Dephasing Dynamics Accessed by High Harmonic Generation: Determination of Electron-Hole Decoherence of Dirac Fermions.

We reveal the critical effect of ultrashort dephasing on the polarization of high harmonic generation in Dirac fermions. As the elliptically polarized laser pulse falls in or slightly beyond the multiphoton regime, the elliptically polarized high harmonic generation is produced and exhibits a characteristic polarimetry of the polarization ellipse, which is found to depend on the decoherence time T2. T2 could then be determined to be a few femtoseconds directly from the experimentally observed polarimetry of high harmonics. This shows a sharp contrast with the semimetal regime of higher pump intensity, where the polarimetry is irrelevant to T2. An access to the dephasing dynamics would extend the prospect of high harmonic generation into the metrology of a femtosecond dynamic process in the coherent quantum control.

Rapid and Modular Access to Multifunctionalized 1,2-Azaborines via Palladium/Norbornene Cooperative Catalysis.

1,2-Azaborines, a unique class of BN-isosteres of benzene, have attracted great interest across several fields. While significant advancements have been made in the postfunctionalization of 1,2-azaborines, challenges still exist for the selective functionalization of the C4 position and access to 1,2-azaborines with five or six independently installed substituents. Here we report a rapid and modular method for C3 and C4 difunctionalization of 1,2-azaborines using the palladium/norbornene (Pd/NBE) cooperative catalysis. Enabled by the C2 amide-substituted NBE, diverse 3-iodo-1,2-azaborines can be used as substrates, showing broad functional group tolerance. Besides ortho arylation, preliminary success of ortho alkylation has also been realized. In addition, a range of alkenes and nucleophiles can be employed for ipso C3 functionalization. The reaction is scalable, and various postfunctionalizations, including forming hexa-substituted 1,2-azaborines, have been achieved.

Modular Synthetic Platform for Interior-Functionalized Dendritic Macromolecules Enabled by the Palladium/Norbornene Catalysis.

Synthesis of interior-functionalized dendritic macromolecules is generally tedious and labor-intensive, which has been a key factor hampering their practical applications. Here, we have revisited this long-standing challenge and devised a modular and convergent platform to synthesize multifunctional dendrons with all-carbon backbones up to four generations via an in situ functionalization strategy. Enabled by the palladium/norbornene cooperative catalysis, different functional groups can be introduced to each generation of dendrons during the dendron growth, making it convenient for systematic comparison of their properties. The utility of this versatile platform is further showcased in the internal-functionalization-dependent properties of dendrons as organogels and aggregation-induced emission materials.

Backbone Engineering of Monodisperse Conjugated Polymers via Integrated Iterative Binomial Synthesis.

Synthesis of sequence-defined monodisperse π-conjugated polymers with versatile backbones remains a substantial challenge. Here we report the development of an integrated iterative binomial synthesis (IIBS) strategy to enable backbone engineering of conjugated polymers with precisely controlled lengths and sequences as well as high molecular weights. The IIBS strategy capitalizes on the use of phenol as a surrogate for aryl bromide and represents the merge between protecting-group-aided iterative synthesis (PAIS) and iterative binomial synthesis (IBS). Long and monodisperse conjugated polymers with diverse irregular backbones, which are inaccessible by conventional polymerizations, can be efficiently prepared by IIBS. In addition, topology-dependent and chain-length-dependent properties have been investigated.

Asymmetric Total Synthesis of (+)-Phainanoid A and Biological Evaluation of the Natural Product and Its Synthetic Analogues.

Here, we report our detailed efforts toward the synthesis of phainanoids, a novel class of dammarane-type triterpenoids with potent immunosuppressive activities and unique structural features. Systematic model studies have been carried out, and efficient approaches have been established to construct the benzofuranone-based 4,5-spirocycle, the D/E/F tricyclic core, the [4.3.1] propellane, and the 5,5-oxaspirolactone moieties. The asymmetric synthesis of (+)-phainanoid A has been achieved through kinetic resolution of the tricyclic core followed by diastereoselective installation of the A/B/C and G/H rings and fragment coupling with the enantioenriched I/J rings. In addition, novel estrone-derived phainanoid analogues have been prepared. The immunosuppressive and cell survival assays revealed that (+)-phainanoid A and some of its synthetic analogues can specifically inhibit stimulation-induced lymphocyte proliferation but not cell survival at their effective concentrations. Preliminary structure-activity relationship information has been obtained, which could inspire future design of immunosuppressive phainanoid analogues.

Wafer-Scale Programmed Assembly of One-Atom-Thick Crystals.

Crystalline films offer various physical properties based on the modulation of their thicknesses and atomic structures. The layer-by-layer assembly of atomically thin crystals provides a powerful means to arbitrarily design films at the atomic level, which are unattainable with existing growth technologies. However, atomically clean assembly of the materials with high scalability and reproducibility remains challenging. We report programmed crystal assembly of graphene and monolayer hexagonal boron nitride, assisted by van der Waals interactions, to form wafer-scale films of pristine interfaces with near-unity yield. The atomic configurations of the films are tailored with layer-resolved compositions and in-plane crystalline orientations. We demonstrate batch-fabricated tunnel device arrays with modulation of the resistance over orders of magnitude by thickness control of the hexagonal boron nitride barrier with single-atom precision and large-scale, twisted multilayer graphene with programmable electronic band structures and crystal symmetries. Our results constitute an important development in the artificial design of large-scale films.

Bidirectional Total Synthesis of Phainanoid A via Strategic Use of Ketones.

Here we report the total synthesis of phainanoid A, a unique dammarane-type triterpenoid (DTT), using an unusual bidirectional synthetic strategy. It features two transition-metal-mediated highly diastereoselective transformations to access the two challenging strained ring systems that branch toward opposite directions from the tricyclic core. This work also highlights the strategic use of ketones (or enol triflates) as versatile handles for rapid growth of molecular complexity in all key transformations, which paves the way for efficient preparations of complex and biologically significant DTTs.

All-Dry Transfer of Graphene Film by van der Waals Interactions.

We report a method that uses van der Waals interactions to transfer continuous, high-quality graphene films from Ge(110) to a different substrate held by hexagonal boron nitride carriers in a clean, dry environment. The transferred films are uniform and continuous with low defect density and few charge puddles. The transfer is effective because of the weak interfacial adhesion energy between graphene and Ge. Based on the minimum strain energy required for the isolation of film, the upper limit of the interfacial adhesion energy is estimated to be 23 meV per carbon atom, which makes graphene/Ge(110) the first as-grown graphene film that has a substrate adhesion energy lower than that of typical van der Waals interactions between layered materials. Our results suggest that graphene on Ge can serve as an ideal material platform to be integrated with other material systems by a clean assembly process.

SUBFOVEAL CHOROIDAL THICKNESS AND VASCULAR DIAMETER IN ACTIVE AND RESOLVED CENTRAL SEROUS CHORIORETINOPATHY.

PURPOSE: To determine the subfoveal choroidal thickness and analyze Haller's layer, Sattler's layer, and large choroidal vessel diameter in eyes with active central serous chorioretinopathy (CSC) and after resolution of CSC. METHODS: Ocular and clinical features of 32 eyes with CSC were analyzed retrospectively from October 2014 to September 2015. Subfoveal choroidal thickness and thicknesses of Haller's layer and Sattler's layer were measured in the active and resolved states. The diameter of the subfoveal choroidal hyporeflective lumen (i.e., the large choroidal vessel in Haller's layer) was also measured. RESULTS: The mean subfoveal choroidal thickness, mean thickness of Haller's layer, and mean choroidal vessel diameter were significantly less after the resolution of CSC (P < 0.001). However, the thickness of Sattler's layer did not change after the resolution of CSC (P = 0.731). There were no significant differences among the different treatment modalities. CONCLUSION: After the resolution of CSC, the subfoveal choroidal thickness and thickness of Haller's layer declined, but the reduced diameter of subfoveal choroidal vessels accounted for only about half of the total thickness changes in the choroid. These results suggest that nonvascular smooth muscle cells might play a role in the thickening of the choroid during CSC and possibly in the pathogenesis and progression of CSC.

Association of statin use and hypertriglyceridemia with diabetic macular edema in patients with type 2 diabetes and diabetic retinopathy.

BACKGROUND: To investigate the effects of dyslipidemia and statin therapy on progression of diabetic retinopathy and diabetic macular edema in patients with type 2 diabetes. METHODS: The medical records of 110 patients with type 2 diabetes (70 statin users and 40 non-users) were retrospectively reviewed. The two outcome measures were progression of diabetic retinopathy by two or more steps on the early treatment diabetic retinopathy study scale and diabetic macular edema based on optical coherence tomography. Serum lipid profiles were analyzed from 6 months prior to diagnosis of diabetic macular edema. RESULTS: Diabetic retinopathy progressed in 23% of statin users and 18% of non-users (p = 0.506), but diabetic macular edema was present in 23% of statin users and 48% of non-users (p = 0.008). Statins reduced low-density lipoprotein cholesterol levels in patients with and without diabetic macular edema (p = 0.043 and p = 0.031, respectively). Among statin users, patients with diabetic macular edema had higher levels of triglycerides (p = 0.004) and lower levels of high-density lipoprotein cholesterol (p = 0.033) than those without diabetic macular edema. Logistic regression analysis showed that statin use significantly lowered the risk of diabetic macular edema [odds ratio (OR): 0.33, 95% confidence interval (CI) 0.12-0.91, p = 0.032]. Hypertriglyceridemia at 6 months prior to development of macular edema was significantly associated with central retinal thickness (OR: 1.52; 95% CI 1.14-2.02, p = 0.005). CONCLUSIONS: Lipid lowering therapy with statins protected against the development of diabetic macular edema and progression of diabetic retinopathy in patients with type 2 diabetes. Hypertriglyceridemia could be used as a surrogate marker for diabetic macular edema.

Hybrid Edge Results in Narrowed Band Gap: Bottom-up Liquid-Phase Synthesis of Bent N = 6/8 Armchair Graphene Nanoribbons.

Scalable fabrication of graphene nanoribbons with narrow band gaps has been a nontrivial challenge. Here, we have developed a simple approach to access narrow band gaps using hybrid edge structures. Bottom-up liquid-phase synthesis of bent N = 6/8 armchair graphene nanoribbons (AGNRs) has been achieved in high efficiency through copolymerization between an o-terphenyl monomer and a naphthalene-based monomer, followed by Scholl oxidation. An unexpected 1,2-aryl migration has been discovered, which is responsible for introducing kinked structures into the GNR backbones. The N = 6/8 AGNRs have been fully characterized to support the proposed structure and show a narrow band gap and a relatively high electrical conductivity. In addition, their application in efficient gas sensing has also been demonstrated.

Plasmon-modulated fluorescence nanoprobes for enzyme-free DNA detection via target signal enhancement and off-target quenching.

Rapid, sensitive, and reliable nucleic acid assay is crucial for the molecular diagnosis of many diseases. For high sensitivity, conventional techniques require time-consuming, high-cost, and complicated procedures, such as enzymatic gene amplification, labeling, and purification, limiting their applications to point-of-care diagnostics. Herein we report a new DNA nanoprobe based on the dual effects of target-specific plasmon-enhanced fluorescence and off-target plasmonic quenching. Janus gold half-shell/polystyrene nanospheres (hsAu/PSs, ∼150 nm diameter) are tethered with capture single-stranded DNA (ssDNA), coupled with a fluorophore-conjugated reporter ssDNA through sandwich-type hybridization with target DNA, resulting in 5-fold increase through plasmon-enhanced fluorescence. Smaller gold nanoparticles (∼13 nm diameter) are subsequently introduced as quenchers to reduce background fluorescence from unhybridized reporter ssDNA, increasing the sensitivity about 103 times. The limit of detection of the dual-mode plasmonic DNA nanoprobe is 16 pM at room temperature in 1 h for the target gene of Klebsiella pneumoniae carbapenemase. The nanoprobe also exhibits a high selectivity enough to discriminate a single-base difference in the target gene. Our strategy harnesses both of the plasmon-mediated fluorescence enhancement and quenching effects through the sophisticated design of nanoscale colloids, which opens a promising avenue to the enzyme-free, simple, sensitive, and selective detection of pathogenic DNA.

Gate-tunable quantum pathways of high harmonic generation in graphene.

Under strong laser fields, electrons in solids radiate high-harmonic fields by travelling through quantum pathways in Bloch bands in the sub-laser-cycle timescales. Understanding these pathways in the momentum space through the high-harmonic radiation can enable an all-optical ultrafast probe to observe coherent lightwave-driven processes and measure electronic structures as recently demonstrated for semiconductors. However, such demonstration has been largely limited for semimetals because the absence of the bandgap hinders an experimental characterization of the exact pathways. In this study, by combining electrostatic control of chemical potentials with HHG measurement, we resolve quantum pathways of massless Dirac fermions in graphene under strong laser fields. Electrical modulation of HHG reveals quantum interference between the multi-photon interband excitation channels. As the light-matter interaction deviates beyond the perturbative regime, elliptically polarized laser fields efficiently drive massless Dirac fermions via an intricate coupling between the interband and intraband transitions, which is corroborated by our theoretical calculations. Our findings pave the way for strong-laser-field tomography of Dirac electrons in various quantum semimetals and their ultrafast electronics with a gate control.

Graphene Nanoribbon Grids of Sub-10 nm Widths with High Electrical Connectivity.

Quasi-one-dimensional (1D) graphene nanoribbons (GNRs) have finite band gaps and active edge states and therefore can be useful for advanced chemical and electronic devices. Here, we present the formation of GNR grids via seed-assisted chemical vapor deposition on Ge(100) substrates. Nucleation seeds, provided by unzipped C60, initiated growth of the GNRs. The GNRs grew toward two orthogonal directions in an anisotropic manner, templated by the single crystalline substrate, thereby forming grids that had lateral stitching over centimeter scales. The spatially uniform grid can be transferred and patterned for batch fabrication of devices. The GNR grids showed percolative conduction with a high electrical sheet conductance of ∼2 µS·sq and field-effect mobility of ∼5 cm2/(V·s) in the macroscopic channels, which confirm excellent lateral stitching between domains. From transconductance measurements, the intrinsic band gap of GNRs with sub-10 nm widths was estimated as ∼80 meV, similar to theoretical expectation. Our method presents a scalable way to fabricate atomically thin elements with 1D characteristics for integration with various nanodevices.

Direct Synthesis of Molybdenum Phosphide Nanorods on Silicon Using Graphene at the Heterointerface for Efficient Photoelectrochemical Water Reduction.

HIGHLIGHTS: MoP nanorod-array catalysts were directly synthesized on graphene passivated silicon photocathodes without secondary phase. Mo-O-C covalent bondings and energy band bending at heterointerfaces facilitate the electron transfer to the reaction sites. Numerous catalytic sites and drastically enhanced anti-reflectance of MoP nanorods contribute to the high solar energy conversion efficiency. Transition metal phosphides (TMPs) and transition metal dichalcogenides (TMDs) have been widely investigated as photoelectrochemical (PEC) catalysts for hydrogen evolution reaction (HER). Using high-temperature processes to get crystallized compounds with large-area uniformity, it is still challenging to directly synthesize these catalysts on silicon photocathodes due to chemical incompatibility at the heterointerface. Here, a graphene interlayer is applied between p-Si and MoP nanorods to enable fully engineered interfaces without forming a metallic secondary compound that absorbs a parasitic light and provides an inefficient electron path for hydrogen evolution. Furthermore, the graphene facilitates the photogenerated electrons to rapidly transfer by creating Mo-O-C covalent bondings and energetically favorable band bending. With a bridging role of graphene, numerous active sites and anti-reflectance of MoP nanorods lead to significantly improved PEC-HER performance with a high photocurrent density of 21.8 mA cm-2 at 0 V versus RHE and high stability. Besides, low dependence on pH and temperature is observed with MoP nanorods incorporated photocathodes, which is desirable for practical use as a part of PEC cells. These results indicate that the direct synthesis of TMPs and TMDs enabled by graphene interlayer is a new promising way to fabricate Si-based photocathodes with high-quality interfaces and superior HER performance.

Plasmonic Heterostructure Functionalized with a Carbene-Linked Molecular Catalyst for Sustainable and Selective Carbon Dioxide Reduction.

Hybridization of homogeneous catalytic sites with a photoelectrode is an attractive approach to highly selective and tunable photocatalysis using heterogeneous platforms. However, weak and unclear surface chemistry often leads to the dissociation and irregular orientation of catalytic centers, restricting long-term usability with high selectivity. Well-defined and robust ligands that can persist under harsh photocatalytic conditions are essential for the success of hybrid-type photocatalysis. Here, we introduce N-heterocyclic carbene as a durable linker for the immobilization of a Rubpy complex-based CO2 reduction site (cis-dichloro-(4,4'-diphosphonato-Rubpy)(p-cymene) (RuCY)) on a p-type gallium nitride/gold nanoparticle (p-GaN/AuNP) heterostructure. The p-GaN/AuNPs/RuCY photocathode was coupled with a hematite photoanode to drive photoelectrochemical CO2 reduction along with water oxidation. Highly selective CO2 reduction into formates, up to 98.2%, was achieved utilizing plasmonic hot electrons accumulated on AuNPs. The turnover frequency was 1.46 min-1 with a faradic efficiency of 96.8% under visible light illumination (243 mW·cm-2). This work demonstrates that the N-heterocyclic carbene-mediated surface functionalization with homogeneous catalytic sites is a promising approach to increase the sustainability and usability of hybrid catalysts.

Universal Route to Impart Orthogonality to Polymer Semiconductors for Sub-Micrometer Tandem Electronics.

A universal method that enables utilization of conventional photolithography for processing a variety of polymer semiconductors is developed. The method relies on imparting chemical and physical orthogonality to a polymer film via formation of a semi-interpenetrating diphasic polymer network with a bridged polysilsesquioxane structure, which is termed an orthogonal polymer semiconductor gel. The synthesized gel films remain tolerant to various chemical and physical etching processes involved in photolithography, thereby facilitating fabrication of high-resolution patterns of polymer semiconductors. This method is utilized for fabricating tandem electronics, including pn-complementary inverter logic devices and pixelated polymer light-emitting diodes, which require deposition of multiple polymer semiconductors through solution processes. This novel and universal method is expected to significantly influence the development of advanced polymer electronics requiring sub-micrometer tandem structures.

Photoresponsive Transistors Based on a Dual Acceptor-Containing Low-Bandgap Polymer.

In this Article, low-bandgap pTTDPP-BT polymers based on electron-accepting pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione (DPP) and benzothiadiazole (BT) and electron-donating thienothiophene (TT) moieties were synthesized. Phototransistors have been fabricated using ambipolar-behaving pTTDPP-BT polymers as active channel materials. The electrical and photoresponsive properties of the pTTDPP-BT phototransistors were strongly dependent on the film annealing temperature. As-spun pTTDPP-BT phototransistors exhibited a low hole mobility of 0.007 cm2/(V·s) and a low electron mobility of 0.005 cm2/(V·s), which resulted in low photocurrent detection due to the limited transport of the charge carriers. Thermal treatment of the polymer thin films led to a significant enhancement in the carrier mobilities (hole and electron mobilities of 0.066 and 0.115 cm2/(V·s), respectively, for 200 °C annealing) and thus significantly improved photoresponsive properties. The 200 °C-annealed phototransistors showed a wide-range wavelength (405-850 nm) of photoresponse, and a high photocurrent/dark-current ratio of 150 with a fast photoswitching speed of less than 100 ms. This work demonstrates that a dual acceptor-containing low band gap polymer can be an important class of material in broadband photoresponsive transistors, and the crystallinity of the semiconducting polymer layer has a significant effect on the photoresponse characteristics.

A Nonchlorinated Solvent-Processable Fluorinated Planar Conjugated Polymer for Flexible Field-Effect Transistors.

High carrier mobilities have recently been achieved in polymer field effect transistors (FETs). However, many of these polymer FET devices require the use of chlorinated solvents such as chloroform (CF), chlorobenzene (CB), and o-dichlorobenzene (DCB) during fabrication. The use of these solvents is highly restricted in industry because of health and environmental issues. Here, we report the synthesis of a low band gap (1.43 eV, 870 nm) semiconducting polymer (PDPP2DT-F2T2) having a planar geometry, which can be readily processable with nonchlorinated solvents such as toluene (TOL), o-xylene (XY), and 1,2,4-trimethylbenzene (TMB). We performed structural characterization of PDPP2DT-F2T2 films prepared from different solvents, and the electrical properties of the films were measured in the context of FETs. The devices exhibited an ambipolar behavior with hole dominant transport. Hole mobilities increased with increasing boiling point (bp) of the nonchlorinated solvents: 0.03, 0.05, and 0.10 cm2 V-1 s-1 for devices processed using TOL, XY, and TMB, respectively. Thermal annealing further improved the FET performance. TMB-based polymer FETs annealed at 200 °C yielded a maximum hole mobility of 1.28 cm2 V-1 s-1, which is far higher than the 0.43 cm2 V-1 s-1 obtained from the CF-based device. This enhancement was attributed to increased interchain interactions as well as improved long-range interconnection between fibrous domains. Moreover, all of the nonchlorinated solutions generated purely edge-on orientations of the polymer chains, which is highly beneficial for carrier transport in FET devices. Furthermore, we fabricated an array of flexible TMB-processed PDPP2DT-F2T2 FETs on the plastic PEN substrates. These devices demonstrated excellent carrier mobilities and negligible degradation after 300 bending cycles. Overall, we demonstrated that the organized assembly of polymer chains can be achieved by slow drying using high bp nonchlorinated solvents and a post thermal treatment. Furthermore, we showed that polymer FETs processed using high bp nonhalogenated solvents may outperform those processed using halogenated solvents.

A survey of fish viruses isolated from wild marine fishes from the coastal waters of southern Korea.

A survey was conducted to investigate viral infection in 253 wild marine fishes harvested in the southern coastal area of Korea from 2010 to 2012. The fish that were captured by local anglers were randomly bought and sampled for virus examination. The samples were tested for presence of virus by virus isolation with FHM, FSP, and BF-2 cells and molecular methods (polymerase chain reaction and sequencing). Of the 253 fish sampled, 9 fish were infected with virus. Aquabirnaviruses (ABVs), Viral hemorrhagic septicemia virus (VHSV), and Red seabream iridovirus (RSIV) were detected in 7, 1, and 1 fish, respectively. Molecular phylogenies demonstrated the detected viruses (ABV, VHSV, and RSIV) were more closely related to viruses reported of the same type from Korea and Japan than from other countries, suggesting these viruses may be indigenous to Korean and Japanese coastal waters.