Programmable Negative Differential Resistance Effects Based on Self‐Assembled Au@PPy Core–Shell Nanoparticle Arrays

The negative differential resistance (NDR) effect observed in conducting polymer/Au nanoparticle composite devices is not yet fully clarified due to the random and disordered incorporation of Au nanoparticles into conducting polymers. It remains a formidable challenge to achieve the sequential arrangement of various components in an optimal manner during the fabrication of Au nanoparticle/conducting polymer composite devices. Here, a novel strategy for fabricating Au nanoparticle/conducting polymer composite devices based on self‐assembled Au@PPy core–shell nanoparticle arrays is demonstrated. The interval between the two Au nanoparticles can be precisely programmed by modulating the thickness of the shell and the size of the core. Programmable NDR is achieved by regulating the spacer between two Au nanoparticles. In addition, the Au/conducting polymer composite device exhibits a reproducible memory effect with read–write–erase characteristics. The sequentially controllable assembly of Au@PPy core–shell nanoparticle arrays between two microelectrodes will simplify nanodevice fabrication and will provide a profound impact on the development of new approaches for Au/conducting polymer composite devices.     

Synthesis and characterization of plasmon resonant gold nanoparticles and graphene for photovoltaics

Here we discuss the use in solar cells of graphene grown by chemical vapor deposition (CVD) and of plasmonic gold nanoparticles (Au NPs) deposited by sputtering. The Au NPs have been coupled with a-Si heterojunction solar cells, with an organic active layer used in organic photovoltaics, and with graphene. Extensive characterization of those three systems by the optical technique of spectroscopic ellipsometry, which is suitable to monitor and analyze the plasmon resonance of the Au NPs, by the microstructural technique of Raman spectroscopy, which is suitable to analyze graphene properties and doping, and by atomic force microscopy has been carried out. Those techniques highlighted interactions between Au NPs and silicon, polymer and graphene, which lead to variation in the plasmon resonance of Au NPs and consequently in the characteristics of the Au NPs/Si, Au NPs/polymer and Au NPs/graphene hybrids. Specifically, we found that an optimal size and density of Au NPs are able to enhance the efficiency of c-Si/a-Si heterojunction solar cells and that exceeding with Au NPs size and density causes device shortcut because of interface interdiffusion between silicon and gold. To discuss organic photovoltaics, Au NPs have been combined with an electro-donating conjugated polymer, the poly[1,4bis(2-thienyl)-2,5-bis-(2-ethyl-hexyloxyphenylenes)]. We found that there is a strong correlation between the thickness and morphology of the organic active layer, which affects the energy and amplitude of the Au NPs plasmon resonance. Finally, Au NPs have been deposited on graphene. We found that Au NPs show the plasmon resonance in the region where graphene is transparent and also yield p-type doping of graphene decreasing its sheet resistance.     

聚合物基纳米复合材料的界面作用研究进展

将聚合物与纳米粒子复合制备性能优异的聚合物基纳米复合材料是近20年来科学界的研究热点,其中聚合物与纳米粒子间的界面作用对复合材料的性能起着关键性作用。从界面结构、力学性能、热性能及计算机仿真模拟等方面综述了聚合物基纳米复合材料的界面研究进展,并对这一领域的研究进行了展望。     

TEM observation of gold nanoparticles deposited on cerium oxide

The structure of Au nanoparticles supported on CeO₂ using the deposition precipitation method was observed using a transmission electron microscope (TEM). The shape of Au nanoparticles and the fine structure of contact interface between the Au nanoparticles and CeO₂ supports were carefully examined. It was found that there was a preferential orientation relationship between Au nanoparticles and the CeO₂ support. It was also observed that small and thin Au nanoparticles disappeared during TEM observation, shrinking layer by layer down to a mono-atomic layer.     

Studying the orientation of bio-objects by nematic liquid crystals

We have studied the ability of a liquid-crystal (LC) matrix to visualize and orient DNA molecules. It is established that the relief of the interface between the LC mesophase and conducting contact can be improved without using an additional high-ohmic polymer layer. Spectroscopic and ellipsometric techniques revealed changes in the refractive properties and structure of composites. The obtained results can be used in creating devices for rapid DNA testing with retained form of biostructures.     

Nonvolatile flexible organic bistable devices fabricated utilizing CdSe/ZnS nanoparticles embedded in a conducting poly N-vinylcarbazole polymer layer

The bistable effects of CdSe/ZnS nanoparticles embedded in a conducting poly N-vinylcarbazole (PVK) polymer layer by using flexible poly-vinylidene difluoride (PVDF) and polyethylene terephthalate (PET) substrates were investigated. Transmission electron microscopy (TEM) images revealed that CdSe/ZnS nanoparticles were formed inside the PVK polymer layer. Current-voltage (I-V) measurement on the Al/[CdSe/ZnS?nanoparticles+?PVK]/ITO/PVDF and Al/[CdSe/ZnS nanoparticles+?PVK ]/ITO/PET structures at 300?K showed a nonvolatile electrical bistability behavior with a flat-band voltage shift due to the existence of the CdSe/ZnS nanoparticles, indicative of trapping, storing and emission of charges in the electronic states of the CdSe nanoparticles. A bistable behavior for the fabricated organic bistable device (OBD) structures is described on the basis of the I-V results. These results indicate that OBDs fabricated by embedding inorganic CdSe/ZnS nanoparticles in a conducting polymer matrix on flexible substrates are prospects for potential applications in flexible nonvolatile flash memory devices.     

Increased permittivity nanocomposite dielectrics by controlled interfacial interactions

The use of nanoparticles in polymer composite dielectrics has promised great improvements, but useful results have been elusive. Here, the importance of the interfacial interactions between the nanoparticles and the polymer matrix are investigated in TiO₂ nanocomposites for dielectric materials using surface functionalisation. The interface is observed to dominate the nanocomposite properties and leads to a threefold increase in permittivity at volume fractions as low as 10%. Surface functionalisation of the filler nanoparticles with silanes allows control of this interface, avoiding significant degradation of the other important material properties, particularly electrical breakdown strength, and resulting in a material that is demonstrated successfully as an active material in a dielectric elastomer actuator application with increased work output compared to the pure polymer. Although further permittivity increases are observed when the interface regions have formed a percolation network, the other material properties deteriorate. The observation of percolation behaviour allows the interface thickness to be estimated.     

纳米粒子链/聚合物基复合体的界面形态及力学行为

介绍了纳米粒子链弹性力学属性，粒子链与高分子链缠结和吸附，以及界面形态和力学行为。同时研究原生粒子结合处的“脖颈”对增强高分子聚合物的作用。     

Mesoporous silica-coated gold nanorods with a thermally responsive polymeric cap for near-infrared-activated drug delivery

In this work, gold nanorods (AuNRs)/mesoporous silica (SiO₂) nanoparticles capped with thermal-responsive polymer were fabricated to couple the photothermal property of AuNRs and the thermal-/pH-responsive properties of polymer in a single nanovehicle. Aliphatic poly(urethane-amine) (PUA) was employed as the smart polymer to cap the mesopores of AuNRs/SiO₂ nanoparticles via in situ polymerization in supercritical CO₂. Thermal-/pH-responsive PUA acted as the on–off switch to control the DOX release due to the stretch and shrinkage of the PUA polymer chains at different temperatures, whereas a remote near-infrared (NIR) light was used to activate the phase change and subsequent drug release. The in vitro drug release studies indicated that Au/SiO₂/PUA nanoparticles exhibited distinguished pH-, thermal-, and NIR-dependent release properties. A short time exposure to NIR irradiation could distinctly increase the local temperature of nanoparticles, and the thermal-responsive polymeric cap enabled the DOX release in a significant reversible way by simply adjusting the NIR laser intensity. The present paper provides an ideal way to fabricate NIR-responsive drug carriers by combining stimuli-responsive polymer with inorganic matrix, which is highly attractive for remote controllable drug delivery.     

PEDOT-Au nanocomposite films for electrochemical sensing of dopamine and uric acid

In this work, conducting polymer impregnated gold nanoparticles are synthesized through a sequence of chemical and electrochemical routes. The nanocomposite film is characterized using UV-vis, FTIR spectroscopy, and SEM techniques to study the formation of oxidized PEDOT and Au0. The advantages of these films are demonstrated for sensing biologically important compounds such as dopamine and uric acid in presence of excess ascorbic acid, one of the major interferants in the detection of DA and UA (mimicking the physiological conditions), with superior selectivity and sensitivity when compared to the polymer film alone. Simultaneous determination is realized at 115 mV and 246 mV for DA and UA, respectively. The PEDOT matrix is recognized to be responsible for the peak separation (selectivity) while also favouring catalytic oxidation of the above compounds and the nanometer-sized gold particles allow nanomolar sensing of DA and UA (sensitivity). Thus, it is possible to detect nanomolar levels of DA and UA in presence of excess of AA. The combined effect of Au nanoparticles and the PEDOT matrix is rationalized that the Aunano surrounded by a "hydrophobic sheath (PEDOT)" tending to reside within these hydrophobic regions of PEDOT, thus favouring the selectivity and sensitivity of the DA/UA detection. This new generation of nanocomposites is expected to enhance the value of electroanalytical techniques, as it is possible to tune their properties suiting the analytical needs.     

Polymer/gold nanoparticles light emitting diodes utilizing high work function metal cathodes

This investigation reports the luminescent and electric properties of phenyl-substituted poly(para-phenylene vinylene) copolymer (HY-PPV) in which Au nanoparticles were incorporated. Incorporating a few amounts of Au nanoparticles into HY-PPV film enhances the electroluminescence (EL) efficiency of HY-PPV-based polymer light emitting diodes (PLEDs) using Al and Cu as cathodes. Blue-shifts in the emission spectra and a decrease in the capacitance of the emitting layer were observed. These unique behaviors are due to the increase in the density of the effective hole trap centers and affect the electronic configuration of HY-PPV, induced by the Au nanoparticles, which increase the probability of hole–electron recombination and shift the emission spectra toward higher photo energies.     

Polyindole-Au nanocomposite produced at the liquid/liquid interface

This letter is a continuation of our previous work on synthesis of polyindole-gold nanocomposite published in this journal. In the present work, we have synthesized the similar hybrid organo-inorganic composite using a novel interfacial polymerization route at water/dichloromethane interface. The hybrid organo-inorganic composite material is based on conducting polymer, polyindole and gold nanoparticles; the redox character of indole (monomer) and chloroauric acid facilitates the polymerization of monomer. Entirely different morphological and structural features are observed compared to our previous results. The contact of monomer and metal salt acid (chloroauric acid) at the interface results in the formation of polyindole-Au nanocomposite (without any need of template or capping agent) of nanorod morphology encapsulating Au nanoparticles. XRD studies shows semi-crystalline nature of the polymer unlike the amorphous polyindole formed using other methods. Tunable photoluminescence spectra show the potential applications of the composite in the field of organic laser and organic optoelectronics.     

A nanoparticulate indium tin oxide field-effect transistor with solid electrolyte gating

Reversible tuning of the transport properties of metallic conducting systems is not reported widely in the literature. Here, we report a junction field-effect transistor (FET) based on a transparent conducting oxide (TCO) nanoparticle channel and a solid polymer electrolyte as a gate. The device principle is based on the variation of the drain current induced by the capacitive double layer charging at the electrolyte/nanoparticle interfaces. A device with a metallic conducting channel made of indium tin oxide (ITO) nanoparticles exhibits an on/off ratio of 2 × 10(3) even when the gate potential is limited within the electrochemical capacitive region to avoid redox reactions at the interface. An FET device with metal-like conductance is always favored for the low dimensions of the device and a high on-state current. The field-effect mobility is calculated to be 24.3?cm(2)?V(-1)?s(-1). A subthreshold swing between 230 and 425?mV?dec(-1) is observed.     

Fibrous Composite Interfaces Studied by Electrical Resistance Measurement

Direct current (DC) electrical resistance measurement is effective for studying the interfaces in fibrous composite materials, particularly carbon fiber composites, which are electrically conducting. The measurement yields information on the fiber–matrix interface, residual stress, and interlaminar interface, and can be made in real time during debonding, residual stress reduction, temperature change, and interlaminar shear. This paper reviews the methods and applications in relation to polymer–matrix and cement–matrix composites.     

Optically active poly(dimethylsiloxane) elastomer films through doping with gold nanoparticles

Poly(dimethylsiloxane) (PDMS) elastomer films synthesized through a cross-linking reaction between hydroxyl-terminated or vinyl-terminated PDMS have been homogeneously doped with silica-coated Au nanoparticles. The nanocomposite synthesis involves mixing a preformed colloid of surface-modified metal nanoparticles with the elastomer film precursors. The homogeneous distribution of nanoparticles is demonstrated through the presence of well defined plasmon absorbance bands in the visible, which clearly show that the composites retain the characteristic optical properties of single Au nanoparticles. The metal particle concentration could be easily tailored either through the amount or the concentration of the nanoparticle colloid added. Since the Au nanoparticles are not cross-linked to the polymer and the concentration of particles is relatively low, we postulate that the presence of the nanoparticles does not affect the mechanical properties of the films, though this remains to be confirmed.     

Tribological properties of polymer nanohybrids containing gold nanoparticles obtained by laser ablation

We have studied polystyrene (PS)+Au particles nanohybrids. Approximately spherical gold nanoparticles with the average diameter of 15 nm were obtained by laser ablation in a liquid environment. Thus any chemical residue on the particles was eliminated. Focused ion beam (FIB) milling plus scanning electron microscopy (SEM) observation show that Au particles are fairly well dispersed inside the polymer matrix, better than when PS is simply dissolved in a nanoparticle solution. The Au particles concentration as low as 0.15 wt% results in dramatic changes in tribological properties, namely dynamic friction and pin-on-disk wear. Both wear and dynamic friction results are explained in terms of high brittleness of PS, abrasion of Au particles against a ceramic indenter, and also effects of density of filler particles in the matrix on tribological properties. Effects of varying normal load on friction are small.     

Role of Au nanoparticles in efficiency enhancement and green band emission quenching of blue polymer light emitting diodes

We studied photoluminescence (PL) and electroluminescence (EL) properties of polymer light emitting diodes (PLEDs) constructed with polyconjugated polymers blends containing Au nanoparticles (DA-Au NPs; 5.3 nm +/- 1.1 nm in diameter) capped by dodecylamine. For the blue light emitting polyfluorene polymers, selective quenching of excimer peaks or so-called green bands was observed in PL as well as in EL when they were mixed with small amounts (1-4 wt%) of DA-Au NP. The influence of DA-Au NPs on the light-emitting characteristics of the PLEDs strongly depended on the nature of the matrix polymer, which was particularly conspicuous for the polymers whose emission wavelength matches or overlaps with the surface plasmon resonance wavelength region of Au nanoparticles. Especially, the purity of the blue color emitted by the poly [2,7-(9,9-di-n-dioctylfluorene) (PF) was greatly improved by Au NPs that suppressed the 'green band.' All the PLEDs doped with DA-Au NPs showed enhanced maximum external quantum efficiency and emitted light intensity when compared to undoped counterparts.     

Photoluminescence quenching of semiconducting polymer nanoparticles in presence of Au nanoparticles

In this report, we have demonstrated the photoluminescence quenching and energy transfer properties of semiconducting polymer nanoparticles, poly (N-vinylcarbazole) (PVK) in presence of different sized Au nanoparticles by steady state and time-resolved spectroscopy. We have described the quenching phenomena by sphere of action static quenching mechanism and both dynamic and static quenching processes are found in these systems. PL quenching values are 24· 22% and 57· 3% for 14?nm and 18?nm Au nanoparticles, respectively. It is found that the radiative and nonradiative decay have been modified with the size of Au nanoparticles. PL quenching and shortening of decay time regarding polymer nanoparticles in presence of Au nanoparticles suggest the nonradiative energy transfer process. The values of energy transfer are 6· 7%, 49· 5% and 53· 38% from PVK polymer nanoparticles to 3?nm, 14?nm and 18?nm Au nanoparticles, respectively. Using FRET and SET equations we have calculated the average distance of donor PVK polymer nanoparticles and acceptor Au nanoparticles.     

Probing hot electron flow generated on Pt nanoparticles with Au/TiO2 Schottky diodes during catalytic CO oxidation

Hot electron flow generated on colloid platinum nanoparticles during exothermic catalytic carbon monoxide oxidation was directly detected with Au/TiO2 diodes. Although Au/TiO2 diodes are not catalytically active, platinum nanoparticles on Au/TiO2 exhibit both chemicurrent and catalytic turnover rate. Hot electrons are generated on the surface of the metal nanoparticles and go over the Schottky energy barrier between Au and TiO2. The continuous Au layer ensures that the metal nanoparticles are electrically connected to the device. The overall thickness of the metal assembly (nanoparticles and Au thin film) is comparable to the mean free path of hot electrons, resulting in ballistic transport through the metal. The chemicurrent and chemical reactivity of nanoparticles with citrate, hexadecylamine, hexadecylthiol, and TTAB (tetradecyltrimethylammonium bromide) capping agents were measured during catalytic CO oxidation at pressures of 100 Torr O2 and 40 Torr CO at 373-513 K. We found that chemicurrent yield varies with each capping agent but always decreases with increasing temperature. We suggest that this inverse temperature dependence is associated with the influence of charging effects due to the organic capping layer during hot electron transport through the metal-oxide interface.     

The role of interfacial interactions on the glass-transition and viscoelastic properties of silica/polystyrene nanocomposite

Filler surface properties and polymer-filler interactions have dominate influence on viscoelastic behavior of polymeric matrix composites. When the filler-filler spacing is on the order of the polymeric matrix molecular size, fillers may agglomerate through direct short-range interactions, also by overlapping of interfacial layers of neighboring fillers. In this work the effect of interfacial layer on the viscoelastic properties of silica/polystyrene composite was investigated.The Si/Ps nanocomposites were prepared by solution mixing method, and dynamic rheometry was employed to determine the viscoelastic behavior in the melt state. Experimental results show that, addition of silica nanoparticles to polystyrene matrix would increase the glass-transition temperature of polymer. This increasing will be accelerated by presence of nanoparticles with more filler-polymer adhesion energy, because of more interfacial layer volume fraction. It is helpful in evaluating the volume fraction and equivalent thickness of interfacial layer in polymer nanocomposites. Likewise it is shown that, the dynamic moduli of nanocomposite is enhanced associated with the increase in the glass-transition temperature. This study implies that the main source of increment in both dynamic modulus and glass-transition temperature of polymer nanocomposites is the presence of the immobilized interfacial layer and the secondary filler network.