Diameter Silver Nanowire Research Articles

Depth mapping of metallic nanowire polymer nanocomposites by scanning dielectric microscopy.

Polymer nanocomposite materials based on metallic nanowires are widely investigated as transparent and flexible electrodes or as stretchable conductors and dielectrics for biosensing. Here we show that Scanning Dielectric Microscopy (SDM) can map the depth distribution of metallic nanowires within the nanocomposites in a non-destructive way. This is achieved by a quantitative analysis of sub-surface electrostatic force microscopy measurements with finite-element numerical calculations. As an application we determined the three-dimensional spatial distribution of ∼50 nm diameter silver nanowires in ∼100 nm-250 nm thick gelatin films. The characterization is done both under dry ambient conditions, where gelatin shows a relatively low dielectric constant, εr∼ 5, and under humid ambient conditions, where its dielectric constant increases up to εr∼ 14. The present results show that SDM can be a valuable non-destructive subsurface characterization technique for nanowire-based nanocomposite materials, which can contribute to the optimization of these materials for applications in fields such as wearable electronics, solar cell technologies or printable electronics.

Sizing single nanoscale objects from polarization forces

Sizing natural or engineered single nanoscale objects is fundamental in many areas of science and technology. To achieve it several advanced microscopic techniques have been developed, mostly based on electron and scanning probe microscopies. Still for soft and poorly adhered samples the existing techniques face important challenges. Here, we propose an alternative method to size single nanoscale objects based on the measurement of its electric polarization. The method is based on Electrostatic Force Microscopy measurements combined with a specifically designed multiparameter quantification algorithm, which gives the physical dimensions (height and width) of the nanoscale object. The proposed method is validated with ~50 nm diameter silver nanowires, and successfully applied to ~10 nm diameter bacterial polar flagella, an example of soft and poorly adhered nanoscale object. We show that an accuracy comparable to AFM topographic imaging can be achieved. The main advantage of the proposed method is that, being based on the measurement of long-range polarization forces, it can be applied without contacting the sample, what is key when considering poorly adhered and soft nanoscale objects. Potential applications of the proposed method to a wide range of nanoscale objects relevant in Material, Life Sciences and Nanomedicine is envisaged.

Increasing Silver Nanowire Network Stability through Small Molecule Passivation

Silver nanowire (AgNW) transparent electrodes show promise as an alternative to indium tin oxide (ITO). However, these nanowire electrodes degrade in air, leading to significant resistance increases. We show that passivating the nanowire surfaces with small organic molecules of 11-mercaptoundecanoic acid (MUA) does not affect electrode transparency contrary to typical passivation films, and is inexpensive and simple to deposit. The sheet resistance of a 32 nm diameter silver nanowire network coated with MUA increases by only 12% over 120 days when exposed to atmospheric conditions but kept in the dark. The increase is larger when exposed to daylight (588%), but is still nearly two orders of magnitude lower than the resistance increase of unpassivated networks. The difference between the experiments performed under daylight versus the dark exemplifies the importance of testing passivation materials under light exposure.

Rice–Bernasconi Gorkov–Eliashberg Effect of Giant Dielectric Permittivity in Silica-Based Films Containing Interrupted Silver Nanowires

Silver nanowires of diameter ~ 5 nm were grown within thick films (0.6 µm thickness) of sol–gel-derived silica-based glasses of composition xAg2O(1 − x)SiO2; x having values of 30 and 40, respectively, by an electrodeposition method. By applying suitable voltage pulses to the composites, interrupted silver nanowires were produced with lengths having values in the range 4000–5000 nm. The samples exhibited dielectric constant with values of the order of 105 and a low dielectric loss (~ 0.01). The dielectric constant values calculated by using Rice–Bernasconi model which originated from Gorkov–Eliashberg theory of metallic nanoparticles were in satisfactory agreement with the experimental results. The present work not only provides strong evidence for the basis of Rice–Bernasconi model but also opens up a simple method to synthesize high dielectric constant materials which will be useful in fabricating devices for very large-scale integration applications, among others.

Giant dielectric permittivity in interrupted silver nanowires grown within mesoporous silica

Nanoglasses in the system Ag2O–SiO2 were formed within the pores of mesoporous silica SBA-15 (Santa Barbara Amorphous). Silver nanowires of diameter 5 nm were grown within SBA-15 by the process of electrodeposition. The nanowires were disrupted by applying a suitable voltage pulse. Detailed transmission and scanning electron microscopy studies were carried out. The disrupted silver strands were found to have an average length of 90 nm. The density of interrupted strands was estimated from the electron micrographs and found to have values in the range (10–20) × 1010 cm−2. Dielectric constant and dielectric loss factors of the nanocomposites of disrupted silver strand—containing Ag2O–SiO2 glass and SBA-15 were found to have values in the range 200–300 and 0.014–0.008 respectively at frequencies in the range 10 kHz–2 MHz. These values were found to be in satisfactory agreement with the theoretical model of Rice and Bernasconi emanating from the theory of Gorkhov and Eliashberg. These nanocomposites are expected to be useful in the fabrication of supercapacitors, after developing suitable electrode system for the material.

Research Update: Synthesis of sub-15-nm diameter silver nanowires through a water-based hydrothermal method: Fabrication of low-haze 2D conductive films

We synthesized ultra-thin Ag nanowire (Ag NWs) with sub-15 nm diameters and aspect ratios of 1000 through a water-based high-pressure hydrothermal method in the presence of a tetrabutylammonium dichlorobromide organic salt and glucose reducing agent. In the crystal growth stage, the diameter of the NWs could be controlled by adjusting the pressure, and 15-nm diameter wires were obtained at a pressure of 190 psi. These 2D conductive Ag NW network films showed an excellent optical performance with low haze value of ≤1.0% and 94.5% transmittance at a low sheet resistance of 20 Ω/sq.

Reduced haze of transparent conductive films by smaller diameter silver nanowires

Silver nanowires (Ag NWs) have received considerable attention for flexible transparent conductive films (TCFs) since they provide a relatively low sheet resistance at a high transmittance. However, the diffuse light scattering, haze, has been regarded as a hurdle to achieve clarity of films. Here we revisit the Mie scattering theory to calculate the extinction and scattering coefficients of Ag NWs which were employed to estimate haze of TCFs. The theory predicted a decrease in haze with a decrease in Ag NW diameter which was supported by experimental investigations carried out using Ag NWs with 5 different diameters (17.6, 19.9, 22.5, 24.3, and 29.6 nm). Overall, excellent properties of TCFs (haze = 0.21%–1.8%, transmittance = 95.33%–98.45%, sheet resistance = 20.87–81.76 Ω sq−1) were obtained. Ag NWs with a diameter of 17.6 nm provided minimum haze values at equivalent sheet resistances (e.g., haze = 0.21%, transmittance = 98.45%, sheet resistance = 77.36 Ω sq−1) compared with ones with lager diameters and the controls in literatures. This work investigated the interdependence between haze and NW diameter and might provide a design guide for flexible Ag NW TCFs.

Synthesis of small diameter silver nanowires via a magnetic-ionic-liquid-assisted polyol process

Silver nanowires (Ag NWs) with a small diameter of 20 nm and aspect ratio of 1000 were synthesized using the polyol method in the presence of a magnetic ionic liquid: 1-butyl-3-methylimidazolium tetrachloroferrate.

Synthesis and optoelectronic characteristics of 20 nm diameter silver nanowires for highly transparent electrode films

We demonstrate the polyol synthesis of ultrathin Ag nanowires with diameters of 20 nm and an aspect ratio as high as ∼1000 under high-pressure conditions.

Silver nanowires decorated with silver nanoparticles for low-haze flexible transparent conductive films.

Silver nanowires have attracted much attention for use in flexible transparent conductive films (TCFs) due to their low sheet resistance and flexibility. However, the haze was too high for replacing indium-tin-oxide in high-quality display devices. Herein, we report flexible TCFs, which were prepared using a scalable bar-coating method, with a low sheet resistance (24.1 Ω/sq at 96.4% transmittance) and a haze (1.04%) that is comparable to that of indium-tin-oxide TCFs. To decrease the haze and maintain a low sheet resistance, small diameter silver nanowires (~20 nm) were functionalized with low-temperature surface-sintering silver nanoparticles (~5 nm) using bifunctional cysteamine. The silver nanowire-nanoparticle ink stability was excellent. The sheet resistance of the TCFs was decreased by 29.5% (from 34.2 to 24.1 Ω/sq) due to the functionalization at a low curing temperature of 85 °C. The TCFs were highly flexible and maintained their stability for more than 2 months and 10,000 bending cycles after coating with a protective layer.

A Tunable Plasmon Resonance in Gold Nanobelts

Plasmonic nanowires with sub-100-nm rectangular cross sections were found to exhibit a strong transverse plasmon peak at visible wavelengths. By correlating atomic force microscopy measurements of individual nanobelts with their dark-field scattering spectra, it is seen that the transverse peak tunes with cross-sectional aspect ratio. Simulations revealed that the scattering plasmonic modes are transverse antisymmetric excitations across the nanobelt width. Unlike larger diameter silver nanowires, these nanobelts exhibit sharp, tunable plasmon resonances similar to those of nanoparticles.

Experimental Demonstration of Plasmon Propagation, Coupling, and Splitting in Silver Nanowire at 1550-nm Wavelength

We experimentally demonstrate silver-nanowire-based plasmonic devices including the nanowaveguide, the nanocoupler, and the nanosplitter at optical communication wavelength of 1550 nm. The plasmon propagation loss in a 300-nm diameter silver nanowire is measured to be 0.3 dB/μm and the effective propagation length is 14.5 μm. This loss is comparatively lower than that at 980 nm. Two types of plasmonic functional devices based on the coupling between two silver nanowires, nanocouplers, and nanosplitters, are realized. For the nanocoupler, the experimental results show that the plasmonic modes can be efficiently coupled between two closely positioned nanowires. While for the nanosplitter, the plasmonic mode is split with a power ratio of 2.6:1. These demonstrations experimentally prove the feasibility of extending the operating wavelength of silver-nanowire-based plasmonic devices to current optical communication wavelength with a lower loss, which are thus important steps for potentially utilizing low-loss nanowire-based plasmonic components for photonic integrated circuits.

Direct measurement of propagation losses in silver nanowires

We demonstrate a simple, direct measurement of propagation losses in single silver nanowires. Using a waveguiding nanoscale fiber taper for highly efficient launching, propagation surface plasmon polaritons are excited in the silver nanowire with high efficiency. The output intensity as light radiation at the end of the nanowire is quantified with high accuracy and repeatability. A typical propagation loss of 0.41 dB radicalmum (for 633 nm light) in a 260 nm diameter silver nanowire is obtained, which suggests that the propagation loss of a single silver nanowire could be lower than previously reported experimental results and should be much lower than those obtained by theoretical calculations.

Stability of Metal Nanowires (d ≥ 15 nm) Against Electromigration

We have studied stability of metal nanowires against electromigration damage when they are subjected to high current density. Silver nanowires of diameter ranging from 15 nm to 100 nm were synthesized with electrochemical method using template route. Electromigration study was accompanied with in-situ low frequency electric resistance fluctuation or 1/f noise measurement in the nanowires. It was observed that nanowires with smaller diameter stayed without substantial damage even after 10 to 14 days of continuous stressing with a current of density of the order of 1012 A/m2, while those with larger diameter get damaged much sooner. Noise measurements show that for nanowires with smaller diameter, noise spectra remains almost same for the entire duration of current stressing whereas in case of nanowires of larger diameter, spectral power of noise (SV(f) infinity 1/falpha) as well as the frequency exponent, alpha, increases as the electromigration process progresses. This is similar to that seen in metal films.

Novel properties of glass–metal nanocomposites

Nanoparticles of silver and copper were grown at the glass–crystal interfaces within a silicate glass by reducing the ion-exchanged glass–ceramic concerned. By controlling the reduction treatment a wide range of surface resistivity e.g., from 0.2 to 10 10 Ω/sq. could be generated. Silver nanowires of diameter ∼40 nm were grown within the pores of a silica gel. They exhibited single electron tunneling as evidenced by conductance maxima at definite intervals of the applied voltage. Silver nanowires of diameter 0.5 nm were grown within the crystal channels of fluorophlogopite mica which were first precipitated in a silicate glass. The nanowires when broken gave giant dielectric permittivity (∼10 7) to the composite. Copper core–copper oxide shell and iron core–iron oxide shell nanostructures respectively were generated within a silica gel. The core–shell structure exhibited electrical conductivity several orders of magnitude higher than that of the precursor gel. An interfacial amorphous phase contributed to this increase in electrical conductivity. Glass–ceramics containing BaTiO 3 and nanoparticles of silver showed a five order of magnitude decrease in electrical resistance as the relative humidity was changed from 25% to 75%. Arrays of metal nanoparticles (silver or copper) grown within a silicate glass exhibited a diode-like behavior. This was explained as arising due to formation of metal–semiconductor nanojunctions – metal particles smaller than 3 nm behaving like a semiconductor. The examples reviewed here show that exploiting the void spaces available in an oxide glass nanophases of a wide variety could be grown within and novel properties generated. This approach could be promising in imparting new functionality to conventional glasses.

Glass–Ceramic–Metal Nanocomposites Containing a Ferroelectric Phase

Ferroelectric crystallites of dimensions—few microns were grown within suitably chosen glass compositions. The glasses were prepared by both melt-quenching and solgel techniques. Typical phases were BaTiO3, Pb(Zr0.5 Ti0.5) and LiNbO3 respectively. Nanoparticles of silver or nickel were synthesized by subjecting the ion exchanged glass-ceramics to a reduction treatment. The dielectric permittivities of the nanocomposites were found to be much higher than those of the glass-ceramic specimens. Space–charge model failed to explain this enhancement. A quantum mechanical model was used to explain this effect. Silver nanowires of diameter ∼5 nm were grown in glass-ceramics containing LiNbO3 crystallites by an electrodeposition technique—the voltage applied being 20 volts. The wires were aligned parallel to the applied field. This is ascribed to the internal field increase due to the presence of ferroelectric crystals. By applying a suitable voltage pulse, break junctions were induced in these wires. Voltage–Current characteristics of the resultant structure showed the field emission effect with a high field enhancement factor.

Silver nanowires grown in the pores of a silica gel

Silver nanowires of diameter ∼40 nm and length ∼0.3 mm have been grown by electrodeposition within the pores of silica gels which were heat treated in the temperature range 523 to 823 K and, subsequently, soaked in a silver nitrate solution. A staircase current–voltage characteristic was observed in the direction of electrodeposition after nanowires were disrupted by the application of a dc voltage pulse. Such gels containing interrupted nanowires of silver showed a dielectric constant value ∼104 both in directions parallel and perpendicular to that of electrodeposition.

Nanowire formation in a polymeric film

Silver nanowires of diameter ∼2 nm and length ∼2 mm have been grown by an electrodeposition method within a polyvinyl alcohol film subjected to a two-stage treatment, viz., in ammonium persulphate and pyrrole solutions, respectively. A staircase current–voltage characteristic has been measured in this composite. Also, the material shows a dielectric constant ∼104. Both these effects are observed when the applied electric field is in a direction perpendicular to that of the electrodeposition process.