Hyung-Kee Seo

Effect of annealing temperature on structural and bonded states of titanate nanotube films

A conversion from commercial titania (TiO2) nanoparticles to nanotubes was achieved by a hydrothermal method. The titanate nanotube (titanate) film was then deposited on a Si (001) substrate using an electrophoretic deposition (EPD) technique. The post hydrothermal treatment was then carried out by annealing the films at 300–1000°C for 30min in the static air. A major amount of intercalated sodium (Na) in as-synthesized titanate nanotubes was removed during the electrodeposition process. The collapse of the tubular structure can be seen clearly when annealed above 500°C. X-ray diffraction data indicate a significant increase in the anatase phase peak intensity with annealing temperature. O 1s peak is found to be built up of subpeaks of H2O, −OH, and Ti–O. Annealing results in an increase of the Ti–O peak intensity while other peaks disappear. Clear changes in the O 1s peak positions, symmetry, and shift towards lower energy (0.8eV) are evident with the increasing annealing temperature. The doublet spectra...

ITO thin films deposited at different oxygen flow rates on Si(100) using the PEMOCVD method

Abstract Indium tin oxide (ITO) thin films were deposited on Si(100) substrates using plasma enhanced metallorganic chemical vapor deposition (PEMOCVD). Precursors used in this study were tris (2,2,6,6-tetramethyl-3,5-heptanedionato) indium(III) and tin(III) acetate of 99.9% purity, which are readily available. The precursors decompose at very low temperatures, giving flexibility to use low temperature substrates. The deposition of ITO films was carried out at different oxygen flow rates (5–20 sccm) and Argon flow rate of 200 sccm. R.F. power and reaction temperature was fixed at 150 W and 300 °C, respectively. The deposited films were analyzed using X-ray diffraction, scanning electron microscopy, α-step profilometer and X-ray photoelectronic spectroscopy (XPS). Sheet resistance of ITO film was measured using four-probe method. XRD analysis shows that grains are aligned in (222) and (400) direction and changes from (222) to (400) direction with the increasing oxygen flow rate. SEM results shows that the size of grains decreases as the oxygen flow rate increases with a slight increase in size at 20 sccm. The thickness of the films is ∼7500 A in all the cases. Sheet resistance of ITO film decreases with increasing oxygen flow rate up to 15 sccm and a little increase in sheet resistance at 20 sccm. XPS results manifested that oxygen atoms are bonded to In and Sn atoms indicating the formation of ITO compound.

Photocurrent Induced by Conducting Channels of Hole Transporting Layer to Adjacent Photoactive Perovskite Sensitized TiO2 Thin Film: Solar Cell Paradigm

A high performance perovskite solar cell was fabricated using the distinguished morphology of polyaniline nanoparticles (PANI-NPs) as an efficient hole transporting layer (HTL) with methylammonium lead iodide perovskite (CH3NH3PbI3) as sensitizer. PANI-NPs were simply synthesized by the oxidative chemical polymerization of aniline monomer at 0-5 °C. A reasonable solar-to-electricity conversion efficiency of ∼6.29% with a high short circuit current (JSC) of ∼17.97 mA/cm(2) and open circuit voltage (VOC) of ∼0.877 V were accomplished by Ag/PANI-NPs/CH3NH3PbI3/mp-anatase-TiO2/bl-TiO2/FTO perovskite solar cell. The transient photocurrent and photovoltage studies revealed that the fabricated solar cell showed better charge transport time, diffusion coefficient, diffusion length, and charge collection efficiency. Herein, the use of PANI-NPs as the HTL improved the charge carrier generation and the charge collection efficiency of the fabricated solar cell.

Mesoporous TiO2 Films Fabricated Using Atmospheric Pressure Dielectric Barrier Discharge Jet

TiO2 nanoparticles were synthesized by a facile method of dielectric barrier discharge jet (DBD jet) for the dye-sensitized solar cell (DSSC) and other potential applications. DBD jet is utilized as a method for deposition of TiO2 nanoparticles with a 9 μm/min growth rate which is more than ×25 faster than reported previously. Their performance was compared with cells fabricated using commercial TiO2 nanoparticles (P25). The crystallinity and chemical bonding states of samples were characterized by XRD and XPS. Photoanodes fabricated by the DBD jet method resulted in approximately 50% higher photoconversion efficiency than ones prepared from P25 nanoparticles.

Electrochemically deposited ruthenium seed layer followed by copper electrochemical plating

Electrochemical deposition of ruthenium as a seed layer was investigated on Ti and TiN as barrier layers for Cu interconnects. The aqueous electrolyte, the N-bridged complex of ruthenium(IV) nitrosyl chloride (RuNC), for ruthenium electrochemical deposition was formed in situ. Electrochemical deposition of copper on the Ru seeded barrier layers was also demonstrated. The chemicals for the acid-bath ruthenium electrochemical deposition were ruthenium(III) chloride hydrate (RuCl 3 .3H 2 O), hydrochloric acid (HCI), sulfamic acid (NH 2 SO 3 H), and polyethylene glycol. The chemicals for the acid-bath copper electrochemical deposition were copper(II) sulfate hydrate (CuSO 4 .5H 2 O), sulfuric acid (H 2 SO 4 ), and polyethylene glycol. Results were analyzed by field-emission scanning electron microscopy, atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Ru-therford backscattering spectrometry. The Ru thin layer with equiaxial grains <10 nm on blanket Ti substrates were obtained by electrochemical deposition. Electrochemical Cu trench fill was successful on patterned TiN 130 nm 2.5 aspect ratio trenches with Ru as a seed layer.

Effective D-A-D type chromophore of fumaronitrile-core and terminal alkylated bithiophene for solution-processed small molecule organic solar cells

A new and novel organic π-conjugated chromophore (named as RCNR) based on fumaronitrile-core acceptor and terminal alkylated bithiophene was designed, synthesized and utilized as an electron-donor material for the solution-processed fabrication of bulk-heterojunction (BHJ) small molecule organic solar cells (SMOSCs). The synthesized organic chromophore exhibited a broad absorption peak near green region and strong emission peak due to the presence of strong electron-withdrawing nature of two nitrile (–CN) groups of fumaronitrile acceptor. The highest occupied molecular orbital (HOMO) energy level of –5.82 eV and the lowest unoccupied molecular orbital (LUMO) energy level of –3.54 eV were estimated for RCNR due to the strong electron-accepting tendency of –CN groups. The fabricated SMOSC devices with RCNR:PC60BM (1:3, w/w) active layer exhibited the reasonable power conversion efficiency (PCE) of ~2.69% with high short-circuit current density (JSC) of ~9.68 mA/cm2 and open circuit voltage (VOC) of ~0.79 V.

Furan-bridged thiazolo [5,4-d]thiazole based D–π–A–π–D type linear chromophore for solution-processed bulk-heterojunction organic solar cells

Novel furan-bridged thiazolo[5,4-d]thiazole based π-conjugated organic chromophore (RFTzR) was formulated and utilized for small molecule organic solar cells (SMOSCs). The presence of furan spacer along with two terminal alkyl units significantly improved its absorption and solubility in the common organic solvents. RFTzR exhibited the reasonable HOMO and LUMO energy levels of −5.36 eV and −3.14 eV, respectively. The fabricated SMOSCs with RFTzR (donor) and PC60BM (acceptor) as photoactive materials presented relatively high power conversion efficiency of ∼2.72% (RFTzR : PC60BM, 2 : 1, w/w) along with good open-circuit voltage of ∼0.756 V and high photocurrent density of ∼10.13 mA cm−2, which might attribute to its improved absorption, electrochemical properties and the presence of strong electron-withdrawing furan moieties.

Growth and morphological study of zinc oxide nanoneedles grown on the annealed titanate nanotubes using hydrothermal method

Hydrothermal growth of ZnO on the annealed titanate nanotube films results in the oriented hexagonal-needlelike structures. The size, shape, density, and alignment of ZnO film are significantly affected by annealing temperature and orientation of the beneath titanate layer. It is believed that oxygen and hydrogen vacancies, generated due to dehydration of interlayered OH groups while annealing of the titanate, are responsible for the changes in the morphology of the ZnO. Microscopic observations clearly resolved nanoneedles with the base diameter of ∼150nm and length of ∼5μm with lattice spacing of 0.52nm, indicating single crystalline ZnO and grown along the (0001) direction. A growth model is presented based on the layer-by-layer growth (three-step growth) as a function of growth time (2–6h). Thicknesses of these three steps were found increasing with growth time. The second step (II) of growth exhibits the same feature as that of the first step (I), i.e., bounded with six crystallographic, lower surfac...

Lonsdaleite diamond growth on reconstructed Si (100) by hot-filament chemical vapor deposition (HFCVD)

In this paper, the growth of Lonsdaleite diamond using hot-filament chemical vapor deposition (HFCVD) on flashed and reconstructed Si (100) is reported. Surface morphology studies using scanning electron microscopy (SEM) show that the film is composed of decahedron and icosahedron diamond particles. The X-ray diffraction (XRD) pattern has a strongest peak at 47° and a peak at 41°, which is indicative of Lonsdaleite nature of the grown diamond film. The Raman spectrum of the film shows a broadened diamond peak at wave number of 1,329 cm−1, which has shifted towards the peak position corresponding to Lonsdaleite nature of the diamond (1,326 cm−1).

TiO2 nanotube arrays via electrochemical anodic oxidation: Prospective electrode for sensing phenyl hydrazine

The TiO2 nanotube (NT) arrays were grown on Ti foil substrate by electrochemical anodic oxidation and utilized as working electrode to fabricate a highly sensitive and reproducible chemical sensor for the detection of harmful phenyl hydrazine chemical. The fabricated chemical sensor based on TiO2 NT arrays electrode exhibited high sensitivity of ∼40.9μA mM−1 cm−2 and detection limit of ∼0.22 μM with short response time (10 s). The enhanced sensing properties were attributed to the presence of depleted oxygen layer on the surface of grown TiO2 NT arrays and its high electron transfer process via good electrocatalytic activity towards phenyl hydrazine chemical.