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Enhancement of Dielectric and Ferroelectric Properties of PbZrO3/PbTiO3 Artificial Superlattices
최택집,이재찬 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
PbZrO3 (PZO)/PbTiO3 (PTO) articial superlattices have been grown on La0:5Sr0:5CoO3 (LSCO) (100)/MgO (100) substrate by pulsed laser deposition with various stacking periods from 1 to 100 unit cells. The PZO/PTO articial lattice exhibited a diraction pattern characteristic of a superlattice structure, i.e., a main diraction peak with satellite peaks. The electrical properties of the superlattices were investigated as a function of the stacking period. The dielectric constant and remnant polarization improved on decreasing the stacking periodicity. The dielectric constant of the superlattice reached 800 at a stacking period of 1unit cell/1unit cell (PZO1/PTO1), which is larger than that of the single PZT solid-solution lm. Moreover, the remnant polarization reached a maximum, 2Pr = 38.7 C/cm2, at a 2-unit-cell stacking period. Progressive enhancement of dielectric constant and remnant polarization in articial PZO/PTO superlattice was accompanied by expansion of the (100)-plane spacing on decreasing the stacking periodicity. These results suggest that the lattice strain developed in the PZO/PTO superlattice may have in uence on dielectric constant and ferroelectric behavior.
Growth Mode of La0.5Sr0.5CoO3 Thin Films with Oxygen Pressure on Stepped SrTiO3 Substrates
김주호,이재찬,정철호,Phan Bach Thang,최택집 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
We have studied the growth mode of La0.5Sr0.5CoO3 (LSCO) thin films as a function of oxygen pressure on stepped SrTiO3 substrate by laser molecular beam epitaxy (Laser MBE). The growth behavior and mode of LSCO thin films are sensitive to oxygen ambient during growth. LSCO thin films grown at low oxygen pressures (<10.3 Torr) exhibited a two-dimensional layer-by-layer growth mode at the initial stage, followed by island growth mode within a few tenths of a unit-cell layer. When the ambient oxygen pressure reached 10 mTorr, the LSCO thin films exhibited a well-defined step-and-terrace structure with atomically flat surface roughness close to the SrTiO3 substrate, which suggests that two-dimensional layer-by-layer growth is obtained through the deposition. Further increasing the oxygen pressure degraded the growing surface, resulting in a gradual increase in surface roughness. This result indicates that two-dimensional growth was obtained in a certain degree of ambient oxygen pressure in the growth of oxide thin film whose oxygen nonstoichiometry is susceptible to oxygen ambient.P
강유전체 BiFeO<sub>3</sub>가 증착된 TiO<sub>2</sub> 전극을 이용한 염료감응형 태양전지의 효율 향상
주호용,홍수봉,이호상,전지훈,박배호,홍성철,최택집,Joo, Ho-Yong,Hong, Su Bong,Lee, Hosang,Jeon, Ji Hoon,Park, Bae Ho,Hong, Sung Chul,Choi, Taekjib 한국전기전자재료학회 2013 전기전자재료학회논문지 Vol.26 No.3
Dye-sensitized solar cells (DSSCs) based on titanium dioxide ($TiO_2$) have been extensively studied because of their promising low-cost alternatives to conventional semiconductor based solar cells. DSSCs consist of molecular dye at the interface between a liquid electrolyte and a mesoporous wide-bandgap semiconductor oxide. Most efforts for high conversion efficiencies have focused on dye and liquid electrolytes. However, interface engineering between dye and electrode is also important to reduce recombination and improve efficiency. In this work, for interface engineering, we deposited semiconducting ferroelectric $BiFeO_3$ with bandgap of 2.8 eV on $TiO_2$ nanoparticles and nanotubes. Photovoltaic properties of DSSCs were characterized as a function of thickness of $BiFeO_3$. We showed that ferroelectric $BiFeO_3$-coated $TiO_2$ electrodes enable to increase overall efficiency of DSSCs, which was associated with efficient electron transport due to internal electric field originating from electric polarization. It was suggested that engineering the dye-$TiO_2$ interface using ferroelectric materials as inorganic modifiers can be key parameter for enhanced photovoltaic performance of the cell.
Phan Bach Thang,이재찬,정철호,최택집 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
Current-voltage (I-V) characteristics of 0.2 % Cr-doped SrTiO3 (Cr-STO) thin film in a metalinsulator- metal (MIM), i.e., Pt/Cr-STO/La0.5Sr0.5CoO3, structure were measured, and the electrical conduction was investigated. The I-V characteristics exhibited hysteretic and asymmetric behaviors. The hysteretic behavior is attributed to bistable resistive switching between a highresistance state (HRS) and a low-resistance state (LRS) with voltage polarity. The voltages that induced the resistance switching were above ±3 V. The resistance ratio between the two conduction states was about two orders of magnitude. An analysis of the I-V characteristics revealed that the electrical conduction behavior followed a trap-controlled space-charge-limited current. The trap-filled limit voltage, VTFL, was .1.6 V.
Ferroelectric BiFeO3/TiO2 nanotube heterostructures for enhanced photoelectrochemical performance
이희진,주호용,윤철민,이준봉,이호진,최진식,박배호,최택집 한국물리학회 2017 Current Applied Physics Vol.17 No.5
Ferroelectric based heterostructures have shown great promises in solar water splitting due to unique photoelectrochemical (PEC) properties including polarization-induced charge separation and tunable electrochemical surface reaction. A highly ordered ferroelectric BiFeO3/TiO2 nanotube (TNT) heterostructures were fabricated by anodic oxidation and pulsed laser deposition. The microscopic morphology, optical, and PEC properties of nanostructures were characterized. The BiFeO3/TNT photoelectrode is photoactive under visible light illumination, which exhibits higher photocurrent from greater water oxidation, compared with the pure TNT photoelectrode. The coating thickness of BiFeO3 strongly affected the photoelectrochemical properties. The enhanced PEC performance could be attributed to the effective charge separation and the favorable band bending for water oxidation, originating from ferroelectric polarization-related internal field.