AgNW Film Research Articles

Enhancement of Antibacterial Properties of a Silver Nanowire Film via Electron Beam Irradiation.

Infectious diseases and the deaths caused due to contact with germ-contaminated surfaces are severe problems worldwide. Antibacterial materials based on silver nanowires (AgNWs) have a structural advantage when addressing this issue; this is because agglomeration is minimized when nanowires are fabricated into a film. Therefore, employing AgNWs for antimicrobial applications has garnered continuous interest, and increased research for further improvements has been observed. In this study, a AgNW film was fabricated onto glass by spin-coating and then subjected to surface irradiation up to a dose of 1200 kGy, using a low-energy electron beam (e-beam). This "e-beam" irradiation changed the surface morphology and chemical composition; consequently, this improved the performance of the film. The generation of a silver oxide (Ag2O and AgO) outer layer was identified over the AgNWs by X-ray photoelectron spectroscopy (XPS). The antibacterial test corresponding to a contact time of 1 h revealed that the e-beam irradiation increased the antibacterial activity in the log reduction from 1.2 to 1.4 for Staphylococcus aureus and from 1.5 to 3.7 for Escherichia coli. Based on the experimental results and the known antibacterial mechanisms of silver (Ag) nanospecies, we discuss the method by which the antibacterial performance of the AgNW film was improved via the e-beam irradiation. This work provides a simple and swift method to functionally enhance the AgNW antibacterial film via e-beam irradiation.

Cost-effective centrifuge coating method for silver nanowire-based transparent conducting electrode

The silver nanowire (Ag NW)-based electrode, a promising candidate for replacing the conventional indium tin oxide (ITO) electrode, is suitable for flexible device fabrication due to low cost production, high electrical conductivity, high transparency, and mechanical flexibility. Although many types of coating processes exist to produce Ag NW films, those methods require post-treatments and a Ag NW solution with a high concentration in excess of 0.5 mg/ml. In this work, we report a cost-effective method to produce a Ag NW electrode on a flexible polyethylene terephthalate (PET) substrate using centrifuge coating with a Ag NW solution with extremely low concentrations of 0.003–0.02 mg/ml without post-treatment. The optimized Ag NW electrode has a sheet resistance of 7.25 Ω/sq and optical transmittance of 73.62% in the visible wavelength region, resulting in a figure-of-merit value (FOM) of 157.13, which is better than that of a commercial ITO electrode. As a result, organic photovoltaic devices based on this Ag NW electrode on a PET substrate exhibited a power conversion efficiency of 7.61%, which is comparable to that of devices based on an ITO electrode.

Silver nanowires for anti-counterfeiting

Silver nanowire (AgNW) films have been widely used as flexible transparent electrodes due to the high electrical conductance and high transmittance in the visible range. The infrared (IR) properties of AgNW films, however, are seldom discussed. Here, we show that ultrathin AgNWs present high transmittance in the visible range (∼95%) and high reflectance (60–70%) in the IR range of 8–14 μm. Such a significant difference makes AgNW films invisible to naked eyes but visible under an IR camera, being an ideal selection for anti-counterfeit technologies, while no excitation is required. We have demonstrated that AgNW films can be spray-coated on either flat or microstructured surfaces with high conformability and high scratch-resistance, and thus these anti-counterfeiting materials can be applied to a variety of applications. The AgNW-based anti-counterfeiting may be helpful for combating counterfeiting crimes in the fields of medicines, artwork, banknotes, brand luxuries, industrial parts, and so on.

Stable heating performance of carbon nanotube/silver nanowire transparent heaters

A flexible silver nanowire transparent heater (AgNW TH) was recently reported. However, the fabrication of AgNW THs that are durable over the long term is an important concern due to nanowire thermal instability. In this work, a thin AgNW film was coated with a dense single-walled carbon nanotube (SWCNT) film on glass and polyimide (PI) substrates. This simple hybrid heater was evaluated for heater performance and long-term working stability. The AgNW TH dried in air was unstable and failed more rapidly at elevated temperatures under Joule heating than that dried in vacuum. The AgNW TH had the same temperature limit irrespective of nanowire coating density due to the low melting point of AgNWs. The SWCNT/AgNW TH displayed a higher heating temperature and longer working stability than the AgNW TH. Based on thermoreflectance imaging and considering a power balance model, the improved thermal stability of the hybrid heater is attributed to thermal uniformity, in turn related to fast heat dissipation via heat transfer pathways of the dense SWCNT film, which delayed deformation and disconnection of the AgNWs. This simple hybrid structure could enhance the long-term working stability of AgNW-based THs in a wide range of practical applications.

Effect of Silver Nanowire Alignment on Electrical Resistance and Mechanical Reliability.

Given the increasing demands for high portability and large screens, electronic devices are evolving toward flexible electronics. Since the flexible devices will be operated by a current generated by repeated mechanical deformations, high mechanical stability, electrical conductivity, and optical properties of transparent conductive electrodes (TCE) under mechanical deformations are required; hence silver nanowire (AgNW) electrodes are attracting much interest. However, the anisotropic shape of AgNW can result in different electrical properties and mechanical reliability depending on the AgNW alignment. In this study, two kinds of AgNW films were prepared by roll-to-roll screening printing. One film has an isotropic arrangement of AgNW, the other an anisotropic arrangement, along the roll-to-roll machine direction (MD). These samples were cut with different directions from the MD. Whereas the isotropic sample exhibited an identical electrical resistance regardless of sample direction, the anisotropically aligned samples showed low resistance when parallel to the MD and high resistance when perpendicular to the MD. The mechanical reliability during repeated bending fatigue according to the AgNW alignment direction was also evaluated. Depending on the direction of alignment of the AgNW, the fatigue lifetime differed because the mechanical stability at the AgNW junction was different.

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%.

Flexible and Transparent Ferroferric Oxide-Modified Silver Nanowire Film for Efficient Electromagnetic Interference Shielding.

Transparent and flexible electromagnetic interference (EMI) shielding film is highly desirable due to the fast-growing flexible electronics. A silver nanowire (Ag NW) film is considered to be an ideal candidate for a transparent and flexible EMI shielding film but suffers low EMI shielding effectiveness (SE) at high transparency and poor bending durability. Herein, we introduce ferroferric oxide (Fe3O4) into a Ag NW film and demonstrate a robust EMI shielding film, which exhibits SE of 24.9 dB at 8.2 GHz and optical transparency of 90%. Fe3O4 exhibits roles of the improved absorption loss for electromagnetic radiation due to its high permeability, the enhanced reflection loss for electromagnetic radiation by increasing the conductivity of Ag NWs film, and the improved stability for the enhanced adhesion of the Ag NW EMI shielding film. Our work provides a facile method for high-performance transparent EMI shielding film, which exhibits great potential for protection for electronic devices.

Coat-and-print patterning of silver nanowires for flexible and transparent electronics

Silver nanowires (Ag NWs) possess excellent optoelectronic properties, which have led to many technology-focused applications of transparent and flexible electronics. Many of these applications require patterning of Ag NWs into desired shapes, for which mask-based and printing-based techniques have been developed and widely used. However, there are still several limitations associated to these techniques. These limitations, such as complicated patterning procedures, limited patterning area, and compromised optical transparency, hamper the efficient fabrication of high-performance Ag NW patterns. Here, we propose a coat-and-print approach for effectively patterning Ag NWs. We printed a polymer-based ink on the spin-coated Ag NW films. The ink acts as a protective layer to help remove excess Ag NWs from the substrate and then dissolves itself into an organic solvent. In this way, we can take advantage of both coating-based techniques (lead to Ag NWs with high transparency) and printing-based techniques (efficiently pattern diverse shapes). The resultant Ag NW patterns exhibit comparable conductivity (sheet resistance: 7.1 to 30 Ohm/sq) and transparency (transmittance: 84 to 95% at λ = 550 nm) to those made by conventional coating methods. In addition, the patterned Ag NWs exhibit robust mechanical stability and reliability, surviving extensive bending and peeling tests. Due to higher conductivity, efficient patterning ability and inherent transparency, this material system and application method is highly suitable for transparent and flexible electronics. As a proof of concept, this research demonstrates a wide-band antenna, operating in the mm-wave range that includes the 5G communication band. The proposed antenna exhibits a wide bandwidth of 26 GHz (from 17.9 GHz to 44 GHz), robust return loss under 1000 cyclic bending (bending radius of 3.5 mm), and decent transparency over the entire visible wavelength (86.8% transmittance at λ = 550 nm). This work’s promising results indicate that this method can be adapted for roll-to-roll manufacturing to efficiently produce patterned and optically transparent devices.

Efficient heat spreader using supersonically sprayed graphene and silver nanowire

Hotspots in high-power and high-density microelectronic devices are a major problem because insufficient thermal dissipation can cause device malfunction. We introduce supersonically sprayed thin films made of reduced graphene oxide (rGO) and silver nanowires (AgNW) that can efficiently dissipate heat to remediate hotspots. Film deposition by cold supersonic spraying provides superior adhesion and requires no post-deposition treatment, making it compatible with a wide range of surface materials. A rGO film heat spreader is deposited on an Al2O3 substrate (10 × 10 cm2), which is Joule-heated using a nickel–chrome wire. Heat quickly dissipates over the entire surface due to the rGO film, eliminating the localized hotspot. The effect of film thickness is investigated to identify the optimal thickness of the deposited rGO film heat spreader. The cooling capability of pure graphene oxide films is characterized and compared to the heat dissipation performance of a hybrid rGO–AgNW film and an uncoated substrate. The morphology and surface properties of the films are characterized using scanning electron microscopy, Raman spectroscopy, optical profilometry, and thermal infrared imaging. An rGO film thickness of 10 μm produced the lowest thermal resistance and the addition of AgNW enhanced film thermal performance by reducing the thermal resistance.

실버 나노와이어 라미네이션 전극을 활용한 반투명 유기태양광전지 제작

A transparent laminated electrode was fabricated, from a multiple stack of silver nanowire (AgNW) and poly (3,4-ethylenedioxythiophene)-poly (styrenesulfonate) (PEDOT:PSS), and applied as the top electrode of an organic photovoltaic (OPV) device. For enhancements in conductivity and adhesiveness, AgNW film was sandwiched between PH 1000 and AI 4083 PEDOT:PSS, respectively. The fabricated electrode showed a sheet resistance of 39 Ω/sq and transmittance of 75%. In addition, it can easily be attached(lamination) or detached(delamination) with a small amount of mechanical force. Performance of the developed laminated electrode was verified by fabricating an OPV with the laminated electrode. The fabricated final OPV exhibits semitransparency, and provided a final photo-conversion efficiency of 1.9%. Slight low efficiency accounts from a high contact resistance between the laminated electrode and organic layer.

Broadband femtosecond nonlinear optical properties of silver nanowire films

In this report, we present results from the investigation of femtosecond (fs) nonlinear optical (NLO) behaviour of silver nanowires (Ag NWs) films. High quality Ag NWs (10 μm length, diameter 50 nm in isopropyl alcohol) were utilzied for the NLO studies employing the standard Z-scan technique in both open and closed aperture configurations at wavelengths of 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, and the corresponding NLO coefficients were estimated from theoretical fits to the experimental data. Nonlinear absorption in the Ag NWs at 800 nm demonstrated a pure reverse saturable absorption (RSA) with a strong two-photon absorption (TPA) coefficient. At 800 nm, intensity dependent Z-scan studies were performed at different peak intensities of 190 MW/cm2, 210 MW/cm2, 260 MW/cm2 and observed that the TPA coeffieicent (~10−5 cm/W) increased significantly as a function of peak intensity. Interestingly, the nonlinear absorption of Ag NWs films demonstrated a complex behavior of saturable absorption (SA), reverse saturable absorption (RSA) and switching from RSA within SA depending on excitation wavelength even though the studies were performed at similar peak intensities. The estimated NLO coefficients were IS = 30 MW/cm2 (βsa = 0), βTPA = 1.6 × 10−5 cm/W, IS = 92 MW/cm2 (βeff = 1.4 × 10−5 cm/W) and IS = 60 MW/cm2 (βsa = 1.72 × 10−5 cm/W) for the wavelengths of 700 nm, 750 nm, 850 nm and 900 nm, respectively. The nonlinear refraction studies at the wavelength 800 nm, investigated by closed aperture Z-scan, demonstrated a positive sign (compared to the studies at other wavelengths) and the obtained intensity dependent nonlinear refractive index was ~1.6 × 10−9 cm2/W.

Atmospherically Stable Silver Nanowire/Hydroxyethyl Cellulose Films and their Application in Flexible Transparent Touch Screen

Silver nanowires (AgNWs) has been extensively studied to replace indium tin oxide as a suitable material for transparent conducting films (TCEs) The networks of nanowires however are prone to degradation due to corrosion when exposed to ambient conditions. In this study, high aspect ratio AgNWs were synthesized with an improved polyol method by varying the reaction temperatures in the nucleation and growth stage. Solutions of AgNWs were deposited on polymer substrates and were exposed to ambient laboratory conditions for several days and the effect on the stability and overall performance of the AgNW films was investigated. Morphological and elemental analysis of the exposed films was done using SEM and EDX, respectively. Hydroxyethyl cellulose (HEC) was introduced as a polymeric binder and protective agent in order to prevent the exposure of the AgNW surface to corrosive agents in air. A TCE with a sheet resistance of 47.50 Ω/sq and transmittance of 89.70% at 550 nm without any harsh post-treatments, was demonstrated. These electrodes were used to fabricate a transparent flexible touch screen.

Protecting the Nanoscale Properties of Ag Nanowires with a Solution-Grown SnO2 Monolayer as Corrosion Inhibitor

The chemical reactivity and/or the diffusion of Ag atoms or ions during thermal processing can cause irreversible structural damage, hindering the application of Ag nanowires (NWs) in transparent conducting films and other applications that make use of the material's nanoscale properties. Here, we describe a simple and effective method for growing monolayer SnO2 on the surface of Ag nanowires under ambient conditions, which protects the Ag nanowires from chemical and structural damage. Our results show that Sn2+ and Ag atoms undergo a redox reaction in the presence of water. First-principle simulations suggest a reasonable mechanism for SnO2 formation, showing that the interfacial polarization of the silver by the SnO2 can significantly reduce the affinity of Ag to O2, thereby greatly reducing the oxidation of the silver. The corresponding values (for example, before coating: 17.2 Ω/sq at 86.4%, after coating: 19.0 Ω/sq at 86.6%) show that the deposition of monolayer SnO2 enables the preservation of high transparency and conductivity of Ag. In sharp contrast to the large-scale degradation of pure Ag-NW films including the significant reduction of its electrical conductivity when subjected to a series of harsh corrosion environments, monolayer SnO2 coated Ag-NW films survive structurally and retain their electrical conductivity. Consequently, the thermal, electrical, and chemical stability properties we report here, and the simplicity of the technology used to achieve them, are among the very best reported for transparent conductor materials to date.

Patterned, Flexible, and Stretchable Silver Nanowire/Polymer Composite Films as Transparent Conductive Electrodes.

The emergence of flexible and stretchable optoelectronics has motivated the development of new transparent conductive electrodes (TCEs) to replace conventional brittle indium tin oxide. For modern optoelectronics, these new TCEs should possess six key characteristics: low cost, solution-based processing; high transparency; high electrical conductivity; a smooth surface; mechanical flexibility or stretchability; and scalable, low-cost patterning methods. Among many materials currently being studied, silver nanowires (AgNWs) are one of the most promising, with studies demonstrating AgNW films and composites that exhibit each of the key requirements. However, AgNW-based TCEs reported to date typically fulfill two or three requirements at the same time, and rare are examples of TCEs that fulfill all six requirements simultaneously. Here, we present a straightforward method to fabricate AgNW/polymer composite films that meet all six requirements simultaneously. Our fabrication process embeds a AgNW network patterned using a solution-based wetting-dewetting protocol into a flexible or stretchable polymer, which is then adhered to an elastomeric poly(dimethylsiloxane) substrate. The resulting patterned AgNW/polymer films exhibit ∼85% transmittance with an average sheet resistance of ∼15 Ω/sq, a smooth surface (a root-mean-square surface roughness value of ∼22 nm), and also withstand up to 71% bending strain or 70% stretching strain. We demonstrate the use of these new TCEs in flexible and stretchable alternating current electroluminescent devices that emit light to 20% bending strain and 60% stretching strain.

Optoelectronic and Electrothermal Properties of Transparent Conductive Silver Nanowires Films.

Silver nanowires (AgNWs) show promise for fabricating flexible transparent conductors owing to their excellent conductivity, high transparency, and good mechanical properties. Here, we present the fabrication of transparent films composed of AgNWs with diameters of 20–30 nm and lengths of 25–30 μm on polyethylene terephthalate substrates and glass slides substrates using the Meyer rod method. We systematically investigated the films’ optoelectronic and electrothermal properties. The morphology remained intact when heated at 25–150 °C and the AgNWs film showed high conductivity (17.6–14.3 Ω∙sq−1), excellent transmittance (93.9–91.8%) and low surface roughness values (11.2–14.7 nm). When used as a heater, the transparent AgNW conductive film showed rapid heating at low input voltages owing to a uniform heat distribution across the whole substrate surface. Additionally, the conductivity of the film decreased with increasing bending cycle numbers; however, the film still exhibited a good conductivity and heating performances after repeated bending.

Self-Limited Nanosoldering of Silver Nanowires for High-Performance Flexible Transparent Heaters.

Silver nanowires (Ag NWs) are key materials to fabricate next-generation flexible transparent electrodes (FTEs). Currently, the applications of Ag NWs are impeded by the large wire-wire contact resistance. Herein, a self-limited nanosoldering method is proposed to reduce the contact resistance by epitaxially depositing silver nanosolders at the Ag NW junctions, which have a negligible effect on the optical transparency, while decreasing the sheet resistance of the Ag NW film from 18.6 to 7.7 Ω/sq at a transmittance of 90%. In addition, the deposited nanosolders at the junctions remarkably improve the electrical and mechanical stabilities of the Ag NW electrodes. Notably, this simple nanosoldering process can be rapidly conducted under room temperature and ambient conditions and is free of any technical support or specific equipment. This technique is easily applied to the nanosoldering of 210 × 297 mm FTEs. Based on these FTEs, a high-performance flexible transparent heater with a sheet resistance 3.7 Ω/sq at a transmittance of 82.5% is constructed. Because of the high heating rate (4.8 °C/s), the heater can produce uniform heating (145 °C) at a short response time (30 s) and low input voltage (6 V).

Force sensor fabrication by AgNWs film using 532 nm pulses laser

This current study investigated the effects of laser direct writing (LDW) on the capacitance force sensor of a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) film mixer with silver nanowire thin films by using a 532-nm laser system. The technique was combined with various scanning speeds (i.e., 800, 1000, and 1200 mm s−1) to investigate the effectiveness of the force sensor. During interdigitated electrode fabrication, the laser fluence and laser pulse repetition frequency were fixed at 5.42 J/cm2 and 40 kHz, respectively. Nonloading force and various loading force states were used to test the function of the electrode under different LDW conditions. A best correlation coefficient of approximately 0.88 confirmed a linear functional dependence between the square of the pattern width and capacitance under the micromachining speed of 1000 mm s−1. Moreover, in the nonloading force state, the capacitance value increased with the increase in the electrode pattern width under a micromachining speed of 800 mm s−1. Regarding the loading force status, the capacitance increased when the loading force increased from 18 to 90 g. When the interdigitated pattern line width was 500 μm and electrode micromachining speed was 800 mm s−1, the maximum capacitance value was 71.5 pF under a loading force of 90 g.

Sandwich-Structured Silver Nanowire Transparent Conductive Films with 3H Hardness and Robust Flexibility for Potential Applications in Curved Touch Screens.

A sandwich-structured bottom hard-coat/silver nanowire/top hard-coat (BHC/AgNW/THC) transparent conductive film (TCF) has been prepared by embedding the functional AgNW layer between two HC layers. The BHC/AgNW/THC TCFs show high scratch resistance with a hardness of 3H due to the enhanced adhesion to the substrate. In addition, the BHC/AgNW/THC TCFs exhibit a transmittance of 90.6% and a haze of 1% at 550 nm under a sheet resistance of 72 Ω/sq. Furthermore, highly enhanced long-term stability has been guaranteed by the HC layers due to their excellent gas barrier property. The amazing fact is that hard coating has little effect on the flexibility of AgNW films especially under extreme bending conditions and negligible resistance change could be observed after bending over thousands of times. Consequently, the greatly improved performance of BHC/AgNW/THC TCFs provided by employing hard coating layers paves the way for real-world applications of flexible AgNWs in vast areas that rigid indium tin oxide is not suitable.

Fully solution processed Ag NWs/ZnO TF/ZnO NR composite electrodes with tunable light scattering properties for thin-film solar cells

Silver nanowire (Ag NWs) films are promising alternatives to conventional indium tin oxide transparent electrodes (TE) for display and solar cells applications. Higher haze factor is one essential factor for TE using in solar cells application. In this work, a controlled ZnO nanorods (NR) were grown on Ag NWs/ZnO seed layers by the hydrothermal method with highly tunable control of the scattering properties (haze) by Ag NWs and ZnO NR a s two independent scatters. Varying the ZnO NR length controlled by different growth times on Ag NWs/ZnO was investigated. The maximum haze (@500 nm) 60% achieved by 3H ZnO NR growth. Overall, ZnO NR grown on Ag NWs/ZnO seed layers providing a straightforward process for controlling light scattering properties by multiple light trapping transparent electrodes in three-dimensional networks. The findings in this work provide a new solution of Ag NWs films replacing ITO for applications in solar cells device.

Length-dependent electro-optical properties of silver nanowires-based transparent conducting films

In this paper, silver nanowires (AgNWs) with mean diameters of 65 nm and mean length of 9.8 µm were synthesized by the polyol solvothermal method. Sonication-induced scission was used to obtain AgNWs with a length range of 7.1–3.3 µm, and further AgNWs solutions were prepared with as-synthesized AgNWs as conductive fillers in the ethanol. A series of AgNWs random networks were prepared on the glass substrate using spray coating technique. Photoelectric properties and microstructure characterizations of AgNWs random networks were conducted to identify changes in such properties and the extent of these changes as a function of the length and content of AgNWs. The results show the sheet resistance and the transmittance of AgNWs network gradually increase as the length of AgNWs decrease. However, as the concentration of AgNWs increase, the sheet resistance and the transmittance of AgNWs networks decreases and increases, respectively. To obtain an approximative Rs of AgNWs film, the concentration of AgNWs with a length of 7.1 µm should be 1.2 times that of AgNWs with a length of 9.1 µm, with a 10% dropped transmittance. These results are attributed to the increase of the contact resistance among AgNWs networks and the density of AgNWs at the same area coverage. As the concentration of AgNWs increases, the deposition density of AgNWs networks increases, and both the sheet resistance and the transmittance decrease gradually.