Atomic and electronic structure of Si dangling bonds in quasi-free-standing monolayer graphene

Nano Research - Si dangling bonds at the interface of quasi-free-standing monolayer graphene (QFMLG) are known to act as scattering centers that can severely affect carrier mobility. Herein, we...     

Highly Conductive and Transparent Large‐Area Bilayer Graphene Realized by MoCl5 Intercalation

Bilayer graphene (BLG) comprises a 2D nanospace sandwiched by two parallel graphene sheets that can be used to intercalate molecules or ions for attaining novel functionalities. However, intercalation is mostly demonstrated with small, exfoliated graphene flakes. This study demonstrates intercalation of molybdenum chloride (MoCl₅) into a large‐area, uniform BLG sheet, which is grown by chemical vapor deposition (CVD). This study reveals that the degree of MoCl₅ intercalation strongly depends on the stacking order of the graphene; twist‐stacked graphene shows a much higher degree of intercalation than AB‐stacked. Density functional theory calculations suggest that weak interlayer coupling in the twist‐stacked graphene contributes to the effective intercalation. By selectively synthesizing twist‐rich BLG films through control of the CVD conditions, low sheet resistance (83 Ω ?^?1) is realized after MoCl₅ intercalation, while maintaining high optical transmittance (≈95%). The low sheet resistance state is relatively stable in air for more than three months. Furthermore, the intercalated BLG film is applied to organic solar cells, realizing a high power conversion efficiency.     

Stretchable Platinum Network‐Based Transparent Electrodes for Highly Sensitive Wearable Electronics

A platinum network‐based transparent electrode has been fabricated by electrospinning. The unique nanobelt structured electrode demonstrates low sheet resistance (about 16 Ω sq^?1) and high transparency of 80% and excellent flexibility. One of the most interesting demonstrations of this Pt nanobelt electrode is its excellent reversibly resilient characteristic. The electric conductivity of the flexible Pt electrode can recover to its initial value after 160% extending and this performance is repeatable and stable. The good linear relationship between the resistance and strain of the unique structured Pt electrode makes it possible to assemble a wearable high sensitive strain sensor. Present reported Pt nanobelt electrode also reveals potential applications in electrode for flexible fuel cells and highly transparent ultraviolet (UV) sensors.     

Ultraflexible Near‐Infrared Organic Photodetectors for Conformal Photoplethysmogram Sensors

Flexible organic optoelectronic devices simultaneously targeting mechanical conformability and fast responsivity in the near‐infrared (IR) region are a prerequisite to expand the capabilities of practical optical science and engineering for on‐skin optoelectronic applications. Here, an ultraflexible near‐IR responsive skin‐conformal photoplethysmogram sensor based on a bulk heterojunction photovoltaic active layer containing regioregular polyindacenodithiophene‐pyridyl[2,1,3]thiadiazole‐cyclopentadithiophene (PIPCP) is reported. The ultrathin (3 µm thick) photodetector exhibits unprecedented operational stability under severe mechanical deformation at a bending radius of less than 3 µm, even after more than 10³ bending cycles. Deliberate optimization of the physical dimensions of the active layer used in the device enables precise on/off switching and high device yield simultaneously. The response frequency over 1 kHz under mechanically deformed conditions facilitates conformal electronic sensors at the machine/human interface. Finally, a mechanically stretchable, flexible, and skin‐conformal photoplethysmogram (PPG) device with higher sensitivity than those of rigid devices is demonstrated, through conformal adherence to the flexuous surface of a fingerprint.     

Catalyst‐Selective Growth of Single‐Orientation Hexagonal Boron Nitride toward High‐Performance Atomically Thin Electric Barriers

The ability to control the crystal orientation of 2D van der Waals (vdW) layered materials grown on large‐scale substrates is crucial for tailoring their electrical properties, as well as for integration of functional 2D devices. In general, multiple orientations, i.e., two or four orientations, appear through the crystal rotational symmetry matching between the material and its substrate. Here, it is reported that hexagonal boron nitride (h‐BN), an ideal electric barrier in the family of 2D materials, has a single orientation on inclined Cu (1 0 1) surfaces, where the Cu planes are tilted from the (1 0 1) facet around specific in‐plane axes. Density functional theory (DFT) calculation indicates that this is a manifestation of only one favored h‐BN orientation with the minimum vdW energy on the inclined Cu (1 0 1) surface. Moreover, thanks to the high interfacial strength with the underlying Cu, the single‐orientation h‐BN is free of thermal wrinkles, and exhibits a spatially homogeneous morphology and tunnel conductance. The findings point to a feasible approach to direct growth of single‐orientation, wrinkle‐free h‐BN thin film for high‐performance 2D electrical devices, and will be of benefit for controllable synthesis of other vdW materials.     

A Study on the Engineering Properties of Sand Improved by the Sand Compaction Pile Method

In order to directly evaluate the effects of soil improvement by the Sand Compaction Pile (SCP) method on the density, deformation, and static and liquefaction strength characteristics of sandy soils, a series of field and laboratory tests were performed. Laboratory tests were performed on high-quality undisturbed samples obtained from sandy soils both before and after soil improvement by the SCP method. The high-quality undisturbed samples were recovered by the in-situ freezing sampling method. The drained shear strength (internal friction angle, φ_d), liquefaction strength (R₁₅: cyclic stress ratio needed to cause 5% double amplitude axial strain in 15 cycles), and cyclic deformation characteristics (G~γ and h~γ relations) were determined by performing a series of laboratory tests on the undisturbed samples. Both the in-situ density and the relative density were measured on the undisturbed samples used in the laboratory tests. A standard penetration test (SPT) and a suspension-type P-S wave logging test were performed to investigate the soil profile of the test site before and after the sand compaction. Both the static and the liquefaction strengths of the sandy soils obtained in the laboratory tests were also compared with those estimated by empirical correlations used in practice based on the SPT N-value and soil gradations.     

Using decomposition analysis to forecast metal usage in the building stock

As large amounts of materials are used and have accumulated in buildings and civil engineering projects, it is necessary to understand material flow in terms of construction sectors for resource management. The consumption, discard and in-use stock of four metals (steel, aluminium, copper and zinc) in Japan's building stock are forecast through to 2050. To clarify the factors that affect metal stocks and flows in construction, the metal consumption was decomposed into annual new floor area constructed and metal intensity (i.e. the amount of metal used per unit floor area). The decomposition was meaningful for understanding characteristic patterns of factors of different metals and for envisaging future scenarios based on past trends. It was estimated that the annual new floor area constructed will remain at current levels, whereas metal intensity will have a significant impact on stocks and flows. The methodology developed in this study can be used to evaluate the impact of technology changes that would take place in building and civil engineering projects.     

Usability of VTL from natural quartz grains for retrospective dosimetry

To develop retrospective dosimetry of unexpected radiation accident, basic studies on violet thermoluminescence (VTL) phenomena were conducted using natural quartz grains. All VTL glowcurves of as-received samples did not exhibit peaks <250 degrees C, although for artificially irradiated quartz samples there were VTL peaks in the temperature region <250 degrees C. Therefore, accident doses could be estimated without the interference of naturally accumulated doses by VTL measurements from natural quartz. The mean lives of VTL were evaluated by the various heating rates method and the range of values was found to be between some days and ten thousands of years depending on each peak. Especially, the mean life of VTL peak at 200 degrees C was years order. Furthermore, the lower detection limit was calculated to be tens of mGy from the response curve. This value was lower than that of other methods such as ESR dosimetry. From these results, we conclude that VTL dosimetry can be preferred for accidental evaluation.