• 한국재료학회지
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• 제25권4호
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• pp.171-176
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• 2015

We present the detection characteristics of nitrogen monoxide(NO) gas using p-type copper oxide(CuO) thin film gas sensors. The CuO thin films were fabricated on glass substrates by a sol-gel spin coating method using copper acetate hydrate and diethanolamine as precursors. Structural characterizations revealed that we prepared the pure CuO thin films having a monoclinic crystalline structure without any obvious formation of secondary phase. It was found from the NO gas sensing measurements that the p-type CuO thin film gas sensors exhibited a maximum sensitivity to NO gas in dry air at an operating temperature as low as $100^{\circ}C$. Additionally, these CuO thin film gas sensors were found to show reversible and reliable electrical response to NO gas in a range of operating temperatures from $60^{\circ}C$ to $200^{\circ}C$. It is supposed from these results that the p-type oxide semiconductor CuO thin film could have significant potential for use in future gas sensors and other oxide electronics applications using oxide p-n heterojunction structures.

• Journal of Magnetics
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• 제21권1호
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• pp.6-11
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• 2016

The magnetic anisotropy energy (MAE) and the saturation magnetization $B_s$ of (110) $Fe_nCo_n$ heterostructures with n = 1, 2, and 3 are investigated in first-principles within the density functional theory by using the precise full-potential linearized augmented plane wave (FLAPW) method. We compare the results employing two different exchange correlation potentials, that is, the local density approximation (LDA) and the generalized gradient approximation (GGA), and include the spin-orbit coupling interaction of the valence states in the second variational way. The MAE is found to be enhanced significantly compared to those of bulk Fe and Co and the magnetic easy axis is in-plane in agreement with experiment. Also the MAE exhibits the in-plane angle dependence with a two-fold anisotropy showing that the $[1{\overline{I}}0]$ direction is the most favored spin direction. We found that as the periodicity increases, (i) the saturation magnetization $B_s$ decreases due to the reduced magnetic moment of Fe far from the interface, (ii) the strength of in-plane preference of spin direction increases yielding enhancement of MAE, and (iii) the volume anisotropy coefficient decreases because the volume increase outdo the MAE enhancement.

• Bulletin of the Korean Chemical Society
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• 제34권2호
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• pp.629-632
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• 2013

Many properties of inorganic compounds are sensitive to changes in the point-defect concentrations. In minerals, such changes are influenced by temperature, pressure, and chemical impurities. Olivines form an important class of minerals and are magnesium-rich solid solutions consisting of the orthosilicates forsterite $Mg_2SiO_4$ and the fayalite $Fe_2SiO_4$. Orthosilicates have an orthorhombic crystal structure and exhibit anisotropic electronic and ionic transport properties. We examined the anisotropy of the electrical conductivity of $Fe_2SiO_4$ under the assumption that the electronic conduction in $Fe_2SiO_4$ occurs via a small polaron hopping mechanism. The anisotropic electrical conductivity is well explained by the electron transfer integrals obtained from the spin dimer analysis based on tight-binding calculations. The latter analysis is expected to provide insight into the anisotropic electrical conductivities of other magnetic insulators of transition metal oxides.

• Journal of Magnetics
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• 제14권1호
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• pp.18-22
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• 2009

The shape anisotropy effect of a giant magnetoresistance-spin valves (GMR-SV) device with a glass/NiO/NiFe/CoFe/Cu/CoFe/NiFe layered structure for use in the detection of magnetic property of molecules within a cell was investigated. The patterned device was given uniaxial anisotropy during the sputtering deposition and vacuum post-annealing, which was performed at $200^{\circ}C$ under a 300 Oe magnetic field. The pattern size of the device, which was prepared through the photolithography process, was $2{\times}15\;{\mu}m^2$. The experimental results confirmed that the best design for a GMR-SV device to be used as a biosensor is to have both the axis sensing current and the easy axis of the pinned NiO/NiFe/CoFe triple layer oriented in the direction of the device's width, while the easy axis of the free CoFe/NiFe bilayer should be pointed along the long axis of the device.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 C
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• pp.1924-1926
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• 2005

Poly(methyl methacrylate) (PMMA) is one of the promising representive of polymer gate dielectric for its high resistivity and sutible dielectric constant. PMMA (Mw=96700) films were prepared on p-Si by spin coating method. PMMA were coated compactively and flatly as observes by AFM. MIS(Al/PMMA/p-Si) structure was made and capacitance-voltage (C-V) and current-voltage (I-V) measurements were done with PMMA films for repeated annealing cycles at $100^{\circ}C$. 1-V measured at various delay times $(0{\sim}20sec)$ showed little change and the absence of hysteresis in the I-V characteristics with delay times, which eliminate the possibility of deep traps in the PMMA films. The observed thermal stability, smooth surfaces, dielectric constant, I-V behavior implies PMMA formed by spin coating can be used as an efficient gate dielectric layer in OTFTs.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.373-374
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• 2007

We have fabricated polymer light-emitting diodes(PLED) in a structure of Glass/ITO/PVK/Al. Poly(N-vinylcabazole) (PVK) was deposited on the ITO glass with the spin coating method. PVK thickness is respectively 500nm, 300nm, 250nm and 200nm with the spin coter rotation speed of 2000, 3000, 4000 and 5000rpm. V-I, wavelength-transmittance, P-L and SEM of the fabricated devices were measured. From the result of P-L measurement, it was kept the optic properties of PVK raw powder when PVK thickness is 250nm. The knee-voltage of PVK PLED with 250nm thickness was 7V.

• Journal of Magnetics
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• 제7권4호
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• pp.132-137
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• 2002

The electronic structures and magnetism of the non-oxide perovskite MgCFe$_3$(001) surface were investigated by using the all-electron full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA). We considered both of the MgFe terminated (MgFe-Term) and the CFe terminated (CFe-Term) surfaces. We found that the minority spin d-bands of Fe(S) of the MgFe-Term are strongly localized and Fermi level (EF) lies just below the sharp peak of the minority spin d-band of Fe(S), while the minority spin d-bands of Fe(S) of the CFe-Term are not localized much and Fermi level (E$_F$) lies in the middle of two peaks of the minority spins. The majority Fe(S) d-band width of MgFe- Term is narrower than that of the CFe-Term. It is found that the magnetic moment of Fe(S) of the MgFe- Term is 2.51 ${\mu}$$_B$, which is much larger than that of 1.97 ${\mu}$$_B$ of the CFe-Term.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 추계학술발표강연 및 논문개요집
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• pp.212-212
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• 2003

Many of the spin valve multilayer structures with FeMn as antiferromagnetic layer consist of a NiFe/FeMn/NiFe trilayer where the bottom NiFe layer is the seed layer to facilitate the growth of (111) gama-FeMn antiferromagnetic phase and the top NiFe layer forms the pinned layer[1], In this study, exchange bias of bottom NiFe layer has been investigated as functions of thicknesses of top and bottom NiFe in NiFe/FeMn/NiFe, prepared by rf magnetron sputtering, MH-loop was measured by vibration sample magnetometer (VSM). Two hysteresis loops are corresponded to bottom and top layers, similar to reported loops in spin valve structure. Exchange bias of bottom NiFe could be induced by the interfacial coupling between bottom NiFe and FeMn. But those coupling are strongly dependent on the top and bottom NiFe thicknesses, revealing anomalous character ul exchange bias of bottom NiFe layer.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 하계학술연구발표회 및 한.일 공동심포지엄
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• pp.24-24
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• 2003

Metallic magnetoelectronic devices have studied intensively and extensively for last decade because of the scientific interest as well as great technological importance. Recently, the scientific activity in spintronics field is extending to the hybrid devices using ferromagnetic/semiconductor heterostructures and to new ferromagnetic semiconductor materials for future devices. In case of the hybrid device, conductivity mismatch problem for metal/semiconductor interface will be able to circumvent when the device operates in ballistic regime. In this respect, spin-valve transistor, first reported by Monsma, is based on spin dependent transport of hot electrons rather than electron near the Fermi energy. Although the spin-valve transistor showed large magnetocurrent ratio more than 300%, but low transfer ratio of the order of 10$\^$-5/ prevents the potential applications. In order to enhance the collector current, we have prepared magnetic tunneling transistor (MTT) with single ferromagnetic base on Si(100) collector by magnetron sputtering process. We have changed the resistance of tunneling emitter and the thickness of baser layer in the MTT structure to increase collector current. The high transfer ratio of 10$\^$-4/ range at bias voltage of more than 1.8 V, collector current of near l ${\mu}$A, and magnetocurrent ratio or 55% in Si-based MTT are obtained at 77K. These results suggest a promising candidate for future spintronic applications.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2003년도 somma/kms meeting
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• pp.109-109
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• 2003