Analysis of welding Au nanowires into T junctions

The effects of temperature and size on the welding of Au nanowires (NWs) into T junctions is studied using molecular dynamics simulations based on the second-moment approximation of the many-body tight-binding potential. Simulation results show that when the top NW approaches the bottom one, it elongates towards the bottom one just before welding due to the interaction of the van der Waals attractive force. During welding, the bottom NW gradually reaches critical bend deformation through successive pressure applied from the top one, followed by buckling of the top NW. The structural order of NWs significantly decreases with increasing welding temperature or decreasing NW width. Welding at high temperatures (700 K or above) causes alignment difficulty due to an unstable NW geometry or even welding failure due to a decrease in NW length. Smaller NWs have larger stress during the welding process.     

Electrode materials for biphenyl-based rectification devices

An ab initio approach was utilized to explore the electronic transport properties of 4′-thiolate-biphenyl-4-dithiocarboxylate (TBDT) sandwiched between two electrodes made of various materials X (X?=?Cu, Ag, and Au). Analysis of current–voltage (I–V) characteristics, rectification performance, transmission functions, and the projected density of states (PDOS) under various external voltage biases showed that the transport properties of these constructed systems are markedly impacted by the choice of electrode materials. Further, Cu electrodes yield the best rectifying behavior, followed by Ag and then Au electrodes. Interestingly, the rectification effects can be tuned by changing the torsion angle between the two phenyl rings, as well as by stretching the contact distances between the end group and the electrodes. For Cu, the maximum rectifying ratio increases by 37 % as the contact distance changes from 1.7 Å to 1.9 Å. This is due to an increase in coupling strength asymmetry between the molecule and the electrodes. Our findings are compared with the results reported for other systems. The present calculations are helpful not only for predicting the optimal electrode material for practical applications but also for achieving better control over rectifying performance in molecular devices.     

Sensitive and Robust Colorimetric Sensing of Sulfide Anion by Plasmonic Nanosensors Based on Quick Crystal Growth

A highly sensitive and selective method for colorimetric sensing of sulfide anions in aqueous solutions is illustrated. The sensing mechanism is based on quick crystallization from Ag to Ag₂S in the presence of sulfide anions which alter the dielectric properties of the Au/Ag core/shell nanorods. The longitudinal surface plasmon resonance peak of the Au/Ag nanorods at about 686 nm undergoes a redshift and the color of the nanorod solution also changes from light green to purple. Sulfide ions at a concentration of 4.0 μM (1.3 ppb) can be detected visually and a sensitivity of 0.5 μM (167 ppt) is achieved by Vis–near-infrared spectrophotometry. Compared to other plasmonic sensors, our Au/Ag nanorod probe does not require surface modification while exhibiting high stability and robustness under different pH conditions. This simple and cost-effective sensing platform provides a rapid and convenient detection for sulfide anions at concentrations far below the hazardous limit in aqueous media.     

Synthesis of Silver and Gold Nanoparticles Using Cashew Nut Shell Liquid and Its Antibacterial Activity Against Fish Pathogens

This study reveals a green process for the production of multi-morphological silver (Ag NPs) and gold (Au NPs) nanoparticles, synthesized using an agro-industrial residue cashew nut shell liquid. Aqueous solutions of Ag⁺ ions for silver and chloroaurate ions for gold were treated with cashew nut shell extract for the formation of Ag and Au NPs. The nano metallic dispersions were characterized by measuring the surface plasmon absorbance at 440 and 546 nm for Ag and Au NPs. Transmission electron microscopy showed the formation of nanoparticles in the range of 5–20 nm for silver and gold with assorted morphologies such as round, triangular, spherical and irregular. Scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction analyses of the freeze-dried powder confirmed the formation of metallic Ag and Au NPs in crystalline form. Further analysis by Fourier transform infrared spectroscopy provided evidence for the presence of various biomolecules, which might be responsible for the reduction of silver and gold ions. The obtained Ag and Au NPs had significant antibacterial activity, minimum inhibitory concentration and minimum bactericidal concentration on bacteria associated with fish diseases.     

Optimization of Surface Plasmon Resonance Biosensor with Ag/Au Multilayer Structure and Fiber-Optic Miniaturization

In this paper, we report a novel wavelength interrogation-based surface plasmon resonance (SPR) system, in which a film of three Ag layers and three Au layers are alternately deposited on a Kretschmann configuration as sensing element. This multilayer film shows higher sensitivity for refractive index (RI) measurement by comparing with single Au layer structure, which is consistent with its theoretical calculation. A sensitivity range of 2056–5893 nm/RIU can be achieved, which is comparable to RI sensitivities of other wavelength-modulated SPR sensors. Compared with Ag film, this Ag/Au multilayer arrangement offers anti-oxidant protection. This SPR biosensor based on a cost-effective Ag/Au multilayer structure is applicable to the real-time detection of specific interactions and dissociation of low protein concentrations. To extend the application of this highly-sensitive metal film device, we integrated this concept on an optical fiber. The range of RI sensitivities with Ag/Au multilayer was 1847–3309 nm/RIU. This miniaturized Ag/Au multilayer-based fiber optic sensor has a broad application in chemical and biological sensing.     

In-season heat stress compromises postharvest quality and low-temperature sweetening resistance in potato (Solanum tuberosum L.)

Key message

High soil temperature during bulking and maturation of potatoes alters postharvest carbohydrate metabolism to attenuate genotypic resistance to cold-induced sweetening and accelerate loss of process quality.

Abstract

The effects of soil temperature during tuber development on physiological processes affecting retention of postharvest quality in low-temperature sweetening (LTS) resistant and susceptible potato cultivars were investigated. ‘Premier Russet’ (LTS resistant), AO02183-2 (LTS resistant) and ‘Ranger Russet’ (LTS susceptible) tubers were grown at 16 (ambient), 23 and 29 °C during bulking (111–164 DAP) and maturation (151–180 DAP). Bulking at 29 °C virtually eliminated yield despite vigorous vine growth. Tuber specific gravity decreased as soil temperature increased during bulking, but was not affected by temperature during maturation. Bulking at 23 °C and maturation at 29 °C induced higher reducing sugar levels in the proximal (basal) ends of tubers, resulting in non-uniform fry color at harvest, and abolished the LTS-resistant phenotype of ‘Premier Russet’ tubers. AO02183-2 tubers were more tolerant of heat for retention of LTS resistance. Higher bulking and maturation temperatures also accelerated LTS and loss of process quality of ‘Ranger Russet’ tubers, consistent with increased invertase and lower invertase inhibitor activities. During LTS, tuber respiration fell rapidly to a minimum as temperature decreased from 9 to 4 °C, followed by an increase to a maximum as tubers acclimated to 4 °C; respiration then declined over the remaining storage period. The magnitude of this cold-induced acclimation response correlated directly with the extent of buildup in sugars over the 24-day LTS period and thus reflected the effects of in-season heat stress on propensity of tubers to sweeten and lose process quality at 4 °C. While morphologically indistinguishable from control tubers, tubers grown at elevated temperature had different basal metabolic (respiration) rates at harvest and during cold acclimation, reduced dormancy during storage, greater increases in sucrose and reducing sugars and associated loss of process quality during LTS, and reduced ability to improve process quality through reconditioning. Breeding for retention of postharvest quality and LTS resistance should consider strategies for incorporating more robust tolerance to in-season heat stress.     

A Highly Sensitive Resonance Scattering Assay for Immunoglobulin M Using Ag(I)–Hydroquinone–Immunonanogold Catalytic Reaction

Ten-nanometer nanogold showed the strongest catalytic effect on the particle reaction between Ag(I) and hydroquinone to form nanosilver particles that exhibited the strongest resonance scattering (RS) peak at 350 nm. The enhanced RS intensity was linear to the nanogold concentration in the range of 30–5,700 nM Au. The nanogold was used to label goat antihuman immunoglobulin M (GIgM) to obtain an immunonanogold probe (AuGIgM) for immunoglobulin M (IgM). Based on the nanogold-labeled immunoreaction between IgM and AuGIgM, centrifugation, and AuGIgM–Ag(I)–hydroquinone nanocatalytic reaction, a highly sensitive and selective immunonanogold-catalytic Ag particle RS assay for 0.2–300 ng mL^?1 IgM was proposed, with a detection limit of 0.1 ng mL^?1. This assay was simple and sensitive and was applied to assay IgM in serum samples, with satisfactory results.     

Effects of crystal orientation and aspect ratio on plastic response of aluminium nanowires under torsion

The plastic response of perfect face-centred cubic single-crystal aluminium (Al) nanowires (NWs) under torsion is studied using molecular dynamics simulations. The Al–Al interaction is described by the many-body tight-binding potential. The effects of the crystal orientation and aspect ratio of the NWs on their deformation are evaluated in terms of atomic trajectories, potential energy, a centrosymmetry parameter and the torque required for deformation. Simulation results clearly show that for NWs, regardless of crystal orientation, dislocations nucleate and propagate on the (1 1 1) close-packed plane. In a NW under torsion, dislocations begin at the surface, extend to the interior along the (1 1 1) close-packed plane and finally diffuse to the middle part. A 〈1 1 0〉-oriented NW has the lowest required torque for deformation due to the occurrence of homogeneous deformation. The mechanism of the plastic response of an Al NW depends on its crystal orientation. For a long NW, geometry instability occurs before material instability (buckling).     

Blue-Shifted SPR of Au Nanoparticles with Ordering of Carbon by Dense Ionization and Thermal Treatment

Thin films of carbon-containing Au nanoparticles (NPs), prepared by the co-sputtering using a neutral Ar atom beam, were irradiated by 120 MeV Ag ions and also annealed, separately, at increasing temperatures in inert atmosphere. The surface plasmon resonance (SPR) band of the nanocomposite film was observed to be blue shifted (～50 nm) in both cases, with increasing fluence and temperature. The structural changes of Au NPs embedded in amorphous carbon matrix were investigated using X-ray diffraction and transmission electron microscopy. A growth of Au NPs was observed with increasing fluence and also with increasing temperature. A percolation of Au NPs was observed at 500 °C. A growth of Au NPs with ion irradiation is explained in the framework of a thermal spike model. Raman spectroscopy revealed the ordering of a-C thin films with increasing fluence and temperature, which is ascribed to a change of refractive index and the blue shift of the SPR band.     

A study on the effects of twin boundaries and surface morphology on deformation behaviours of silver nanowires

Nanoscale twin boundaries (TBs) and surface morphology play a significant role in the yield behaviour of nanowires (NWs). However, few studies have directly compared their effects on the mechanical response of metal NWs. In this article, the mechanical properties of three 〈1 1 1〉 silver NWs with a diameter of 12.2 nm are studied using molecular dynamics simulations. The 〈1 1 1〉 silver NWs are single crystalline rectangular NWs (SCNW), twinned rectangular NWs (TRNW) and faceted twinned NWs (FTNW), respectively. Comparing SCNW and the twinned NWs, we found that a superior combination of higher strength and elasticity was achieved in the twinned NWs by introducing the TBs in elastic region. Then, we also found that the yield strain of FTNW have a strong dependence on TB spacing. Furthermore, a comparison of the incipient plastic deformation between TRNW and FTNW has been made by monitoring defects evolution. To identify the defects evolution, a centrosymmetry parameter was defined and implemented in the self-developed program. And we also compared the effect of TB and surface morphology on mechanical response of three silver NWs. In general, it can be concluded that TBs significantly influence the mechanical properties of metallic NWs and it is more essential than surface morphology.     

The Effects of Selenium on Physiological Traits, Grain Selenium Content and Yield of Winter Wheat at Different Development Stages

The paper evaluated the effects of Se application time and rate on physiological traits, grain Se content, and yield of winter wheat by field experiment. Se application significantly increased grain Se content and yield, and the increased amount treated with 20 and 30 mg Se?L^?1 was the highest. At blooming–filling stage, Se application significantly increased grain Se content, but did not affect yield. Chlorophyll content was increased by Se application, and the increased amount at heading–blooming stage was higher than that in wheat leaves at the other stages. At four development stages, Se treatments (except for 10 mg Se?L^?1 at jointing–heading stage) significantly decreased the rate of superoxide (O₂ ^?) radical production. At heading–blooming (except for 50 mg Se?L^?1) and blooming–filling stages, hydrogen peroxide (H₂O₂) content was significantly decreased by Se treatments. The rate of O₂ ^? production and H₂O₂ content at 20 and 30 mg Se?L^?1 was the lowest. Se treatments (except for 10 mg Se?L^?1 at regreening–jointing and blooming–filling stages) also induced an evident decrease in malondialdehyde content. Proline content induced by Se treatments at jointing–heading and heading–blooming stages was higher than that in wheat leaves at regreening–jointing and blooming–filling stages. At four development stages, Se treatments all significantly increased glutathione peroxidase activity, and the treatments with 20 and 30 mg Se?L^?1 also evidently increased reduced glutathione content. These results suggested that Se application at different development stages increased antioxidant capacity of wheat, reduced oxidant stress to some extent, and the effects of Se treatments was the best if Se concentration ranged between 20 and 30 mg Se?L^?1. In addition, Se application time was more beneficial for Se accumulation and yield in wheat grain at heading–blooming stage.     

Twin boundary spacing-dependent deformation behaviours of twinned silver nanowires

Twin boundary spacing (TBS) plays a significant role in the yield behaviour of twinned nanowires (NWs). However, few studies have shown an overall view of the effects on the mechanical response of twinned silver NWs under tensile loading. In this article, the mechanical properties of 〈111〉-oriented NWs with different TBSs are studied using molecular dynamics simulations. In elastic region, it is found that the addition of twin boundaries (TBs) to crystalline NWs can not only cause strengthening but also softening effect, which depending on the S_T/S_F (the ratio of the total area of TBs to the area of lateral free surfaces). Furthermore, our simulation results show that the evolution of reduced number of different types of atoms in twinned Ag NWs has a strong dependence on TBS. For twinned NWs with larger TBSs, the dislocation–TB interaction dominates the plastic deformation process. While for twinned NWs with smaller TBSs, shear banding is activated as the incipient plastic deformation, leading to the atoms clustering into disorder near the surfaces. The study will be helpful to the further understanding of TB-related mechanical properties of nanomaterials.     

Highest Efficiency Plasmonic Polycrystalline Silicon Thin-Film Solar Cells by Optimization of Plasmonic Nanoparticle Fabrication

Excitation of surface plasmons in metallic nanoparticles is a promising method for increasing the light absorption in solar cells and hence the cell photocurrent. Comprehensive optimization of a nanoparticle fabrication process for enhanced performance of polycrystalline silicon thin-film solar cells is presented. Three factors were studied: the Ag precursor film thickness, annealing temperature and time. The thickness of the precursor film was 10, 14 and 20 nm; annealing temperature was 190, 200, 230 and 260 °C; and annealing time was varied between 20 and 95 min. Performance enhancement due to light-scattering by nanoparticles was calculated by comparing absorption, short-circuit current density and energy conversion efficiency in solar cells with and without nanoparticles formed under different process conditions. Nanoparticles formed from 14-nm-thick Ag precursor film annealed at 230 °C for 53 min result in the highest absorption enhancement in the 700–1,100 nm wavelength range, in the highest enhancement of total short-circuit current density. The highest photocurrent enhancement was 33.5 %, which was achieved by the cell with the highest absorption enhancement in the 700–1,100 nm range. The plasmonic cell efficiency of 5.32 % was achieved without a back reflector and 5.95 % with the back reflector; which is the highest reported efficiency for plasmonic thin-film solar cells.     

Optical and Thermal Enhancement of Plasmonic Nanofluid Based on Core/Shell Nanoparticles

The plasmonic effect is introduced in solar thermal areas to enhance light harvest and absorption. The optical properties of plasmonic nanofluid are simulated by finite difference time domain (FDTD) method. Due to the excitation of localized surface plasmon resonance (LSPR) effect, an intensive absorption peak is observed at 0.5 μm. The absorption characteristics are sensitive to particle size and concentration. As the particle size increases, the absorption peak is broadened and shifted to longer wavelength. The absorption of SiO₂/Ag plasmonic nanofluid is improved gradually as the volume concentration increases, especially in the UV region. The absorption edge is shifted from 0.6 to 1.0 μm as the volume concentration increases from 0.001 to 0.01. The thermal simulation of suspended SiO₂/Ag nanoparticle shows a uniform temperature rise of 17.91 K under solar irradiation (AM 1.5), while under the same condition, the temperature rises in Ag nanoparticle and Al nanoparticle are 11.12 and 5.39 K, respectively. The core/shell plasmonic nanofluid exhibits a higher photothermal performance, which has a potential application in photothermal areas. A higher temperature rise can be obtained by improving the incident light intensity or optical absorption properties of nanoparticles.     

Ab initio molecular dynamics simulations of the adsorption of the methylguanidine or methylguanidinium on Ag(111)

A density-functional and Car–Parrinello molecular dynamics methods were employed to study the adsorption of the methylguanidine or methylguanidinium on Ag(111) surface with Vanderbilt pseudopotentials and PBE functional. The geometry, interacting energy, vibrational frequency, Mayer bond order and electrostatic fit charges were calculated. The results show that the methylguanidine interacts with the Ag(111) surface mainly through the interaction between the sp² hybridisation imine nitrogen and its nearest silver atom on top site, assisted with the Ag???H interaction, with the most stabilising interacting energy ?78.83 kJ/mol. The Car–Parrinello molecular dynamics results at 293.15 or 300.00 K indicate that the Ag???N interaction exists stably for more than 6 ps and the Mayer bond order analysis shows that it is the main interaction in adsorption. For the methylguanidinium on Ag(111) surface, the weak interaction between N?H and its neighbour silver atoms, with the energy of ?40.73–?42.68 kJ/mol and the interacting time of 0.2–0.3 ps at 300 K, could not keep it steady on Ag(111). The CP dynamics results show that only the methylguanidine could adsorb on Ag(111) at the room temperature.     

Temperature Sensor Based on Hollow Fiber Filled with Graphene-Ag Composite Nanowire and Liquid

A temperature sensor based on hollow fiber (HF) filled with graphene-Ag composite nanowire and liquid is presented. The coupling properties and sensing performance are numerically analyzed by finite element method using wavelength and amplitude interrogations. Results show that the sensor exhibiting strong birefringence with x-polarized peak provides much higher sensitivities and better signal-to-noise ratio (SNR) than y-polarized, which is more suitable for temperature detection. The graphene-Ag composite nanowire can not only solve the oxidation problem but also avoid the metal coating. Moreover, it provides better performance than other similar works like Au-Ag nanowire-filled, Au nanowire-filled, and Ag nanowire-filled sensors. Contrary to the blue shift of traditional SPR temperature sensors, the resonance peak shifts to the longer wavelength in our device when temperature increases and the high sensitivity 9.44 nm/ °C is obtained. The influences of nanowire diameter, grapheme-layer thickness on the designed sensor, are also investigated. This work can provide a reference for developing a high sensitivity, real-time, remote sensing, and distributed temperature SPR sensor.     

Simultaneous Photoluminescence and SERS Observation of Nanodiamond at Laser Deposition on Noble Metals

The metal-modified luminescence and surface-enhanced Raman scattering (SERS) occurring near nanostructured surfaces of noble metals recently have been observed for different kinds of nanocrystals associated with the metal nanostructures. In the present work, the photoluminescence and Raman scattering of diamond nanocrystals of sizes 100 and 300 nm patterned on Ag and Au thin nanostructured films via laser accelerated deposition using a femtosecond laser are discussed. The laser accelerated deposition forms ordered periodical nanodiamond–metal nanostructures and allows adjusting the interaction between nanodiamond and metal by varying the laser acceleration parameters as well as by using different metals (Ag and Au), and varying the structure of the metal film. Correspondingly, the spectroscopic properties of the system determined by interaction between nanoparticles and metal are tuned. The enhancement of nanodiamond photoluminescence together with SERS of graphite fraction and disordered carbon of nanodiamonds are observed for nanodiamond–Ag structures at 488- and 532-nm excitations, while for the nanodiamond–Au structure some characteristic SERS effects are observed at 785-nm excitation. The mechanisms of enhancement are discussed considering the nanodiamond–metal interaction and laser acceleration effect on nanodiamond.     

Destabilization of mayonnaise induced by lipid crystallization upon freezing

The thermal and rheological history of mayonnaise during freezing and its dispersion stability after the freeze-thaw process were investigated. Mayonnaise was cooled to freeze and stored at ?20 to ?40 °C while monitoring the temperature; penetration tests were conducted on the mayonnaise, which was sampled at selected times during isothermal storage at ?20 °C. Significant increases in the temperature and stress values due to water-phase crystallization and subsequent oil-phase crystallization were observed. The water phase crystallized during the cooling step in all the tested mayonnaise samples. The oil phases of the prepared mayonnaise (with rapeseed oil) and commercial mayonnaise crystallized during isothermal storage after 6 and 4 h, respectively, at ?20 °C. The dispersion stability was evaluated from the separation ratio, which was defined as the weight ratio of separated oil after centrifuging to the total amount of oil in the commercial mayonnaise. The separation ratio rapidly increased after 4 h of freezing. This result suggests that crystallization of the oil phase is strongly related to the dispersion stability of mayonnaise.     

Non-equilibrium molecular dynamics study of nanoscale thermal contact resistance

Interfaces play an important role in microscale and nanoscale heat transfer processes with molecular dynamics (MD) simulations often used to study these interfacial phenomena. In this study, two models were used to simulate thermal conduction across micro contact points and the thermal contact resistance using non-equilibrium molecular dynamics simulations with consideration of the near field radiation. When the ratio of the length of the micro contact to the length of the conduction region is less than 0.125, the influence of the near field radiation should be considered; but when the ratio is larger than 0.2, it can be neglected. When the computational domain sizes are 8.50 × 10.62 × 8.50 nm and 10.62 × 10.62 × 10.62 nm, the MD results show that the thermal contact resistance exponentially increases with decreasing area of the micro contact point and increases with increasing micro contact layer thickness. The MD thermal contact resistances in nanoscale are much larger than that of the classical thermal analysis since the material thermal conductivity reduction is ignored in the classical model. The results also show that material defects increase the thermal resistance.     

Adsorption behaviors of hydrogen sulphide on Au(110) nanoslit array surfaces using molecular dynamics simulations

The adsorption behaviour of gas molecules on detector surfaces has a profound influence on the sensitivity of the detector. For this reason, this study used molecular dynamics simulation to explore the dynamic adsorption behaviour of hydrogen sulphide (H₂S) molecules on various types of Au surfaces, including a planar Au(1?1?0) structure and three types of slit array structures. The influence of system temperature, adsorbate concentration and the slit width of nanoarrays on diffusivity, average adsorption energy and static adsorption amount were systematically examined. Simulation results indicate that the self-diffusivity of the adsorbate molecules increases with temperature but decreases with adsorbate concentration. At low concentrations (~3 mol/L), each type of Au(1?1?0) surface structure shows good capacity to adsorb all H₂S molecules. With increasing concentration at 6.5 mol/L, the high concentration leads to adsorption saturation and many free H₂S molecules in the planar Au(1?1?0) structure. Moreover, desorption also begins to appear on the planar structures at a temperature of 300 K (at 6.5 mol/L). The simulation results indicate that the columnar array structures with a slit width ≥5.76 Å allow molecules to swiftly spread into the slits and provide more stable adsorption sites (i.e. with a higher adsorption energy), which can effectively address the issues of high-temperature desorption and adsorption saturation. Particularly at low temperatures (≤100 K), slit structures presented a level of static adsorption of H₂S that was 30% to 35 higher than that of planar structures.