23 research outputs found
Empirical study on the location patterns of retail trade adjacent to large-scale discount store
νμλ
Όλ¬Έ (μμ¬)-- μμΈλνκ΅ λνμ : 건μ€ν경곡νλΆ, 2011.2. μ 창무.Maste
A ν΄λμ€ μ€νΌμ€λΉλ© μμ₯μ κΈλ‘λ² κ²½μλ ₯ : λ€μ΄μλͺ¬λ λͺ¨λΈμ μ΄μ©ν μμΈ, λμΏ, ν콩, μ±κ°ν¬λ₯΄ μμ₯μ λΉκ΅λΆμ
νμλ
Όλ¬Έ(μμ¬) --μμΈλνκ΅ κ΅μ λνμ :κ΅μ νκ³Ό(κ΅μ ν΅μμ 곡),2009.8.Maste
Polarization Switching Kinetics in Ferroelastic BiFeO3 Films
Multiferroic BiFeO3 (BFO) has recently attracted plenty of interest due to the coexistence of robust room-temperature ferroelectricity and antiferromagnetism. Understanding the effect of various disorders (e.g., strain and defects) is of great significance for device application of BFO thin films. In BFO, which has strong coupling between ferroelectic polarization and ferroelastic domain, the crystallographic structure is susceptible to strain. At the ferroelastic boundaries accompanying structural distortion, the presence of impurity phase or misfit dislocation has been reported. Additionally, point defects are easily created during the film deposition because of the volatility of Bi ion. There have been recent reports on how such disorders affect intriguing static material properties in BFO films. But, the detailed investigation of dynamic properties has been rare.
The control of domain walls in ferroic materials is currently an important issue for the potential application of domain wall motion to microelectronic devices. It has been recently proposed that the controlled movement of domain walls in magnetic nanowires can be utilized for nonvolatile racetrack memory of high performance. In addition, domain wall-induced conductivity modulation in a BFO thin film was reported, providing a basis for new device concepts using the ferroelectric domain walls. These domain wall devices require precise control of motion as well as location of the domain walls. We report on the directional growth of ferroelectric domains in a multiferroic BFO thin film, which was epitaxially grown on a vicinal (001) SrTiO3 (STO) substrate. A detailed structural analysis of the film shows that a strain gradient, which can cause a symmetry breaking in ferroelectric double-well potential, causes ferroelectric domains to grow with preferred directionality under an electric field. Our results reveal the possibility of controlling the direction of domain growth using an electric field by imposing constraints on ferroelectric films, such as a strain gradient.
In epitaxial BFO(111) capacitors with disordered top and well-ordered bottom interfaces, we report intriguing switching-polarity dependence in the polarization reversal. Ferroelectric coercive voltages and polarization switching behaviors in BFO(111) capacitors are quite different for the polarity of applied electric bias. Piezoresponse force microscopy revealed that the ferroelectric domain evolution is governed either by nucleation or by domain wall motion depending on the direction of external electric field. The polarity dependence of ferroelectric switching kinetics is attributed to asymmetric local internal fields near the film/electrode interfaces. It is probably due to differences in various disorders by structural relaxation such as defects, elastic strain, and surface roughness.
In Bi-deficient BFO films, we show a reversible change of ferroelectric hysteresis under voltage stress. Surprisingly, for negative voltage stress, pristine hysteresis loops were shrunk with the decrease of remnant polarization and coercive voltage. For positive recovery bias, the shrunk hysteresis loops in stressed states were recovered to the original those. Upward polarization switching under negative voltage stress is explained by defect-mediated domain nucleation and thermally-activated domain wall motion. It is highly likely that pinning of the switched upward domains is attributed to a charge trapping process of injected carrier at domain walls, resulting in hysteresis contraction. The charge-trapped domain walls might be responsible for the transient behavior of current density.
The better understanding of disorder effects in ferroelectric domain switching dynamics plays a crucial role for device application of BFO thin films.
Keywords: thin film, ferroelectric, ferroelastic, BiFeO3, polarization switching kinetics, domain wall, strain, defect, hysteresis.
Student number: 2006-20324μ΅κ·Ό BiFeO3 (BFO)λ μμ¨ κ°μ μ μ±κ³Ό λ°κ°μμ±μ 곡쑴μΌλ‘ μΈν΄ λ§μ κ΄μ¬μ λ°κ³ μλ λ€κ°μ²΄ λ¬Όμ§μ΄λ€. κ·Έλ¬ν BFOμμ μλ ₯μ΄λ κ²°ν¨κ³Ό κ°μ 무μ§μ μμλ€μ΄ μ΄λ ν μν₯μ λΌμΉλ μ§λ₯Ό μ΄ν΄νλ κ²μ BFO λ°λ§μ μμ μμ©μ μν΄ λ§€μ° μ€μνλ€. μ€μ λ‘, BFO λ΄μ κ°μ μ μ± λΆκ·Ήκ³Ό κ°νμ± κ΅¬μ‘° μ¬μ΄μ κ°ν κ²°ν©μΌλ‘ μΈν΄ κ·Έ κ²°μ ꡬ쑰λ μλ ₯μ λ§€μ° λ―Όκ°νλ€. μ΄λ―Έ ꡬ쑰μ λΉλ€μ΄μ§μ λλ°νλ κ°νμ± κ²½κ³μμ λΆμλ¬Ό μμ΄λ 격μ μ΄κΈλ¨μ μ‘΄μ¬κ° λ³΄κ³ λμλ€. λν, BFO λ°λ§ μ¦μ°© μ€μλ λΉμ€λ¬΄μ€ μ΄μ¨μ νλ°μ± λλ¬Έμ μ κ²°ν¨λ€μ΄ μ½κ² μμ±λλ€. μ΅κ·Ό, μ΄λ¬ν 무μ§μ μμλ€μ΄ BFO λ°λ§ λ΄μ μ μ μΈ λ¬Όμ±μ μ΄λ»κ² μν₯μ λΌμΉλ μ§μ λν λ§μ λ³΄κ³ λ€μ΄ μμ΄μλ€. νμ§λ§, λμ μΈ νΉμ±μ λν μμΈν μ‘°μ¬λ λ§€μ° λλ¬Όμλ€.
κ°μ μ λλ κ°μμ± λ¬Όμ§λ€μμ ꡬμλ²½μ μ‘°μ νλ κ²μ ꡬμλ²½ μ΄λμ μ΄μ©ν μλ‘μ΄ λ§μ΄ν¬λ‘ μμ κ°λ°μ μν΄ λ§€μ° μ€μν μ΄μμ΄λ€. μ΅κ·Ό, μμ±μ²΄ λλ
Έμ μμ ꡬμλ²½ μ΄λμ μ‘°μ ν¨μΌλ‘μ¨ μλ‘μ΄ ννμ κ³ μ±λ₯ λΉνλ°μ± μꡬ벽 λ©λͺ¨λ¦¬ (μ¦, racetrack λ©λͺ¨λ¦¬)κ° μ μλμλ€. λν, BFO λ°λ§μμλ ν₯λ―Έλ‘μ΄ κ΅¬μλ²½ μ λμ±μ΄ λ°κ²¬λμλ€. κ·Έλ¬ν ꡬμλ²½ μ λμ±μ κ°μ μ ꡬμλ²½μ μ΄μ©ν μ κ°λ
μμ κ°λ°μ μν κΈ°μ΄κ° λμλ€. μ΄λ¬ν ꡬμλ²½ μμμ κ°λ°μ μν΄μλ ꡬμλ²½μ μ΄λ λΏλ§ μλλΌ μμΉκΉμ§ μ νν μ‘°μ νλ κ²μ΄ λ§€μ° μ€μνλ€. μ¬κΈ°μ, μ°λ¦¬λ κ²½μ¬μ§ SrTiO3 (STO) κΈ°ν μμ μ¦μ°©λ BFO λ°λ§μμ κ°μ μ ꡬμμ΄ μ΄λ€ λ°©ν₯μ±μ κ°μ§κ³ μ±μ₯νλ κ²μ λ³΄κ³ νλ€. μμΈν ꡬ쑰μ μΈ λΆμμ ν΅ν΄ μ°λ¦¬λ BFO λ°λ§ λ΄ μλ ₯ gradientκ° μ‘΄μ¬νλ κ²μ λ°κ²¬νμλ€. κ·Έλ¬ν μλ ₯ gradientλ κ°μ μ μμ°λ¬Ό ν¬ν
μ
μ λμΉμ±μ κΉ¨λ¨λ¦¬κ³ , κ°μ μ ꡬμλ€μ΄ μΈλΆ μ κΈ°μ₯ νμμ νΉμ λ°©ν₯μ μ νΈνλ©΄μ μ±μ₯νλλ‘ νλ€. μ΄ κ²°κ³Όλ κ°μ μ 체 λ°λ§μμ μλ ₯ gradientλ₯Ό ν΅ν ꡬμ μ±μ₯μ λ°©ν₯μ±μ μ κΈ°μ μΌλ‘ μ‘°μ κ°λ₯νλ€λ κ²μ 보μ¬μ€λ€.
무μ§μν μλΆ κ³λ©΄κ³Ό 무μ§μνμ§ μμ νλΆ κ³λ©΄μ κ°μ§ μΌμμ BFO(111) μΊν¨μν°μμ μ°λ¦¬λ κ°μ μ λΆκ·Ή λ°μ μ΄ κ·Ήμ± μμ‘΄μ±μ λ³΄κ³ νλ€. μ¬κΈ°μμλ, κ°μ μ coercivityμ λΆκ·Ή λ°μ μ΄ κ°ν΄μ€ λ°μ΄μ΄μ€μ κ·Ήμ±μ λ°λΌ λ§€μ° λ€λ₯΄λ€. μμ κ°μ ν νλ―Έκ²½μ κ°μ μ ꡬμ μ±μ₯μ΄ κ°ν΄μ€ μ κΈ°μ₯μ λ°©ν₯μ λ°λΌ ꡬμ ν΅ νμ± λλ ꡬμλ²½ μ΄λμ μν΄ μ§λ°°λλ κ²μ 보μ¬μ£Όμλ€. μ΄λ¬ν κ°μ μ ꡬμ λ°μ μ κ·Ήμ± μμ‘΄μ±μ λ°λ§/μ κ·Ή κ³λ©΄μμμ λ΄λΆ κ΅μ μ κΈ°μ₯μ λΉλμΉμ λΆν¬μ μν΄μ κΈ°μΈνλ€. ꡬ쑰μ νλ¦Όμ μν 무μ§μ μμ (κ²°ν¨, μλ ₯, νλ©΄ κ±°μΉ κΈ°)μμμ μ°¨μ΄κ° μ΄λ¬ν λΉλμΉ λ΄λΆ κ΅μ μ κΈ°μ₯μ μΌκΈ°νμ κ² κ°λ€.
λΉμ€λ¬΄μ€ μ΄μ¨μ΄ λΆμΆ©λΆν BFO λ°λ§μ λν΄, μ°λ¦¬λ μΈλΆ μ μ stressμ μν΄μ κ°μ μ 체 μ΄λ ₯곑μ μ΄ κ°μμ μΌλ‘ λ³ννλ κ²μ 보μ¬μ€λ€. λλκ²λ, μκ·Ή μ μ stressμ λν΄μ μ΄λ ₯곑μ μ μλ°λΆκ·Ήκ³Ό coercive μ μμ κ°μλ₯Ό λλ°νλ©΄μ μλ μνλ‘λΆν° μμΆλμλ€. ννΈ, μκ·Ή μ μ stressμ λν΄μ κ·Έ μμΆλ μ΄λ ₯곑μ μ μλ μνλ‘ ν볡λμλ€. μκ·Ή μ μ stress νμμμ μμͺ½ λΆκ·Ή μνλ‘μ λ°μ μ κ²°ν¨μ΄ 맀κ°λ ꡬμ ν΅ νμ±κ³Ό μ΄μ μΌλ‘ νμ±νλ ꡬμλ²½ μ΄λμ μν΄μ μ€λͺ
λ μ μλ€. λ°μ λ μμͺ½ ꡬμμ pinning νμμ μΈλΆμμ μ£Όμ
λ μ νμ ꡬμλ²½μμμ trapping κ³Όμ μΌλ‘ μΈν΄ μΌμ΄λλ κ² κ°λ€. κ·Έλ¦¬κ³ , μ΄λ¬ν pinning νμμ΄ μ΄λ ₯곑μ μ μμΆμ μΌκΈ°νλ€. κ·Έλ¬ν μ νκ° trapλ ꡬμλ²½μ΄ μ λ₯λ°λμμμ μΌμμ μΈ λ³νμ μ±
μμ΄ μλ κ² κ°λ€.
κ°μ μ ꡬμ λ°μ λμνμμμ 무μ§μ ν¨κ³Όμ λν κ·Έλ¬ν λ λμ μ΄ν΄λ BFO λ°λ§μ μμ μμ©μ μμ΄μ κ²°μ μ μΈ μν μ ν κ²μ΄λ€.
μ£Όμμ΄: λ°λ§, κ°μ μ 체, κ°νμ±μ²΄, λΉμ€λ¬΄μ€ νλΌμ΄νΈ, λΆκ·Ή λ°μ λμν, ꡬμλ²½, μλ ₯, κ²°ν¨, μ΄λ ₯νμ.
νλ² 2006-20324Docto
λ§μ± Cν κ°μΌμ λν μ΄κΈ° κ³ μ©λ μΈν°νλ‘ λ¦¬λ°λΉλ¦° λ³ν© μΉλ£ : κΈ°μ‘΄ μΈν°νλ‘ λ¦¬λ°λΉλ¦° λ³ν©μΉλ£μμ λΉκ΅
νμλ
Όλ¬Έ(μμ¬)--μμΈλνκ΅ λνμ :μνκ³Ό λ΄κ³Όνμ 곡,2002.Maste
Cνκ°μΌλ°μ΄λ¬μ€μ PKR κ²°ν©λΆμ λμ°λ³μ΄ λΆμ : νλ°μ΄λ¬μ€ μΉλ£μ λν λ°μκ³Όμ μ°κ΄μ±
Thesis (doctoral)--μμΈλνκ΅ λνμ :μνκ³Ό λ΄κ³Όν μ 곡,2004.Docto
ν μΈλν°λ₯Ό μ μ©ν μκ³λͺ¨λꡬλ 컨λ²ν°μ λͺ¨λΈλ§ λ° λΆμ
νμλ
Όλ¬Έ(μμ¬)--μμΈλνκ΅ λνμ :μ κΈ°Β·μ»΄ν¨ν°κ³΅νλΆ,2004.Maste