[Show abstract][Hide abstract] ABSTRACT: Complementary inverters consisting of p-type organic and n-type metal oxide semiconductors have received considerable attention as key elements for realizing low-cost and large-area future electronics. Solution-processed ZnO thin-film transistors (TFTs) have great potential for use in hybrid complementary inverters as n-type load transistors because of the low cost of their fabrication process and natural abundance of active materials. The integration of a single ZnO TFT into an inverter requires the development of a simple patterning method as an alternative to conventional time-consuming and complicated photolithography techniques. In this study, we used a photo-curable polymer precursor, zinc acrylate (or zinc diacrylate, ZDA), to conveniently fabricate photo-patternable ZnO thin films for use as the active layers of n-type ZnO TFTs. UV-irradiated ZDA thin films became insoluble in developing solvent as the acrylate moiety photo-crosslinked; therefore, we were able to successfully photo-pattern solution-processed ZDA thin films using UV light. We studied the effects of addition of a tiny amount of indium dopant on the transistor characteristics of the photo-patterned ZnO thin films and demonstrated low-voltage operation of the ZnO TFTs within ± 3 V by utilizing Al2O3/TiO2 laminate thin films or ion-gels as gate dielectrics. By combining the ZnO TFTs with p-type pentacene TFTs, we successfully fabricated organic/inorganic hybrid complementary inverters using solution-processed and photo-patterned ZnO TFTs.
No preview · Article · Feb 2016 · ACS Applied Materials & Interfaces
[Show abstract][Hide abstract] ABSTRACT: Two oxygen plasma treated InP samples with different plasma powers of 100 and 250 W were prepared and a comparative study on the electrical properties of Cu/n-type InP Schottky diode measured at 300 and 100 K was performed to investigate the current transport mechanism in detail. The forward and reverse bias current-voltage (I-V) characteristics were analyzed with considering various transport models. The fitting to the forward bias I-V characteristics revealed that relatively high ideality factor at 300 K for untreated sample were related with the generation-recombination (GR) current and the large E00 value at 100 K for 100 W plasma treated sample were associated with more significant tunneling effect. The analyses on the reverse bias current characteristics showed the suitable current transport model has changed from thermionic emission (TE) to TE combined with barrier lowering for both untreated and 250 W treated samples and from TE + BL to thermionic field emission for 100 W treated sample with increasing temperature from 100 to 300 K.
Full-text · Article · Jan 2016 · Current Applied Physics
[Show abstract][Hide abstract] ABSTRACT: Nanolamination has entered the spotlight as a novel process for fabricating highly dense nanoscale inorganic alloy films. OFET commercialization requires, above all, excellent dielectric properties of gate dielectric layer. Here, we describe the fabrication and characterization of Al-O-Ti (AT) nanolaminate gate dielectric films using a PEALD process, and their OFET applications. The AT films exhibited a very smooth surface (Rq < 0.3 nm), a high dielectric constant (17.8), and a low leakage current (8.6 × 10-9 A/cm2 at 2 MV/cm) compared to single Al2O3 or TiO2 films. Importantly, a 50 nm thick AT film dramatically enhanced the value of μFET (0.96 cm2/V) on a pentacene device, and the high off-current level in a single TiO2 film was effectively reduced. The nanolamination process removes the drawbacks inherent in each single layer so that the AT film provides excellent dielectric properties suitable for fabricating high-performance OFETs. Triethylsilylethynyl anthradithiophene (TES-ADT), a solution-processable semiconductor, was combined with the AT film in an OFET, and the electrical properties of the device were characterized. The excellent dielectric properties of the AT film render nanolamination a powerful strategy for practical OFET applications.
No preview · Article · Jan 2016 · Organic Electronics
[Show abstract][Hide abstract] ABSTRACT: Dispersion of clay in polymer matrices is important to improve their engineering performances. Here we report the effect of solvent on dispersion of montmorillonite (MMT) in an epoxy matrix by examining transmission electron micrographs and X-ray diffraction of MMT/epoxy composites prepared with solvents with different polarities. We found that N-metyl-2-pyrrolidone (NMP) used as a polar solvent exhibited the improved dispersion of MMT in the epoxy owing to positive interaction energies with components, which prevents the aggregation of MMT platelets. The solvent-assisted dispersion of MMT significantly increased the corrosion resistance of MMT/epoxy nanocomposites pre-coated onto steel plates.
No preview · Article · Jan 2016 · Journal of Nanoscience and Nanotechnology
[Show abstract][Hide abstract] ABSTRACT: An electrohydrodynamic (EHD) printing process was optimized for the printing of a (3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) conductive polymer by manipulating the surface tension of a PEDOT:PSS solution. A stable cone-jet mode was confirmed by adjusting the process parameters of the EHD printing process, such as applied voltage, flow rate, and working distance. The addition of a nonionic surfactant, Triton X-100, enabled both printing of PEDOT:PSS conductive lines with widths ranging from 335 μm to 90 μm in a low-power operation (0.5 kV), as well as a 100-fold increase in conductivity of the PEDOT:PSS film compared with that of the pristine one. To utilize printed PEDOT:PSS lines for high functional applications, a multi-deposition technique was carried out, which results in a decrease in line resistance from 1.3 × 104 Ω mm−1 to 0.2 × 103 Ω mm−1.
[Show abstract][Hide abstract] ABSTRACT: We successfully fabricated highly stable pentacene-based bottom-contact organic field-effect transistors (OFETs) with good charge injection properties at the electrode/organic semiconductor interface, obtained by optimizing the composition of solution-processed (poly(3,4-ethylenedioxythiophene):polystyrene sulfonate):polytetrafluoroethylene ((PEDOT:PSS):PTFE)-treated Au source/drain (S/D) electrodes. The (PEDOT:PSS):PTFE layer was deposited on the Au layer by spin-coating a mixture solution. The work function of the electrode increased from 4.84 to 5.21 eV as the PTFE concentration increased, accompanied by an interface dipole at the electrode surface. The optimized (PEDOT:PSS):PTFE (0.95:0.05)-treated electrodes significantly reduced the charge injection barrier at the electrode/semiconductor interface to achieve efficient charge transfer in the OFETs. Bottom-contact OFETs prepared with the optimized (PEDOT:PSS):PTFE-treated S/D electrodes had a field-effect mobility of 0.16 cm2/(V·s), which exceeded that of PEDOT:PSS-treated S/D electrodes (0.073 cm2/(V·s)). The operational stability of the optimized device was remarkable under gate-bias stress (VG = −40 V over 3 h).
No preview · Article · Dec 2015 · The Journal of Physical Chemistry C
[Show abstract][Hide abstract] ABSTRACT: Encapsulation is essential for protecting the air-sensitive components of organic light-emitting diodes (OLEDs), such as the active layers and cathode electrodes. Thin film encapsulation approaches based on an oxide layer are suitable for flexible electronics, including OLEDs, because they provide mechanical flexibility, the layers are thin, and they are easy to prepare. This study examined the effects of the oxide ratio on the water permeation barrier properties of Al2O3/TiO2 nanolaminate films prepared by plasma-enhanced atomic layer deposition. We found that the Al2O3/TiO2 nanolaminate film exhibited optimal properties for a 1 : 1 atomic ratio of Al2O3/TiO2 with the lowest water vapor transmission rate of 9.16 × 10(-5) g m(-2) day(-1) at 60 °C and 90% RH. OLED devices that incorporated Al2O3/TiO2 nanolaminate films prepared with a 1 : 1 atomic ratio showed the longest shelf-life, in excess of 2000 hours under 60 °C and 90% RH conditions, without forming dark spots or displaying edge shrinkage.
No preview · Article · Dec 2015 · Physical Chemistry Chemical Physics
[Show abstract][Hide abstract] ABSTRACT: The surface functionality of the gate dielectrics is one of the important variables to have a huge impact on the electrical performance of organic field-effect transistors (OFETs). Here, we describe the impact of energetically engineered dielectrics on charge transport in vacuum-deposited 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) thin films for eventually realizing high-performance OFETs. A variety of self-assembled monolayers (SAMs) bearing amino, methyl, phenyl (PTS), or fluoro end groups were introduced onto the SiO2 dielectric surfaces to design energetically engineered surfaces that can be used to explore the impact of surface functionalities at a TIPS-pentacene/gate dielectric interface. The solvent-free vacuum deposition of TIPS-pentacene was used to exclude solution-processing effects resulting from fluid flows and solvent drying processes. The TIPS-pentacene layer on the PTS-SAM yielded the best morphological and crystalline structures, which directly enhanced the electrical properties, exhibiting field-effect mobilities as high as 0.18 cm2/(V s). Furthermore, the hysteresis, turn-on voltage, and threshold voltage were correlated with the surface potentials of various SAM-dielectrics. We believe that systematic investigation of the energetically engineered dielectrics presented here can provide a meaningful step toward optimizing the organic semiconductor/dielectric interface, thereby implementing flexible and high-performance OFETs.
No preview · Article · Dec 2015 · The Journal of Physical Chemistry C
[Show abstract][Hide abstract] ABSTRACT: We employed oxygen plasma treatment to improve the electrical properties in Cu/n-type Ge Schottky junctions and investigated temperature dependent current transport mechanism in the temperature range of 100-300 K. The Schottky barrier height increased commensurate with increasing temperature, which was attributed to barrier inhomogeneity. The inhomogeneity of the barrier was represented by a double Gaussian distribution, each one prevailing in a distinct temperature range: a high-temperature range from 220 to 300 K and a low-temperature range from 100 to 180 K. Modified Richardson plots revealed a Richardson constant of 160.0 Acm-2 K-2 for the high-temperature region (220-300 K), which is comparable to the theoretical value of 140.0 Acm-2 K-2 for n-type Ge. Reverse current analysis revealed that Poole-Frenkel and Schottky emissions were dominant in the lower and higher voltage regions, respectively.
[Show abstract][Hide abstract] ABSTRACT: Understanding charge trapping in a polymer dielectric is critical to the design of high-performance organic field-effect transistors (OFETs). We investigated the OFET stability as a function of the dielectric polymer stereostructure under a gate bias stress and during long-term operation. To this end, iso-, syn-, and atactic poly(methyl methacrylate) (PMMA) polymers with identical molecular weights and polydispersity indices were selected. The PMMA stereostructure was found to significantly influence the charge trapping behavior and trap formation in the polymer dielectrics. This influence was especially strong in the bulk region, rather than in the surface region. The regular configurational arrangements (isotactic > syntactic > atactic) of the pendant groups on the PMMA backbone chain facilitated closer packing between the polymer inter-chains and led to a higher crystallinity of the polymer dielectric, causing a reduction in the free volumes that act as sites for charge trapping and air molecule absorption. The PMMA dielectrics with regular stereostructures (iso- and syn-stereoisomers) exhibited more stable OFET operation under bias stress compared to devices prepared using irregular a-PMMA in both vacuum and air.
No preview · Article · Oct 2015 · ACS Applied Materials & Interfaces
[Show abstract][Hide abstract] ABSTRACT: Two donor-acceptor conjugated copolymers comprised of a novel dithienophosphole (DTP) as the acceptor unit and bithiophene (BT) or decylthiophenebenzodithiophene (DTBDT) as the donor unit were synthesized and characterized to elucidate the relationship between donor-acceptor (D-A) architecture and organic field-effect transistors (OFETs) performance. These characteristics of D-A copolymers were affected by the structural suitability of donor and acceptor units. Poly(DTP-BT) had an ordered structure that facilitated charge carrier transfer. The crystallinity of poly(DTP-BT) increased as annealing temperature (Tann) increased. In contrast, poly(DTP-DTBDT) was amorphous regardless of Tann due to the long alkyl chains of the DTBDT units. OFET devices made with poly(DTP-BT) and annealed at 200°C exhibit a highly crystalline morphology and a relatively high field-effect mobility (4.9 × 10-3 cm2/(V·s)).
No preview · Article · Oct 2015 · Dyes and Pigments
[Show abstract][Hide abstract] ABSTRACT: We successfully fabricate high performance bottom-contact organic field-effect transistors (OFETs) using AgNW networks electrodes by spray deposition. The synthesized AgNWs have the dimension of 40-80 nm in diameter and 30-80 µm in length and were randomly distributed and interconnected to form a 3D hollow framework. The AgNWs film, deposited by spray coating, yielded an average optical transmittance of up to 88 % and a sheet resistance as low as 10 ohm/sq. For using AgNWs as source/drain electrodes of OFETs with bottom-contact configuration, the large contact resistance at AgNWs/organic channel remains critical issue for charge injection. To enhance charge injection, we fabricate semiconductor crystals on the AgNW using adsorbed residual poly(N-vinylpyrrolidone) layer. The resulting bottom-contact OFETs exhibit high mobility up to 1.02 cm2/Vs, and are similar to that of the top-contact Au electrodes OFETs with low contact resistance. A morphological study shows that the pentacene crystals coalesced to form continuous morphology on the nanowires, and were highly interconnected with those on the channel. These features contribute to efficient charge injection and encourage the improvement of the bottom-contact device performance. Furthermore, large contact area of individual AgNWs spreading out to the channel at the edge of the electrode also improves device performance.
No preview · Article · Jun 2015 · ACS Applied Materials & Interfaces
[Show abstract][Hide abstract] ABSTRACT: We fabricated the Cu Schottky contact on an n-type Ge wafer and investigated the forward bias current-voltage (I-V) characteristics in the temperature range of 100~300 K. The zero bias barrier height and ideality factor were determined based on the thermionic emission (TE) model. The barrier height increased and the ideality factor decreased with increasing temperature. Such temperature dependence of the barrier height and the ideality factor was associated with spatially inhomogeneous Schottky barriers. A notable deviation from the theoretical Richardson constant (140.0 Acm-2K-2 for n-Ge) on the conventional Richardson plot was alleviated by using the modified Richardson plot, which yielded the Richardson constant of 392.5 Acm-2K-2. Finally, we applied the theory of space-charge-limitedcurrent (SCLC) transport to the high forward bias region to find the density of localized defect states (Nt), which was determined to be 1.46 × 1012 eV-1cm-3.
No preview · Article · Jun 2015 · Transactions on Electrical and Electronic Materials
[Show abstract][Hide abstract] ABSTRACT: Cisplatin is a potent chemotherapeutic agent, but its nephrotoxicity, which results in acute kidney injury (AKI), often limits its clinical application. Although many studies have attempted to target the mechanism responsible for its nephrotoxicity, no such method has been demonstrated to be effective in clinical trials. Recently, a dipeptidyl peptidase-4 (DPP4) inhibitor has been reported to have a renoprotective effect in a mouse model of cisplatin-induced AKI. Therefore, we will evaluate whether a DPP4 inhibitor protects the kidney from cisplatin-induced injury in humans.
This is a single-center, prospective, randomized, double-blind, placebo-controlled trial. A total of 182 participants who are scheduled for cisplatin treatment will be enrolled and randomly assigned to receive either a DPP4 inhibitor (gemigliptin) or a placebo. Participants will take the study drugs for 8 days starting 1 day before cisplatin treatment. The primary outcome of interest is the incidence of AKI at 7 days after finishing treatment with cisplatin. The secondary outcomes include changes in serum creatinine levels and estimated glomerular filtration rates from baseline to 7 days after cisplatin treatment.
This is the first clinical trial to investigate the effect of a DPP4 inhibitor on cisplatin-induced AKI.
ClinicalTrials.gov number NCT02250872, December 26, 2014.
[Show abstract][Hide abstract] ABSTRACT: The electrical stabilities of low-voltage organic field-effect transistors (OFETs) were improved by graftable fluorinated polymer (gPFS) layers and applying these layers onto poly(4-vinyl phenol)-based crosslinked dielectrics (cPVP). As a result, smooth and hydrophobic surface is formed and the dielectric film displayed a low leakage current density. The chemisorbed gPFS groups enabled the solution processing of an overlying 5,11-bis(triethylsilylethynyl)anthradithiophene (TES-ADT) semiconductor, which formed favorable terrace-like crystalline structures after solvent annealing. The top-contact OFETs showed superior operational stability compared to the cPVP-based OFETs. The hysteresis behavior in this top-contact OFET was negligible, and the off current of the transfer curve was one order of magnitude lower than the off current obtained from the cPVP-based OFET. The threshold voltage shift, measured after a sustained gate bias stress over 1 h, decreased significantly upon introduction of the hydrophobic gPFS treatment, the energetic barrier to creating charge trapping sites increased, and the trap distribution narrowed, as supported by a stretched exponential function model.
No preview · Article · May 2015 · Physical Chemistry Chemical Physics
[Show abstract][Hide abstract] ABSTRACT: Two host materials based on carbazole/pyridine end-capping group were designed and synthesized for green phosphorescent organic light-emitting diodes (PHOLEDs). One of those, 9-[9,9-diethyl-2-(6-methylpyridin-2-yl)-9H-fluoren-7-yl]-9H-carbazole (1) exhibited excellent properties for efficient green PHOLEDs as host material. A device using compound 1 as host material with the green phosphorescence dopant bis[2-(1,1′,2′,1″-terphen-3-yl)pyridinato-C,N]iridium(III)(acetylacetonate) ((tphpy)2Ir(acac)) showed the external quantum efficiency (EQE) of 10.7 %, a power efficiency (PE) of 17.27 lm/W and luminous efficiency (LE) of 39.72 cd/A at 20 mA/cm2, respectively, with the Commission International de L’Eclairage (CIE) chromaticity coordinates of (0.34, 0.62) at 8.0 V.
No preview · Article · May 2015 · New Journal of Chemistry