Jai-Yeoul Lee

Effect of BaTiO3 buffer layer on multiferroic properties of BiFeO3 thin films

BiFeO3 (BFO) films were processed on BaTiO3 (BTO) buffered (111) Pt/Ti/SiO2/Si substrate by pulsed laser deposition. Improved ferroelectric properties, as well as induced ferromagnetism, were observed by the insertion of a BTO layer for rather thick BFO films (450 nm) deposited at an oxygen pressure of 40 mTorr. Reduced leakage current, coercive field, and increased ferroelectric saturation of BFO/BTO bilayer films were obtained and compared with those of BFO films. In order to better understand the buffer layer effect on the magnetic properties, two thinner (140 and 220 nm) BFO films were also deposited and investigated. Both films showed ferromagnetic hysteresis loops and larger in-plane magnetization than out-of-plane magnetization. By introducing the BTO barrier layer, the remnant and saturated magnetizations were also increased. These results demonstrated not only the interface constraint effect but also a coupling between ferroelectric BTO and magnetic BFO, which deserve further investigation.

MAGNETIC PROPERTIES OF MULTIFERROIC BiFeO3/BaTiO3 Bi-LAYER THIN FILMS

ABSTRACT Magnetic properties of multiferroic bi-layer BiFeO3 (BFO)/BaTiO3 (BTO) thin films were studied. It was found that the magnetization increased by the insertion of BTO buffer layer even though the interfacial stress was slightly relaxed, which indicated a coupling between the ferroelectric and ferromagnetic orders. Furthermore, with slight increase of BFO film thickness, both BFO and BFO/BTO bi-layer films showed anisotropic magnetic properties with higher in-plane magnetization than the values measured out-of-plane. These are attributable to strain constraint effect at the interface.

Properties of multilayer gallium and aluminum doped ZnO(GZO/AZO) transparent thin films deposited by pulsed laser deposition process

Multilayer gallium and aluminum doped ZnO (GZO/AZO) films were fabricated by alternative deposition of Ga-doped zinc oxide(GZO) and Al-doped zinc oxide(AZO) thin film by using pulsed laser deposition(PLD) process. The electrical and optical properties of these GZO/AZO thin films were investigated and compared with those of GZO and AZO thin films. The GZO/AZO (1:1) thin film deposited at 400 °C shows the electrical resistivity of 4.18×10−4 ωcm, an electron concentration of 7.5×1020/cm3, and carrier mobility of 25.4 cm2/(V·s). The optical transmittances of GZO/AZO thin films are over 85%. The optical band gap energy of GZO/AZO thin films linearly decreases with increasing the Al ratio.

Thin film processing and multiferroic properties of Fe-BaTiO3 hybrid composite

Multiferroic bi-layer Fe/BaTiO3 (BTO) thin films were successfully deposited on Pt(200)/MgO(100) substrates using ion beam sputter deposition (IBSD), and the mutiferroic properties were studied at room temperature. X-ray diffraction (XRD) analyses showed that BTO films were c-axis oriented and epitaxially grown on platinum coated MgO substrates, and (110) epitaxial Fe films were subsequently grown on (001) BTO films. Fe/BTO bi-layer films showed good ferroelectric and ferromagnetic properties at room temperature and the multiferroic coupling was observed, which should be attributed to the hybridization of Fe and Ti occurring at the ferromagnetic-ferroelectric interface.

Magnetoelectric Coupling of CuFe2O4/Pt/Pb(Zr0.52Ti0.48)O3 Multilayer Thin Films

CuFe2O4/Pt/Pb(Zr0.52Ti0.48)O3 (PZT) multilayer thin films were grown on (111)-oriented Pt/TiO2/SiO2/Si<100> substrate. PZT layer was fabricated by the sol-gel method. Afterwards, Pt layer was deposited by ion beam sputtering method. Finally, CuFe2O4 layer were deposited using pulsed laser deposition method (PLD). The film structure is tri-layered type, where the bottom PZT layer covered the whole substrate, while Pt and CuFe2O4 layers were deposited through circular shadow masks to measure ferroelectric and magnetoelectric properties. Film microstructure was observed using XRD and FE-SEM. Magnetoelectric coefficients were calculated by measured magnetoelectric voltages using magnetoelectric measurement system.

Magnetoelectric Coupling Effect in Ferroelectric and Ferromagnetic Hybrid Thin Films

Magnetoelectric (ME) effect in multiferroic or ferroelectric/ferromagnetic composite thin films occurs through the elastic coupling between the piezoelectric properties of ferroelectric and magnetostrictive properties of ferromagnetic component. To obtain high elastic coupling and ME effect, we introduced PZT [Pb(Zr0.52, Ti0.48)O3] as a ferroelectric materials and CuFO (CuFe2O4) as ferromagnetic materials because of their high piezoelectric coefficient and magnetostrictive properties among various metal-oxide materials. To evaluate ME effect, we prepared CuFO/Pt/PZT/Pt hybrid thin films directly on Pt/TiO2/SiO2/Si substrate by using ion beam sputtering and spin-coating method. We investigated the microstructures and morphologies of hybrid thin films by XRD and SEM, the ferroelectric and ferromagnetic behaviors of hybrid films were examined by measuring polarization and magnetization hysteresis loops vs. electric and magnetic field. Magnetoelectric coefficients were calculated by measured magnetoelectric voltages using magnetoelectric measurement system. In this research, we’ll discuss the relations between annealing temperatures and multiferroic properties.

Influence of Annealing Temperature on Magnetoelectric Properties of CoFe2O4/Pt/Pb(Zr0.3Ti0.7)O3 Thin Films

CoFe2O4/Pt/Pb(Zr0.3Ti0.7)O3 thin films were grown on Pt/Ti/SiO2/Si substrate in order to investigate the magnetoelectric properties of ferromagnetic/ferroelectric multilayer thin films. Thin Pt layer was introduced to prevent inter-diffusion between CoFe2O4 and Pb(Zr0.3Ti0.7)O3 (PZT) layers. PZT thin film was grown directly on top of Pt substrate by utilizing sol-gel spin coating technique. In order to investigate the possible annealing effect on film microstructure and magnetoelectric properties, multilayer thin film stack was heat-treated at different temperatures ranging from 550°C to 650°C. The structural properties of the films were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Ferroelectric and ferromagnetic behaviors were analyzed by measuring polarization and magnetization – electric and magnetic field hysteresis. Magnetoelectric coefficients were calculated by measuring magnetoelectric voltages using magnetoelectric measurement system. Both the magnetoelectric properties and the coupling effect of CoFe2O4/Pt/PZT films on ferromagnetic and magnetoelectric properties are discussed as a function of heat-treatment temperature.

SnO2: CuSb2O6 Thin Films Prepared by Pulsed Laser Deposition

SnO2 thin films doped with CuSb2O6 were prepared by pulsed laser deposition method, in an attempt to evaluate the effect of Cu and Sb co-doping on optical and electrical properties. Alkaline-free borosilicate glass substrates were used as substrate where the substrate temperature was maintained in the range of 575∼650°C during deposition with oxygen pressure of 3∼5 mTorr and laser energy density of 1 Jcm−2. The minimum electrical resistivity value was obtained from SnO2:8%CuSb2O6 films, which was approximately 1.3 × 10−3 Ωcm, while its optical transmittance is relatively poor with ∼46% at 6000Å. The highest optical transmittance value was obtained from SnO2:2%CuSb2O6 films, which was about 80% at 6000Å, where its electrical resistivity value was 5.9 × 10−3 Ωcm.

The Effect of Ion-Beam Treatment on TiO 2 Coatings Deposited on Polycarbonate Substrates

The effect of an Ar plasma treatment on polycarbonate substrates was investigated using coatings produced by reactive ion-beam assisted sputtering. The typical pressure used during sputtering was about Torr. After the Ar plasma treatment, the contact angle of a water droplet was reduced from to and then further decreased to with the addition of oxygen into the chamber. The surface of the polycarbonate substrate hanged from hydrophobic to hydrophilic with these treatments and revealed its changing nano-scale roughness. The films on the treated surface showed various colors and periodic ordering dependant on the film thickness due to optical interference.

Characteristics of the Li–Ni Doped Cobalt Oxide Thin Films Prepared by Pulsed Laser Deposition

Cobalt oxide spinel thin films doped with Ni and Li were deposited on c-sapphire single crystal substrates at various substrate temperatures and oxygen partial pressures by pulsed laser deposition. The effects of the doping and processing parameters on the crystal structure, electrical and optical properties of cobalt oxide base spinel thin films were analyzed by XRD, four point probe and UV spectrometry. The electrical conductivity increased with increasing Ni doping concentration, x, up to x = 0.7. The thin films grew on the sapphire substrates with a strong (111) preferred orientation. Li0.1Ni0.6Co2.3O4 spinel phase decomposed to a rock salt phase when the oxygen partial pressure was lower than 5 mtorr. The electrical conductivity decreased rapidly with the formation of a rock salt phase due to the limited charge transfer between the divalent and trivalent cations.