Jeon Kook Lee

Metalorganic chemical vapor deposition of TiO2:N anatase thin film on Si substrate

Titanium dioxide thin film doped with nitrogen was deposited at 420u2009°C on p‐type silicon substrate by metalorganic chemical vapor deposition using titanium tetra‐isopropoxide and nitrous oxide. From an x‐ray diffraction result, when deposited at 420u2009°C, only the anatase (101) peak and (200) peak were observed. Raman spectroscopy confirmed the presence of anatase phase without any rutile or TiN phase. X‐ray photoelectron spectrum revealed that nitrogen was doped into the lattice of TiO2 anatase. In the bulk of the film nitrogen peak was observed, and the spectrum of Ti 2p core level confirmed titanium–nitrogen bonding due to nitrogen incorporation into the anatase lattice.

Structural and ferroelectric properties of the c‐axis oriented SrBi2Ta2O9 thin films deposited by the radio‐frequency magnetron sputtering

Radio‐frequency magnetron sputtering was used to deposit SrBi2Ta2O9 ferroelectric thin films on Pt(111)/Ti/SiO2/Si(001) substrates. Thin films were deposited at room temperature with argon pressures of 0.5–100 mTorr and with sputtering power of 2.5 W/cm2. The crystal orientations of thin films were strongly affected by the argon pressures, the c‐axis oriented SrBi2Ta2O9 thin film was obtained with argon pressure of 30 mTorr. The crystal structures of the c‐axis oriented SrBi2Ta2O9 thin film were investigated by x‐ray diffraction methods: θ‐2θ scan, rocking curve, and φ scans. The well aligned microstructure was observed with the average grain size of about 2000 A in an atomic force microscopic image. Ferroelectric properties were observed for the c‐axis oriented thin film: Pr*−PrΛ and Ec were 9.7 μC/cm2 and 50 kV/cm, respectively, with excitation voltage of 3 V.

Bulk glass formation in the Ni-Zr-Ti-Nb-Si-Sn alloy system

In this study, the effect of addition of Nb on glass formation in Ni–Ti–Zr–Si–Sn alloys has been studied. The composition range for bulk glass formation with D max > 2 mm ( D max , maximum diameter for glass formation by injection cast method) becomes wider when compared with the non-Nb–containing alloy. The Δ T x (= T x – T g ; T x , crystallization onset temperature; T g , glass transition temperature), T rg (= T g / T l ; T l , liquidus temperature) and γ [= T x /( T l + T g )] values for the alloys D max > 2 mm are in the range of 40–59, 0.638–0.651, and 0.410–0.419, respectively. The compositions of the alloys ( D max > 2 mm) are closer to pseudo-eutectic composition than that of the alloy without Nb, showing an improved glass forming ability. The critical cooling rate for glass formation ( D max = 5 mm) is estimated to be order of approximately 40 K/s.

Electrical characterization of Pt/SrBi2Ta2O9/Pt capacitors fabricated by the pulsed laser ablated deposition technique

Pulsed laser ablation deposition was used to synthesize polycrystalline SrBi2Ta2O9 layered ferroelectric thin films on the platinized silicon substrate. The surface roughness of the deposited film was an average of 4 nm. The titanium element was diffused to the SrBi2Ta2O9 layer through the platinum layer. P‐E hysteresis loop for the Pt/SrBi2Ta2O9/Pt/Ti capacitor was well saturated and symmetric (Pr=3 μC/cm2, Ec=25 kV/cm).

Bipolar Resistive Switching Behavior of a Pt/NiO/TiN Device for Nonvolatile Memory Applications

Bipolar resistive switching behavior was observed in a Pt/NiO/TiN device. The device exhibited switching behavior that was stable over 100 cycles and did not degrade after 104 s. An electroforming process was required to obtain these bipolar resistive switching properties, and the conduction behavior of the low resistance state followed Ohms law, indicating that conductive filaments formed during the electroforming process. The conductive filaments consisted of oxygen vacancies and the Pt electrode behaved as an oxygen reservoir. The bipolar resistive switching of the Pt/NiO/TiN device was explained by the generation and annihilation of oxygen vacancies in the filaments.

Precipitation of icosahedral phase from amorphous Zr65Cu17.5− xAl7.5Ni10Ag x ( x = 0, 5) alloys

Crystallization behavior of amorphous Zr 65 Cu 17.5− x Al 7.5 Ni 10 Ag x ( x = 0, 5) alloys prepared by melt spinning and injection casting techniques has been studied using differential scanning calorimetry, x-ray diffractometry, and transmission electron microscopy. Ag addition changes crystallization sequence of the amorphous phase. The amorphous Zr 65 Cu 17.5 Al 7.5 Ni 10 alloy crystallizes via simultaneous precipitation of icosahedral phase and NiZr 2 phase in the first crystallization step whereas that in Zr 65 Cu 12.5 Al 7.5 Ni 10 Ag 5 alloy crystallizes via precipitation of only icosahedral the phase. Partial replacement of Cu by Ag in Zr 65 Cu 17.5 Al 7.5 Ni 10 alloy stabilized the icosahedral phase relative to competing intermetallic phases resulting in suppression of the precipitation of the NiZr 2 phase, enhancement of the precipitation of icosahedral phase, and reduction of undercooled liquid range. Crystallization behavior of the amorphous Zr 65 Cu 12.5 Al 7.5 Ni 10 Ag5 alloy is not affected by cooling rate during solidification. Johnson–Mehl–Avrami analysis of isothermal transformation data suggests that the formation of the quasicrystalline phase is not entirely polymorphic in nature and may involve partitioning of the solute at later state.

Fabrication of excess PbO-doped Pb(Zr0.52Ti0.48)O3 thin films using radio frequency magnetron sputtering method

As a method for lowering deposition temperature, the effect of 50% excess Pb addition in Pb(Zr0.52T0.48)O3 ceramic target on Pb(Zr0.52T0.48)O3 thin films (4000–5000 A thickness) was studied. The PZT thin films were grown on Pt/Ti/SiO2/Si(100) substrates by using radio frequency magnetron sputtering method. The existing phase of PZT thin films was confirmed with x-ray diffraction analysis, and growth morphologies were studied with scanning electron microscopy. At the substrate temperature of 440u2009°C, only the pyrochlore phase existed, and as the substrate temperature was increased, the amount of perovskite phase also increased. It was finally found that the PZT thin films without pyrochlore phase could be fabricated at the temperature as low as 520u2009°C. It was also observed that the quality of the final phases after the postannealing process severely depends on the initial perovskite phase purity during deposition. The electrical properties of PZT thin films were characterized through P–E hysteresis curves, ...

Effects of Ambient Gas Pressure on the Resistance Switching Properties of the NiO Thin Films Grown by Radio Frequency Magnetron Sputtering

NiO films were grown on a Pt substrate by radio frequency (RF) magnetron sputtering using a NiO ceramic target. A crystalline NiO phase with the [111] preferred orientation was formed for the films grown above 100 °C. Resistance switching behavior was not observed in the NiO films annealed in the air or in ambient O2 after film deposition. However, the NiO films annealed in ambient N2 exhibited resistance switching properties. The stability of the switching voltage was considerably influenced by the oxygen to argon ratio during film growth. In particular, the NiO film grown under an 8.0 mTorr oxygen partial pressure exhibited stabilized switching voltages (Vset~1.45±0.20 V and Vreset~0.62±0.09 V). Therefore, the control of the ambient gas pressure during the growth and annealing of the NiO films was important for obtaining good resistance switching properties.

The Nature of Metastable AA' Graphite: Low Dimensional Nano- and Single-Crystalline Forms.

Over the history of carbon, it is generally acknowledged that Bernal AB stacking of the sp2 carbon layers is the unique crystalline form of graphite. The universal graphite structure is synthesized at 2,600~3,000u2009°C and exhibits a micro-polycrystalline feature. In this paper, we provide evidence for a metastable form of graphite with an AA’ structure. The non-Bernal AA’ allotrope of graphite is synthesized by the thermal- and plasma-treatment of graphene nanopowders at ~1,500u2009°C. The formation of AA’ bilayer graphene nuclei facilitates the preferred texture growth and results in single-crystal AA’ graphite in the form of nanoribbons (1D) or microplates (2D) of a few nm in thickness. Kinetically controlled AA’ graphite exhibits unique nano- and single-crystalline feature and shows quasi-linear behavior near the K-point of the electronic band structure resulting in anomalous optical and acoustic phonon behavior.

Surface morphologies effects on electroluminescent properties in metal-oxide-based quantum dot light emitting devices(QD-LED)

QDs are suited for lumophores in LED for large-area planar lighting. We selected ZnO:SnO 2 and InGaZnO x as a CTL. The decrease in QD luminescence can be attributed to additional quenching by the free carriers in the ETL.