One-Step Synthesis of Transition Metal Dichalcogenide Quantum Dots Using Only Alcohol Solvents for Indoor-Light Photocatalytic Antibacterial Activity.

In this study, we report a one-step direct synthesis of molybdenum disulfide (MoS2) and tungsten disulfide (WS2) quantum dots (QDs) through a solvothermal reaction using only alcohol solvents and efficient Escherichia coli (E. coli) decompositions as photocatalytic antibacterial agents under visible light irradiation. The solvothermal reaction gives the scission of molybdenum-sulfur (Mo-S) and tungsten-sulfur (W-S) bonding during the synthesis of MoS2 and WS2 QDs. Using only alcohol solvent does not require a residue purification process necessary for metal intercalation. As the number of the CH3 groups of alcohol solvents among ethyl, isopropyl, and tert(t)-butyl alcohols increases, the dispersibility of MoS2/WS2 increases. The CH3 groups of alcohols minimize the surface energy, leading to the effective exfoliation and disintegration of the bulk under heat and pressure. The bulky t-butyl alcohol with the highest number of methyl groups shows the highest exfoliation and yield. MoS2 QDs with a lateral size of about 2.5 nm and WS2 QDs of about 10 nm are prepared, exhibiting a strong blue luminescence under 365 nm ultraviolet (UV) light irradiation. Their heights are 0.68-3 and 0.72-5 nm, corresponding to a few layers of MoS2 and WS2, respectively. They offer a highly efficient performance in sterilizing E. coli as the visible-light-driven photocatalyst.

Effects of polyimide curing on image sticking behaviors of flexible displays.

Flexible displays on a polyimide (PI) substrate are widely regarded as a promising next-generation display technology due to their versatility in various applications. Among other bendable materials used as display panel substrates, PI is especially suitable for flexible displays for its high glass transition temperature and low coefficient of thermal expansion. PI cured under various temperatures (260 °C, 360 °C, and 460 °C) was implemented in metal-insulator-metal (MIM) capacitors, amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFT), and actual display panels to analyze device stability and panel product characteristics. Through electrical analysis of the MIM capacitor, it was confirmed that the charging effect in the PI substrates intensified as the PI curing temperature increased. The threshold voltage shift (ΔVth) of the samples was found to increase with rising curing temperature under negative bias temperature stress (NBTS) due to the charging effect. Our analyses also show that increasing ΔVth exacerbates the image sticking phenomenon observed in display panels. These findings ultimately present a direct correlation between the curing temperature of polyimide substrates and the panel image sticking phenomenon, which could provide an insight into the improvement of future PI-substrate-based displays.

Threshold voltage instability and polyimide charging effects of LTPS TFTs for flexible displays.

In this paper, we investigate the Vth shift of p-type LTPS TFTs fabricated on a polyimide (PI) and glass substrate considering charging phenomena. The Vth of the LTPS TFTs with a PI substrate positively shift after a bias temperature stress test. However, the Vth with a glass substrate rarely changed even with increasing stress. Such a positive Vth shift results from the negative charging of fluorine stemmed from the PI under the gate bias. In fact, the C-V characterization on the metal-insulator-metal capacitor reveals that charging at the SiO2/PI interface depends on the applied gate bias and the PI material, which agrees well with the TCAD simulation and SIMS analyses. As a result, the charging at the SiO2/PI interface contributes to the Vth shift of the LTPS TFTs leading to image sticking.

Phase-Selective Disordered Anatase/Ordered Rutile Interface System for Visible-Light-Driven, Metal-Free CO2 Reduction.

Visible-light-driven photocatalytic CO2 reduction using TiO2 that can absorb light of all wavelengths has been sought for over half a century. Herein, we report a phase-selective disordered anatase/ordered rutile interface system for visible-light-driven, metal-free CO2 reduction using a narrow band structure, whose conduction band position matches well with the reduction potential of CO2 to CH4 and CO. A mixed disordered anatase/ordered rutile (Ad/Ro) TiO2 was prepared from anatase and rutile phase-mixed P25 TiO2 at room temperature and under an ambient atmosphere in sodium alkyl amine solutions. The Ad/Ro TiO2 showed a narrow band structure due to multi-internal energy band gaps of Ti3+ defect sites in the disordered anatase phase, leading to high visible light absorption and simultaneously providing fast charge separation through the crystalline rutile phase, which was faster than that of pristine P25 TiO2. The band gap of Ad/Ro TiO2 is 2.62 eV with a conduction band of -0.27 eV, which matches well with the reduction potential of -0.24 VNHE of CO2/CH4, leading to effective electron transfer to CO2. As a result, the Ad/Ro TiO2 provided the highest CH4 production (3.983 µmol/(g h)), which is higher than that of even metal (W, Ru, Ag, and Pt)-doped P25, for CO2 reduction under visible light.

FeIn2S4 Nanocrystals: A Ternary Metal Chalcogenide Material for Ambipolar Field-Effect Transistors.

An ambipolar channel layer material is required to realize the potential benefits of ambipolar complementary metal-oxide-semiconductor field-effect transistors, namely their compact and efficient nature, reduced reverse power dissipation, and possible applicability to highly integrated circuits. Here, a ternary metal chalcogenide nanocrystal material, FeIn2S4, is introduced as a solution-processable ambipolar channel material for field-effect transistors (FETs). The highest occupied molecular orbital and the lowest unoccupied molecular orbital of the FeIn2S4 nanocrystals are determined to be -5.2 and -3.75 eV, respectively, based upon cyclic voltammetry, X-ray photoelectron spectroscopy, and diffraction reflectance spectroscopy analyses. An ambipolar FeIn2S4 FET is successfully fabricated with Au electrodes (EF = -5.1 eV), showing both electron mobility (14.96 cm2 V-1 s-1) and hole mobility (9.15 cm2 V-1 s-1) in a single channel layer, with an on/off current ratio of 105. This suggests that FeIn2S4 nanocrystals may be a promising alternative semiconducting material for next-generation integrated circuit development.

Highly Efficient Thin-Film Transistor via Cross-Linking of 1T Edge Functional 2H Molybdenum Disulfides.

Thin-film transistors (TFTs) have received great attention for their use in lightweight, large area, and wearable devices. However, low crystalline materials and inhomogeneous film formation limit the realization of high-quality electrical properties for channels in commercial TFTs, especially for flexible electronics. Here, we report a field-effect TFT fabricated via cross-linking of edge-1T basal-2H MoS2 sheets that are prepared by edge functional exfoliation of bulk MoS2 with soft organic exfoliation reagents. For edge functional exfoliation, the electrophilic 4-carboxy-benzenediazonium used as the soft organic reagent attacks the nucleophilic thiolates exposed at the edge of the bulk MoS2 with the help of an amine catalyst, resulting in 1T edge-functional HOOC-benzene-2H basal MoS2 nanosheets (e-MoS2). The cross-linking via hydrogen bonding of the negatively charged HOOC of the e-MoS2 sheets with the help of a cationic polymer, polydiallyldimethylammonium chloride, results in a good film formation for a channel of the solution processing TFT. The TFT exhibits an extremely high mobility of 170 cm2/(V s) at 1 V (on/off ratio of 106) on SiO2/Si substrate and also a high mobility of 36.34 cm2/(V s) (on/off ratio of 103) on PDMS/PET substrate.

Chemically modulated graphene quantum dot for tuning the photoluminescence as novel sensory probe.

A band gap tuning of environmental-friendly graphene quantum dot (GQD) becomes a keen interest for novel applications such as photoluminescence (PL) sensor. Here, for tuning the band gap of GQD, a hexafluorohydroxypropanyl benzene (HFHPB) group acted as a receptor of a chemical warfare agent was chemically attached on the GQD via the diazonium coupling reaction of HFHPB diazonium salt, providing new HFHPB-GQD material. With a help of the electron withdrawing HFHPB group, the energy band gap of the HFHPB-GQD was widened and its PL decay life time decreased. As designed, after addition of dimethyl methyl phosphonate (DMMP), the PL intensity of HFHPB-GQD sensor sharply increased up to approximately 200% through a hydrogen bond with DMMP. The fast response and short recovery time was proven by quartz crystal microbalance (QCM) analysis. This HFHPB-GQD sensor shows highly sensitive to DMMP in comparison with GQD sensor without HFHPB and graphene. In addition, the HFHPB-GQD sensor showed high selectivity only to the phosphonate functional group among many other analytes and also stable enough for real device applications. Thus, the tuning of the band gap of the photoluminescent GQDs may open up new promising strategies for the molecular detection of target substrates.

Cancer therapy using ultrahigh hydrophobic drug-loaded graphene derivatives.

This study aimed to demonstrate that curcumin (Cur)-containing graphene composites have high anticancer activity. Specifically, graphene-derivatives were used as nanovectors for the delivery of the hydrophobic anticancer drug Cur based on pH dependence. Different Cur-graphene composites were prepared based on polar interactions between Cur and the number of oxygen-containing functional groups of respective starting materials. The degree of drug-loading was found to be increased by increasing the number of oxygen-containing functional groups in graphene-derivatives. We demonstrated a synergistic effect of Cur-graphene composites on cancer cell death (HCT 116) both in vitro and in vivo. As-prepared graphene quantum dot (GQD)-Cur composites contained the highest amount of Cur nano-particles and exhibited the best anticancer activity compared to the other composites including Cur alone at the same dose. This is the first example of synergistic chemotherapy using GQD-Cur composites simultaneous with superficial bioprobes for tumor imaging.

An electrolyte-free flexible electrochromic device using electrostatically strong graphene quantum dot-viologen nanocomposites.

A strong electrostatic MV(2+) -GQD nanocomposite provides an electrolyte-free flexible electrochromic device wih high durability. The positively charged MV(2+) and negatively charged GQD are strongly stabilized by non-covalent intermolecular forces (e.g., electrostatic interactions, π-π stacking interactions, and cation-π electron interactions), eliminating the need for an electrolyte. An electrolyte-free flexible electrochromic device fabricated from the GQD-supported MV(2+) exhibits stable performance under mechanical and thermal stresses.

Facile preparation of an n-type reduced graphene oxide field effect transistor at room temperature.

We introduce a facile method to prepare an n-type reduced graphene oxide field effect transistor at room temperature via a typical Benkeser reduction using lithium and ethylenediamine.