Jinsoo Joo

High-detectivity multilayer MoS(2) phototransistors with spectral response from ultraviolet to infrared.

Phototransistors based on multilayer MoS(2) crystals are demonstrated with a wider spectral response and higher photoresponsivity than single-layer MoS(2) phototransistors. Multilayer MoS(2) phototransistors further exhibit high room temperature mobilities (>70 cm(2) V(-1) s(-1) ), near-ideal subthreshold swings (~70 mV decade(-1) ), low operating gate biases (<5 V), and negligible shifts in the threshold voltages during illumination.

Hybrid nanostructures using π-conjugated polymers and nanoscale metals: synthesis, characteristics, and optoelectronic applications

Pi-conjugated organic systems have been used as optoelectronic and sensing materials due to their characteristics of efficient light emission or absorption, and p-type charge transport. The hybrid nanostructures of pi-conjugated organic systems with nanoscale metals offer surface plasmon (SP)-enhanced luminescence, which can be applied to organic-based optoelectronics, photonics, and sensing. Various hybrid nanostructures using light-emitting polymers with nanoscale metals have been fabricated and have shown considerable enhancement of photoluminescence efficiency due to energy and charge transfer effects in SP resonance coupling. In this tutorial review, recent conceptual and technological achievements in light-emitting polymers-based hybrid nanostructures are described.

Electrochemical and physical characterization of lithium ionic salt doped polyaniline as a polymer electrode of lithium secondary battery

Abstract Polyaniline films doped with lithium ionic salts such as LiPF 6 and LiBF 4 were prepared by using the electrolyte solution mixture of ethylene carbonate and dimethyl carbonate. The doping level of the polyaniline films was confirmed by X-ray photoelectron spectroscopy and dc conductivity experiments. A doping mechanism of lithium ion through the interaction with a nitrogen at imine site is proposed. Electrochemical cells of Lipolyaniline-LiPF 6 or Lipolyaniline-LiBF 4 were assembled to investigate electrical capacity and its trends over the repeated charge/discharge cycles. The capacity of Lipolyaniline cell was increased and then saturated over 15 cycles. However, it did not reach the half of theoretical capacity of polyaniline material. The mechanism of electrochemical reaction during charge/discharge process of Lipolyaniline cell is presented.

CHARACTERISTICS OF ELECTRICALLY CONDUCTING POLYMER-COATED TEXTILES

Intrinsically conducting polymer (ICP)/textile composites were prepared by coating polypyrrole (PPy) or poly (3,4-ethylenedioxythiopene) (PEDOT) on the fabrics through chemical and electrochemical oxidation of pyrrole or EDOT. We investigated the effects of the preparation conditions on the properties of the resulting composite such as ICP content, electrical conductivity, surface morphology, and electromagnetic interference shielding effectiveness (EMI SE). The specific volume resistivity of the composite was as low as 0.3 Ω-cm, giving rise to about 36 dB of EMI SE over the wide range of frequency up to 1.5 GHz. We also prepared the elastic textile composites, exhibiting a monotonic increase of the electrical resistance with the elongation up to 50%. We, therefore, propose the elastic textile composite can be used as a strain sensor for large deformation.

Physical characterization of emulsion intercalated polyaniline-clay nanocomposite

Using emulsion polymerization method, polyaniline (PAN)‐Na a ‐montmorillonite (MMT) clay nanocomposites were synthesized. Dodecylbenzenesulfonic acid (DBSA) was used as an emulsifier and dopant during emulsion polymerization. The X-ray diAraction patterns showed that PAN‐DBSA was intercalated between clay layers in the order of nanoscale. The room temperature (RT) dc conductivities of nanocomposites were 1‐10 ˇ3 S=cm depending on the molar ratio of dopants used. Temperature dependence of dc conductivity for the nanocomposites followed a quasi-one-dimensional (1D) variable range hopping (VRH) model. From temperature dependence of electron paramagnetic resonance experiments, magnetic properties and the density of states of the systems were obtained. The doping level of the nanocomposites was deduced from the results of X-ray photoelectron spectroscopy experiments. From the comparison of physical properties between PAN with clay and PAN without clay, the eAects of dopant and the layer of clay on charge transport and structure are discussed. ” 2001 Elsevier Science B.V. All rights reserved.

Remarkable Mobility Increase and Threshold Voltage Reduction in Organic Field‐Effect Transistors by Overlaying Discontinuous Nano‐Patches of Charge‐Transfer Doping Layer on Top of Semiconducting Film

An effective strategy for significantly increasing the organic transistor mobility with simultaneous reduction of the threshold voltage utilizing discontinuous nano-patches of charge-transfer doping layer is demonstrated. By overlaying the nano-patches on top of a given semiconducting film, mobility and threshold voltage of p-type pentacene are remarkably improved to 4.52 cm(2) V(-1) s(-1) and -0.4 V, and those of n-type Hex-4-TFPTA are also improved to 2.57 cm(2) V(-1) s(-1) and 4.1 V.

Field emission characteristics of electrochemically synthesized nickel nanowires with oxygen plasma post-treatment

The field emissive, electrical, magnetic, and structural characteristics of nickel (Ni) nanowires synthesized using the electrochemical deposition method with an alumina nanoporous template are reported. The synthesis and formation of Ni nanowires were confirmed by XRD, SEM, and HR-TEM experiments. Ferromagnetic hysteresis curves and the metallic temperature dependence of the current-voltage characteristics were observed for the Ni nanowire systems. The nanotip emitters of the field emission cells of the Ni nanowires after O(2) plasma treatment were easily patterned using the solution drop casting (SDC) method, in which the Ni nanowires were homogeneously dispersed in organic solvents, and then dropped and dried on an n-type doped Si substrate as the cathode. For the O(2) plasma treated Ni nanowires, we observed that the inhomogeneous oxidized layer on their surface was reduced, that the current density of the field emission cell increased from approximately 3.0 x 10(-9) to approximately 1.0 x 10(-3) A cm(-2) due to field emission, and that the lowest threshold electric field was approximately 4 V microm(-1). The field enhancement factor was estimated as approximately 1300 for the O(2) plasma treated Ni nanowires. The evolution of the field emission obtained from the phosphor screen was observed at different applied electric fields.

Comparison of lithium//polyaniline secondary batteries with different dopants of HCl and lithium ionic salts

Polyanilines doped either with a protonic acid (HCl) or an electrolytic solution containing a lithium ionic salt (LiPF6 or LiBF4) are prepared and their electrochemical characteristics for use as polymer electrodes of lithium secondary batteries are investigated. An emeraldine base (EB) film doped with HCl has the highest d.c. conductivity (∼10 S/cm). An EB-LiPF6 film has higher conductivity (∼0.52 S/cm) than an EB-LiBF4 (∼0.082 S/cm) film. X-ray photoelectron spectroscopic analysis of the films shows that some of the quinoid rings in EB are transformed into benzeniod rings through a doping process to generate polarons. The charge–discharge characteristics of lithium secondary batteries using the polyaniline films as positive electrodes are determined. The cell using the EB-LiPF6 film and an electrolytic solution containing LiPF6 exhibits the highest specific discharge capacity (∼50 mA h/g), whereas the cell using EB-HCl and LiPF6 solution has superior performance in the rapid saturation of discharge capacity and in stability.

Light-emitting color barcode nanowires using polymers: nanoscale optical characteristics.

We report on the light-emitting color barcode nanowires (LECB-NWs), which were fabricated by alternating the electrochemical polymerization of light-emitting polymers with various luminescence colors and efficiencies. The nanoscale photoluminescence characteristics of LECB-NWs were investigated using a laser confocal microscope with a high spatial resolution. The alternating light emissions of the LECB-NWs showed orange-yellow, red, and green colors due to the serial combination of poly(3-butylthiophene), poly(3-methylthiophene), and poly(3,4-ethylenedioxythiophene), respectively, with distinct luminescence intensities. The optical detection sensitivity and stability of LECB-NWs have been enhanced through a nanoscale Cu metal coating onto the NWs, based on surface plasmon resonance coupling and protection against oxidation. The flexibility of the LECB-NWs has been investigated through the folding and unfolding of the NWs by an applied nanotip impetus. The flexible LECB-NWs can be used as highly sensitive optical identification nanosystems for nanoscale or microscale products with complex physical shapes.

Poly(3-hexylthiophene)/multiwalled carbon hybrid coaxial nanotubes: nanoscale rectification and photovoltaic characteristics.

We fabricate hybrid coaxial nanotubes (NTs) of multiwalled carbon nanotubes (MWCNTs) coated with light-emitting poly(3-hexylthiophene) (P3HT). The p-type P3HT material with a thickness of approximately 20 nm is electrochemically deposited onto the surface of the MWCNT. The formation of hybrid coaxial NTs of the P3HT/MWCNT is confirmed by a transmission electron microscope, FT-IR, and Raman spectra. The optical and structural properties of the hybrid NTs are characterized using ultraviolet and visible absorption, Raman, and photoluminescence (PL) spectra where, it is shown that the PL intensity of the P3HT materials decreases after the hybridization with the MWCNTs. The current-voltage (I-V) characteristics of the outer P3HT single NT show the semiconducting behavior, while ohmic behavior is observed for the inner single MWCNT. The I-V characteristics of the hybrid junction between the outer P3HT NT and the inner MWCNT, for the hybrid single NT, exhibit the characteristics of a diode (i.e., rectification), whose efficiency is clearly enhanced with light irradiation. The rectification effect of the hybrid single NT has been analyzed in terms of charge tunneling models. The quasi-photovoltaic effect is also observed at low bias for the P3HT/MWCNT hybrid single NT.