• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.333-333
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• 2012

$Co_3O_4$ 계열 스피넬(spinel) 전이금속 산화물 $TCo_2O_4$ (T = 3d 전이금속)는 화학적 촉매, 센서, 이차전지, 연료전지 등으로의 응용성에 기인하여 최근 주목을 받고 있으며, 특정 응용분야와 관련하여 그 박막 시료 제작 및 물리적, 화학적 성질들에 대한 세밀한 연구의 필요성이 제기되고 있다. 본 연구에서는 졸-겔 방법을 이용하여 $TCo_2O_4$ 박막이 $Al_2O_3$ (0001) 기판 위에 균일한 두께로 제작될 수 있는 최적 조건을 찾고자 하였으며, 후열처리 조건 변화에 따르는 박막의 구조적 성질 변화를 조사하였다. 후열처리는 공기 중에서 이루어졌으며 온도 ${\sim}800^{\circ}C$에서 최적 결정성을 갖는 다결정 박막이 얻어졌다. 또한, 박막에 작은 시간(~10 min) 동안의 전자선(electron beam) 조사를 통한 다결정 박막의 형성도 관측되었다. $TCo_2O_4$ 박막들에 대한 X-ray diffraction, X-ray photoelectron spectroscopy, spectroscopic ellipsometry 측정들을 수행하여 그 구조적, 광학적 성질을 조사 하였다.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.1-5
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• 2006

The crystallographic properties and cation distribution of oxyspinels ferrite $Co_xFe_{1-x}O_4$ thin films have been explored by X-ray diffraction, vibrating sample magnetometer (VSM), and conversion electron $M\"{o}ssbauer$ spectroscopy (CEMS). Thin films are prepared by sol-gel method. Normal spinel structure is transformed to inverse spinel structure with increasing Co concentration CEMS results indicate that most of $Fe^{3+}$ ions are substituted to $Co^{3+}$ions. Accordingly $Co^{2+}$ ions on octahedral site migrate to tetrahedral site. Magnetic moment is decreased with increasing Co concentration, which means high spin $Fe^{3+}$ ions are replaced by low spin $Co^{3+}$.

• Journal of the Korean Vacuum Society
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• v.20 no.3
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• pp.205-210
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• 2011

Structural and electrochemical properties of spinel oxide $LiMn_2O_4$ thin films prepared by using a sol-gel method on Pt/Ti/$SiO_2$/Si substrates were investigated. When Li/Mn molar ratio of the film was smaller than 0.5, $Mn_2O_3$hase was found to coexist with $LiMn_2O_4$. Half-cell batteries fabricated using the $LiMn_2O_4$ films as the cathode were put into chargedischarge (C-D) cycles and the change in structural properties of the cathode after the cycles was examined by X-ray diffraction and Raman spectroscopy. As the C-D cycle number increases, the discharge capacity of pure $LiMn_2O_4$ battery gradually decreases, being reduced to 72% of the initial capacity at 300 cycles. Such capacity fading is attributable to the decrease in the number of $Li^+$ ions that return to the tetrahedral sites of the spinel structure during the discharge step and the resultant increase in $Mn^{4+}$ density in the film. Also, $Mn_2O_3$ phase gradually appeared in the film as the cycle number increases.

• Korean Journal of Materials Research
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• v.9 no.7
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• pp.657-662
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• 1999

Mn-Ni oxide thin films for NTC thermistor application were sputtered on alumina substrates at $320^{\circ}C$ Effects of various oxygen partial pressures and annealing temperatures on the microstructure, crystal phase, resistivity and B constant were investigated. In general, microstructure of the films deposited was columnar grain structure. After annealing at $700^{\circ}C$, the microstructure was begun to transform to equiaxed grain structure. Most of the phases were mixture of cubic spinel and $Mn_2$$O_3$. As the oxygen concentration increased, the resistivity and B constant were greatly decreased, and these values become low and stable after annealing between $600^{\circ}C$ and $700^{\circ}C$.

• Korean Journal of Materials Research
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• v.8 no.5
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• pp.424-428
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• 1998

Mn-Ni oxide thin films for NTC thermistor application were deposited on alumina substrates by using rf magnetron sputter. Effects of various substrate temperatures and annealing temperatures on the microstructure. crystal phase, resistivity and B constant were investigated. Microstructure of the films deposited below 178$^{\circ}C$ was fibrous microcrystalline and at 32$0^{\circ}C$and 40$0^{\circ}C$their microstructure was changed to columnar grain structure. After annealing at 90$0^{\circ}C$, the microstructure was transformed to equiaxed grain structure. Most of the phases were mixture of cubic spinel and $Mn_2O_2$ The crystal phase of the film deposited at 40$0^{\circ}C$ was changed to cubic spinel after annealing above 700"c. As the substrate temperature increased, the resistivity and B constant were greatly decreased, and these values become low and stable after annealing between $600^{\circ}C$and $700^{\circ}C$, All thin films deposited in the present study showed NTC thermistor characteristicsstics.

• Journal of the Korean Magnetics Society
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• v.17 no.2
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• pp.51-54
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• 2007

By substituting Cr in inverse-spinel $Fe_3O_4,\;Cr_xFe_{3-x}O_4$ thin film samples were prepared by sol-gel spin-coating method and their structural electronic, and magnetic properties were analyzed. X-ray diffraction indicates that the lattice constant decrease with increasing Cr composition (x). This result can be explained in terms of occupation of octahedral sites by $Cr^{3+}$ ions with smaller ionic radius than that of $Fe^{3+}$ Vibrating sample magnetometry measurements on the samples at room temperature revealed that saturation magnetization ($M_s$) decrease by Cr substitution, explainable by comparing spin magnetic moment among the related transition-metal ions. A decrease of magnetoresistence effect with x was observed, similar to that of $M_s$. The coercivity of the $Cr_xFe_{3-x}O_4$ films was found to increase with x, attributed to the increase of magnetic anisotropy by the existence of octahedral $Cr^{3+}(d^3)$.

• Journal of the Korean Vacuum Society
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• v.15 no.5
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• pp.527-533
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• 2006

Spinel $LiNi_xMn_{2-x}O_4$ thin films were synthesized up to x = 0.9 by a sol-gel method employing spin-coating. The Ni-substituted films were found to maintain cubic structure at low x but to exhibit tetragonal structure for $x{\geq}0.6$. Such cubic-tetragonal phase transition indicates that $Ni^{3+}(d7)$ ions with low-spin $(t_{2g}^6,e_g^1)$ state occupy the octahedral sites of the compound, thus being subject to the Jahn-Teller distortion. By x-ray photoelectron spectroscopy both $Ni^{2+}$ and $Ni^{3+}$ ions were detected. Optical properties of the $LiNi_xMn_{2-x}O_4$ films were investigated by spectroscopic ellipsometry (SE) in the visible?ultraviolet range. The measured dielectric function spectra by SE mainly consist of broad absorption structures attributed to charge-transfer (CT) transitions, $O^{2-}(2p){\rightarrow}Mn^{4+}(3d)$ for 1.9 $(t_{2g})$ and $2.8{\sim}3.0$ eV $(e_g)$ structures and $O^{2-}(2p){\rightarrow}Mn^{3+}(3d)$ for 2.3 $(t_{2g})$ and $3.4{\sim}3.6$ eV $(e_g)$ structures. Also, sharp absorption structures were observed at about 1.6, 1.7, and 1.9 eV, interpreted as due to d-d crystal-field transitions within the octahedral $Mn^{3+}$ ion. The strengths of these absorption structures are reduced by the Ni substitution. Rapid reduction of the CT transition strength involving the eg states for x = 0.6 is attributed to the reduced wavefunction overlap between the $e_g$ and the $O^{2-}(2p)$ states due to the tetragonal extension of the lattice constant by the Jahn-Teller effect.

• Korean Journal of Materials Research
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• v.8 no.4
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• pp.323-327
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• 1998

All solid state lithium based rechargeable batteries were fabricated in a cell structure of Li/PEO-$LiCIO_4$-PC /$LIMn_2O_4$$LIMn_2O_4$ thin films were prepared by RF magnetron sputtering and the spinel structure could be obtained by Rapid Thermal Annealing (RT A) process at the temperature of around 750$750^{\circ}C$ . Room temperature cycling of this cell showed a nearly constant cell potential of 4 V( us. Li) and good reversibility.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.3
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• pp.99-105
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• 2014

$LiCoO_2$ thin film have received attention as cathodes of thin-film microbatteries. In this study, $LiCoO_2$ thin films were synthesized on Au substrates by sol-gel spin coating method and electrochemical properties were investigated under annealing temperature and time. The phycochemical properties of $LiCoO_2$ thin film were investigated by X-ray diffraction, scaning electron microscopy and atomic force microscopy. The electrochemical properties were characterized using galvanostatic charging/discharging cycling tests. From X-ray diffraction, as-grown films annealed at $550^{\circ}C$ and $750^{\circ}C$ are presumed to be spinel structure and a single phase of the layered-rock-salt, respectively. The RMS roughness and grain size of the films which annealed at $750^{\circ}C$ has similar values for annealing time 10 and 30 min, while for annealing time 120 min surface roughness, grain size increase and pore appearance were observed. The first discharge capacity of $LiCoO_2$ thin films annealed at $750^{\circ}C$ for 10, 30 and 120 min is about 54.5, 56.8 and $51.87{\mu}Ah/cm^2{\mu}m$, respectively. Corresponding capacity retention at 50th cycle is 97.25, 76.69, 77.19%.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.23-27
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• 2006

By substituting Mn or Cr for Co in inverse spinel $CoFe_2O_4,\;Mn_xCo_{1-x}Fe_2O_4\;and\;Cr_xCo_{1-x}Fe_2O_4$ and thin films were prepared by sol-gel method and their structural and magnetic properties were investigated. X-ray diffraction indicates that the cubic lattice constant increase for the Mn substitution while it hardly changes for the Cr substitution. Substitution of $Mn^{2+}$ for octahedral $Co^{2+}$ sites can explain the increase of lattice constant in $Mn_xCo_{1-x}Fe_2O_4$. On the other hand, Substitution of $Cr^{3+}$ for octahedral $Co^{2+}$ and subsequent reduction of $Fe^{3+}$ ion into $Fe^{2+}$ are expected to happen. Mossbauer spectroscopy measurements on $Cr_xCo_{1-x}Fe_2P_4$ indicate the existence of tetrahedral $Fe^{2+}$ ions that are created through reduction of tetrahedral $Fe^{3+}$ ions in order to compensate charge imbalance happened by $Cr^{3+}$ substitution for octahedral $Co^{2+}$ sites. On the other hand, no $Fe^{2+}$ ions were detected by Mossbauer spectroscopy for $Mn_xCo_{1-x}Fe_2O_4$. A migration of $Fe^{3+}$ ions from octahedral to tetrahedral sites In $Mn_xCo_{1-x}Fe_2O_4$ was detected by Mossbauer spectroscopy for x>0.47. Vibrating sample magnetometry measurements on the samples at room temperature revealed that the saturation magnetization increases by Mn and Cr substitution for certain range of x, qualitatively explainable in terms of the comparison of spin magnetic moment among the related transition-metal ions.