Seok-Joo Wang

Effects of dopant ion and Mn valence state in the La1−xAxMnO3(A=Sr,Ba) colossal magnetoresistance films

The structural and electrical properties of Mn-based colossal magnetoresistance (CMR) thin films with controlled tolerance factor and Mn ion valance ratio were studied using crystal structure and chemical bonding character analyses. La0.7Sr0.3MnO3, La0.7Ba0.3MnO3, and La0.82Ba0.18MnO3 thin films with different contents of divalent cations and Mn3+/Mn4+ ratios were deposited on amorphous SiO2/Si substrate by rf magnetron sputtering at a substrate temperature of 350 °C. The films showed the same crystalline structure as the pseudocubic structure. The change in the sheet resistance of films was analyzed according to strain state of the unit cell, chemical bonding character of Mn–O, and Mn3+/Mn4+ ratio controlling the Mn3+–O2−–Mn4+ conducting path. Mn L-edge x-ray absorption spectra revealed that the Mn3+/Mn4+ ratio changed according to different compositions of Sr or Ba and the Mn 2p core level x-ray photoelectron spectra showed that the Mn 2p binding energy was affected by the covalence of the Mn–O bond and...

Investigation of Ag-poly(3,4-ethylenedioxythiophene):polystyrene sulfonate nanocomposite films prepared by a one-step aqueous method

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) hybrid films containing Ag nanoparticles were synthesized by a one-step aqueous method. The embedded Ag nanoparticles were produced using PEDOT as a reducing agent and PSS as a stabilizer. We have also demonstrated nanoparticle growth with increasing reaction time and silver nitrate content. Finally, as a nanocomposite-containing nanoparticle without surface-capping molecules and embedded in a conducting polymer matrix, the Ag NPs-PEDOT:PSS nanocomposite is interesting because it represents a type of material in which a metallic nano-island is embedded in the semiconducting matrix with a pure interface. One-step synthesized silver nanoparticles were found to induce a lowering of the work function and an increase of the highest occupied molecular orbital level in pristine PEDOT:PSS films by electron exchange with PEDOT, and also induced an inhibition of the electrostatic bond between PEDOT and PSS.

Effects of H2 Addition in Magnetized Inductively Coupled C2F6 Plasma Etching of Silica Aerogel Film

Effect of H2 addition to C2F6 plasma etching of SiO2 aerogel film was examined for low-k dielectric application. In this experiment, H2 plasma in itself was responsible for pore blocking and bond breaking of the SiO2 aerogel. With increasing hydrogen from 0 to 50%, etch rate of SiO2 aerogel was severely dropped at 20% of H2 addition. According to the increase in H2 addition, transition from fluorine-rich residue to carbon-rich one was gradually happened in SiO2 aerogel. Surface microstructure of SiO2 aerogel was so influenced with the increasing H2 addition that they transformed to be planar by the interaction between residue/network and ion bombardment and the condensation reaction of surface chemicals with H2 plasma.

X-ray photoelectron spectroscopic analysis on plasma-etched SiO2 aerogel with CHF3 gas

Abstract SiO 2 aerogel has great potential as a promising intermetal dielectric with low dielectric constant due to its porous nature. Dry etching of porous SiO 2 should be carefully investigated for its application as an intermetal dielectric. The etching behaviour of SiO 2 aerogel with inductively coupled CHF 3 plasma etching was investigated and compared with thermally grown SiO 2 . A basic three-dimensional network structure, composed of SiO 2 particles and internal pores, was maintained on the etching process. From angle-resolved X-ray photoelectron spectroscopy analyses, it was revealed that the etching process occurred not only at the aerogel film surface but also at the large internal surface. However, the effective etch rate was slower, from the consideration of 70% film porosity, compared with thermally grown SiO 2 . This is related to the large content of C and H in the SiO 2 aerogel film.

Electronic properties of hybridized poly (3, 4-ethylenedioxythiophene): Polystyrene sulfonate with surface-capped CdSe nanocrystals

The chemical state and electronic properties of hybrid material based on poly (3, 4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) and pyridine-capped CdSe nanocrystals have been investigated using photoemission spectroscopy, near-edge x-ray absorption fine structure, and ultraviolet photoelectron spectroscopy. With a high dipole moment as well as high physical momentum, CdSe nanocrystals hindered the rearrangement of PEDOT:PSS and induced PSS-rich surface during film formation. Thus, the work function value was decreased by dedoping of PEDOT or charge localization in PEDOT. Through heat treatment, the behavior of π-π∗ transition in C 1s and the work function value was nearly restored, gradually; these mean recovery of electrostatic bonding nature between PEDOT and PSS. However, the ionization potential (IP) was slightly increased by 0.3 eV with CdSe nanocrystal incorporation and interpreted as dielectric property and local electron transfer from highest occupied molecular orbital of PEDOT to ...

Effect of Silica Nanoparticle Content on the Structure and Electrostatic Bonding of PEDOT:PSS

Conducting poly(3,4-ethylenedioxythiophene):poly(styrene-4-sulfonate) (PEDOT:PSS) containing hydroxyl surface rich SiO2 nanoparticles were investigated. Rearrangement and bonding of PEDOT:PSS were affected by the content of SiO2 nanoparticles, which resulted in the modification of an electronic band structure and electrical characteristics. A slight decrease in work function and a shift of the highly occupied molecular orbital edge to the Fermi level were induced by SiO2 nanoparticle addition. The current path was also tuned by SiO2 nanoparticles and resistance of the composite film was diminished. SiO2 nanoparticles affect electrostatic bonding between PEDOT:PSS and doping of PEDOT as well as increase the packing density of PEDOT:PSS.

Investigation of the surface chemical and electronic states of pyridine-capped CdSe nanocrystal films after plasma treatments using H2, O2, and Ar gases

Surface chemical bonding and the electronic states of pyridine-capped CdSe nanocrystal films were evaluated using x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy before and after plasma treatments using H2, O2, and Ar gases from the viewpoint of studying the effects of surface capping organic molecules and surface oxidation. Surface capping organic molecules could be removed during the plasma treatment due to the chemical reactivity, ion energy transfer, and vacuum UV (VUV) of the plasma gases. With O2 plasma treatment, surface capping organic molecules were effectively removed but substantial oxidation of CdSe occurred during the plasma treatment. The valence band maximum energy (EVBM) of CdSe nanocrystal films mainly depends on the apparent size of pyridine-capped CdSe nanocrystals, which controls the interparticle distance, and also on the oxidation of CdSe nanocrystals. Cd-rich surface in O2 and H2 plasma treatments partially would compensate for the decrease in EVBM. After...

Effect of Annealing Temperature with Silver Nanoparticles Incorporation on the Electronic Structure of Poly (3, 4-ethylenedioxythiphene) : poly (styrenesulfonate) Film

)Abstract The effect of silver nanoparticles (NPs) incorporation on the electronic properties of poly (3, 4-ethylenedioxythiphene) : poly(styrenesulfonate) (PEDOT : PSS) films was investigated. The surface of silverNPs was stabilized with trisodium citrate to control the size of silver NPs and prevent their aggregation. Weobtained ca. 5 nm sized silver NPs and dispersed NPs in PEDOT : PSS solution. Sheet resistance, surfacemorphology, bonding state, and work function values of the PEDOT : PSS films were modified by silver NPsincorporation as well as annealing temperature. Sodium in silver NPs solution could lead to a decrease of workfunction of PEDOT : PSS; however, large content of silver NPs have an effect on the increase in work function,resulting from charge localization on the silver NPs and a decrease in the number of charge-trapping-relateddefects by chemical bond formation.Key wordsPEDOT : PSS; silver; nanoparticle; work function; charge localization.

The effects of surface terminal bonds and microstructure of SiO2 aerogel films on dry etching

Abstract The effects of microstructure and surface terminal bonds of SiO 2 aerogel films on dry etching were investigated using Ar, SF 6 , and C 2 F 6 plasma gases. With Ar plasma etching, physical effect of ion bombardment on porous film was found. In residue-free SF 6 plasma etching, reactive etchant transport and high-mass ion bombardment were observed. With C 2 F 6 plasma etching, fluorocarbon residue layer was revealed to maintain surface morphology as acting a barrier to radical transport and ion bombardment. An etching of 450°C-annealed SiO 2 aerogel showed that a dense surface induced the decrease in reaction area, inhibition of etchant transport, and then uniform etching.

Microstructure and Ferroelectric Properties of Direct-Patternable Bi3.25La0.75Ti3O12 Films Prepared by Photochemical Metal-Organic Deposition

The microstructure and ferroelectric properties of Bi 3.25 La 0.75 Ti 3 O 12 films prepared by photochemical metal-organic deposition using photosensitive precursors were characterized. The diffraction intensities showed a distribution similar to Bi 3.25 La 0.75 Ti 3 O 12 ceramics, and Pt(111) was found to not influence the growth orientation of Bi 3.25 La 0.75 Ti 3 O 12 films. The values of measured remnant polarization and dielectric constant of Bi 3.25 La 0.75 Ti 3 O 12 films annealed at 650 and 700°C were 8.7, 16.0 μC/cm 2 and 172, 276, respectively. The films remained free of fatigue up to 10 9 switching cycles. These results suggest the possible application of ferroelectric Bi 3.25 La 0.75 Ti 3 O 12 film, relatively easily and without high cost process such as dry etching.