Ultra-long silver nanowires prepared via hydrothermal synthesis enable efficient transparent heaters.

Ultra-long silver nanowires (AgNWs) with an aspect ratio of >2000 were prepared by the hydrothermal synthesis method. The influence of reaction time (4-32 h), reaction temperature (150-180 °C), polyvinylpyrrolidone (PVP) molecular weight (10 000-1 300 000 g mol-1), PVP concentration (50-125 mM), glucose concentration (5.6-22.4 mM) and CuCl2 concentration (2-20 µM) on the AgNW length was investigated systematically. The optimum conditions provided nanowires with an average diameter of 207 nm, an average length of 234 µm and a maximum length of 397 µm. Finally, a AgNW electrode was prepared on a glass substrate and used in transparent heater application. The transparent heater enabled outstanding heat-generating properties, reaching >200 °C within 70 s with an applied voltage of 5 V. Our results demonstrate how increasing the aspect ratio of ultra-long AgNWs is beneficial for both optical and electronic applications in terms of increased transmission and a more efficient Joule effect in the heater application. In addition, our results show that AgNWs with different lengths can be simply obtained by tuning synthesis parameters.

Perspective about Cellulose-Based Pressure and Strain Sensors for Human Motion Detection.

High-performance wearable sensors, especially resistive pressure and strain sensors, have shown to be promising approaches for the next generation of health monitoring. Besides being skin-friendly and biocompatible, the required features for such types of sensors are lightweight, flexible, and stretchable. Cellulose-based materials in their different forms, such as air-porous materials and hydrogels, can have advantageous properties to these sensors. For example, cellulosic sensors can present superior mechanical properties which lead to improved sensor performance. Here, recent advances in cellulose-based pressure and strain sensors for human motion detection are reviewed. The methodologies and materials for obtaining such devices and the highlights of pressure and strain sensor features are also described. Finally, the feasibility and the prospects of the field are discussed.

Preparation of Transparent Conductive Electrode via Layer-By-Layer Deposition of Silver Nanowires and Its Application in Organic Photovoltaic Device.

Solution processed transparent conductive electrodes (TCEs) were fabricated via layer-by-layer (LBL) deposition of silver nanowires (AgNWs). First, the AgNWs were coated on (3-Mercaptopropyl)trimethoxysilane modified glass substrates. Then, multilayer AgNW films were obtained by using 1,3-propanedithiol as a linker via LBL deposition, which made it possible to control the optical transmittance and sheet resistance of multilayer thin films. Next, thermal annealing of AgNW films was performed in order to agent their electrical conductivity. AgNW monolayer films were characterized by UV-Vis spectrometer, field emission scanning electron microscopy, optical microscopy, atomic force microscopy and sheet resistance measurement by four-point probe method. The high performances were achieved with multilayer films, which provided sheet resistances of 9 Ω/sq, 11 Ω/sq with optical transmittances of 71%, 70% at 550 nm, which are comparable to commercial indium tin oxide (ITO) electrodes. Finally, an organic photovoltaic device was fabricated on the AgNW multilayer electrodes for demonstration purpose, which exhibited power conversion efficiency of 1.1%.

Solution-Processable transparent conducting electrodes via the self-assembly of silver nanowires for organic photovoltaic devices.

Solution-processed transparent conducting electrodes (TCEs) were fabricated via the self-assembly deposition of silver nanowires (Ag NWs). Glass substrates modified with (3-aminopropyl)triethoxysilane (APTES) and (3-mercaptopropyl)trimethoxysilane (MPTES) were coated with Ag NWs for various deposition times, leading to three different Ag NWs samples (APTES-Ag NWs (PVP), MPTES-Ag NWs (PVP), and APTES-Ag NWs (COOH)). Controlling the deposition time produced Ag NWs monolayer thin films with different optical transmittance and sheet resistance. Post-annealing treatment improved their electrical conductivity. The Ag NWs films were successfully characterized using UV-Vis spectroscopy, field emission scanning electron microscopy, optical microscopy and four-point probe. Three Ag NWs films exhibited low sheet resistance of 4-19Ω/sq and high optical transmittance of 65-81% (at 550nm), which are comparable to those of commercial ITO electrode. We fabricated an organic photovoltaic device by using Ag NWs as the anode instead of ITO electrode, and optimized device with Ag NWs exhibited power conversion efficiency of 1.72%.

Fabrication of a transparent conducting electrode based on graphene/silver nanowires via layer-by-layer method for organic photovoltaic devices.

A solution-processed transparent conducting electrode was fabricated via layer-by-layer (LBL) deposition of graphene oxide (GO) and silver nanowires (Ag NWs). First, graphite was oxidized with a modified Hummer's method to obtain negatively-charged GO sheets, and Ag NWs were functionalized with cysteamine hydrochloride to acquire positively-charged silver nanowires. Oppositely-charged GO and Ag NWs were then sequentially coated on a 3-aminopropyltriethoxysilane modified glass substrate via LBL deposition, which provided highly controllable thin films in terms of optical transmittance and sheet resistance. Next, the reduction of GO sheets was performed to improve the electrical conductivity of the multilayer films. The resulting GO/Ag NWs multilayer was characterized by a UV-Vis spectrometer, field emission scanning electron microscope (FE-SEM), optical microscope (OM) and sheet resistance using a four-point probe method. The best result was achieved with a 2-bilayer film, resulting in a sheet resistance of 6.5Ω sq-1 with an optical transmittance of 78.2% at 550nm, which values are comparable to those of commercial ITO electrodes. The device based on a 2-bilayer hybrid film exhibited the highest device efficiency of 1.30% among the devices with different number of graphene/Ag NW LBL depositions.

Fabrication of gold patterns via multilayer transfer printing and electroless plating.

Gold patterns were fabricated on Si wafer substrate via multilayer transfer printing of polyelectrolytes, followed by selective deposition of gold nanoparticles (AuNPs) and then electroless plating of gold. First, PDMS stamp was coated with (PAH)(1)/(PSS/PDAC)(10) multilayer system, followed by transfer printing on the piranha cleaned fresh Si wafer substrate. Next, the substrate was dipped in AuNP solution for deposition of the nanoparticles on PAH layer. Then, the substrate was subjected to electroless plating to obtain the gold patterns. Very clean and precise gold patterns with electrical conductivity of 2.5 × 10(5) Ω(-1) cm(-1) were obtained.

Sonication-assisted layer-by-layer deposition of gold nanoparticles for highly conductive gold patterns.

Sonication-assisted layer-by-layer (LBL) deposition of gold nanoparticles (GNPs) was carried out in an attempt to prepare highly conductive gold patterns on polyimide substrates. First, sonication time was optimized with GNPs (12.8 nm) whose size was large enough to be analyzed by FE-SEM in order to evaluate the surface coverage. Next, multilayer formation (4, 8 and 12 layer) was confirmed using ethanedithiol (EDT) as linker molecules under optimized conditions by measuring their UV absorption, near-IR (NIR) transmittance, thickness, and electrical conductivity. Finally, 20-layer films using small GNPs (2.5 nm) were prepared with or without patterning, followed by sintering at 150 °C for 1h, which provided clean gold patterns with high electrical conductivity (2.5 × 10(5) Ω(-1) cm(-1)).

Preparation of gold patterns on polyimide coating via layer-by-layer deposition of gold nanoparticles.

Gold patterns were prepared via the microcontact printing (MCP) of 3-aminopropyltriethoxysilane (γ-APS) on plasma etched polyimide films, followed by the layer-by-layer (LBL) deposition of gold nanoparticles (GNPs), O(2) plasma etching, and sintering. First, the polyimide film on silicon wafer was modified via water plasma etching, followed by the MCP of γ-APS using a flat polydimethylsiloxane (PDMS) stamp. Next, the multilayer of GNPs was formed on the γ-APS layer by the LBL deposition of citrate-capped GNPs and poly(ethyleneimine) (PEI). Then, the samples were subjected to O(2) plasma etching to remove PEI and citrates, and then sintering to produce metallic gold. Finally, gold patterns were prepared with a patterned PDMS stamp (line width of 10µm). The GNP multilayer was characterized by UV-vis/near-IR spectrometer, atomic force microscopy (AFM), optical microscopy (OM), alpha-step and electrical conductivity measurement by two-point probe method. Very clean gold patterns with electrical conductivity of 4.1×10(4)Ω(-1)cm(-1) (20-layer GNP) were obtained.

Au-coated 3-D nanoporous titania layer prepared using polystyrene-b-poly(2-vinylpyridine) block copolymer nanoparticles.

New nanoporous structures of Au-coated titania layers were prepared by using amphiphilic block copolymer nanoparticles as a template. A 3-D template composed of self-assembled quaternized polystyrene-b-poly(2-vinylpyridine) (Q-PS-b-P2VP) block copolymer nanoparticles below 100 nm was prepared. The core-shell-type nanoparticles were well ordered three-dimensionally using the vertical immersion method on the substrate. The polar solvents were added to the polymer solution to prevent particle merging at 40 degrees C when considering the interaction between polymer nanoparticles and solvents. Furthermore, Au-coated PS-b-P2VP nanoparticles were prepared using thiol-capped Au nanoparticles (3 nm). The 3-D arrays with Au-coated PS-b-P2VP nanoparticles as a template contributed to the preparation of the nanoporous Au-coated titania layer. Therefore, the nanoporous Au-coated titania layer was fabricated by removing PS-b-P2VP block copolymer nanoparticles by oxygen plasma etching.

Preparation of gamma-APS monolayer with complete coverage via contact printing.

A monolayer film of 3-aminopropyltriethoxysilane (gamma-APS) was prepared by contact printing with featureless PDMS stamp. First, gamma-APS ink solutions in dry toluene were prepared in a dry nitrogen-filled glove box and immediately used for spin coating onto a PDMS stamp, followed by printing on a silicon wafer. Next, water contact angles and film thicknesses were measured as a function of ink concentration (5-100 mM) and printing time (1-60 min) after printing, as well as after aging in toluene for 24 h. In addition, surface coverage, topology, RMS roughness and surface amine density were also evaluated, while the chemical structure of gamma-APS monolayer was analyzed by FT-IR/ATR. Optimum conditions for gamma-APS monolayer with complete coverage were determined to be ink concentration of 20 mM and printing time of 30 min, which resulted in a water contact angle of 93 degrees, film thickness of 0.78 nm and surface amine density of 7.6 molecules/nm(2).