SiOx quantum well structure for solar cells applications

The SiOx/Si quantum wells (QWs) structures were fabricated by using the successive deposition technique, as quantum confinement device to increase the effective energy bandgap and passivation effect in Si surface for the third generation solar cell applications. In Si/SiOx QWs, the thicknesses of Si layers and SiOx layers were varied between 1 to 5 nm, respectively. The roughness of sputter-deposited Si on SiOx was less than 4 Å in the thickness of 2 nm. By using the SiOx/Si QW structures on Si surfaces, the lifetime measured by u-PCD technique increased as a result of passivated surface effects. The tunneling phenomena and good interface properties were observed in the fabricated QWs structures.

The Relaxation of Nonlinear Optical Properties in a Poled Polymer

Laser and Optical Information Engineering, Cheongju Uninersity, Cheongju 360-764, Korea(Received April 26, 2010; Revised May 14, 2010; Accepted May 23, 2010)Abstract: The relaxation behavior of aligned electric dipoles in a mixed polymer of P2ANS with P(VDF-TrFE) is studied with optical second harmonic generation (SHG). In this work, a macroscopic noncentrosymmetry of the spin coated film was achieved by an electrical poling. The relaxation of induced polar order of nonlinear optic(NLO) chromophores after poling leads to an insufficient long-term stability of NLO properties. In this work, we develop a new technique to suppress such kind of dipole relaxation in a poled polymer. We found that the poled dipoles in a NLO polymer were effectively immobilized by the internal electric field created by a thermally annealed ferroelectric polymer. The long-term stability in a mixed system of NLO polymer/ferroelectric polymer was successively accomplished by a series of thermal treatments applied to the mixed polymer system at a temperature of 140℃ for at least 1hour after poling. Keywords: Dipole relaxation, P(VDF-TrFE), SHG, NLO, Polymer

Structural Properties of P(VDF-TrFE) LB Films

We report the studies on the structrural properties of Langmuir Blodgett (LB) films fabricated from the copolymer of vinylidenefluoride (VDF) with trifluoroethylene(TrFE). The formation of nanomesas induced by thermal annealing at for 1 hour was investigated with the atomic force microscope (AFM) and the X-ray diffractometer (XRD). From the result of surface morphology change in 30 monolayer LB film, we find that the annealing treatment on the P(VDF-TrFE) LB film result in the plastic deformation of crystalline polymer. The phase crytalline structure in annealed LB film was clearly confirmed from the XRD peak at .

The Surface Morphology of Polymer Langmuir Film

The Langmuir monolayers of polyamic acid salts with three kinds of alkyl chains have been investigated by means of conventional -A isotherms and second harmonic generation measurements proposed in this paper. The surface molecular density dependence of second harmonic intensity clearly shows the region of aggregation while corresponding -A isotherm doesn`t show any changes in the surface morphology at the same region. The surface morphology analysis based on the second harmonic measurement was consistent with the Brewster angle microscope measurement results.