Name: a fabrication method for highly stretchable conductors with silver nanowires
Uploaded: 2016-01-21T15:00:00
Description: Watch this Scientific Journal Video about A Fabrication Method for Highly Stretchable Conductors with Silver Nanowires at JoVE.com

The authors are grateful for the financial support from Ministry of Science and Technology.

1. Preparation of Silver Precursor Ink
<ol>
	<li>Add 1.85 g of diethanolamine (DEA) in 3.15 ml deionized water.</li>
	<li>Dissolve 0.15 g of silver nitrate in 5 ml deionized water.</li>
	<li>Mix the aqueous silver nitrate solution with DEA at a 1:1 volume ratio to have 10 ml silver precursor ink right before use.</li>
</ol>
2. Fabrication of Stretchable Conductive Thin Films
<ol>
	<li>Preparation of AgNW ink
	<ol>
		<li>Dilute 2 ml of 0.5 wt% AgNWs in isopropanol with 18 ml de...

<ol>
	<li>Rogers, J. A., Someya, T., Huang, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Materials+and+mechanics+for+stretchable+electronics.">Materials and mechanics for stretchable electronics.</a> Science. 327 (5973), 1603-1607 (2010).</li><li>Mazzeo, A. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Paper-based,+capacitive+touch+pads.">Paper-based, capacitive touch pads.</a> Adv. Mater. 24 (21), 2850-2856 (2012).</li><li>Yang, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silver+nanowires:+from+scalable+synthesis+to+recyclable+foldable+electronics.">Silver nanowires: from scalable synthesis to recyclable foldable electronics.</a> Adv. Mater. 23 (27), 3052-3056 (2011).</li><li>Sekitani, T., Someya, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stretchable,+Large-area+Organic+Electronics.">Stretchable, Large-area Organic Electronics.</a> Adv. Mater. 22 (20), 2228-2246 (2010).</li><li>Lipomi, D. J., Tee, B. C., Vosgueritchian, M., Bao, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stretchable+organic+solar+cells.">Stretchable organic solar cells.</a> Adv. Mater. 23 (15), 1771-1775 (2011).</li><li>Liang, J., Li, L., Niu, X., Yu, Z., Pei, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Elastomeric+polymer+light-emitting+devices+and+displays.">Elastomeric polymer light-emitting devices and displays.</a> Nat. Photonics. 7 (10), 817-824 (2013).</li><li>White, M. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrathin,+highly+flexible+and+stretchable+PLEDs.">Ultrathin, highly flexible and stretchable PLEDs.</a> Nat. Photonics. 7 (10), 811-816 (2013).</li><li>Chang, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Performance+enhancement+in+bendable+fuel+cell+using+highly+conductive+Ag+nanowires.">Performance enhancement in bendable fuel cell using highly conductive Ag nanowires.</a> Int. J. Hydrogen Energ. 39 (14), 7422-7427 (2014).</li><li>Yan, C. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+Intrinsically+Stretchable+Nanowire+Photodetector+with+a+Fully+Embedded+Structure.">An Intrinsically Stretchable Nanowire Photodetector with a Fully Embedded Structure.</a> Adv. Mater. 26 (6), 943-950 (2014).</li><li>Lee, M. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-performance,+transparent,+and+stretchable+electrodes+using+graphene-metal+nanowire+hybrid+structures.">High-performance, transparent, and stretchable electrodes using graphene-metal nanowire hybrid structures.</a> Nano Lett. 13 (6), 2814-2821 (2013).</li><li>Xu, F., Zhu, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+conductive+and+stretchable+silver+nanowire+conductors.">Highly conductive and stretchable silver nanowire conductors.</a> Adv. Mater. 24 (37), 5117-5122 (2012).</li><li>Yun, S., Niu, X., Yu, Z., Hu, W., Brochu, P., Pei, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Compliant+silver+nanowire-polymer+composite+electrodes+for+bistable+large+strain+actuation.">Compliant silver nanowire-polymer composite electrodes for bistable large strain actuation.</a> Adv. Mater. 24 (10), 1321-1327 (2012).</li><li>Lee, P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+stretchable+and+highly+conductive+metal+electrode+by+very+long+metal+nanowire+percolation+network.">Highly stretchable and highly conductive metal electrode by very long metal nanowire percolation network.</a> Adv. Mater. 24 (25), 3326-3332 (2012).</li><li>Akter, T., Kim, W. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reversibly+Stretchable+Transparent+Conductive+Coatings+of+Spray-Deposited+Silver+Nanowires.">Reversibly Stretchable Transparent Conductive Coatings of Spray-Deposited Silver Nanowires.</a> ACS Appl. Mater. Interfaces. 4 (4), 1855-1859 (2012).</li><li>Madaria, A., Kumar, A., Ishikawa, F., Zhou, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Uniform,+highly+conductive,+and+patterned+transparent+films+of+a+percolating+silver+nanowire+network+on+rigid+and+flexible+substrates+using+a+dry+transfer+technique.">Uniform, highly conductive, and patterned transparent films of a percolating silver nanowire network on rigid and flexible substrates using a dry transfer technique.</a> Nano Res. 3 (8), 564-573 (2010).</li><li>Lee, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Room-Temperature+Nanosoldering+of+a+Very+Long+Metal+Nanowire+Network+by+Conducting-Polymer-Assisted+Joining+for+a+Flexible+Touch-Panel+Application.">Room-Temperature Nanosoldering of a Very Long Metal Nanowire Network by Conducting-Polymer-Assisted Joining for a Flexible Touch-Panel Application.</a> Adv. Funct. Mater. 23 (34), 4171-4176 (2013).</li><li>Tokuno, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+silver+nanowire+transparent+electrodes+at+room+temperature.">Fabrication of silver nanowire transparent electrodes at room temperature.</a> Nano Res. 4 (12), 1215-1222 (2011).</li><li>Garnett, E. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-limited+plasmonic+welding+of+silver+nanowire+junctions.">Self-limited plasmonic welding of silver nanowire junctions.</a> Nat. Mater. 11 (3), 241-249 (2012).</li><li>Zhu, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transferable+self-welding+silver+nanowire+network+as+high+performance+transparent+flexible+electrode.">Transferable self-welding silver nanowire network as high performance transparent flexible electrode.</a> Nanotechnology. 24 (10), 1321-1327 (2013).</li><li>Han, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fast+Plasmonic+Laser+Nanowelding+for+a+Cu-Nanowire+Percolation+Network+for+Flexible+Transparent+Conductors+and+Stretchable+Electronics.">Fast Plasmonic Laser Nanowelding for a Cu-Nanowire Percolation Network for Flexible Transparent Conductors and Stretchable Electronics.</a> Adv. Mater. 26 (33), 5808-5814 (2014).</li><li>Chen, S. P., Liao, Y. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Highly+stretchable+and+conductive+silver+nanowire+thin+films+formed+by+soldering+nanomesh+junctions.">Highly stretchable and conductive silver nanowire thin films formed by soldering nanomesh junctions.</a> Phys. Chem. Chem. Phys. 16 (37), 19856-19860 (2014).</li><li>Chen, S. P., Kao, Z. K., Lin, J. L., Liao, Y. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Silver+conductive+features+on+flexible+substrates+from+a+thermally+accelerated+chain+reaction+at+low+sintering+temperatures.">Silver conductive features on flexible substrates from a thermally accelerated chain reaction at low sintering temperatures.</a> ACS Appl. Mater. Interfaces. 4 (12), 7064-7068 (2012).</li></ol>

The chemical soldering process can help reinforce the contact between silver nanowires. As shown in Figure 4b, the wire/wire junctions are covered with silver after applying the reactive silver ink over the spray coated AgNW thin film. The silver recovery relies strongly on the formaldehyde generated from DEA degradation, and thus the soldering process or silver reduction can be accelerated with increasing temperature.22 Because the metal surfaces of AgNWs provide effective electron exchange s...

Deformable electronic devices with large stretchability have been identified as critical parts to the realization of wearable and portable electronics in the next generation.1 Those stretchable electronic devices not only show great flexibility as those electronic devices on plastic sheets,2, 3 but also exhibit excellent performance under severe stretching or twisting conditions.4 To realize the stretchable electronics, materials with great electric performance under large deformation is needed. Recent advancements in material sciences have shown the possibility to synthesize such functional materials and have used them to design stretchable optoelectronic devices 5-9 with great tolerance to complex shape deformations. Among all the electronic functional materials, stretchable conductors are necessary to supply electrical power to those optoelectronic devices and thus are of critical importance for device performance. Because regular conducting materials, like metal or indium tin oxide, lack of mechanical robustness under large deformation, interconnects made of these materials are unable to exhibit good electrical conductivity under stretching process. Thus, elastic substrates covered with a thin layer of flexible conductive materials, such as carbon nanotube,1 graphene,10 or AgNWs,11-14 are designed for conductors with excellent stretchability. Because of the high bulk conductivity, AgNW thin films have been shown to be the most promising material for composite stretchable conductors.13 The percolating networks of AgNW thin films can effectively accommodate large elastic deformations in stretching process with great electrical conductance, and are considered as a promising stretchable electrode candidate. To implement AgNW thin films as stretchable conductors, it is necessary to have effective electrical contacts between AgNWs. After liquid deposition and drying on substrate surfaces, AgNWs regularly stack together to form a percolating mesh with loose contact points, which yield in large electrical resistances. Thus, one needs to anneal the contacts between nanowires by high-temperature or high-pressure annealing methods15-20 to reduce the contact resistances.
In contrast to these annealing processes in the literature, here, we will demonstrate a simple chemical method to anneal AgNW network connections under regular laboratory conditions.21 The fabrication process is shown in Figure 4A. A reactive ink is used to sinter the spray coated AgNW thin films on a glass plate. After reaction, the contacts between nanowires are covered with silver and hence the AgNW network is soldered chemically together. A cast-and-peel method is then used to transfer the soldered AgNW network to a stretchable PU substrate to form a composite conductor, which can exhibit no obvious change in electrical conductivity even at large tensile strain of 120%.

<table border="0" cellpadding="0" cellspacing="0" width="833">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:173px;">Silver nanowire</td>
			<td style="width:195px;">Sigma-Aldrich</td>
			<td style="width:117px;">778095-25ML</td>
			<td style="width:349px;">AgNW, 120 nm in diameter and 20-50 mm in length, 0.5 wt% in IPA</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Silver nitrate crystal</td>
			<td>Macron Fine Chemicals</td>
			<td>MK216903</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Diethanolamine</td>
			<td>Sigma-Aldrich</td>
			<td>D8885-500G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Polyurethane emulsion</td>
			<td>First Chemical</td>
			<td>20130326036</td>
			<td>35 wt% water-based anionic polyester-polyurethane emulsion</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Airbrush</td>
			<td>Taiwan Airbrush &#38; Equipment</td>
			<td>AFC-sensor&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Desktop robot</td>
			<td>Dispenser Tech</td>
			<td>DT-200&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Digital dispenser controller</td>
			<td>Dispenser Tech</td>
			<td>9000E&#160;</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:173px;">Auto-spraying program</td>
			<td style="width:195px;">Dispenser Tech</td>
			<td style="width:117px;">Smart robot edit version 3.0.0.5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Air compressor&#160;</td>
			<td>PUMA Industrial</td>
			<td>NCS-10&#160;</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Linear motorized stage</td>
			<td>TANLIAN E-O</td>
			<td>Customized</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:173px;">Stage control software</td>
			<td style="width:195px;">TANLIAN E-O</td>
			<td style="width:117px;">Customized</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Digital multimeter</td>
			<td>HILA INTERNATIONAL</td>
			<td>DM-2690TU</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:173px;">Digital multimeter software</td>
			<td style="width:195px;">HILA INTERNATIONAL</td>
			<td style="width:117px;">NA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Power supply</td>
			<td>CHERN TAIH</td>
			<td>CT-605</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">LED</td>
			<td>PChome</td>
			<td>M08330766</td>
			<td>http://www.pcstore.com.tw/sun-flower/M08330766.htm</td>
		</tr>
	</tbody>
</table>

a fabrication method for highly stretchable conductors with silver nanowires

Stretchable electronics are identified as a key technology for electronic applications in the next generation. One of the challenges in fabrication of stretchable electronic devices is the preparation of stretchable conductors with great mechanical stability. In this study, we developed a simple fabrication method to chemically solder the contact points between silver nanowire (AgNW) networks. AgNW nanomesh was first deposited on a glass slide via spray coating method. A reactive ink composed of silver nanoparticle (AgNPs) precursors was applied over the spray coated AgNW thin films. After heating for 40 min, AgNPs were preferentially generated over the nanowire junctions to solder the AgNW nanomesh, and reinforced the conducting network. The chemically modified AgNW thin film was then transferred to polyurethane (PU) substrates by casting method. The soldered AgNW thin films on PU exhibited no obvious change in electrical conductivity under stretching or rolling process with elongation strains up to 120%.

The morphology of the AgNW thin film after chemical soldering process is shown in Figure 4B. Recovered AgNPs preferentially grow on the surface of AgNWs and wrap over the wire/wire junctions. Figure 5 shows the variation in sheet resistance with applied elongation strains for the unsoldered and the soldered thin films containing different amount of AgNWs. After the chemical soldering process, AgNW thin film conductors can maintain high conductivity under ...

Watch this Scientific Journal Video about A Fabrication Method for Highly Stretchable Conductors with Silver Nanowires at JoVE.com

A Fabrication Method for Highly Stretchable Conductors with Silver Nanowires

A simple synthesis method is used to chemically solder silver nanowire thin film to fabricate highly stretchable and conductive metal conductors.

Stretchable electronics are identified as a key technology for electronic applications in the next generation. One of the challenges in fabrication of ...

The overall goal of this procedure is to provide a simple method to fabricate highly stretchable conductors for applications in stretchable electronics. This method can help answer key questions in developing stretchable electronics such as the mechanical of connecting conductors. The main advantage of this technique is that it's a simple fabrication method.And the amount of silver there was in the fabrication of the conductors can be greatly reduced. To begin, prepare 10 milliliters of fresh aqueous silver nitrate solution, with DEA at a one to one volume ratio. Next, fabricate the stretchable conductive thin films.First, make the silver nanowire ink by diluting two milliliters of 0.5%silver nanowire in isopropanol, into 18 milliliters of water. Sonicate this mixture for 30 seconds. Next, use a pipette to transfer 16 milliliters of this mixture to an airbrush.Mount the loaded airbrush to a computer-controlled robot. Then, on the heated airbrushing stage, arrange eight glass rectangles to cover a four by five centimeter area. Use heat-resistant tape to fix the slides in place.Then, set the stage to 100 degrees Celsius, and set the airbrush to three bars. Now, in the software control of the robot, select the brush motion command sequence under the command column. Then, input the necessary parameters to complete the auto spraying program, and run the program.Consult the text protocol for more details. After spraycoating the glass, bake the silver nanowire thin films on a hot plate at 120 degrees Celsius for 10 minutes. Once baked, cast 400 microliters of the prepared silver precursor ink over the thin film.Then bake the films on a hot plate set to 100 degrees Celsius for 40 minutes. Later, carefully rinse the coatings under deionized water to remove the unreacted chemical residues. Then, air-dry the coated films.The next step is to cast 200 microliters of water-based PU emulsion over the silver nano-composite thin films. Then, let the films air-dry for 10 hours so they are fully solidified. Once fully solidified, peel the samples off the glass using forceps, and proceed with testing them.First, execute a stretch test. Begin by warming up a linear motorized stage. Now, in the software control of the stage, set the number of the moving steps for the motor to 8000.Then, click X+in the stage control software to move the mobile stage until it touches the fixed stage. When contact is made, click Set 0"in the stage control software. Then, click X-to move the mobile stage backward.Move the stage until there is a one centimeter gap between the two stages. Now, secure the sample across the gap with wired holders. This creates a testable one by one centimeter area.Next, connect the alligator clips to the digital multimeter, and record the resistance across the test area. Then, set the number of the moving steps of the motor to 800 and click X-to move the mobile stage one millimeter further away from the fixed stage to create a 10%strain on the sample. After producing a 10%strain, record the resistance.Repeat this step until the resistance increases significantly, which may require a strain of 150%Then, proceed with the next sample or the next test. Next, conduct a stability test. Setup is like the stretch test, however, for this test, connect the multimeter to a computer so the computer can record the data.In the stage control software, key in the number of cycles, and click on run 1 2 3"in the program panel to execute the stability test. This moves the mobile stage in a reciprocating motion to stretch the sample, with elongation cycles in triangular wave form. The final test is the LED lighting test.Set up the test material as before, and connect the wired holders in series with an LED and a power supply. Now, increase the power supply from zero to nine volts. This should light up the LED.Then, in the software, create strain as done for the strain test, until the LED becomes dim. Once a sample passes all these tests, it can be considered an effective conductor in the applications of stretchable electronics. The morphology of the silver nanowire thin film after the chemical soldering process shows that the recovered silver nanoparticles preferentially grow on the surface of silver nanowire and wrap over the wire-wire junctions.Elongation strain was placed on unsoldered and soldered thin films, containing different amounts of silver nanowire. Both showed sheet resistance below 100 ohms, when strains below 120%were applied. The composite stretchable conducting thin films showed great mechanical stability in this dynamic deformation process.When subjecting the thin film to elongation cycles in a triangular waveform at a fast strain rate, no obvious resistance changes were observed at strain amplitudes of 50%When the strain amplitude was 100%the peak resistance increased with the pulsation cycles. After the pulsation stopped, the resistance of the film returned to the original value. This method can produce highly stretchable conductors to serve us in effective interconnect for next generation stretchable electronics.

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A Method to Fabricate Disconnected Silver Nanostructures in 3D

The standard nanofabrication toolkit includes techniques primarily aimed at creating 2D patterns in dielectric media. Creating metal patterns on a submicron scale requires a combination of nanofabrication tools and several material processing steps. For example, steps to create planar metal structures using ultraviolet photolithography and electron-beam lithography can include sample exposure, sample development, metal deposition, and metal liftoff. To create 3D metal structures, the sequence is repeated multiple times. The complexity and difficulty of stacking and aligning multiple layers limits practical implementations of 3D metal structuring using standard nanofabrication tools. Femtosecond-laser direct-writing has emerged as a pre-eminent technique for 3D nanofabrication.1,2 Femtosecond lasers are frequently used to create 3D patterns in polymers and glasses.3-7 However, 3D metal direct-writing remains a challenge. Here, we describe a method to fabricate silver nanostructures embedded inside a polymer matrix using a femtosecond laser centered at 800 nm. The method enables the fabrication of patterns not feasible using other techniques, such as 3D arrays of disconnected silver voxels.8 Disconnected 3D metal patterns are useful for metamaterials where unit cells are not in contact with each other,9 such as coupled metal dot10,11or coupled metal rod12,13 resonators. Potential applications include negative index metamaterials, invisibility cloaks, and perfect lenses.
In femtosecond-laser direct-writing, the laser wavelength is chosen such that photons are not linearly absorbed in the target medium. When the laser pulse duration is compressed to the femtosecond time scale and the radiation is tightly focused inside the target, the extremely high intensity induces nonlinear absorption. Multiple photons are absorbed simultaneously to cause electronic transitions that lead to material modification within the focused region. Using this approach, one can form structures in the bulk of a material rather than on its surface.
Most work on 3D direct metal writing has focused on creating self-supported metal structures.14-16 The method described here yields sub-micrometer silver structures that do not need to be self-supported because they are embedded inside a matrix. A doped polymer matrix is prepared using a mixture of silver nitrate (AgNO3), polyvinylpyrrolidone (PVP) and water (H2O). Samples are then patterned by irradiation with an 11-MHz femtosecond laser producing 50-fs pulses. During irradiation, photoreduction of silver ions is induced through nonlinear absorption, creating an aggregate of silver nanoparticles in the focal region. Using this approach we create silver patterns embedded in a doped PVP matrix. Adding 3D translation of the sample extends the patterning to three dimensions.

Femtosecond-laser direct-writing is frequently used to create three-dimensional (3D) patterns in polymers and glasses. However, patterning metals in 3D remains a challenge. We describe a method for fabricating silver nanostructures embedded inside a polymer matrix using a femtosecond laser centered at 800 nm.

The standard nanofabrication toolkit includes  techniques primarily aimed at creating 2D patterns in dielectric media. Creating  metal patterns on a ...

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

Evaluating Plasmonic Transport in Current-carrying Silver Nanowires

Plasmonics is an emerging technology capable of simultaneously transporting a plasmonic signal and an electronic signal on the same information support1,2,3. In this context, metal nanowires are especially desirable for realizing dense routing networks4. A prerequisite to operate such shared nanowire-based platform relies on our ability to electrically contact individual metal nanowires and efficiently excite surface plasmon polaritons5 in this information support. In this article, we describe a protocol to bring electrical terminals to chemically-synthesized silver nanowires6 randomly distributed on a glass substrate7. The positions of the nanowire ends with respect to predefined landmarks are precisely located using standard optical transmission microscopy before encapsulation in an electron-sensitive resist. Trenches representing the electrode layout are subsequently designed by electron-beam lithography. Metal electrodes are then fabricated by thermally evaporating a Cr/Au layer followed by a chemical lift-off. The contacted silver nanowires are finally transferred to a leakage radiation microscope for surface plasmon excitation and characterization8,9. Surface plasmons are launched in the nanowires by focusing a near infrared laser beam on a diffraction-limited spot overlapping one nanowire extremity5,9. For sufficiently large nanowires, the surface plasmon mode leaks into the glass substrate9,10. This leakage radiation is readily detected, imaged, and analyzed in the different conjugate planes in leakage radiation microscopy9,11. The electrical terminals do not affect the plasmon propagation. However, a current-induced morphological deterioration of the nanowire drastically degrades the flow of surface plasmons. The combination of surface plasmon leakage radiation microscopy with a simultaneous analysis of the nanowire electrical transport characteristics reveals the intrinsic limitations of such plasmonic circuitry.

Silver nanowires can simultaneously transport electrons and optical information in the form of surface plasmons. A procedure is described here to realize such a shared circuitry and the limitations at propagating both information carriers are evaluated.

Plasmonics is an emerging technology capable of simultaneously transporting a plasmonic signal and an electronic signal on the same information ...

Preparation and Use of Photocatalytically Active Segmented Ag|ZnO and Coaxial TiO2-Ag Nanowires Made by Templated Electrodeposition

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and reduction half reactions, and fast electron (hole) diffusion and charge separation. Nanowires present suitable architectures to meet these requirements. Axially segmented Ag|ZnO and radially segmented (coaxial) TiO2-Ag nanowires with a diameter of 200 nm and a length of 6-20 &#181;m were made by templated electrodeposition within the pores of polycarbonate track-etched (PCTE) or anodized aluminum oxide (AAO) membranes, respectively. In the photocatalytic experiments, the ZnO and TiO2 phases acted as photoanodes, and Ag as cathode. No external circuit is needed to connect both electrodes, which is a key advantage over conventional photo-electrochemical cells. For making segmented Ag|ZnO nanowires, the Ag salt electrolyte was replaced after formation of the Ag segment to form a ZnO segment attached to the Ag segment. For making coaxial TiO2-Ag nanowires, a TiO2 gel was first formed by the electrochemically induced sol-gel method. Drying and thermal annealing of the as-formed TiO2 gel resulted in the formation of crystalline TiO2 nanotubes. A subsequent Ag electrodeposition step inside the TiO2 nanotubes resulted in formation of coaxial TiO2-Ag nanowires. Due to the combination of an n-type semiconductor (ZnO or TiO2) and a metal (Ag) within the same nanowire, a Schottky barrier was created at the interface between the phases. To demonstrate the photocatalytic activity of these nanowires, the Ag|ZnO nanowires were used in a photocatalytic experiment in which H2 gas was detected upon UV illumination of the nanowires dispersed in a methanol/water mixture. After 17 min&#160;of illumination, approximately 0.2 vol% H2 gas was detected from a suspension of ~0.1 g of Ag|ZnO nanowires in a 50 ml 80 vol% aqueous methanol solution.

Preparation and Use of Photocatalytically Active Segmented Ag|ZnO and Coaxial TiO2-Ag Nanowires Made by Templated Electrodeposition

Procedures are outlined to prepare segmented and coaxial nanowires via templated electrodeposition in nanopores. As examples, segmented nanowires consisting of Ag and ZnO segments, and coaxial nanowires consisting of a TiO2 shell and a Ag core were made. The nanowires were used in photocatalytic hydrogen formation experiments.

Photocatalytically active nanostructures require a large specific surface area with the presence of many catalytically active sites for the oxidation and ...

Atomically Traceable Nanostructure Fabrication

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process being used in order to maintain exquisite control over both feature size and feature density. Here, we demonstrate a method for tracking atomically resolved and controlled structures from initial template definition through final nanostructure metrology, opening up a pathway for top-down atomic control over nanofabrication. Hydrogen depassivation lithography is the first step of the nanoscale fabrication process followed by selective atomic layer deposition of up to 2.8 nm of titania to make a nanoscale etch mask. Contrast with the background is shown, indicating different mechanisms for growth on the desired patterns and on the H passivated background. The patterns are then transferred into the bulk using reactive ion etching to form 20 nm tall nanostructures with linewidths down to ~6 nm. To illustrate the limitations of this process, arrays of holes and lines are fabricated. The various nanofabrication process steps are performed at disparate locations, so process integration is discussed. Related issues are discussed including using fiducial marks for finding nanostructures on a macroscopic sample and protecting the chemically reactive patterned Si(100)-H surface against degradation due to atmospheric exposure.

We report a protocol for combining the atomic metrology of the Scanning Tunneling Microscope for surface patterning with selective Atomic Layer Deposition and Reactive Ion Etching. Using a robust process involving numerous atmospheric exposures and transport, 3D nanostructures with atomic metrology are fabricated.

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process ...

Fabrication Process of Silicone-based Dielectric Elastomer Actuators

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an elastomeric dielectric membrane sandwiched between two compliant electrodes. The large actuation strains of these transducers when used as actuators (over 300% area strain) and their soft and compliant nature has been exploited for a wide range of applications, including electrically tunable optics, haptic feedback devices, wave-energy harvesting, deformable cell-culture devices, compliant grippers, and propulsion of a bio-inspired fish-like airship. In most cases, DETs are made with a commercial proprietary acrylic elastomer and with hand-applied electrodes of carbon powder or carbon grease. This combination leads to non-reproducible and slow actuators exhibiting viscoelastic creep and a short lifetime. We present here a complete process flow for the reproducible fabrication of DETs based on thin elastomeric silicone films, including casting of thin silicone membranes, membrane release and prestretching, patterning of robust compliant electrodes, assembly and testing. The membranes are cast on flexible polyethylene terephthalate (PET) substrates coated with a water-soluble sacrificial layer for ease of release. The electrodes consist of carbon black particles dispersed into a silicone matrix and patterned using a stamping technique, which leads to precisely-defined compliant electrodes that present a high adhesion to the dielectric membrane on which they are applied.

This manuscript shows the fabrication process for the manufacture of dielectric elastomer soft actuators based on silicone membranes. The three key stages of production are presented in detail: blade casting of thin silicone membranes; pad printing of compliant electrodes; and the assembly of all the components.

This contribution demonstrates the fabrication process of dielectric elastomer transducers (DETs). DETs are stretchable capacitors consisting of an ...

Challenges in Rheological Characterization of Highly Concentrated Suspensions &#8212; A Case Study for Screen-printing Silver Pastes

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the manifold requirements during processing and application of such complex fluids. In this investigation, measuring protocols for a conclusive assessment of different process relevant rheological parameters have been evaluated. This includes the determination of yield stress, viscosity, wall slip velocity, structural recovery after large deformation and elongation at break as well as tensile force during filament stretching.
The importance of concomitant video recordings during parallel-plate rotational rheometry for a significant determination of rheological quantities is demonstrated. The deformation profile and flow field at the sample edge can be determined using appropriate markers. Thus, measurement parameter settings and plate roughness values can be identified for which yield stress and viscosity measurements are possible. Slip velocity can be measured directly and measuring conditions at which plug flow, shear banding or sample spillover occur can be identified clearly. 
Video recordings further confirm that the change in shear moduli observed during three stage oscillatory shear tests with small deformation amplitude in stage I and III but large oscillation amplitude in stage II can be directly attributed to structural break down and recovery. For the pastes investigated here, the degree of irreversible, shear-induced structural change increases with increasing deformation amplitude in stage II until a saturation is reached at deformations corresponding to the crossover of G' and G'', but the irreversible damage is independent of the duration of large amplitude shear. 
A capillary breakup elongational rheometer and a tensile tester have been used to characterize deformation and breakup behavior of highly filled pastes in uniaxial elongation. Significant differences were observed in all experiments described above for two commercial screen-printing silver pastes used for front side metallization of Si-solar cells.

Challenges in Rheological Characterization of Highly Concentrated Suspensions &amp;#8212; A Case Study for Screen-printing Silver Pastes

A protocol for a robust and application relevant rheological characterization of highly concentrated suspensions is presented. Silver pastes used for screen-printing application in solar cell production are employed as model systems.

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the ...

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.&#160; Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.

We present a detailed method for fabricating ultra-thin color films with improved characteristics for optical coatings. The oblique angle deposition technique using an electron beam evaporator allows improved color tunability and purity. Fabricated films of Ge and Au on Si substrates were analyzed by reflectance measurements and color information conversion.

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present ...

Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of nanowires. DEP is used for nanowire analysis, characterization, and for solution-based fabrication of semiconducting devices. The method works by applying an alternating electric field between metallic electrodes. The nanowire formulation is then dropped onto the electrodes which are on an inclined surface to create a flow of the formulation using gravity. The nanowires then align along the gradient of the electric field and in the direction of the liquid flow. The frequency of the field can be adjusted to select nanowires with superior conductivity and lower trap density. 
In this work, flow-assisted DEP is used to create nanowire field effect transistors. Flow-assisted DEP has several advantages: it allows selection of nanowire electrical properties; control of nanowire length; placement of nanowires in specific areas; control of orientation of nanowires; and control of nanowire density in the device. 
The technique can be expanded to many other applications such as gas sensors and microwave switches. The technique is efficient, quick, reproducible, and it uses a minimal amount of dilute solution making it ideal for the testing of novel nanomaterials. Wafer scale assembly of nanowire devices can also be achieved using this technique, allowing large numbers of samples for testing and large-area electronic applications.

In this paper, flow assisted dielectrophoresis is demonstrated for the self-assembly of nanowire devices. The fabrication of a silicon nanowire field effect transistor is shown as an example.

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of ...

A Fabrication and Measurement Method for a Flexible Ferroelectric Element Based on Van Der Waals Heteroepitaxy

Flexible non-volatile memories have received much attention as they are applicable for portable smart electronic device in the future, relying on high-density data storage and low-power consumption capabilities. However, the high-quality oxide based nonvolatile memory on flexible substrates is often constrained by the material characteristics and the inevitable high-temperature fabrication process. In this paper, a protocol is proposed to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica. The versatile deposition technique and measurement method enable the fabrication of flexible yet single-crystalline non-volatile memory elements necessary for the next generation of smart devices.

In this paper, we present a protocol to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica.