Bulk Silver Value Research Articles

Photo-Sintered Silver Thin Films by a High-Power UV-LED Module for Flexible Electronic Applications.

In recent printed electronics technology, a photo-sintering technique using intense pulsed light (IPL) source has attracted attention, instead of conventional a thermal sintering process with long time and high temperature. The key principle of the photo-sintering process is the selective heating of a thin film with large light absorption coefficients, while a transparent substrate does not heat by the IPL source. Most research on photo-sintering has used a xenon flash lamp as a light source. However, the xenon flash lamp requires instantaneous high power and is unsuitable for large area applications. In this work, we developed a new photo-sintering system using a high-power ultraviolet light emitting diode (UV-LED) module. A LED light source has many merits such as low power consumption and potential large-scale application. The silver nanoparticles ink was inkjet-printed on a polyethylene terephthalate (PET) and photo-sintered by the UV-LED module with the wavelength of 365 and 385 nm. The electrical resistivity as low as 5.44 × 10−6 Ω·cm (just about three times compared to value of bulk silver) was achieved at optimized photo-sintering conditions (wavelength of 365 nm and light intensity of 300 mW/cm2).

Low temperature sintering of Ag nanoparticles/graphene composites for paper based writing electronics

With the great demand in the applications of flexible electronics, the methods leading to improvements in the electrical and mechanical performance have been widely investigated. In this work, we firstly prepared a hybrid composite ink using Ag nanoparticles and graphene. Then, a hot-press sintering process was deployed to obtain the desired electrical tracks which could be applied in flexible electronics. We have systematically investigated the effects of sintering time, pressure and temperature, as well as the different percentage of weight (wt%) of graphene for the electrical and mechanical performance of sintered electrical tracks. We achieved reasonably low electrical resistivity at low sintering temperature (120 °C). Specifically, the resistivity reaches 6.19 × 10−8 Ω · m which is just 3.87 times higher than the value of bulk silver. Additionally, the prepared hybrid composite ink obtained better electrical reliability against bending test comparing with Ag nanoparticle ink. Finally, the optimal wt% of graphene and potential effect to the electrical and mechanical performance were also investigated.

IR-sintering efficiency on inkjet-printed conductive structures on paper substrates

The use of fibre-based materials as substrates in printed electronics has been increasing, mainly due to its attractive characteristics, such as low-cost or wide availability. Additionally, paper enables recycling and it shows attractive features, such as high thermal stability, when compared to traditional polymer-based substrates (Tobjörk and Österbacka, 2011 [1]). Nevertheless, one of the drawbacks of using paper substrates is that the surface usually is very rough, typically, showing roughness values above 10μm2. In most cases, printing structures that need to be highly uniform, without disruptions, require additional coating. Inkjet printing provides sharp detail reproduction and strict lines on printed structures. Sintering is required for drying the ink. Thermal sintering is the traditionally used method, but requires long periods of time and promotes the ageing of the paper due to a long exposure at high temperature. When printing conductive structures on paper alternative photonic sintering methods such as IR-sintering show some attractive characteristics. IR-sintering is compatible with roll-to-roll fabrication, providing low-cost, fast and localized sintering, which makes it suitable for fibre-based substrates (Tobjörk et al., 2012 [3]). This work has been carried out to study and compare the efficiency of thermal and IR sintering of conductive structures on different paper and polymer substrates. All substrates were printed using silver based ink, which was applied on the substrate surface by inkjet. Resistivity values of the printed structures were used to compare the performance on the substrates. IR-sintering showed the best results in terms of achieved conductivity of the printed lines when using short sintering time of no more than 10min. The conductivity values of the inkjet-printed silver lines on Lumi silk substrate reached about 40% of the bulk silver value after IR-sintering, whereas with thermal-sintering this value only reached about 20% of the bulk silver value. IR-sintering improves the sintering process, increasing the conductivity of the printed structures and at the same time reducing significantly the sintering time. In the case of Lumi silk substrate, high conductivity was observed after only two minutes of sintering time when IR-oven was used.Both techniques can be used in a roll-to-roll mass manufacturing process, enabling the fabrication in large scale of flexible electronic devices, on paper substrates, without the need for extra steps, such as coatings.

Poisson's ratio of individual metal nanowires.

The measurement of Poisson’s ratio of nanomaterials is extremely challenging. Here we report a lateral atomic force microscope experimental method to electromechanically measure the Poisson’s ratio and gauge factor of individual nanowires. Under elastic loading conditions we monitor the four-point resistance of individual metallic nanowires as a function of strain and different levels of electrical stress. We determine the gauge factor of individual wires and directly measure the Poisson’s ratio using a model that is independently validated for macroscopic wires. For macroscopic wires and nickel nanowires we find Poisson’s ratios that closely correspond to bulk values, whereas for silver nanowires significant deviations from the bulk silver value are observed. Moreover, repeated measurements on individual silver nanowires at different levels of mechanical and electrical stress yield a small spread in Poisson ratio, with a range of mean values for different wires, all of which are distinct from the bulk value.

Sintering of inkjet printed silver tracks with boiling salt water

This paper demonstrates a simple two-step method to sinter inkjet printed silver tracks with boiling salt water. As the temperature during the sintering process stays at 110 degrees Celsius, the method is compatible with most polymer substrates. UV light is used to enhance adhesion between the printed silver layer and the substrate film to prevent delamination of silver tracks during salt water treatment. After 20 min immersion in boiling salt water, the printed silver lines exhibit electrical resistivity only two times higher than the bulk silver value as measured using a four wire resistance meter.

Preparation of solid silver nanoparticles for inkjet printed flexible electronics with high conductivity

Silver nanoparticles (NPs) which could be kept in solid form and were easily stored without degeneration or oxidation at room temperature for a long period of time were synthesized by a simple and environmentally friendly wet chemistry method in an aqueous phase. Highly stable dispersions of aqueous silver NP inks, sintered at room temperature, for printing highly conductive tracks (∼8.0 μΩ cm) were prepared simply by dispersing the synthesized silver NP powder in water. These inks are stable, fairly homogeneous and suitable for a wide range of patterning techniques. The inks were successfully printed on paper and polyethylene terephthalate (PET) substrates using a common color printer. Upon annealing at 180 °C, the resistivity of the printed silver patterns decreased to 3.7 μΩ cm, which is close to twice that of bulk silver. Various factors affecting the resistivity of the printed silver patterns, such as annealing temperature and the number of printing cycles, were investigated. The resulting high conductivity of the printed silver patterns reached over 20% of the bulk silver value under ambient conditions, which enabled the fabrication of flexible electronic devices, as demonstrated by the inkjet printing of conductive circuits of LED devices.

A new molecular silver precursor for the preparation of thin conductive silver films

The synthesis and characterization of a new molecular silver precursor is reported. The presented complex [Ag(DioxoNic)2]NO3 (DioxoNic=(2,2-Dimethyl-1,3-dioxolan-4-yl)methyl nicotinate) can be obtained by the reaction of silver(I) nitrate and (2,2-Dimethyl-1,3-dioxolan-4-yl)methyl nicotinate in ethanol. The product crystallizes in the monoclinic space group P21/c (No. 14). Concentrated ethanolic solutions allow the fabrication of thin films via dip coating. Using UV-irradiation and subsequent moderate temperature treatment compact films of elemental silver can be obtained. The resulting silver films show excellent electrical properties with sheet resistances down to 0.7Ω/sq at a film thickness of 25nm corresponding to a specific electrical resistance of 1.75×10−8Ωm very close to the value of bulk silver. For the potential application in optoelectronic devices, the complex was tested as an ink in a soft printing process for the preparation of patterned silver films.

A new approach causing the patterns fabricated by silver nanoparticles to be conductive without sintering

Silver nanoparticles (Ag NPs) with a mean size of about 90 nm were synthesized by polyol reduction of silver nitrate with ethylene glycol (EG) in the presence of poly(vinyl pyrrolidone) (PVP). The Ag NPs undergo a spontaneous coalescence in the presence of chloride ions even without a traditional sintering process which occurs at a relatively high temperature. Such behavior can cause a rapid decrease in the resistivity of the patterns fabricated by Ag NPs. Conductive silver lines were successfully fabricated on FR-4 substrate using this method. The resulting conductivity of the silver lines reached about 16% of the bulk silver value, which enables fabrication of conductive patterns on some electronic devices.

Synthesis of colourless silver precursor ink for printing conductive patterns on silicon nitride substrates

Silver precursor ink was synthesised by a simple and environmentally friendly method based on chemical reduction. The stability, particle size, viscosity and surface tension of the ink were adjusted by adding polyvinylpyrrolidone (PVP) and ethylene glycol (EG). The silver patterns were fabricated on the silicon nitride substrate and were characterised by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrical measurements. The thickness of the sample printed three times was approximately 0.66μm, and it increased to 2.43μm after 12 printings. The ink-jet-printed silver patterns exhibited good conductivity when the samples were sintered at temperatures above 200°C. The resistivity value was observed to decrease to 3.1μΩcm after sintering at 500°C for 60min, twice the value of bulk silver (1.6μΩcm). The low resistivity of silver patterns suggests applications for ink-jet printing of electronics devices.

Low Temperature Plasma Sintering of Silver Nanoparticles for Potential Flexible Electronics Applications

ABSTRACTDeposition of solution-processed functional materials generally requires additional post-processing to optimize the functionality of the material. We study sintering of Ag nanoparticle (NP) (with average diameter 77nm) deposits for improved electrical conductivity, with emphasis on Argon plasma methods compatible with the low temperature requirements of regular low-cost flexible polymer substrates. The relationship between plasma parameters (such as power and treatment time) versus sintering results (sintered structure depth, film continuity and electrical sheet resistance) will be reported. According to our efforts so far, we have achieved the electrical resistivity of the sintered film at about 20 times greater than the value of bulk silver using a process compatible with the low temperature requirements of common flexible polymer substrates.

Current Collecting Grids for R2R Processed Organic Solar Cells

ABSTRACTExposure to highly focussed flash light (photonic flash sintering) has been developed as a technology to successfully cure printed metal inks on temperature sensitive plastic substrates. In contrast to the traditional approach of thermal oven sintering, conductivities up to 30 % of the value of bulk silver can be achieved within a few seconds without foil deformation. The compatibility of this technology with R2R production has been demonstrated with line speeds up to 5 m/min. As a consequence, our approach is expected to enable the high throughput fabrication of current collecting grids for organic solar cells in order to replace transparent electrodes based on metal oxides such as ITO. Additionally, our new sintering technology has enabled us to process a new generation of conductive inks, based on copper complexes, which cannot be processed by oven sintering.

Low‐temperature sintered conductive silver patterns obtained by inkjet printing for plastic electronics

AbstractSilver metal patterns onto plastic substrates have been obtained by inkjet printing with commercial ink based on silver nanoscale particles. Morphological characterization by scanning electron microscopy of spin‐coating processed films indicates that a sintering treatment at 250 °C for 30 min is enough to sinterize the silver metal nanoparticles. X‐ray photoelectron spectroscopy characterization of sintered metal films shows that the sinterization is accompanied by a reduction of carbon surface concentration coming from carbon‐containing chemical compounds present in the ink formulation. After sintering at 250 °C for 30 min, the material shows typical electrical resistivity of 4.6 × 10−6 Ωcm (i.e. about three times the value of bulk silver).Printed test structures show typical resistivity after sintering at 250 °C for 30 min in the range of 5–7 × 10−6 Ωcm. Copyright © 2010 John Wiley & Sons, Ltd.

Inkjet Printing and Argon Plasma Sintering of an Electrode Pattern on Polymer Substrates Using Silver Nanoparticle Ink

Inkjet printing and plasma sintering of a silver electrode pattern on polymer substrates for applications in microfluidic systems is presented. The pattern consists of several finger electrodes and contact pads that exhibit lateral dimensions of 30 × 80 mm2. The pitch between neighboring finger electrodes is 270 μm and the smallest linewidth of the finger electrodes realized is 90 μm. Commercially available silver nanoparticle dispersion is used as ink. The electrode layout is printed onto a cyclic olefin polymer (COP) substrate. Prior to printing the substrate is activated using argon plasma in order to ensure good wetting. The as-printed features are then sintered using argon plasma. This sintering technique enables sintering of the nanoparticles in a selective manner without heating the substrate above its glass transition temperature. Sintering times are in the range of 5 to 15 minutes and the resulting resistivity of the printed features is approximately 57 times the bulk silver value.

One-step inkjet printing of conductive silver tracks on polymer substrates

A one-step process to fabricate conductive features on flexible polymer substrates by inkjetprinting an organometallic silver ink directly onto a substrate that is heated to130 °C is presented. This process led to the immediate sintering of the printed features. Thesamples were left for 5 min at elevated temperature, which resulted in conductive silverfeatures with a resistivity of eight times the bulk silver value. The combination ofthis ink and the simultaneous printing/sintering process opens up routes for thedirect fabrication of conductive features on common polymer substrates thatcould be applied, for example, in roll-to-roll production of flexible microelectronicsystems.

Effect of the dipole interaction between island particles on the optical properties of an aggregated silver film

If an aggregated metal film is assumed to consist of ellipsoidal particles of the same shape, the complex dielectric constant ε of the film is represented by the equation ε−ε = q ε i−ε a 1+ ƒ(ε i−ε a) ε a ƒ=ƒ 0+β where ε a and ε i are the dielectric constants of the medium and the island material, respectively, q is the packing factor, ƒ 0 the depolarizing factor of the particles and β the term that arises from the dipole interaction. Assuming that the island particles are distributed in a square array of lattice parameter α with mean thickness d w, β is estimated approximately to be −0.36 d w α for an electric field parallel to the substrate. If ε 1 ( = ε 1 − i ε 2) is known as a function of wavelength, ƒ can be determined from the transmittance spectrum, because Im(ε), the absorption, shows a sharp maximum when ƒ = (−ε 1 + ε a)ε a [(ε 1 − ε a) 2 + ε 2 2] . However, it is usually impossible to determine ƒ 0 and β separately. In our work separation was attempted by changing α by isotropic expansion of the substrate. When the rate of square expansion is denoted by r, ƒ is expressed by ƒ 0 − ( 0.36d w α )r − 3 2 . Using the value of bulk silver as ε i, ƒ was calculated for two values of ε a. Since the ƒ versus r − 3 2 relation was approximated well by a straight line, ƒ 0 and α could be determined from the intercept on the ordinate and the slope of the straight line, respectively.