Chinho Park

Effects of nitrogen flow rate on titanium nitride films deposition by DC facing target sputtering method

TiN films were deposited onto a glass substrate by DC facing target sputtering, and the effects of N2 flow rate on the film properties were investigated. Prepared TiN films had a rock salt (NaCl-type) structure with a very low resistivity (∼30 μΩ·cm) and gold-like color. Increase in the N2 flow rate played an important role in controlling the properties of TiN films, such as Ti/N ratio and growth orientation. The growth orientation changed from a (111) phase to (200), with the ratio of N/Ti becoming near stoichiometric. The change in the growth orientation was caused by the increase in the N2 flow rate, which weakens the kinetic energy of the bombarding particles. The observed phenomenon is explained by an energy loss in the reactive plasma due to the difference in the inner degree of freedom of the molecular gas causing the reduction in the effective energy for radicals.

Characterization of Parylene Deposition Process for the Passivation of Organic Light Emitting Diodes

The chemical vapor condensation process of Parylene-N thin films was investigated and applied to the passivation of the organic light emitting diodes (OLEDs). The effects of process variables on the deposition rate were studied, and it was found that the deposition rate of Parylene increases with increasing precursor sublimation temperature but decreases with increasing substrate temperature. The dependence of deposition rate was well explained by the condensation polymerization model of the monomer on the surface. The Parylene film was used as a passivation layer for OLEDs, and as a result, the lifetime of the passivated OLEDs was increased by a factor of about 2.3 compared with that of non-passivated OLEDs.

Fabrication of red, green, and blue organic light-emitting diodes using m-MTDATA as a common hole-injection layer

Organic light-emitting diodes (OLEDs) of metal-semiconductor-metal (MSM) structure have been fabricated by using m-MTDATA [4,4′,4′’-tris (3-methylphenylphenylamino) triphenylamine] as a hole-injection layer (HIL). The m-MTDATA is shown to be an effective hole-injecting material for the OLED, in that the insertion of m-MTDATA greatly reduces the roughness of anode surface, lowers the turn-on voltage, and increases the luminous efficiency. Red, green and blue OLEDs were fabricated, and their color coordinates in CIE chromaticity were found to be (0.600, 0.389), (0.240, 0.525) and (0.171, 0.171), respectively. The luminous efficiencies of the fabricated OLEDs were 1.4 lm/W at 106 cd/m2 for red, 1.4 lm/W at 100 cd/m2 for green, and 2.0 lm/W at 104 cd/m2 for blue.

Modified electrical properties and transport mechanism of Ti/p-InP Schottky structure with a polyvinylpyrrolidone (PVP) polymer interlayer

This paper reviews the electrical and transport properties of Ti/polyvinylpyrrolidone (PVP)/p-InP metal/interlayer/semiconductor (MIS) Schottky diode and compared its results with the Ti/p-InP metal/semiconductor (MS) diode. Analysis results showed that the barrier height (BH) and ideality factor of the MIS diode are found to be improved compared to the MS diode. This indicates that the effective BH is modified by the PVP interlayer since it creates physical barrier between the Ti metal and the p-InP substrate. It is noted that the evaluated BH by Cheung’s and ψS-V plots is in good concurrence with one another. Also, the series resistance of the MS and MIS diodes is estimated by Cheung’s functions. The insertion of the PVP interlayer led to a decrease of the interface state density in the Ti/p-InP MS diode. In addition, the relevant junction mechanisms are explained by feasible energy level band diagrams. The Poole–Frenkel emission is the governing conduction mechanism in the Ti/p-InP MS diode. However, at lower voltage region the Poole–Frenkel is conquered, whereas at higher voltage region the Schottky emission is occupied for the Ti/PVP/p-InP MIS diode.

Bright luminescence from pure DNA-curcumin–based phosphors for bio hybrid light-emitting diodes

Recently, significant advances have occurred in the development of phosphors for bio hybrid light-emitting diodes (Bio-HLEDs), which have created brighter, metal-free, rare-earth phosphor-free, eco-friendly, and cost-competitive features for visible light emission. Here, we demonstrate an original approach using bioinspired phosphors in Bio-HLEDs based on natural deoxyribonucleic acid (DNA)-curcumin complexes with cetyltrimethylammonium (CTMA) in bio-crystalline form. The curcumin chromophore was bound to the DNA double helix structure as observed using field emission tunnelling electron microscopy (FE-TEM). Efficient luminescence occurred due to tightly bound curcumin chromophore to DNA duplex. Bio-HLED shows low luminous drop rate of 0.0551 s−1. Moreover, the solid bio-crystals confined the activating bright luminescence with a quantum yield of 62%, thereby overcoming aggregation-induced quenching effect. The results of this study herald the development of commercially viable large-scale hybrid light applications that are environmentally benign.

Investigation of an upflow cold-wall CVD reactor by gas phase Raman spectroscopy

The gas phase dynamics of an inverted, stagnation point flow CVD reactor were studied by both experiment and modeling. The axial centerline temperature profile in the reactor was measured by analysis of the rotational Raman spectra from the carrier gas ( No r H) as a function of the inlet flow velocity and the reactor aspect ratio.It was found that a larger temperature gradient 22 normal to the susceptor surface was obtained with higher gas flow velocity, larger aspect ratio, and the use of a N carrier gas. 2 A two-dimensional axisymmetric model with detailed heat transfer descriptions predicted the experimental data well.The validated model clearly demonstrates that recirculation flows are less likely in inverted reactor geometry. 2002 Elsevier Science B.V. All rights reserved.

Synthesis and thermal annealing treatment of octylphosphonic acid-capped CdSe-tetrapod nanocrystals for bulk hetero-junction solar cell applications

CdSe-tetrapod nanocrystals (NCs) were synthesized by using octylphosphonic acid (OPA) as a capping ligand and cadmium oxide (CdO) as a cadmium precursor. The effects of thermal annealing in nitrogen (N2) environment on the chemical composition, morphology, crystal structure and optoelectronic properties of the CdSe-tetrapods have been investigated. Remarkable difference in the morphological and optoelectronic properties between as-synthesized and N2-annealed CdSe NCs was observed. The photoluminescence (PL) peak of N2-annealed CdSe NCs shifted to lower energy and UV-vis absorption spectra shifted to longer wavelength, indicating the size increase and improvement of the crystallinity of the CdSe tetrapods. The power conversion efficiency of bulk hetero-junction solar cells made with the annealed CdSe NCs showed higher value compared with the efficiency of cells made with as-synthesized CdSe NCs.

Structural and Optoelectronic Properties of CdSe Tetrapod Nanocrystals for Bulk Heterojunction Solar Cell Applications

Semiconducting CdSe tetrapod nanoparticles were prepared, and their structural and optical properties were examined. The surface capping molecule, octylphosphonic acid, was replaced with butylamine after the particle synthesis. The exchange of surface ligands changed the physical properties of the nanocrystals, which resulted in a slight decrease in the nanoparticles size. The effects of changing surface ligands of CdSe tetrapod nanocrystals on the structural and optoelectronic properties were investigated, and it was found that the surfactant of nanoparticles could affect the device performance by enhancing the charge carrier separation at the active layer interfaces. Power conversion efficiency of the bulk heterojunction solar cells having the structure of glass/ITO/PEDOT:PSS/(CdSe

Study of MEH–PPV/PCBM active layer morphology and its application for hybrid solar cell performance

Surface morphologies of MEH–PPV:PCBM active layers were optimized by investigating ITO substrate treated with oxygen and nitrogen plasma. This treatment effectively improved smoothness, transmittance, and contact angle of ITO’s, resulting in good anode contacts for hybrid device structures. The consistently improved performance of hybrid solar cells was also achieved. The surface properties of treated and untreated ITO substrates were compared by contact angle, four point probe, scanning electron microscopy, and atomic force microscopy.

Preparation of anodic aluminum oxide (AAO) nano-template on silicon and its application to one-dimensional copper nano-pillar array formation

Anodized aluminum oxide (AAO) nanotemplates were prepared using the Al/Si substrates with an aluminum layer thickness of about 300 nm. A two-step anodization process was used to prepare an ordered porous alumina nanotemplate, and the pores of various sizes and depths were constructed electrochemically through anodic oxidation. The optimum morphological structure for large area application was constructed by adjusting the applied potential, temperature, time, and electrolyte concentration. SEM investigations showed that hexagonal-close-packed alumina nano-pore arrays were nicely constructed on Si substrate, having smooth wall morphologies and well-defined diameters. It is also reported that one dimensional copper nanopillars can be fabricated using the tunable nanopore sized AAO/Si template, by controlling the copper deposition process.