Jing-Yuan Wu

Synthesis of Silver Nanostructures by Multistep Methods

The shape of plasmonic nanostructures such as silver and gold is vital to their physical and chemical properties and potential applications. Recently, preparation of complex nanostructures with rich function by chemical multistep methods is the hotspot of research. In this review we introduce three typical multistep methods to prepare silver nanostructures with well-controlled shapes, including the double reductant method, etching technique and construction of core-shell nanostructures. The growth mechanism of double the reductant method is that different favorable facets of silver nanocrystals are produced in different reductants, which can be used to prepare complex nanostructures such as nanoflags with ultranarrow resonant band bandwidth or some silver nanostructures which are difficult to prepare using other methods. The etching technique can selectively remove nanoparticles to achieve the aim of shape control and is widely used for the synthesis of nanoflowers and hollow nanostructures. Construction of core-shell nanostructures is another tool to control shape and size. The three methods can not only prepare various silver nanostructures with well-controlled shapes, which exhibit unique optical properties, such as strong surface-enhanced Raman scattering (SERS) signal and localized surface plasmon resonance (LSPR) effect, but also have potential application in many areas.

Investigation on the role of the molecular weight of polyvinyl pyrrolidone in the shape control of high-yield silver nanospheres and nanowires

Serving as shape control agent, polyvinyl pyrrolidone (PVP) has been widely used in chemical synthesis of metal nanoparticles. However, the role of molecular weight (MW) of PVP has been rarely concerned. In this study, we show a facile method to control the shapes of silver nanocrystals using PVP with different MWs. PVPMW=8,000, PVPMW=29,000, PVPMW=40,000, and PVPMW=1,300,000 are compared in the present study. Surprisingly, high-yield silver rodlike nanostructures, nanospheres, and nanowires can be obtained under the same growth environment and reactant concentrations by simply changing the MW of PVP. The mechanism studies of the role of PVP with different MWs in the growth process were carried out systemically using the morphology and spectroscopic measurement, FT-IR spectrum analysis, and seed crystallization monitoring. The results indicate that the MW of PVP plays a determinant role in the morphology and optical property control of the silver nanocrystals. Meantime, the concentration of PVP was found to be an assistant factor to further improve the shape and the yield of the synthesized nanocrystals.

Integrated optical gyroscope using active Long-range surface plasmon-polariton waveguide resonator

Optical gyroscopes with high sensitivity are important rotation sensors for inertial navigation systems. Here, we present the concept of integrated resonant optical gyroscope constructed by active long-range surface plasmon-polariton (LRSPP) waveguide resonator. In this gyroscope, LRSPP waveguide doped gain medium is pumped to compensate the propagation loss, which has lower pump noise than that of conventional optical waveguide. Peculiar properties of single-polarization of LRSPP waveguide have been found to significantly reduce the polarization error. The metal layer of LRSPP waveguide is electro-optical multiplexed for suppression of reciprocal noises. It shows a limited sensitivity of ~10−4 deg/h, and a maximum zero drift which is 4 orders of magnitude lower than that constructed by conventional single-mode waveguide.

High quantum-yield luminescent MoS2 quantum dots with variable light emission created via direct ultrasonic exfoliation of MoS2 nanosheets

We report a sonication combined with ion intercalation method in an alkaline environment to fabricate MoS2 quantum dots (QDs), with the quantum-yield of the QDs increasing from 0.99% to 4.84% with the additive sodium hydroxide. The QDs displaying variable photoluminescence emission were systematically studied and applied to the bio-imaging field.

Seeds triggered massive synthesis and multi-step room temperature post-processing of silver nanoink—application for paper electronics

Paper electronics based on ink-jet printing has become a promising technology for building new concepts of flexible and three dimensional (3D) electronic circuits and devices in a simple, cost-effective and untraditional way. In this paper, we focus on the development of massive silver nanoink syntheses and room temperature post-processing methods to meet the particular technical features of paper electronics. We firstly proposed a seed triggered synthesis method to achieve uniform silver nanoparticles without the existence of large nanostructures. Such a silver nanoparticle solution can be easily centrifuged to nanoink at a relatively low speed. Then we showed that the electric conductivities of the printed silver tracks can be improved significantly by a multi-step room temperature post-processing (MRTP) method including organic solution washing, white LED irradiation and electroless deposition in sequence. Conductivities of up to 17% of that of bulk silver can be achieved which is nearly 2 times that of the printed silver tracks treated by a conventional heating process at 120 °C for a long time. Moreover, by combining together with 3D paper folding art, we systematically investigated the electrical performances of the printed circuits associated with the printing uniformity, mechanical flexibility and strain sensitivity. These overall characteristics of the room temperature treated printing technology show great potential for the development of innovative 3D electronic products in the future.

Numerical simulation of the heat transfer performance of trisection helical baffled electric heaters

ABSTRACT Trisection helical baffled electric heaters are proposed to overcome the defects of low heat transfer coefficient and nonuniform tube spacing in conventional segmental baffled electric heaters with multicircular U-tube layouts. Novel trisection helical baffled electric heaters are of equilateral triangle tube layout distributed annularly in groups of one-plus-two U-tube units. Numerical simulation and comparison were conducted on the flow and heat transfer performance and the tube wall temperature uniformity of five helical baffled electric heaters and two segmental baffled ones. Each helical baffle scheme consists of nine one-plus-two U-tube units with a total of twenty-seven Φ16 mm U-tubes supported by the trisection helical baffles of 15 or 20° inclined angle, while each segmental baffle scheme consists of thirty Φ16 mm U-tubes of two-ring annular layout supported by segmental baffled plates spanned either 200 or 300 mm. The calculation results with compressed nitrogen show that the average heat transfer coefficient and comprehensive index (h/Δp1/3) of the helical baffled H15°-1862 scheme with only 68.5% effective heating area are, respectively, 68.2 and 34.3% higher than those of the segmental baffled S200-2462 scheme, while the average tube wall temperature of the H15°-1862 scheme is 31.7 K lower than that of S200-2462 scheme.

Investigation of simultaneously existed Raman scattering enhancement and inhibiting fluorescence using surface modified gold nanostars as SERS probes

One of the main challenges for highly sensitive surface-enhanced Raman scattering (SERS) detection is the noise interference of fluorescence signals arising from the analyte molecules. Here we used three types of gold nanostars (GNSs) SERS probes treated by different surface modification methods to reveal the simultaneously existed Raman scattering enhancement and inhibiting fluorescence behaviors during the SERS detection process. As the distance between the metal nanostructures and the analyte molecules can be well controlled by these three surface modification methods, we demonstrated that the fluorescence signals can be either quenched or enhanced during the detection. We found that fluorescence quenching will occur when analyte molecules are closely contacted to the surface of GNSs, leading to a ~100 fold enhancement of the SERS sensitivity. An optimized Raman signal detection limit, as low as the level of 10−11 M, were achieved when Rhodamine 6 G were used as the analyte. The presented fluorescence-free GNSs SERS substrates with plentiful hot spots and controllable surface plasmon resonance wavelengths, fabricated using a cost-effective self-assembling method, can be very competitive candidates for high-sensitive SERS applications.

Silver nanoplate aggregation based multifunctional black metal absorbers for localization, photothermic harnessing enhancement and omnidirectional light antireflection

Plasmonic absorbers with broadband light confinement and high photothermic harnessing efficiency are of current interest in various fields with industrialization prospects, such as solar energy harvesting, photothermic conversion and light antireflection. Here we present simple and cost-effective chemical synthesis and electrophoretic deposition methods for the fabrication of large-scale plasmonic absorber layers constructed by silver nanoplate aggregations (SNPAs) with unique morphology. Using numerical simulation and experiments including surface enhanced Raman scattering (SERS) measurement and in situ monitoring of photothermic water evaporation, we revealed the multiple physical processes including far-field scattering suppression, near-field localized light enhancement and highly efficient light-to-heat conversion when SNPAs are under illumination. Owing to these unique optical effects, the SNPAs exhibited multifunctionality with excellent performances. They exhibited an antireflective efficiency of nearly 100% ranging from 400 nm to 1100 nm which is useful in broadband light antireflection. Meanwhile, highly efficient light trapping and super hydrophilic surface characteristics enable them to exhibit significantly enhanced evaporation velocity acceleration of nearly 7 fold, highly competitive in solar energy induced water purification. They are also competent to serve as highly sensitive SERS substrates with a sensitivity of 10−8 M for R6G molecule detection owing to their significant near-field light enhancement capacity.

Performance comparison of helical baffle electric heaters with different baffle configurations

ABSTRACT Numerical simulations were conducted on nine U-tube electric heater models of 45 U-tubes with a unique tube layout of one-plus-two units, including eight helical baffle schemes of different baffle shapes and assembly configurations and a segmental one. Secondary flow and leakage flow are presented on eccentric longitudinal slices and unfolded concentric hexagonal slices, respectively. The tube surface temperature contours are also demonstrated. The results indicate that the average values of heat transfer coefficient and comprehensive index of h·Δp−1/3 of the folded helical baffle scheme with axial separation FH20(10)° are, respectively, 15.93 and 30.28% higher than those of segment scheme S200.

Synthesis of silver nanoplate based two-dimension plasmonic platform from 25 nm to 40 μm: growth mechanism and optical characteristic investigation in situ

Silver nanoplates (SNPs) with single-crystalline structures are highly expected building blocks for the construction of a two-dimensional (2D) plasmonic platform regarded as an advanced tool for the development of subwavelength light management technologies. One barrier for SNP fabrication is how to achieve structures with a lateral size large enough and a thickness thin enough for large-scale light manipulation. Here we propose a multistep chemical synthesis strategy which overcomes this bottleneck and greatly enriches the morphological features of SNPs by deliberately enhancing the behaviors of selective etching and self-assembly during a dynamic crystal growth process. Growth mechanisms were comprehensively studied with the help of real-time microscopic monitoring in situ. Three types of SNP with different morphology features including 100% yield small SNPs with a controllable surface plasmon resonance band, large SNPs decorated with hot spots and giant SNPs (up to ∼40 μm) with an ultra-high aspect ratio (over 1000 : 1) and ultrathin thickness were successfully achieved. Using such an engineered 2D platform combining waveguiding and nanoantenna effects, we demonstrated that plasmon enhanced optical information in deep subwavelength volumes can be remotely excited, transferred and scattered into free space directionally. Subwavelength light transmission with multiple excitation wavelengths and tunable one-dimensional (1D) and zero-dimensional (0D) light scattering as well as photoluminescence enhancement of light emitters was exhibited. It represents significant advances in in situ light manipulation which are useful in various applications for nanophotonics and remote sensing.