Nicole R. Bieri

Conductor microstructures by laser curing of printed gold nanoparticle ink

The laser-based curing of printed nanoparticle ink to create microlines (resistors) of electrical resistivity approaching that of bulk gold was investigated. The present work relies on laser absorption in both the nanoparticle ink and the sintered gold layer, as well as the transport of thermal energy in the substrate and the resulting solvent vaporization and nanoparticle deposition and sintering. The morphology and electrical properties of the gold line can be controlled by modulating the spatial distribution of the laser beam intensity. Based on the understanding of the underlying physics, a process that circumvents a serious drawback on the functionality of cured gold microlines is produced. Microconductors with resistivity approaching that of bulk gold are produced, while loss of gold nanoparticles and cross sectional nonuniformities are avoided.

Microstructuring by printing and laser curing of nanoparticle solutions

In this letter, the process of printing and laser curing of nanoparticle solutions is presented. A liquid solvent is employed as the carrier of gold nanoparticles (the material of interest in this study) possessing a low melting temperature compared to that of bulk gold. Using a specifically designed printing system, the gold nanoparticle solution is deposited on a substrate and cured with laser radiation. In this manner, the potential of writing gold structures on temperature sensitive substrates is demonstrated. The interaction between the laser radiation and nanoparticles drives the solvent evaporation and controls the quality of the microstructures printing process. The latter is also affected by thermocapillary flow at the free surface, developing during the curing process. An optical method for estimating the curing times is also developed and discussed.

Damage-Free Low Temperature Pulsed Laser Printing of Gold Nanoinks On Polymers

In this study, pulsed laser based curing of a printed nanoink (nanoparticle ink) combined with moderate and controlled substrate heating was investigated to create microconductors at low enough temperatures appropriate for polymeric substrates. The present work relies on (1) the melting temperature depression of nanoparticles smaller than a critical size, (2) DOD (drop on demand) jettability of nanoparticle ink, and (3) control of the heat affected zone induced by pulsed laser heating. In the experiments, gold nanoparticles of 3–7 nmdiameter dissolved in toluene solvent were used as ink. This nanoink was printed on a polymeric substrate that was heated to evaporate the solvent during or after printing. The overall morphology of the gold microline was determined by the printing process and controlled by changing the substrate temperature during jetting. In addition, the printed line width of about 140 m at the room temperature decreased to 70– 80 m when the substrate is heated at 90° C. By employing a microsecond pulsed laser, the nanoparticles were melted and coalesced at low temperature to form a conductive microline which had just 3–4 times higher resistivity than the bulk value without damaging the temperature sensitive polymeric substrate. This gold film also survived after Scotch tape test. These are remarkable results, considering the fact that the melting temperature of bulk gold is 1064° C and the polymeric substrate can be thermally damaged at temperatures as low as 500° C. DOI: 10.1115/1.1924627

Laser based hybrid inkjet printing of nanoink for flexible electronics

Many applications require delivery of small quantities of functional materials into locations on a substrate in the form of liquid solution. Consequently, interest in nongraphical inkjet printing is growing. In addition, higher resolution for printing flexible electronics is becoming more critical to enhance the performance of printing electronics. Since the resolution of inkjet process is limited by the nozzle size and the statistical variation of droplet flight and spreading phenomena, hybrid inkjet printing has emerged as an attractive processing method. In this work, surface monolayer protected gold nanoparticle was printed in a liquid solution form and cured by laser irradiation to fabricate electrically conductive microlines on glass or polymer substrate at a reduced temperature. Continuous laser curing enabled local heating and the morphology could be controlled as well. Thermal penetration into the substrate could be minimized by using pulsed laser beam. Nanoparticle film was effectively removed by applying femtosecond laser, so that small feature size was obtained. Printing on a heated substrate has advantages over room temperature printing. The solvent evaporates soon after contact, so that a thick layer can be deposited with high jetting frequency. The rapid liquid evaporation also eliminated uneven wetting problems and the smaller feature size was obtained.

Manufacturing of Electrically Conductive Microstructures by Dropwise Printing and Laser Curing of Nanoparticle-Suspensions

A novel method for the manufacturing of electric microconductors for semiconductor and other devices is presented. The method brings together three technologies: controlled (on demand) printing, laser curing, and the employment of nanoparticles of matter, possessing markedly different properties (here, melting point) than their bulk counterparts. A suspension of gold particles in toluene solvent is employed to print electrically conducting line patterns utilizing a modified on demand ink jet printing process. To this end, microdroplets of 80–100 μm diameters are deposited on a moving substrate such that the droplets form continuous lines. Focused laser irradiation is utilized in order to evaporate the solvent, melt the metal nanoparticles in the suspension, and sinter the suspended particles to form continuous, electrically conducting gold microlines on a substrate. The ultra fine particles in the suspension have a diameter size range of 2 – 5 nm. Due to curvature effects of such small particles, the melting point is markedly lower (400°C) than that of bulk gold (1063°C). Thermodynamic aspects of the effect of particle size on the melting and evaporation temperatures of gold and toluene, respectively, are discussed in the paper. The structure and line width of the cured line as a function of the laser irradiation power and stage velocity are reported in detail. Preliminary measurements of the electrical conductivity are represented.Copyright

Laser curing of gold nanoparticle inks

The concept of effective laser curing of nanoparticle suspensions (NPS) with a laser beam is presented in this paper. A toluene solvent is employed as the carrier of gold nanoparticles possessing a lower melting temperature than that of bulk gold. Using a modified drop-on-demand jetting system, the gold nanoparticle suspended solution is printed on a glass substrate and cured with laser irradiation. The laser energy coupling to the nanoparticles in conjunction with thermocapillary effects and the evaporation of the solvent are critical to the quality of the electrically conductive gold microlines. By employing a intensity-modulated double laser beam processing scheme, to optimize the curing process, it is demonstrated for the first time, that the gold nanoparticles could be sintered on a glass substrate to form a gold line of resistivity close to that of bulk gold. This is a noticeable result, compared to recently published microconductor manufacturing with nanoparticle suspensions with oven [1] or low power single laser beam [2] curing reporting resistivities four to five times higher than that of bulk gold. As a consequence, in addition to their scientific value, the current results demonstrate the potential of laser printing for use in the microelectronics manufacturing for the first time. It was also shown that the morphology of the gold line could be modified by appropriate design of the shape of the processing laser beam.Copyright

Microconductors on polymer by nanoink printing and pulsed laser curing

In this study, pulsed laser based curing of a printed nanoink (nanoparticle ink) combined with moderate and controlled substrate heating was investigated to create microconductors at low enough temperatures appropriate for polymeric substrates. The present work relies on (1) melting temperature depression of nanoparticles smaller than a critical size, (2) DOD (drop on demand) jettability of nanoparticle ink and (3) small heat affected zone of pulsed laser heating. In the experiment, gold nanoparticles of 3–7nm diameter dissolved in toluene solvent was used as ink. This nanoink was printed on a polymeric substrate which was heated to evaporate the solvent during or after printing. The overall morphology of the gold microline was determined during the printing process and was controlled by changing the substrate temperature during jetting. By employing a micro-second pulsed laser, the nanoparticles were melted and coalesced at a low temperature to form a conductive microline which has 4–5 times higher resistivity than the bulk value without damaging the temperature sensitive polymeric substrate.Copyright

On Two Phase Flow Regimes in a Microscale Direct Methanol Fuel Cell

The area of microfluidics has experienced a tremendous increase in research activities in recent years with a wide range of applications, such as micro heat exchangers and energy conversion devices, microreactors, lab-on-chip devices, micro total chemical analysis systems (μTAS) etc. The occurrence of two phase flow can lead to several mechanisms enhancing or extending the performance of single phase microfluidic devices [1]. On the other hand, in a micro fuel cell the second, non-immiscible phase is considered to hamper the performance of the fuel cell [2]. Regardless of its effect, two phase flows in microfluidics deserve special research attention.© 2008 ASME