Cedric Dockendorf

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

Individual carbon nanotube soldering with gold nanoink deposition

A method for soldering carbon nanotubes lying on microfabricated metal pads is presented. By employing the fountain-pen principle, the authors deposited a gold nanoparticle suspension (nanoink) film on the area where the carbon nanotube contacts the metal pad. The nanoink was deposited by using a capillary tube that was pulled into a micropipette with the tip outer diameter of 2μm. Individual carbon nanotubes were aligned selectively across the electrodes dielectrophoretically. After annealing and sintering of the nanoink pattern the four-point-probe resistance of the carbon nanotubes was measured, resulting in a good Ohmic or near-Ohmic contact (2–15kΩ).

Size reduction of nanoparticle ink patterns by fluid-assisted dewetting

A novel method is proposed to considerably reduce the size of partially wetting patterns of nanopaticle solutions (nanoinks) on a substrate. A nanoink prepared by suspending gold nanoparticles in toluene was deposited on a glass substrate by writing a thin line with the width of 70μm. A water droplet of about 100μl covering the pattern was employed to shrink the pattern by transport of the toluene from the nanoink to the water region triggered by controlled heat addition from the substrate, which increased the solubility of toluene into water (these two liquids are practically immiscible at room temperature). During the dewetting phase, the three-phase-contact line is pulled by the uncompensated Young’s force. The dewetting dynamics is explained by the action of thermocapillarity enhanced by the convection microflow generated in the water layer.

3-D InGaAs/GaAs Helical Nanobelts for Optoelectronic Devices

This article systematically characterizes conductometric InGaAs/GaAs helical nanobelts for use with optoelectronic sensing. The responsiveness, energy conversion efficiency, and external quantum efficiency are improved compared to conventional sensors by reducing the length of 3-D helical nanobelts without losing exposure area. Nanorobotic assembly and characterization of 3-D helical in/out-of-plane nanobelt photodetectors allowed for stable intrinsic property characterizations. When compared to nanotube bundles, impovement in properties such as energy conversion efficiency, responsiveness, and external quantum efficiency are experimentally demonstrated in both an optical microscope and scanning electron microscope. A probe-type photodetector was assembled using nanorobotic manipulation and in-situ gold nanoparticle ink soldering. The highly efficient and sensitive 3-D InGaAs/GaAs helical nanobelt photodetectors enable many optoelectronic device applications such as being the probes for the near field optical microscopy, confocal microscopy, fluorescence microscopy, or spatial detection with further characterizations.

Maskless writing of a flexible nanoscale transistor with Au-contacted carbon nanotube electrodes

A flexible polymer field effect transistor with a nanoscale carbon nanotube channel is conceptualized and realized herein. Carbon nanotubes (CNTs) were dispersed on a polyimide substrate and marked in an scanning electron microscope with focused ion beam such that they could be contacted with gold nanoink. The CNTs were divided into two parts forming the source and drain of the transistor. A micropipette writing method was used to contact the carbon nanotube electrodes with gold nanoink and to deposit the poly(3-hexylthiophene) as an active layer. The mobility of the transistors is of the order of 10−5cm∕Vs. After fabrication, the flexible transistors can be peeled off the substrate.

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.

Multilayer Direct-Writing of Electrical Conductors With Gold Nanoinks Using the Fountain-Pen Principle

Previous publications showed the potential of gold nanoparticle inks in microelectronic manufacturing. The main advantage of using nanoparticles for the production of microelectronic conductors is their low melting point. Indeed the melting point of gold nanoparticles decreases dramatically with decreasing size. This interesting property presents us with an uncomplicated way in which to produce electronic conductors on plastics, thus manufacture flexible electronics. Microelectronic applications which make use of materials other than silicon make their appearance ever more often. In this paper we present a method of manufacturing multilayered electronic circuits using a scanning-probe-inspired technology to deposit and anneal a gold nanoink on various substrates. We then tested the quality of this technology by applying it to a real complete electronic circuit.Copyright

In-situ nanorobotic soldering of three-dimensional helical nanobelts using gold nanoink

In this paper, we report an in-situ nanosoldering technique to make electrically conductive interconnections between three-dimensional (3D) helical micro-/nanostructures and electrodes for the nanorobotic assembly of nanoelectromechanical systems (NEMS) using gold nanoparticle ink. 3D helical nanobelts are placed onto pre-fabricated gold electrodes using nanorobotic manipulation inside a scanning electron microscope (SEM), and then deposited with gold nanoparticle ink using fountain-pen method to improve the electrical conductivity. Electrical and mechanical characterization shows the stable reduction of contact resistance and strength of the assembled structures, which is important to build 3D NEMS devices based on nanorobotic assembly.

InGaAs/GaAs helical nanobelts as building blocks for nanoscale optoelectronic devices

In this paper, we present the length reduction of optoelectronic sensors using conductometric InGaAs/GaAs helical nanobelts. The helical nanobelt contributes to improve the unit length responsivity of photodetector while maintaining high external quantum efficiency (EQE) per unit length. A nanorobotic assembly and characterization of 3-D helical nanobelts to create in-/out-of-plane optoelectronic sensors has been shown. High optoelectronic sensitivity was revealed from experimental investigation under an optical microscope and from light emitting diodes (LEDs) inside a scanning electron microscope (SEM). A probe type photodetector was assembled using nanorobotic manipulation and in-situ gold nanoparticle ink soldering.

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