Tae-Sik Yoon

Use of fluorine-doped tin oxide instead of indium tin oxide in highly efficient air-fabricated inverted polymer solar cells

The stability and efficiency of organic solar cells (OSCs) were improved using thermally stable fluorine-doped tin oxide (FTO) as the bottom electrode and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and TiO2 as the buffer layers. The TiO2 layer between FTO and the P3HT:PCBM active layer improved the interface characteristics for a better charge transfer. The PEDOT:PSS layer retarded the oxygen diffusion to the active layer. A maximum power conversion efficiency of 4.3% was obtained for the inverted structure of FTO/TiO2/P3HT:PCBM/PEDOT:PSS/Ag with a stable performance, and the cell retained over 65% of its initial efficiency after 500 h. Additionally, the OSCs were fabricated using all-solution based vacuum-free processes with screen printing for the Ag electrode and the results were comparable to the device that used an evaporated Ag electrode.

Nucleation kinetics of Ru on silicon oxide and silicon nitride surfaces deposited by atomic layer deposition

The nucleation behavior of Ru deposited by atomic layer deposition (ALD) using bis(ethylcyclopentadienyl)ruthenium precursor and O2 reactant is investigated as a function of the number of ALD cycles. The substrates are thermally grown SiO2, NH3 plasma-treated SiO2, and chemical vapor deposited SiNx. The nucleation of Ru strongly depends on the substrate and is much enhanced on the nitride substrates. Transmission electron microscopy analysis reveals that the maximum density of the nuclei is 5.7×1010cm−2 on the SiO2 surface at 500 ALD cycles, 1.2×1012cm−2 on SiNx at 160 ALD cycles, and 2.3×1012cm−2 on NH3 plasma-nitrided SiO2 at 110 ALD cycles. Although the kinetics of Ru nucleation is different on the various substrates, the overall nucleation process in each case consists of an initial slow nucleation stage and a subsequent fast nucleation stage before the coalescence of the nuclei occurs. Considering the adsorption of Ru precursor on the substrate and the surface diffusion of deposited Ru during an ALD ...

Colloidal Nanoparticle-Layer Formation Through Dip-Coating: Effect of Solvents and Substrate Withdrawing Speed

The effect of solvents of colloidal solution and substrate withdrawing speed during dip-coating on the nanoparticle-layer formation of sterically stabilized iron oxide (γ-Fe 2 O 3 ) nanoparticles on Si substrates is investigated. From the solutions with 10 13 -10 14 mL -1 particle concentrations dispersed in hexane, octane, decane, and tetradecane, the multilayer is formed from hexane while the uniform monolayer is formed from octane, decane, and tetradecane. Because the particle layer is formed by direct adsorption and convective flux of particles from solution to substrate, the multilayer formation from hexane is due to the highest interaction energy between particle and substrate and the highest convective flux to the meniscus region of the substrate caused by the highest evaporation rate. Lowering the substrate withdrawing speed increases the particle coverage from ∼60 to ∼80% at 0.001 mm/s as locally forming the multilayer regions, which is explained by increased convective flux at reduced speed. These results verify that the colloidal particle delivery to the substrate is determined by factors such as particle-substrate interactions, substrate withdrawing speed, and the evaporation rate of solvent.

Effects of B2H6 Pretreatment on ALD of W Film Using a Sequential Supply of WF6 and SiH4

The effects of diborane pretreatment on atomic layer deposition (ALD) of tungsten (W) thin film using a sequential supply of and on thermally grown and TiN films at 300°C were investigated. The results show that the pretreatment reduces the incubation time for film growth. X-ray photoelectron spectroscopy and scanning electron microscopy analysis suggest that elemental B on , released during pretreatment, induce rapid W nucleation. The drastically improved step coverage of ALD-W film is achieved at the ultrahigh aspect ratio contact (height: and top diameter: ) by the enhanced nucleation and growth via pretreatment. The effects of pretreatment on the properties of ALD-W films such as roughness, phase, microstructure, and resistivity are also investigated.

Digital versus analog resistive switching depending on the thickness of nickel oxide nanoparticle assembly

The thickness-dependent digital versus analog resistive switching of nickel oxide (NiOx) nanoparticle assemblies was investigated in a Ti/NiOx/Pt structure. The NiOx nanoparticles were chemically synthesized with ∼5 nm diameter. The Ti/NiOx/Pt structure with assembly thickness of ∼60 nm exhibited the digital-type bipolar resistive switching. However, the assembly with a thickness of ∼90 nm presented analog resistive switching with gradually decreasing resistance when sweeping −V while increasing resistance after applying +V. Repeating −V pulses decreased the resistance sequentially, but the high resistance was restored sequentially by repeating +V pulses, which is analogous to the potentiation and depression of adaptive synaptic motion.

A Nanopore Structured High Performance Toluene Gas Sensor Made by Nanoimprinting Method

Toluene gas was successfully measured at room temperature using a device microfabricated by a nanoimprinting method. A highly uniform nanoporous thin film was produced with a dense array of titania (TiO2) pores with a diameter of 70∼80 nm using this method. This thin film had a Pd/TiO2 nanoporous/SiO2/Si MIS layered structure with Pd-TiO2 as the catalytic sensing layer. The nanoimprinting method was useful in expanding the TiO2 surface area by about 30%, as confirmed using AFM and SEM imaging. The measured toluene concentrations ranged from 50 ppm to 200 ppm. The toluene was easily detected by changing the Pd/TiO2 interface work function, resulting in a change in the I–V characteristics.

Organic memory device with polyaniline nanoparticles embedded as charging elements

Polyaniline nanoparticles (PANI NPs) were synthesized and fabricated as charging elements for organic memory devices. The PANI NPs charging layer was self-assembled by epoxy-amine bonds between 3-glycidylpropyl trimethoxysilane functionalized dielectrics and PANI NPs. A memory window of 5.8 V (ΔVFB) represented by capacitance-voltage hysteresis was obtained for metal-pentacene-insulator-silicon capacitor. In addition, program/erase operations controlled by gate bias (−/+90 V) were demonstrated in the PANI NPs embedded pentacene thin film transistor device with polyvinylalcohol dielectric on flexible polyimide substrate. These results can be extended to development of fully organic-based electronic device.

Multimode threshold and bipolar resistive switching in bi-layered Pt-Fe2O3 core-shell and Fe2O3 nanoparticle assembly

The bias-polarity dependent multimode threshold and bipolar resistive switching characteristics in bi-layered Pt-Fe2O3 core-shell and γ-Fe2O3 nanoparticles assembly were investigated. The Ti/Pt-Fe2O3-core-shell-nanoparticles (∼20 nm)/γ-Fe2O3-nanoparticles (∼40 nm)/Pt structure exhibited a threshold switching upon applying −V at Ti electrode. However, the filaments were formed at +V and subsequently ruptured at −V, featured to be bipolar switching. After rupturing filaments, it returned to threshold switching mode. The presence of core-shell nanoparticles facilitates the threshold switching either by temporary formation of filaments or enhanced charge transport. Also, the oxygen reservoir role of Ti electrode was essential to form stable filaments for bipolar switching.

Electrical charging of Au nanoparticles embedded by streptavidin-biotin biomolecular binding in organic memory device

In this study, electrical charging phenomena in an organic memory structure using Au nanoparticles (NPs) conjugated with a specific binding mechanism were demonstrated. Monolayer of streptavidin-passivated Au NPs was incorporated on biotin-coated SiO2 in structure of metal-pentacene-insulator-silicon (MPIS) device. Clockwise and counter-clockwise capacitance-voltage (C-V) hysteresis loops were measured depending on the oxide thickness. For 30 nm, a clockwise C-V hysteresis having memory window of 0.68 V was obtained under (+/−)12 V sweep range, while a counter-clockwise C-V hysteresis having memory window of 6.47 V was obtained under (+/−)7 V sweep range for 10 nm thick oxide.

Completely Filling Anodic Aluminum Oxide with Maghemite Nanoparticles by Dip Coating and Their Magnetic Properties

Anodic aluminum oxide (AAO) nanotemplates were completely filled with maghemite (γ-Fe 2 O 3 ) nanoparticles by a dip-coating process and their magnetic properties were investigated. Maghemite particles with ―20 nm diameter and stabilized by oleic acid were selectively deposited into AAO pores with ∼100 nm diameter. The multiple layers of particles were obtained by repeating the procedures of dip coating and removing oleic acids from the particles. The magnetic moment of AAO with particles increased in proportion to the number of layers. These results demonstrate the possibility of integrating nanoparticles into nanotemplates and controlling their properties.