Hyun-June Jung

Phase-change InSbTe nanowires grown in situ at low temperature by metal-organic chemical vapor deposition.

Phase-change InSbTe (IST) single crystalline nanowires were successfully synthesized at a low temperature of 250 degrees C by metalorganic chemical vapor deposition (MOCVD). The growth of IST nanowires by MOCVD, at very high working pressure, was governed by supersaturation. The growth mechanism of the IST nanowires by MOCVD is addressed in this paper. Under high working pressure, the InTe phase was preferentially formed on the TiAlN electrode, and the InTe protrusions were nucleated on the InTe films under high supersaturation. The Sb was continuously incorporated into the InTe protrusions, which was grown as an IST nanowire. Phase-change-induced memory switching was realized in IST nanowires with a threshold voltage of about 1.6 V. The ability to grow IST nanowires at low temperature by MOCVD should open opportunities for investigation of the nanoscale phase-transition phenomena.

Growth Mechanism of the Copper Oxide Nanowires from Copper Thin Films Deposited on CuO-Buffered Silicon Substrate

The growth mechanism of the CuO single-crystal nanowires (NWs) for future device applications has been demonstrated using the copper films deposited on CuO-buffered SiO 2 /Si substrates. The mechanism involves a two-step process: In the first step, hillocks of copper are formed to relieve the compressive stress existing on the copper films at high temperature for a long duration of time in air and then Cu 2 O phase is formed by the oxidation of the hillocks in air ambient. The second step involves a continuous supply of copper through the porous Cu 2 O seed and then the transformation of the Cu 2 O phase to CuO NW. The CuO NW was grown by a continuous supply of both copper from the copper films and oxygen from air. The indispensable requirements for CuO NW growth from the copper films are the presence of compressive stress in the copper films and the presence of the Cu 2 O seed phase on the copper films at a high temperature in air.

Realization of Large-Area Wrinkle-Free Monolayer Graphene Films Transferred to Functional Substrates

Structural inhomogeneities, such as the wrinkles and ripples within a graphene film after transferring the free-standing graphene layer to a functional substrate, degrade the physical and electrical properties of the corresponding electronic devices. Here, we introduced titanium as a superior adhesion layer for fabricating wrinkle-free graphene films that is highly applicable to flexible and transparent electronic devices. The Ti layer does not influence the electronic performance of the functional substrates. Experimental and theoretical investigations confirm that the strong chemical interactions between Ti and any oxygen atoms unintentionally introduced on/within the graphene are responsible for forming the clean, defect-free graphene layer. Our results accelerate the practical application of graphene-related electronic devices with enhanced functionality. The large-area monolayer graphenes were prepared by a simple attachment of the Ti layer with the multi-layer wrinkle-free graphene films. For the first time, the graphene films were addressed for applications of superior bottom electrode for flexible capacitors instead of the novel metals.

Low-Temperature Nanocluster Deposition (NCD) for Improvement of the Structural, Electrical, and Optical Properties of ITO Thin Films

Indium tin oxide (ITO) thin films were grown using nanocluster deposition (NCD) on glass substrates in low temperature range from 170 to 250°C. X-ray diffraction pattern revealed that ITO thin films deposited above 200°C were preferentially oriented along (1 1 1) direction. A dramatic change in electrical properties of ITO thin films deposited from 200 to 170°C was attributed to the change in microstructure and chemical bonding states. The ITO thin films deposited at 170°C exhibited semiconducting properties with high optical transmittance of 95% at 550-nm wavelength. Films of approximately 140 ± 5 nm thicknesses exhibited both the lowest resistivity of 7 × 10^-4 Ω·cm and the figure-of-merit value of 1.3 × 10^-2 Ω^-1. The NCD technique is possible for deposition of ITO films crystallized at low temperatures below 200°C on glass or flexible polymer substrates.

Electrical Property and Long-Term Stability of Transparent Capacitors Using Multi-Layer Transparent Conducting Oxide Electrodes

Transparent capacitors of Al0.016In0.003Zn0.981O (AIZO)/Ag/AIZO/Bi2Mg2/3Nb4/3O7 (BMN)/AIZO/glass were prepared using BMN films with various thicknesses grown on AIZO/glass (Corning 1737) substrates by pulsed laser deposition. The BMN films deposited at 150 °C on the AIZO electrode exhibited a dielectric constant of 49–55, a dielectric loss of 3–7% at the frequency of 100 kHz and the leakage current densities of ~10-8 A/cm2 at 200 kV/cm, in the range of the thickness from 50 to 200 nm. After damp heat treatment for 300 h under the condition of 85% relative humidity at 85 °C, the electrical properties in the BMN capacitors were slightly degraded. The AIZO/Ag/AIZO/BMN/AIZO capacitors maintained the optical transmittance of approximately 77% at a wavelength of 500 nm after damp heat treatment.

Characterization of Al-doped ZnO (AZO) Transparent Conductive Thin films Grown by Atomic Layer Deposition

AZO transparent conductive thin films were grown on /Si and glass substrates using diethylzinc (DEZ) and trimethylaluminium (TMA) as the precursor and as oxidant by atomic layer deposition. The structural, electrical, and optical properties of the AZO films were characterized as a function of film thickness at a deposition temperature of . The AZO films with various thicknesses show well-crystallized phases and smooth surface morphologies. The 190-nm-thick AZO films grown on Coming 1737 glass substrates exhibit rms(root mean square) roughness of 8.8 nm, electrical resistivity of , and an optical transmittance of 84% at 600nm wavelength. Atomic layer deposition technique for the transparent conductive oxide films is possible to apply for the deposition on flexible polymer substrates.

ITO/CNT Nano Composites as a Counter Electrode for the Dye-Sensitized Solar Cell Applications

The ITO/Cabon Nano Tube (CNT) nano composites were deposited by nano cluster deposition (ITO) and arc discharge deposition (CNT) on glass substrates. The structural, optical and photovoltaic performance of ITO/CNT nano composites as a counter electrode of dye-sensitized solar-cells (DSSCs) such films were investigated. At low temperature below , the ITO films deposited on CNT. The ITO/CNT nano composit showed a good optical and electrical property for the counter electrode of DSSCs. When the as-prepared ITO/CNT nano composites are used for the counter electrodes, the photovoltaic parameters are