We show that short-pulse laser-induced classical ripples on dielectrics, semiconductors, and conductors exhibit a prominent “non-classical” characteristicin normal incidence the periods are ...definitely smaller than laser wavelengths, which indicates that the simplified scattering model should be revised. Taking into account the surface plasmons (SPs), we consider that the ripples result from the initial direct SP-laser interference and the subsequent grating-assisted SP-laser coupling. With the model, the period-decreasing phenomenon originates in the admixture of the field-distribution effect and the grating-coupling effect. Further, we propose an approach for obtaining the dielectric constant, electron density, and electron collision time of the high-excited surface. With the derived parameters, the numerical simulations are in good agreement with the experimental results. On the other hand, our results confirm that the surface irradiated by short-pulse laser with damage-threshold fluence should behave metallic, no matter for metal, semiconductor, or dielectric, and the short-pulse laser-induced subwavelength structures should be ascribed to a phenomenon of nano-optics.
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Understanding the influence of grain boundaries (GBs) on the electrical and thermal transport properties of graphene films is essentially important for electronic, optoelectronic and thermoelectric ...applications. Here we report a segregation-adsorption chemical vapour deposition method to grow well-stitched high-quality monolayer graphene films with a tunable uniform grain size from ∼200 nm to ∼1 μm, by using a Pt substrate with medium carbon solubility, which enables the determination of the scaling laws of thermal and electrical conductivities as a function of grain size. We found that the thermal conductivity of graphene films dramatically decreases with decreasing grain size by a small thermal boundary conductance of ∼3.8 × 10
W m
K
, while the electrical conductivity slowly decreases with an extraordinarily small GB transport gap of ∼0.01 eV and resistivity of ∼0.3 kΩ μm. Moreover, the changes in both the thermal and electrical conductivities with grain size change are greater than those of typical semiconducting thermoelectric materials.
Transition-metal dichalcogenide (TMD) semiconductors have attracted interest as photoelectrochemical (PEC) electrodes due to their novel band-gap structures, optoelectronic properties, and ...photocatalytic activities. However, the photo-harvesting efficiency still requires improvement. In this study, A TMD stacked heterojunction structure was adopted to further enhance the performance of the PEC cathode. A
P
-type WSe
2
and an
N
-type MoS
2
monolayer were stacked layer-by-layer to build a ultrathin vertical heterojunction using a micro-fabrication method. In situ measurement was employed to characterize the intrinsic PEC performance on a single-sheet heterostructure. Benefitting from its built-in electric field and type II band alignment, the MoS
2
/WSe
2
bilayer heterojunction exhibited exceptional photocatalytic activity and a high incident photo-to-current conversion efficiency (IPCE). Comparing with the monolayer WSe
2
cathode, the PEC current and the IPCE of the bilayer heterojunction increased by a factor of 5.6 and enhanced 50%, respectively. The intriguing performance renders the MoS
2
/WSe
2
heterojunction attractive for application in high-performance PEC water splitting.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Light–matter resonance coupling is a long-studied topic for both fundamental research and photonic and optoelectronic applications. Here we investigated the resonance coupling between the magnetic ...dipole mode of a dielectric nanosphere and 2D excitons in a monolayer semiconductor. By coating an individual silicon nanosphere with a monolayer of WS2, we theoretically demonstrated that, because of the strong energy transfer between the magnetic dipole mode of the nanosphere and the A-exciton in WS2, resonance coupling evidenced by anticrossing behavior in the scattering energy diagram was observed, with a mode splitting of 43 meV. In contrast to plexcitons, which involve plasmonic nanocavities, the resonance coupling in this all-dielectric heterostructure was insensitive to the spacing between the silicon nanosphere core and the WS2 shell. Additionally, the two split modes exhibited distinct light-scattering directionality. We further experimentally demonstrated the resonance coupling effect by depositing silicon nanospheres with different diameters onto a WS2 monolayer and collecting the scattering spectra of the resulting heterostructures under ambient conditions. We further demonstrated active control of the resonance coupling by temperature scanning. Our findings highlighted the potential of our all-dielectric heterostructure as a solid platform for studying strong light–matter interactions at the nanoscale.
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Zinc oxide (ZnO) nanowires are prepared for application in large area gated field emitter arrays (FEAs). By oxidizing Al-coated Zn films, the population density of the ZnO nanowires was tuned ...precisely by varying the thickness of the Al film. The nanowire density decreased linearly as the thickness of the Al film increased. Optimal field emission properties with a turn-on field of 6.21 V μm–1 and current fluctuations less than 1% are obtained. This can be explained by the minimized screening effect and good electrical conductivity of the back-contact layer. The mechanism responsible for the linear variation in the nanowire density is investigated in detail. Addressable FEAs using the optimal ZnO nanowire cathodes were fabricated and applied in a display device. Good gate-controlled characteristics and the display of video images are realized. The results indicate that ZnO nanowires could be applied in large area FEAs.
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A facile all‐chemical vapor deposition approach is designed, which allows both sequentially grown Gr and monolayer MoS2 in the same growth process, thus allowing the direct construction of MoS2/Gr ...vertical heterostructures on Au foils. A weak n‐doping effect and an intrinsic bandgap of MoS2 are obtained from MoS2/Gr/Au via scanning tunneling microscopy and spectroscopy characterization. The exciton binding energy is accurately deduced by combining photoluminescence measurements.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Utilizing the coupled piezoelectric and semiconducting dual properties of ZnO, we demonstrate a piezoelectric field effect transistor (PE-FET) that is composed of a ZnO nanowire (NW) (or nanobelt) ...bridging across two Ohmic contacts, in which the source to drain current is controlled by the bending of the NW. A possible mechanism for the PE-FET is suggested to be associated with the carrier trapping effect and the creation of a charge depletion zone under elastic deformatioin. This PE-FET has been applied as a force/pressure sensor for measuring forces in the nanonewton range and even smaller with the use of smaller NWs. An almost linear relationship between the bending force and the conductance was found at small bending regions, demonstrating the principle of nanowire-based nanoforce and nanopressure sensors.
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Electrically insulating boron nitride (BN) nanosheets possess thermal conductivity similar to and thermal and chemical stabilities superior to those of electrically conductive graphenes. Currently ...the production and application of BN nanosheets are rather limited due to the complexity of the BN binary compound growth, as opposed to massive graphene production. Here we have developed the original strategy “biomass-directed on-site synthesis” toward mass production of high-crystal-quality BN nanosheets. The strikingly effective, reliable, and high-throughput (dozens of grams) synthesis is directed by diverse biomass sources through the carbothermal reduction of gaseous boron oxide species. The produced BN nanosheets are single crystalline, laterally large, and atomically thin. Additionally, they assemble themselves into the same macroscopic shapes peculiar to original biomasses. The nanosheets are further utilized for making thermoconductive and electrically insulating epoxy/BN composites with a 14-fold increase in thermal conductivity, which are envisaged to be particularly valuable for future high-performance electronic packaging materials.
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Steering incident light into specific directions at the nanoscale is very important for future nanophotonics applications of signal transmission and detection. A prerequisite for such a purpose is ...the development of nanostructures with high-efficiency unidirectional light scattering properties. Here, from both theoretical and experimental sides, we conceived and demonstrated the unidirectional visible light scattering behaviors of a heterostructure, Janus dimer composed of gold and silicon nanospheres. By carefully adjusting the sizes and spacings of the two nanospheres, the Janus dimer can support both electric and magnetic dipole modes with spectral overlaps and comparable strengths. The interference of these two modes gives rise to the narrow-band unidirectional scattering behaviors with enhanced forward scattering and suppressed backward scattering. The directionality can further be improved by arranging the dimers into one-dimensional chain structures. In addition, the dimers also show remarkable electromagnetic field enhancements. These results will be important not only for applications of light emitting devices, solar cells, optical filters, and various surface enhanced spectroscopies but also for furthering our understanding on the light–matter interactions at the nanoscale.
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Due to its difficulty, experimental measurement of field emission from a single-layer graphene has not been reported, although field emission from a two-dimensional (2D) regime has been an attractive ...topic. The open surface and sharp edge of graphene are beneficial for field electron emission. A 2D geometrical effect, such as massless Dirac fermion, can lead to new mechanisms in field emission. Here, we report our findings from in situ field electron emission characterization on an individual singe-layer graphene and the understanding of the related mechanism. The measurement of field emission from the edges was done using a microanode probe equipped in a scanning electron microscope. We show that repeatable stable field emission current can be obtained after a careful conditioning process. This enables us to examine experimentally the typical features of the field emission from a 2D regime. We plot current versus applied field data, respectively, in ln(I/E 3/2) ∼ 1/E and ln(I/E 3) ∼ 1/E 2 coordinates, which have recently been proposed for field emission from graphene in high- and low-field regimes. It is observed that the plots all exhibit an upward bending feature, revealing that the field emission processes undergo from a low- to high-field transition. We discuss with theoretical analysis the physical mechanism responsible for the new phenomena.
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