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We report a graphene oxide (GO)-based composite, featuring GO/cross-linking agent (CA) nanoparticles, inspired by a nacre-like hierarchical structure present in nature. The as-prepared GO/CA composite was powdered to nanoscale particles and then mixed with pure GO to be GO/CA/GO (GCG) composite forming hierarchical GO/CA nanoasperities on the GO surface. The strength and toughness of the nacre-inspired GCG composite films were simultaneously improved by adjusting the nanoparticle concentration and hierarchical level of the GO-based films. Compared to pristine GO films and GO/CA composites, which exhibit a low level of hierarchy in their structures, the tensile strength and toughness of the GCG composites with higher hierarchy were enhanced 3.1 and 1.6 times and 47.6 and 10.9 times, respectively. Furthermore, a plausible mechanism of increasing mechanical properties based on nanoscale asperities and homogeneous interactions between GO and CA has been discussed.

High-quality molecular markers are essential for marker-assisted selection to accelerate breeding progress. Compared with diploid species, recently diverged polyploid crop species tend to have highly similar homeologous subgenomes, which is expected to limit the development of broadly applicable locus-specific single-nucleotide polymorphism (SNP) assays. Furthermore, it is particularly challenging to make genome-wide marker sets for species that lack a reference genome. Here, we report the development of a genome-wide set of kompetitive allele specific PCR (KASP) markers for marker-assisted recurrent selection (MARS) in the tetraploid minor crop perilla. To find locus-specific SNP markers across the perilla genome, we used genotyping-by-sequencing (GBS) to construct linkage maps of two F2 populations. The two resulting high-resolution linkage maps comprised 2,326 and 2,454 SNP markers that spanned a total genetic distance of 2,133 cM across 16 linkage groups and 2,169 cM across 21 linkage groups, respectively. We then obtained a final genetic map consisting of 22 linkage groups with 1,123 common markers from the two genetic maps. We selected 96 genome-wide markers for MARS and confirmed the accuracy of markers in the two F2 populations using a high-throughput Fluidigm system. We confirmed that 91.8% of the SNP genotyping results from the Fluidigm assay were the same as the results obtained through GBS. These results provide a foundation for marker-assisted backcrossing and the development of new varieties of perilla.

One of the major challenges in the field of nanotechnology is the facile and inexpensive fabrication of

Many petals in nature have a hierarchical structure that imparts various optical properties. Among these, the petals of the Queen of the Night tulip exhibit an iridescent and glossy color due to the diffraction and scattering of light. Herein, we report a bioinspired micro-/nanohierarchical structure that mimics Queen of the Night tulip petal surfaces. Using a method that combined soft lithography and UV-ozone treatment, we fabricated nanoscale line patterns with a linewidth of 600 nm on microwrinkles of 15 μm width and 3 μm height. Using optical microscopy in the dark-field mode and monochromatic light diffraction measurements, we found that these hierarchical structures on a poly(dimethylsiloxane) (PDMS) substrate synergistically improved the scattering and diffraction effects, unlike the pristine, nano-, and microstructures. In addition, using a dye-colored PDMS material, we fabricated artificial Queen of the Night petals with iridescent and glossy effects. They show great potential for a range of applications, such as coloring, smart displays, dynamic gratings, and light-control devices.

We report a graphene oxide/cross-linking agent (GO/CA) composite inspired by the nacre structure. Based on the "brick-and-mortar" concept of nacre, graphene oxide and a cross-linking agent are covalently conjugated in the form of nacre. The mechanical characteristics of the nacre-mimetic GO/CA composite film can be controlled by adjusting the preparation method, degree of cross-linking, and cross-linking times. As a result, the cross-linking strategy can drastically enhance the tensile strength [142.9 ± 6.4 MPa (∼2.3-fold)], modulus [4.7 ± 0.36 GPa (∼15.7-fold)], and hardness [917.4 ± 85.7 MPa (∼9.0-fold)], which are superior to those of pristine materials. The cross-linking agent-based chemical bonding method for mechanically improved integration is mainly attributed to the formation of strong cross-linked networks between the GO-based 2D interfaces and CA. The facile fabrication process provides many opportunities to design advanced, robust, and integrated nacre-like GO/CA composites, which can be applied to future aerospace utilizations, electronic protectors, robotic elements, and permeable membranes.

Aesthetically appealing photovoltaic (PV) panels with colorful layers are used in numerous applications involving color matching with the surroundings. To develop a colored film for a PV system, appropriate optical properties such as high transparency and low angle sensitivity are necessary because the colored layers can reduce the efficiency of the PV system by causing variations in the transmittance and angle of incidence. Herein, we propose a facile fabrication method for bioinspired three-dimensional (3D) photonic crystal (PC) films that exhibit broad angle-insensitive transmission and reflection, for application in colorful PV. This structure, patterned on a sequentially stacked 11-layer film of SiO

Atomically thin transition metal dichalcogenides (TMDs) have recently attracted great attention since the unique and fascinating physical properties have been found in various TMDs, implying potential applications in next-generation devices. The progress towards developing new functional and high-performance devices based on TMDs, however, is limited by the difficulty in producing large-area monolayer TMDs due to a lack of knowledge of the growth processes of monolayer TMDs. In this work, we have investigated the growth processes of monolayer WS2 crystals using a thermal chemical vapor deposition method, in which the growth conditions were adjusted in a systematic manner. It was found that, after forming WO3-WS2 core-shell nanoparticles as nucleation sites on a substrate, the growth of three-dimensional WS2 islands proceeds by ripening and crystallization processes. Lateral growth of monolayer WS2 crystals subsequently occurs by the surface diffusion process of adatoms toward the step edge of the three-dimensional WS2 islands. Our results provide understanding of the growth processes of monolayer WS2 by using chemical vapor deposition methods.

Silver grid electrode is a promising candidate for transparent conductive film because of its outstanding electrical, thermal, and optical properties, which can be easily tuned by changing the line width, spacing, and thickness of the metal pattern. Here, we presented the fabrication method of transparent Ag electrode with line-pattern using contact transfer technique with thermal release tape (TRT) that is easy to adhere and/or release to the substrate. To fabricate a line-patterned Ag electrode, the following efficient processes were developed: 1) preparation of line-patterned recess using thermal-roll imprinting, 2) surface modification by the anti-adhesion layer coating, 3) Ag infilling into the line-patterned recess using a doctor blade, 4) transfer of Ag electrode to the target substrate using TRT. As a result, the Ag line-patterned film with low sheet resistance (17.94 Ω/sq) and high transparency (90.28% at 550 nm) was obtained. This film can be tailored on requirement for various electronic applications.

Graphene oxide membrane (GOM) has attracted extensive attraction as a molecular sieve for the separation of water, ions, and gases. However, A-level control of the GOM interlayer spacing for separating the specific size of gas molecule is difficult and the vertical transport mechanism of molecules through the GOM is highly complex because of the existence of several possible pathways. Here we fabricated GOMs with different A-scale interlayer spacing through heat treatment and made them allow horizontal entrance and transport of gas molecules. The GOMs with angstrom channels exhibited superior performance in permeance in horizontal mode and moderate selectivity for H2/CO2 and He/CO2 by tuning the sieving size of the channels. Molecular dynamics (MD) simulations reveal that the precisely controlled interlayer spacing plays a primary role as a molecular sieve indeed, but increased graphitic area, a result of heat treatment, also affects observed selectivity. Our results provide insight into the transport mechanism of gas molecules through GO nanochannel, which has not been accurately identified due to its complex behavior and suggest the possibility of studying nanochannels as effective vehicle for separating molecules precisely.

Monolayer graphene grown by chemical vapor deposition has been intensively studied for applications such as transparent conductive films, electronic devices, sensors, molecular barriers, and electrodes. However, technology to transfer monolayer graphene from metal film must be improved through environmentally friendly and non-defective methods on arbitrary target substrates. Here, we report a clean and direct method for transferring monolayer graphene from Cu foil without defects and over a large area. In a water bath at 90–95 °C, we floated Cu foil with graphene on the water surface. After 5 h, a Cu2O layer formed uniformly at the interface between the graphene and the Cu. Subsequently, the monolayer graphene on the Cu foil was delaminated from the thermal release tape, releasing the graphene to the target substrate (SiO2/Si and PET). The Cu2O formation and defect changes were monitored at each step via various characterization methods. The Cu2O layer was uniformly established and no defects were generated after the transfer. Finally, we fabricated a graphene field effect transistor that exhibited an excellent electronic performance.

Atomically thin transition metal dichalcogenides (TMDs) have recently attracted great attention since the unique and fascinating physical properties have been found in various TMDs, implying potential applications in next-generation devices. The progress towards developing new functional and high-performance devices based on TMDs, however, is limited by the difficulty of producing large-area monolayer TMDs due to a lack of knowledge of the growth processes of monolayer TMDs. In this work, we have investigated the growth processes of monolayer WS2 crystals using a thermal chemical vapor deposition method, in which the growth conditions were adjusted in a systematic manner. It was found that, after forming WO3-WS2 core-shell nanoparticles as nucleation sites on a substrate, the growth of three-dimensional WS2 islands proceeds by ripening and crystallization processes. Lateral growth of monolayer WS2 crystals subsequently occurs by surface diffusion process of adatoms. Our results provide understanding of the growth processes of monolayer WS2 by using chemical vapor deposition methods.

A low-powered and highly selective photomechanical sensor system mimicking stomata in the epidermis of leaves harvested from nature is demonstrated. This device uses a light-responsive composite consisting of 4-amino-1,1'-azobenzene-3,4'-disulfonic acid monosodium salt (AZO) and poly(diallyldimethylammonium chloride) (PDDA) coated on a membrane with tens of nanometer-size pores. The ionic current change through the pore channels as a function of pore size variation is then measured. The tran-cis isomerism of AZO-PDDA during light irradiation and the operation mechanism of photomechanical ion channel sensor are discussed and analyzed using UV-vis spectroscopy and atomic force microscopy analysis. It presents the discriminative current levels to the different light wavelengths. The response time of the photoreceptor is about 0.2 s and it consumes very low operating power (≈15 nW) at 0.1 V bias. In addition, it is found that the change of the pore diameter during the light irradiation is due to the photomechanical effect, which is capable of distinguishing light intensity and wavelength.

We present a pressure-conductive rubber sensor using a liquid-metal-polydimethylsiloxane (PDMS) composite suitable for incorporation onto surfaces with a complex curvature such as the human body. The composite is synthesized by physical mixing of Galinstan and PDMS based on magnetic stirring. This composite is conductive only when a mechanical pressure exceeding the threshold value or strain is applied; the pristine state of the composite is not conductive. The threshold value can be controlled by adjusting the mixing ratio of liquid metal and PDMS. This material is mechanically robust, allowing it to operate reliably under various elastic deformations such as pressing, stretching, and bending without structural failure and performance degradation. Moreover, a fabricated sensor array can detect the distribution of the applied pressure in plane. As a feasibility study, we demonstrate a pressure-conductive rubber sensor for detecting finger movements and bio-signals such as blood pressure and respiration rate. Our results reveal that our rubber sensor is practical as a wearable sensor because of its mechanical robustness and electrical reliability.

We report a clean, facile, and fast transfer method for uniform and ultrathin graphene oxide (GO) films. Using vacuum filtration, we make the GO film with less 5 nm thicknesses and transfer to the target substrates (silicon oxide, glass, PET, PI) and bend surfaces by vaporizing pressure of hot water. The quality of a transferred GO film is characterized by optical microscopy, AFM, SEM, Raman spectroscopy, and demonstrate the successful transfer of GO films without defects on a film and residuals on a supporting membrane. We also demonstrated that GO films coated substrates exhibit the improved anti-scratching properties and controlled hydrophilicity than non-coated substrates.

The atomic-layered semiconducting materials of transition metal dichalcogenides are considered effective light sources with both potential applications in thin and flexible optoelectronics and novel functionalities. In spite of the great interest in optoelectronic properties of two-dimensional transition metal dichalcogenides, the excitonic properties still need to be addressed, specifically in terms of the interlayer interactions. Here, we report the distinct behavior of the A and B excitons in the presence of interlayer interactions of layered MoS2 crystals. Micro-photoluminescence spectroscopic studies reveal that on the interlayer interactions in double layer MoS2 crystals, the emission quantum yield of the A exciton is drastically changed, whereas that of the B exciton remains nearly constant for both single and double layer MoS2 crystals. First-principles density functional theory calculations confirm that a significant charge redistribution occurs in the double layer MoS2 due to the interlayer interactions producing a local electric field at the interfacial region. Analogous to the quantum-confined Stark effect, we suggest that the distinct behavior of the A and B excitons can be explained by a simplified band-bending model.